HomeMy WebLinkAboutSite Certifications - 11/01/2006November 1, 2006
Mr. Jay Barber
City of Fort Collins
Storm Water Utility
700 Wood Street
Fort Collins, CO 80521
Re: Water Quality Pond Certification Rigden Farm Filing 6
JR Project 39164.41
Dear Mr. Barber,
ft)
J•R ENGINEERING
A Westrian Company
The purpose of this letter is to serve as a Water Quality Pond Certification for Water Quality
Pond 1 and Water Quality Pond 2 in the Rigden Farm Filing Six Subdivision. JR Engineering
has reviewed the following items through field observations and a survey completed by Nolte
and Associates, Inc:
o Water Quality Capture Volumes
o Water Quality Outlet Structure
o Spillway Length and Elevation
o General Structural Integrity of Ponds
o Erosion control measures
Enclosed with this letter you will find as -built stage -storage calculations for Water Quality
Pond I and Water Quality Pond 2. The required water quality capture volumes (WQCV)
were obtained from the "Final Drainage and Erosion Control Report Rigden Farm — Filing
Six" (JR Eng. February 8, 2002), approved on May 20, 2002.
V
It should also be noted that the elevations for Water Quality Pond 1 and Water Quality Pond 2
may change subsequent to the date of the surveys due to natural and/or artificial actions.
Water Quality Pond 1 was observed to have approximately eight inches of standing water at
the time of the field visit. The invert of the outlet structure is higher than the bottom of the
pond. Water Quality Pond I is required to have a water quality capture volume (WQCV) of
0.13-acre-feet at an elevation of 4909.90'. From the survey data, it was found that the existing
grading provides a WQCV of approximately 0.13 acre-feet at an elevation of 4909.80'. The
structural integrity, side slopes, and compaction of the berm for Water Quality Pond I were
observed to be adequate. The top of berm elevation is 4912.15', which is lower than the 4913'
design elevation. From the survey data, it is noted that the spillway elevation for Water
Quality Pond 1 is at an elevation of approximately 4912.15'. This is slightly higher than the
design elevation of 4912.00'. JR Engineering has reviewed the permanent erosion control
measures and it appears that riprap has been installed in general accordance with the design
plans. JR Engineering also observed that temporary erosion control measures such as silt
fence and mulching were being utilized in the area of Water Quality Pond 1. The orifice plate
2620 Fast Prospect Road, Suite 190, Fort Collins, CO 80525
970-491-9888 • Fax: 970-491-9984 • w jrengineering.wm
November 1, 2006
Page 2 of 2
was observed to have 8 holes with a diameter of %2". The design called for 6 holes with a
diameter of It is recommended that the orifice plate be replaced to meet the design.
Water Quality Pond 2 was observed to have approximately six inches of standing water at the
time of the field visit. The invert of the outlet structure is higher than the bottom of the pond.
Water Quality Pond 2 is required to have a water quality capture volume (WQCV) of 0.08
acre-feet at an elevation of 4906.60'. From the survey data, it was found that the existing
grading provides a WQCV of approximately 0.13 acre-feet at an elevation of 4906.50'. The
structural integrity, side slopes, and compaction of the berm for Water Quality Pond 2 were
observed to be adequate. The top of berm elevation is 4908.72', which is lower than the 4909'
design elevation. From the survey data, it is noted that the spillway elevation for Water
Quality Pond 2 is at an elevation of approximately 4908.72'. This is higher than the design
elevation of 4908.00'. JR Engineering has reviewed the permanent erosion control measures
and it appears that riprap has been installed in general accordance with the design plans. JR
Engineering also observed that temporary erosion control measures such as silt fence and
mulching were being utilized in the area of Water Quality Pond 2. The orifice plate was
observed to have 8 holes with a diameter of The design called for 6 holes with a diameter
of/2". It is recommended that the orifice plate be replaced to meet the design.
In summary, it is expected that the orifice plates be replaced for both ponds. Based upon our
field visits and provided survey information, it is our opinion that the water quality facilities
as noted above for Rigden Farm Filing Six have been constructed in general conformance to
the approved plans.
Sincerely,
JR Engineering; LLC
Prepared By:
Eric Tracy, EI
Design Engineer
XA3910000.all\3916441\Word\ReportsWs-built Pond Cert.doc
Water Quality Ponds Along Foothills Regoinal Channel
Proposed Detention Pond - Stage/Storage
DESIGN
LOCATION:
Rigdm
PROJECT NO:
39164.12
COMPUTATIONS BY:
B. Strand
SUBMITTED BY:
JR ENGINEERING
DATE:
7/4/2001
V = 1/3 d (A + 8 + sgrt(A'8))
where V = volume between contours, ft3
d = depth between contours, It
A = surface area of contour
Wafer n...H6 Pnnd I
Pond Inv.
Pipe Inv -
Elev of WQ orifice -
WQCV.
Top of WQ structure -
top of berm -
Pond Inv.
Pipe Inv -
E/ev of WQ orifice -
WQCV-
Top of WQ structure -
top of berm -
Stage
(ft)
Surface
Area
(fe)
Incremental
Storage
(ac-ft)
Total
Storage
(ac-ft)
4906.49
0
4907
255
0.00
0.00
4908
1,303
0.02
0.02
4908.2
1.582
0.01
0.02
4908.49
1.986
0.01
0.04
4909
2,696
0.03
0.06
4,069
0,07
0,13
4,222
0.01
0.14
5,082
0.05
0.20
E49099,990
5,941
0A2
0.26
7,840
0.16
0.42
Stage
(ft)
Surface
Area
(ft`)
Incremental
Storage
(ac-ft)
Total
Storage
(ac-ft)
4903
0
4904
337
0.00
0.00
4905
929
0.01
0.02
4905.3
1,199
0.01
0.02
4906
1,828
0.03
0.05
4906.60
2,637
0.03
0.08
4907
3,176
0.03
0.10
4907.3
3,741
0.02
0.13
4908
5,059
0.09
0.20
4909
1 6,569
0.13
0.33
AS -BUILT
LOCATION:
Rigden
PROJECT NO:
39164.12
COMPUTATIONS BY:
ELT
SUBMITTED BY:
1R ENGINEERING
DATE:
11/l/2006
V = 1 /3 d (A + B + sgrt(A-B))
where V = volume between contours, f?
d = depth between contours, It
A = surface area of contour
wife. m..nf.. P....d I
Pond Inv.
WQCV-
top of berm -
Pond Inv.
WQCV-
top of berm
Stage
(ft)
Surface
Area
(ft`)
Incremental
Storage
(ac-ft)
Total
Storage
(ac-ft)
4906.34
0
4907
336
0.00
0.00
4908
1,479
0.02
0.02
4909
2,781
0.05
0.07
4909.8
4,068
0.06
0.13
4910
4,390
0.02
0.15
4911
1 6,167
0.12
0.27
4912
1 8,068
0.16
0.43
4912.15
1 9,763
1
0.47
Wafer n... lif Pnnd 9
Stage
(ft)
Surface
Area
(W) I
Incremental
Storage
(ac-ft)
Total
Storage
(ac-ft)
4903.62
0
4904
327
0.00
0.00
4905
1,164
0.02
0.02
4906
2,001
0.04
0.05
4906.5
2,710
0.03
0.08
4907
3,419
0.04
0.12
4908
5,162
0.10
0.21
4908.72
6,958
0.10
0.31
Pond Certification
4914.73 4914.35 4914"
4914.97 x ' i919.
491 .89 X 64 49 x 46
x .
x
4915.92
491 x
4915.92
4913.90 4913.75
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x
4915.44 4914.55
x
4915.76
4912.93 4912.76 ]491284
9a6 ]
.9D)aS
X.906.79 x�906 ].
x�90].]0 ..
SPILLWAY LENL7M - 5D'
2.46 4912.15
491 .70 491314
x 4913.34
4913.83
�- 4913.76 4911.23
4914.29 4914.03
4913.12
4913.02
4913.34
30 15 0 30 60
SCALE: 1" = 30'
r'
WATER QUALITY POND 1
RIGDEN FARM FILING 6
JOB NO. 39164.41
11/01/06
SHEET 1 OF 2
J•R ENGINEERING
A Westrian Company
26M F34I RmpEd R24 && W- Fat WkA (b 8M
97&-4%-W • Fax 970-4.%-M • wwwrevempn
4910.20 x4909,81
491180 Xx X4909.79 �908.70
x 491 z491
X 49096' \�
491097 9- 4909.03
08.07 x4 4 A907.14
x4907 BR
4912.38x 49 9. 1 X19 4907.78 X4907.58 9D6.95
490 .9 4 X 490 . X4907.58 I
x 90
4912.67
4912,13 4912.05
x
4912.78
x
4912.59 x
4912.48
3a'
0 � tH 4
4908.70
x
x4908.40 x4908.72 X 4908.74 x
_ 8.7 /
x
4912.55
x
4912,66
4
x
4912.94
I
4908.54 �4909.11
4908.x4909.447 X
X 3
4909.37
x 82 X49D9.33 x4909.66
3.23 6
D
82 X4 7,4
9 4.
4910.07 X4911.31
'
9 7. 6
X1903.62 X, 40
X4903,6 4912.21
9D3.85 0 0 0 3 X4912.35 ..
X49 .06 903
X4904.20 4912.09
X X
4913.44
4913.33
30 15 0 30 60
SCALEI 1° = 30'
WATER QUALITY POND 2
RIGDEN FARM FILING 6
.JOB NO. 39164.41
11/01/06
SHEET 2 OF 2
J•R ENGINEERING
A WesWan Company
262D East Rmped 834 m 190 • Fat Oft DD 8M
970-4%-M • Fex 97D- 0 -M • wwwrarsmanwIn