HomeMy WebLinkAboutSite Certifications - 07/09/20201218 W. ASH, STE. A, WINDSOR, COLORADO 80550
June 26, 2020
Mr. Shane Boyle
City of Fort Collins Stormwater
700 Wood Street
Fort Collins, CO 80522
Re: Hoffman Mill Fuel Station–Site Certification
Dear Shane,
Please accept this letter as the Site and Drainage Certification for the City of Fort Collins
Hoffman Mill Fuel Station project. Survey of the site was completed on June 17, 2020 by
King Surveyors. A site visit was conducted by Bob Almirall of Interwest Consulting Group
on June 19, 2020.
My assessment is that the items constructed are in general conformance with the approved
design with the minor exception of the downstream outfall channel. This channel was
designed and approved to be a long earthen bottom channel at 0.5%. The as-built survey
grades indicate short segments of the channel being less than the design channel slope;
however, these segments are short and the overall flow of the channel to the east is
consistent with the design intent. Minor repairs to the westernmost channel embankment
and enhanced erosion control measures are also being performed in conjunction with the
adjacent Streets Department Scale Project.
I have attached the as-built survey of the site super-imposed on the grading plan, as-built
detention pond and sand filter calculations, the contractor’s During Construction Checklist,
and the Overall Site and Drainage Certification Form and Checklist. The site grading is
finished and seeding for the site is nearly complete.
We appreciate your time and consideration in reviewing this certification. If you have any
questions or need additional information, please feel free to call at any time (970) 460-
8487.
Sincerely,
Robert Almirall, P.E.
Colorado Professional Engineer 33441
Page 1
OVERALL SITE and DRAINAGE CERTIFICATION
Commercial, Multi-Family and Subdivision Certification Form and Checklist
Project Name:
Date:
Building Permit Numbers:
(Commercial or multi-family)
Per the requirement in Fort Collins Stormwater Criteria Manual (FCSCM) Chapter 3, Section 3.0 to certify as-
built construction to the approved drainage and grading plans, please fill in all applicable items in this
Certification Form for Commercial, Multi-Family and Overall Single Family sites. NOTE: several items must be
verified during construction. A copy of the approved grading plan must be submitted with the as-built grading
plan. (As-built elevations must be written in red next to the approved elevations.)
•Use “Yes” for items completed as described.
•Use “N/A” for items that are not applicable to the site being certified.
•If any blanks are “No,” attach an explanation referencing the item number below.
Attach an explanation or description of the as-built condition for any items listed or for anything not listed but
shown on the approved construction plans.
Provide an as-built redline or Mylar drawing with the following:
I.Water Quality and Quantity Detention Basin - FCSCM Ch. 6 and 7
For multiple detention basins on a site, provide the following for each basin separately:
A. Volume: As-built topographic verification is attached at 1-foot (or less) contour intervals and
volume verification calculations for the water quality capture volume and the 100-year detention storage
volume.
1. Detention basin topography was prepared by a professional land surveyor registered in the state
of Colorado.
2.Both proposed and as-built contours are shown on the same plan sheet (dashed lines for
proposed and solid lines for as-built).
3.All critical spot elevations as shown on the approved construction plans have been verified and
the as-built elevations are shown on the plan sheet.
4.Stage-storage-discharge tables are provided on a separate document.
5.Verification that designed drain time is in compliance with Colorado Revised Statute § 37-92-
602(8) is attached and has been uploaded to the Statewide Compliance Portal
(tinyurl.com/COCompliancePortal) for approval. Uploaded documents must include:
a.The cover sheet from the approved drainage report
b.The stamped certification page from the approved drainage report
c.As-built topographic survey
d.Stamped certification page from the Overall Site & Drainage Certification
e.PDF output from the Stormwater Detention and Infiltration Design Data Speadsheet
11/19
SECTION 5 TO BE COMPLETED AFTER AN INITIAL REVIEW BY CITY STAFF AS REQUESTED
Hoffman Mill Fuel Station
June 26, 2020
Yes
Yes
Yes
Yes
Yes
Page 2
B.Water Quality and Quantity Detention Basin Grading: Attached is as-built verification that there is
a minimum 2% positive fall into the concrete trickle pans or flow-line(s) from all areas in the bottom of
the detention pond. If there is a “soft pan” in the flow-line, all areas still must meet the minimum 2%
grade requirement.
1.Low Flow: Choose one of the following detention basin low flow options as applicable:
a. Turf swale for low flow path in detention basin.
There is a minimum 2% grade in the flow-line(s) of the detention basin. The flattest as-built grade
is .
b.Concrete pan for low flow in detention basin.
There is a concrete pan installed that meets the grades as shown on the approved construction
plans. (Show as-built spot elevations.)
c.Soft pan for low flow in detention basin.
•Verify and document the soft pan material gradation, trench width and depth - to be verified
during construction by engineer. Picture documentation is preferred or engineer’s statement of
visual inspection and compliance. (Choose one below.)
o There is a soft pan with an underdrain installed that meets the design on the approved
construction plans. (Show the underdrain grades, bedding material, geotextile, spot elevations,
bends, cleanouts, etc.)
o There is soft pan installed without an underdrain but there is a type A or B soil. The soil
type must be documented by supplying verification from a registered professional geotechnical
engineer.
NOTE: Spot elevations are to be within 0.2 ft. +/-.
2. Side Slopes: The as-built side slopes of the detention basin have been calculated and are shown.
Indicate the side slope with an arrow and a numerical value (e.g., 6.25:1). The maximum slope allowed
is 4:1. Small areas of 3:1 may be acceptable, but slopes steeper than 3:1 must be stabilized or re-
graded. Provide documentation if a variance was granted for steeper slopes during the design process.
3.Spillway: The following items must be field verified:
a.The location of the spillway is indicated on the as-built plan.
b.The width of the spillway is indicated on the as-built plan.
c.The elevation(s) of the spillway is shown on the as-built plan.
d.A concrete ribbon defines the location and grade of the spillway.
e.There is downstream scour protection in the spillway as per the construction plans. Indicate
type: (riprap size “D50” gradation and bedding type, geotextile, buried
riprap with inches of bury, etc.).
f.There are no obstructions in the spillway, such as trees, bushes, sidewalks, landscape
features, rocks, etc.
11/19
Yes
Yes
Yes
Yes
Yes
Yes
N/A
N/A
Yes
Page 3
4.Outlet Structure:
a.The orifice plate for the approved release rate is installed with the correct size and location of
the orifice.
b.The orifice plate for the water quality outlet is installed with the correct hole size, number of
rows and columns of holes.
c.The bottom hole on both the water quality and quantity outlets are at the bottom of the plate
so no water ponds in front of the plate.
d.The well screen is the correct material and is installed as shown on the construction plans.
e.100-year overflow grate elevation is . (Elev. A on detail D-46)
f.The top elevation of the water quality capture volume is . (Elev. B on detail
D-46)
g.Overflow grate is made of the correct material, has the correct bar spacing, is hinged at the
top and bolted at the bottom.
h.The bottom of the outlet box has no obstructions or misalignments that will cause it to retain
runoff water and is sloped at 2% towards outlet.
II.Channels/Swales - FCSCM Ch. 8, Sec. 2.0 and Ch. 9, Sec. 5.0
A. Capacity: The as-built capacity of all the major channels and swales has been verified. They meet
or exceed capacity requirements shown in the approved drainage study for this project.
1.All swales are located within the drainage easements as shown on the construction plans.
2.Longitudinal slopes and side-slopes (cross-sections) have been verified. Design criteria requires
longitudinal slopes of 2% min. (on vegetated swales) and side-slopes no steeper than 4:1. If these
criteria are not met, the certification engineer will write a justification and propose mitigation for each
instance or have the issues corrected. If variances to these criteria have previously been approved and
are shown on the construction plans, no justification is needed.
3.As-built spot elevations on channels/swales are shown that correspond to spot elevations
shown on the approved construction plans.
4.All permanent erosion control measures are installed as shown on the approved construction
plans (e.g., drop structures, riprap, TRMs, etc.). (Include pictures and verification of the materials used
as part of this verification.)
5.All pans, curbs, storm pipes or other appurtenances appropriately tie into each other in the
system. (Pictures at tie-in points suggested.)
6.The minimum freeboard is provided for all channels and swales as shown on the approved
construction plans or as identified in the approved drainage study. (Show the freeboard provided on
the cross-sections as on the construction plan set or attached as separate documentation.)
7.The low flow portion of all channels or swales is clear of obstructions. (No landscaping, trees,
shrubs, sod, etc. infringe on the low flow portion of channels or swales.)
11/19
Yes
N/A
Yes
N/A
N/A
Yes 4947.70
N/A
N/A
N/A
Yes
No
Yes
Yes
Yes
N/A
Yes
Page 4
III.Storm Pipes (aka storm drains) - FCSCM Ch. 9, Sec. 4.0
A. Storm Drain Pipe Capacity: The as-built capacity of all pipes installed on this project has been
verified and meets or exceeds the capacity requirements shown in the approved drainage study for this
project.
1.All storm drain pipe sizes and materials have been verified and are in conformance with the
approved construction plans. (Indicate on the plan and profile sheets that they have been verified.)
Material and size substitutions must be approved prior to installation. If a pipe size or material was
changed during construction, the certification engineer must attach the approval documents or supply
them with this certification. Approval documents must include a calculation documenting the capacity
equivalency (equal or greater) of the substituted size.
2.The longitudinal slope of the pipe is as shown on the approved construction plans. The
acceptable minimum slope is 0.4%. All slopes flatter than the designed slope on the construction plans
must be justified with capacity calculations on an attached sheet.
3.The as-built invert elevations have been verified and are shown on the plan and profile sheets of
the approved construction plans.
B.Storm Drain Pipe Installation Requirements: All pipes are installed in accordance with the
approved construction plans and construction specifications.
1.The minimum cover requirements for all pipes have been met as shown on the approved
construction plans. These will be called out in critical locations.
2.All encasements and clearances as specified on the approved construction plans have been met.
3.Any specific joint types or construction methods specified on the approved construction plans
have been met. (List on a separate sheet and attach to this certification.)
IV.Concrete Pans - FCSCM Ch. 8, Sec. 2.0
A. Construction/Installation: All concrete pans have been constructed in accordance with the
approved construction plans.
1.The concrete pans are the correct size/width as shown on the approved construction plans.
2.The longitudinal slopes of the pans are as shown on the approved construction plans. The
certification engineer must justify or mitigate longitudinal slopes less than the minimum of 0.4% unless
a flatter slope was approved and is shown on the approved construction plans. Provide mitigation or
justification by separate document.
3.The cross-section of the pan is as shown on the construction plans. (Specifically, the pan cross-
section is “V” shaped and meets the side slope shown on the detail.)
4.The concrete pans are a minimum of 6 inches thick without reinforcement and a minimum of 4
inches thick with a minimum of 6X6-W14xW14 reinforcement per detail D20B and D20C. (Provide
documentation of the reinforcement used if different than shown on the details or on the approved
construction plans.)
5.The spot elevations shown on the concrete pan(s) have been verified and are shown on the as-
built drawings.
11/19
N/A
N/A
Yes
Yes
Yes
Yes
Yes
Yes
Page 5
V. Storm Drain Inlets - FCSCM Ch. 9, Sec. 3.0
A. Construction/Installation: All storm drain inlets have been constructed in accordance with the
approved construction plans and construction specifications.
1.The size and type of inlets are consistent with the inlets shown on the approved construction
plan. Indicate by writing “Verified” on each inlet on the plan sheet or list on a separate document the
inlet number(s), type and size (length). If the inlet installed is other than the one on the approved
construction plan detail sheet, provide the name and source of the detail with justification for equal or
better capacity.
2.The size of the inlet opening is consistent with the approved detail. (Check height and width.)
3.The elevation of the grate (if applicable) is at the elevation shown on the street profile or as
indicated by a spot elevation on the construction plans.
4.The as-built invert elevations of all pipes entering and leaving the inlet are shown on the plan
and profile sheets within construction tolerance of 0.2 feet. If substantially different, provide
justification and capacity calculations to show the capacity is not affected or propose mitigation.
5.The as-built size of the inlet box is as shown on the construction plans or an explanation or
justification is attached.
6.All Type C, R, 13 and 16 inlet covers are stenciled or stamped with the following designation (or
an equivalent): NO DUMPING – DRAINS TO POUDRE RIVER.
VI.Culverts - FCSCM Ch. 9, Sec. 4.0
A. Construction/Installation: All culverts have been constructed and/or installed in accordance with
the approved construction plans and construction specifications.
1.All culvert sizes have been verified as indicated on the as-built construction plans as correct.
2.The culvert material type for all culverts installed is as on the approved construction plans and is
indicated on the as-built plans.
3.The as-built invert “in and out” elevations have been verified and are indicated on the as-built
construction plans.
4.The culvert headwalls or wing walls have been installed as shown on the approved construction
plans. Headwalls or wing walls may be needed in the as-built conditions onsite if the slopes adjacent to
the culvert are greater than 4:1. Please note areas needing stabilization in the certification narrative.
An alternative to consider is a turf reinforcement mat (TRM).
VII.Sub-Drains
A. Construction/Installation: All sub-drains shown on the construction plans have been installed in
accordance with those plans and the construction specifications. Sub-drains installed with the sanitary
sewer are to be verified on the sanitary sewer plan and profile sheets of the construction plans. (NOTE:
Indicate any sub-drains installed after the plans were approved on the as-built plans.)
1.The size of the sub-drains are as approved on the construction plans and are indicated on the as-
built plans.
2.The type of sub-drain, in particular the perforated and non-perforated sections of the drain, are
as indicated on the approved construction plans.
11/19
UNDERDRAINS INSTALLED IN SAND FILTER SYSTEM. REFER TO DURING
CONSTRUCTION INSPECTION CHECKLIST FOR UNDERDRAIN INFORMATION.
Yes
Yes
Yes
N/A
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Page 6
3.The cover requirements per the construction plans are provided.
4.The cleanouts have been installed at the locations shown on the construction plans and are
accessible for cleaning. (Cleanouts can be buried a maximum of 6 inches deep with their locations
marked.)
5.The backfill materials for sub-drains are as shown on the approved construction plans. (This
includes the type, depth and width.)
6.The geo-textile liner completely wraps the sub-drain and the permeable backfill material unless
shown otherwise on the approved construction plans. (Sub-drain pipe wrapped in a sock filter material
is accepted only if approved prior to installation.)
VIII.Curb Cuts
A. Construction: All curb cut openings are constructed in accordance with the approved construction
plans and construction specifications.
1.The size (width) of the curb cut opening is as shown on the approved construction plans.
2.The curb cut openings tie into a downstream swale, pipe, or other appurtenances with a smooth
transition and there no obstructions such as riprap or sod impeding the flow downstream of the curb
cut.
IX.Sidewalk Culverts & Chases
A. Construction/Installation: All sidewalk culverts have been installed at the locations shown on the
approved construction plans.
1.The size (width and length) of the culverts are as shown on the approved construction plans.
2.The cover plate is a minimum 5/8-inch galvanized plate bolted to a galvanized angle iron per the
detail shown on the approved construction plans or per the City’s detail.
3.The sidewalk culvert invert “in and out” elevations have been verified and are indicated on the
as-built plans.
4.The sidewalk culvert opening is as shown on the approved construction plans or per the City’s
detail.
5.There is a smooth transition both on the inlet and outlet ends of the sidewalk culvert with no
obstructions such as riprap or sod impeding the flow into or out of the sidewalk culvert.
X. Site Grading - FCSCM Ch. 8
A. Construction: All common open spaces have been graded in accordance with the approved
construction plans.
1.The grading on all common open spaces bordering private lots has been verified as correct and
the as-built rear lot corner elevations have been shown on the as-built plans.
11/19
Yes
N/A
Yes
Yes
N/A
N/A
Yes
Yes
Page 7
2.The as-built contours for “overlot grading” are shown on the as-built construction plans for all
common open spaces, tracts, outlots, etc. If not in compliance, please attach a narrative describing the
situation for noncompliance and when it may be corrected. An escrow for overlot grading may be
required. (NOTE: Residential Lot Grading Certification is a separate process from this Overall Site
Certification. It is understood that residential lots will be brought to final grade once the foundation is
backfilled so they may be lower than the plan shows at this Overall Site Certification stage.)
3.All turf reinforcement mats (TRMs) have been installed as shown on the approved construction
plans and the slopes are stabilized.
XI.Permanent Erosion Control BMPs - FCSCM Ch. 9, Sec. 7.0
A. Construction: All permanent erosion control BMPs have been installed per the approved
construction plans.
1.All riprap has been installed in the locations and sizes indicated on the approved construction
plans.
2.All fabric has been installed in the locations and sizes indicated on the approved construction
plans.
a.All fabric was installed per the details on the approved construction plans.
XII.Post-Construction Site Cleanup - FCSCM Ch. 3, Sec. 2.0
A. Construction: All construction debris and obstructions of any kind have been removed from
drainage paths.
1.All construction debris has been removed except in staging area(s).
2.All ruts have been smoothed out in all construction areas.
3.All areas needing reseeding have been identified and future stabilization goals have been
coordinated with the Erosion Control Inspector and in accordance with FCSCM Vol.2 Chapter 12. Note
the area needing stabilization in the narrative.
XIII.Certification of LID and Water Quality Facilities - FCSCM Ch. 7
A.Attached are the During Construction Inspection Checklist for Low Impact Development (LID) and
other items to be verified during construction, along with pictures and other required documentation.
B.Attached is verification of the rain garden and/or sand filter flat surface area(s) and ponding
volume(s). This verification includes survey of critical elevations.
C.Attached is verification of the underground infiltration required volume(s), weir elevations,
orifices, inspection ports and filtering fabric. This verification includes survey of critical elevations.
D.All visible LID design features were verified as part of the engineer's site visit.
11/19
N/A
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
N/A
Yes
11/19 Page 8
XIV.Certification of Other Permanent BMPs
A.The construction of other permanent BMPs not specifically addressed in this certification is in
accordance with the approved plan. This may include grade control structures, rundowns, bridges, stream
access/improvements, etc.
Please specify other permanent BMPs included on this site:
XV. Certification and Erosion Control Measures - FCSCM Ch. 3
A. All temporary erosion control measures shall be removed upon stabilization. If at the time of preparing
this certification there are any erosion control measures still remaining on the site, please note them in
the narrative and verify that they need to remain at this time. If in doubt as to the need for any control
measure, please consult with the Erosion Control Inspector at erosion@fcgov.com.
XVI.Statement of Compliance - FCSCM Ch. 3
A. This certification is signed and stamped. By signing this form, the engineer(s) attests that he/she has
visited and observed the site, and to the best of his/her knowledge, the as-built conditions of the drainage
facilities are as described in the above form and in the enclosed as-built plans.
B.Failure to properly disclose all known information could result in the rejection of this certification and
prevent the release of any and all Stormwater Utility permit holds on Building Permits and/or Certificates
of Occupancy within this development.
XVII. Signature and Stamp by a Colorado-Registered Professional Engineer
Engineer’s contact information:
Name:
Email:
Phone:
Company:
Address:
PE Stamp
06-26-2020
Channel Check Dams and Stone on West Channel Berm
N/A
Robert Almirall
ralmirall@interwestgrp.com
970-460-8487
Interwest Consulting Group
1218 W Ash Street, Suite A
Windsor, CO 80550
HOFFMAN MILL ROAD
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POND CROSS-SECTION PROFILE
HORIZ. SCALE: 1"=10'
VERT. SCALE: 1"=5'
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CALL BEFORE YOU DIG
CALL UTILITY NOTIFICATION
CENTER OF COLORADO
1-800-922-1987
or 8-1-1
CALL 2-BUSINESS DAYS IN ADVANCE
BEFORE YOU DIG, GRADE OR EXCAVATE FOR THE
MARKING OF UNDERGROUND MEMBER UTILITIES.
CHECKED BY:
Date
City of Fort Collins, Colorado
UTILITY PLAN APPROVAL
Parks and Recreation
Traffic Engineer
Stormwater Utility
Water & Wastewater Utility
City Engineer
CHECKED BY:
APPROVED:
Environmental Planner
CHECKED BY:
CHECKED BY:
CHECKED BY:
CHECKED BY:
Date
Date
Date
Date
Date
Date
0
10'
2010510
SCALE: 1" =
LEGEND
EXISTING MAJOR CONTOUR
EXISTING MINOR CONTOUR
PROPOSED MAJOR CONTOUR
PROPOSED MINOR CONTOUR
NOTES:
1.CONTRACTOR TO PROVIDE AND MAINTAIN ALL NECESSARY EROSION CONTROL MEASURES PRIOR TO
AND THROUGHOUT CONSTRUCTION.
2.ALL SUBGRADE TO BE PLACED/COMPACTED PER GEOTECHNICAL ENGINEER RECOMMENDATIONS.
3.LENGTH OF STORM PIPE LISTED INCLUDES FLARED END SECTIONS.
4.THE WEST END OF THE CONCRETE PAN SHALL HAVE A 12" TURNED-DOWN EDGE TO PREVENT
PIPING/UNDERMINING OF THE DRAIN PAN. INSTALL COBBLE OR RIPRAP AT THE WEST END OF THE PAN
AND ALONG THE ROOF DRAIN/SUMP PUMP DRAINAGE PATHWAY AS NEEDED TO PREVENT EROSION.
WQCV SPILLWAY CROSS-SECTION
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RECORD DRAWING
DATE: 6/18/20
ASBUILT CONTOUR
13.4 ft
113.8 sf
HOFFMAN MILL ROAD
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CALL BEFORE YOU DIG
CALL UTILITY NOTIFICATION
CENTER OF COLORADO
1-800-922-1987
or 8-1-1
CALL 2-BUSINESS DAYS IN ADVANCE
BEFORE YOU DIG, GRADE OR EXCAVATE FOR THE
MARKING OF UNDERGROUND MEMBER UTILITIES.
CHECKED BY:
Date
City of Fort Collins, Colorado
UTILITY PLAN APPROVAL
Parks and Recreation
Traffic Engineer
Stormwater Utility
Water & Wastewater Utility
City Engineer
CHECKED BY:
APPROVED:
Environmental Planner
CHECKED BY:
CHECKED BY:
CHECKED BY:
CHECKED BY:
Date
Date
Date
Date
Date
Date
0
30'
60301530
SCALE: 1" =
LEGEND
EXISTING MAJOR CONTOUR
EXISTING MINOR CONTOUR
PROPOSED MAJOR CONTOUR
PROPOSED MINOR CONTOUR
NOTES:
1.CONTRACTOR TO PROVIDE AND MAINTAIN ALL NECESSARY
EROSION CONTROL MEASURES PRIOR TO AND THROUGHOUT
CONSTRUCTION.
2.ALL SUBGRADE TO BE PLACED/COMPACTED PER
GEOTECHNICAL ENGINEER RECOMMENDATIONS.
RECORD DRAWING
DATE: 5/29/20
ASBUILT CONTOUR
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
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
As-Built Detention Pond - Stage/Storage
LOCATION:Detention
PROJECT NO:
COMPUTATIONS BY: LAJ
DATE: 6/18/2020
V = 1/3 d ( A + B + sqrt(A*B))
where V = volume between contours, ft3
d = depth between contours, ft
A = surface area of contour
Detention Pond
Surface Incremental Total
Stage Area Storage Storage
(ft)(ft2)(ac-ft) (ac-ft)
44.4 0
44.7 150 0.00 0.00
45.0 450 0.00 0.00
45.5 940 0.01 0.01
47.2 4170 0.09 0.10
47.3 0 0.00 0.11
47.4 0 0.00 0.11
47.5 0 0.00 0.11
47.6 0 0.00 0.11
47.7 0 0.00 0.11
47.8 0 0.00 0.11
47.9 0 0.00 0.11
48.0 0 0.00 0.11
48.1 0 0.00
48.2
48.3
48.4
1344-095-00 As-Built Pond Vol Calc_LAJ 2020-06-18.xls
51907643.xlsm, SF 6/26/2020, 9:52 AM
Design Procedure Form: Sand Filter (SF)
UD-BMP (Version 3.06, November 2016)Sheet 1 of 2
Designer:B. Almirall
Company:Interwest Consulting Group
Date:June 26, 2020
Project:Hoffman Mill Fueling Site
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 =0.82 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 =114 sq ft
E) Volume Provided VT =303 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
Choose One
Choose One
18" CDOT Class B or C Filter Material
Other (Explain):
YES
NO
As-Built Conditions
51907643.xlsm, SF 6/26/2020, 9:53 AM
Design Procedure Form: Sand Filter (SF)
Sheet 2 of 2
Designer:B. Almirall
Company:Interwest Consulting Group
Date:June 26, 2020
Project:Hoffman Mill Fueling Site
Location:
5.Impermeable Geomembrane Liner and Geotextile Separator Fabric
A) Is an impermeable liner provided due to proximity
of structures or groundwater contamination?
6-7.Inlet / Outlet Works
A) Describe the type of energy dissipation at inlet points and means of
conveying flows in excess of the WQCV through the outlet
Notes:
Choose One
YES NO