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Home My WebLink AboutDrainage Reports - 07/12/2013' City of Ff. Collins.- Ap rove Plans Approved By Date %- UPDATE TO FINAL DRAINAGE AND EROSION CONTROL REPORT FOR CARGILL SECONDARY USE BUILDING (CARGILL GREENHOUSE) c UPDATE TO FINAL DRAINAGE AND EROSION CONTROL REPORT FOR CARGILL SECONDARY USE BUILDING (CARGILL GREENHOUSE) Prepared for: Steve Stadelmaier Cargill 2540 East Drake Road Fort Collins, CO 80525 Prepared by: North Star Design 700 Automation Drive, Unit I Windsor, Colorado 80550 (970)686-6939 June 27, 2013 Job Number 339-01 s 1 North Star mow design 700 Automation Drive. Unit 1 Windsor. CO 80550 Phone:470-686-6939 Fax: 970-686-1188 June 27, 2013 Glen Schlueter City of Fort Collins Stormwater 700 Wood Street Fort Collins, CO 80522 RE: Update to Final Drainage and Erosion Control Report for Cargill Secondary Use Building Dear Glen, 1 am pleased to submit for your review and approval, this Update to Final Drainage and Erosion Control Report for Cargill Secondary Use Building (Cargill Greenhouse). This report is intended to update the information provided in "Final Drainage and Erosion Control Report for Cargill Secondary Use Building" by DMW Civil Engineers dated May 5, 2007. 1 certify that this update for the drainage design of the Cargill Greenhouse was prepared in accordance with the criteria in the City of Fort Collins Storm Drainage Manual. I appreciate your time and consideration in reviewing this submittal. Please call if you have any questions. TABLE OF CONTENTS TABLEOF CONTENTS............................................................................................................... iii 1. GENERAL LOCATION AND DESCRIPTION 1.1 Location...................................................................................................................1 1.2 Description of Property............................................................................................1 1.3 Major Basin Description..........................................................................................1 1.4 Sub Basin Description..............................................................................................I 2. DRAINAGE DESIGN CRITERIA 2.1 Regulations..............................................................................................................1 2.2 Development Criteria Reference and Constraints....................................................2 2.3 Hydrologic Criteria..................................................................................................2 2.4 Hydraulic Criteria....................................................................................................2 3. DRAINAGE FACILITY DESIGN 3.1 General Concept.......................................................................................................2 3.2 Specific Flow Routing.............................................................................................3 3.3 Drainage Summary ..................................................................................................3 4. STORMWATER MANAGEMENT CONTROLS 4.1 SWMP contact information.....................................................................................3 4.2 Identification and location of all potential pollution sources...................................4 4.3 Best Management Practices (BMP's) for Stormwater Pollution Prevention ........... 5 4.4 BMP Implementation...............................................................................................7 5. CONCLUSIONS 5.1 Compliance with Standards..................................................................................10 5.2 Drainage Concept...................................................................................................10 6. REFERENCES..................................................................................................................I 1 APPENDICES A Vicinity Map B Hydrologic Computations C Water Quality Pond Calculations D Excerpts from Previous Reports iii 1. GENERAL LOCATION AND DESCRIPTION 1.1. Location The site is located in Section 20, Township 7 North, Range 68 West of the 61h P.M. in the City of Fort Collins, CO. The site is bounded by East Drake Road on the south, the Sidehill development on the west and undeveloped property to the north and east. 1.2. Description of Property Refer to the original "Final Drainage and Erosion Control Report for Cargill Secondary Use Building" by DMW Civil Engineers dated May 5, 2007 for a detailed description of the overall site. The proposed development is the addition of a greenhouse, a head house and an asphalt loop road located west of the existing greenhouses on site. 1.3. Major Basin Description This site is located in the Foothills Drainage Basin. The site is not located within the FEMA designated 100 year floodplain or the City designated flood plain. 1.4. Sub -basin Description This site is located in Subbasin 56 of the Foothills Basin Master Plan. Stormwater runoff from the Cargill site drains overland generally from north to south at slopes ranging from 0.5% to 2.0%. Runoff from the entire Cargill site flows to Drake Road where it is captured in inlets and conveyed to the Poudre River. 2. DRAINAGE DESIGN CRITERIA 2.1. Regulations Drainage for this site has been designed to meet or exceed the "City of Fort Collins Stormwater Criteria Manual' specifications, the City of Fort Collins Cache la Poudre Basin Master Plan and the update to Chapter 26 of the City Code. Where applicable, the criteria established in the "Urban Storm Drainage Criteria Manual" (UDFCD), 2001 has been used. 2.2. Development Criteria Reference and Constraints Stormwater runoff from this site has been routed to conform to the requirements of the City Stormwater Department. Detention would normally be required for this site but because the master plan assumes a maximum 40 percent imperviousness for the entire 30.73 acres and the proposed improvements do not increase the site imperviousness to that level, detention will not be provided. Water quality facilities are required for the improvements and are being provided by an existing water quality pond and proposed grassed swales on the site. 2.3. Hydrologic Criteria Runoff computations were prepared for the 10 year minor and 100 year major storm frequency utilizing the Rational Method. All hydrologic calculations associated with the basins are included in Appendix B of this report. 2.4. Hydraulic Criteria Necessary hydraulic calculations are provided and prepared in accordance with the City of Fort Collins Drainage Criteria and the Urban Area Drainage Criteria Manual. 3. DRAINAGE FACILITY DESIGN 3.1. General Concept All of the runoff from this site historically sheet flows to the adjacent streets and is intercepted by the existing inlets located in East Drake Road. With the previous development of the Secondary Use Building, a water quality pond was provided and will be enlarged with this proposal. The proposed improvements will disturb approximately 1.2 acres of the entire 30.73 acres on the Cargill campus. Runoff from this site will flow through the existing water quality pond located along the north edge of Drake Road. The pond will be enlarged to incorporate the increased imperviousness. 3.2. Specific Flow Routing Originally, in the DMW report, the site was divided into 7 basins. An additional basin will be defined with this proposed development. A summary of the drainage patterns within each basin is provided in the following paragraphs. Basin GHI encompasses the Greenhouse site. This basin includes the proposed 2 greenhouse and headhouse, concrete aprons around the Phase 1 buildings and an asphalt loop drive beyond the concrete. Runoff from this basin will either directly enter the existing water quality pond or will be collected in a grassed swale and conveyed south and east into the existing water quality pond. The master plan drainage model for the Foothills Basin assumes a developed imperviousness for the site of 40 percent. Although the imperviousness of the proposed developed area exceeds 40 percent, the imperviousness of the overall 30.73 acres remains below 40 percent, therefore on site detention is not provided. 3.3. Drainage Summary Drainage for this site was designed to conform to the City of Fort Collins stormwater and water quality requirements. Water quality is provided for a majority of the site utilizing grassed swales. Water quality for the site is also provided by routing runoff through the existing water quality pond. 4. STORMWATER MANAGEMENT CONTROLS 4.1 SWMP contact information Permit holder: Name: Dohn Construction Address: 2642 Midpoint Drive, Fort Collins, CO Phone Number: 970-490-1855 Email Address: tannand@dohnconstruction.com 3 Appointed agent: Name: Address: Phone Number: Email Address: 4.2 Identification and location of all potential pollution sources Potential Pollutant Source Activity Potential Pollutant Generated Applicable to this project. Disturbed Areas Sediment X Soil stockpiles Sediment X Travel to adjacent public streets Tracked sediment X Contaminated soils Sediment, chemicals Loading and unloading chemicals Chemicals Outdoor storage of chemicals Chemicals On site equipment maintenance Oil, grease On site equipment fueling Diesel, gasoline X Dust generating activities Particulates, sediment X Use of fertilizer, pesticides, herbicides Fertilizer, pesticides Use of detergents, solvents, oils Detergents, solvents, oil X Waste dumpsters, waste piles Chemicals X Concrete washout Concrete, sediment X On site equipment washing Detergents, oil On site asphalt batch plant Asphaltic cement, sediment On site concrete batch plant Cement, sediment Portable toilets Domestic sewage X 4.3 Best Management Practices (BMP's) for Stormwater Pollution Prevention Structural Practices for Erosion and Sediment Control Structural practices for the site will consist mainly of silt fence and rock sock filters and are described in detail in the following paragraphs. These BMP's are expected to change as the construction progresses and it is the responsibility of the contractor to ensure appropriate BMP's are in place and/or removed at the appropriate time in the construction sequence. 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 rock sock filters shall be in place prior to commencement of construction activities. During clearing and grubbing necessary for silt fence installation, all cleared material shall be placed on the uphill side so that if erosion occurs from the cleared material, the sediment will be trapped and not transported downstream. Rock socks shall be implemented in the existing curb line as shown on the Drainage & Erosion Control Plan. Inlet Protection shall be located around the existing curb inlet. All BMP's shall be installed per the details shown on the construction plan set. Temporary & Permanent Structural BMP's: Structural BMP Approximate location on site Applicable to this Project Silt Fence Site perimeter, refer to site map X Straw bale dams Rock Socks At existing pond outlet, refer to site map X Earthen diversion dams Vegetated swales Maintain existing vegetation in swale X Sediment trap/pond Pipe slope drains Geogrid Inlet/outlet protection Culverts Riprap At pipe outlet, refer to site map X Erosion control mats Inlet protection Non -Structural Practices for Erosion and Sediment Control: Soils exposed during the earthwork phase and landscape prep phase shall be kept in a roughened condition by ripping or disking along land contours until mulch, vegetation, or other permanent erosion control is installed. No large amount of soils (in excess of 15 yards) will be allowed to be stock piled on site. Overburden from the utility pipe trenching will be piled adjacent to trenches upstream of sediment controls and will be replaced in the trenches within 72 hours. Excess excavated materials from the demolition and grading phases of the project that cannot be reused on site will be exported as it is excavated. This includes any asphalt pavement from the existing site that is to be removed. A vehicle tracking pad will be installed at a location most beneficial to the site construction as determined by the contractor. Vehicles will not be permitted in the excavated area if soil is muddy. Gravel sub base will be placed and compacted in the areas indicated for pavement following excavation. In the current pre construction state the site enables tracking of silt onto the adjacent streets during wet conditions. During construction activities the street will be monitored for foreign debris tracked out of the site and mechanical sweeping and clean up will be performed as needed. No area shall remain exposed by land disturbing activity for more than thirty (30) days before required temporary or permanent erosion control (e.g. seed/mulch, landscaping, etc.) is installed. Temporary & Permanent non-structural BMP's: Non -Structural BMP Approximate location on site Applicable to this Project Surface roughening Entire construction area X Soil stockpile height limit (less than 10') Perimeter vegetative buffer South, west and north sides of construction X area Minimization of site disturbance Entire site X Mulch Seed & mulch stockpiles after 30 days Stockpile toe protection (silt fence, wattles or ditch) Preservation & protection of South, west and north sides of construction X existing vegetation & trees area Good site housekeeping (routine Entire Construction area X cleanup of trash & constr debris) Heavy equip staged on site, properly maintained & inspected Staging area X daily (no onsite maintenance) 0 4.4 BMP Implementation 1) Phased BMP Implementation BMP's are expected to change as the construction progresses and it is the responsibility of the contractor to ensure appropriate BMP's are in place and/or removed at the appropriate time in the construction sequence. All BMP's shall be inspected and repaired or replaced as required to satisfy the conditions of the Stormwater Discharge Permit. All BMP's must be maintained and repaired as needed to assure continued performance of their intended function. The following phase depictions and erosion controls are suggestions to the contractor on! and are in no way intended to dictate construction phasing or control of the work on site. The contractor shall be responsible to control construction phasing and provide adequate erosion control associated with each phase in order to comply with the SWM Plan and Permit that is obtained by the contractor (or owner) for the site. Phase I — Mobilization Install silt fence, Install rock sock at existing outlet structure, install straw wattles in existing swale, set dumpster. Phase 2 — Overlot Grading Cut and fill on site to achieve building pad elevations Phase 3 - Utilities Excavate and install for water service, excavate and install dry utilities Phase 4 —Site Paving Install sub base, install Asphalt pavement Phase 5 — Building construction Install concrete washout, install concrete foundation, remove concrete washout. Complete building construction Phase 6 — Landscape installation Backfill asphalt pavement and final shape swale and planting areas, Landscape plant installation, Install mulch ground cover, seed & sod Phase 7 — Final Stabilization Final stabilization is complete when constructed improvements are in place, Inspect completed construction for possible sources of erosion and amend the plan as required to trap sediments. 7 2) Materials Handline and Soill Prevention: Materials Handling &Spill Approximate location on site Applicable to this Prevention BMP Project Portable toilets, anchored & Refer to site map X located away from drainages Fuel storage located in bulk tanks with secondary containment & spill kit Mobile fueling performed at least 200 feet away from drainages & Refer to site map X fully attended Fertilizers, form oil, solvents, cleaners, detergent stored in 55 gal Refer to site map X or smaller containers, kept in storage units Dumpsters containing used chemicals containers & liquid Refer to site map X wastes kept covered Equipment cleaning (on site) uses no detergents & flows to onsite retention basin In case of a release of fuel or other chemicals, absorbent booms or earthen berms will be immediately Location of spill X constructed to contain the spill & prevent runoff to adjacent surface waters MSDS sheets for onsite chemicals will be kept at the construction Construction Trailer X trailer to facilitate spill response & cleanup 3) Dedicated Asphalt or Concrete Batch Plant: Not proposed with this development 4) Vehicle Tracking Pad: Vehicle tracking control pad shall be installed wherever construction vehicle access routes intersect paved public roads. Vehicle tracking control pads shall be installed to minimize the transport of sediment (mud) by runoff or vehicles tracking onto the paved surface. Any mud tracked to public roads shall be removed on a daily basis and after any significant storm that causes sediment to be transported. It is unlawful to track sediment/mud onto public streets and may be enforced by the City of Fort Collins or by the State of Colorado. 5) Waste Management and Disposal: Portable toilets will be anchored & periodically maintained by waste management company. Dumpsters on site will be covered & periodically emptied by waste management company. Concrete waste will be allowed to harden and then will be removed from site. No washing activities will occur on site. Location of the concrete washout is shown on the site map. The washout will be sufficiently deep to accommodate all anticipated concrete truck wash water. Waste concrete will be allowed to harden and be removed from site periodically as the washout reaches 50% of its capacity. Truck wash water will not be allowed to reach the curb & gutter or any other water course. 6) Groundwater and Stormwater Dewatering: No groundwater encountered during soils exploration therefore not anticipated to be an issue. If groundwater is encountered a groundwater discharge permit shall be obtained and a detailed report shall be completed describing the location and the route of where pumped groundwater will be conveyed and the measures taken to prevent the transport of any pollutants to downstream waters. SEDIMENT/EROSION CONTROL BEST MANAGEMENT PRACTICES (BMPs) COST OPINION SPREADSHEET Cargill Greenhouse Item No. BMP ID Unit Installation Unit Cost Maintenance as % of Installation Installation & Maintenanc Quantity Cost 1 Check Dam CDR LF 25% $0.00 $0.00 2 Check Dam (Reinforced) CDR LF 25% $0.00 $0.00 3 Concrete Washout Area CWA EA $1,200.00 200% $3,600.00 1 $3,600.00 4 Construction Fence CF LF 25% $0.00 $0.00 5 lConstruction Markers CM I LF 1 50% $0.00 1 $0.00 6 Culvert Inlet Filter CIF LF 25% $0.00 $0.00 7 Dewatering DW EA 50% $0.00 $0.00 8 Diversion Ditch (Unlined) DD LF 25% $0.00 $0.00 9 Diversion Ditch (ECM or plastic) DD LF 10% $0.00 $0.00 10 Sediment/Erosion Control Matting ECM SY 25% $0.00 $0.00 11 Inlet Protection IP LF 50% $0.00 $0.00 12 Reinforced Rock Berm RRB LF 25% $0.00 $0.00 13 SedimentBasin(n SB LF 1 25% $0.00 $0.00 14 Sediment Control Log (Wattle) SCL LF $4.60 25% $5.75 24 $138.00 15 Seeding and Mulching SM AC 50% $0.00 $0.00 16 Silt Fence SF LF $3.00 75% $5.25 815 $4,278.75 17 Rock Sock RS LF $10.00 10% $11.00 30 $330.00 18 Stabilized Staging Area SSA SY 50% $0.00 $0.00 19 Surface Roughening SR AC 25% $0.00 $0.00 20 ITemporary Stream Crossing TSC EA 25% $0.00 $0.00 21 ITopsoil (6-inch Lift) TSL AC 25% $0.00 $0.00 22 Vehicle Tracking ControllZl VTC EA $1,500.00 100% $3,000.00 1 $3,000.00 Contractor Added BMP(s) I'I 23 % $0.00 24 % $0.00 25 % $0.00 26 % $0.00 27 % $0.00 48 % $0.00 SUBTOTAL COST $11,346.75 CONTINGENCY 15% $1,702.01 TOTAL COST I4t 1 $13,048.76 7) Inspection & Maintenance: It is required that routine site inspections are performed to effectively address maintenance and repair of Best Management Practices (BMP's). The site inspections are to performed by the contractor or an inspector designated by the administrator at a minimum of once every fourteen (14) calendar days on active construction sites and after any significant storm event (an event causing runoff). As part of the site inspections the inspector is required to keep documentation of all inspections and BMP maintenance, including an updated Site Map indicating new BMP's or the removal of BMP's since the previous inspection. Any maintenance, repair, or necessary installation of BMP's that are noted during the inspection must be completed within seven (7) calendar days from the date of the inspection. 5. CONCLUSIONS 5.1. Compliance with Standards All computations that have been completed within this report will be in compliance with the City of Fort Collins Erosion Control Reference Manual for Construction Sites and the City of Fort Collins Stormwater Criteria Manual. 5.2. Drainage Concept The proposed drainage concepts presented in this report and on the construction plans, will adequately provide for stormwater quality treatment for the proposed improvements. Conveyance elements have been designed to convey required flows in the proposed grassed swales and the existing water quality facility and ultimately to the Cache la Poudre River. If, at the time of construction, groundwater is encountered, a Colorado Department of Health Construction Dewatering Permit will be required. lD 6. REFERENCES City of Fort Collins, "Storm Drainage Criteria Manual", (SDCM), dated March 1999. 2. Urban Drainage and Flood Control District, "Urban Storm Drainage Criteria Manual", Volumes 1 and 2, dated June 2001, and Volume 3 dated September 2001. 3. "Final Drainage and Erosion Control Report for Cargill Secondary Use Building" by DWM Civil Engineers dated May 5, 2007. APPENDIX A VICINITY MAP n ,-�— ■ ■ now .un i ■ � now O, lung lnul !'o , 1 1 =1= Inn11nn16nJ �' QLOMA gloullp i �1 • .�. a e►.��m�� p � : �= �uuuu�.• • � nmmn� �= �m��p►�� muun� :p m��a►o�� Dil. � !��nmimi �► ��iimlllli BBLL9=16 :xed 6g opejo'oo' spu!m OSSOB ope�olo�'iospuiM u anu uoi ewo n Ian' a l i vooz •oul ,u6lsep -m1$' u/.r0N1 A9 ,',`�,arn.."' >y,Eic'e iw; o w .� aed ...: �>o %P NV�d l0aUN00 N0IS0d3 28 39VNIV?JO avow 3�1Vaa 3 ovsz 3sn0HN33H!E) 11198VO F Ll 1 w o Ndd :(q pau6isa0 ave AB NOISIA36 fl/6/L a o0 a�q s€ 2 000 3<A U u $po a a 6$oaaa � s II i C II II u 0 ® ® oOQ � 1 i 1 i 1 1 1 1 L--r-_- --------- I 31 I al =1IIR 44 I , r � 1 S ' I I i W I b�3 I I is o v a g 00 r I(7 1 I I I 1 Q \ \ \ b 8v -- EAST DRAKE ROAD MMMMM I.r 1 1 1 r T 0 oA ozS, Hco =g3w oia e -4 0 .o U �:$N 52p za D� T / s i '• 1 I L 1 ' 1 ( I F9 I! I +szs- Q — — 0 . 11 - - li .r I O11001, Yt _ pia, irl-C �C (`I Ipli 0 APPENDIX B HYDROLOGIC COMPUTATIONS N J O y m z Q O F Z Z 4 O F f-- F U :D V D F O O a LL O S N N Z W - O V o � U LL LL LL W j O V o o c � U LL LL m Z w � O U O U 'g T ' E w a m ¢ _ m a a Z Q v N 5 w >w= M N <a� ¢ 0 W W K w U K N m Q v m 00 U F w b Z N ry a p Q LL O W n b o p N K Q m ~O a N Q <Cli m w o F O ¢ z n m v o � i " w U v LE Z 0 r a r z W U Z d U w O CW C r Y Q f K C Z � E LL = O y o r U m v 2 W U Z y m o - o n - o u J W - N z ¢ z U 4. O U m = v W m w o 0 1- W F ry W O m O 2 y O O O Q J C - O J ¢ r z_ O o 6 0 n Q ? u v m y a m z m m y N y y 2 F ¢ m y w m y Z u � Z y w LL y y - m K H w U N O O O O R R q U x L in m tJ a a m u o W W N E N E E C L LL LL 0 z ND LL Y a w a � oa O W 0 W � v J z z 0 P A Y ¢1 z z o° zz< — F F 4 F UO ` i o O 4 moo m o UEO E O o 0 N 5 0 t Q a 0 o c Z o Y K Q W K N N U o m C J A ~~ () V p N N N O lh f Q m N N N O U m N N t7 t N of ri vi ri �o mm V E N N N LL LL O Z F N (O N N V U o O o 0 W K u o Q N �n m❑ m x E m I°- '� w z � v 0 m E w LL LL O Z 7 Y Q W a Q o W O } = o H O W � J Q 2 O Q w 9 C C n n w � o 0 A V A q N V U a c J � f Q e r m N < N t o m r r n .ti m m V E N N N LL Q J U U o o 0 W � O a o r a v i E -m tt F w w z ^ « 0 EE m o a m p o w U d APPENDIX C WATER QUALITY POND CALCULATIONS 6/27/2013 LOCATION: ITEM: COMPUTATIONS BY: SUBMITTED BY: DATE: Cargill Water Quality Pond Sizing PPK North Star Design, Inc 6/2712013 From Urban Storm Drainage Criteria Manual, June 2001 (Referenced figures are attached in Appendix D) Use 40-hour brim -full volume drain time for extended detention basin Water Quality Capture Volume = WQCV = (required storage/12)'(tributary drainage area) MAJOR BASIN Trib. area (ac)'• % Imperv. Req. Storage (in. of runoff) from Fig. 3-2 WQCv (ac-ft) Dwo (ft) req. vol WQCV'1.2 (ac-ft) req. area/row (in'/row) from Fig. EDB-3 POND 4.64 46.0 0.20 0.08 3.20 0.091 . 0.12 " Includes all developed area on site. WQ outlet sizing From Figure 5, for 3/8 in, hole diameter Area of hole = 0.11 in # of columns = 1 Area provided/row = 0.11 in' Use 1 column of 318" diam holes WQVOL.xis STAGE -STORAGE TABLE LOCATION: Cargill PROJECT NO: 339-01 COMPUTATIONS B)ppk SUBMITTED BY: North Star Design DATE: 6/27/2013 WQ WSEL PROPOSED POND VOLUME WQ volume Rcq'd= 3963.96 cu.ft. = 0.091 ac.ft (volume accomodates all existing improvements and all proposed improvements) Stage (ft) Surface Area (ft) Incrernenta Storage (ac-ft) Total Storage (ac-ft) 4921.0 0 4922 335 0.003 0.00 4923 1191 0.017 0.02 4924 3558 0.052 0.07 4924.20 4302 0.018 0.090 4925 7206 0.121 0.19 APPENDIX D EXCERPTS FROM PREVIOUS REPORTS 0 ' Final Drainage and Erosion Control Report for Cargill Secondary Use Building Fort Collins, Colorado ' May 5, 2007 1 Prepared for. ' Steve Stadelmaier Cargill, Inc. 2540 East Drake Road Fort Collins, Colorado 80525 Prepared by: t l CIVIL ENGINEERS� 'J 1435 W. 29' Street ' Loveland, Colorado 80538 Phone:(970)461-2661 Fax: (970)461-2665 ' Project Number. 0512.00-CAR his unofficial copy was downloaded on May-02-2013 from the City of Fort Collins Public Records Website: http://citydoes.fe.-ov.com- .1 Final Drainage and Erosion Control Report for ' Cargill Secondary Use Building Fort Collins, Colorado May 5, 2007 I. INTRODUCTION ' 1.1 Objective This study documents the results of a final hydrologic and hydraulic analysis of post -development conditions for the proposed Cargill Secondary Use Building project. The utility plans which accompany this report are entitled Cargill Secondary Use Building prepared by DMW Civil Engineers, Inc. This report will also assist the contractor,in the preparation of a Stormwater Management Plan ' (SWMP). 1.2 Mapping and.Surveving ' Field survey information and topographic mapping with a contour interval of 1-foot was obtained by DMW Civil Engineers from King Surveyors, Windsor, Colorado. ' Additional topography outside of the project boundary was taken from City of Fort Collins Aerial Topography with a two (2) foot contour interval. II GENERAL LOCATION AND DESCRIPTION 2.1 Location ' The site is located in Section 20, Township 7 North, Range 68 West of the 6th Principal Meridian in the City of Fort Collins, Colorado. The site is bounded by the Drake Road to the South, the Sidehill development to the West, and undeveloped ' property to the north and east (see vicinity map). 2.2 Description of Property The Cargill Secondary Use Building site is approximately 1.22 acres of the total ' 30.73 acre Cargill property. There are a total of five buildings on the Cargill property. The existing buildings include offices, laboratories and greenhouses. The site had approximately 95% pervious coverage and is vegetated with native weeds and grasses and irrigated crops. Onsite soils on the Cargill property are both - Hydrologic Groups B and C, according to the Soil'.Survey for Larimer County,,bythe ' Soil Conservation Service. The actual building site is predominantly'Hytlrologic Group B. The existing runoff coefficient for the overall site prior to construction is estimated to be 0.20 for the design storm. The site is zoned :Low Density Mixed ' Use Neighborhood (LMN). The site is within Flood Insurance Zone C,=the areas determined to.be outside the 500-year flood plain, according to the FEMA Flood Insurance Rate Map, Community -Panel No. 080101-0193-E, dated March 18,1996. ' his unofficial copy was downloaded on May-02-2013 from the City of Fort Collins Public Records Website: http://ci(ydocs.fcgov.com k ' Final Drainage and Erosion Control Report DMW Civil Engineers, Inc. Cargill secondary Use Building May 5, 2007 Ill. DRAINAGEBASINS AND SUB -BASINS' 3.1 Maior°Basin Description ' The Cargill site is within the Foothills Basin, according to the City of Fort Collins Master;Drainage Plan. ' The, Foothills;Basin_is centrally located in Fort Collins and covers about 3,200 acres generally betvireen;Taft Hill and Ziegler Roads, and between HorsetoothandrDrake ' Roads. Thb :basin is mostly developed, with commercial development along CollegeMe,nue and mixed -use residential in the remainder of the basin. The basin drains from west to east through open channels or the storm sewer system to the ' Fossil Creek Reservoir inlet ditch. Three irrigation canals intercept storrnwater to transport rtt out of the basin, but runoff spills into the basin when their capacity is exceeded' 3.2 ' Sub -Basin Description The Cargill site is located in Sub -Basin 56 of the Foothills Basin Master Plan. Stormwater runofffrom the Cargill site drains overland generally fromnorthto south. at slopes ranging from 0.5%n to 2.0% into borrow ditches along adjacent streets. Stormwater runoff is currently conveyedfromthe site towards the southrwhere it is captured in inlets along Drake Road. These inlets discharge into a storm sewer that flows to the east and ultimately discharges into the Poudre River. ' IV. DESIGN CRITERIA 4.1 Desion'Criteria and Constraints Drainage design criteria specified in the City of Fort Collins Storm'Drainage design Criteria and Construction Standards manual and the Urban Storm drainage Criteria Manual, Volume 3 by the Urban Drainage and Flood Control District have been referenced in the preparation of this study. 4.2 Hydrologic Criteria The rational method' has been used to estimate peak stormwater runoff from the project site. An initial 10-year and major 100-year design storms helve been used to evaluate the proposed' drainage system. Calculations made as part of this investigation, along with other supporting material, are contained in Appendix A. Rainfall. intensity data for the rational method -has been taken from rainfall intensity data tables contained in the City of Fort Collins Storm Drainage Design Criteria and Construction Standards manual (see Figure 3-1 a). Composite runoff coefficients were generated using Table 3-3 and 3-9 of the City of'Fort Collins. Stone Drainage Desion Criteria and Construction'Standards manual ■ Page`? ' his unofficial copy was downloaded on May 02 2013"from the City of Fort Collins Public Records Website http://citydocs.fegov.com I ' Final Drainage and Erosion Control Report DMW Civil Engineers, Inc. Cargill Secondary Use Building May 5,2007 I 1 I 4.3 Hydraulic Criteria The computer program "Flowmaster°'has been used to analyze the capacity of proposed pipes and chases forthesite, A number of spreadsheets, provided by the Urban Drainage and Flood Control District have also been used as a design aid for inlets and the onsite pond. Hydraulic calculations are included in Appendix B. V. DRAINAGE FACILITIES DESIGN 5`1 Proposed Site Development Development of the Cargill Secondary Use Building site will consist of construction of new building on what is currently agricultural use ;land. The proposed site infrastructure includes the new building along with any necessary utility service lines; Approximately 2.0 acres of the:30.73 acre site will be disturbed with the construction of this project. The runoff coefficient for the 'building site after construction is estimated to be approximately 0.5 for the design storm. 5.2. Developed Drainage Patterns The developed site has been divided into eight (7) onsite drainage basins. Stormwater runoff will be conveyed overland, through concrete pans or grass swales to a water quality pond and then released into the storm sewer. Some stormwater runoff is permitted to flow directly into the storm sewerfrom the eastern part of the new building site. Basins 1, 2, 4, 5, and 6 (2.44 acres) includes most of the building site as well as some adjacent crop areas. Runoff from these basins drains to the southwest into an existing ditch along a field service road. The 10 and 100-yearpeak discharges from these basins are 4.3 and 11.1 cfs, respectively. Basins 3 and 7 (1.10 acres) are farm field and existing greenhouse areas. Runoff from these basins also flows to the proposed pond and are conveyed to the south 'in the aforementioned ditch_ The total 10 and 1'00-yearpeak discharges from these and the the on -site basins into the pond are 6.4 and 16.2'cfs, respectively. 53 Detention The existing impervious surf,, 1 is located at the south ed< purposes only. The master a developed imperviousnes; for.this;portion of the site is zl farrnland on this sitewithimt of;the sub -basin will remain pond will release runoff in E Page 3 Mhered-in for stormwaterpurposes. Pond gill site and ,is designed for water quality le model for the Foothills Basin assumes of.40 percent. Although imperviousness 82 percent, there are almost 30 acres of 1. Therefore, the overall imperviousness rcent and detention is not provided. The water quality control volume through a his nnoffictal copy was downloaded on May o2 2613'from the City of Fort Coll ins Public Records Website httpl/citydocs.fegov.corn .' ' Final Drainage and Erosion Control Report DMW Civil Engineers, Inc, CargillSecondary Use Building May 5, 2007 grated inlet and an eighteen inch diameter storm sewer. t 5.4 Erosion Control The erosion control, plan presented here is intended to control` rainfall erosion. The Erosion Control 'Reference Manual for Construction Sites (ECRM), City of Fort ' Collins, has been,refereneed for this erosion control plan. Appendix C contains worksheets forerosion control design,aswell asforerosion control escrow security. ' The proposed rainfall erosion control ,plan during construction will consist of minimizing soil exposure„ •protection of exposed soils and temporary structural ' sediment control measures. Temporary structural sediment control for the site will consist of silt fence surrounding the areas of construction, wattle filters, and a temporary sediment - control pond. All temporary structural sediment control measures shall be inspected and maintained as needed after every storm event. See the Grading ' and Erosion Control Plan for locations' of proposed sediment control measures. 5.5 Water Quality Structural Best Management Practices (BMPs) are proposed for the Cargill ' Secondary Use Building site to improve water quality of runoff as recommended by; the Urban Storm Drainage Criteria Manual. The detention ponds will incorporate ' extended detention basins -for water quality purposes. An extended detention basin(EDB) is a sedimentation basin which uses a much ' smaller outlet that extendstheemptyingtime ofthe morefrequentlyoccurring runoff events to facilitate pollutant removal. Soluble pollutant removal can be somewhat enhanced by providing a smal{wetland marsh or;ponding area in the basin's bottom ' to promote biological uptake: The basins are considered to be "dry" because they are designed not to have•- significant; permanent pool of water remaining between storm runoff events. However, ,EDB may develop wetland vegetation and 1 sometimes shallow pools in the bottom portions of the facilities. Pond 1 has been designed, to provide.15'10 cubic feet of water quality capture volume in addition to 302 cubic feet of sediment storage with a water surface elevation of 4923.62. Release•of the captured water is controlled by a steel plate ' with one column of eight 0.25" (1/4") circular, perforations. I Page 4 ' his unofficial copy was downloaded on May--N-2013 from the City of Fort Collins Pol'ic Records We6site: http://citydocs.legov.co- c �Cl � EOM rn u�rnmN Vl0 = O O O O 0 KJ' U ' 01 C I � o m . !� !� aif 2 v � a (1) " t!J CD. i. 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