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HomeMy WebLinkAboutDrainage Reports - 05/24/20191P1TZ,W T C.O.N S.0 LS 1.N.G G.R O ULV May 22, 2019 Mr. Wes Lamarque Fort Collins Utilities = Stormwater 760 Wood Street Fort Collins, CO 80522 Re: 221 East Mountain Final.Sto;m Drainage Letter Dear Wes, Please accept the following letter describing the storm drainage intent demonstrating the proposed site improvement's ability to comply with the City's stormwater requirements. INTRODUCTION The 221 East ouotain is a redevelopment project proposed to construct a mixed -use condominium building with Iv supporting utility infrastructure and site accesses (pedestrian/vehicular). The site is located at the southwest corner of the intersection of E. Mountain Ave and Mathews St. There is a 20' public alley to the south, and 10' public alley along the west. The roadway frontages Will be improved along E. Mountain Ave and Mathews St, along with the alleys to the south and west. The legal description is as follows: Lots 1 thrq 6, Block 131, Town of Fort Collins, located in part of the Northwest Quarter of Section 12,Township 7 North, Range 69 West of the 0 Principal Meridian, City of Fort Collins, County of Larimer, State of Colorado. The property is addresses as 221 E. Mountain Ave. A vicinity map is attached for reference. EXISTING The project site is located within the Udall drainage basin. The existing site consists of a vehicle maintenance shoptshowroom, and a parking lot. The site is approximately 0.45 acres and is impervious except for a 40 sgft gravel area near the existing vehicle entrance off of E. Mountain Ave. The site generally slopes to the east at 1.0% grade. Approximately 4,250 sqft drains to E. Mountain Ave, and the remaining drains to Mathew St. All existing improvements will be removed from the site to accommodate the new construction. The existing southern alley is entirely paved, and the existing western. alley appears to be unimproved. We -are not aware of any site -specific drainage studies for this site. The project is not located within a FEMA mapped 100-yrfloodplain and is not within a defined City of Fort Collins floodplain. W. ASH, STE. A, Wt 70.674.3300 - FAX t221 East Mountain Final Storm Drainage Letter May 22,2019 Page 2 of 4 PROPOSED DEVELOPMENT The proposed redevelopment improvements will consist of constructing a 4-story mixed -use multi -family condominium building, with below grade parking, and will include the supporting utility infrastructure and pedestrian/vehicle accesses. The project is planned to be constructed in a single phase. The project has zero setback requirements, encouraging zero -lot line construction. The proposed building footprint is approximately 18,420 sgft, consuming 94% of the site. The improvements will generally be 100% impervious, consistent with the existing conditions. The proposed improvements are divided into onsite drainage basins and 2 offsite drainage basins: Basin D1 consists of the northwest portion of the proposed roof area and the runoff will be conveyed through storm drains to the existing Type R inlet on E. Mountain Ave. Basin DI will be treated by a FloGard Water Quality Filter system designed by Old Castle prior to being conveyed to the existing inlet. Basin D2 consists of the northeast portion of the proposed roof area and. the runoff will be conveyed through storm drains to the existing Type R inlet on E. Mountain Ave. Basin D2 will be treated by a FloGard Water Quality Filter system designed by Old Castle prior to being conveyed to the existing inlet. Basin D3 consists of the south portion of the proposed roof area and the runoff will be conveyed through a proposed sidewalk chase to the flowline of Matthews Street where the runoff will be conveyed north to an existing Type R inlet. Basin D3 will be treated by a FloGard Water Quality Filter system designed by Old Castle prior to being conveyed to the sidewalk chase. Basin OS1 consists of the southern alley and several adjacent rooftops and parking areas. The basin was delineated by survey elevations of the alley visually observing the existing conditions, and buildings in the vicinity of the project site.. In general,, the proposed drainage patterns of this basin will not change from existing, draining along the improved alley east to Mathews Street. This offsite drainage basin can be viewed in more detail by reviewing the attached Offsite Drainage Basin Exhibit. The iunoffassociated with this basin was modeled at key locations along the east -west alley corridor to determine the water surface elevation of the alley flows in a 100-yr event. The 100-yr peak runoff from this basin is estimated to be 5.56 cfs. To ensure building protection, the modeled flow depths within the alley were increased by 33% to 7.40 cis and do not enter the building openings. Basin OS2 consists of the western DDA owned alley.. This alley will be paved and the runoff from this alley will be collected in an area inlet and directed to the interior of the building where it will be combined with flows from Basin Dl and D2 prior to being conveyed to the existing inlet on E. Mountain Ave. The proposed improvements do not create an increase in impervious area over 5,000 sq-ft which would require onsite detention. Standard water quality is provided downstream within the Udall Basin and is not required onsite. Low Impact Development (LID) code would require that 50% of the site area be treated with an adopted BMP treatment method. See below for more detail on the proposed FloGard Filters.. All calculations and exhibits are attached for reference.. 121 East Mountain Final Storm Drainage Letter 1 May 22-2019 Page 3 of 4 LOW IMPACT DEVELOPMENT TECHNIQUES In reference to the code requirements for implementation of Low Impact Development (LID) techniques, the use of 100% treatment of the roof area via three (3) FloGard Filters is proposed to satisfy these requirements. These filter systems are an emerging technology that has been adopted in other regions of the country but is not currently on an approved list of approved treatment methods. After extensive evaluation of alternative methods including Planter Box Rain Gardens, Bio-retention within the public street parkway, and water quality tree well systems, it was determined that the various site constraints for the 221 East Mountain project made those alternatives not viable. Therefore, we are proposing the use of the roof filtering systems to treat 100% of the roof area in lieu of the required 50% treatment area. ■ Below is a description of the 4 step process for selecting structural BMPs: Urban Drainage and Flood Control District (UDFCD) recommends a Four Step Process for receiving water protection that focuses on reducing runoff volumes, treating the water quality capture volume (WQCV), stabilizing drainageways and implementing long-term source controls. The Four Step Process applies to the management of smaller,. frequently occurring events. Step 1: Employ Runoff Reduction Practices To reduce runoff peaks, volumes, and pollutant loads from urbanizing areas, implement Low Impact Development (LID) strategies, including Minimizing Directly Connected Impervious Areas (MDCIA). Runoff from 100% of the roof will be directed to one of three (3) FloGard Filter systems in the building prior to being released into the adjacent storm drain systems. 1 Step 2: Implement BMPs that Provide a Water Quality Capture Volume with Slow Release The roof filter systems do not have a water qualiy capture volume component. Step 3: Stabilize Drainageways Natural Drainageways are subject to bed and bank erosion due to increases in frequency, duration, rate and volume of runoff during and following development. Because the site will drain to an existing roadway and storm system, bank stabilization is unnecessary with this project. Step 4: Implement Site Specific and Other Source Control BMPs Proactively controlling pollutants at their source by preventing pollution rather than removing contaminants once they have entered the stormwater system or receiving waters is important when protecting storm systems and receiving waters. This can be accomplished through site specific needs such as construction site runoff control, post -construction runoff control and pollution prevention / good housekeeping. It will be the responsibility of the contractor to develop a procedural best management practice for the site. 1 All calculations are attached for reference. 221 East Mountain Final Storm Drainage Letter May 22, 2019 Page 4 of 4 EROSION CONTROL Erosion and sedimentation will be controlled on -site by use of sediment control logs, inlet protection, a gravel construction entrance, seeding, mulch, and turf. The measures are designed to limit the overall sediment yield increase due to construction as required by the City of Fort Collins. Inning overlot and final grading the soil will be roughened and furrowed perpendicular to the prevailing winds. During the performance of the work required by these specifications or any operations appurtenant thereto, whether on right-of-way provided by the City or elsewhere, the contractor shall furnish all labor, equipment, materials, and means required; The Contractor shall carry out proper efficient measures wherever and as necessary to reduce dust nuisance, and to prevent dust nuisance that has originated from his operations from damaging crops, orchards, cultivated fields; and dwellings, or causing naissance to persons. The Contractor will be held liable for any damage resulting from dust originating from his operations under these specifications on right=of-way or elsewhere.. It is unlawful to track or cause to be tracked mud or other debris onto city .streets or rights -of -way. Wherever construction vehicles -access routes or intersect paved public roads, previsions must be made to nun.iri»ze the transport of sediment by runoff or vehicles tracking onto the paved surface. Stabilized construction entrances are required with base material consisting of 6" coarse aggregate. The contractor will be responsible for clearing mud tracked onto city streets; daily. All temporary and permanent erosion and sediment control practices must be maintained and repaired as needed to assure continued performance of their intended function. Silt fence and sediment control logs will require periodic replacement. Maintenance is the responsibility of the contractor. All disturbed areas must be seeded and mulched within 30 days of project start Vegetation shall not be considered established until a ground cover is achieved which is demonstrated to be mature enough to control soil erosion to the satisfaction of the City Inspector and to survive severe weather condition. Thank you in advance for your time and if you have any questions or continents please contact me at (970) 674-3300. Sincerely, 1 �- Logan Johnson, P.E. Interwest Consulting Group Attachments Robert Alrnirall, P.E. Interwest Consulting Group REG/ 05-22-19 }v • ,.....:•e�,11S¢ /Oue1 E DRIVE PROJECT VICINITY MAP N.T.S. PROJEC'LV ERTICAL.DATUM:_NAV D88 CITY OF FORT COLLINS BENCHMARK 1-13: SOUTHWEST CORNER OF COI LEGEAVE.AND MAPLE ST., ON A CONCRETE TRAFFIC SIGNAL BASE. ELEVATION = 4979.75 (NAV088) FORT COLLINS BENCHMARK 500: LOCATED ON THE TOP OF A CURB OF A SIGNAL POLE BASE AT THE NORTHWEST CORNER OF LINDEN ST. AND JEFFERSON ST. ELEVATION = 4978.05 (NAVD88) ' PLEASE NOTE: THIS PLAN SET IS USING NAVD88 FOR A VERTICAL DATUM. SURROUNDING DEVELOPMENTS HAVE USED NGVD29 UNADJUSTED FOR THEIR VERTICAL DATUMS. IF NGVD UNADJUSTED DATUM IS REQUIRED FOR ANY PURPOSE. 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CHECREDBY Y M6L KD.13tp0]l 7 OF 1 1 IM 1111111M 1=11111 MI =11 � IM IM m 1 m o Ik _ ------------ I� 1 1 I I II I I I I I I I 1 I I I I 1 - 7 " �I I Cl ,a I II — — — — �• - -------I'--------- 1 1 1 1 1 1 1 1 1 1 1 1 1 a 0 ^N C m 'r DATE: 09/12/18 ]GALE IHI: I 10' ICALEIVI'. N/A DEBIGNED BY'. ITC CHECXEDBYt JTC PROJECTNAME 221 EAST MOUNTAIN OFFSITE DRAINAGE BASIN EXHIBIT PREPAREDFOR NEENAN COMPANY 3325 S. TIMBERLINE RD. FORT COLLINS, CO 80525 PHONE: 970,493.8747 A, c!e 3� �§ LULU � § .� . to . . . W, \ A / § Jf \ A 0 �k � $ § § ■ �: ...._.. © , . ! ) ■■■■■ ■m � o , ° 00 L.a0 J §| Jf...� . } r �. . Ji0_00 0, J} LULU+§ ) }r ■° )\i2i5f! 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B$]]§ Li J !!§ !§ - ! # ;a ■■ � „ ..j■//}\f CL ! \ � CL ! \ � {]§§ ■! � ■!4 ®® !§§G !# !! ))8 8 sl !! !§!!!! % - !§§§ !§ ) |2cic; ,- % /- ! l,4; ;2 k !! !8 \ k ! / Channel Report Hydraflow Express Extension for Autodesk® AutoCAD® Civil 3D® by Autodesk, Inc. 221 E Mountain - Southern Alley Flow Depth XS 1 ' User -defined Highlighted Invert Elev (ft) = 4978.52 Depth (ft) 'Slope (%) = 3.00 Q (cfs) N-Value = 0.013 Area (sgft) 'Calculations Velocity (fUs) Wetted Perim (ft) Compute by: Known Q Crit Depth, Yc (ft) Known Q (cfs) = 7.40 Top Width (ft) EGL (ft) (Sta, El, n)-(Sta, El, n)... (-11.30, 4978.75}{10.00, 4978.98, 0.013)-(13.45, 4979.20, 0.013) Elev (ft) Section �980.00 1 F979.50 li979.00 F978.50 L978.00 -5 0 5 10 ' Sta (ft) 15 Wednesday, May 22 2019 = 0.22 = 7.400 = 1.68 = 4.40 = 15.46 = 0.31 = 15.45 = 0.52 Depth (ft) 1.48 0.98 0.48 -0.02 0.52 20 Channel Report ' Hydraflow Express Extension for Autodesk® AutoCAD& Civil 3DO by Aulodesk, Inc. 221 E Mountain - Southern Alley Flow Depth XS 2 ' User -defined Highlighted Invert Elev (ft) = 4978.42 Depth (ft) Slope (%) = 1.80 Q (Cfs) I' N-Value = 0.013 Area (sgft) Velocity fts) 'Calculations Wetted Perim (ft) Compute by: Known Q Crit Depth, Yc (ft) Known Q (Cfs) = 7.40 ' Top Width (ft) EGL (ft) (Sta, El, n)-(Sta, El, n)... (-11.30, 4978.75)-(10.00, 4978.89, 0.013)-(13.45, 4979A 2, 0.013) 1 1 Elev (ft) Section t980.00 4979.50 1 t979.00 �978.50 1 4978.00 1 - - t977.50 -5 0 5 10 ' Sta (ft) 15 Wednesday, May 22 2019 = 0.27 = 7.400 = 1.95 = 3.79 = 14.46 = 0.35 = 14.45 = 0.49 Depth (ft) I 1.58 1.08 0.58 M 2. -0.42 -0.92 20 Channel Report ' Hydraflow Express Extension for Autodesk® AutoCAD® Civil 3D® by Autodesk, Inc. 221 E Mountain - Southern Alley Flow Depth XS 3 ' User -defined Highlighted Invert Elev (ft) = 4977.56 Depth (ft) 'Slope (%) = 0.48 Q (Cfs) N-Value = 0.013 Area (sqft) Velocity (ft/s) 'Calculations Wetted Perim (ft) Compute by: Known Q Crit Depth, Yc (ft) Known Q (Cfs) = 7.40 Top Width (ft) ' EGL (ft) (Sta, El, n)-(Sta, El, n)... (-10.00, 4977.95}(8.50, 4977.82, 0.013)-(10.00, 4977,95, 0.013)-(10.00, 4979,12. 0.013) 1 Elev (ft) Section ,980.00 k979.50 - - �979.00 t978.50 - 1 4978.00 1 - �977.50 977.00 -2 0 ' Sta (ft) 2 4 6 Wednesday, May 22 2019 = 0.31 = 7.400 = 3.09 = 2.39 = 18.17 = 0.32 = 18.16 = 0.40 L it Depth (ft) 2.44 1.94 1.44 [MI 0.44 K. -0.56 12 I Channel Report 1 Hydraflow Express Extension for Autodesk® AutoCADO Civil 3D® by Aulodesk, Inc. 221 E Mountain - Southern Alley Flow Depth XS 4 1 User -defined Highlighted Invert Elev (ft) = 4977.60 Depth (ft) 1 Slope (%) = 0.48 Q (Cfs) N-Value = 0.013 Area (sqft) Velocity (ft/s) 'Calculations Wetted Perim (ft) Compute by: Known Q Crit Depth, Yc (ft) Known Q (cfs) = 7.40 Top Width (ft) 1 EGL (ft) (Sta, Eli n)-(Sta, Eli n)... (-10.00. 4977.95)-(8.50, 4978,01, 0.013)-(10.00, 4978.09, 0.013)-(10.00, 4979.32. 0.013) i 1 1 Elev (ft) Section f a980.00 14979.50 - --- -- - - - 14979.00 978.50 4978.00 �977.50 14977.00 -2 0 1 Sta (ft) 2 4 6 Wednesday, May 22 2019 = 0.33 = 7.400 = 3.07 = 2.41 = 16.63 = 0.33 = 16.62 = 0.42 8 10 Depth (ft) 2.ao UM 1.40 W,O 0.40 -0.10 Channel Report Hydraflow Express Extension for Autodesk® AutoCAD® Civil 31D® by Autodesk, Inc. 221 E Mountain - Southern Alley Flow Depth XS cJ User -defined Highlighted Invert Elev (ft) = 4976.99 Depth (ft) 'Slope (%) = 0.42 Q (cfs) N-Value = 0.013 Area (sqft) Velocity (fUs) 'Calculations Wetted Perim (ft) Compute by: Known Q Crit Depth, Yc (ft) Known Q (cfs) = 7.40 Top Width (ft) EGL (ft) (Sta, El, n)-(Sta, El, n)... (-10.00, 4977.25)-(7.79, 4977.14, 0.013)-18.29, 4977.30, 0.013) ' Elev (ft) Section �978.00 F977.50 F977.00 - t976.50 t - 14976.00 -2 0 2 4 6 1 Sta (ft) Wednesday, May 22 2019 = 0.24 = 7.400 = 3.20 = 2.31 = 18.23 = 0.24 = 18.07 = 0.32 8 10 Depth (ft) I 1.01 0.51 0.01 -0.49 Inlet Flow Calculation for Area Inlet (24" Drop ADS Inlet) Project: 221 E. Mth Job Number: 1324-028-60 Calculations by :.laj Data: 5/1/2019 Objective: to find the number of inlet grates required WSEI Geometry at inlet.: -Grate Open. Area and. information: Square feet Open"(A) 1.145 sf Reduction Factor (F): 50 Grate Flow I DP.L Use the orifice equation 0, = C'AtSQRT(2`g'H).to find, the ideal inlet capacity.' "See Hydraulic Design Handbook by McGrew-HIII for vedfilmton of equation use and Gvalue C= Orifice discharge coefficient-- 0.67 A = Orifice area (ft') - Open. area of grate g = gravitational. constant = 32.2 fVs2 H = head.on grate centroid, ponding depth (feet) Then multiply by the reduction factor for the allowable capacity: 00 =.QI'(1-F) 0= 0.30 offs Q100 H = 0.01 it A= 1.15 112 01 C'A'SQRT(2tg•H) 0.62 cfs QG= 01'F 0.31.ofs OK Q= Req'd.. Head d=- Available. Head Prior to. Overtopping_ 0.30 ds 0.01 n 0.48 e Interwest Consulting Group 1218 W. Ash, Suite A Windsor, CO 80550 Paget 221. East Mountain Low Impact Development Design Engineer: L. Johnson Design Firm: Interwest Consulting Group Project Number: 1324-028-00 Date:-. May 1, 2019 DESIGN CRITERIA Urban Storm Drainage Criteria Manual, Urban Drainage and Flood Control District, January 2010 City of Fort Collins - Ordinance No. 007, 2016 -Treat at least 75% of any newly developed or redeveloped impervious area using one or a combination of LID techniques, or - Treat at least'50 of any newly developed or redeveloped impervious.area using one or a combination of LID techniques when 25% of Private driveabie surfaces are permeable. This project is required to treat 50 of any newly developed or redeveloped impervious`area using one or a combination of LID techniques. Low Impact Development Summary Developed Area Summary Total Total Roof Area: 15,496 sgft ated by FloGa►d Roof Filters: 20,085sgft (includes balconies) Pe[cent Area Treated by LID: 103.0% Elevations Credit Union Roof Drain Filters Basin 2-yr (cfs) 0.55x2-yr (cfs) 0.55x2-yr (gpm) 100-yr 100-yr (cfs) (gpm) Unit Size Capacity Bypass Capacity (gpm) (gpm) D1 0.30 0.17 76 1.12 8" 185 D2 0.30 0.17 76 1.12 8" 185 D3 0.59 0.32 144 2.21 10" 325 ` Oldcastle Infrastructure a 4 CNN COMPANY RECONDITION Rooftop Runoff G Removes Non -Soluble Solids such as sediment, debris, metals and hydrocarbons. Corrosion -Resistant stainless steel accepts standard diameter downspout pipes. Variable Design can be flush mounted or recessed. M FLOGARD04 DOWNSPOUT FILTEI Inline Filter Specially Designed for Downspouis The Flogard Downspout Filter is typically installed on downspout pipes of commercial buildings for the removal of non -soluble pollutants normally found on building roofs and parking decks. The inline downspout filter is an ideal solution for urban sites with little -to -no property area outside of the building perimeter. It is designed to provide effective filtering at low flows and incorporates a high -flow bypass to ensure conveyance is not impeded. Installation & Maintenance is easy and economical by design. Custom Downspout adapter shapes and sizes are available. Filter Medium can be customized depending on the pollutants of concern. INLET FILTRATION 0Oldcastle Infrastructure' ' A CAN COMPANY ' Fully Scalable Solution for Stormwater Treatment The Flogafd Downspout Filter can be installed as a stand-alone treatment device ' or used in conjunction with other Oldcastle products as part of a total stormwater management solution. 1 ' Waterproof access door and gasket assembly 1 1 1 \ Removable slide -in t collection basket with geotextile liner ' SPECIFICATIONS Inlet ID Box ID Solid Storage Model No. (dia, in) (in x in x in) (cu ft) ' FG-DS4 4 14 x 29 x 7.5 0.35 FG-DS6 6 14 x 29 x 7.5 0.35 FG-DS8 8 220307.5 1.70 FG-DS10 10 22 x 33 x 17.5 1.70 Storage capacay reflects 80%of maximum solids collection prior to impeding filtering bypass. ' Filtered flow rate includes a safety factor of 2 to 1. Available with standard Fossil Rock or other custom absorbents. Should be used in conjunction with a regular maintenance program. ' Refer to manufacturer's recommended guidelines. O RECONDITION Rooftop Runoff Standard round downspout inlet connection Standard round downspout outlet connection Filtered Flow (gpm) Bypass Capacity (gpm) 30 145 B5 425 185 915 325 1,650 CITY OF LOS ANGELES * Research report k5584 * Filter is approved for use in the city of Los Angeles. (800) 579-8819