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HomeMy WebLinkAboutStormwater, Water, & Sewer Summary COO =NC I N==.1 1 N6 1011I l 11.1 �pNTA Glen Lake Commerce Subdivision, Block 1, Lot 1 RY B' 1 TAL Water, Sewer, Stormwater Summary 15833PE The following is a summary of the current and anticipated water,sewer, and stormwater conditions for the proposed Ugly Onion site development planned for Glen Lake Commerce Subdivision, Block 1, Lot 1. Water Service Water service for the site will be provided via connection to the stubs from the existing 8-inch water main located in Iron Horse Road. This main will provide domestic water service as well as fire suppression service for the structure proposed. According to the Water and Sewer Main Extension Design Reports for Glen Lake Subdivision, Madison Engineering, May 2018,the City of Bozeman has adequate service to supply both domestic water and fire suppression service to the proposed development. The report states a static pressure of 140 psi and a residual pressure under fire flow of 1,695 gpm of fire flow of 128 psi. At minimum residual pressure,the fire flow is indicated to be 3,154 gpm. This is significantly more than the required fire flows at any peak hour demand forthe subdivision, including this development. The proposed development will have approximately 82 fixture units (80 gpm peak flow)which results in a need for a 1"service and meter to service the structure. The reported pressures are well within the range to handle this demand. The 4-inch fire suppression service will be used to provide sprinkler fire service to the structure. Given the reported pressures and flows in the original analysis,there is adequate pressure and flow to service the fire suppression line for the structure. Sewer Service Sewer service for the site will be provided via connection to the existing 4-inch sewer service that is currently extended onto the lot. At minimum grade,this 4-inch service can handle 0.355 cfs,which is beyond the anticipated peak flow of 0.0055 cfs.The anticipated wastewater flows from the proposed structure are as follows: • 1 2-bedroom apartment=225 gpd • 2 1-bedroom apartments(150 gpd each)=300 gpd • A restaurant facility serving 100 meals per day(3 gpd per meal)=300 gpd • This results in an anticipated total of 825 gpd on average. • Utilizing the subdivision peaking factor in the report from Madison Engineering of 4.35,this gives a peak flow rate=4.35 x.5729 gpm =2.49 gpm or 0.0055 cfs. The anticipated flow for this lot(0.224 acres)was contemplated in the original subdivision design report under M-1 zoning(960 gal/acre/day) at 215 gallons per day. The original subdivision report indicates this lot would produce a peak flow of 0.65 gpm or.0014 cfs. This shows the proposed anticipated peak flow to be approximately 1.84 gpm or.0041 cfs higher than the flow contemplated in the original report. COO NCIN==r�INC�()Llli I(INi However,the report states the capacity of the existing 8-inch sewer main in Iron Horse Road is 0.64 cfs and the original anticipated peak flow for the entire subdivision in the main to be 0.11 cfs. Increasing the total peak flow from 0.11 cfs to 0.1141 cfs will keep the main well below the stated capacity of 0.64 cfs. Stormwater Stormwater runoff for the site will be handled via sheet flow across the site to the existing gutter and stormwater infrastructure installed during the construction of the original subdivision infrastructure. The stormwater runoff from the site was contemplated in the original subdivision Stormwater Design Report for Glen Lake Subdivision, Madison Engineering, May 2018. Basins indicated in the original stormwater report were followed regarding site grading and drainage so altering the original drainage basins is not necessary. Based on M-1 zoning,the original stormwater report utilized a runoff coefficient "C" of 0.65. The structure proposed on the site best suits the"commercial neighborhood", "C"=0.60, designation as outlined in the Bozeman Design Standards. In addition,the site has the following runoff coefficient values based on the Civil Engineering Reference Manual: • Total lot area=9,760 SF • Total impervious surface area=7,520 SF with "C"=0.8 • Total lawn surface area =2,240 SF with "C"=0.10 • Average runoff coefficient"C"= ((7,520/9,760) x 0.8)+((2,240/9,760)x 0.10) =.64 Given the original runoff coefficient utilized in the subdivision is greater than or equal to the proposed use of the site, no further stormwater mitigation is necessary.