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HomeMy WebLinkAbout006.1 - Sewer Waiver Request Memo1. CLUBHOUSE CLUBHOUSE SANITARY SEWER CAPACITY MEMORANDUM 1.1. OVERVIEW AND SUMMARY OF REQUIREMENTS This memorandum has been prepared to support the design of the proposed 4-inch diameter sanitary sewer lateral serving the clubhouse (Building 2, as shown in the engineering plans). The proposed sewer lateral is designed with a slope of 2.0 percent and is connected to the proposed 8-inch sanitary sewer main. The design is based on the criteria outlined in the City of Bozeman Design and Construction Standards (October 2024 edition), as well as the Montana Department of Environmental Quality Circular DEQ-2. ). This memorandum seeks to provide an exemption from BMC 5.2.9 Sanitary Sewer Services maximum side sewer service length by providing calculations that verify a 4” Side Sewer Service sloped at 2% has adequate capacity to serve the clubhouse. To establish that the deviation is acceptable, this memorandum includes calculations to demonstrate that required capacity will be met at the clubhouse without a sewer main extension. 1.2. DESIGN CRITERIA The sanitary sewer service line has been designed in accordance with the following parameters, in compliance with City of Bozeman standards and DEQ-2: • Minimum slope of 4-inch sanitary sewer lateral: 2.0% (per DEQ-2) • Maximum allowable flow depth: 75% of pipe diameter (per City Standards) • Pipe material: SDR-35 PVC • Manning’s coefficient: 0.013 1.3. FLOW CAPACITY AND PEAK FLOW ANALYSIS Per the Sanitary Sewer Design Report prepared for the DEVCO Alder Ridge & Sage Peak Apartments (March 2024), a 4-inch lateral at 2.0% slope has a calculated capacity of 108 gpm, as shown in Table 4-2 of the report. With a clubhouse peak hour flow of 15 gpm, the pipe will operate at only 14% of its full capacity. This complies with the City of Bozeman Design and Construction Standards, which limit flow depth to 75% of the pipe diameter during peak conditions. Therefore, the proposed 4-inch sewer lateral is adequately sized and can convey the anticipated wastewater flow from the clubhouse without exceeding design thresholds. 1.4. CODE COMPLIANCE The design complies with the following relevant provisions of the City of Bozeman Design and Construction Standards and Montana DEQ-2: • Section 5.2.2.B: Sewer lines must be sized for design flow, not available slope. • Section 5.2.9: Minimum slope for 4-inch service line stubs is 1/4 inch per foot (2%). • Section 5.2.2.A: Pipes must be designed to flow no more than 75% full at peak hour flow. • Table 4-2 of Sanitary Sewer Design Report: 4-inch lateral at 2% slope conveys 108 gpm. 1.5. CONCLUSION Based on the calculations and design standards referenced above, the proposed 4-inch diameter sewer lateral at 2.0% slope is sufficient to serve the anticipated peak flows from the clubhouse. No sewer main extension is required at this time. Taylor Bellefeuille, PE ONSITE SEWER SCALE: 1" = 20' H 1" = 2' V 4960 4964 4968 4972 4976 4980 4984 4960 4964 4968 4972 4976 4980 4984 2.79'3.17'4.00' MIN'SWATERMECHBUILDING 3C4.10©ALDER RIDGE & SAGE PEAKAPARTMENTSPREPARED FORGRAF STREETAPARTMENTS, LLC.® BEFORE YOU DIG, CALL 1-800-424-5555 NORTHBUILDING 3 - SEWER DRIVE AISLE ISIDE SEWERPROFILESIDE SEWER SERVICE BUILDING 2STAUDAHER ST