HomeMy WebLinkAboutPROSPECT SPORTS CLUB - PDP230009 - SUBMITTAL DOCUMENTS - ROUND 2 - VARIANCE REQUEST'
A LTERNATIVE C OMPLIANCE AND V ARIANCE R EQUESTS
P ROSPECT S PORTS C LUB
F ORT C OLLINS ,CO
19 OLD TOWN SQUARE #238 | FORT COLLINS, CO 80524 | 970-530-4044 | www.unitedcivil.com
July 28, 2023
DAN MOGEN
700 WOOD STREET
FORT COLLINS,CO 80522
RE: STORMWATER ALTERNATIVE COMPLIANCE AND VARIANCE REQUESTS
PROSPECT SPORTS CLUB –1600 EAST PROSPECT ROAD
PROJECT NUMBER:U22014
Dan,
This letter is being submitted on behalf of the owners of the Prospect Sports Club development. The project is currently in
the Preliminary Development Plan process and currently one (1) alternative compliance and one (1) variance are being
requested to modify portions of the Fort Collins Stormwater Criteria Manual as follows:
ALTERNATIVE COMPLIANCE REQUEST –STORMWATER QUALITY AND LOW IMPACT DEVELOPMENT STANDARDS
DESIGN CRITERIA OF VARIANCE BEING REQUESTED
Section 1.0 within the Fort Collins Stormwater Criteria Manual which states:
FCU requires that water quality treatment systems for stormwater are installed for all applicable development sites,
including the incorporation of enhanced water quality treatment for stormwater, which has been required since 2013.
Section 6.0 within the Fort Collins Stormwater Criteria Manual which states:
Integration of LID systems into the drainage design is required for all development projects in order to comply with
the City’s policies on LID, the requirements of this Manual, the City Code and the Land Use Code. LID systems provide
a higher degree of stormwater quality treatment than that provided with standard water quality design. The
implementation of LID systems requires one of the following two options:
1)50% of the newly added or modified impervious area must be treated by LID techniques and 25% of new paved
(vehicle use) areas must be pervious.
2)75% of all newly added or modified impervious area must be treated by LID techniques.
HARDSHIP REGARDING REQUIREMENT
The site is located at 1600 East Prospect Road within Prospect Park East P.U.D and is surrounded by existing fully developed
commercial properties to the south (Advanced Energy) and west (Larimer County Coroner) along with Prospect Road and
Sharp Point to the north and east respectively.
The original subdivision development planned for drainage to be conveyed via overland flow to the drainage facility located
south of the site; therefore, no storm sewer currently exists on the site. However, the original subdivision plat did not include
drainage easements on the property to allow for the conveyance of 100-year stormwater runoff from the site, across the
property to the south and to the existing drainage facility. After discussion with the south property owner and their attorney,
the southern property owner has denied any new easements on their property. Refer to Appendix A for an email from the
south property owner regarding the denial of new easements. Therefore, storm sewer for the project, required to convey
both water quality and 100-year developed stormwater flows, is proposed to convey runoff to the east across Sharp Point to
A LTERNATIVE C OMPLIANCE AND V ARIANCE R EQUESTS
P ROSPECT S PORTS C LUB
F ORT C OLLINS ,CO
19 OLD TOWN SQUARE #238 | FORT COLLINS, CO 80524 | 970-530-4044 | www.unitedcivil.com
the existing property also owned by the developer of the Prospect Sports Club facility to avoid the need for drainage
easements south of the site.
These site and storm sewer configurations generated by the design of the existing subdivision and the inability to modify the
southern property easements/agreements culminate into hardships with providing standard water quality and LID treatment
techniques that are approved by the City:
1.Standard water quality by way of extended detention is not viable due to space and grade limitations on the site.
Note that the open landscaped area north of the building is located within an existing pedestrian easement and is
also located on the high side of the property.
2.Underground detention/infiltration is not viable in the parking lot area due to available depths of storm sewer, is
not viable on the south or east due to the proximity of the proposed building to the property line and is likely not
viable on the north due to lack of access for maintenance.
3.Bioretention for the development is largely not viable due to the location available to provide the feature. Although
there is potentially room north of the building, the amount of impervious area that would drain to the area is limited
to small portions of hardscape due to grade limitations. Additionally, this area is located on the north side of the
building, during winter months it is probable that roof drainage if allowed to pond on frozen bioretention areas
would not infiltrate causing maintenance and safety concerns.
PROPOSED ALTERNATE DESIGN
The development team understands that water quality is an important aspect of every new development, not only to simply
meet City standards, but to protect downstream infrastructure and environments. Therefore, the design team is requesting
that the development, due to the hardships documented, is allowed to meet the following reduced/modified water quality
and LID treatment requirements:
1.Provide permeable pavers for a minimum of 25% of new vehicle use pavement meeting City LID requirements but
provide less than 50% of total site water quality via LID treatment techniques.
2.Provide water quality techniques not included in the City of Fort Collins Stormwater Criteria Manual but still meet
criteria within the City’s MS4 permit with the State of Colorado.
With that basis, the development team proposes to provide the following:
1.Provide grass lined swales along the north and east sides of the building within Basins A1, A3 and A4 to provide,
albeit non-standard / non-quantitative, water quality treatment for limited hardscape to be located on the north
and east sides of the building.
2.Provide permeable pavers within Basins A4 and A6 for the parking lot which is anticipated to generate the most
pollutants on the site. Approximately, 6,960 square-feet of permeable pavers are provided which is sufficient to
treat the portions of the parking lot and plaza areas that drain to the pavers within Basins A4 and A6. Excess runoff
from the basins is collected via storm sewer and directed east, through a water quality manhole containing a Snout®
and sump located east of Sharp Point Drive prior to being conveyed to the existing pond to the east.
3.Provide a water quality manhole as previously noted located east of Sharp Point Drive to treat Basins A1-A6. Note
that this structure will be the primary treatment technique for Basin A2 which includes the entirety of the proposed
building roof. With Basin A2 containing only roof area, it is anticipated that the basin will generate less pollutants
than those expected in the parking area.
As noted above, Basin A1-A3 and A5 are the areas of the site being proposed to be treated with techniques not provided
within the City Stomrwater Criteria Manual while the majority of Basins A4 and A6 are treated with a City approved LID
technique (i.e. permeable pavers). Therefore, the following section documents the alternate compliance related to the water
quality treatment of Basins A1-A3 and A5 as it relates to satisfying the City’s MS4 permit with the State of Colorado.
Per Part I, Section E.4.a.iv.B of the City’s MS4 Permit, the following “Pollutant Removal Standard” criterion has been used to
analyze Basins A1-A3 and A5 regarding this alternative compliance request: The control measure(s) is designed to treat at a
minimum the 80th percentile storm event. The control measure(s) shall be designed to treat stormwater runoff in a manner
expected to reduce the event mean concentration of total suspended solids (TSS) to a median value of 30 mg/L or less. Refer
to Appendix A for the section of the MS4 permit referenced.
A LTERNATIVE C OMPLIANCE AND V ARIANCE R EQUESTS
P ROSPECT S PORTS C LUB
F ORT C OLLINS ,CO
19 OLD TOWN SQUARE #238 | FORT COLLINS, CO 80524 | 970-530-4044 | www.unitedcivil.com
To meet the noted MS4 requirement, a starting TSS concentration must first be determined.A Nationwide Urban Runoff
Program (US EPA 1983) land use table regarding event mean concentrations is utilized to determine the median event mean
concentrations of total suspended solids (TSS) assuming the site is included as an urban commercial development. Per Table
4-1 of the EPA report, a concentration of 69 mg/l is assumed for urban commercial improvements. Refer to Appendix A for
the referenced table.
Basins A1 and A3 are first treated with grass swales and then treated with the Snout®. Basin A2 and Basin A5 are treated only
with the Snout®. Per 3rd party performance testing, Snouts® provide a TSS pollutant removal rate ranging between 53%-85%.
Per a National Pollutant Removal Performance Database, grass lined water quality swales provide a removal rate for TSS
pollutants of 81%. Additional documentation from a research program by the Wisconsin Department of Transportation
provides that grass swales in excess of 21-meters have an approximate TSS removal rate of 90.4%. For this analysis the more
conservative removal rates for both the Snout® and grass swales of 53% and 81% respectively have been used. Documents
regarding these removal rates can be found in the Appendix of this request. Using these TSS removal rates and a starting
concentration of 69 mg/l, the treatment techniques proposed result in a final median TSS concentration of 24.68 mg/l,
exceeding the MS4 permit standard of 30 mg/l. Detailed calculations to determine the final TSS concentration follow:
As the vast majority of the proposed site is being treated for water quality, and that the treatment techniques proposed are
either accepted by the City of Fort Collins or are shown within this variance to remove total suspended solids to levels
acceptable to the City’s MS4 permit with the State of Colorado, the design team anticipates that the alternative compliance
proposed with this request will not have a negative impact on City infrastructure, downstream properties or the safety of the
public.
VARIANCE REQUEST –STORMWATER DETENTION STANDARDS
DESIGN CRITERIA OF VARIANCE BEING REQUESTED
Section 6.0 within the Fort Collins Stormwater Criteria Manual which states:
Onsite detention is required for all development projects. The required minimum detention volume and maximum
release rate(s) for the developed condition 100-year recurrence interval storm must be determined in accordance
with the conditions and regulations established in the appropriate Master Drainage Plan(s) for that area of the City,
for the development and in accordance with the criteria set forth in this Manual.
HARDSHIP REGARDING REQUIREMENT
As noted in the alternative compliance section of this letter, the site is located within a developed subdivision, does not have
storm sewer located on the project site, and the original subdivision plat did not include drainage easements on the property
to allow for 100-year developed flows to be conveyed to the existing detention facility located south of the project site.
Therefore, the site cannot utilize the detention system within the subdivision that it was designed to drain to.
Basin Area Starting TSS
Concentration
1st WQ Treatment
Method
1st Treatment TSS
Removal Rate
Resultant TSS
Concentration
2nd WQ Treatment
Method
2nd Treatment
TSS Removal
Rate
Resultant TSS
Concentration
(acres)(mg/l)(%)(mg/l)(%)(mg/l)
A1 0.10 69.0 Swale 81%13.11 Snout 53%6.16
A2 0.81 69.0 Snout 53%32.43 N/A 0%32.43
A3 0.48 69.0 Swale 81%13.11 Snout 53%6.16
A5 0.58 69.0 Snout 53%32.43 N/A 0%32.43
Total Weighted Average TSS Concentration Basins A1-A3 = 24.68
Alternative Compliance Treatment
A LTERNATIVE C OMPLIANCE AND V ARIANCE R EQUESTS
P ROSPECT S PORTS C LUB
F ORT C OLLINS ,CO
19 OLD TOWN SQUARE #238 | FORT COLLINS, CO 80524 | 970-530-4044 | www.unitedcivil.com
PROPOSED ALTERNATE DESIGN
The existing subdivision detention facility located south of the project site drains to the existing pond located east of Sharp
Point prior to being released to the Poudre River. Coincidentally, the property east of Sharp Point where this existing pond
is located is also owned by the developer of the Prospect Sports project. As such, the development team proposes to drain
100-year undetained flows from the Prospect Sports site directly to this existing pond, bypassing the subdivision detention
facility and negating the need for drainage easements on properties south of the development site. The following sections
of this variance request document the negligible impacts this alternate design will cause the downstream pond and property.
The existing detention facility was analyzed in the approved drainage report entitled, “Final Drainage and Erosion Control
Plan – Advanced Energy Buildings 7 & 8”, by Park Engineering Consultants and dated June 11, 1999, see Appendix A for
excerpts. In said report, the detention facility was found to require a total volume of 8.94 ac-ft; however, the facility only has
a volume of 7.69 ac-ft to the centerline of Sharp Point prior to overtopping, by approximately 0.32-feet, and draining directly
to the existing pond east of Sharp Point. With this request, it is calculated that the proposed development would account for
approximately 0.45 ac-ft of the required volume in the existing detention facility. By piping the undetained 100-year flows
from the proposed development directly to the existing pond east of Sharp Point:
1.The existing detention storage deficit in the facility to the south is reduced.
2.The amount of flow overtopping of Sharp Point is reduced.
3.The net volume of undetained storage the existing pond east of Sharp Point remains the same.
Additionally, it should be noted that the existing pond east of Sharp Point is approximately 6.1-acres in size. With the required
detention volume of the site of 0.45 ac-ft being attenuated within the existing pond, rather than detained onsite, the rise in
depth in the existing pond would be less than 1-inch.
Based on the information provided for this detention variance request, it is the design teams opinion that the proposed design
will improve the function of downstream infrastructure (i.e. the existing detention facility to the south and the overtopping
of Sharp Point), will have negligible impacts to the existing pond east of Sharp Point and will have no negative impacts on City
infrastructure, downstream properties or the safety of the public.
On behalf of the owners of the Prospect Sports Club and the design team, we thank you for the consideration of these two
(2) requests. If you should have any questions or comments regarding these requests, please feel free to contact us at your
convenience.
Sincerely,
United Civil Design Group, LLC
Kevin Brazelton, PE
Principal
APPENDIX A – Referenced Materials
A PPENDIX A
R EFERENCED M ATERIALS
From: Jerad Nielsen <JNielsen@capitalsq.com>
Sent: Monday, January 9, 2023 12:10 PM
To: Erika Ashauer <eashauer@rbbarchitects.com>
Cc: Terri Hanna <terri@wwreynolds.com>; Jeff Wingert <jwingert@wwreynolds.com>
Subject: RE: 1600 E. Prospect Road Fort Collins, CO
Hi Erika –
Just tried your office line and missed you.
I believe there is currently an easement in place that allows access off Sharp Point Drive through our
existing drive lane to your proposed site.
We are not interested in entering into a parking share agreement or providing additional
easements. Please note that our tenant (Advanced Energy) does not have the authority to enter into
any arrangement.
Please call me if you would like to discuss further – 804.357.1852. As reference, I have copied our local
management team who oversees the property management of this building and also the association.
Thank you,
Jerad Nielsen, CPM ®, CCIM ®
Vice President, Asset Management
10900 Nuckols Road, Suite 200 |Glen Allen, VA 23060
P: 804.290.7900 | E: jnielsen@capitalsq.com
C: 804.357.1852
From: Erika Ashauer <eashauer@rbbarchitects.com>
Sent: Wednesday, December 28, 2022 5:20 PM
To: Jerad Nielsen <JNielsen@capitalsq.com>
Subject: 1600 E. Prospect Road Fort Collins, CO
Hi Jerad,
Please see below emails regarding agreements and easements between our property at Prospect Park
East PUD and your property (Advanced Energy).
Thank you,
Erika Ashauer, ALEP | Project Coordinator
Direct: (970) 488-3870
From: Erika Ashauer
Sent: Wednesday, December 21, 2022 10:25 AM
To:jnielsen@capitalsquare1031.com
Subject: FW: 1600 E. Prospect Road
Good morning, Jared.
I wanted to follow up with you on the below email regarding agreements and easements at Prospect
Park East PUD. Feel free to give me a call (number below in signature) if that would be easier to discuss.
Happy Holiday’s!
Erika Ashauer, ALEP | Project Coordinator
Direct: (970) 488-3870
From: Erika Ashauer <eashauer@rbbarchitects.com>
Sent: Wednesday, December 14, 2022 3:42 PM
To:jnielsen@capitalsquare1031.com
Cc: 2204 Prospect East <2204ProspectEast@rbbarchitects.com>
Subject: 1600 E. Prospect Road
Hi Jerad,
I am part of the architectural team at RB+B Architects working on the Prospect Sports facility being
developed in Prospect Park East PUD, Lot 5. I will be the liaison between the Prospect Sports owner and
our team, and the adjacent property owners. Have you been able to locate any existing access
agreements between your property (Advanced Energy) and ours? I have not yet found any existing
agreements in public records.
If there are no existing agreements, we would like to submit the following for your consideration:
1.Access Easement: We would like to share the same drive used to access the Advanced Energy
buildings off of Sharp Point Drive as the main point of entry to our site
2.Emergency Access Easement: Our site is relatively small, and we have determined that the fire
department cannot access our lot off Prospect Rd. and will need access on the southern side of
the site.
The emergency access would impact the AE site by extending the lane to the eastern portion of
the property so the fire lane can wrap around our property to the East. This would cause a loss
of a few parking spaces and trees on your property.
3.Parking Share Easement: Since our lot is relatively small for the proposed building of
approximately 35,000 square feet, we are limited to the number of parking spaces on our
lot. We are currently planning on 49 parking spaces on our property. The City of Fort Collins
routinely allows for parking share agreements between adjacent properties so that adequate
parking is available while not creating an abundance of hardscaped areas dedicated to parking.
Prospect Sports is expected to experience high vehicular parking during off-business hours: the
evenings and weekends. We hope that patrons of Prospect Sports could use the AE parking lot
as overflow parking during these peak times and the Prospect Sports parking would be available
for AE use as well.
I have attached a site plan with the proposed easements diagramed. Please do not hesitate to reach out
to me should you want to discuss further.
Thank you,
Erika Ashauer, ALEP| Project Coordinator
RB+B Architects
Direct: (970) 488-3870
eashauer@rbbarchitects.com | rbbarchitects.com
Page 26 of 63
Permit No. COR090000
(B) A list of citation(s) and location(s) of applicable documents that demonstrate that the
permittee conducts initial site plan reviews, including the citation(s) and location(s) of
supporting documents.
vi. Site Inspection: A list of citation(s) and location(s) of applicable documents that
demonstrate that the permittee has written procedures for conducting site inspections,
including the citation(s) and location(s) of supporting documents that describe the
following:
(A) The process for determining, implementing, and documenting the inspection
frequencies.
(B) The process for inspection follow-up, including determining, implementing, and
documenting the nature of the follow-up action.
(C) The process and tools used for documenting inspections.
vii. Enforcement Response: A list of citation(s) and location(s) of applicable documents that
demonstrate that the permittee has written procedures for enforcement response. The
document(s) must detail the types of escalating enforcement responses the permittee will
take in response to common violations and time periods within which responses will take
place, including as a minimum:
(A) Construction commencing without site plan review in accordance with I.E.3.a.v.
(B) Control measures not maintained in operational condition at time of permittee
inspection, including sites that have temporarily shut down construction activities.
(C) Uncorrected finding(s) from previous inspections.
(D) Failure to implement a control measure for a pollutant source or inadequate control
measure resulting in a discharge of pollutants from the applicable construction site or
to the MS4.
viii. Training: A list of citation(s) and location(s) of the training program and supporting
documents.
ix. For Applicable Construction Activities that Overlap Multiple Permit Areas: A list of
citation(s) and location(s) of applicable documents that demonstrate that the permittee
meets all permit requirements in Part I.E.3 for construction activities for which the
permittee is the owner or operator, if different than procedures for private sites.
4. Post-Construction Stormwater Management in New Development and Redevelopment
The permittee must implement a program to reduce the discharge of pollutants to the MS4 from
applicable development sites.
Applicability: Applicable development sites must meet the requirements of Part I.E.4.
“Applicable development sites” are those that result in land disturbance of greater than or equal
to one acre, including sites less than one acre that are part of a larger common plan of
development or sale, unless excluded below. Applicable development sites include all new
development and redevelopment sites for which permanent water quality control measures were
required in accordance with an MS4 permit. “New Development” means land disturbing activities;
structural development, including construction or installation of a building or structure, creation of
impervious surfaces; and land subdivision for a site that does not meet the definition of
redevelopment. “Redevelopment” includes a site that is already substantially developed with 35%
or more of existing imperviousness; with the creation or addition of impervious area (including
removal and/or replacement), to include the expansion of a building footprint or addition or
replacement of a structure; structural development including construction, replacement of
impervious area that is not part of a routine maintenance activity; and land disturbing activities. At
a minimum, applicable development sites includes all sites meeting the criteria of the previous MS4
Page 27 of 63
Permit No. COR090000
permit for renewal permittees and completed after the date in Part I.H for all (renewal and new)
permittees.
a. The following requirements apply:
i. Excluded Sites: Permittees may exclude the following from the requirements of an
applicable development site.
(A) “Pavement Management Sites”: Sites, or portions of sites, for the rehabilitation,
maintenance, and reconstruction of roadway pavement, which includes roadway
resurfacing, mill and overlay, white topping, black topping, curb and gutter
replacement, concrete panel replacement, and pothole repair. The purpose of the site
must be to provide additional years of service life and optimize service and safety. The
site also must be limited to the repair and replacement of pavement in a manner that
does not result in an increased impervious area and the infrastructure must not
substantially change. The types of sites covered under this exclusion include day-to-day
maintenance activities, rehabilitation, and reconstruction of pavement. “Roadways”
include roads and bridges that are improved, designed or ordinarily used for vehicular
travel and contiguous areas improved, designed or ordinarily used for pedestrian or
bicycle traffic, drainage for the roadway, and/or parking along the roadway. Areas
primarily used for parking or access to parking are not roadways.
(B) Excluded Roadway Redevelopment: Redevelopment sites for existing roadways, when
one of the following criteria is met:
1) The site adds less than 1 acre of paved area per mile of roadway to an existing
roadway, or
2) The site does not add more than 8.25 feet of paved width at any location to the
existing roadway.
(C) Excluded Existing Roadway Areas: For redevelopment sites for existing roadways, only
the area of the existing roadway is excluded from the requirements of an applicable
development site when the site does not increase the width by two times or more, on
average, of the original roadway area. The entire site is not excluded from being
considered an applicable development site for this exclusion. The area of the site that is
part of the added new roadway area is still an applicable development site.
(D) Aboveground and Underground Utilities: Activities for installation or maintenance of
underground utilities or infrastructure that does not permanently alter the terrain,
ground cover, or drainage patterns from those present prior to the construction activity.
This exclusion includes, but is not limited to, activities to install, replace, or maintain
utilities under roadways or other paved areas that return the surface to the same
condition.
(E) Large Lot Single Family Sites: A single-family residential lot, or agricultural zoned lands,
greater than or equal to 2.5 acres in size per dwelling and having a total lot impervious
area of less than 10 percent. A total lot imperviousness greater than 10 percent is
allowed when a study specific to the watershed and/or MS4 shows that expected soil
and vegetation conditions are suitable for infiltration/filtration of the WQCV for a
typical site, and the permittee accepts such study as applicable within its MS4
boundaries. The maximum total lot impervious covered under this exclusion shall be 20
percent.
(F) Non-Residential and Non-Commercial Infiltration Conditions: This exclusion does not
apply to residential or commercial sites for buildings. This exclusion applies to
applicable development sites for which post-development surface conditions do not
result in concentrated stormwater flow during the 80th percentile stormwater runoff
event. In addition, post-development surface conditions must not be projected to result
in a surface water discharge from the 80th percentile stormwater runoff events.
Specifically, the 80th percentile event must be infiltrated and not discharged as
Page 28 of 63
Permit No. COR090000
concentrated flow. For this exclusion to apply, a study specific to the site, watershed
and/or MS4 must be conducted. The study must show rainfall and soil conditions present
within the permitted area; must include allowable slopes, surface conditions, and ratios
of impervious area to pervious area; and the permittee must accept such study as
applicable within its MS4 boundaries.
(G) Sites with Land Disturbance to Undeveloped Land that will Remain Undeveloped:
Permittees may exclude sites with land disturbance to undeveloped land (land with no
human-made structures such as buildings or pavement) that will remain undeveloped
after the site.
(H) Stream Stabilization Sites: Permittees may exclude stream stabilization sites.
(I) Trails: Permittees may exclude bike and pedestrian trails. Bike lanes for roadways are
not included in this exclusion, unless attached to a roadway that qualifies under another
exclusion in this section.
(J) Oil and Gas Exploration: Permittees may exclude facilities associated with oil and gas
exploration, production, processing, or treatment operations, or transmission facilities,
including activities necessary to prepare a site for drilling and for the movement and
placement of drilling equipment, whether or not such field activities or operations may
be considered to be an applicable construction activity.
(K) County Growth Areas: Permittees that are counties may exclude the following when
they occur within a county growth areas:
1) Construction activities on sites that began as part of a plan of development prior to
July 1, 2019, which is the deadline in Part I.H to implement a construction sites
program in the county growth areas.
2) Agricultural facilities and structures on agricultural zoned lands (e.g., barn, stables).
3) Residential development site or larger common plans of development for which
associated construction activities results in a land disturbance of less than or equal
to 10 acres and have a proposed density of less than 1,000 people per square mile.
4) Commercial or industrial development site or larger common plans of development
for which associated construction activities results in a land disturbance of less than
or equal to10 acres.
ii. Regulatory Mechanism: To the extent allowable under state or local law, implement a
regulatory mechanism to meet the requirements in Part I.E.4.a., including:
(A) Require control measures to be implemented for all applicable development sites.
(B) Enforce the conditions of the exclusions above, if applicable.
(C) Require the long-term operation and maintenance of control measures.
(D) Ensure that mechanisms are in place as necessary to meet this requirement for control
measures used to meet the requirements of this permit by an applicable development
site in the permit area that are located outside of the jurisdictional control of the
permittee.
(E) Implement sanctions against entities responsible for applicable development sites and
for the long-term operation and maintenance of the control measures.
iii. Regulatory Mechanism Exemptions: Procedures must be implemented to ensure that any
exclusions, exemptions, waivers, and variances included in the regulatory mechanism are
applied in a manner that complies with the terms and conditions of this permit.
iv. Control Measure Requirements: The permittee’s requirements and oversight for applicable
development sites must be implemented to address the selection, installation,
implementation, and maintenance of control measures in accordance with requirements in
Part I.B. The “base design standard” is the minimum design standard for new development
Page 29 of 63
Permit No. COR090000
and redevelopment. The control measures for applicable development sites shall meet one
of the following base design standards listed below:
(A) WQCV Standard: The control measure(s) is designed to provide treatment and/or
infiltration of the WQCV and:
1) 100% of the applicable development site is captured, except the permittee may
exclude up to 20 percent, not to exceed 1 acre, of the applicable development site
area when the permittee has determined that it is not practicable to capture runoff
from portions of the site that will not drain towards control measures. In addition,
the permittee must also determine that the implementation of a separate control
measure for that portion of the site is not practicable (e.g., driveway access that
drains directly to street).
2) Evaluation of the minimum drain time shall be based on the pollutant removal
mechanism and functionality of the control measure implemented. Consideration of
drain time shall include maintaining vegetation necessary for operation of the
control measure (e.g., wetland vegetation).
(B) Pollutant Removal Standard: The control measure(s) is designed to treat at a minimum
the 80th percentile storm event. The control measure(s) shall be designed to treat
stormwater runoff in a manner expected to reduce the event mean concentration of
total suspended solids (TSS) to a median value of 30 mg/L or less.
1) 100% of the applicable development site is captured, except the permittee may
exclude up to 20 percent not to exceed 1 acre of the applicable development site
area when the permittee has determined that it is not practicable to capture runoff
from portions of the site that will not drain towards control measures. In addition,
the permittee must also determine that the implementation of a separate control
measure for that portion of the site is not practicable (e.g., driveway access that
drains directly to street).
(C) Runoff Reduction Standard: The control measure(s) is designed to infiltrate into the
ground where site geology permits, evaporate, or evapotranspire a quantity of water
equal to 60% of what the calculated WQCV would be if all impervious area for the
applicable development site discharged without infiltration. This base design standard
can be met through practices such as green infrastructure. “Green infrastructure”
generally refers to control measures that use vegetation, soils, and natural processes or
mimic natural processes to manage stormwater. Green infrastructure can be used in
place of or in addition to low impact development principles.
(D) Applicable Development Site Draining to a Regional WQCV Control Measure: The regional
WQCV control measure must be designed to accept the drainage from the applicable
development site. Stormwater from the site must not discharge to a water of the state
before being discharged to the regional WQCV control measure. The regional WQCV
control measure must meet the requirements of the WQCV in Part I.E.4.a.iv(A).
(E) Applicable Development Site Draining to a Regional WQCV Facility: The regional WQCV
facility is designed to accept drainage from the applicable development site.
Stormwater from the site may discharge to a water of the state before being discharged
to the regional WQCV facility. Before discharging to a water of the state, at least 20
percent of the upstream imperviousness of the applicable development site must be
disconnected from the storm drainage system and drain through a receiving pervious
area control measure comprising a footprint of at least 10 percent of the upstream
disconnected impervious area of the applicable development site. The control measure
must be designed in accordance with a design manual identified by the permittee. In
addition, the stream channel between the discharge point of the applicable
development site and the regional WQCV facility must be stabilized.
The regional WQCV facility must meet the following requirements:
Page 30 of 63
Permit No. COR090000
1) The regional WQCV facility must be implemented, functional, and maintained
following good engineering, hydrologic and pollution control practices.
2) The regional WQCV facility must be designed and maintained for 100% WQCV for its
entire drainage area.
3) The regional WQCV facility must have capacity to accommodate the drainage from
the applicable development site.
4) The regional WQCV facility be designed and built to comply with all assumptions for
the development activities planned by the permittee within its drainage area,
including the imperviousness of its drainage area and the applicable development
site.
5) Evaluation of the minimum drain time shall be based on the pollutant removal
mechanism and functionality of the facility. Consideration of drain time shall include
maintaining vegetation necessary for operation of the facility (e.g., wetland
vegetation).
6) The permittee shall meet the requirements in Parts I.E.4.a.v. and vii. and Part
I.E.4.b. for the regional WQCV facility consistent with requirements and actions for
control measures.
7) The regional WQCV facility must be subject to the permittee’s authority consistent
with requirements and actions for a Control Measure in accordance with Part
I.E.4.a.iv.
8) Regional Facilities must be designed and implemented with flood control or water
quality as the primary use. Recreational ponds and reservoirs may not be considered
Regional Facilities. Water bodies listed by name in surface water quality
classifications and standards regulations (5 CCR 1002-32 through 5 CCR 1002-38) may
not be considered regional facilities.
(F) Constrained Redevelopment Sites Standard:
1) Applicability: The constrained redevelopment sites standard applies to
redevelopment sites meeting the following criteria:
(a) The applicable redevelopment site is for a site that has greater than 75%
impervious area, and
(b) The permittee has determined that it is not practicable to meet any of the
design standards in Parts I.E.4.a.iv(A),(B), or (C). The permittee’s determination
shall include an evaluation of the applicable redevelopment sites ability to install
a control measure without reducing surface area covered with the structures.
2) Constrained Redevelopment Sites Design Standard: The control measure(s) is
designed to meet one of the following:
(a) Provide treatment of the WQCV for the area captured. The captured area shall
be 50% or more of the impervious area of the applicable redevelopment site.
Evaluation of the minimum drain time shall be based on the pollutant removal
mechanism and functionality of the control measure implemented,
(b) The control measure(s) is designed to provide for treatment of the 80th
percentile storm event. The control measure(s) shall be designed to treat
stormwater runoff in a manner expected to reduce the event mean
concentration of total suspended solids (TSS) to a median value of 30 mg/L or
less.
A minimum of 50% of the applicable development area including 50% or more of
the impervious area of the applicable development area shall drain to the control
measure(s). This standard does not require that 100% of the applicable
4 - 8
Table 4-1. Median Event Mean Concentrations for Urban Land Uses
Pollutant Units Residential Mixed Commercial Open/
Non-Urban
Median COV Median COV Median COV Median COV
BOD mg/l 10 0.41 7.8 0.52 9.3 0.31 ----
COD mg/l 73 0.55 65 0.58 57 0.39 40 0.78
TSS mg/l 101 0.96 67 1.14 69 0.85 70 2.92
Total Lead µg/l 144 0.75 114 1.35 104 0.68 30 1.52
Total Copper µg/l 33 0.99 27 1.32 29 0.81 ----
Total Zinc µg/l 135 0.84 154 0.78 226 1.07 195 0.66
Total Kjeldahl
Nitrogen
µg/l 1900 0.73 1288 0.50 1179 0.43 965 1.00
Nitrate +
Nitrite
µg/l 736 0.83 558 0.67 572 0.48 543 0.91
Total
Phosphorus
µg/l 383 0.69 263 0.75 201 0.67 121 1.66
Soluble
Phosphorus
µg/l 143 0.46 56 0.75 80 0.71 26 2.11
COV: Coefficient of variation
Source: Nationwide Urban Runoff Program (US EPA 1983)
Results from NURP indicate that there is not a significant difference in pollutant
concentrations in runoff from different urban land use categories. There is a significant difference,
however, in pollutant concentrations in runoff from urban sources than that produced from non-
urban areas.
The pollutants that are found in urban storm water runoff originate from a variety of
sources. The major sources include contaminants from residential and commercial areas, industrial
activities, construction, streets and parking lots, and atmospheric deposition. Contaminants
commonly found in storm water runoff and their likely sources are summarized in Table 4-2.
MD Office : Ph. (800) 504-8008 Fax (410) 687-6757 CT Office: Ph. (860) 434-0277 Fax (860) 434-3195
www.bmpi nc.com
DOCUMENTED 3rd PARTY PERFORMANCE:
Performance measured in multiple catch basins with SNOUT (drop inlets) over 2
year period in Peekskill, NY (Dutchess County) with flow to Peekskill Lake.
Mean TSS removals of 53% were recorded.1
Monitoring in Lower Makefield Twp., PA (Bucks County) with flow to Core Creek/
Lake Luxemburg of 9 SNOUT drop inlets show minimum TSS removals of 58%.2
Floatable Trash and Debris Removals with hooded catch basins in New York City
show average litter retention of 85%.3
ANECDOTAL PERFORMANCE MEASUREMENTS:
Multiple in line structures can improve solids removal performance and exceed
70% TSS removals. Various sites including Bryn Mawr Regional Stormwater
Facility, Bryn Mawr, PA
Removals of free oils can exceed 50%. Use of Bio-Skirts recommended for
longest term retention and 80%+ removals. Various sites around North America.
SOURCES:
1. Revised Restoration/Management Plan for Lake Luxembourg/CoreCreek
Watershed, Core Creek Park, Bucks County, Pennsylvania, Project No: 121.012
PA DEP, March 2005, (Princeton Hydro for Bucks County
Conservation District)
2. Structural Restoration Practices: A Collection of Successful Examples, F.
Lubnow, PhD, Princeton Hydro, February 2007
3. Combined Sewer Overflow Technology Fact Sheet Floatables Control
United States Environmental Protection Agency, Washington, D.C. EPA 832-
F99-008, September 1999
Grass Swales: Gauging Their Ability to Remove Pollutants
From Highway Stormwater Runoff
Prepared for
Bureau of Equity and Environmental Services
Division of Transportation System Development
Prepared by
CTC & Associates LLC
WisDOT Research & Library Unit
June 5, 2007
Transportation Synthesis Reports are brief summaries of currently available information on topics of interest to
WisDOT staff throughout the department. Online and print sources for TSRs include NCHRP and other TRB
programs, AASHTO, the research and practices of other transportation agencies, and related academic and
industry research. Internet hyperlinks in TSRs are active at the time of publication, but changes on the host server
can make them obsolete. To request a TSR, e-mail research@dot.state.wi.us or call (608) 261-8198.
Request for Report
Stormwater runoff from highways can contain metals, organic materials and other pollutants that pose a threat to the
health of the nation’s water resources. Federal and state transportation agency responsibilities for effective
stormwater management are guided by a series of environmental laws, executive orders and policies that have been
developed to address this risk. Wisconsin DOT has employed several structural best management practices for
removing contaminants from stormwater runoff, including roadside swales—broad, shallow channels with a dense
stand of vegetation that promote infiltration and trap pollutants. The Bureau of Equity and Environmental Services
asked us to locate recently completed and ongoing research studies that quantify the effectiveness of grass swales at
removing contaminants from highway runoff.
Summary
We located a number of research studies performed by state DOTs, the U.S. Environmental Protection Agency,
NCHRP and other entities that quantify grass swales’ effectiveness at removing pollutants from roadway runoff.
Overall, the results of these studies suggest that properly designed and sited grass swales can be effective tools for
removing pollutants from highway runoff. For example, a September 2004 U.S. EPA study notes:
“In general, the current literature reports that a well-designed, well-maintained swale system can be expected
to remove 70% of total suspended solids, 30% of total phosphorus, 25% of total nitrogen, and 50 to 90% of
trace metals (Barret et al., 1993, and GKY and Associates Inc., 1991). The nitrogen removals may be fairly
optimistic, given that studies conducted by Yousef et al. (1985) and others produced negative nitrogen removal
in many cases. It is theorized that the outwelling of nitrogen from grass clippings and other organic materials
from the swale produced these results… (Swale) removal efficiencies reported in the literature vary, but
generally fall into the low to medium range, with some swale systems recording no water quality effects at
all… Pollutant removal efficiencies for many constituents can be markedly different during the growing and
dormant periods (Driscoll and Mangarella, 1990).”
We present our findings in two sections. State DOT Research summarizes recent studies by seven DOTs that
quantify the effectiveness of grass swales. One of these studies, performed by the Western Transportation Institute
Sediment and Contaminant Removal by Dual Purpose Detention Basins: Draft Final Report
Washington State University, May 1993
http://www.wsdot.wa.gov/research/reports/fullreports/336.1.pdf
The purpose of this project was to generate a database that could be used in the development of a rational design
approach for stormwater sedimentation basin design. The investigation included a review of the pollutant removal
efficiencies of grass swales.
From Chapter 1, Introduction, Removal Efficiencies of Grassy Swales and Grass Lined Channels (pages 14 and 15
of the PDF):
Yousef reports metal removal rates of grass lined swales for Pb, Zn, Cu, and Cd of 2.61, 5.76, 0.60, and 0.26
mg/m2.hr, respectively. In another study, respective removals for Pb, Zn, and Cu were reported as 1.14, 1.85,
and 0.42 mg/m2.hr.[18] It is important to note that removal efficiencies are related to many site specific
conditions including stormwater characteristics and swale design. For example, removal as a function of swale
length for TSS, VSS, Pb, Cu, Cd, and Zn reported by Wang[9] are summarized in Tables 2 and 3.
Table 2. Grass channel removal as a function of length for TSS and VSS.
9
Grass swales in Basins
A1 and A3 exceed 21 m
in length
This unofficial copy was downloaded on Jul-06-2022 from the City of Fort Collins Public Records Website: http://citydocs.fcgov.com
For additional information or an official copy, please contact City of Fort Collins Utilities 700 Wood Street Fort Collins, CO 80524 USA
This unofficial copy was downloaded on Jul-06-2022 from the City of Fort Collins Public Records Website: http://citydocs.fcgov.com
For additional information or an official copy, please contact City of Fort Collins Utilities 700 Wood Street Fort Collins, CO 80524 USA
This unofficial copy was downloaded on Jul-06-2022 from the City of Fort Collins Public Records Website: http://citydocs.fcgov.com
For additional information or an official copy, please contact City of Fort Collins Utilities 700 Wood Street Fort Collins, CO 80524 USA
This unofficial copy was downloaded on Jul-06-2022 from the City of Fort Collins Public Records Website: http://citydocs.fcgov.com
For additional information or an official copy, please contact City of Fort Collins Utilities 700 Wood Street Fort Collins, CO 80524 USA
EXISTING
DETENTION
FACILITY
SITE LOCATION
EXISTING POND
LOCATION
OUTLET AND
OVERTOPPING OF
DETENTION FACILTY
PAST SHARP POINT
FLOWS INTO
EXISTING POND
DETENTION POND VOLUME (FAA Method)
Prospect Sports
POND ID:Required Onsite Pond Volume Calculation for Variance Request
100 Year Storm Into Detention Facility
Area =106,130 square feet
Area =2.44 acres
C 100 = 0.79
Q 100 = 15.41 cfs
Release Rate Out of Pond
Q OUT = 1.48 cfs
Unit Flow =0.61 cfs/acre
T C =11.0 minutes
Notes:
1. Release Rate controlled by 2 yr historic
Detention Volume Calculations
Rainfall Rainfall Inflow Rate Inflow Volume Adjustment
Factor
Average Outflow Volume Required
Duration (T)Intensity (I)Qin= ∑C100*Area*I Vi=(Qin*T*60)Factor Outflow Rate Vo=Qav*T *60 Storage Volume
m= 0.5(1 + Tc/T) Qav = m*Qout Vs=Vi-Vo
min in/hr cfs ft 3 cfs ft 3 ft 3
5 9.95 19.2 5,745 1.00 1.48 444 5,301
10 7.72 14.9 8,916 1.00 1.48 888 8,028
15 6.52 12.5 11,295 0.87 1.28 1,154 10,140
20 5.60 10.8 12,934 0.78 1.15 1,376 11,558
25 4.98 9.6 14,378 0.72 1.07 1,598 12,780
30 4.52 8.7 15,660 0.68 1.01 1,820 13,839
35 4.08 7.9 16,491 0.66 0.97 2,042 14,449
40 3.74 7.2 17,277 0.64 0.94 2,264 15,012
45 3.46 6.7 17,981 0.62 0.92 2,486 15,495
50 3.23 6.2 18,651 0.61 0.90 2,708 15,943
55 3.03 5.8 19,246 0.60 0.89 2,930 16,315
60 2.86 5.5 19,817 0.59 0.88 3,152 16,665
70 2.59 5.0 20,938 0.58 0.86 3,596 17,341
80 2.38 4.6 21,988 0.57 0.84 4,040 17,948
90 2.21 4.3 22,970 0.56 0.83 4,484 18,486
100 2.06 4.0 23,790 0.56 0.82 4,928 18,862
110 1.94 3.7 24,645 0.55 0.81 5,372 19,272
120 1.84 3.5 25,499 0.55 0.81 5,816 19,683
Required Detention Volume
V 100 = 19,683 cubic feet
V 100 = 0.45 acre-ft
Date: 7/19/2023 C:\United Civil Dropbox\Projects\U22014 - Prospect Park East\Reports\Drainage\Calculations\NDE Mock Calc of Detention Size.xlsm