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05-0540 Review letter 1 010407 City of Yelm Community Development Department 105 Yelm Avenue West P.O. Box 479 Yelm, WA 98597   January 4, 2007 Michael N. Antonoff, P.E. 3316 Deer Island Drive E. Lake Tapps, WA 98391 RE: McCammant Fourplexes – SPR-05-0540-YL Initial Review of Civil – Site Construction Documents Mr. Antonoff: The City of Yelm has completed the initial review of the proposed subdivision. Your application included: Civil Engineering Plans Stormwater Drainage Report We have reviewed the plans for compliance with the City of Yelm Development Guidelines, the DOE Stormwater Manual and general standards of civil engineering practice. The following comments need to be addressed before the plans may be approved for construction. Our comments are summarized below: Storm Drainage Report – Project Engineer Certification – This section should be signed and sealed by the engineer. Storm Drainage Report Section 1 – Proposed Project Description – Stormwater management should be provided for all disturbed areas both pervious and impervious. Erosion Control Report Section 2 – Trapping Sediment – Grading and construction activities have the potential for creating sediments. Please add a discussion as to what construction practices will be used to trap sediment. The erosion plan shows a silt fence and a construction entrance which are for this purpose. Storm Drainage Report Appendix B – Storm Drainage Facility Calculations – The drainage basin should include all disturbed areas as redlined in the report. Storm Drainage Report Appendix B – Storm Drainage Facility Calculations – Please provide a summary of the modeling output information and how required infiltration gallery size has been established. Also provide a statement of how much volume is required versus how much has been provided. Storm Drainage Report Appendix B – Storm Drainage Facility Calculations – Please provide drawdown calculations. According to Section III-3.6.5 of the 1992 Department of Ecology (DOE) Stormwater Manual, infiltration trenches shall be designed to completely drain stored runoff within one day following the occurrence of the 10 year, 24 hour storm and within two days of the 100 year, 24 hour storm. Storm Drainage Report Appendix B – Storm Drainage Facility Calculations – What is proposed for stormwater treatment? Treatment of stormwater is required prior to infiltration to groundwater. Please provide plans, details, calculations, and a discussion about treatment. Construction Plans: The following comments apply to all sheets: Some minor redline comments have not been called out in the letter but need to be addressed in the revised plans. Sheet 1 of 4: Please provide the Hearing’s Examiner Conditions of Approval on this sheet or provide a cover sheet with this information. The plans as currently shown are not stakable. Location information for structures needs to be provided. In addition, this location information needs to be tied to something such as a benchmark. Show locations of proposed inlet protection. Please provide a cross section of Crystal Springs Road frontage improvements showing proposed improvements and existing conditions. In order to construct the proposed curb and gutter along Crystal Springs Road, please provide a 2 foot sawcut in to existing asphalt to provide a clean edge for matching. The legend indicates a hatch for proposed asphalt, but this is not shown on the parking area. The roof drain encroaches into the setback area. The parking grades are too flat to provide positive flow. Please provide a minimum of 0.5% of slope. Additional spot grades and proposed slopes should also be shown. Currently, not enough grading detail is provided. Please call out the pipe size, type, and slope from CB #1 to CB #2. The invert elevation for CB #2 is unclear and cannot be read. If the elevation is 325.8, this may not provide enough depth for a type 2 catch basin. For a 12 inch pipe, a type 2 catch basin typically needs a minimum of about 4.8 feet from rim to invert. Please clarify and revise as required. Parking lot striping has not been shown. According to the Conditions of Approval, a minimum of 16 stalls are required. Further, a minimum of 1 handicapped stall shall be provided. Please show the proposed parking lot striping to demonstrate how these conditions have been satisfied. What is proposed parking lot pavement thickness? As shown, the infiltration trench has a top elevation of 329 feet. This is one foot or less below the top of asphalt in the parking area. Depending on the proposed pavement section, this is likely not deep enough to provide adequate separation between the top of the gallery and the bottom of the pavement section. It is unclear how the water will be metered. A total of 8 units are proposed but only 4 meters are shown. Will 2 units share one meter? Backflow prevention is required for the water services. Double Check Valve assembly’s are required behind potable water meters. A fire hydrant is required to provide adequate fire protection unless it can be shown that an existing hydrant meets spacing requirements to serve this site. As the STEP tank shown is for 8 units which is not listed in Table 1B, sizing calculations should be provided. Further, the required tank size should be referenced on the plans. Please provide size, type, and slope information of the sewer pipe connecting the buildings to the STEP tank. The driveway shown on this sheet does not match the detail provided on sheet 3. Please revise so the driveway matches the detail. A sidewalk connection should be provided from the frontage sidewalk to the existing edge of pavement. This can be an asphalt sidewalk. A sidewalk connection should be provided between the parking area and the buildings. Please show the proposed easement for the Yelm Creek Shoreline as required by Condition of Approval #9. According to Condition of Approval #11, a refuse collection area needs to be provided with adequate screening. This sheet contains erosion control, grading, stormwater, frontage improvement, and utility information. This is a lot of information for a small site, especially at a 30 scale. It is recommended that additional sheets be provided to separate the proposed information. Further, a separate site plan of the proposed improvements would also be helpful. This plan could show items such as the parking lot striping, trash enclosure, and other requested items. If these items are added to this sheet, it will further serve to clutter the plan. Sheet 2 of 4: According to the control structure detail, the minimum size of the type 2 catch basin shall be 54 inches. On sheet 1 the catch basin is called out to be 48 inches. Please revise. Two different types of inlet protection details are provided (the second is on Sheet 3). Please only provide one type of inlet protection. A cleanout detail should be provided. The construction sequence references the installation of a bioswale. Is a bioswale proposed? The infiltration gallery detail shows an overlap of the mirafi filter fabric but a dimension is not provided. The rock construction entrance should be a minimum of 100 feet in length. Sheet 3 of 4: Please add City of Yelm Detail 6-7 unless it can be proven that a fire hydrant is not required. Additional Comments: Please provide a detailed landscape and irrigation plan reflecting land use condition of approval #10. Note on plan that well is to be decommissioned pursuant to Washington State Department of Ecology standards. Irrigation meters must be shown, and double check valve assembly’s are required behind meters. Please review and revise the plans to address the above referenced comments. When the project is resubmitted you will need to submit 4 sets of plans, 2 stormwater reports. The project engineer should include a written response with the resubmittal, indicating how all the review comments above have been addressed or responded to. This will significantly expedite our review of the project. If you have any additional questions or comments please do not hesitate to call or contact me at jimg@ci.yelm.wa.us. Community Development Department Respectfully, Jim Gibson P.E. Development Review Engineer Bryan McCammant Ronald McCammant enc.