HomeMy WebLinkAboutKING SOOPERS #146 MIDTOWN GARDENS MARKETPLACE - PDP200012 - DOCUMENT MARKUPS - ROUND 2 - DRAINAGE REPORTPREPARED FOR:
Dillon Companies/King Soopers, Inc.
55 Tejon Street
Denver, Colorado 80223
Phone: (303) 778-3053
PREPARED BY:
Galloway & Company, Inc.
6162 S. Willow Drive, Suite 320
Greenwood Village, CO 80111
DATE:
July 28, 2020
MIDTOWN GARDENS MARKETPLACE
KING SOOPERS STORE #146
Fort Collins, Colorado
PRELIMINARY DRAINAGE REPORT
Galloway & Company, Inc. Page 2 of 18
6162 S. Willow Drive, Suite 320
Greenwood Village, CO 80111
303.770.8884 • GallowayUS.com
Galloway & Company, Inc. Page 3 of 18
6162 S. Willow Drive, Suite 320
Greenwood Village, CO 80111
303.770.8884 • GallowayUS.com
PRELIMINARY DRAINAGE REPORT
Midtown Gardens Marketplace
King Soopers Store #146
Legal Description
Lots 1,2, and 4 of K-Mart Plaza, and all of Lot 2 of the extension of K-Mart Plaza, situated in the
Southeast 1/4 of Section 23, Township 7 North, Range 69 West, of the 6th Principle Meridian, City
of Fort Collins, County of Larimar, State of Colorado.
Preparation Date
July 28, 2020
Prepared for
Dillon Companies/King Soopers, Inc.
55 Tejon Street
Denver, Colorado 80223
Phone: (303) 778-3053Client
Address
City, State, Zip
Prepared by: Reviewed by:
________________________________________ ____________________________
Name Name
Midtown Gardens Marketplace
7/28/2020
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ENGINEER’S STATEMENT
I hereby attest that this report and plan for the preliminary drainage design for Midtown Gardens
Marketplace was prepared by me or under my direct supervision, in accordance with the provisions of the
Fort Collins Stormwater Criteria Manual. I understand that the City of Fort Collins does not and will not
assume liability for drainage facilities designed by others.
Phil Dalrymple, PE # 41171 Date
For and on behalf of Galloway & Company, Inc.
DEVELOPER’S CERTIFICATION
“King Soopers, Inc. hereby certifies that the drainage facilities for Midtown Gardens Marketplace shall be
constructed according to the design presented in this report. I understand that the City of Fort Collins
does not and will not assume liability for the drainage facilities designed and/or certified by my engineer
and that the City of Fort Collins review))s drainage plans pursuant to the Municipal Code; but cannot, on
behalf of Midtown Gardens Marketplace, guarantee that final drainage design review will absolve King
Soopers, Inc. and/or their successors and/or assigns of future liability for improper design.”
Authorized Signature Date
King Soopers, Inc.
Midtown Gardens Marketplace
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I. General Location and Existing Information ................................................................................................ 6
Location ............................................................................................................................................ 6
Description of Property..................................................................................................................... 6
II. Master Drainage Basin Description .......................................................................................................... 6
Major Basin Description ................................................................................................................... 6
Sub- Basin Description..................................................................................................................... 7
III. Floodplain Information .............................................................................................................................. 7
IV. Project Description ................................................................................................................................... 7
V. Drainage Design Criteria .......................................................................................................................... 7
Regulations ...................................................................................................................................... 7
The Four Step Process (Low Impact Development) ........................................................................ 7
Development Criteria Reference and Constraints ........................................................................... 8
Hydrologic Criteria ............................................................................................................................ 8
Hydraulic Criteria .............................................................................................................................. 9
VI. Proposed Drainage Facilities ................................................................................................................. 10
General Concept ............................................................................................................................ 10
Specific Details ............................................................................................................................... 10
VII. Variance Requests ............................................................................................................................... 11
VIII. Erosion Control .................................................................................................................................... 11
Construction Material & Equipment ............................................................................................... 11
Maintenance ................................................................................................................................... 12
IX. Conclusions ........................................................................................................................................... 12
Compliance with Standards ........................................................................................................... 12
Variances ....................................................................................................................................... 12
Drainage Concept .......................................................................................................................... 12
VI. References ............................................................................................................................................ 13
VII. Appendices ........................................................................................................................................... 14
A. Exhibits & Figures ............................................................................................................... 14
B. Hydrologic Computations .................................................................................................... 14
C. Hydraulic Computations ...................................................................................................... 14
D. Drainage Maps .................................................................................................................... 14
TABLE OF CONTENTS
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I. General Location and Existing Information
Location
Midtown Gardens Marketplace (hereafter referred to as “the site” or “project site”) will be located at
the northwest corner of South College Avenue and West Drake Road. It is bounded on north by an
existing commercial development; on the south by West Drake Road (including a Jiffy Lube and Loaf
‘N Jug to remain); on the east by College Avenue; and on the west by the MAX-BRT Bus Line.
Spring Creek is located north of the site. More specifically, the site is located in the Southeast Quarter
of Section 23, Township 7 North, Range 69 West in the City of Fort Collins, County of Larimer and
State of Colorado. Refer to Appendix A for a Vicinity Map.
Description of Property
The project site is approximately 11.34 acres, and consists of a currently vacant Kmart store, a small
retail building at the northeast corner of the site, and an existing Loaf N’ Jug fueling station. Existing
grades on the site range from one to four percent, with historic runoff generally draining to the north
and east across the site. There are no major drainage ways passing through the project site.
According to the USDA NRCS Web Soil Survey, ‘Nunn Clay loam, 0 to 1 percent slopes’ covers the
entire project site. This soil is associated with Hydrologic Soil Group (HSG) ‘C’. HSG ‘C’ soils have a
slow infiltration rate when thoroughly wet and consist chiefly of soils having a layer that impedes the
downward movement of water or soils of moderately fine texture or fine texture. These soils have a
slow rate of water transmission. Refer to Appendix A for additional soils information.
The Midtown Gardens Marketplace will be developed in one phase and is approximately 11.34 acres.
The existing vacant Kmart building along with the vacant retail building at the northeast corner of the
site will be removed. A new King Soopers Marketplace will replace the Kmart, while a new King
Soopers fueling station will replace the vacant retail building. The existing parking lot will be
reconstructed to accommodate the new structures. The lot containing the Loaf N’ Jug will remain
vacant for future development but is included in this report in its developed condition.
During the water quality storm event, surface runoff will flow into one of several stormwater quality
features located on the site. The stormwater quality features include the use of an underground
storage system. During the minor (i.e., 2-year) and major (i.e., 100-year) storm events, runoff volume
in excess of the water quality event will bypass the WQ system and and enter the existing storm
sewer system.
II. Master Drainage Basin Description
Major Basin Description
The project site is located in the Spring Creek drainage basin. According to the City of Fort Collins
website (http://www.fcgov.com/utilities/what-we-do/stormwater/drainage-basins/spring-creek-basin),
this basin “is a major watercourse that flow from Spring Canyon Dam at Horsetooth Reservoir to its
confluence with the Poudre River. The basin is dominated by residential development, but also
includes open space, parks, and isolated areas of commercial and industrial development.”
According to the City of Fort Collins, detention storage for the site is provided offsite near Spring
Creek. Therefore, on-site detention storage is not required for the site. Water quality for the site has
been provided in accordance with the City of Fort Collins LID requirements for the redeveloped
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portions of the site. Water Quality structures have been sized for the redeveloped portions of the site
in the form of an underground water quality basin. Preliminary calculations for underground basin
have been provided, and can be found in Appendix C.
Sub- Basin Description
The site historically drains north and east towards the adjacent commercial development and College
Avenue. There are several storm inlets along the northern property line and throughout the site which
collect runoff. These storm sewer mains ultimately drain to Spring Creek. The historic drainage
patterns for the site will remain unchanged as part of the redevelopment of the site with minor
rerouting due to the proposed site layout.
At the sub-basin level, no offsite runoff is anticipated to enter the site, with the exception of a small
amount of runoff at the southwest corner or the site coming from the MAX/BRT bus station, which is
currently tributary to the site. A portion of the site along W Drake Rd. and S College Ave. will drain
offsite, which is consistent with the current drainage pattern. The site has been broken into four
basins, each with their own set of sub-basins. A description of each basin and their characteristics
can be found later in the report.
There are no irrigation, reservoir, or other facilities that influence, or are influenced by, the local
drainage.
III. Floodplain Information
The project site is shown on FEMA Map Number 08069C0987G (refer to Appendix A for FEMA
Firmette). This map shows that the project is not impacted by an existing floodplain/floodway. Refer to
Appendix A for a copy of the Firmette.
IV. Project Description
The Midtown Gardens Marketplace will be developed in one phase and is approximately 11.34 acres.
The existing vacant Kmart building along with the vacant retail building at the northeast corner of the
site will be removed. A new King Soopers Marketplace will replace the Kmart, while a new King
Soopers fueling station will replace the vacant retail building. The existing parking lot will be
reconstructed to accommodate the new structures. The lot containing the Loaf N’ Jug will remain
vacant for future development but is included in this report in its developed condition.
V. Drainage Design Criteria
Regulations
This preliminary drainage design presented herein is prepared in accordance with the Fort Collins
Stormwater Criteria Manual, November 2017 (FCSCM), the Mile High Flood District (MHFD) Urban
Storm Drainage Criteria Manual, January 2016 (USDCM), and Chapter 10, Flood Prevention and
Protection, of the Fort Collins City Code. No other drainage reports could be provided for the site by
the City of Fort Collins.
The Four Step Process (Low Impact Development)
At this preliminary stage of the design process, we developed a commensurate implementation of the
‘The Four-Step Process’ for stormwater quality management. Per Ordinance No. 007, 2016, ‘No less
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than seventy-five percent (75%) of any developed or redeveloped area . . . must be treated using one
or a combination of LID techniques.’ As previously mentioned, the developer proposes to replace the
existing Kmart with a new King Soopers Marketplace. The runoff for the modified areas collected
onsite will be treated using and underground LID water quality system. Appropriate spill containment
will be provided in the area of the proposed fuel station.
Step 1 - Employ runoff reduction practices
The attached drainage map (see Appendix D) delineates the proposed drainage basins, each of
which drains to a proposed underground water quality system. Underground systems are an
accepted LID method when surface BMPs are infeasible, and consist of an underground chamber
that provide stormwater quality treatment via sedimentation, screening, filtration, and other physical
and chemical processes.
Step 2 - Implement BMPs that provide a Water Quality Capture Volume (WQCV)
Due to site constraints, and underground storage system will provide the necessary Water Quality
Capture Volume.
Step 3 - Stabilize drainageways
The developed runoff generated by the proposed redevelopment will drain to an existing storm drain
system located along the west side of South College Avenue. This system drains north and outfalls
into Spring Creek. Our work assumes that an appropriate level of stabilization exists at the outfall into
Spring Creek.
Step 4 - Implement site specific and other source control BMPs
Site specific considerations such as material handling/storage and other site operations will be
addressed in the Stormwater Management Plan (SWMP).
Development Criteria Reference and Constraints
This preliminary drainage design presented herein is prepared in accordance with the Fort Collins
Stormwater Criteria Manual, November 2017 (FCSCM) and the Mile High Flood District (MHFD)
Urban Storm Drainage Criteria Manual, January 2016 (USDCM). No other drainage reports could be
provided for the site by the City of Fort Collins.
Existing runoff for the proposed site generally drains to the north and east across the site. The
majority of the on-site runoff is captured by an existing storm sewer system which has three
connections to the offsite system downstream. The site drains into an existing 24” storm pipe just
north of the site (2 connections), and a 15” storm pipe along College Avenue. Capacity calculations
for the proposed and existing portions of the storm sewer system have been provided in Appendix C.
Hydrologic Criteria
For urban catchments that are not complex and are generally 160 acres or less in size, it is
acceptable that the design storm runoff be analyzed using the Rational Method. The Rational Method
is often used when only the peak flow rate or total volume of runoff is needed (e.g., storm sewer
sizing or simple detention basin sizing). The Rational Method was used to estimate the peak flow at
each design point. Routing calculations (i.e., time attenuation) that aggregate the basins draining to a
specific design point are include in the Rational Method calculations in Appendix B.
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The Rational Method is based on the Rational Formula:
Q = CiA
Where:
Q = the maximum rate of runoff, cfs
C = a runoff coefficient that is the ratio between the runoff volume from an area and the average
rate of rainfall depth over a given duration for that area
i = average intensity of rainfall in inches per hour for a duration equal to the Time of
Concentration (Tc)
A = area, acres
Runoff Coefficients were determined based on Tables 3.2-1, 3.2-2, and 3.2-3 of the the FCSCM. The
one-hour rainfall Intensity-Duration-Frequency tables for use with the Rational Method of runoff
analysis are provided in Table 3.4-1 of the FCSCM.
The 2-year and 100-year storm events serve as the basis for the drainage system design. The 2-year
storm is considered the minor storm event. It has a fifty percent probability of exceedance during any
given year. The 100-year storm is considered the major storm event. It has a one percent probability
of exceedance during any given year.
The 2-year drainage system, at a minimum, must be designed to transport runoff from the 2-year
recurrence interval storm event with minimal disruption to the urban environment. The 100-year
drainage system, as a minimum, must be designed to convey runoff from the 100-year recurrence
interval flood to minimize life hazards and health, damage to structures, and interruption to traffic and
services.
Hydraulic Criteria
There are three on-site basins which drain to the existing and proposed storm sewer system, which
are identified in the proposed drainage map (Appendix D) as Basins A, B, and C. Runoff from each
basin will be collected by storm sewer inlets and pipes and conveyed offsite to existing detention
ponds and ultimately Spring Creek, approximately 1 mile north of the site. Basin A is collected by a
storm sewer system on the west side of the proposed building and discharges to an existing storm
sewer pipe just north of the site. Basin B discharges to an existing storm sewer pipe along the west
side of College Avenue. Basin C is collected by a storm sewer system on the northeast corner of the
site and discharges to an existing storm sewer pipe just north of the site. Additional areas for the site
not collected by the proposed storm drain system are designated as Off Site Basins (OS) and will
drain offsite to existing storm drain infrastructure, consistent with the existing drainage pattern. Runoff
from these offsite basins will be released undetained toward W Drake Rd, S College Ave, and
existing inlet north of the site.
Inlet Capacity Analysis
Inlet calculations are not required to be included with this preliminary report and will provided with the
Final Drainage Report.
Storm Drain Capacity Analysis
The preliminary storm drain system is typically sized to convey the sum of the 100-year developed
runoff at each design point draining into the system. The pipes are sized to convey this runoff without
surcharging (full-flow capacity). This method should provide a conservative estimate of total runoff
and pipe sizes. It appears that the 100-year developed runoff for the site will not be able to be
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conveyed in the existing storm sewer system downstream of the site. Therefore, the preliminary
design of the storm sewer system for the site has been sized to handle a minimum of the 2-year
storm event. For this preliminary Drainage Study, Flowmaster was used to size the proposed
system, and provide capacity calculations, using a minimum slope of 0.5%. The Flowmaster
summaries in Appendix C show the max flows for the proposed storm drains at the minimum slope.
VI. Proposed Drainage Facilities
General Concept
This final design presents the detailed design of the proposed system for collecting and conveying
developed runoff from current and proposed development at the Midtown Gardens Marketplace site
to the Stormwater quality features and offsite regional facilities. The existing site runoff drains to
existing storm sewer inlets within the parking lot. The proposed design matches this existing
drainage pattern and includes the implementation of and underground Stormtech system to provide
water quality for the site.
Specific Details
The site has been broken into three basins, each with their own set of sub-basins. A description of
each basin and their characteristics can be found below. The intent of the drainage design is to have
the runoff from the majority of the site collected and drain through water quality facilities prior to
entering the existing storm sewer system offsite. An underground Stormtech system has been sized
based on the City of Fort Collins LID requirements for the necessary portions of the site, which will be
located at the various connection points to the existing storm drain system. The stormwater from the
site will travel in the existing storm sewer system, and ultimately reach Spring Creek in accordance
with the existing drainage pattern.
Basin A
Basin A consists of the western half of the site and is comprised of 6 sub-basins. The basin includes
the proposed building, the south parking lot, and the areas to the west of the proposed building.
Runoff from Basin A will be collected by the proposed storm sewer system and conveyed north, and
ultimately discharge into the existing storm sewer system just north of the site. An underground water
quality facility will be provided just upstream of the tie-in point with the existing system.
Basin B
Basin B consists of the southeastern portion of the site and is comprised of 4 sub-basins. The basin
includes the southern portion of the access drive, the southeast portion of the main parking lot, and
the existing Loaf N’ Jug site (which will remain vacant as part of this project but is included in the
drainage calculations in its future developed condition). Runoff from Basin B will be collected by the
proposed storm sewer system and conveyed north and east, and ultimately discharge into the
existing storm sewer system in College Ave. An underground water quality facility will be provided
just upstream of the tie-in point with the existing system.
Basin C
Basin C consists of the eastern half of the site and is comprised of 4 sub-basins. The basin includes
the proposed fuel center and the northern portion of the main parking lot. Runoff from Basin C is
collected by the proposed storm sewer system and conveyed north and ultimately discharges into the
existing storm sewer system just north of the site. An underground water quality facility will be
provided just upstream of the tie-in point with the existing system.
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Offsite Basins
The remainder of the site consists of basins that flow offsite, as is current with the existing drainage
pattern. These basins are located along W Drake Rd, S College Ave, and the northern portion of the
site between the building and the adjacent property. These basins include sidewalk, tree lawn, and
landscape areas between the sidewalk and the parking lot, and access drives off of S College Ave
and W Drake Rd, as well as paved areas joining the site with the adjacent property. Flows from these
areas historically sheet flow to either the existing roadways adjacent to the site or to existing inlets on
the adjacent property north of the site, and ultimately drain to an existing inlet located in College
Avenue near the northeast corner of the site and an existing inlet at the northwest corner of College
and Drake. The characteristics of the tributary areas draining to these inlets will remain virtually the
same, so anticipated flow rates generated should be the same and not negatively impact the existing
storm sewer system. Once in the existing storm sewer inlets, the stormwater from this basin is
conveyed through the existing storm sewer system and ultimately reaches Spring Creek.
VII. Variance Requests
No variances are being requested with the proposed improvements described herein.
VIII. Erosion Control
A General Permit for Stormwater Discharge Associated with Construction Activities issued by the
Colorado Department of Public Health and Environment (CDPHE), Water Quality Control Division
(WQCD), will be acquired for the site. A Stormwater Management Plan (SWMP) should be prepared
to identity the Best Management Practices (BMPs) which, when implemented, will meet the
requirements of said General Permit. Below is a summary of SWMP requirements which may be
implemented on-site.
The following temporary BMPs may be installed and maintained to control on-site erosion and
prevent sediment from traveling off-site during construction:
• Silt Fence – a woven synthetic fabric that filters runoff. The silt fence is a temporary barrier that is
placed at the base of a disturbed area.
• Vehicle Tracking Control – a stabilized stone pad located at points of ingress and egress on a
construction site. The stone pad is designed to reduce the amount of mud transported onto public
roads by construction traffic.
• Straw Wattles – wattles act as a sediment filter. They are a temporary BMP and require proper
installation and maintenance to ensure their performance.
• Inlet protection – Inlet protection will be used on all existing and proposed storm inlets to help
prevent debris from entering the storm sewer system. Inlet protection generally consists of straw
wattles or block and gravel filters.
Compliance with Erosion Control Criteria and all Erosion Control Materials in greater detail will be
provided with the Final Drainage Report
Construction Material & Equipment
The contractor shall store all construction materials and equipment and shall provide maintenance
and fueling of equipment in confined areas on-site from which runoff will be contained and filtered.
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Maintenance
The temporary BMPs will be inspected by the contractor at a minimum of once every two weeks and
after each significant storm event. The property owner will be responsible for routine and non-routine
maintenance of the temporary BMPs. Routine maintenance includes:
• Remove sediment from the bottom of the temporary sediment basin when accumulated sediment
occupies about 20% of the design volume or when sediment accumulation results in poor
drainage.
• Debris and litter removal-remove debris and litter to minimize outlet clogging and improve
aesthetics as necessary.
• Inspection of the facility-inspect the facility annually to ensure that it functions as initially intended.
• Cleaning and repair of BMP’s is required when sediment has built up or the BMP is not working
properly.
IX. Conclusions
Compliance with Standards
The design presented in this final drainage report for the Midtown Gardens Marketplace has been
prepared in accordance with the design standards and guidelines presented in the Fort Collins
Stormwater Criteria Manual and the MHFD Urban Storm Drainage Criteria Manual.
Variances
No variances are being requested with the proposed improvements described herein.
Drainage Concept
The proposed Midtown Gardens Marketplace storm drainage improvements should provide adequate
collection and Water Quality protection for the developed site. The proposed drainage design will
sufficiently drain the proposed development and should not negatively impact the existing condition of
the overall storm drainage system.
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VI. References
1. Fort Collins Stormwater Criteria Manual, November 2017
2. Urban Storm Drainage Criteria Manual, Mile High Flood District, January 2016 (with current
revisions).
3. Flood Insurance Rate Map – Larimer County, Colorado and Incorporated Areas Community
Panel No. 08069C0987G, Effective May 2, 2012.
4. Soil Map – Larimer County Area, Colorado as available through the Natural Resources
Conservation Service National Cooperative Soil Survey web site via Web Soil Survey 2.0.
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VII. Appendices
A. Exhibits & Figures
· Vicinity Map
· USGS Soil Survey Data
· FEMA Flood Insurance Rate Map
B. Hydrologic Computations
· Basin characteristics
· Rational Method computations
· Minor and major storm runoff computations for developed runoff conditions
· Water quality volume required and provided calculations
C. Hydraulic Computations
· Flowmaster pipe capacity calculations
D. Drainage Maps
· Impervious Area Exhibit
· Proposed Drainage Map
(i) (ii) (iii) (iv) (v) (vi) (vii) (viii) (ix) (x) (xi) (xii)
Vault ID
Total
Required WQ
Volume (cf)
Flow, WQ
(cfs)
Chamber
Type
Chamber
Release Rate
(cfs)
Chamber
Volume (cf)
Installed
Chamber
Volume with
Aggregate
(cf)
Minimum No.
of Chambers
Total Release
Rate
(cfs)
Required
Storage
Volume by
FAA Method
(cf)
Minimum No.
of Chambers
Storage
Provided
within the
Chambers
(cf)
Total
Installed
System
Volume (cf)
A 8,199 7.55 MC-3500 0.036 109.9 178.9 46 1.656 3,231 30 5055 8229
B 4,324 3.85 SC-310 0.016 14.7 31.0 140 2.240 485 33 2058 4340
C 1,949 1.65 SC-740 0.024 45.9 74.9 27 0.648 384 9 1239 2022
(i) Calculated WQCV
(ii) 1/2 of the 2-year developed flow rate for the basin being sized (use half of the 2-year intensity for the time of concentration used in the calc - i.e. for 5 min Tc, use 1.425)
(iii) Per ADS, these equate to different chamber sizes they have available.
(iv) Flow rate thru the bottom of the Isolator Row chamber which is equal to the area of the bottom of the chamber multiplied by the flow rate per unit area (.35 gpm/sf).
(v) Volume within chamber only, not accounting for void spaces in surrounding aggregate.
(vi) Volume includes chamber and void spaces (40%) in surrounding aggregate, per chamber unit.
(vii) Number of chambers required to provide full WQCV within total installed system, including aggregate. (i) / (vi)
(viii) Release rate per chamber times number of chambers. (iv) * (vii)
(ix) FAA calc based on Flow, WQ and Total Release Rate.
(x) Number of chambers required to provide required FAA storage volume stored within the chamber only (no aggregate storage). (ix) / (v)
(xi) Volume provided in chambers only (no aggregate storage). This number must meet or exceed the required FAA storage volume. Greater of (vii) or (x) * (v)
(xii) System volume includes total number of chambers, plus surrounding aggregate. This number must meet or exceed the required WQCV. Greater of (vi) or (x) * (vi)
WQ System Calculation Summary
H:\King Soopers - City Market\CO, Fort Collins - KSS000146 -#18 College Drake\3.04 Grading-Drainage Studies\3.04.2 Proposed Drainage Reports-Info\Hydrology\KSS 146_Rational_Routing.xls
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