HomeMy WebLinkAboutHOFFMAN MILL FUEL SITE - MINOR AMENDMENT - MA180043 / BDR180015 - SUBMITTAL DOCUMENTS - ROUND 2 - DRAINAGE RELATED DOCUMENT1218 W. ASH, STE. A, WINDSOR, COLORADO 80550
TEL. 970.674.3300 – FAX 970.674.3303
September 26, 2018
Ms. Heather McDowell, P.E.
Fort Collins Utilities – Stormwater
700 Wood Street
Fort Collins, CO 80522
Re: Hoffman Mill Fueling Site
Final Storm Drainage Letter
Dear Heather,
Please accept the following letter describing the storm drainage intent demonstrating the proposed site
improvement’s ability to comply with the City’s stormwater requirements.
INTRODUCTION
The Hoffman Mill Fueling Site project proposes to construct a gas and diesel fueling station on the
Hoffman Mill recycling/crushing operations site. The site is located north of Hoffman Mill Road, east of
Lemay Avenue and south of the Cache La Poudre River and is only a portion of the recycling/crushing
operations site. The fueling site is proposed to be located south of the existing building, closest to
Hoffman Mill Road.
A vicinity map is attached for reference.
EXISTING CONDITIONS
The project site is located within the Cache La Poudre drainage basin. The existing site consists of
miscellaneous material storage and is generally undeveloped. The site generally slopes from the
northwest to the southeast at approximately 1.0% grade. All existing material storage and miscellaneous
site improvements will be removed from the site to accommodate the new construction.
We are not aware of any site-specific drainage studies for this site.
The project is not located within a FEMA mapped 100-yr floodplain and is not within a defined City of
Fort Collins floodplain.
PROPOSED DEVELOPMENT
The prosed redevelopment improvements will consist of a constructing a 24 ft wide looping drive lane
and fuel storage/dispensing equipment. A detention pond and sand filter are proposed to satisfy the storm
drainage detention and Low Impact Development (LID) requirements. A long swale is proposed to be
constructed along the north side of Hoffman Mill Road and will provide a gravity outfall for the site’s
storm drainage runoff. The project is planned to be constructed in a single phase.
Hoffman Mill Fueling Site
Final Storm Drainage Letter
September 26, 2018
Page 2 of 4
The proposed improvements are included in a single drainage basin with one offsite basin drainage to and
being conveyed through the proposed improvements. These basins consist of:
Basin D1 consists of the fueling site and is approximately 0.59 acres and 44.8% impervious. The
detention and water quality facilities are located within this basin and outfall to the proposed swale.
Basin OS1 consists of the are north and west of the proposed site that drains to Basin D1. The basin is
approximately 3.05 acres and is 12.4% impervious. The runoff from this basin will be routed through the
detention pond.
An outfall swale is proposed along the north side of Hoffman Mill Road and will discharge to the existing
water quality structure, similar to as is has historically. Due to grade limitations, the swale is designed
with a 0.5% slope. This slope will help sediment settle from the adjacent crushing operations areas and
provide a gravity outfall for the fuel site.
All calculations and exhibits are attached for reference.
Detention Pond
The proposed detention pond detains the developed runoff to the historic 2-yr runoff rate. The historic 2-
yr runoff rate is 0.50 cfs and combined with the offsite flows routed through the pond of 7.2 cfs, provides
a release rate of 7.70 cfs. The required 100-yr detention volume is 2,788 cu-ft with a water surface
elevation of 4946.90 ft. Majority of the site improvement’s runoff surface drains to the sand filter and
spills into the detention pond when runoff rates exceed the capacity of the sand filter. The water quality
capture volume for the sand filter is 283 cu-ft. Combined with the 100-yr detention volume, the required
pond volume is 3,071 cu-ft. The water quality capture volume water surface elevation is controlled by the
spillway with an elevation of 4947.70 ft. The sand filter is intended to provide water quality enhancement
and to satisfy the Low Impact Development (LID) requirements.
All calculations and exhibits are attached for reference.
LOW IMPACT DEVELOPMENT TECHNIQUES
In reference to the code requirements for implementation of Low Impact Development (LID) techniques,
the use of sand filter is proposed to satisfy these requirements. The sand filter will slow runoff, promote a
reduction of runoff through infiltration, and will also capture sediment prior to discharging through the
perforated underdrain.
Below is a description of the 4 step process for selecting structural BMPs:
Urban Drainage and Flood Control District (UDFCD) recommends a Four Step Process for receiving
water protection that focuses on reducing runoff volumes, treating the water quality capture volume
(WQCV), stabilizing drainageways and implementing long-term source controls. The Four Step Process
applies to the management of smaller, frequently occurring events.
Step 1: Employ Runoff Reduction Practices
To reduce runoff peaks, volumes, and pollutant loads from urbanizing areas, implement Low Impact
Development (LID) strategies, including Minimizing Directly Connected Impervious Areas (MDCIA).
Hoffman Mill Fueling Site
Final Storm Drainage Letter
September 26, 2018
Page 3 of 4
The sand filter will slow runoff, promote infiltration, and filter runoff prior to being released into the
adjacent storm drain system.
Step 2: Implement BMPs that Provide a Water Quality Capture Volume with Slow Release
The sand filter will provide a slow release by infiltration through the sand media.
Step 3: Stabilize Drainageways
Natural Drainageways are subject to bed and bank erosion due to increases in frequency, duration, rate
and volume of runoff during and following development. The site will ultimately drain to an existing
swale that is well vegetated and addition bank stabilization is unnecessary with this project.
Step 4: Implement Site Specific and Other Source Control BMPs
Proactively controlling pollutants at their source by preventing pollution rather than removing
contaminants once they have entered the stormwater system or receiving waters is important when
protecting storm systems and receiving waters. This can be accomplished through site specific needs
such as construction site runoff control, post-construction runoff control and pollution prevention / good
housekeeping. It will be the responsibility of the contractor to develop a procedural best management
practice for the site.
A spill control structure is proposed with this project. Runoff from the dispensing area and fuel storage
area will drain to a modified Type R inlet. The inlet is modified to provide a baffle to capture spilt fuel.
It also has a valve to control the flow leaving the inlet during a spill event. It will the operators’
responsibility to frequently observe structure and removed any accumulated fuel and also close the outlet
valve during a spill event.
All calculations are attached for reference.
EROSION CONTROL
Erosion and sedimentation will be controlled on-site by use of sediment control logs, inlet protection, a
gravel construction entrance, seeding, mulch, and turf. The measures are designed to limit the overall
sediment yield increase due to construction as required by the City of Fort Collins. During overlot and
final grading the soil will be roughened and furrowed perpendicular to the prevailing winds.
During the performance of the work required by these specifications or any operations appurtenant
thereto, whether on right-of-way provided by the City or elsewhere, the contractor shall furnish all labor,
equipment, materials, and means required. The Contractor shall carry out proper efficient measures
wherever and as necessary to reduce dust nuisance, and to prevent dust nuisance that has originated from
his operations from damaging crops, orchards, cultivated fields, and dwellings, or causing naissance to
persons. The Contractor will be held liable for any damage resulting from dust originating from his
operations under these specifications on right-of-way or elsewhere.
It is unlawful to track or cause to be tracked mud or other debris onto city streets or rights-of-way.
Wherever construction vehicles access routes or intersect paved public roads, previsions must be made to
minimize the transport of sediment by runoff or vehicles tracking onto the paved surface. Stabilized
Hoffman Mill Fueling Site
Final Storm Drainage Letter
September 26, 2018
Page 4 of 4
construction entrances are required with base material consisting of 6” coarse aggregate. The contractor
will be responsible for clearing mud tracked onto city streets on a daily basis.
All temporary and permanent erosion and sediment control practices must be maintained and repaired as
needed to assure continued performance of their intended function. Silt fence and sediment control logs
will require periodic replacement. Maintenance is the responsibility of the contractor.
All disturbed areas must be seeded and mulched within 30 days of project start. Vegetation shall not be
considered established until a ground cover is achieved which is demonstrated to be mature enough to
control soil erosion to the satisfaction of the City Inspector and to survive severe weather condition.
Thank you in advance for your time and if you have any questions or comments please contact me at
(970) 347-8917.
Sincerely,
Jason T. Claeys, P.E., LEED AP
Interwest Consulting Group
Attachments
SITE
Vicinity Map
Scale: 1" = 1000'
PROJECT DATUM: NAVD88
CITY OF FORT COLLINS BENCHMARK #17-92
300 FEET SOUTH OF THE SOUTHWEST CORNER OF EAST DRAKE RD
AND TIMBERLINE RD, IN THE TOP OF AN IRRIGATION STRUCTURE
ELEV= 4938.70
CITY OF FORT COLLINS BENCHMARK #8-02
ON THE SOUTHEAST CORNER OF THE INTERSECTION OF LEMAY AVE AND
MULBERRY ST, IN THE CURB, ON THE SOUTHEAST SIDE OF A TRIANGULAR
ISLAND THAT CONTAINS THE TRAFFIC SIGNAL.
ELEV= 4939.27
PLEASE NOTE: THIS PLAN SET IS USING NAVD88 FOR A VERTICAL DATUM.
SURROUNDING DEVELOPMENTS MAY HAVE USED NGVD29 UNADJUSTED
FOR THEIR VERTICAL DATUMS
IF NGVD29 UNADJUSTED IS REQUIRED FOR ANY PURPOSE, THE FOLLOWING
EQUATIONS SHOULD BE USED:
NGVD UNADJUSTED = (NAVD88) - 3.19
HOFFMAN MILL ROAD
1218 W. Ash, Suite A
Windsor , Colorado 80550
Phone: (970) 674-3300
Fax: (970) 674-3303
I N T E R W E S T C O N S U L T I N G G R O U P
PREPARED FOR
PROJ. NO.
DATE:
SCALE (H):
SCALE (V):
CHECKED BY:
DESIGNED BY:
PROJECT NAME
HOFFMAN MILL FUELING SITE
HISTORIC DRAINAGE BASINS
06/06/18
1" = 60'
N/A
JTC
JTC
1344-095-00
1 of 1
BASIN COEFFICIENT (100-YR)
BASIN DESIGNATION
BASIN AREA
DESIGN POINT
DRAINAGE FLOW ARROW
DRAINAGE BASIN
BOUNDARY
DRAINAGE BASIN
FLOW PATH
LEGEND
SCALE 1" =
0
60'
30 60
Design Engineer:
Design Firm:
Project Number:
Date:
%
Impervious
Runoff
Coefficient C
Return
Period
Frequency
Adjustment
Factor (Cf)
100% 0.95
2-year to
10-year
1.00
90% 0.95 100-year 1.25
90% 0.95
40% 0.50
0% 0.25
C2 to C10 C100
OS1 133,035 3.054 0 8,330 9,935 0 114,770 12.4% 0.35 0.43
H1 25,833 0.593 0 2,480 3,038 0 20,315 19.2% 0.40 0.50
Apavers
(sq feet)
Alawn
(sq feet)
Weighted %
Impervious
COMPOSITE
Hoffman Mill Fuel Site
EXISTING IMPERVIOUS AREA CALCULATION
Urban Storm Drainage Criteria Manual by Urban Drainage and Flood Control District, June 2001 (Revised January 2016)
DESIGN CRITERIA:
BASINS:
% Impervious values from Table RO-3 in the Urban Storm Drainage Criteria Manual
Sub-basin
Designation
Atotal
(sq feet)
Atotal
(acres)
Apaved
(sq feet)
Aroof
(sq feet)
Awalk/RAP
(sq feet)
Lawns
(Heavy, 2-7% Slope)
J.Claeys
Interwest Consulting Group
1344-095-00
June 6, 2018
Runoff Coefficients and Frequency Adjustment Factors for City of Fort Collins - Storm Water Criteria Manual
Land Use
Paved
Roof
Walks/RAP
Design Engineer:
Design Firm:
Project Number:
Date:
EQUATIONS:
-Equation 6-2 -Equation 6-4 -Urbanized Check Equation 6-5
- CoFC Overland Flow
CONSTRAINTS:
300 ft - Overland flow shall not exceed for developed condition
500 ft - Overland flow shall not exceed for undeveloped condition
Final t c = minimum of t i + t t and urbanized basin check
recommended minimum t c = 5 min for urbanized basins
Time of Concentration (2-yr to 10-yr)
Type of Travel
Surface
Cv
OS1 OS1 12.4% 0.35 3.054 300 0.0157 21.02 234 0.0120 Paved Areas 20 2.19 1.78 22.80 0.0141 21.16 21.16
H1 H1 19.2% 0.40 0.593 88 0.0291 8.63 154 0.0093 Paved Areas 20 1.93 1.33 9.96 0.0165 17.01 9.96
June 6, 2018
Hoffman Mill Fuel Site
HISTORIC TIME OF CONCENTRATION
J.Claeys
Interwest Consulting Group
1344-095-00
LENGTH
(ft)
DESIGN CRITERIA:
Urban Storm Drainage Criteria Manual by Urban Drainage and Flood Control District, June 2001 (Revised January 2016)
Overland Flow Equations for City of Fort Collins - Storm Water Criteria Manual
SUB-BASIN DATA
INITIAL/OVERLAND TIME
(ti
)
TRAVEL TIME (tt
)
tc
=ti
+tt
(min)
Urban Check Final
tc
(min)
DESIGN
POINT
Sub-basin
%
Impervious
C2-10
AREA
(acres)
tt
(min)
OVERALL SLOPE
(ft/ft)
tc
(min)
SLOPE
(ft/ft)
ti
(min)
Design Engineer:
Design Firm:
Project Number:
Date:
EQUATIONS:
-Equation 6-2 -Equation 6-4 -Urbanized Check Equation 6-5
- CoFC Overland Flow
CONSTRAINTS:
300 ft - Overland flow shall not exceed for developed condition
500 ft - Overland flow shall not exceed for undeveloped condition
Final t c = minimum of t i + t t and urbanized basin check
recommended minimum t c = 5 min for urbanized basins
Time of Concentration (100-yr)
Type of Travel
Surface
Cv
OS1 OS1 12.4% 0.43 3.054 300 0.0157 18.61 234 0.0120 Paved Areas 20 2.19 1.78 20.39 0.0141 21.16 20.39
H1 H1 19.2% 0.50 0.593 88 0.0291 7.40 154 0.0093 Paved Areas 20 1.93 1.33 8.73 0.0165 17.01 8.73
June 6, 2018
Hoffman Mill Fuel Site
HISTORIC TIME OF CONCENTRATION
J.Claeys
Interwest Consulting Group
1344-095-00
LENGTH
(ft)
DESIGN CRITERIA:
Urban Storm Drainage Criteria Manual by Urban Drainage and Flood Control District, June 2001 (Revised January 2016)
Overland Flow Equations for City of Fort Collins - Storm Water Criteria Manual
SUB-BASIN DATA
INITIAL/OVERLAND TIME
(ti
)
TRAVEL TIME (tt
)
tc
=ti
+tt
(min)
Urban Check Final
tc
(min)
DESIGN
POINT
Sub-basin
%
Impervious
C100
AREA
(acres)
tt
(min)
OVERALL SLOPE
(ft/ft)
tc
(min)
SLOPE
(ft/ft)
ti
(min)
Design Engineer:
Design Firm:
Project Number:
Date:
EQUATIONS: I = rainfall intensity (in/hr)
Q n = n -yr peak discharge (cfs) P 1 = one-hour point rainfall depth (in)
C n = n -yr runoff coefficient t c = time of concentration (min)
I n = n -yr rainfall intensity (in/hr) P 1-2yr = 0.82 in
A n = Basin drainage area (ac) P 1-10yr = 1.40 in
P 1-100yr = 2.86 in
BASIN SUMMARY:
tc (min)
Runoff Coeff
(C2)
C(A) (acres)
Intensity
(in/hr)
Q (ft3/s) tc (min)
Runoff Coeff.
(C10)
C(A) (acres)
Intensity
(in/hr)
Q (ft3/s) tc (min)
Runoff Coeff.
(C100)
C(A) (acres)
Intensity
(in/hr)
Q (ft3/s)
OS1 OS1 3.054 21.16 0.35 1.06 1.56 1.65 21.16 0.35 1.06 2.67 2.82 20.39 0.43 1.32 5.45 7.20
H1 H1 0.593 9.96 0.40 0.24 2.22 0.53 9.96 0.40 0.24 3.79 0.90 8.73 0.50 0.30 7.74 2.29
June 6, 2018
Hoffman Mill Fuel Site
HISTORIC PEAK RUNOFF
J.Claeys
Interwest Consulting Group
1344-095-00
DESIGN CRITERIA:
Urban Storm Drainage Criteria Manual by Urban Drainage and Flood Control District, June 2001 (Revised August 2006)
Design
Point
Sub-basin Area (acres)
2-yr Peak Runoff 10-yr Peak Runoff 100-yr Peak Runoff
Q n = C n I n A n
0.786651)
1
( 10 )
28 . 5
t c
P
I
+
=
1344-095-00 Rational Calcs (FC).xlsx Page 4 of 4 Interwest Consulting Group
Design Engineer:
Design Firm:
Project Number:
Date:
%
Impervious
Runoff
Coefficient C
Return
Period
Frequency
Adjustment
Factor (Cf)
100% 0.95
2-year to
10-year
1.00
90% 0.95 100-year 1.25
90% 0.95
40% 0.50
0% 0.25
C2 to C10 C100
D1 25,836 0.59 0 2,481 10,384 0 12,971 44.8% 0.60 0.75
Hoffman Mill Fuel Site
DEVELOPED IMPERVIOUS AREA CALCULATION
DESIGN CRITERIA:
Urban Storm Drainage Criteria Manual by Urban Drainage and Flood Control District, June 2001 (Revised January 2016)
BASINS:
% Impervious values from Table RO-3 in the Urban Storm Drainage Criteria Manual
J.Claeys
Interwest Consulting Group
1344-095-00
June 6, 2018
Land Use
Paved
Roof
Walks
Runoff Coefficients and Frequency Adjustment Factors for City of Fort Collins - Storm Water Criteria Manual
Gravel/Pavers
Lawns
(Heavy, 2-7% Slope)
Sub-basin
Designation
Atotal
(sq feet)
Atotal
(acres)
Weighted %
Impervious
Apaved COMPOSITE
(sq feet)
Aroof
(sq feet)
Awalk
(sq feet)
Agravel/pavers
(sq feet)
Alawn
(sq feet)
1344-095-00 Rational Calcs (FC).xlsx Page 1 of 4 Interwest Consulting Group
Design Engineer:
Design Firm:
Project Number:
Date:
EQUATIONS:
-Equation 6-2 -Equation 6-4 -Urbanized Check Equation 6-5
- CoFC Overland Flow
CONSTRAINTS:
300 ft - Overland flow shall not exceed for developed condition
500 ft - Overland flow shall not exceed for undeveloped condition
Final t c = minimum of t i + t t and urbanized basin check
recommended minimum t c = 5 min for urbanized basins
Time of Concentration (2-yr to 10-yr)
Type of Travel
Surface
Cv
D1 D1 44.8% 0.60 0.593 156 0.0072 13.08 150 0.0229 Paved Areas 20 3.03 0.83 13.90 0.0149 13.11 13.11
June 6, 2018
Hoffman Mill Fuel Site
DEVELOPED TIME OF CONCENTRATION
J.Claeys
Interwest Consulting Group
1344-095-00
LENGTH
(ft)
DESIGN CRITERIA:
Urban Storm Drainage Criteria Manual by Urban Drainage and Flood Control District, June 2001 (Revised January 2016)
Overland Flow Equations for City of Fort Collins - Storm Water Criteria Manual
SUB-BASIN DATA
INITIAL/OVERLAND TIME
(ti
)
TRAVEL TIME (tt
)
tc
=ti
+tt
(min)
Urban Check Final
tc
(min)
DESIGN
POINT
Sub-basin
%
Impervious
C2-10
AREA
(acres)
tt
(min)
OVERALL SLOPE
(ft/ft)
tc
(min)
SLOPE
(ft/ft)
ti
(min)
LENGTH
Design Engineer:
Design Firm:
Project Number:
Date:
EQUATIONS:
-Equation 6-2 -Equation 6-4 -Urbanized Check Equation 6-5
- CoFC Overland Flow
CONSTRAINTS:
300 ft - Overland flow shall not exceed for developed condition
500 ft - Overland flow shall not exceed for undeveloped condition
Final t c = minimum of t i + t t and urbanized basin check
recommended minimum t c = 5 min for urbanized basins
Time of Concentration (100-yr)
Type of Travel
Surface
Cv
D1 D1 44.8% 0.75 0.593 156 0.0072 9.18 150 0.0229 Grassed Waterway 15 2.27 1.10 10.28 0.0149 13.11 10.28
June 6, 2018
Hoffman Mill Fuel Site
DEVELOPED TIME OF CONCENTRATION
J.Claeys
Interwest Consulting Group
1344-095-00
LENGTH
(ft)
DESIGN CRITERIA:
Urban Storm Drainage Criteria Manual by Urban Drainage and Flood Control District, June 2001 (Revised January 2016)
Overland Flow Equations for City of Fort Collins - Storm Water Criteria Manual
SUB-BASIN DATA
INITIAL/OVERLAND TIME
(ti
)
TRAVEL TIME (tt
)
tc
=ti
+tt
(min)
Urban Check Final
tc
(min)
DESIGN
POINT
Sub-basin
%
Impervious
C100
AREA
(acres)
tt
(min)
OVERALL SLOPE
(ft/ft)
tc
(min)
SLOPE
(ft/ft)
ti
(min)
LENGTH
Design Engineer:
Design Firm:
Project Number:
Date:
EQUATIONS: I = rainfall intensity (in/hr)
Q n = n -yr peak discharge (cfs) P 1 = one-hour point rainfall depth (in)
C n = n -yr runoff coefficient t c = time of concentration (min)
I n = n -yr rainfall intensity (in/hr) P 1-2yr = 0.82 in
A n = Basin drainage area (ac) P 1-10yr = 1.40 in
P 1-100yr = 2.86 in
BASIN SUMMARY:
tc (min)
Runoff Coeff
(C2-10)
C(A) (acres)
Intensity
(in/hr)
Q (ft3/s) tc (min)
Runoff Coeff
(C2-10)
C(A) (acres)
Intensity
(in/hr)
Q (ft3/s) tc (min)
Runoff Coeff.
(C100)
C(A) (acres)
Intensity
(in/hr)
Q (ft3/s)
D1 D1 0.593 13.11 0.60 0.36 1.98 0.70 13.11 0.60 0.36 3.37 1.20 10.28 0.75 0.44 7.64 3.39
10-yr Peak Runoff 100-yr Peak Runoff
Hoffman Mill Fuel Site
DEVELOPED PEAK RUNOFF
Urban Storm Drainage Criteria Manual by Urban Drainage and Flood Control District, June 2001 (Revised August 2006)
DESIGN CRITERIA:
Design
Point
Sub-basin Area (acres)
J.Claeys
Interwest Consulting Group
1344-095-00
June 6, 2018
2-yr Peak Runoff
Q n = C n I n A n
0.786651)
1
( 10 )
28 . 5
t c
P
I
+
=
1344-095-00 Rational Calcs (FC).xlsx Page 4 of 4 Interwest Consulting Group
Design Engineer:
Design Firm:
Project Number:
Date:
DESIGN CRITERIA
Detention Volume Calculation
0.60
1.25
0.75 ft3 acre-ft
0.59 acres 2,788 0.064
0.50 cfs
Time
(min)
100-yr
Intensity
(I , in/hr)
Q100
(cfs)
Accumulative
Runoff Volume
(ft3)
Release
Volume
(ft3)
Detained
Volume
(ft3)
Detained
Volume
(acre-ft)
0 0.00 0.00 0.00 0.00 0.00 0.0000
5 9.95 4.40 1,320.86 150.00 1,170.86 0.0269
10 7.72 3.42 2,049.66 300.00 1,749.66 0.0402
15 6.52 2.89 2,596.59 450.00 2,146.59 0.0493
20 5.60 2.48 2,973.60 600.00 2,373.60 0.0545
25 4.98 2.20 3,305.48 750.00 2,555.48 0.0587
30 4.52 2.00 3,600.18 900.00 2,700.18 0.0620
35 4.08 1.81 3,791.34 1,050.00 2,741.34 0.0629
40 3.74 1.65 3,971.88 1,200.00 2,771.88 0.0636
45 3.46 1.53 4,133.84 1,350.00 2,783.84 0.0639
50 3.23 1.43 4,287.83 1,500.00 2,787.83 0.0640
55 3.03 1.34 4,424.56 1,650.00 2,774.56 0.0637
60 2.86 1.27 4,555.98 1,800.00 2,755.98 0.0633
65 2.72 1.20 4,694.04 1,950.00 2,744.04 0.0630
70 2.59 1.15 4,813.52 2,100.00 2,713.52 0.0623
75 2.48 1.10 4,938.30 2,250.00 2,688.30 0.0617
80 2.38 1.05 5,055.12 2,400.00 2,655.12 0.0610
85 2.29 1.01 5,167.96 2,550.00 2,617.96 0.0601
90 2.21 0.98 5,280.80 2,700.00 2,580.80 0.0592
95 2.13 0.94 5,372.39 2,850.00 2,522.39 0.0579
100 2.06 0.91 5,469.30 3,000.00 2,469.30 0.0567
105 2.00 0.89 5,575.50 3,150.00 2,425.50 0.0557
110 1.94 0.86 5,665.77 3,300.00 2,365.77 0.0543
115 1.89 0.84 5,770.64 3,450.00 2,320.64 0.0533
120 1.84 0.81 5,862.24 3,600.00 2,262.24 0.0519
125 1.79 0.79 5,940.56 3,750.00 2,190.56 0.0503
130 1.75 0.77 6,040.13 3,900.00 2,140.13 0.0491
135 1.71 0.76 6,129.07 4,050.00 2,079.07 0.0477
140 1.67 0.74 6,207.39 4,200.00 2,007.39 0.0461
145 1.63 0.72 6,275.09 4,350.00 1,925.09 0.0442
Sheet 1 of 2
Designer:
Company:
Date:
Project:
Location:
1. Basin Storage Volume
A) Effective Imperviousness of Tributary Area, Ia Ia = 100.0 %
(100% if all paved and roofed areas upstream of sand filter)
B) Tributary Area's Imperviousness Ratio (i = Ia/100) i = 1.000
C) Water Quality Capture Volume (WQCV) Based on 12-hour Drain Time WQCV = 0.40 watershed inches
WQCV= 0.8 * (0.91* i3 - 1.19 * i2 + 0.78 * i)
D) Contributing Watershed Area (including sand filter area) Area = 8,500 sq ft
E) Water Quality Capture Volume (WQCV) Design Volume VWQCV = 283 cu ft
VWQCV = WQCV / 12 * Area
F) For Watersheds Outside of the Denver Region, Depth of d6 = 0.43 in
Average Runoff Producing Storm
G) For Watersheds Outside of the Denver Region, VWQCV OTHER = 283 cu ft
Water Quality Capture Volume (WQCV) Design Volume
H) User Input of Water Quality Capture Volume (WQCV) Design Volume VWQCV USER = cu ft
(Only if a different WQCV Design Volume is desired)
2. Basin Geometry
A) WQCV Depth DWQCV = 0.75 ft
B) Sand Filter Side Slopes (Horizontal distance per unit vertical, Z = 4.00 ft / ft
4:1 or flatter preferred). Use "0" if sand filter has vertical walls.
C) Minimum Filter Area (Flat Surface Area) AMin = 106 sq ft
D) Actual Filter Area AActual = 219 sq ft
E) Volume Provided VT = cu ft
3. Filter Material
4. Underdrain System
A) Are underdrains provided?
B) Underdrain system orifice diameter for 12 hour drain time
i) Distance From Lowest Elevation of the Storage y = ft
Volume to the Center of the Orifice
ii) Volume to Drain in 12 Hours Vol12 = N/A cu ft
iii) Orifice Diameter, 3/8" Minimum DO = in
Hoffman Mill Fueling Site
Design Procedure Form: Sand Filter (SF)
J.Claeys
Interwest Consulting Group
June 6, 2018
UD-BMP (Version 3.06, November 2016)
Choose One
Choose One
18" CDOT Class B or C Filter Material
Other (Explain):
YES
NO
UD-BMP_v3.06.xlsm, SF 6/5/2018, 5:10 PM
Hoffman Mill Fueling Site
Critical Pond Elevations
Design Engineer:
Design Firm:
Project Number:
Date:
DESIGN CRITERIA
Urban Storm Drainage Criteria Manual, Urban Drainage and Flood Control District, June 2001 (Revised April 2008)
Volume obtained utilizing 2018 AutoCAD Civil3D
Storage Summary
4947.00 ft
283 cu-ft
290 cu-ft
4947.70 ft
2,788 cu-ft
3,071 cu-ft
4944.56 ft
3,164 cu-ft
4946.90 ft
Require 100-yr Detention Volume
Total Detention Volume Provided
100-yr WSE
J.Claeys
Interwest Consulting Group
1344-095-00
September 25, 2018
Pond Invert Elevation
Sand Filter Invert Elevation
Required Water Qualtiy Capture Volume (WQCV)
WQCV Provided
WQCV Water Surface Elevation (WSE)
Combined Required 100-yr Detention & WQCV
1344-095-00 PondCalcs.xls - Pond Stage Storage Page 1 of 3 Interwest Consulting Group
Hoffman Mill Fueling Site
Emergency Overflow Spillway Calculations
Design Engineer:
Design Firm:
Project Number:
Date:
Broad-Crested Weir Equation-Trapezoidal Shape
where: Q = Discharge (cfs)
C = Weir Coeffecient
L = Weir Length (ft)
H = Average Weir Head (ft)
H:V =Side Slope
Calculations
Knowns: 4.00
0.25 ft
2.6
4947.70 ft
3.39 cfs
9.43 ft
10 ft
0.00 ft
0.25 ft
4947.95 ft
Side Slopes (H:V)
Desired Spillway Head
Weir Coefficient
Spillway Elevation
J.Claeys
Interwest Consulting Group
1344-095-00
September 25, 2018
Top of Berm Elevation
100-yr Pond Inflow
Calculated Spillway Length
Use Spillway Length
Total Spillway Depth
Spillway Freeboard
2
5
2
3
H
V
H
QCLH C
= +
1344-095-00 PondCalcs.xls - Spillway Page 2 of 3 Interwest Consulting Group
Hoffman Mill Fueling Site
Circular Orifice Plate Sizing
Design Engineer:
Design Firm:
Project Number:
Date:
Orifice Equation
where: C = Orifice Discharge Coefficient
A o = Orifice Area (ft
2
)
g = Gravity (32.2 ft/s
2
)
Dh = Difference in Elevation Head (ft)
D o = Orifice Diameter (in)
Calculations
100-yr Orifice Sizing 100-yr Orifice Rating Table
Knowns: 100-yr Release Rate 7.7 cfs
100-yr WSEL 4946.90 ft 4944.56 0.00
4945.00 0.00
Pond Outlet Invert 4944.56 ft 4946.00 5.36
4946.90 7.70
Discharge Coefficient 0.65
Tailwater Elevation 4944.94 ft
Orifice Diameter 14 5/16 in
Orifice Area 1.118 ft
2
Centroid Elevation 4945.16 ft
Actual Release Rate 7.70 cfs
J.Claeys
Interwest Consulting Group
1344-095-00
September 25, 2018
Elevation
(ft)
Discharge
(cfs)
C g h
Q
QCA o g h A o ∆
= ∆ ⇒ =
2
2
π
o
o
A
D
= 576
1344-095-00 PondCalcs.xls - Outlet Orifice Plate Sizing Page 3 of 3 Interwest Consulting Group
Culvert Report
Hydraflow Express Extension for Autodesk® AutoCAD® Civil 3D® by Autodesk, Inc. Tuesday, Jun 5 2018
Hoffman Mill Fuel Station - Culvert Sizing
Invert Elev Dn (ft) = 100.00
Pipe Length (ft) = 32.00
Slope (%) = 0.50
Invert Elev Up (ft) = 100.16
Rise (in) = 18.0
Shape = Circular
Span (in) = 18.0
No. Barrels = 1
n-Value = 0.012
Culvert Type = Circular Concrete
Culvert Entrance = Square edge w/headwall (C)
Coeff. K,M,c,Y,k = 0.0098, 2, 0.0398, 0.67, 0.5
Embankment
Top Elevation (ft) = 102.50
Top Width (ft) = 24.00
Crest Width (ft) = 20.00
Calculations
Qmin (cfs) = 0.00
Qmax (cfs) = 10.00
Tailwater Elev (ft) = (dc+D)/2
Highlighted
Qtotal (cfs) = 8.00
Qpipe (cfs) = 8.00
Qovertop (cfs) = 0.00
Veloc Dn (ft/s) = 4.92
Veloc Up (ft/s) = 5.79
HGL Dn (ft) = 101.30
HGL Up (ft) = 101.25
Hw Elev (ft) = 101.98
Hw/D (ft) = 1.21
Flow Regime = Inlet Control
Channel Report
Hydraflow Express Extension for Autodesk® AutoCAD® Civil 3D® by Autodesk, Inc. Tuesday, Jun 5 2018
Hoffman Mill Fuel Site - Ditch Capacity
Triangular
Side Slopes (z:1) = 4.00, 4.00
Total Depth (ft) = 2.00
Invert Elev (ft) = 100.00
Slope (%) = 0.50
N-Value = 0.030
Calculations
Compute by: Known Q
Known Q (cfs) = 8.00
Highlighted
Depth (ft) = 0.98
Q (cfs) = 8.000
Area (sqft) = 3.84
Velocity (ft/s) = 2.08
Wetted Perim (ft) = 8.08
Crit Depth, Yc (ft) = 0.76
Top Width (ft) = 7.84
EGL (ft) = 1.05
0 2 4 6 8 10 12 14 16 18 20
Elev (ft) Depth (ft)
Section
99.50 -0.50
100.00 0.00
100.50 0.50
101.00 1.00
101.50 1.50
102.00 2.00
102.50 2.50
103.00 3.00
Reach (ft)
150 1.60 0.71 6,372.00 4,500.00 1,872.00 0.0430
155 1.57 0.69 6,460.94 4,650.00 1,810.94 0.0416
160 1.54 0.68 6,541.92 4,800.00 1,741.92 0.0400
165 1.51 0.67 6,614.93 4,950.00 1,664.93 0.0382
170 1.48 0.65 6,679.98 5,100.00 1,579.98 0.0363
175 1.45 0.64 6,737.06 5,250.00 1,487.06 0.0341
180 1.42 0.63 6,786.18 5,400.00 1,386.18 0.0318
185 1.40 0.62 6,876.45 5,550.00 1,326.45 0.0305
190 1.38 0.61 6,961.41 5,700.00 1,261.41 0.0290
195 1.36 0.60 7,041.06 5,850.00 1,191.06 0.0273
200 1.34 0.59 7,115.40 6,000.00 1,115.40 0.0256
205 1.32 0.58 7,184.43 6,150.00 1,034.43 0.0237
210 1.30 0.58 7,248.15 6,300.00 948.15 0.0218
215 1.28 0.57 7,306.56 6,450.00 856.56 0.0197
220 1.26 0.56 7,359.66 6,600.00 759.66 0.0174
225 1.24 0.55 7,407.45 6,750.00 657.45 0.0151
230 1.22 0.54 7,449.93 6,900.00 549.93 0.0126
235 1.21 0.54 7,549.49 7,050.00 499.49 0.0115
240 1.20 0.53 7,646.40 7,200.00 446.40 0.0102
Adjusted Runoff Coefficient (CC f )
Area (A )
Allowed Release Rate
Required Detention
Urban Storm Drainage Criteria Manual, Urban Drainage and Flood Control District, June 2001 (Revised April 2008)
City of Fort Collins - Storm Water Criteria Manual
June 6, 2018
Runoff Coefficient (C )
Frequency Factor (C f )
100-yr Detention Volume - FAA Method
Hoffman Mill Fuel Station
J.Claeys
Interwest Consulting
1344-095-00
(ft)
SLOPE
(ft/ft)
Table RO-2 VELOCITY
(ft/s)
t c = t i + t t 0 . 5
V = C v S w
V
L
tt 60
=
��
= 18 − 15� +
�
60 24� + 12 �
��
=
1.87(1.1 − ��
��
) �
� �
1344-095-00 Rational Calcs (FC).xlsx Page 3 of 4 Interwest Consulting Group
(ft)
SLOPE
(ft/ft)
Table RO-2 VELOCITY
(ft/s)
t c = t i + t t 0 . 5
V = C v S w
V
L
tt 60
=
��
= 18 − 15� +
�
60 24� + 12 �
��
=
1.87(1.1 − ��
��
) �
� �
1344-095-00 Rational Calcs (FC).xlsx Page 2 of 4 Interwest Consulting Group
LENGTH
(ft)
SLOPE
(ft/ft)
Table RO-2 VELOCITY
(ft/s)
t c = t i + t t 0 . 5
V = C v S w
V
L
tt 60
=
��
= 18 − 15� +
�
60 24� + 12 �
��
=
1.87(1.1 − ��
��
) �
� �
1344-095-00 Rational Calcs (FC).xlsx Page 3 of 4 Interwest Consulting Group
LENGTH
(ft)
SLOPE
(ft/ft)
Table RO-2 VELOCITY
(ft/s)
t c = t i + t t 0 . 5
V = C v S w
V
L
tt 60
=
��
= 18 − 15� +
�
60 24� + 12 �
��
=
1.87(1.1 − ��
��
) �
� �
1344-095-00 Rational Calcs (FC).xlsx Page 2 of 4 Interwest Consulting Group
Gravel/Pavers
1344-095-00 Rational Calcs (FC).xlsx Page 1 of 4 Interwest Consulting Group