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HomeMy WebLinkAboutDrainage Reports - 04/24/2015City of Ft. Collins Andro d Plans Approved By ' Date �t- "*-IS North Star �`„ design 700 Automation Drive, Unit I Windsor, CO 80550 Phone:970-686-6939 Fax:970-686-1188 February 24, 2015 Wes Lemarque City of Fort Collins Utilities 700 Wood Street Fort Collins, Colorado 80525 Mr. Lemarque, This letter is to serve as an addendum to the drainage report prepared by North Star Design for the Timberline Center located west of Timberline Road in Fort Collins. This addendum applies to the proposed development location on Lot 2 which is intended to be a Big O Tire store. The Lot is located in Sub -basins 17, 18 and 20 which are described below. Sub -basin 17 contains the southwest portion of the site and will drain to a sump inlet in the private drive located west of Lot 2. The system drains to the existing detention pond between Lots 1-3 and Timberline Road. Sub -basin 18 contains the northwest corner of the Lot and will drain west into the private drive and to a sump inlet. Sub -basin 20 contains the east half of the lot and the detention pond located east of Lot 2. This has been designed to detain Basins 17 through 20 and release directly to the storm system in Timberline. In general, the site conforms to these basin delineations with small deviations. Basin 20 area is smaller by 1079 square feet, Basin 18 is larger by 237 square feet and Basin 17 is larger by 842 square feet. This causes the 100 year flow in Basin 20 to decrease from 7.9 cfs to 7.6 cfs, in Basin 18 to increase from 5.9 cfs to 6.0 cfs and in Basin 17 to increase from 17.9 cfs to 18.1 cfs: This is a maximum of 1.75% increase in the 100 year flow which would be considered negligible. andlq bsvoiggA 2,.iiiloO J! io VVO y8 b9vozggA gist] The building. does extend further east than originally planned for in the overall development which will require the owner to vacate a portion of the.drainage easement for the detention.pond. The 100 year high water elevation for this pond is 4940.30 which is achieved in the remaining drainage easement. The building floor elevation is set at 4943.0 which provides sufficient freeboard for the pond. The finished grade along the east side of the building (detention pond side) will be set at 4940.30 in order to not encroach on the existing volume of the pond. The imperviousness dictated in the Timberline Center drainage report will be met with this development and no additional on -site detention or runoff calculations will be required. 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Written Analysis The soils on this site are classified by the USGS Soil Survey as Nunn Clay Loam and are classified in the hydrologic group C. The soils are described as having a slow infiltration rate when thoroughly wet and the hazard of water erosion is moderate and the hazard of wind erosion is low. The site is surrounded by lots undergoing development and existing public and private streets. A detention pond exists on the east side of the site. The construction shall utilize silt fence around the perimeter to control sediment transport from rainfall and from wind. Rock socks will be utilized in the existing detention pond, around existing inlets and in the newly constructed concrete channels to capture sediments that are not fully contained by the silt fence placement. The site will also utilize two vehicle tracking control pads to minimize sediment from being tracked onto adjacent pavements. Sediment that is tracked will be removed and placed within the site or permanently disposed of offsite. A concrete washout will be used on site during the concrete placement. All hardened concrete will be disposed of offsite. These BMP's have been located on the site map but may be located as construction dictates due to the fact that the site is very small and these BMP's will need to be placed by the contractor in locations that are most beneficial and will minimize disruption of adjacent traffic. Permanent erosion control consists of covering the soils with a building, concrete walks, concrete drives and sod. No soil will be left exposed to erosion after the construction is complete. Refer to the landscape plan for areas of and instructions for placement of sod and soil amendments required prior to placement of sod. Refer to the erosion control plan for this site for the timing of the construction phases and the sequential installation of all BMP phasing for this site. Refer to the end of this section for the Erosion Control Surety calculations. 2. SWMP contact information Permit holder: Name: Address: Phone Number: Email Address: Appointed agent: Name: Address: Phone Number: Email Address: 3. 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 Unloading of building materials Trash, debris X 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, trash, debris X Concrete washout Concrete, sediment, wash water 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. 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. 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 new sidewalk culverts, at existing inlet, refer to site map X Earthen diversion dams Vegetated swales Rock Berm East boundary of site, in existing det pond X Pipe slope drains Geogrid Inlet/outlet protection Culverts Riprap Erosion control mats Inlet protection Vehicle Tracking Control Pad At site entrances, refer to site map X Concrete Washout To be located by Contractor, near site entry X 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 site X Soil stockpile height limit (less than 10') Perimeter vegetative buffer East boundariyof site X Minimization of site disturbance Mulch Seed & mulch stockpiles after 30 days Stockpile toe protection (silt fence, wattles or ditch) Preservation & protection of existing East boundary of site X vegetation & trees Good site housekeeping (routine Entire Site X cleanup of trash & constr debris) Sweeping & scraping of hardscape On and off site pavements X areas Heavy equip staged on site, properly maintained & inspected daily (no Staging area X onsite maintenance) 5. 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. A construction sequence schedule has been included on the Erosion Control Plan in the construction plans for this site. 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. Refer to Appendix D for the BMP schedule and estimated costs. 2) Materials Handling and Spill Prevention: Materials Handling & Spill Approximate location on site Applicable to this Prevention BMP Project Portable toilets, anchored & Contractor to determine 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 & Contractor to determine X fully attended Fertilizers, form oil, solvents, cleaners, detergent stored in 55 gal Contractor to determine X or smaller containers, kept in storage units Dumpsters containing used chemicals containers & liquid Contractor to determine 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 Contractor to determine 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, by the State of Colorado or by the EPA. 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 was encountered during soils exploration therefore ground water is 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. 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 be 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 Example Erosion and Sediment Control Escrow/Security Calculation for The City of Fort Collins Project: Big O Tires, Lot 2 Timberline Center EROSION CONTROL BMPs Silt Fence Rock Sock Vehicle Tracking Control Pad Concrete Washout Rock Berm (add all other BMPs for the site in this list) BMP Amount Estimated Units Quantity L.F. 265 each 7 each 2 each 1 each 1 Disturbed Acres: 0.61 Unit Price $3.00 $85.00 $1, 500.00 $1,200.00 $65.00 Sub -Total: 1.5 x Sub -Total: Amount of security: Reseeding Amount Total Acres x Price/acre: Total Price $795.00 $595.00 $3,000.00 $1,200.00 $65.00 $5,655.00 $8,482.50 $8,482.50 $732.00 Unit Price of Seeding per acre: $1,200.00 Sub -Total: $732.00 1.5 x Sub -Total: $1,098.00 Amount to Re -seed: $1,098.00 Miniumum Escrow Amount Minimum escrow amount: $3,000.00 Final Escrow Amount Erosion Control Escrow: $8,48Z50 "The amount of the securip• must be based on one and one-half times the estimate of the cost to install the approved measures, or one and one-half times the cost to re -vegetate the disturbed land to dry land grasses based upon unit cost deterodned br the Ciny s Annual Revegetation and Stabilization Bid. whichever is greater. In no instance, will the amount of security- be less than one thousand five hundred dollars ($1,500) for residential development or three thousand dollars ($3, 000) for commercial development" 2/24/20151:44 PM MSTARWrojWsH77-0e Big onms nmberone ceMeMminaee%EaaMle Esa xls