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HomeMy WebLinkAboutNEWTON SINGLE-FAMILY DETACHED - BASIC DEVELOPMENT REVIEW - BDR180019 - SUBMITTAL DOCUMENTS - ROUND 3 - DRAINAGE REPORT1 Kai Kleer September 21st , 2018 City Planning Department 0309.18 281 N College City of Fort Collins 80524 RE: 1520 West Vine Drive – Site Drainage and Erosion Control Report Dear Kai, GENERAL INFORMATION The proposed development located at 1520 West Vine Drive includes the construction of a four bedroom single family residence on a large vacant lot. The total structure square footage is 2,593 including the two car garage and will be situated on a 1.45 acre site. Access will be utilized from the existing driveway at 1516 West Vine Drive and onto West Vine Drive. A separate emergency pervious gravel surface access will be constructed adjacent to the existing 1516 West Vine Drive and will access onto West Vine Drive. SITE DRAINAGE The site is located just north of West Vine Drive and slopes gradually less than 0.33% to the southeast towards West Vine Drive. Due to the small footprint of the proposed structure and driveway that are located on 1.44 acres, runoff is expected to be very minimal. There are no proposed storm sewer or detention pond designed for this site. Drainage is likely to infiltrate into the soil or gradually migrate to West Vine Drive and very slowly drain to the east. The impervious area is about 3,200 square feet and approximately 5.2 percent of the lots gross area. This is well below the 30 percent assumed impervious area of the West Vine Drainage Master Plan. As shown in the attachment, the Q100 pre-development runoff from the site is 0.93 cfs versus the Q100 post development runoff of 1.79 cfs. The additional runoff pre-development versus post- development is 987 cubic feet of water or 0.02 acre feet. The site is also located in both the City Floodway and City Flood Fringe. The finish floor, ductwork, HVAC, and electrical components of the proposed structure will be constructed at an elevation 2 2.5 feet above the 100 year water surface elevation for that area. For the City Floodway area, all proposed development will be constructed to the existing elevation or just below the existing elevation to prevent a rise in the water surface elevation. An elevation certification will be provided once construction is completed for both the structure and the portions of the driveway constructed in the floodway. The structure will be elevated with existing soil material backfilled, compacted and sloping down from the just below the finish floor at a 4:1 slope to the existing ground. This slope will provide positive drainage away from the structure. EROSION CONTROL Site Description This project includes the construction of a single family residence on a large vacant lot. The site is currently covered with dense pasture grasses and bordered with numerous trees. The site is, and has been used for grazing and hay production. It is the intent to minimize impacts to the existing trees and vegetation as much as possible to construct the single family home. Construction phasing includes installing the erosion control features prior to any other construction activities. This includes the silt fence, tracking pad and inlet protection devices to minimize sediment runoff. Following the installation of the erosion control measures, striping vegetation and topsoil will follow to the limits for the proposed grading, structure, utilities and access. Topsoil will be stored in manageable piles outside of the proposed grading areas but inside the silt fence area. Once the site is stripped, the foundation limits for the house will be excavated and stored inside the silt fence area. While the contractor is waiting for the concrete to cure and gain strength, utilities will be installed from the main connection points to the foundation. Typical utility installation includes excavating the utility trench, installing the proposed utility, backfilling and compacting. The utility work will be confined within the silt fence limits. Once the foundation concrete has cured and of sufficient strength, the foundation will be backfilled with the excavation material. Once the foundation is backfilled, construction of the home will begin. The proposed home includes typical framing, sheeting, and standard home construction. The proposed home construction is common for the area and will minimize erosion control issues. 3 Conservatively, it is estimated 32,234 square feet or 0.75 total acres will be disturbed for construction purposes. Of the 32,234 square feet, approximately 13,000 square feet will be disturbed for the major grading and foundation construction, ~4,500 square feet will be disturbed for utility construction, ~3,670 square feet for access construction and ~9,000 square feet of disturbance for staging areas. Actual disturbance may vary depending on activities. The gross site area is 1.45 acres, drains to the southeast and will focus most of the erosion control measures in the 0.60 acre area to prevent material from being transported offsite. The receiving waters downstream is the Cache La Poudre River. Construction flow path includes installing bmp’s, striping/storing topsoil, gravel access, foundation excavation, backfilling foundation, vertical construction, concrete flatwork, placing topsoil, seeding, mulching, and tree planting. AT any time during the construction flow path, silt fence and tracking pad may trap materials in which the Contractor shall remove these materials as required. This may vary pending on storm events and construction activities. Stormwater Management Controls Erosion Control measures for the proposed improvements have been shown on the Landscape and Erosion Control Plan. Erosion control measures include silt fence surrounding and located just outside the construction limits of the project, tracking pad at the entrance, and inlet protection for the approach culvert. The site is relatively flat which will help minimize sediment runoff. During rain events, sediment will be captured by the silt fence, tracking pad, and inlet protection measures to prevent from traveling offsite. After rain events, the stormwater manager will evaluate the site and to determine if best management practices need to be altered to better accommodate the site conditions. The site will also include a sediment tracking pad at the construction site exit. This will include larger aggregate or fabricated pad to be selected by the project Contractor. This will minimize material being tracked offsite onto West Vine Drive. In the event material is tracked offsite, the Contractor will be responsible to remove said material and dispose of properly. The site includes one storm sewer pipe culvert that is located at West Vine Drive and the proposed emergency access. Straw waddles will be placed at the entrance of the pipe culvert to minimize sediment entering said pipe culvert. In the event sediment enters the pipe, the Contractor will be responsible to remove said material and dispose of properly. 4 The Contractor will modify erosion control measures as necessary for conditions, and construction phases. The final stages of construction will include seeding and reclamation efforts. Once the site has been stabilized to a minimum uniform vegetative density of 70% across all disturbed and seeded areas, the Owner or Contractor will be able to remove the silt fence, straw waddles, and tracking pad. SWMP Administrator Following is the stormwater administrator and his contact information. Jordan Ishii Prevail Homes Jordan.prevail@hotmail.com (970) 416-9300 (720) 641-5912 – mobile Jordan will be responsible for all aspects of the storm water management plan and implementing changes as required. Potential Pollutant Sources Potential pollutant sources include sediment and typical pollutants associated with construction equipment and materials. Sediment will be contained on site per the erosion control features and bmp’s established onsite. During fueling or service of machinery onsite may result in a small fuel spill or other small pollutants such as grease or other fluids. In the event of a fuel spill or other contamination, the swmp administrator will identify the area and remove the contaminated material offsite immediately after it occurs to prevent the material from permanently contaminating the site. Other potential pollutants include, concrete, drywall, paint and sealants. These are typically contained on a construction site, but if a spill or release occurs, the Contractor shall clean the contaminated area thoroughly and dispose of materials properly and lawfully. Stockpiling of Stored Soils Stockpiling of dirt during construction may be necessary for the sequencing of construction activities and should be somewhat minimal and temporary for this site. Stockpiles that are generated shall be contained within the silt fence area to minimize sediment issues. It is 5 anticipated stockpile material will be utilized to backfill around the concrete foundation once concrete strength has been achieved. Vehicle Tracking or Sediments The owner and site manager realizes that vehicle tracking of sediments is a major potential pollution source and will be fully engaged to minimize this risk. A tracking pad will be installed at the entrance as main mitigation for offsite tracking. The site will also only utilize one entrance/exit to the site as well. If tracking of offsite material does occur, the swmp manager will remove the material by scraping and sweeping up of said material. Not only will the site utilize a tracking pad, but a gravel approach from the tracking pad to the construction site. Said gravel approach shall be constructed prior to other construction activities. Management of Contaminated Soils The owner has not discovered any existing contaminated soils on-site but if discovered during construction, the swmp administrator will stop construction, notify the Owner, determine what they are and dispose of properly and legally. Loading and Unloading Operations Traffic operations include delivering materials from Vine Drive via the single entrance to the construction site. Due to small proposed structure, site deliveries will be minor in amount. Materials will be delivered as needed and required. Delivery vehicles will be limited to the gravel driveway and will minimize driving through disturbed surfaces to minimize impacts and tracking material offsite. Outdoor Storage Activities Construction materials such as lumber, roofing shingles, drywall, shall be temporarily stored on site during construction. Materials will either be elevated, or stored inside to prevent interacting with stormwater and causing pollutant sources to migrate. Typically lumber and plywood is elevated with blocks and covered on site to protect against rain or snow. Typically roofing materials are delivered and stored on the plywood roof until used. Once the home is enclosed, items such as paint, doors, windows, drywall, etc will be stored in the garage area until used. In the event, material is delivered and not stored in the garage, it will be elevated and covered on site. 6 Vehicle, Equipment Maintenance and Fueling Operations Equipment maintenance and fueling operations will likely occur on a weekly basis but very minimal due to the size of the construction site. If contamination occurs during maintenance procedures or operations, the contaminated soil will be removed and disposed of properly. Significant Dust or Particulate Processes On site dust can occur during construction but will be controlled by wetting the area frequently. This will minimize dust pollution generated during construction. Other potential airborne particulates are not anticipated from the site. The Contractor shall review the dust control manual adopted by the city for further details to prevent particulate migration. The manual is located at https://www.fcgov.com/airquality/fugitive- dust.php On-Site Waste Management Practices All waste material will be stored in a covered self-contained industrial dumpster to be stored at a minimum of 50 feet from any inlet, structures, or watercourses. Concrete Truck Washout Facilities Concrete trucks, especially during the pouring of the foundation will need to wash on site, so a concrete washout facility will be constructed onsite and is shown on the erosion control plan. Dedicated Asphalt and Concrete Batch Plants There are no dedicated asphalt and or concrete batch plants planned for this project. Non-Industrial Waste Sources Portable toilets or PortaJons will be located onsite but 50 feet from any inlets, drainage features or watercourses. There are no other non-industrial waste sources anticipated for this project. Other Potential Spills No other potential spill sources are anticipated for this project. 7 Establishment of Dryland Vegetation Establishment of dryland vegetation is very important to the Owner as they prefer to have vegetation established as quickly as possible both for aesthetic and erosion control purposes. Once vegetation has been established to a minimum of 70 percent coverage or better, it means less work for the Owner in regards to erosion control maintenance. The existing soil types include clay, sandy, moist to wet, medium stiff, dark brown (CL) in the top two feet followed by sand/gravel, wet, medium dense to dense brown (SP, GP, GW, SP-SM) to a depth of 10-15 feet. The topsoil and material excavated for the foundations will be stored separately from each other during construction. This will minimize topsoil from mingling with the subgrade/sterile soils to promote the rapid growth of plants in the topsoil not in the subgrade. Once construction is complete, the existing topsoil will be placed at a thicker depth than original site and will contain seed from the original vegetation as in accordance with City code 12-130 through 12-132. The Contractor will seed and mulch with a seed mix for all exposed areas at a rate of 15.92 lbs/pls/acre. Straw mulch will be weed free and crimped into the soil to minimize erosion immediately after seed is applied. It is anticipated that reclamation efforts will be performed in the spring of 2019 taking advantage of the optimum growing season. The Owner will water intermediately if needed to assist with germination and plant growth until a uniform vegetative density of 70 percent across all seeded areas has been obtained. Once established, the Owner will provide weed control as needed. Construction Phasing and Sequencing The construction phasing is as follows: 1) Install pipe culvert extension, tracking pad, gravel approach, inlet protection, and silt fence. Later Summer/Fall 2018. 2) Clearing, grubbing, topsoil removal for utilities and foundation. Topsoil storage piles will be created storing materials onsite. Fall 2018. 3) Excavate for foundation, and store materials on-site and out of the way for construction. Fall 2018. 4) Install utilities, backfill and compact trenches. Fall 2018. 5) Backfill foundation and compact with foundation excavation materials once foundation has cured. Adjust bmp’s as needed. Late Fall 2018. 6) Vertical construction such as framing, roofing, flooring, windows and all other tasks associated with normal home construction. Winter 2018/2019. 8 7) Placing topsoil, reclamation efforts including seeding, mulching, and planting trees. Later Winter 2019/Early Spring 2019. 8) Once vegetation has been established, the Owner will remove silt fence and inlet protection devices. Summer 2019. Fortunately, the site is large enough and the construction activities small requiring little adjustment to the proposed bmp’s. Structure Construction The excavated material in and around the proposed building area will be contained during construction so sediment is not transported to the parking lot during storm events. This should be contained by means of silt fence or straw wattles. Dirt that will remain for an extended period of time shall be covered with reinforced poly plastic sheets ore seeded. SUMMARY Due to existing conditions, slopes of the property and comparing the size of the proposed development to the existing lot, no negative impacts are anticipated for this development or create issues for adjacent properties. I appreciate your time and consideration in reviewing this submittal. Please contact me at 970- 420-0086 or kent@avipc.com if you have any questions. Respectfully Submitted, AVI PROFESSIONAL CORPORATION Thomas Kent, P.E. 9 Appendix Drainage Calculations