CORNERSTONE RIVER VALLEY VILLAGE FILING NO. 1 STORMWATER MANAGEMENT PLAN

Transcription

1 CORNERSTONE RIVER VALLEY VILLAGE FILING NO. 1 STORMWATER MANAGEMENT PLAN SITUATED IN THE SW ¼ OF SECTION 18, T.2S., R.67W., OF THE 6 TH P.M. COUNTY OF ADAMS, STATE OF COLORADO PREPARED FOR: Thornton Cornerstone LLC 558 Castle Pines Parkway Suite B4-321 Castle Pines, CO Ph: Attn: Joseph H. Quinn PREPARED BY: Contact: David R. Addor, P.E. ORIGINAL DATE PREPARED: April 27, 2016 REVISED:

2 INTENT OF THE STORMWATER MANAGEMENT PLAN (SWMP) The intent of the Stormwater Management Plan (SWMP) is to minimize water Pollution by providing guidance on how to protect storm drain inlets and waterways during construction activities from grading, utility construction, millings/grinding operations, concrete saw water, waste materials such as concrete washout, and any disturbances to dirt/earth. Protect as much existing vegetation as possible, slow down runoff, prevent or minimize erosion form construction activities, provide incremental phased seeding and mulching, avoidance and minimization, stabilization, implementation, seeding and scheduling of the plan. Stabilize earth disturbances; prevent sediment from reaching the receiving or surface waters. CONTACT INFORMATION AND RESPONSIBLE PARTIES SWMP Administrator: Thornton Cornerstone LLC Attn: Joseph H. Quinn 558 Castle Pines Parkway Suite B4-321 Castle Pines, CO Ph: Site Superintendent: Erosion Control Consultant: Engineering Service Company 1300 S. Potomac St, Suite 126 Aurora, Colorado (303) voice (303) fax PROJECT SITE DESCRIPTION 1. This Stormwater Management Plan is being prepared for the development of a single family residential subdivision. The site covers acres and will be subdivided into 79 lots. Construction will consist of overlot grading, utility installation, storm sewer and street construction. Initial activity will be stripping of the top soil and stock piling for future use. Overlot grading will proceed with specific effort to establish the subgrade for the interior streets. Following street grading, the sanitary sewer and storm sewer will be installed with the water main installation completing the wet utility installation. Dry utility lines will then be installed. The concrete work will commence during this time period with installation of the curb and gutter in preparation for paving. The street paving will follow closely behind the curb installation. Walks will be installed concurrent with or following the paving. With completion of the streets, fine grading for final overlot grades will be completed to leave the lots ready for development.

3 2. Stormwater from this site discharges to storm sewer within the site as well as along the peripheral streets. This storm sewer discharges into the existing detention facility that services the entire River Valley Village complex. RECEIVING WATER NAME: PLATTE RIVER WETLAND IMPACTS? NO STREAM IMPACTS? NO THREATENED OR ENDANGERED SPECIES? NO 3. The existing soils are primarily Ulm-Loam, 3-5 percent. This and all other nearby soils are hydrologic group C or D soils with a moderate runoff potential. They are only moderately susceptible to water or wind erosion, have a K factor of 0.24 and a WEG of 6, both factors to the low to moderate end of their respective scales for erosion. 4. The total acres of disturbance, including all clearing, grading, excavation activities, areas receiving overburden (e.g. stockpiles), demolition areas and areas with heavy equipment/vehicle traffic and storage that will disturb existing vegetative cover is _14.35_ acres. Total area (acres) of construction site: _14.35 Total area (acres) of disturbance: The site grades primarily from the northwest corner towards the southeast with grades in the 2 to 4 percent range. Thornton Parkway is elevation along the south side of this property with embankment grades of 3 and 4 to 1. Currently the drainage is collected along the curb in Clermont Street and flows to the inlet in the low point in the street. 6. Existing vegetation is sparse to moderate cover of native grasses and weeds. 7. There are no sensitive areas on this site that would require special protection. 8. There are no non-stormwater sources of runoff on or adjacent to this site. THE STORMWATER MANAGEMENT PLAN The SWMP will be implemented in two phases: 1) first construction activity, 2) during construction with final stabilization. Site Map Components During construction items will be added as necessary to render the SWMP current, such as: 1. Areas used for storage of building materials, soils or wastes. 2. Location of work access routes during construction. 3. Location of borrow and waste locations. First Construction Activities Mobilization on site is anticipated to be August 1, Prior to Work Commencing

4 1. Sediment control measures will be implemented in accordance with the approved schedule prior to any construction. 2. Perimeter control will be established as the first item on the SWMP. 3. BMPs for other pollutants such as equipment maintenance and vehicle washing will be identified and implemented. 4. The locations of any additional BMPs will be added to the SWMP. Offsite Drainage There are very limited offsite areas that contribute runoff to this site. Drainage along the north side of the site will be controlled by the proposed stock pile area and stabilized staging area. This is a very limited offsite area that is tributary to this property line. No other offsite areas contribute drainage to this site. BMP s Installed: Initial Phase VEHICLE TRACKING CONTROL The construction entrance to the site will be from Clermont Street at the northeast corner of this property. It will be through the existing drive entrance from the roundabout area. Should off-site tracking occur, all practicable measures to clean roads and storm drainage ways, at a minimum by the end of each work day, will be utilized. STABILIZED STAGING AREA A stabilized staging area will be established for all construction equipment and parking. This is the area for all employee parking as well as sanitary facilities. Special areas will be prepared for any equipment maintenance or refueling activities to protect against spills or contaminant runoff. SILT FENCE Silt fence is shown on the Stormwater Management Plan at specific locations to protect against transport of sediment offsite. This silt fence will be installed prior to any construction activity. SEDIMENT BASIN The sediment basin will be graded out in the southeast corner of the site. This is the low corner of the property. Most of the site naturally drains to this location. DIVERSION DITCH A short section of diversion ditch may be necessary along the east property line to direct the drainage in this area into the sediment basin. INLET PROTECTION Inlet protection will be provided at the two inlets on Clermont Street during the initial BMP installation. Additional inlet protection will be added as the onsite storm sewer system is installed.

5 During Construction Grading and slope stabilization is anticipated to begin on August 15, Installation of utilities is anticipated to begin on September 15, Street construction is anticipated to begin on October 15, Building construction is anticipated to begin on November 15, Stabilizing Disturbances 1. Disturbed surfaces will be left in a roughened condition at all times by equipment tracking, scarifying or disking the surface on contour with a 2 to 4 inch minimum variation in soil surface. 2. Disturbed areas where work is temporarily halted will be temporarily stabilized within 14 calendar days after activity has ceased unless work is to be resumed within 45 calendar days after the activity ceased as authorized by the City Engineer. 3. During the seasons when seeding does not produce vegetative cover, temporary stabilization will occur. Temporary stabilization will consist of 1.5 tons certified weed free forage per acre, mechanically crimped into the soil in combination with an organic mulch tackifier. BMP s Installed: Construction Phase STOCK PILE PROTECTION A stockpile area has been identified along a portion of the north property line. This area will be protected by silt fence. INLET PROTECTION Inlets will receive protection immediately after installation. This protection will be upgraded after every modification to the inlet and every paving operation. SURFACE ROUGHENING All areas will be surface roughened as the final treatment when brought to final grade. SEEDING AND MULCHING Any area left undisturbed for more than 45 days will be seeded with temporary seed and mulched. CONCRETE WASHOUT The concrete washout will be installed prior to commencing any concrete work. This will remain in place until all concrete construction activities are complete. Inspection and Maintenance of Erosion Control Devices Inspections will be conducted at least every 14 days and after any significant precipitation event where erosion may have occurred. Replacement of failed BMPs will be conducted immediately. Maintenance of sediment and erosion control measures will be conducted whenever an

6 inspection has revealed a deficiency Sediment will be cleaned out on a regular basis to maintain the proper function of the erosion control device. The construction site perimeter, all disturbed areas, material and/or waste storage areas that are exposed to precipitation, discharge locations, and locations where vehicles access the site shall be inspected for evidence of, or the potential for, pollutants leaving the construction site boundaries, entering the stormwater drainage system, or discharging to state waters. All erosion and sediment control practices identified in the SWMP shall be evaluated to ensure that they are maintained and operating correctly. Final Stabilization Final stabilization for the overlot grading and street installation is anticipated to be completed on November 1, Thereafter, individual lot development will occur. BMP s Installed SURFACE ROUGHENING Surface roughening will be the primary final stabilization for this site. SEEDING AND MULCHING Any area left undisturbed for more than 45 days will be seeded with temporary seed and mulched. INLET PROTECTION The inlet protection will remain in place until site home construction is complete. LOT LANDSCAPING The final erosion control for each lot will be the installation of the landscape material for that lot including trees, shrubs, mulches, seeding and sod. Potential pollutants/materials handling and spill prevention Potential sources of pollutants would involve equipment fueling or maintenance, paving operations, material storage or waste disposal. To the extent possible, fueling and maintenance, material storage and waste receptacles are to be restricted to the designated area within the Stabilized Staging Area. Any materials stored onsite are to be stored in enclosed containers or covered to prevent exposure to rainfall or drainage. Materials are to be maintained on site for rapid response to any spill and quick containment and cleaning. Personnel are to be trained in effective spill prevention and clean up. For large spill exceeding 25 gallons, contact the City of Thornton, Thornton Fire Department (911) and the Colorado Department of Public Health and Environment ( ).

7 RECORDKEEPING 1. Accurate and complete records will be kept, and maintained for three years after the Site Development Permit is terminated. 2. The SWMP should be considered a "living document" that will be continuously reviewed and modified, including but not limited to: additions, deletions, and changing locations of BMPs. These changes will be marked in the plans, dated and signed at time of occurrence. Amendments to the SWMP may also arise from the recognition of additional sources of pollutants, selection of additional BMP s or maintenance requirements for existing BMP s, or interim or final stabilization requirements. These changes should be made as soon as the need is recognized. 3. All inspection and maintenance activities or other repairs will be documented and the records available for review by the City. 4. Records of spill, leaks or overflows that result in the discharge of pollutants must be documented and maintained. Information that should be recorded for all occurrences include the time and date, weather conditions, reasons for spill, etc. A release of any chemical, oil, petroleum product, sewage, etc., which may enter state waters must be reported immediately to the City and the State of Colorado Spill Hotline at Incidents of noncompliance, such as uncontrolled releases of pollutants including mud, muddy water or measurable quantities of sediment found off-site will be noted, along with a brief explanation as to measures taken to prevent future violations and measures taken to clean up sediment that has left the site. CORRECTIVE ACTION LOG Create as an attachment, a corrective action log. This log should describe repair, replacement, and maintenance of BMPs undertaken based on the inspections and maintenance procedures, date completed, and note the person that completed the work. Actions related to the findings of an inspection should reference the specific report. This log will also describe changes and updates to the SWMP, including additions of new BMPs, replacement of failed BMPs, significant changes in the activities or their timing on the project, changes in personnel, changes in inspection and maintenance procedures, and updates to site maps, etc. TRAINING Staff and subcontractors will be trained to identify stormwater BMPs and how to prevent problems with them, such as not driving onsite unless through the vehicle tracking control or taking care to not to damage BMPs. Documentation on training at safety meetings or otherwise will be kept on file with the SWMP, including dates, number of attendees, subjects covered, and length of the training.

8 APPENDICES Appendix A Appendix B Appendix C Appendix D Appendix E Appendix F Appendix G Appendix H General Location map Site Maps Copy of the State Construction General Permit Copy of the City Site Development Permit Inspection Reports Corrective Action Log Training Records BMP Specifications and Details

9 APPENDIX A

10 APPENDIX B

11 APPENDIX C

12 APPENDIX D

13 APPENDIX E

14 APPENDIX F

15 APPENDIX G

16 APPENDIX H