HomeMy WebLinkAboutBOXELDER SANITATION DISTRICT, LAGOON SYSTEM EXPANSION - SITE PLAN ADVISORY REVIEW - 23-95 - SUBMITTAL DOCUMENTS - ROUND 1 - CITY STAFFTable 2-2: Pipe Sizes Within Boaelder Collection System
Line Size
Length of Line
--------------------------------(ink--------------------.....--------
............................ (4- ---------------------------------
6
6,850
8
72,700
10
27,250
12
21,750
15
7,900
18
13,500
21
28,550
24
10,300
27
32,000
30
5Q
Total Length
1927550
No. of Manholes = 609
' 2.4.2 INFILTRATION/INFLOW
Water Usage:
' The degree of potential infiltration/inflow (M) can be estimated by comparing the metered water
usage versus the metered sewage flow. The sewage flow should be equal to or less than the
metered water use if no 1/1 were occurring and there are no significant private wells in the system.
Since the District is served by the East Larimer County Water District (EL CO), this examination
can be accomplished by looking at ELCO's water records. Table 2-3 compares the metered water
use for the first four (4) months of 1993 with the metered sewage flow for the same period.
' Table 2-3: Water Usage Data Within the Boaelder Service District (1993)
Boaelder Plant Data
Month Water Usage (gals) Sewer Influent (gals) Apparent M
Jan. 16,2702000 43,1012000 26,831,000
Feb. 17,324,000 44,2002000 262876,000
Mar. 15X82000 41,4327000 26,0747000
' April 19,107,000 42,466,000 23,140,000
6810591000 17171991000 1037104,000
' (567,160 GPD) (1,426,660 GPD) (859,200 GPD)
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EXISTING WASTEWATER
TREATMENT SYSTEM
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maintenance buildings, and plat site improvement. Adequate funds are now on hand to
accomplish all of the above capital investments.
CURRENT DISTRICT POLICIES
A. The Board policy is to oppose any contractual assignment of part of the District
operations as it would violate bond covenants now in place. The Board also would expect
to look at a ballot issue as a proper prelude to any intergovernmental agreements.
' B. The entire Boxelder Sanitation District ,Board has, however, been on record as favoring
the consolidation of ALL water treatment service providers in the Cache La Poudre
watershed downstream to the Windsor area by means of the creation of an Authority.
Documentation of much of the above is available.
1. A 10-15 year planning,period would enable amortizing capital investments prior to
connection to a regional facility.
2. Consolidation should only occur if combined flows do not discharge effluent at
volumes or velocities creating erosion or other environmental impacts.
C. The District will continue to cooperate with the City in addressing mutual water quality
concerns.
1. In response to City concerns over pass -through and aspects adversely affecting
Cache La Poudre water quality and the adequacy of industrial controls, Boxelder
has implemented not only a comprehensive pretreatment program but also a
' pollution prevention program involving all commercial discharges.
2. District is rehabilitating collection systems to reduce flows.
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9. The Board and staff very early recognized that the collection system piping and
manholes had been disregarded by prior management and prior staff except for
remediation of stoppages. The new staff immediately instituted a manhole location
and inspection program with 85% of all critical manholes located and raised within
the first year. During 1994, over 75 manholes were rebuilt to stop major
infiltration. This program was a major source of pollution discharge identification.
Quality control mechanisms were put into place at this time.
10. During 1993, a complete hydraulic flow study of segments of the collection system
was completed. This was done in coordination with new metered influent data and
a new computer program for flow data retrieval. This later is an aid in
identification of potential pollutant dischargers with inordinately high flows and
aids in the implementation of both the pretreatment and pollution prevention
programs.
The Boxelder Sanitation District, by all of the 10 actions delineated above, believes that it is
setting a standard for small districts on water quality control.
DISTRICT FINANCIAL AND STAFFING CAPABILITY
A. The District Board has always taken a very conservative stance regarding its financial
management, maintaining in excess of a 1 to 1 Current Ratio.
B. The present staff is quite adequate to discharge all responsibilities of accounts receivable,
account payable, accounting, in-house engineering, quality control, sampling and testing,
public relations, the pretreatment and pollution programs, infiltration/inflow remediation,
line cleaning and TV inspection, manhole raising and repair, new installation inspection,
line locations, and new subdivision engineering review. All of the above can be
accomplished with District -owned equipment, facilities, and personnel.
C. By obtaining a bond refunding issue in the spring of 1994, the District Board responded to
a low in the municipal debt market and its need for capital investment funds to satisfy
permit compliance schedule requirements - specifically the need to expand hydraulic
capacity, contact basin sizing, chlorine feed controls, yard piping, office and equipment
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2. Instituted a Pollution Prevention Program in May of 1992 for more than 550
commercial users. This is a District initiative, not a permit requirement, but is, in
the opinion of the District Board, our most effective water quality control
program.
3. During 1992, the District staff completed a thorough upgrade of all electrical,
mechanical, and process control components at the plant site with increased water
quality monitoring and control as a result. An early notice (2 minute) alarm
reporting system for eight mechanical or electrical systems reporting to six stations
(people) within a total of six minutes was instituted in March of 1992. This was an
early and very effective control mechanism to guard against the possibility of water
quality damage.
4. District staff instituted a data base for all water quality discharge parameters
starting in late 1992 retrieving all prior data, as well as collecting updates to insure
effective water quality control.
5. Other than one test failure likely due to no control on pH changes during the test,
there have been no wet failures for 18 months, indicating good treatment capability
to protect the stream.
6. District staff has obtained a P.Q.L. for mercury with appropriate relief given on the
reporting data for D.M.R.'s and more accurate water quality testing control.
7. The District staff has completed an extensive water quality study within its
collection system manholes to characterize both discrete residential and
commercial waste steams for most discharge permit limitation parameters,
including metals.
8. The District Board approved and has commenced a joint CSU-District study of the
lagoon treatment system waters and the microbiological activity, wind, and
temperature effects and some other very site specific measuring on lagoon B,
including sludge. The District will gain valuable water quality control information
from this study. A Doctoral dissertation and two Master theses will also be a
result of this joint venture.
retirement, pre-treatment enforcement, collection line maintenance, and other
administrative services would remain as a continuing cost. This cost would be
over and above the $.85/1000 necessarily paid to Fort Collins. Sewer use fees
would presumably increase from $19.22 to $21.00
DISTRICT OPERATIONAL CAPABILITY
A. The Boxelder District is a duly constituted and separate division of the Colorado state
government as described in C.R.S. Title 32. It operates under the sole control and
direction of an elected Board of five directors who have full and final authority over all of
the financial matters, operation and planning policies, staffing, the setting of rates and
charges, the issuance of debt instruments, and any contractual agreements. The Board is
also responsible for implementation of all actions necessary to maintain compliance with
permit condition - especially water quality control.
B. Since March of 1992, a newly instituted District Board, management, and staff have been
in control. Prior to March of 1992, the Boxelder Sanitation District was under the
operational control of the ELCO Board, the Water District. Notice of cancellation of the
long-standing, harmonious relationship between ELCO and Boxelder was unilaterally
given by ELCO in August of 1991. On March 1992, the Boxelder Sanitation District
Board of Directors instituted internal control of all management and operations of the
District, including staff, equipment, and a new office location.
C. It is stated District policy to maintain full compliance with all water quality, stream
standard and compliance scheduled requirements of the discharge permit.
D. The District has been in compliance, for the most part, since 1965.
E. Beginning in March of 1992, the newly instituted District Board and staff responded to the
extremely restrictive NPDES permit conditions with the following actions:
1. Began the process of submittals to the Division for the purpose of obtaining a
complete Pretreatment Program including local limits, a seminal accomplishment
for a lagoon treatment system in EPA Region 8. This was approved by the
Division and EPA on July 5, 1994. The Pretreatment Program was a major water
quality control initiative by the Board prior to permit requirements.
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10. Even if Cooper Stough remained in the ownership and control of the District and
only that volume delivered to Fort Collins is surcharged, if that surcharge is the
current $.85/1000 gallons (based on District estimates), as compared to the
District's $.15/1000 gallons, then the District's costs would increase significantly.
11. If Fort Collins' treatment costs increase as a result of nitrification and/or
phosphorus removal requirements, then the customers on this line would be
surcharged for those extra costs. This would result in disparate costs charged
within the District. It would not be equitable to impose a additional charge on the
entire District for treatment not given to all wastes discharged.
12. Transfer of flows to the City would reduce discharges to Boxelder Creek and the
Cache La Poudre River. This results in less instream flow for a stream fully
diverted upstream of the confluence with Boxelder Creek.
DISSOLUTION OF DISTRICT
1. If all flows were diverted to Fort Collins and the District were dissolved, it would
cost Fort Collins at least $.85 to treat those flows (based on District estimates
using the City's budget).
2. Current District indebtedness would have to be eliminated prior to dissolution.
That indebtedness is $1.8 million. Current indebtedness is scheduled to be paid
back by the year 2012. That indebtedness is dependent upon revenues from sewer
fees.
3. Diversion of all flows would significantly reduce instream flows for six miles of the
Cache La Poudre.
DIVERSIONS OF ALL FLOWS TO FORT COLLINS
1. If the District remains the operational entity by contract with Fort Collins for the
treatment of all flows, then costs for customers will increase from $.15/1000 to
more than $.85/1000 (based on District estimates). District capital indebtedness
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the City Utility Department assuming a portion of the operations and management
of the District.
Over a period of one to two years, the District Board discussed with City Staff the
possibility of connecting the western portion of the District service area (that area
which constitutes only commercial users) at a point opposite the Comfort Inn
where City lines currently exist. City Utility staff rejected this option. Engineering
concerns for both staffs existed.
City staff studied "taking over" a $1,400,000 main collector installed in 1975-76,
identified as the Cooper Slough Collector, which is utilized by Anheuser Busch
and three residences. This interceptor delivers approximately 25,000 GPD gallons
per day currently.
The District and City jointly conducted studies on the possibility of constructing a
three unit gate structure and a large transfer line capable of carrying The Cooper
Slough flow from just north of the District's Treatment Works to City Plant No. 2
for purposes of determining the costs involved. This resulted in an estimate of
$465,000 in 1988 dollars, which may cost in 1995 dollars approximately $680,000.
Additional engineering at $68,000 and payment to the District for unused prior
constructed facilities would be $700,000. Total cost would be $1,448,000.
For Fort Collins to "take over" the Cooper Slough Connector, the District would
have to be reimbursed $1,400,000 plus any lost revenues necessary to assure
bonded indebtedness payment.
Presumably, all existing connected users to that interceptor would be charged the
Fort Collins sewer tap fee of $1,600.
Boxelder would lose approximately $45,000/yr: in revenues if the Cooper Slough
Interceptor is diverted to Fort Collins. Bond Covenants would be violated because
the District cannot abrogate or threaten future revenues necessary to pay
indebtedness.
To reduce the District's potential revenue base, a District election for voter
approval would be necessary for any contract to sell, assign, or otherwise eliminate
the available revenues from any interceptor.
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NEED FOR THE ACTION
The need for expansion is that current hydraulic loading occasionally exceeds permitted levels. 1/I
remediation had reduced hydraulic loading by 13%. However, further growth is now anticipated
to require expansion of hydraulic capacity. The proposed new lagoon would expand capacity by
.84 MGD per day for a total plant capacity of 2.34 MGD.
ALTERNATIVES
A. Expansion of current site by addition of new lagoon of 7 MG.
1. Discharge to Boxelder Creek and then to the Cache La Poudre River is a benefit to
the Cache La Poudre by providing water to an otherwise dried stream bed due to
upstream diversions. Boxelder effluent provides stream flow for several miles
downstream before Fort Collins effluent via Fossil Creek Reservoir returns to
Cache La Poudre River.
' 2. Discharge of additional treated wastewater to Boxelder Creek and Cache La
Poudre River will not have adverse water quality impacts to the classified use of
' the stream (as presented in Appendix A).
a. All metals discharged are within effluent limitations and standards. The
range discharged for most parameters is often significantly lower than the
standard.
3. Should un-ionized ammonia treatment be required, space is available within the
lagoon treatment system for the addition of necessary treatment facilities and
capacity for such treatment.
a. Treatment alternatives for un-ionized ammonia are conversion of system to
an External Aeration Activated Sludge Process.
B. Connection of an intercepting line to Fort Collins treatment facility.
1. Connection of the Cooper Slough intercepter would currently remove 25,000
' gallons per day from the Boxelder plant; (connection of other interceptors could
transfer up to 1 MG per day.)
2. Prior to August 1991, the Boxelder Board of Directors had numerous discussions
With the Water Utility staff of the City of Fort Collins regarding the possibility of
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Appendix B
Supplemental Narrative for Site Approval Application
(Prepared by District)
ISSUE
Should the Boxelder Sanitation District expand by the addition of a 7 MG lagoon in order to
expand its hydraulic and treatment capacity? Expansion is in lieu of further inflow and infiltration
remediation actions which are ongoing but not conclusively likely to increase hydraulic capacity
sufficiently to meet anticipated future growth requirements. Alternatives to expansion are (1)
further inflow and infiltration remediation, (2) connecting a portion of the collections system to
the Fort Collins treatment plant, (3) connection of all of the Boxelder Collection System to the
Fort Collins treatment plant, or (4) no further action.
PERMIT REQUIREMENTS
The NPDES permit issued by the State of Colorado in 1992 included a compliance schedule for
infiltration and inflow (M) remediation. Despite significant reduction of I/I, the permit was
,revised in January,1995 to provide a compliance schedule for expansion. A site application is to
be filed prior to May 31, 1995; construction is to be completed by December 31, 1995.
STATUTORY/REGULATORY CRITERIA
The primary statutory and regulatory criteria (C.R.S. 25-8-72 and 5 C.C.R. 1002-12) for location
approval is to minimize potential adverse impacts on water quality on a long-term basis. This
criteria is reviewed in light of any long range plan, operational management, the objective of other
water quality regulations, and consolidation of treatment facilities where feasible. By C.R.S. 25-
8-102(5), the water quality benefits of a water pollution control program must have a reasonable
relationship to the economic, environmental, energy, and public health costs and impacts. _
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Appendix B
Supplemental Narrative for Site Approval Application
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feet per second (CFS), the proposed plant flow of 3.6 CFS, and the stream standard of 0.003 mg/L into
a Total Residual Chlorine effluent limitation. The effluent limitation for TRC based on the 1.5 MGD
flow was 0.009 mg/L. The effluent limitation for TRC based on the 2.34 MGD flow is 0.007 mg/L.
There is no operational difference between these two effluent limitations. The detection of Total
Residual Chlorine in any sample is considered a violation and the failure to detect TRC is considered
proof of compliance. Both effluent limitations will require that the effluent continue to be dechlorinated
prior to discharge.
IV. FECAL COLIFORM
The stream standards for Fecal Coliform bacteria on both the Cache La Poudre and Boxelder Creek are
2000 organisms per 100 ml. Performing a mass balance between the Boxelder Discharge and Boxelder
Creek will insure that the fecal coliform standard in both streams will be maintained. The measured
upstream value for Boxelder Creek from Table II1-4 of the Rationale is 360 organisms/100m1. The mass
balance equation was used to convert this background value, the lowest monthly chronic flow on
Boxelder Creek from Table III-5 of the Rationale, 4.4 cubic feet per second (CFS), and the proposed
plant flow of 3.6 CFS, and the stream standard of 2000 organisms/100 nil into a fecal coliform effluent
limitation. The effluent limitation for fecal coliform based on the 1.5 MGD flow was 5100
organisms/100 ml which was rounded to 5000 organisms/100 ml and applied as a 30-day geometric
mean. A seven (7) day geometric mean of 10,000 organisms/100 ml (2 times the 30 day limit) was also
imposed. The effluent limitation for fecal coliform based on the 2.34 MGD flow is 4004 mg/L which
was is expected to be rounded to 4000 organisms✓100 ml and applied as a 30 day geometric mean. A
seven (7) day geometric mean of 8,000 organisms/100 ml (2 times the 30 day limit) was also imposed.
There is no operational difference between these two effluent limitations. These fecal coliform levels will
require the continued use of chlorine disinfection. The proposed facility will be designed for disinfection
with chlorine.
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T.M. 17i. A mmnn:o 1i Mszan4 T .imi49*innc
MONTH
OLD LIMITS
NEW LIMITS
JAN
156.9 mg/L as N
111.1 mg/L as N
FEB
127.5
90
MAR
58.2
43.5
APRIL
53.3
40.4
MAY
58.5
44.2
JUNE
34.0
25.7
JULY
34.6
26.2
AUG
37.9
29.1
SEPT
37.2
28.7
OCT
40.3
31.1
NOV
73.5
53.7
DEC
142.8
103.1
These calculated ammonia effluent limitations are still greater than concentrations that have been
measured in the Boxelder WWTP discharge or which were expected from a similar type of facility. No
effluent limitations for ammonia are expected. The proposed plant design is expected to easily meet
these effluent limitations. The same monitoring requirements for ammonia should be sufficient to
demonstrate compliance.
IIL TOTAL RESIDUAL CHLORINE
The stream standard for Total Residual Chlorine (TRC) on the Cache La Poudre is 0.003 mg/L. Since
the distance from the Boxelder discharge point into Boxelder Creek to the confluence with the Cache La
Poudre is relatively short, the stream standard of 0.003 mg/L was applied to Boxelder Creek. The
assumption is that an effluent limitation that keeps the TRC below 0.003 mg/L will not cause a violation
of the stream standard below the confluence of Boxelder Creek. The mass balance equation was used to
convert the lowest monthly chronic flow on Boxelder Creek from Table III-5 of the Rationale, 4.4 cubic
Yam:
T..sa. V. 19..v...:n Tn#al Ammnnia Qtroam Ctandard
MONTH
BACKGROUND
AMMONIA
30E3 FOR
THE
CACHE LA
POUDRE
EFFLUENT
LIMITATION
FOR FORT
COLLINS
WWTP
CALCULATED
STREAM
STANDARD
JAN
.31 mg/L as N
4.2 CFS
33.3 mg/L as N
29.5 mg/L as N
FEB
.86
4.2
25.0
22.2
MAR 1
.36
3.9
18.2
16.3
APR
.15
3.9
18.7
16.7
MAY
.19
3.9
20.5
18.3
.04
6.7
12.6
10.4
.13
6.7
12.8
10.6
.19
3.9
14.7
13.1
F
.53
3.9
14.4
'12.9
.41
3.9
15.6
14.0
.06
4.8
19.6
17.1
06
4.8
36.8
32.0
The Total Ammonia Allowed values from Table III-3 of the Rationale, the Boxelder Creek Low Flows
from Table III-5 of the Rationale, and the proposed plant expansion flow of 2.34 MGD were used to
calculate the effluent limitation for ammonia. The background total ammonia concentration in the
Boxelder Creek was set at a value of 0.2 mg/L. This value is given in Table 1114 of the Rationale.
Table VI lists the old limits from Table VII-2 which were based on the 1.5 MGD plant capacity and the
' new limits which are based on the 2.34 MGD flow.
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Local Limits in the Pretreatment Program to reflect the lower effluent limitations. There should be no
significant impact on the limitations applied to industrial users.
H. AMMONIA
The Allowable Instream Total Ammonia was determined by a study done by Lewis and Saunders. This
study considered in -stream pH recovery and ammonia decay as part of the Colorado Ammonia Model,
which accounts for diurnal variations in stream temperature and pH. This study was performed on the
Cache La Poudre and was used to determine the effluent limitations for Fort Collins WWTP #2. The
mass balance equation was then used to calculate the Maximum Allowable Instream Ammonia in Table
111-3 of the Rationale. These values were used as the stream standards for total ammonia. Using the
same rationale as metals, the effluent limitation for the Boxelder Sanitation District is based on assuring
that the Boxelder discharge does not raise the instream Total Ammonia concentrations above the stream
standards for the Cache la Poudre listed in Table III-3. The effluent limitation is based on the stream
standards from Table III-3, the Chronic and Acute low flows from Boxelder Creek from Table 111-5, and
the proposed design flow of 2.34 MGD (3.6 Os). The chronic and acute effluent limitations were
calculated for each month. The mass balance equation given in Section VH B was used to determine the
effluent concentrations that would not violate the allowable stream standard.
Table V summarizes the key data that was used to determine the chronic maximum allowable instream
total ammonia (based on the study from Saunders and Lewis) ammonia data from the Nature Center, the
30E3 flow from USGS Gauge Number 06752280, and the standard mixing equation.
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daily maximum and no 30-day average (chronic limit) was specified. This is consistent with the footnote
to Table V11-3 of the Rationale.
Table IV: Existing And New Effluent Metals Limitations Based On Table Vii-3 Of The Rationale
Document. And New Flow Rate (2.34 MGD).
METAL
OLD LIMIT
NEW LIMIT
Aluminum
434 mg/L
333 mg/L
Arsenic
434
333.
Cadmium
6.9
5.3
Chrome III
1301
1000
Chrome VI (Acute)
29.8
24.9
Chrome VI (Chronic)
31.8
24.4
Copper (Acute)
67.9
59.1
Copper (Chronic)
76.9
56.8
Iron
2892
2222
Lead
43.1
33.1
Manganese
2892
2222
Mercury
.03
.02
Nickel
568
436
Selenium
49.2
37.8
Silver
4.7
3.6
Thallium
43.4
33.3
Uranium (Acute)
10389
8688
Uranium (Chronic)
12335
9478
Zinc
211
162
The recalculated metals values are well within the treatment capabilities of the proposed plant and the
control objectives of the District's EPA approved Pretreatment Program. The District will reevaluate the
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the Water Quality Control Division and were listed in Table 111-5 of the Rationale. Table III lists the
Boxelder Creek low flows.
Tohla M - Rnva]Aar rraalr I nw Finwc
MONTH
CHRONIC LOW FLOW
ACUTE LOW FLOW
JAN
10.0 Cubic Feet per Second
7.7 Cubic Feet per Second
FEB
11.0
4.7
MAR
6.0
8.5
APR
5.1
2.3
MAY
5.1
2.0
JUNE
5.3
2.1
DULY
5.3
4.0
AUG
4.4
4.0
SEPT
4.4
2.0
OCT
4.4
2.0
NOV
7.7
6.3
DEC
8.0
8.2
The effluent limitations for the Boxelder Sanitation District are based on assuring that the Boxelder
discharge does not raise the instream metals concentrations above the stream standards for the Cache La
Poudre listed in Table 1II-2. The effluent limitations are based on the stream standards from Table III-2,
the Chronic and Acute low flows from Boxelder Creek from Table III-5, and the proposed design flow
of 2.34 MGD (3.6 ft3/s). The chronic and acute effluent limitations were calculated for each month, and
the most stringent value was designated as the chronic limit. The mass balance equation given in Section
VII B was used to determine the effluent concentrations that would not violate the allowable stream
standard. Table IV gives a comparison of the most stringent effluent metals limitations given in Table
VII-3 of the Rationale document for a 1.5 MGD flow to the values that we calculated for the 2.34 MGD
flow. In cases where the acute limit is more stringent than the chronic, the acute limit was applied as a
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The acute and chronic standards were calculated from the acute and hardness values given in Table 111-1.
These values were listed in Table 111-2 of the Rationale on a month- by -month basis. Table 11 lists the
lowest monthly chronic and acute value for each parameter from Table III-1 to give a general indication
of the magnitude of the stream standard.
m..M. Tr. 7 .... m4 M^"*16lw Al mvtn unA lrhniw Volnae (RPf TYIIIP m-t Pprmit RatinnAlP. 1101
METAL
Acute Stream Standard
Chronic Stream Standard
Aluminum*
950 mg/L
150 mg/L
Arsenic*
360
150
Cadmium
23.4
2.29
Chrome 111
3250
421
Chrome VI*
16
11
Copper
36.5
24.8
Iron*
1000
1000
Lead
330
13.3
Manganese*
1000
1000
Mercury*
2.4
.01
Nickel
1650
185
Selenium*
135
17
Silver
7.6
1.42
Thallium*
15
15
Uranium
5585
3902
Zinc
405
62.5
*The metals standard for this parameter is not a function of hardness
The effluent limitation is calculated from the acute and chronic flows in Boxelder Creek The flows used
to calculate the acute and chronic effluent limitations are the one day in three year low flow (10) and
the 30 day in three year low flow (30E3) respectively. The flows were estimated for Boxelder Creek by
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L METALS
Boxelder Creek is a water quality limited stream that discharges into Segment 12 of the Cache La Poudre
River. Boxelder Creek and Segment 12 of the Cache La Poudre River are classified for Recreation Class 2,
Aquatic Life Class 2 (Warm), and Agriculture. The metals limitations are based on the, acute and chronic
Table Value Standards from Table III of the Basic Standards and MethodoloWes for Surface Waters. The
numeric values for many of these values are based on the hardness of the receiving water/effluent mixture
below the discharge point.
A special study performed by Lewis and Saunders determined the appropriate hardness values and stream
standards for Segment 12 of the Cache La Poudre River. Since the flow of Boxelder Creek plus the flow of
Boxelder Sanitation District discharge is relatively small compared to the combined flow of the Cache La
Poudre River and the Fort Collins plant, it was assumed that the hardness values below the confluence with
Boxelder Creek and the metals standards calculated from these hardness values would apply to both the Fort
Collins and the Boxelder Sanitation District plants. Table III-1 from the Permit Rationale lists the hardness
values based on the Chronic and Acute flows. Table I is a summary ofthe information from Table III-1.
7. Q.. ..1'T..Idn M-1 Va. St I)otinnola I late
Month
Chronic
Acute
January
245 mg/L as CaCO3
234 mg/L as CaCO3
February
238
227
March
242
235
April
250
243
May
267
280
June
302
295.
July
317
310
August
288
247
September
273
231
October
258
215
November
258
256
December
254
252
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Appendix A
An Evaluation Of Water Quality Based Effluent Limitations For The Expansion Of The
Boxelder Sanitation District Plant
The Boxelder Sanitation District is authorized to discharge from its domestic wastewater treatment
facility by CPDES Pen -nit No. CO-0020748. This permit specifies the effluent limitations, monitoring
requirements, and other conditions that the discharge from this facility must meet to comply with water
quality standards and other applicable State and Federal regulations. The Boxelder Sanitation District is
requesting that the design capacity of the domestic wastewater facility be expanded from the 1.5 million
gallons per day (N4GD) specified in the present permit to a new design capacity of 2.34 MGD. Since the
receiving stream (Boxelder Creek) is a water quality limited stream, the effluent limitations are based on
the design capacity of the treatment facility; and the expansion to 2.34 MGD will result in lower effluent
limitations. The Boxelder Sanitation District has calculated the effluent limitations that should apply to
the expanded facility and has determined that, in all cases, the proposed design of the expanded facility
should provide a level of treatment that will meet the revised effluent limitations.
The revised effluent limitations were calculated using the data and assumptions that were included in the
Rationale for Public Notice for Permit No. CO-0020478. These assumptions were used to calculate
revised effluent limitations that are identical to the effluent limitations that would have been calculated if
the Boxelder Sanitation District had proposed a design capacity of 2.34 MGD during the permitting
process. No additional data or changes in the assumptions have been made.
Revised effluent limitations were evaluated for 16 metals, ammonia, total residual chlorine, and fecal
coliform. The changes in effluent limitations related to the increase in capacity from 1.5 MGD to 2.34
MGD are well within the capabilities of the expanded plant design. The present stream standards will be
maintained, and the increased flow in the Cache La Poudre is expected to provide a net environmental
benefit for aquatic organisms and habitat during periods of low flow.
A-1
1
_t
1
1
I
I
�aJ
11
r
i
I
1
Appendix A
An Evaluation Of Water Quality Based Effluent Limitations For The Expansion Of The Boxelder
Sanitation District Plant
1
APPENDICES
I
L
8. ADMINISTRATIVE ARRANGEMENTS
8.1 FINANCIAL SUMMARY
The Boxelder Sanitation District has the capability to pay for these improvements to their WWTP.
To finance the upgrades, bonded indebtedness was increased in May 1994 to $1.8 million. The
District is in sound fiscal condition and will not have to sell additional bonds or otherwise borrow
loan funds for these proposed improvements.
8.2 IMPLEMENTATION PLAN AND SCHEDULE
The following schedule data is based on the compliance schedule found within permit No. CO-
0020478
1. Begin construction of the expanded facility by October 1995.
2. Complete construction of the expanded facility by December 31, 1995.
57
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t
I
I )
1,
11
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UTEC
ADMINISTRATIVE ARRANGEMENTS
I
7. FLOODPLAIN ANALYSIS
In accordance with the latest data obtained through the City of Fort Collins from a study
performed by the US Army Corps of Engineers, the flood plain ranges from El. 4865 to 4870 at
the Boxelder facility. On the basis that the dikes at Boxelder facility are at elevation 4873, the
biological treatment processes would not be interrupted in the event of a 100-year flood.
56
I
UTEC
FLOODPLAIN ANALYSIS
i
Advanced Facultative Ponds
An Advanced Facultative Pond (AFP) consists of a facultative pond with a depth of 10-12 feet
along with internal fermentation pits located an additional 10-12 feet below the bottom of the
facultative pond. The AFP has an aerobic zone in the upper part of the pond and one or more
anaerobic pits in the bottom of the pond. There are berms built around the edges of the pits to
help prevent cold, oxygen -bearing water from entering the pit when the wind causes circulation of
the upper layers, or when there is a thermal turnover. The wastewater influent, after grit and
inorganic solids removal, is released vertically downward near the bottom of the pit where it helps
stir the sludge already deposited. This stirring action helps to provide ready access for the
anaerobic bacteria to digest the organic material. The detention time within the facultative
portion of the pond is 10-12 days while the detention time within the fermentation pit is 2-3 days.
The pit cross section is large enough that the upward velocity of the flow out of the pits is less
than the fall velocity of parasite eggs which, therefore, remain in the pit where they are eventually
digested. On the downwind edge of the pond is a scum ramp on which floating materials collect
and can be removed manually.
The costs of an AFP system would be 10 - 20% more than the proposed plan delineated in this
report. The lack of cold climate data for an AFP system, along with high groundwater levels in
the vicinity of the new lagoon, currently prohibits the recommendation of an AFP system. '
55
The estimated costs of constructing the Extended Aeration system are given below in Table 6-1:
Table 6-1: Extended Aeration System
Opinion Of Costs
ITEM DESCRIPTION QUANTITY UNIT UNIT COST EXTENSION
1. PUMP STATION
Variable Gpm Pumps
3
EA
$ 12,000
$ 36,000
2.
HEADWORKS - Grit
1
LS
150,000
3..
YARD PIPING HYDRAULICS: 1
LS
. $ 20,000
20,000
4.
AERATION SYSTEM
1
LS
750,000
5.
CONCRETE
400
CY
$ 300
120,000
6.
BASIN LINER
1
LS
50,000
7.
SEEDING
3000
SY
$ 0.50
12500
8.
DIGESTER TANK
1
LS
51000
9.
BLOWER BLDG.
525
SF
$ 75
39,000
10. ELECTRICAL
1
LS
$ 40,000
40,000
Subtotal
$17211,500
Contingencies
121,115
ESTIMATED CONSTRUCTION COST $1,332,615
Engineering, Legal & Admin. $133,261
ESTIMATED TOTAL PROJECT COST $114651876
54
The mechanics of the system involve the detention of the waste stream in a reactor for
approximately 20 to 36 hours. The stability of the system is attributable to the lengthy detention
time as compared to other activated sludge systems which generally range from 4 to 7 hours.
While in residence, the wastewater is continually aerated and mixed to facilitate contact with
aerobic bacteria which flourish in the environment provided. The bacteria aerobically digest both
the influent organics in the basin as well as in the sludge which is recycled from the final clarifiers.
Subsequently, a separate digester is normally not required. The reactor for an extended aeration
system would utilize the volume of the existing third lagoon which would be lined with synthetic
material or concrete. For a 24-hour detention period, the basin would have to contain a volume
of 2.34 MG and would require 12 aeration headers and three aeration blowers. The means of air
disbursal would be by fine bubble diffusers. The operating horsepower is estimated at 120 Hp for
a 3 MGD capacity (installed horsepower at 225 Hp). After treatment in the aeration basin, the
waste stream is conveyed to integral final clarifiers where sludge settling (and recycle) is
accomplished. Disinfection and Dechlorination occur prior to discharge. The major components
of the system are comprised of the following:
• Screening and Grit Removal
• Extended Aeration Basin
• Final Clarifiers
• Sludge Recycle Pumps
• Modification of Cell A to a Sludge Holding Tank
• Chlorination/Dechlorination
• Sludge Disposal
This system would utilize the existing pumping station and would, therefore, require the
' upgrading costs in that area as previously discussed. Also, the process would require a means of
sludge disposal which is normally accomplished by hauling the sludge in liquid form to farm or
pasture ground. To accomplish this, a sludge hauling vehicle would be required.
I
11
53
i
11
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U
Water supplies in the area are adequate with a few large industrial water consumers obtaining
water from both private wells and ELCO. A reuse system could not compete economically with
their current arrangement. The topographic location of the treatment plant deters the use of plant
effluent for the enhancement of surface water recreational facilities. Due to the relatively non-
existent need for some form of wastewater reuse system, no further consideration was given to
this treatment category.
Wetlands
The use of wetlands to assist with the treatment of wastewater discharges has become
increasingly popular in recent years due, in part, to a growing national concern over the decrease
in available wetlands for wildlife and the use of more "environmentally sensitive" waste treatment
systems. The application of this system has some merit for the Boxelder System in that a suitable
site is nearby and the City has undertaken detailed studies to ascertain the performance of
wetlands in this area. Continued study is necessary, however, before a recommendation for
implementation could be made. Wetlands are mentioned again hereinafter under the discussion of
future treatment options where the existing lagoon is expanded to handle the immediate need for
capacity.
6.3 ALTERNATIVE WASTEWATER PLANS
Extended Aeration Activated Sludge
This plan investigates the use of a quasi -mechanical type treatment facility. The treatment scheme
used is commonly referred to as an extended aeration activated sludge plant. The particular type
of extended aeration system would be constructed inside of the existing settling lagoon. It would
be constructed with an integral clarifier for solids removal and sludge return. This type of facility
is the least expensive of the mechanical activated sludge plants and the most stable in terms of
performance and ease of operation. The costs are generally less than other mechanical systems
because there are no primary clarifiers or sludge digestion facilities such as aerobic digesters.
This system is capable of a high degree of treatment and could be made to reduce ammonia and
phosphorus if ever required. An activated sludge system could be built entirely upon the existing
treatment plant site.
52
6. ALTERNATIVE TREATMENT SYSTEMS
6.1 GENERAL
Several wastewater treatment alternatives were analyzed and the most viable were evaluated. All
of the alternatives considered fall into one of the following treatment categories: wastewater
reuse, treatment and discharge, and land application. A preliminary screening of specific
treatment alternatives by treatment category was undertaken in order to eliminate from further
consideration those proposals which were not feasible.
6.2 WASTEWATER TREATMENT CATEGORIES
Complete Retention
This wastewater management category consists of treatment systems utilizing biological action in
the soil and plant growth for the breakdown and stabilizing of pollutants. One such system
utilizes evaporation ponds designed to dispose of wastewater through evaporation and exfiltration
through the soil. This alternative did not prove feasible due to the large land requirement (over
250 acres), lack of a suitable location, potential problems with new groundwater regulations and
potential problems with water rights.
Land Application
Another method of land application involves irrigation of pasture and cropland with treatment
plant effluent. This treatment system requires an irrigation lagoon with 120 days storage. As
before, no further consideration was given to this alternative due to the large amount of land area
(over 640 acres) required, lack of a suitable location, water rights complications, and compliance
with new groundwater regulations.
Wastewater Reuse
This category of wastewater management systems involves planning a system around a specific
need for water. Specific water reuse applications include such uses as industrial process water,
groundwater recharge, enhancement of surface water supply, and recreational lakes. Preliminary
investigations revealed that potential wastewater reuses are limited within the planning area.
51
UTEC
ALTERNATIVE TREATMENT SYSTEMS
II
I
REQUIRED PROPERTY
LINE
EXISTING
PROPERTY LINE
TRANSFER BOX-,
r
TRANSFERIBO
FLOATING BAFFLES-!
POND 0
FLOATING BA,FFLE---
NEW
DISCHARGE
PONID 13 F ST A
V REVISE PIPING
REVISE CL2/SO2FEED
NEW CONTACT
. ................. --------
ELEC. BASIN
/CABLE
BAS' N
NEW FLUME
SPLITTFR BOX
. . . ...........
EXISTING
k)UTFALL'/
CONTACT
EFFLUENT BO r CHLORINE LINE
BAIS I N
......................................... .. . .....
LEGEND
EXISTING SYSTEM
PROPOSED SYSTEM
FIGURE NO. 7
EXPANDED LAGOON SYSTEM!
BOXELDER SANITATION DISTRICT
FORT COLLNS, COLORADO
JANUARY 1995
94-044
The Engineering Company
9404410
Table 5-1: Upgraded WWTP Operating Condition Summary
Number of Basins
2 Each
Independent Trains
2 Each
Length/Width Ratio
18:1
G. DECHLORINATION FACILITY
Feed Rate
30 lbs./day
Re -aeration Method
Aeration Tray
H. EFFLUENT FLUME
Type: 12" - Parshall
Capacity 0-10 MGD
Condition level
5.2 COST ESTIMATE
Table 5-2 provides information on the approximate costs to expand the Boxelder wastewater
facility.
Table 5-2: Expanded Pond System
Opinion Of Costs
ITEM DESCRIPTION
QUANTITY
UNIT
UNIT COST
EXTENSION
1.
PUMP STATION
1,600 GPM (Impellers)
3
EA
$ 5,000
$ 15,000
1.
SURFACE AERATORS
4
EA
$ 16,000
$ 64,000
2.
YARD PIPING HYDRAULICS: 1
LS
$ 20,000
20,000
3.
POND BAFFLING - Settling
205
LF
$ 35
7,175
4.
NEW POND - 7.0 MG
Earthwork - Cut & Fill
23,000
CY
$ 7
161,000
Sealing
200
TN
$ 150
30,000
5.
SEEDING
3000
SY
$ 0.50
1,500
6.
GRAVEL SURFACING
800
SY
$ 5
4,000
7.
ELECTRICAL
1
LS
$ 25,000
25,000
Subtotal $327,675
Contingencies $ 33,325
ESTIMATED CONSTRUCTION COST $361,000
Engineering $ 32,500
ESTIMATED TOTAL PROJECT COST $393,500
50
Table 5-1: Upgraded WWTP Operating Condition Summary
BOD Loading
lbs./1000 Ft3
4.66 lbs./1000 ft3
Aerators
4 Each
- Total Horsepower
60 Hp
- Horsepower/MG
12.7 HP/MG
- Oxygen Transfer(Site)
2,174 lbs. 02/day
D. AERATED CELL - 2nd (Series)
Number
1
Volume
4.7 MG
Depth
10 Feet
Detention Time
@ 2.34 MGD
2.01 Days
BOD Loading
lbs./1000 Ft3/day
2.09/1000 Ft3
Aerators
4 Each
- Total Horsepower
60 Hp
- Horsepower/MG
12.7 Hp/MG
- Oxygen Transfer (Site)
2,174 lbs. 02/day
E. FACULTATIVE/SETTLING CELL C
Number
1 Each
Volume
7.0 MG
Depth
10 Feet
Detention Time
@ 2.34 MGD
3.0 Days
Area
2.3 Acres
BOD Load
lbs./1000 Ft3
<0.1 lbs./1000 Ft3
F. FACULTATIVE/SETTLING CELL D
Number
1 Each
Volume
7.0 MG
Depth
10 Feet
Detention Time
@ 2.34 MGD
3.0 Days
Area
2.3 Acres
BOD Load
lbs./1000 Ft3
<0.1 lbs./1000 Ft3
F. CHLORINATION FACILITY
Volume 58,500 Gallons Total
Detention Time
@ 2.34 MGD 36 Minutes
49
However, operator flexibility would be built in to the extent that either aerated pond could be first
in line, providing parallel operation which would allow any Cell to be taken out of service without
interrupting operation. The specific mode of operation would be initially altered from the present
"aerated facultative" to a combination of "Complete and Partial Mix" system with the first pond
being operated in the complete mix mode and the second pond in a partial mix mode. Effluent
from the second pond would be split to two independent settling/maturation ponds prior to
chlorination. A plan layout of the Expanded Pond System is provided on Figure No. 7. Table 5-1
outlines the operating conditions for the upgraded system.
Table 5-1: Upgraded WWTP Operating Condition Summary
PARAMETER VALUE
Avg. Daily Flow
2.34 MGD
Minimum Flowrate
350 GPM
Maximum Flowrate
3000 GPM
Organic Load
2,929 lbs./day (150 mg/1)
Solids Load
3,906 lbs./day (200 mg/1)
pH Range
6-9
Unit Process Upgraded Condition
A. HEADWORKS
Grinder & Rotating Screen
- Number
1 Each
- Capacity (Each)
3000 GPM
Bypass
Manual Screen
Flow Measurement
0-6 MGD
B. PUMP STATION
Wet Well >5.0 Minimum Cycle Time
Centrifugal Pumps:
- Number 3 Each
- Capacity (Each) 1600 GPM
- Firm Capacity 4.61 MGD
C. AERATED CELL - 1 st
Number 1
Volume 4.7 MG
Depth 10 Feet
Detention Time
@ 2.34 MGD (Series) 2.01 Days
48
1 5. UPGRADING AND EXPANDING THE EXISTING PLANT
' The existing plant began operating in 1965 as a single lagoon serving an area adjacent to Highway
14. Since 1965, the plant has been through numerous modifications including the addition of two
aeration lagoons. The physical condition of the existing structures is' quite good, and the
performance of the plant is better than many advanced wastewater treatment facilities. The plant
' is meeting current standards and can be modified to perform full-time nitrification and phosphorus
removal if that should ever become necessary. Consequently, it makes sense to repair or update
' old equipment to extend the life of the system.
5.1 UPGRADING REQUIREMENTS
' As delineated earlier in this report, this plan proposes to upgrade and expand the existing aerated
pond system as was presented in 1986. The plan proposes to mirror image the second half of the
' existing system thereby producing two treatment trains which would function in the same manner
as the existing system. The layout of the existing yard piping and splitter boxes would allow the
system to operate in series or in parallel. This "doubling" of the system yields a hydraulic capacity
' of 2.34 MGD which is equal to an estimated 20-year design flow (2.9 MGD) with the excessive
' I/I flows removed (56 MGD). The upgrading would consist of the following:
• Replacing Pumps
' • Revise Yard Piping
• Increase Aeration Capacity
• Construct an Additional 7 MG Lagoon
• Install Pond Baffling
The pumping, piping, aeration, and disinfection facilities would be upgraded to handle an average
' daily flow of 2.34 MGD capacity.
Expansion of the aerated pond scheme to 2.34 MGD would require an additional pond for
aeration, settling, and maturation. The new pond would maintain a 10 foot to 12 foot water
depth with a volume of approximately 7.0 MG. The Chlorination Basin would also double in size
to allow adequate 30 minute detention time. The system would be designed to operate in series.
47
1
' UPGRADING & EXPANDING
EXISTING PLANT
4.5 PROCESS LIMITING FACTORS
There are three items identified previously which could be termed process -limiting factors which
theoretically limit the capacity of the existing system. Those items include the hydraulic detention
time of the system, the firm aeration capacity of the system, and the chlorination basin capacity
' and configuration. Each of these processes is discussed below.
' 4.5.1 HYDRAULIC DETENTION TIME
State design guidelines require that aerated lagoons be comprised of three cells and provide at
least 10 days of detention time with no more than five days of detention in the settling lagoon.
' Presently, the Boxelder plant provides 11.2 days of detention time at an average flow rate of 1.46
' MGD. Subsequently, the system is at 90 percent of its hydraulic detention capacity. When a
treatment system reaches 80 percent of hydraulic capacity, the State requires further planning to
determine the most cost-effective manner to expand the system.
' 4.5.2 AERATION CAPACITY
As mentioned previously, the permitted capacity of this system is 1,543 lbs. of BOD/day based
upon the operation of four aerators (three in the first lagoon and one in the second lagoon). This
is deemed the firm capacity of the system by virtue of the fact that one aerator is out of service in
' each lagoon. With all six of the aerators running, the capacity of the system is 2,329 lbs. of
BOD/day using 1.51 lbs. 02 per Hp-Hr and 1.4 lbs. 02 per pound of BOD oxidized (plus 86
lbs./day for surface area).
' . 4.5.3 CHLORINATION CAPACITY
As was delineated in the plant operating conditions summary (Table 4-1), the chlorination basin is
undersized for present flows and, therefore, does not provide the required 30 minutes detention
ttime at average flows. With a volume of 21,315 gallons, the system has a capacity of 1.12 MGD
which was exceeded routinely some time ago. Fortunately, the lack of adequate volume has not
created any problems. The system has not had any significant violations over the last 36 months.
1 Phase I of the plant expansion will add an additional chlorine contact basin increasing the total
detention time to 36 minutes.
Iri
Table 4S: BOD Removal Basedon the Marais -Shaw
anon
Scenario Influent # of Lagoons k
Detention
FIMent
Flow Rate
Plant Capacity
"n" Factor
Time
(mg/1) (Mg/1) k(t)
(days)
(mg/1)
(MGD)
(Ibs/day)
1 150 1 1.1
2.00
46.88
2.34
2948.40
46.88 1 0.267
2.00
30.56
2 150 1 1.1
2.00
46.88
2.34
2948.40
46.88 1 1.1
2.00
14.65
Scenario 1: 4 aerators in lagoon B, 2 aerators in
lagoon B
Scenario 2: 4 aerators in lagoon B, 4 aerators in
lagoon B
Plant Capacity based on an influent BOD concentration of 150
/l 2.34 M®
Considering a future configuration of using four aerators on lagoon A and B and two aerators on
the west portion of lagoons C and D, the daily oxygen input amounts to 6,522 lbs./day at 20
degrees C. Allowing 1.41bs. of oxygen per pound of BOD removed, the capacity of the system is
4,658 lbs. day. An additional 86 lbs./day could be added to that figure at a surface area loading of
20 lbs./acre/day yielding a total organic capacity of 4,781 lbs. BOD/day. If the oxygen utilization
interference is less than 0.4 lbs. per pound of BOD removed, the real capacity of the system lies
somewhere between 4,500 lbs./day and 5,000 lbs./day. The plant evaluation portion of the
CDOH permit sets the (firm) organic capacity of the system at 3,200 lbs./day based on four
aerators in lagoons A and B. Table 4-6 defines the total BOD removed from the system based on
the total number of aerators, oxygen producing output of each aerator, and total surface area of
the system.
Table 4-6: BOD Removal Based on Aeration Efficiencies
Scenario # of
Aerators
. Aerator OZ Produced BOD
Output Removal
(#02/da) (# 02/day) Ns/I)
Surface Area O= Produced
of Lagoons
(sores) (# ovda)
BOD
Removal
(ma/1)
Total BOD
Removed
(m8/1)
1
4
543.5
2174
1552.86
4.30
86
61.43
1614.29
2
8
543.5
4348
3105.71
6.60
132
94.29
3200.00
Scenario 1: Existing configuration with 3 aerators in lagoon B and 1 in lagoon A
Scenario 2: Proposed configuration with 4 aerators in lagoon B and 4 in lagoon A
45
The most popular equation utilized (and the one we have found the most accurate in predicting
the performance of a given system) is the Marais -Shaw Equation:
C;
+ k(t)o
n
Where: Ci = Influent BOD in mg/l
C. = Effluent BOD in mg/l
n = Number of lagoons in series with same characteristics
t Detention time of lagoon (system in series)
K = Temperature dependent Metabolism Factor
This formula can fairly accurately model an existing system if care is taken to utilize a metabolism
factor that accurately depicts, the field conditions. As is explained in detail in the EPA Design
Manual, the K-factor is influenced greatly by the amount of mixing/aeration imparted into the
lagoon. At mixing levels of greater than 15 Hp/MG (pp 105), a complete mix K.. value of 2.5
can be used (at 20 degrees Q. Others indicate that complete mixing requires 30 Hp/MG. At
aerated facultative levels of 6 to 8 Hp/MG, a partial mix V-pn value of 0.276 is used (@ 20 degrees
Q. We normally use 0.276 at low levels of mixing (6-8 Hp/MG), 1.50 at aerobic mixing levels
(15 Hp/MG), and 2.5 at complete mixing levels of 25 Hp/MG or more. With the first pond at
Boxelder being mixed at an energy input level of 12.7 Hp/MG, a K. value of 1.1 is appropriate.
In the second pond, a K. value of 0.276 is appropriate for a mixing level of 6.4 Hp/MG at 20
degrees Centigrade.
Table 4-5 considers two configuration scenarios and calculates the reduction in BOD through
lagoon A and B based on the Marais -Shaw equation. Notice that the proposed plan configuration
in scenario 2 uses eight 15 Hp aerators and produces a BOD effluent of 14.6 mg/l.
44
Figure No. 6
30
'& 25
E 20
15
10
w 5
0
Boxelder WWTP - Regression
Power Curves
500 1000 1500 2000 2500 3000 3500 4000 4500 5000
Influent Load - Ibs BOD/day
—x--All Data +Edited Data
A second analysis was conducted after throwing out the two high load conditions, but the results
were still not realistic. A straight line approach to the data points yields an approximate capacity
of 5,000 Ibs. BOD/day. Due to the consistency of the effluent produced, none of the typical
statistical approaches to modeling are deemed to be accurate in predicting the performance of this
system. Modeling using an aerated lagoon equation approach is examined on the following page.
The design of high rate aerated lagoon system is as much an art as it is a science. There are no
equations which will accurately describe the performance of a system with a relative degree of
accuracy as compared to activated -sludge or fixed -growth systems. Some of the more popular
methods of design for aerated lagoons are discussed in the EPA manual for Design of Municipal
Wastewater Stabilization Ponds (EPA-625/1-83-015). Several design approaches are discussed in
that manual for different types of aerated lagoons.
43
1
typical temperature variations the system might otherwise see. If the amount of infiltration into
the system is reduced via a comprehensive I/I correction program, the system might see a greater
. , degree of variation in the future.
In an attempt to model the performance of this system for the purposes of determining the organic
removal capacity based upon, actual data, several mathematical regression analyses were
performed including: 1) linear regression and, 2) power curve regression on variations of the
data. The results of the linear regression are graphed over the data points depicted in Figure No
1 5.
i
II
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1
I
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ICI
!_ J
1
Figure No. 5
Boxelder WWTP
Statistical Performance Curves
30
E 20 straight L vie
-15 0 0
ib
10 o 13 o
uJ 5
- Lmear R im
0
0 500 1,000 1,500 2,000 2,500 3,000 3,500 4,000 4,500 5,000
Influent Load - Ibs BOD/day
Due to the consistency of the effluent quality over wide ranges of influent, the linear regression
model is of little value since it indicates that you will probably never exceed 30 mg/1 in the effluent
at this facility. Knowing that a process breakthrough would be reached at some point, the linear
regression approach was dropped in favor of the Power Curve formulae (Y=axb) which generally
depicts an upward parabolic curve. Again, the -actual data points warp the curve downward
indicating a capacity beyond 5,000 as depicted in Figure No. 6.
42
1
Table 4-4:
Boxelder Summer Performance
Influent
--- - - - -- ------ ----------------------
-------------------
----------------
Effluent
- ---------------
---------- --- --------------------
Date
-------------
Flow
BOD
----
BOD
BOD
BOD
---------- --- --- -
Percent
-------------- ---
TSS
(Mo/Yr)
(MGD)
(mg/1)
(ibs./day)
(mg/1)
(lbs./day)
Removal
(mg/1)
.5/92
1.59
92
1220
6
80
93.5
12
6
1.86
61
946
5
78
91.8
9
7
1.69
82
1156
7
99
91.5
8
8
1.83
62
946
5
76
91.9
7
9
1.6
62
827
5
67
91.9
8
10
1.41
93
1094
6
71
93.5
4
5/93
1.48
106
1251
13.5
144
87
24
6
1.99
81
1324
8.9
133
89
17
7
1.91
95
1475
10.7
163
88
18
8
1.63
89
1225
8.9
121
90
9
9
1.68
81
1082
8.4
115
89
11
10
2.37
92
1819
7.1
96
92
10
5/94
1.58
83
1351
7
78
94
14
6 •
1.86
103
1396
5
79
94
'17
7
1.66
94
1227
4
43
96
13
8
1.60
89
1288
8
106
91
17
9
1.31
97
1212
7
74
94
16
10
1.0
LU
im
2
12
24
1$
Average
1.69
92
1,233
7.2
94
91.8
12.9
s The foregoing data indicates that there is very little variation in the performance of this system
between winter and summer months. Effluent BOD values over the past three years have
averaged 7.9 ing/1 in the winter and 7.2 mg/l in the summer. The corresponding removal
percentages are 91.9% and 91.8%. Further examination of this rather unusual phenomenon
revealed that there is little variation in the water temperature going into the system on an annual
basis. Over the last three years, the mean annual temperature has been 57 degrees Fahrenheit with
a minimum of 50 degrees Fahrenheit and a maximum of 67 degrees Fahrenheit. We believe this
relative .lack of temperature variation results in a very stable environment for the bacteria with
little stress effected by temperature or loading variations. It is theorized that the water
temperature is stabilized by the amount of groundwater infiltration into this system. With the
groundwater having a relatively constant water temperature, it has the effect of leveling out the
' 41
IF]
temperatures, biologic activity is greatly reduced resulting in lower treatment efficiencies. To
examine seasonal variations at Boxelder, data was broken down from Table 4-1 into winter and
summer months. Summer months include May through October with all other months falling into
the winter category. Tables 4-3 and 44 delineate the results:
Table 4-3:
Boaelder Winter Performance
Influent
- ------------------
--------------------....................................................-.....................................................
Effluent
.......................................................
Date
Flow
------------------------------
BOD
BOD
BOD
BOD
Percent
TSS
(Mo/Yr)
(MGD)
(mg/1)
(lbs./day)
(mg/1)
(lbs./day)
Removal
(mg/1)
1/92
1.27
102
1080
9
95
91.2
5 -
2
1.29
99
1065
7
75
92.9
8
3
1.64
72
985
5
68
93.1
5
4
1.56
78
1015
7
91
91.6
36
11
1.44
121
1453
5
60
95.9
7
12
1.38
73
840
5
58
93.2
21
1/93
1.35
93
1049
6
64
93.0
19
2
1.10
89
889
7
91
92.0
20
3
1.19
100
996
12
127
88.0
17
4
1.47
100
1226
17
223
82.0
26
11
1.65
83
1144
5
61
95.0
9
12
1.54
93
1194
7
83
93.0
21
1/94
1.49
111
1378
8
100
93.0
13
2
1.44
136
1421
11
117
92.0
29
3
1.36
99
1135.
7
78
93.0
27
4
1.31
101
1109
10
104
91.0
28
11
1.31
99
1083
7
73
93.0
22
12
L2A
2Z
im
$
M
22-
12
Average 1.31 97 11116 7.9 95 91.9 18.4
40
DATE
Mo/Yr
Table 4-2 Continued: Boxelder Monthly Operating Data
INFLUENT EFFLUENT
----------------------------------- -----------------------------------------------------
FLOW BOD BOD BOD BOD % BOD
(MGD) (mo/l) LBS./DAY (mg/1) LBS./DAY REMOVED
TSS
(mg/1)
11
1.65
83
1144
4.9
61
95
9
12
1.54
93
1194
6.7
83
93
21
1/94
1.49
111
1378
8.0
100
93
13
2
1.44
136
1421
11
117
92
29
3
1.36
99
1135
7
78
93
27
4
1.31
101
1109
10
104
91
28
5
1.58
103
1351
7
78
94
14
6
1.86
94
1396
5
79
94
17
7
1.66
89
1227
4
43
96
13
8
1.60
97
1288
8
106
91
17
9
1.31
111
1212
7
74
94
16
10
1.37
119
1358
7
77
94
18
11
1.31
99
1083
7
73
93
22
12/94
1.24
22
1212
$
$C
22
12
Average
1.50
94.5
19174
7.5
94.5
91.8
15.6
As is illustrated on the preceding table, this plant has performed exceptionally well over the past
years. There have been no permit violations regarding effluent BOD (mg/1), TSS (mg/1), or in
percent removal (91.8% average). Likewise, the system has not had any Fecal Coliform
infractions over this time. period. The organic loads on the plant have varied from 827 to 2,449
lbs./day with little variation in the effluent quality which indicates that the plant maintains a very
stable process.
The remarkably stable performance of the system raised questions as to the variability of the plant
during changing seasons. Most aerated lagoons display a much lower performance during cold
weather months due to lower water temperatures. Seasonal variations from 35 degrees
Fahrenheit in the winter to 70 degrees Fahrenheit in the summer are common. At the lower
' 39
1
4.4 PLANT PERFORMANCE
Subsequent to reviewing the system layout and operating conditions, a review of the performance
of the system over the past few years is necessary to assess its ability to perform adequately (or
inadequately) under varying conditions. The influent -effluent records over the last three years for
the system were examined to ascertain the relative performance of the system. A summary of the
- values are presented in the Table 4-2:
------------------------------------------------------
DATE
Mo/Yr
Table 4-2: Bozelder Monthly Operating Data
INFLUENT EFFLUENT
-------------------------------------------------------
FLOW BOD BOD BOD BOD % BOD
(MGD) (mg/1) LBS./DAY (mg/1) LBS./DAY REMOVED
TSS
(mg/1)
1/92
1.27
102
1,080
9
95
91.2
5
2
1.29
99
1,065
7
75
92.9
8
3
1.64
72
985
5
68
93.1
5
4
1.56
78
1,015
7
91
91.0
36
5
1.59
92
11220
6
80
93.5
12
6
1.86
61
946
5
78
91.8
9
7
1.69
82
1,156
7
99
91.5
8
8
1.83
62
946
5
76
91.9
7
9
1.6
62
827
5
67
91.9
8
10
1.41
93
1,094
6
71
93.5
4
11
1.44
121
1,453
5
60
95.9
7
12
1.38
73
840
5
58
93.2
21
1/93
1.35
93
1049
6.1
64
93
19
2
1.10
89
889
7.5
91
92
20
3
1.19
100
996
12.4
127
88
17
4
1.47
100
1226
17.8
223
82
26
5
1.48
106
1252
13.5
144
87
24
6
1.99
81
1342
8.9
133
89
17
7
1.91
95
1475
10.7
163
88
18
8
1.63
89
1225
8.9
121
90
9
9
1.68
81
1082
8.4
115
89
11
10
2.37
92
1819
7.1
96
92
10
W.
Table 4-1: Boaelder 1994 WWTP Operating Condition Summary
lbs./1000 Ft'
1.71 lbs./1000 ft3
Aerators
4 Each
- Total Horsepower
60 Hp
- Horsepower/MG
12.7 HP/MG
- Oxygen Transfer(Site)
2,174 lbs. 02/day
D. AERATED CELL - 2nd (Series)
Number
1
Volume
4.7 MG
Depth
10 Feet
Detention Time
@ 1.46 MGD
3.22 Days
BOD Loading
lbs./1000 Ft'/day
<0.5 lbs./1000 Ft'
Aerators
2 Each
- Total Horsepower
30 Hp
- Horsepower/MG
6.4 Hp/MG
- Oxygen Transfer (Site)
1,087 lbs. 02/day
E. FACULTATIVE/SETTLING
CELL C
Number
1 Each
Volume
7.0 MG
Depth
10 Feet
Detention Time
@ 1.46 MGD
4.79 Days
Area
2:3 Acres
BOD Load
lbs./1000 Ft'
<0.1 lbs./1000 Ft3
F. CHLORINATION FACILITY
Volume
21,315 Gallons Total
Detention Time
@ 1.46 MGD
21 Minutes
Number of Basins
1 Each
Independent Trains
2 Each
Length/Width Ratio
l 8:1
G. DECHLORINATION FACILITY
Feed Rate
30 lbs./day
Re -aeration Method
Aeration Tray
H. EFFLUENT FLUME
Type: 6" - Parshall
Capacity 0-6 MGD
Condition Unlevel
37
r
effluent is immediately re -aerated in trays below the basin. A Parshall flume for measuring plant
effluent flows is located just beyond the re -aeration tray. Effluent flows travel about 200 feet to
Boxelder Creek where it is discharged.
4.3 PLANT OPERATIONAL PARAMETERS
rUtilizing the 1994 average loads and flows, the unit process conditions at the plant were examined
with respect to required or typical operating conditions for aerated lagoons. This examination is
summarized in Table 4-1.
II
1,
r�
r
Table 4-1: Boxelder 1994 WWTP Operating Condition Summary
PARAMETER VALUE
Avg. Daily Flow
1.46 MGD
Minimum Flowrate
350 GPM
Maximum Flowrate
3000 GPM
Organic Load
1279 lbs./day (105 mg/1)
Solids Load
20101bs./day (165 mg/1)
pH Range
6-9
Unit Process Existing Condition
A. HEADWORKS
Grinder & Rotating Screen
- Number 1 Each
- Capacity (Each) 3000 GPM
Bypass Manual Screen
Flow Measurement 0-6 MGD
B. PUMP STATION
Wet Well >5.0 Minimum Cycle Time
Centrifugal Pumps:
- Number 3 Each
- Capacity (Each) 1300 GPM
- Firm Capacity 3.74 MGD
C. AERATED CELL - I st
Number
1
Volume
4.7 MG
Depth
10 Feet
Detention Time
@ 1.46 MGD (Series)
3.22 Days
BOD Loading
36
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I
I
I
I
11
I
4.2.5 SYSTEM HYDRAULIC CAPACITY
The hydraulic capacity of the pumping system and transfer lines all fall within a 5.5 to 6.0 MGD
flow rate range. Starting at the effluent box from the settling lagoon and working upstream, the
system can handle a 5.75 MGD flowrate and still maintain freeboard in the first lagoon.
Obviously, hydraulic capacity is not a limiting issue for the purposes of this report.
With a total lagoon volume of 16.4 MG, the system can handle a 1.64 MGD average daily flow
and provide a 10-day detention time across the system as suggested in the CDOH design
guidelines for aerated lagoons. The proposed plan for the addition of a 7 MG lagoon would
increase the total volume of the lagoons to 23.4 MG which would provide a 10-day detention
time across the system at a flow rate of 2.34 MGD.
4.2.6 CHLORINATION
Chlorine is injected into the flow stream in the line ahead of the chlorination basin. The
chlorination system utilizes a standard chlorine gas ejector system. Plant product water is used to
carry the chlorine solution to the flow stream. Product water is supplied by one of two pumps
located in the lower level of the pumping station. The chlorination system is set up to handle one -
ton gas cylinders.
The chlorination basin is constructed in a two -train arrangement with each side containing a
volume of 12,500 gallons. The prior total volume is 23,000 gallons which provides the required
30 minutes detention time at flows of 1.14 MGD (767 GPM) or less. At an average daily flow
rate of 1.42 MGD, the chlorination contact time is 23.3 minutes which is not adequate to meet
State guidelines (30 minutes). Technically, this is a process limiting factor. The addition of a new
43,000 gallon contact basin, currently in the approval process, would increase the detention time
within the basins to 30 minutes at a peak flow rate of 3000 GPM (4.35 MGD).
4.2.7 DECHLORINATION SYSTEM
Sulphur dioxide is used to perform dechlorination after the contact basin. The sulphur dioxide gas
is supplied through a diffuser located just ahead of the effluent weir in the chlorination basin. The
35
�J
I
11
I
1
r
H
I
power input to the 4.7 MG pond is 12.7 Hp/MG which is above that of a normal aerated
facultative lagoon and below the threshold for complete mix (25 HP/MG). This mid -range is
commonly referred to as an aerated - aerobic lagoon system.
The second aerated lagoon has two 15 Hp, floating surface aerators. Both of these units are
utilized continuously. The energy input into the second aerated lagoon is 6.4 Hp/MG which is
within the range of an aerated facultative lagoon (6 - 8 Hp/MG).
The amount of oxygen dispersed by the aeration units in each lagoon is dependent upon the actual
water temperature, but the units themselves are each rated at 3.14 lbs. 07/Hp-Hr at standard
conditions. This converts to approximately l .51 to 1.61bs. 02/Hp-Hr at site conditions for water
temperatures of 18 to 20 degrees, respectively.
4.2.4 SETTLING LAGOON
Flow from the aerated lagoons is transferred to the 7.0 MGD settling lagoon for solids separation
prior to chlorination and discharge. The settling lagoon is divided into two sections by a floating
baffle situated at the midpoint of the lagoon. Flows from the aerated lagoon are discharged into
the upstream portion of the settling pond which must pass through two submerged windows in
the baffle to enter the second portion of the pond. The settling lagoon is approximately 10 feet
deep and has a surface area of 2.3 acres. Effluent is drawn off at depth through one of two
discharge lines. One is located at a depth of approximately 7 feet and the other at a depth of
about 3 feet below the water surface. This arrangement limits the degree of algae influence on the
effluent solids count.
Solids removals from this plant have been excellent over the years. The average effluent over the
past five years is 14 mg/1 against a 75 mg/l NPDES standard. At a current average daily flow rate
of 1.46 MGD, the detention time in the settling pond is 4.79 days which is within the 2 to 5-day
time period suggested in the CDOH design guidelines. At the permitted flow rate of 1.5 MGD,
the average detention time is at 4.67 days.
34
I
I
I
I
I
I
I
original system is comprised of a rotating screen and one grinder. The flume has a capacity of 0
to 6 MGD. The headworks also contains a bypass channel with a manual barscreen which allows
the operator to bypass the flume and grinders for maintenance purposes.
4.2.2 PUMPING STATION
The pumping station is built as a wetwell-drywell system with the pumps housed in the lower level
of the drywell. Flow into the wetwell is pumped (by three pumps) up to a splitter box for
distribution to the aerated lagoons. In 1988, the pumps in the station were replaced with three
vertical centrifugal units each with a capacity of 1,300 gpm (1.87 MGD). The resulting maximum
pumping capacity is 5.6 MGD with a firm 2 pump capacity of 3.74 MGD. The force main is a 14-
inch diameter ductile iron pipe. The pumps are controlled on and off by a bubbler -type system
with the lead pump being rotated manually every week.
4.2.3 AERATION LAGOON SYSTEM
The Boxelder system contains two aerated lagoons that are presently configured to operate in
series. Both lagoons have a water depth of approximately 10 feet and have surface dimensions of
about 200 feet by 200 feet. The side slope of the inward walls is three to one, and the resulting
liquid volume per lagoon is 4.7 MG. The piping network from the sputter box allows either
aerated lagoon to serve as the primary lagoon thereby allowing the other to be taken out of
service. Each aerated lagoon has a drain back to the pumping station, and flow from each lagoon
can be routed directly to the settling lagoon. This arrangement allows parallel or series operation
of the aerated lagoons. For series operation, there is a transfer line between the two aerated
Ilagoons.
11
I
The first lagoon is aerated by four 15 Hp, floating surface aerators. These propeller -type aerators
pump the wastewater up through the center of the unit and sling or splash the waste out around
the periphery of the unit. The District does not operate all of these units continuously since the
plant is able to maintain adequate dissolved oxygen levels and perform adequate treatment using
only two or three of the four units most of the year. Four units are used periodically during warm
summer months when transfer efficiencies are at their lowest. With four units operating, the
33
4. EXISTING WASTEWATER TREATMENT SYSTEM
4.1 GENERAL
Examination of the existing facilities is necessary to determine the capabilities of the system in
operation under the following conditions:
• Existing Conditions
• Future Conditions with Upgrades
The performance of the system, both past and present, yields valuable information as to the ability
of the system to meet new BOD and flowrate demands. The degree of these new demands affects
whether or not there are modifications that can be implemented which would cost-effectively
extend the life of the existing system. A good working knowledge as to the condition and
effectiveness of the various components of the system is essential to making sound decisions.
4.2 UNIT PROCESS REVIEW
Examination of the existing facilities is necessary to determine the operating capabilities of the
system under both existing and future conditions. The basic treatment components consist of the
following:
• Preliminary Treatment
• Pumping
' • Aeration in Ponds A & B
• Settling & Maturation Pond C
' • Chlorination & Dechlorination
• Flow Measurements
4.2.1 HEADwoRKS
The headworks is situated within a pumping station wetwell. The influent channel is housed on a
mid -level platform at the elevation of the influent line and directs influent flow through a Parshall
flume. After the flume, flow is directed through a grinder unit before being discharged down into
the wetwell. Both the flume and the maceration system were installed in the 1988 upgrade. The
' 32
consistency in flows through our treatment plant. Any scenario involving flow significant variability at
the headworks would require a new evaluation of local limits. Users of the District system have been
informed as to the requirements of the program, and many have already incorporated substantial
additions and improvements to their processes and facilities in order to comply with our local limits.
Any diversion or partial diversion of flows would invalidate local limits criteria and is, thus, not a
feasible option for the District at this time.
The additional lagoon is a necessary facility expansion to assist the District with its pretreatment
program evaluation since it will make possible the most efficient and effective control over plant
operations and performance. The additional lagoon will make possible the temporary removal of any
single lagoon from the flow path to gain access for dry sludge removal and compliance with 503 sludge
disposal regulations, as well as the accurate characterization of sludge for pollutants of concern. This is
a major justification for the site application submitted not to mention the need for redundancy of the
operational systems in the plant.
Finally, the District Board of Directors has decided that it is not feasible, nor could it be cost-effective,
to consider any partial flow diversion to another treatment facility. Any consideration of a total flow
diversion to a regional facility, should long-range planning efforts result in the creation of such a
facility, would be predicated on effluent flows only from the existing plant which would continue to be
operated as a pretreatment facility.
31
Summary
' The Boxelder Sanitation District has developed an exemplary pretreatment program with a strong
' element of pollution prevention capable of protecting the POTW and maintaining an excellent record of
discharge permit compliance while providing the highest level of service to the public. Legal authority
' to implement the program and enforce requirements of the Rules and Regulations of the District has
been established, and the users of the POTW have been identified. Regular and routine inspection of
' commercial and industrial users has been conducted and remains a high priority for the future of the
District. Effective local limits have been developed for the commercial and industrial users of the
' POTW and are currently being enforced. Increasingly dependable and accurate assessment of
wastestream pollutant concentrations and WWTP removal efficiencies will be facilitated as the
District's pretreatment program progresses and the likelihood of slug discharges of pollutants of
concern diminishes. The District remains committed to enforcing its pretreatment program which
protects the health and safety of POTW personnel and environmental integrity while maintaining
limitations for commercial and industrial dischargers that are attainable and reasonable.
' 3.4.2 PRETREAT EWF CONTROL AND LOCAL Limos
' The District has committed to comply with all of the requirements of the NPDES compliance schedule
conditions including the Industrial Waste Management (IWM) Program (Pretreatment) Regulations.
' USEPA Region VIII representatives responsible for administration of Pretreatment Programs have
carefully examined the District's IWM program, and their approval of the program was granted in July
' 1994
' This IWM program includes the development of local limits unique to the District's aerated lagoon
treatment system. The District believes that Boxelder was the first case where local limits for a lagoon
system, including the determination of maximum allowable headworks loading (MARL) for metals
(both chronic and acute) and the maximum allowable industrial loading (MAIL) for each metal, has
' been accomplished in this region.
' A considerable investment of capital was made by the District to accomplish this task which is central
to the IWM program. The local limits now in force in the District are dependent on maintaining
' 30
local limits ineffective. Since the local limits are based upon allowable headworks loading, these limits
' are completely site -specific and unique to the District's treatment works. Practically speaking, it would
' be impossible to administer enforceable, technology -based local limits where flows might be split
between two or more treatment facilities because of differences in allowable headworks loadings and
' the variability in proportionate flows to each facility.
' Ongoing Water Quality Monitoring
A considerable investment of time and expense is appropriated to monitoring of water quality in the
' collection system in order to monitor and control sources of pollution and to assure that costs of
service are equitably distributed. Configuration of the sewer collection system in the District is such
that, in most areas, flows contributed by commercial and industrial users may be distinguished from
those of residential users. During 1994, the District conducted a comprehensive evaluation of flows in
' the collection system. Water quality parameters monitored included oil and grease (O&G), total
suspended solids (TSS), five-day biochemical oxygen demand (BOD), and the eight metals affected by
' local limits. Sampling was performed by District Staff using District -owned equipment. All samples
were of a 24-hour, flow -proportioned composite type.
Analytical results of the 1994 monitoring program show highly variable pollutant concentrations
' among sample sites. Residential flows contributed consistently higher concentrations of pollutants than
commercial flows. Average flow -weighted BOD concentrations do not vary greatly between the
' respective sources, with 131 mg/L from residential and 128 mg/L from commercial. Total mass
' loading of BOD of 324 lb./day was contributed by residential flows and 3861b./day was contributed by
commercial flows. TSS concentrations in residential flows were significantly higher than in commercial
' flows, with flow -weighted average of 266 mg/L in residential as compared to 202 mg/L for
commercial. Total mass loading of 654 lb./day TSS was contributed by residential flows and 613
lb./day was contributed by commercial flows. O&G concentrations were higher for residential at 11.3
mg/L than for commercial at 8.6 mg/L. Total mass loading of 251b./day was contributed by residential
' flows and 26 lb./day was contributed by commercial flows. Most metals concentrations were found to
be below detection limits; therefore there were no instances of exceeding of local limits. The District
' plans to continue water quality monitoring in the collection system on a regular basis in the future.
29
5. Calculation of maximum allowable industrial load (MATT. in lb./d) for each metal for both
chronic (30-day max) and acute,(daily max). This MAIL incorporates a safety factor of 25%
of which 10% is an allowance for future growth and the remaining 15% is a mandatory
minimum.
' 6. Determination of a concentration -based local limit for each metal for both chronic and acute
conditions.
11
Local limits for concentrations of metals in discharges from industrial users to the Boxelder Sanitation
District POTW are summarized in Table 3-8:
Table 3-8: Local Limits for Boxelder Sanitation District
METAL
LOCAL LIMIT (mg/L)
CHRONIC (30 day max) ACUTE (daily
max)
Cadmium
0.53
7.68
Hexavalent Chromium 0.67
0.86
Copper
2.97
6.34
Lead
5.11
170
Mercury
0.0002
0.14
Nickel
14.49
N/A
Silver
0.72
4.24
Zinc
50
50
Continued compliance with NPDES discharge permit limitations and protection of POTW personnel
health are foremost concerns of the District. The conservative approach used to develop Boxelder
Sanitation District's local limits provides reasonable concentration -based limits and provides the highest
degree of reliability for continued compliance with the District's NPDES discharge permit. The District
intends to revisit its local limits periodically over the next three years while enforcing the local limits
currently in effect. It may be appropriate to amend local limits after establishing a more comprehensive
baseline monitoring record, assuring that the most appropriate local limits are enforced in the Boxelder
service area.
It is worthwhile to note that, as the maximum allowable headworks loading is the key element in the
determination of local limits, any significant change in flows through the headworks would render the
28
metals regulated by the District's discharge permit. These metals have been routinely monitored in the
' final effluent on a monthly basis since January 1992 per discharge permit requirements.
The District followed local limits development guidance provided by EPA Region VIH pretreatment
' program personnel and submitted its Local Limits documentation for approval by EPA and CDPH&E
in May 1993 as required by Boxelder.'s Sanitation District's effective NPDES discharge permit. After
' review by EPA and CDPH&E, the District was directed in December, 1993 to re-evaluate these limits
with some modifications in approach. This re-evaluation of local limits documentation (with
' accompanying historic data and calculations) was conducted and submitted by the District and
approved by EPA and CDPH&E for incorporation in the Pretreatment Program.
' . Boxelder's WWTP consists of an aerated lagoon system in which residual sludge is subject to detention
' times measured in terms of several years. Sludge sampling has indicated metals concentrations far
below the most restrictive ceiling concentrations listed in 40 CFR 503. The consequence of the
' relatively low metals concentrations in the sludge is that NPDES discharge permit limits on WWTP
effluent metals concentration/loading control local limits determination. Thus, local limits development
. is based on historic data from monitoring water quality of wastewater flows into and out of the
treatment plant.
Guidance for local limits development that has been available through the Colorado Department of
Health and EPA has been utilized as much as possible. This guidance indicates the following steps:
' 1. Collection of historic metals monitoring data for residential contributions to POTW system
flows and WWTP influent and effluent, as well as POTW flow data and significant industrial
' user (STU) flow data.
2. Comparison of metals concentrations in WWTP influent and effluent for the purpose of
calculating removal efficiencies.
' 3. Calculation of maximum allowable headworks loading (MARL in lb./d) for each metal for both
chronic and acute conditions.
' 4. Estimation of domestic (residential) contribution to metals loading at WWTP headworks.
27
Staff of the District routinely and regularly conduct unannounced inspections of all non-residential
users' facilities to determine compliance with District Rules and Regulations and assess the potential for
discharges posing risks of interference, upset, or pass through. Attention is given to the type and
nature of the users operations, materials and chemicals used or stored in areas where discharge is
possible, flow rates and pollutant concentrations normally discharged to the system, pretreatment
equipment used, practices and policies for chemical spill prevention and/or response in use, as well as
any other consideration applicable to administration of the program. In any instance where the
inspector finds a reasonable potential for a problematic discharge, the inspector may obtain copies of
maintenance records, material safety data sheets, and samples are obtained for laboratory analysis of
pollutant concentration. The District maintains a policy of paying the costs of the first sampling event
required by the District.
Local Limits
An integral element of a pretreatment program is the development of technically -based effluent
limitations (local limits). The District has maintained standards for pollutant loadings from various
types of users for many years, along with a surcharge schedule for the assessment of additional charges
for excessive loadings. The Pretreatment Program also requires the determination by the District of
Local Limits for pollutants of concern. These local limits are numeric limits for amounts of pollutants
discharged from non-residential users of the POTW.
In order to develop local limits for the Boxelder Sanitation District in accordance with the District's
NPDES permit, it was necessary to first determine which substances might pose risks to the integrity of
the Boxelder wastewater treatment plant (WWTP) and collection system. This was accomplished by
means of a comprehensive priority pollutant scan performed on Boxelder WWTP influent in June of
1992 as part of Boxelder.'s Sanitation District's "Draft Plan of Study for the Sampling Phase of the
Local Limits Evaluation" submitted to EPA and Colorado Department of Health in November 1992.
The EPA and CDPH&E (the regulatory agencies responsible for administration of industrial
pretreatment programs in Colorado) recommended that Boxelder.'s Sanitation District's proceed with
implementation of the program as proposed at that time. The findings of this evaluation project
identified eight metals ('pollutants of concern') for which local limits have been developed. These are
the metals cadmium, hexavalent chromium, copper, lead, mercury, nickel, silver, and zinc; the same
26
In 1991, the District conducted its first survey of industrial users. This survey was submitted to the
' Colorado Department of Health in 1992. Subsequently, walking surveys were commenced in 1993 in
order to refine the data base, particularly in regard to users of multiple space buildings in the District.
As a result of the comprehensive surveys performed by District personnel, there is a very high level of
' confidence that all users have been identified. All users identified are required to complete and sign
questionnaires which provide basic information about the users operations and discharges and provide
a basis for prioritization for scheduling future inspections.
Discharge Permits
' A significant change in District policy was implemented in 1993, requiring that all non-residential users
obtain discharge permits. Off -site Owners of buildings occupied by commercial or industrial users are
' now required to obtain from the District a Type A Limited Liability Pen -nit. Further, all non-residential
users occupying any space with direct access to a discharge point are now required to obtain a Pennit
' to Discharge Pollutant Wastes. These permits provide the basis for identification of users and the
maintenance of District records of commercial and industrial users; acknowledgment by the users (both
' owners and occupants) of the Rules and Regulations of the District; and the right of access to premises
for inspection, sampling, and enforcement by District personnel or agents.
' Inspection
District personnel regularly conduct unannounced inspections of users' facilities., to determine
compliance with District Rules and Regulations and assesses the potential for discharges posing risks of
interference, upset, or pass through. Attention is given to the type and nature of the user's operations;
materials and chemicals used or stored in areas where discharge is possible; flow rates and pollutants
concentrations normally discharged to the system; pretreatment equipment used; practices and policies
for chemical spill prevention and/or response; as well as any other consideration applicable to
administration of the program. Based upon these inspections, if the inspector finds any reasonable
' concern that there may be a problematic discharge, representative discharge samples are obtained for
laboratory analysis. The District maintains a policy of paying costs for the first sampling event required
' by the District, whereas the user is normally required to pay all costs for water quality monitoring.
25
collection system, for instance oils and greases that build up and block flow or highly acidic wastes that
deteriorate pipe materials. Upset means anything that disrupts the physical, chemical, or
microbiological processes used in the treatment facilities, for instance a slug loading of a toxic chemical
killing off the microorganisms which remove pollutants from the wastestream. Pass through means
anything that results in pollutants passing through the treatment facility untreated, for instance metals
which are not amenable to conventional treatment that remain in solution and are present in the final
discharge.
The Boxelder Sanitation District is unique in the diversity and proportion of commercial and industrial
users as compared to residential users. The District also recognizes the importance of pollution
prevention in the reduction or elimination of point source pollution. As such, the pretreatment
program has been developed to incorporate the objectives of pollution prevention by including a more
broad collection system monitoring program and public education and information program than that
specifically required by Federal or State law.
The District's Rules and Regulations set forth uniform requirements for all users of the District's
wastewater collection and treatment system and enables the District to comply with all applicable
provisions of State and Federal laws related to the operation of publicly owned treatment .works. The
District's pretreatment program is composed of several elements: this includes the District's Rules and
Regulations; Legal Authority; Inspection; Sampling and Reporting; Enforcement Response Plan;
Implementation Evaluation; and Local Limits. The elements of the Pretreatment Program together
authorize the issuance of wastewater discharge permits; provide for monitoring and enforcement
activities; establish administrative review procedures; require user reporting; and provide for the setting
of fees for equitable distribution of costs resulting from the operation of the District system.
How is the program implemented?
Identification
The first step in implementing the program is to identify all possible industrial and commercial users,
particularly Significant Industrial Users and Categorical Industrial Users, who are subject to the
pretreatment program. The District has completed several surveys of commercial and industrial users.
24
' Table 3-7: NPDES Permitted Values for Boaelder Sanitation District
Parameter Monthly Avg Weekly Avg
Biochemical Oxygen Demand 30 mg/1 45 mg/1
Total Suspended Solids 75 mg/l 110 mg/l
' Ammonia Nitrogen - N N/A N/A
Fecal Coliform 3,710 MPN 7,420 MPN
pH 6-9 6-9
Residual Chlorine (Instream) .008 mg/l .008 mg/1
' The preceding limits are for a discharging lagoon/pond system as evidenced by the higher
suspended solids level of 75 mg/l versus a more common value of 30 mg/1 used for mechanical
' plants. The higher effluent solids standard is normally allowed for lagoon systems to account for
' problems with algae in the effluent which adversely affects the solids testing procedures.
3.4 INDUSTRIAL PRETREATMENT PROGRAM
3.4.1 OVERVIEW OF THE INDUSTRIAL PRETREATMENT PROGRAM
In July of 1994, the USEPA approved the Boxelder Sanitation District's Industrial Pretreatment
Program. The District is required, through its Colorado Discharge Permit, to administer and enforce its
' Pretreatment Program. The purpose of establishing industrial pretreatment programs for publicly
owned treatment works (POTWs) as stated in 40 Code of Federal Regulations (CFR) 403 is to prevent
' interference in collection system components, upset or pass through in the treatment operations, and to
improve opportunities for beneficial use of sludge. Industrial Pretreatment simply means that industrial
users, as well as certain commercial users, be required to remove or reduce the concentration of
hazardous or incompatible pollutants from their wastewater before discharge into the public sewer
' system. A functional Pretreatment Program reduces the potential of hazardous wastes being
introduced into a sewage treatment facility and/or being discharged into the environment.
Under the Federal Clean Water Act, Publicly Owned Treatment Works are responsible for preventing
' interference in the collection system, upsets in the treatment facilities, and pass through of pollutants to
waterways. Interference means anything that inhibits the normal transfer of wastewater through the
23
Table 3-6: Design Parameters
Parameter Design Value
Average Daily Flow 2.34 MGD (adjusted for I/I Removal)
Minimum Flowrate 0.43 MGD (300 GPM)
Maximum Flowrate 5.0 MGD (3,500 GPM)
Organic Loading 2,929 lbs. BOD/Day (150 mg/1)
Solids Loading 3,906 lbs. TSS/Day (200 mg/1)
Hydrogen Ion (pH) 6-9
3.3 EFFLUENT LIMITATIONS
In recent years, public awareness concerning the deterioration of the nation's surface .waters has
greatly increased. This increased awareness led to the enactment of the Federal Water Pollution
Control Act Amendments of 1972 (P.L. 92-500). This Act authorized the State pollution control
agencies to work in cooperation with the EPA to set goals, administer the process, and enforce
the regulations as necessary to achieve the national goals.
As a result, the EPA (through each State agency) publishes regulations establishing minimum
treatment criteria for public treatment works discharging to public water courses. Subsequently,
the Colorado Department of Health publishes water quality criteria for all streams in the State.
These standards are used to derive limits for the NPDES Permits issued to each treatment facility.
Located in Appendix A is a report titled An Evaluation Of Water Quality Based Effluent Limitations
For The Expansion Of The Boxelder Sanitation District Plant that projects the new reduced effluent
limitations for metals and ammonia based on the assumptions that were included in the Rationale for
Public Notice for Permit No. CO-0020478 and the increased plant flow rate of 2.34 MGD.
The existing NPDES permit for the Boxelder Wastewater treatment facility is outlined in Table 3-
7.
07K
I
1
I
I
3.2 WASTELOAD AND FLOW FORECAST
3.2.1 FLow
On the basis of the foregoing actual tap projection of 1,900 and the previously derived average of
11530 GPD per tap, a design average daily flow of 2,900,000 gallons (2.90 MGD) is derived. For
examination of factors affected by minimum and maximum flowrates, a minimum flowrate of 300
gpm (432,000 GPD) and a maximum flowrate of 3,000 GPM (4.35 MGD) will be utilized.
The District is implementing an I/I reduction program aimed at reducing the excessive amount of
I/I entering the collection system. As indicated in the I/I Analysis Report, approximately 0.56
MGD of extraneous flow can be cost-effectively removed from the system. Subtracting this value
from the design figure derived above yields an adjusted average daily design flow of 2.34 MGD.
3.2.2 BIOCHEMICAL OXYGEN DEMAND (BOD5)
The discussions presented earlier regarding the relative strength of the organic load received at
the plant classified the BOD as relatively weak. The average strength over the last three years
was 94 mg/l. For examination of design conditions, a conservative value of 150 mg/1 will be used.
This concentration converts to a daily loading of 2,9291bs. BOD per day at 2.34 MGD.
3.2.3 TOTAL SUSPENDED SOLIDS (TSS)
The average suspended solids value over the last 3 years is 116 mg/1 with annual averages ranging
from 113 mg/1 to 165 mg/1. To insure that an adequate examination of conditions that could
prevail at the plant over a period of time is conducted, a value of 200 mg/1 SS will be used. This
concentration converts to an average daily solids loading of 3,906 lbs./day at 2.34 MGD.
3.2.4 DESIGN LOAD AND FLOW SUMMARY
Table 3-6 provides a summary of the basic design parameters to be used in examining future
treatment needs at the Boxelder Wastewater Treatment Plant:
21
Table 3-4 provides a summary of the suspended solids loading at the plant over the last five years
Table 3-4: Suspended Solids Strength and Load
Year
Avg. Annual
Avg. Annual .
Concentration (mg/1)
Load (lbs../day)
......................................................................................................
1990
.... ..............
108
............ . .. . .............................. ... ... ...............
1,189
1991
127
1,472
1992
113
11414
1993
124
1666
1994
165
2,010
3.1.4 SUMMARY OF WASTEWATER CHARACTERISTICS
The strength of the wastewater discharged to the treatment plant over the past five years can be
considered to be relatively weak with regard to the major design parameters of BOD5 and SS.
The pH level of the wastewater received at the plant is normal. Table 3-5 provides a summary of
the waste characteristics discussed in this section. All values in the table are based on daily dry
weather averages.
Table 3-5: Wastewater Characteristics Summary
Year Flow BOD Suspended Solids
(MGD) (mg/l ) (lbs./day) (mg/1) (lbs.day)
1990
1.32
125
1381
108
1189
1991
1.39
113
1290
127
1472
1992
1.50
86
1072
113
1414
1993
1.61
92
1273
124
1666
1994
1.46
105
1279
165
2010
20
around 200 mg/l. Values of 100 mg/l are considered weak and 300 mg/l very strong. The
majority of the monthly average values for Boxelder fall within a 60 to 120 mg/l bracket.
Since the per capita contribution (analyzed above) appeared to be normal or slightly above
normal, the question arises as to why the BOD strength received is so weak. The answer lies in
the occurrence of 14 and the relatively high percentage of commercial and industrial contribution
at low strength. Accounting for the excessive I/I alone would change the 1994 average BOD
concentration from 105 to 170 mg/l. The annual average BOD strength and load over the past
five years are outlined in Table 3-3.
Table 3-3: BOD Strength and Load
Year Avg. Annual Avg. Annual
(mg/1) Load (lbs../day)
1990
125
1,381
1991
113
1,290
1992
86
1,072
1993
92
1,223
1994
105
1,279
Without any significant reduction in M, it is anticipated that the BOD waste strength will remain
in the neighborhood of 90 to 110 mg/l.
3.1.3 SUSPENDED SOLIDS (SS)
The solids in municipal wastewater contain both organic (volatile SS) and inorganic (inert SS)
substances. The organic substances generally include excrement, soaps, garbage, rags, and by-
products from industrial processes. The inorganic substances are clay, sand, grit, plastic
materials, dissolved minerals, and some by-products from industrial processes. The total amount
of solid matter and the proportions of various materials will vary considerably with the type and
source of the wastewater and with the season of the year. Suspended solids are that portion of
the total solids which is not dissolved in the water. Wastewater from a primarily residential area
has been shown to have a SS content of approximately 0.20 lbs. per capita per day. Under normal
conditions, this translates to an average concentration of 225 mg/1 SS.
M
Table 3-2: Annual Average Boxelder Sanitation District WWTP Flows
Year Average Annual Flow
1990
1.32 MGD
1991
1.39 MGD
1992
1.50 MGD
1993
1.61 MGD
1994
1.46 MGD
3.1.2 BIocI IEMIcAL, OXYGEN DEMAND (BODO
BOD is an indication of the amount of biodegradable organic matter in the wastewater. If oxygen
is furnished to wastewater containing aerobic microorganisms, aerobic decomposition will occur
until the oxygen and nutrient supplies are depleted or the demand is satisfied. The amount of
oxygen required by the microorganisms to process the nutrients in the wastewater during the first
five days of the stabilization process is referred to as the 5-day biochemical oxygen demand (BOD
5). This organic parameter is utilized in the design of treatment processes. The rate at which
oxygen is processed is dependent upon many factors including: the type of organic matter; the
manner in which oxygen is applied; the environment of utilization; temperature; pH; and others.
Normal domestic wastewater from residential communities has been shown to have a daily BOD5
value of 0.17 pounds per capita. For ease in handling design parameters, the BOD of sewage is
sometimes converted to a population equivalent basis using this value.
Approximately 1,524 of the total number of EQR's (2,632) are residential in nature which yields a
theoretical residential population figure of 4,880 using a unit factor of 3.2/people per EQR.
During 1994, the District averaged 1,2491bs.. BOD/day which equates to a unit loading rate of
0.26 lbs./day per capita. The typical unit loading rate value is 0.17 lbs.. BOD/day per capita
which generally includes light commercial concerns but does not include heavy industrial wastes.
The higher value illustrated at Boxelder is an indication of the comparatively high number of
commercial accounts on the system. Typical domestic wastes are received at a concentration of
18
3.1.1.1 Sources of Flow
The flow received at the treatment plant is a combination of liquids derived from domestic, and
commercial wastes. Table 3-1 provides a 1992 sewer tap breakdown:
Table 3-1: Tap Breakdown in Boaelder Service District
1992 - Tap Breakdown
Type Actual Number of Tans
Residential - S.F.
712
Residential - Duplex
56
Residential - Fourplex
7
Residential - Simplex
2
Commercial
M
Total = 1,011
3.1.1.2 Extraneous Flows
The information derived as a result of the Infiltration/Inflow Analysis prepared for the District
indicates that the system does have excessive inflow/infiltration in portions of the system. The
conclusion to be reached from the data is that numerous subsystems should be rehabilitated. It is
estimated that a total of 557,000 gallons per day of I/I could potentially be removed by
rehabilitating these systems based upon the information derived by the District.. The 0.557 MGD
represents roughly one third of the current average daily influent flow. The estimated capital
costs required to rehabilitate these subsystems is $244,965. The average annual flows over the
past five years are depicted in"Table 3-2.
17
3. WASTEWATER CHARACTERISTICS
3.1 EXISTING CHARACTERISTICS
Sewage treatment plants are designed to provide optimum conditions for the conversion of
collected wastes into an acceptable effluent and to dispose of the solids removed in the process.
Prior to reviewing the adequacy of an existing plant or proceeding with the design of a new plant,
it is imperative to determine:
1. the characteristics of these wastes;
2. the required characteristics of the effluent;
3. the required degree of treatment.
When considering long-range improvements, allowances should be made for changes in the
characteristics of the wastes and for modifications in the regulatory requirements for the quality of
effluent. The primary characteristics for which sewage treatment plant design parameters are
established are flow, biochemical. oxygen demand (BOD), suspended solids (SS), and hydrogen
ion concentration (pH). Other constituents which can impact design when they are included in the
effluent permit are ammonia, phosphorus, and heavy metals. The established design parameters
are generally based upon sewage that is primarily domestic. Sewage characteristics which
radically depart from the norm require adjustment of the design parameters and, on occasion, the
development of new parameters through laboratory investigations. and pilot plant studies.
3.1.1 Flow
The quantity of wastewater received at the sewage treatment plant governs the hydraulic design
of the various treatment units and plant piping. This design factor is not only related to the total
volume received but also to the peak and, sometimes, minimum flow rates of the liquid wastes
entering the treatment plant. Historical flow conditions were established from plant records with
the flow values being obtained from the effluent flow meter at the treatment plant.
1GM
TEC
WASTEWATER CHARACTERISTICS
2.5.2 LONG RANGE MANAGEMENT PLAN - REGIONALIZATION AND WATER QUALITY CONCERNS
The District has had numerous discussions with the City of Fort Collins Water Department on an
ongoing basis since prior to the plant upgrade of 1987-89 on the subject of regionalization and
any benefits to water quality which may accrue. The City Waste Water Utility (Enterprise) has
indicated that it is studying the concept of an Authority, wherein the City Waste Water Enterprise
would beseparated separated from the City government, join with other service providers including
Boxelder, possibly South Fort Collins Sanitation District, LaPorte, Cherry Hills, and Spring Creek
Entities. The Enterprise would construct a new treatment facility west of Windsor and has hired
consultants to provide a conceptual study for the proposed facility. The Boxelder Board Long
Range Management plan is to be pro -active regarding this concept. The Boxelder Board has as
its primary focus compliance with the Water Quality Permit conditions, and control of water
quality is the first priority.
Future discussions with any or all parties which may be included in the Authority would await
North Front Range Water Quality Association (NFRWQ.A) approval of the regional 208 plan for
the consolidated facility. There is no such regional plan in place at this time.
The many questions which must be answered to the satisfaction of all parties to be included in the
regionalization plan would flow from capital investment concerns, capital recovery plans,
operations and management costs, and the allocation mechanism to be used. Also, the
consideration of possible adverse impacts upon the receiving waters at a single point for all water
treatment facilities in the watershed must be considered.
15
The preceding figure indicates that 60% of the flow at the wastewater plant is attributable to an
infiltration and inflow problem. The EPA standards for an allowable degree of I/I in a collection
system are generally considered to be in the range of 1,200 to 1,500 gallons per day per inch of
pipe diameter per mile of sewer pipe. Using 1,200 GPD with the figures given for the system
inventory given earlier, the allowable I/I for Boxelder is approximately 563,000 GPD.
Subtracting this figure from the foregoing I/I value yields a potentially excessive VI flow of at
least 300,000 GPD.
Groundwater
Since the flow rates at the plant are relatively "flat" by examination of the flow charts (i.e., little
variation in minimum or maximum as compared to average), groundwater infiltration into the
system is suspected to be the primary contributor to the extraneous flows experienced at the
plant. The goundwater table is fairly high in areas where the sewer system is shallow.
Precipitation
The other means of incurring extraneous flows results from rainfall entering the system during
periods of wet weather. This occurrence is generally referred to as "Inflow". In the Boxelder
system, wet weather inflow produces a peak inflow rate of 245 GPM following 1.1 inches of rain
over a two-day period. It takes several days (in some cases) for the flow rate to subside which
indicates that a substantial portion of the precipitation inflow into the system occurs in the form of
infiltration.
2.5 FUTURE WASTEWATER COLLECTION SYSTEM
2.5.1 GENERAL
As development continues within the existing service area, peak flow rates will continue to
increase and use more of the remaining capacity of the existing system. Eventually, this could
create additional problems in some segments of the existing sewer system.
14
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JANUARY 1995
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' and will occur in and around existing urban centers. The County Plan states that within
designated urban
' areas, and should provide for phased extension of support systems (roads and utilities). The
recommended method for achieving the goals of the Land Use Plan is the development and
' adoption of a detailed plan for the urbanizing areas which may include city land use plans and
master plans. Figure No. 4 outlines the zoning regions within the District.
The projected land use densities used in this report are, for the most part, based on the land use
plan adopted by the County. Generally, the plan provides for densities of three to four units per
acre within the urban growth area and 0.4 units per acre for rural areas. There have been a
number of meetings recently discussing the possibility of expanding or increasing service to
include:
1. Streamside P.U.D.
2. Water Glen P.U.D.
3. Cloverleaf Park Mobile Homes
4. Mountain View Mobile Home Park
5. 19th Green Subdivision
6. Pioneer Mobile Home Park
2.4 EXISTING WASTEWATER COLLECTION SYSTEM
2.4.1 GENERAL
The collection system contains roughly 36.5 miles of line with pipe sizes ranging from 6 inches up
to 30 inches. Table 2-2 delineates the makeup of the collection system.
12
3500
K111
p 2500
co
2000
1500
E
Z 1000
500
Sewer Tap Projections
Boxelder Sanitation District
GrowthEnvelop
................................................
........
.... _..1
.......
I
....... ........
t
.........�..............1........
i
-....,........ ........ ........ I ....... I ..... _F.......t
Straight Line
.
f
i
t
:...._..
_.....t....._.
.......
......_........;.......A--......;........;........i.............................................,.
Projection
,........:.
i9oo
1.
(........1.
I
i.....
-.f
f
!
i.....
4.......
.......,............................j........t........
..............-....b.......
.....
(
i
....._
i
t
1 1
�
.................�.
�..........._
.........:........:.....
........;......:......�.......�.
..
.�...._
ILi
I
0
1970 1978 1986 1994 2000 2008 2016
1974 1982 1990 1998 2004 2012
Time - Years
Figure No. 3
P = P eK(t-t0)
0
Where P = future population
Po = base population in year t0
t = year of future population
to = base year
K = growth constant
e = 2.71, natural log base
Using the formulae for determining the growth constant "K", a value was derived for a 20-year
time frame from the District's tap history. Having determined the growth constant (K), it was
applied to the District's tap figures. The resulting growth projections are illustrated on Figure No.
3 - "Tap Projections". The figures range from 1,700 up to 2,250 actual taps in the year 2014. A
straight line projection over the past 20 years extended to the year 2014 yields a value of 1,900
actual taps.
Using the high rate projection (2,250) as the upper limit and the low growth rate (1,700) as the
lower value, a growth envelope is formed. Examination of the growth envelope reveals that the
straight line projection (1,900) nearly halves the growth envelope. This would appear to be a
reasonable figure from a relatively straightforward approach to forecasting the District's future
actual tap count. Subsequently, The Design Tap figure to be utilized in developing future flows
and loads is 1,900. This figure represents is a 62% growth over the current tap count of 1,178.
From the relationship developed earlier between forecast and equivalent tap counts (1 Tap = 2.55
EQR's), the design figure of 1,900 actual taps converts to an equivalent tap count of 4,845 in the
year 2014.
2.3 LAND USE
Land use in much of the District's service area is rapidly changing from agricultural to municipal.
The Larimer County Land Use'Plan anticipates that most development will be'of urban intensity
11
The history of total taps in the District is provided below in Table 2-1:
Table 2-1: Tap Growth Within the Boxelder District
Year Total Taps
1973
1974
1975
1976
1977
1978
1979
1981
1982
1983
1984
1985
1986
1987
1990
1992
1994
223
304
343
374
492
573
631
707
723
742
770
793
853
863
924
1011
1178
In order for growth studies to be meaningful, they must produce results that are reliable, yet
flexible enough to reflect the consequences of local change, and sufficiently detailed to serve as a
basis for the design of local facilities. However, even under the best conditions, making
projections that accurately indicate future conditions are difficult. ,
The tap forecast for the District is based on past population trends as determined from U.S.
Census records and specific characteristics of the area population. From discussions with local
planners, it is believed that growth will continue in the area but at a more moderate rate than was
experienced in the late 70's and earlier 80's.
The geometric method of population forecasting uses past population trends correlated to time
intervals to determine a constant percentage of growth. The geometric method assumes that this
constant percentage of growth will continue in the future. The equation used in the geometric
projections is as follows:
10
I
1
1
i
1
11
i
i
i
1
[1
1
1
1
11
1
1
rI
1
2. THE SERVICE AREA
2.1 DESCRIPTION
The District began operation in 1965 with a single lagoon serving an area adjacent to Highway
14. Flow was transported through a 12-inch line which is still in service. The District has grown
considerably since then 'with the plant having been expanded three times to its present
configuration which has a permitted capacity of 1.5 MGD. A layout of the sewer service area is
illustrated on Figure No. 2 on the following page.
2.2 POPULATION PROJECTIONS
The treatment capabilities required of a wastewater treatment system must be determined from
analyses of present and probable future quantities of wastewater flow, organics, and solids. Both
population forecasting and land use planning play an important role in projecting future waste
loads and flows. Since analyses and projections of population growth are the basis for almost all
major planning decisions, population projections are used to determine the level of demand for
future facilities and serve as indices of past and future development. Future waste loads and flows
are estimated using existing data and the population forecast. Since an accurate population figure
is difficult to derive for the District, the history and growth rates of the total tap connections are
used to forecast District growth.
0
THE SERVICE AREA
' 4. Facilities Plan For Wastewater Treatment completed for Boxelder Sanitation District in
October of 1993 by The Engineering Company.
5. Site Application for Wastewater Treatment Improvements completed for Boxelder Sanitation
District in August of 1994 by The Engineering Company.
I
I
ILI
ul
A
infiltration and inflow rehabilitation program which is predicted to remove 0.56 MGD of
extraneous flow.
The plan to expand the facility proposes maximum use of the existing system and structures. This
plan would upgrade and expand the existing aerated pond system as was presented in 1986. The
plan proposes to mirror image the second half of the existing system thereby producing two
treatment trains which would function in the same manner as the existing system. The plan would
also allow the system to be operated in series or in parallel. This "doubling" of the system yields a
hydraulic capacity of 2.34 MGD which is equal to an estimated 20-year design flow (2.9 MGD)
with the excessive I/I flows removed (reference item 3 below). The upgrading would consist of
the following:
• New 7.0 MGD Pond
• New Yard Piping
• Increase Aeration Capacity
• Electrical Revisions
• Revise Yard Piping
• Install Pond Baffling
Expansion of the aerated pond scheme to 2.34 MGD would require an additional pond for
aeration, settling, and maturation. The new pond would maintain a 10 foot to 12 foot water
depth with a volume of approximately 7.0 MG. The pumping, piping, and disinfection facilities
would also be upgraded per a previous site application dated August 1994 to handle an average
daily flow of 2.34 MGD.
Several sections of this report represent a summary of the results of detailed analyses and
investigations presented in the following reports:
1. Preliminary Design Report for Plant Expansion completed in December of 1991 by The
Engineering Company.
2. Boxelder WWTP Capacity completed in April of 1993 by The Engineering Company
3. Infiltration / Inflow Analysis for the Boxelder Sanitation District completed in August of 1993
by The Engineering Company.
7
TATION
TRANSFE
�O
OG+�
FIGURE NO.1
EXISTING SYSTEM
BOXELDER SANITATION DISTRICT
FORT COLLINS, COLORADO
JANUARY 1995
94-044
The Engineering Company
1. SUMMARY
The Boxelder Sanitation District encompasses 10 square miles of area in Larimer County. More
specifically, the service area is located on the east-northeast side of Fort Collins with the
treatment plant being situated south of Prospect Road (County Road 44) and west of I-25.
The Boxelder Wastewater Treatment Plant is a 1.5 MGD aerated lagoon system composed of two
aerated lagoons and a settling lagoon operated in series. Influent is lifted into the first lagoon via
a cast -in -place pumping station which contains a headworks facility with a flume, bypass channel,
and one macerater/grinder. Effluent from the lagoon system is chlorinated in a contact chamber
and dechlorinated using sulphur dioxide. The original lagoon system was built as a single
facultative lagoon in the 1960's and was upgraded in the 1970's to include a pumping station, two
aerated lagoons, and a chlorination facility (see Figure No. 1). In 1988, the plant was upgraded to
improve the headworks, increase pumping and aeration capacity, and rectify hydraulic problems in
the lagoons. In 1989, sludge was hydraulically removed from all of the lagoons.
The treatment plant influent is a combination of liquids derived from domestic and commercial
wastes. The District estimates that the number of equivalent residential taps (EQR's) is 2,632 taps
for all residential and commercial units. The foregoing tabulation indicates that the District is
continuing to grow and that there is a relatively high percentage of commercial to total taps in the
District.
On the basis of the data received from the District, the average daily flow for 1994 was 1.46
MGD, up from an average 1.39 MGD reported in 1991. Using the average of the figures derived
for 1994 (1.46 MGD) and dividing by the actual number of taps (1,178 in 1994) yields an average
"actual" tap contribution of 1,239 GPD per tap.
While the District has experienced a 37% increase in metered water use in recent years, the
sewage flow has increased by 190% during the same time period. Since there are no large water
users on the system or dischargers with private well(s), this comparison would lead one to suspect
that the degree and amount of extraneous flow occurring in the sewer system has increased
dramatically over the past few years. The District is. currently implementing an extensive
0
TEC
SUMMARY
0
APPENDICES
Appendix A:
Appendix B:
An Evaluation Of Water Quality Based Effluent Limitations For The
Expansion Of The Boxelder Sanitation District Plant
Supplemental Narrative for Site Approval Application
5
FIGURES
Figure No. 1: Existing System
Figure No. 2: Sewer System Map
Figure No. 3: Sewer Tap Projections
Figure No. 4: Zoning Map
Figure No. 5: Boxelder WWTP Statistical Performance Curve
Figure No. 6: Boxelder WWTP Regression Performance Curve
Figure No. 7: Expanded Lagoon System
4
TABLES
Table 2-1: Tap Growth Within the Boxelder District
10
Table 2-2: Pipe Sizes Within Boaelder Collection System
13
Table 2-3: Water Usage Data Within the Boaelder Service District
13
Table 34: Tap Breakdown in Boaelder Service District
Table 3-2: Annual Average Boaelder Sanitation District WWTP Flows
17
18
'
Table 3-3: BOD Strength and Load
19
Table 34: Suspended Solids Strength and Load
20
Table 3-5: Wastewater Characteristics Summary
20
Table 3-6: Design Parameters
22
Table 3-7: NPDES Permitted Values for Boaelder Sanitation District
23
Table 3-8: Local Limits for Boaelder Sanitation District
28
'
Table 4-1: Boaelder 1994 WWTP Operating Condition Summary
36
Table 4-2: Boaelder Monthly Operating Data
38
'
Table 4-3: Boaelder Winter Performance
40
Table 44: Boaelder Summer Performance
41
'
Table 4-5: BOD Removal Based on the Marais -Shaw Equation
45
Table 4-6: BOD Removal Based on Aeration Efficiencies
45
'
Table 5.1: Upgraded WWTP Operating Condition Summary
48
Table 5-2: Expanded Pond System Cost Estimate
50
Table 6-1: Extended Aeration System Cost Estimate
54
.1
li
N
'
4. EXISTING WASTEWATER TREATMENT SYSTEM
32
4.1 GENERAL
32
'
4.2 UNIT PROCESS REVIEW
32
4.2.1 HEADWOM
32
'
4.2.2 PUMPING SYSTEM
33
4.2.3 LAGOON SYSTEM
33
'
4.2.4 SETTLING LAGOON
34
4.2.5 SYSTEM HYDRAULIC CAPACITY
35
'
4.2.6 CHLORINATION
35
4.2.7 DECHLORINATION
35
4.3 PLANT OPERATIONAL PARAMETERS
36
4.4 PLANT PERFORMANCE
38
'
4.5 PROCESS LIMITING FACTORS
46
4.5.1 HYDRAULIC DETENTION TIME
46
4.5.2 AERATION CAPACITY
46
4.5.3 CHLORINATION CAPACITY
46
r5. UPGRADING & EXPANDING EXISTING PLANT 47
5.1 UPGRADE REQUIREMENTS
5.2 COST ESTIMATES
47
50
6. ALTERNATIVE TREATMENT SYSTEMS 51
6.1 GENERAL
' 6.2 WASTEWATER TREATMENT CATEGORIES
6.3 ALTERNATIVE WASTEWATER PLANS
51
51
52
7. FLOODPLAIN ANALYSIS 56
8. ADMINISTRATIVE ARRANGEMENTS 57
8.1 FINANCIAL SUMMARY 57
8.2 IMPLEMENTATION PLAN AND SCHEDULE 57
2
TABLE OF CONTENTS
1. SUMMARY 6
2. THE SERVICE AREA 9
2.1 DESCRIPTION
9
2.2 POPULATION PROJECTIONS
9
23 LAND USE
11
2.4 EXISTING WASTEWATER COLLECTION SYSTEM
12
2.4.1 GENERAL
13
2.4.2 INFILTRATION/INFLOW
13
2.5 FUTURE WASTEWATER COLLECTION SYSTEM
14
2.5.1 GENERAL
14
2.5.2 LONG RANGE MANAGEMENT PLAN - REGIONALIZATION AND WATER QUALITY CONCERNS
15
3. WASTEWATER CHARACTERISTICS
16
3.1 EXISTING CHARACTERISTICS
16
3.1.1 FLOW
16
3.1.2 BIOCHEMICAL OXYGEN DEMAND (BODS)
18
3.1.3 SUSPENDED SOLIDS (SS)
19
3.1.4 SUMMARY OF WASTEWATER CHARACTERISTICS
20
3.2 WASTELOAD AND FLOW FORECAST
21
3.2.1 FLOW
21
3.2.2 BIOCHEMICAL OXYGEN DEMAND (BODY)
21
3.2.3 TOTAL SUSPENDED SOLIDS (TSS)
21
3.2.4 DESIGN LOAD AND FLOW SUMMARY
21
3.3 EFFLUENT LIMITATIONS
22
3.4 INDUSTRIAL PRETREATMENT PROGRAM
23
3.4.1 OVERVIEW OF THE INDUSTRIAL PRETREATMENT PROGRAM
23
3.4.2 PRETREATMENT CONTROL AND LOCAL LIMITS
30
1
V
ATTACHMENT TO SITE APPLICATION
i
' In accordance with C.R.S. 1981, 25-8-702 (2)(a), (b), and (c), and the "Regulations for Site
Applications for Domestic Wastewater Treatment Works", the Water Quality Control Division mue
determine that each site location is consistent with the longrange, comprehensive planning fc
the area in which it is to be located, that the plant on the proposed site will be managed tc
' . minimize the potential adverse impacts on water quality, and must encourage the consolidation
of wastewater treatment works whenever feasible.
' In making this determination, the Division requires each applicant for a site approval for a
domestic wastewater treatment works to supply an engineering report describing the project an
showing the applicant's capabilities to manage and operate the faility over the life of the
project to determine the potential adverse impacts on water quality. The report shall be
considered the culmination of the planning pr9cess and as a minimum shall address the
following:
' Service area definition including existing population and population projections,
flow/loading projections, and relationship to other water and wastewater treatment plants
in the area.
' Proposed effluent limitations as developed in coordination with the Planning and Standard:
Section of the Division. (Allow minimum four weeks processing time.)
' Analysis of existing facilities including performance of those facilities.
' Analysis of treatment alternatives considered.
Flood plain and natural hazard analysis.
Detailed description of selected alternatives. including legal description of the site,
treatment system description, design capacities, and operational staffing needs.
' Legal arrangements showing control of site for the project life.
Institutional arrangements such as contract and/or covenant terms for all users which will
' be finalized to accomplished acceptable waste treatment.
Management capabilities for controlling the wastewater throughout and treatment within the
capacity limitations of the proposed treatment works, i.e., user contracts, operating
agreements, pretreatment requirements.
Financial system which has been developed to provide for necessary capital and continued
' operation, maintenance, and replacement through the life of the project. This would
Include, for example, anticipated fee structure.
Implementation plan and schedule including estimated construction time and estimated
' start-up date.
Depending on the proposed project, some of the above items may not be applicable to address.
In such cases, simply indicate on the application form the non applicability of those.
1
44
-4-
WQCD-3 (Revised 8-83)
C. If the facility will be located on or adjacent to a site that is owned or managed by a
Federal or State agency, send the agency a copy of this application.
D. Recommendation of governmental authorities:
Please address the following issues in your recommendation decision. Are the proposed
facilities consistent with the comprehensive plan and any other plans for the area,
including the 201 Facility Plan or 208 Water Quality Management Plan, as they affect water
quality? If you have any further comments or questions, please call 320-8333, Extension
5272.
Recommend Recommend No
' Dates oAnvroval Disap Comment Signature of Representative
' Management Agency
2.
' Local Government: Cities or Towns (If
site is inside boundary or within three
miles) and Sanitation Districts.
3.
Board of County Commissioners
4.
'Local Health Authority
5.
City County Planning Authority
Council of Governments/Regional Planning
7•
State Geologist
' (For lift stations, the signature of the State Geologist is not required. Applications for
treatment plants require all signatures.)
' I certify that I am familiar with the requirements of the "Regulations for Site Applications
For Domestic Wastewater Treatment Works," and have posted the site in accordance with the
regulations. An engineering report, as described by the regulations, has been prepared and is
enclosed.
DATE
Signature of Applicant TYPED NAME
4
-3-
WQCD-3 (Revised 8-83)
' S. Who has the responsibility for operating the proposed facility? -
I Boxelder Sanitation District (Subdivision of State Gov't - Title 32)
9. Who owns the land upon which the facility will be constructed?
Boxelder Sanitation District (Subdivision of State Gov't - Title 32)
' (Please attach copies of the document creating authority in the applicant to
construct the proposed facility at this site.)
10. Estimated project cost:
' Who is financially responsible for the construction and operation of the facility?_
Boxelder Sanitation District
' 11. Names and addresses of all water and/or sanitation districts within 5 miles
downstream of proposed wastewater treatment facility site. ELCO Water District,
North Weld County Water District, Fort Collins - Loveland Water District
' Note: None of these entities draw from nor discharge to the Boxelder (Cache la
Poudre)
(Attach a separate sheet of paper if necessary.)
12. Is the facility in a 100 year flood plain or other natural hazard area? Yes
If so, what precautions are being taken? Existing and new dikes will be above
' 100-year flood plain.
Has the flood plain. been designated by the Colorado Water Conservation Board,
Department of Natural Resources or other Agency? Yes - All of above.
(Agency Name)
' If so, what is that designation? No. 128 - January 1979
13. Please include all additional factors that might help the Water Quality Control
Division make an informed decision on your application for site approval.
'
A) 1986 Pre -Design Report
B) Memorandum updating 1986 report.
'
C) Continued use of existing facility is acceptable based on the treatment history
of the system which has met or exceeded all discharge water quality limitations
'
and has performed exceedingly well since the 1987 upgrade. This proposal is an
extension ot that upgrade.
D) Pretreatment program and pollution prevention programs in place for 2 years.
B. Information regarding lift stations:
1.
The proposed lift station when fully developed will generate the following additional
'
2.
load: Peak Hydraulic (MGD) P.E. to be served
Is
the site located in a 100 year flood plain?
If yes, on a separate sheet of paper describe the protective measures to be taken.
'
3.
Describe emergency system in case of station and/or power failure.
'
4.
Name and address of facility providing treatment:
5.
The proposed lift station when fully developed will increase the loading of the
'
treatment plant to X of hydraulic and % of organic capacity and
agrees to treat this wastewater? YesNo
(Treatment Agency)
•
Date Signature and Title
-2-
WQCD-3 (Revised 8-83)
(iEMvE r .
COLORADO DEPARTMENT OF HEALTH
'Water Quality Control Division AM ' ' 91,
4210 East llth Avenue
Denver, Colorado 80226
APPLICATION FOR. SITE APPROVAL FOR CONSTRUCTION OR EXPANSION OF:
' A) DOMESTIC WASTEWATER TREATMENT WORKS (INCLUDING TREATMENT PLANTS,
OUTFALL SEWERS, AND LIFT STATIONS) OVER 29000 GPD CAPACITY.
' B) INTERCEPTORS (IF REQUIRED BY C.R.S. 25-8-702 (3))
APPLICANT: Boxelder Sanitation District
' ADDRESS: 2217 Airway Ave. #3 ELCO CO 80524
Consulting Engineer's flame and Address: TEC, The Engineering Co. PHONE: 303-498-0604
2310 East Prospect, Fort Collins, CO 80525
PHONE: 303-484-7477
�. Summary of information regarding new sewage treatment plant: Lagoon
x7x}xArmctifl[Tnit D)
1. Proposed Location: (Legal Description) NW 1/4NE
1/4, Section 28
' Township 7N , Range 68W
Larimer County. ,
' 2. Type and capacity of treatment facility proposed: Processes Used Screening,
Pumping, aerated lagoons, settling lagoons, CL2 - S02r Chlor - Dechlor
1
Hydraulic 2.34 MGD Organic 3200
gal/day .lbs. BOD/day
S
Present PE 9730. Design PE 15,600 Commercial
Y. Domestic 84 3. Location Z TK3ff4111(FH 16
of facility: ase on flow)
1 4.
a
At:acii a map of the area which includes the following:
(a) 5-mile radius: all sewage treatment plants, lift stations, and domestic
water, supply intakes.
(b) 1-mile radius: habitable buildings, location of potable water wells, and
an approximate indication of the to o r h
P g ap y•
Effluent disposal: Surface discharge to watercourse
Subsurface disposal NA Boxelder Creek
Land
Evaporation NA
Other
State water quality classification of receiving watercourse(s) AG, Fishing, Swimming
Proposed Effluent Limitations developed in conjunction with Planning and Standards
Section, WQCD: BODE 30 m /l SS 75
g mg/l Fecal Coliform 3710 /100 ml
Total Residual Chlorine .008
mg/1 Ammonia N/A mg/1 Other
Will a State or Federal grant be sought to finance any portion of this NO
Present zoning of site area? Farming/Agricultural Project.
Zoning with a 1-mile radius of site? Agricultural/Industrial/Commercial
What is the distance downstream from the discharge to the nearest domestic water
supply intake? None
(Name of Supply)
(Address of Supply)
What is the distance downstream from the discharge to the nearest. other point of
diversion? 5.4 miles: Larimer-Weld Irrigation Co.
%..awe or user)
1605 Canton Lane, Fort Collins, CO 80525
(Address of User.)
-1-
WQCD-3 (Revised 8-83)
March 9, 1995
FILE: 94-069
RE: Boxelder Sanitation District
Site Application
Wastewater Treatment Improvements, Phase II
Respected Officials:
Enclosed is the Site Application for the Wastewater Treatment Improvements that are being
proposed for construction in the Boxelder Sanitation District. This application is submitted for
review by all appropriate governing agencies and the Colorado Department of Health Water
Quality Control Division. We respectfully request that you review, comment, and recommend
approval of the site application. The enclosed copy is for your review and records; the original
site application will be routed to you and each of the required reviewers for signature and
comments and then submitted to the State for final approval.
The Engineering Co. and the Boxelder Sanitation District would like to thank you in advance for
your review. If you have any questions, please do not hesitate to contact this office.
Sincerely,
John R. Heidmiller
The Engineering Co.
The Engineering Co.
2310 East Prospect
Ft. Collins. CO 80525
Phone (303) 484-7477
FAX (303) 484-7488
' ENGINEER'S REPORT
' Site Application for
Wastewater Treatment Improvements
' for
' Boxelder Sanitation District
Phase II
' March 1994
TEC