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Home My WebLink AboutENG 6 Sewer Engineering Report 2021-05-24 BOULDERS APARTMENT - BOZEMAN SEWER IMPROVEMENTS SANITARY SEWER BASIS OF DESIGN REPORT May 2021 PREPARED BY: MMI #: 4192.025 Table of Contents INTRODUCTION ........................................................................................................................................... 1 1 PROBLEM DEFINED ........................................................................................................................... 1 2 DESIGN CONDITIONS ......................................................................................................................... 1 3 IMPACT ON EXISTING WASTEWATER FACILITIES ........................................................................ 2 4 PROJECT DESCRIPTION .................................................................................................................... 2 5 DESIGN CRITERIA .............................................................................................................................. 3 6 SITE INFORMATION ............................................................................................................................ 3 7 ENVIRONMENTAL IMPACTS .............................................................................................................. 3 8 OPERATION AND MAINTENANCE .................................................................................................... 3 APPENDICES Appendix A – Laurel Glen Lift Station Capacity Design Report, May 3, 2020 Prepared by: Morrison-Maierle, Inc. 2880 Technology Blvd. W. Bozeman, Montana 59771 Phone: (406) 587-0721 Fax: (406) 922-6702 Written By: CMS Checked By: MEE Approved By: MEE PROJECT NO.: 1 INTRODUCTION This design report provides a basis of design for the Boulder Creek development sewer main extension improvements project and is submitted in conjunction with the completed plans and specifications. The sewer distribution system serving the Boulder Creek development will be designed and installed in accordance with the Montana Department of Environmental Quality (MDEQ) Circular No. 2, Chapter 10, Section 11.1, Engineering Reports; Montana Public Works Standard Specifications (MPWSS); The City of Bozeman Modifications to MPWSS; and the City of Bozeman Wastewater Facility Plan. The design report is to verify that there is an adequate capacity to receive wastewater flows from the Boulder Creek development. The following design report follows the section numbering of the Circular DEQ-2 Standards for Public Sewage Systems, June 3, 2016. The Boulder Creek Apartments are located off Abigail Lane and Sherwood Way on Lots 1-4 of the Boulder Creek Subdivision, Bozeman, Montana. See the vicinity map for location details. ` 1 PROBLEM DEFINED (DEQ 11.11) This project involves the installation of an 8-inch sewer service that will tie into the existing 8- inch main along Abigail Ln. Sewer facilities included in this project will be designed in accordance with Montana Department of Environmental Quality (MDEQ) regulations. Adequate capacity will be provided to allow for growth in areas adjacent to the actual project areas. Flow and population data for the project will be consistent with the City’s approved Facilities Plan, where applicable. 2 DESIGN CONDITIONS The Boulder Creek Apartments are located off of Abigail Lane on Lots 1-4 of the Boulder Creek Subdivision. Three apartment buildings are currently proposed, two 12-plexes and one 18-plex, the eastern 12-plex will be serviced using the proposed sewer main. There are four additional buildings that will be constructed in the future, however only two of the future buildings will be serviced by the proposed water main, one 12-plex and one 18-plex. The Boulder Creek Apartments are located on property zoned R-4 (Residential) per the City of Bozeman’s zoning map. The capacity requirement for the sewer main extension is calculated as follows: Flows to Proposed 8” Sewer Main Residential 42 each apartment units proposed x 2.17 people per dwelling unit (COB Design Standards V- B4) = 91.14 people Total Average Flow Wastewater Flow Rate = 91.14 people x 64.4 gallons per capita day (COB Design Standards V- B4) = 5,869.42 gallons per day (gpd) = 4.08gpm 2 Total Peak Flow Population = 92 people Peaking Factor (PF) = (18+(population/1000)^.5)/(4+(population/1000)^.5) Peaking Factor = 4.25 Peak Flow = 5,869.42gpd (avg daily flow) x 4.25 = 24,964.4gpd = 17.34 gpm Total Flows from Lots 1-4 Residential 96 each apartment units proposed x 2.17 people per dwelling unit (COB Design Standards V- B4) = 208.32 people Total Average Flow Wastewater Flow Rate = 208.32 people x 64.4 gallons per capita day (COB Design Standards V-B4) = 13,415.81 gallons per day (gpd) = 9.32gpm Total Peak Flow Population = 209 people Peaking Factor (PF) = (18+(population/1000)^.5)/(4+(population/1000)^.5) Peaking Factor = 4.14 Peak Flow = 13,415.81gpd (avg daily flow) x 4.14 = 55,554.87gpd = 38.58gpm Please refer to the table below for comparisons between maximum flows and proposed flows and see that that proposed piping is adequate. LOT PEAK FLOW (gpm) PROPOSED CONVEYANCE *MAXIMUM FLOW FOR 8” MAIN (gpm) 1-4 35.58 Future 8-inch sewer main 346 *8-inch pipe at minimum grade (0.4%) with a roughness coefficient (n) value of 0.013 3 IMPACT ON EXISTING WASTEWATER FACILITIES Analysis of the contributing flows to the Laurel Glen Lift Station were done by C&H in a report titled Laurel Glen Lift Station Analysis Design Report May 3, 2020 (attached) to determine if there is additional capacity in the lift station to allow for the construction of the next phase of the Rosa Apartments project. As a part of this report, C&H provided a table of original (2006) flow allocation including Lots 1 through 4 of Block 5 of the Boulder Creek Subdivision. Table 1 in the attached report has the Boulder Creek R-4 Zoning (2002) originally being allocated with 4.27gpm. The total average flow of the three proposed apartment buildings is 4.08gpm. Therefore, the Laurel Glen Lift Station has adequate capacity for this project. 4 PROJECT DESCRIPTION This project involves the installation of 732 feet of an 8-inch sewer service which ties into an existing 8-inch main along Abigail Lane. 3 5 DESIGN CRITERIA Design criteria including average and peak flows as well as sewer depth information were provided in previous sections. The proposed sewer service conforms to the State’s minimum vertical and horizontal separation criteria for sewer services. The proposed conventional gravity sewer collection system is to be constructed to City of Bozeman and the 6th Edition of Montana Public Works (MPW) standard specifications. The sewer service shall be 8-inch diameter SDR 35 Polyvinyl Chloride (PVC) pipe. 6 SITE INFORMATION The project site has been zoned B-2 by the City of Bozeman. The existing site is bound by Lowe’s Home Improvement to the South, Baxter Ln to the North, Simmental way to the West and Sacco Drive to the East. The site has existing grades of less than 4% and has Saypo silt loam and Enbar loam soil deposits (see the USDA Soil Survey information attached). The site is not located in a floodway or floodplain. 7 ENVIRONMENTAL IMPACTS There are no expected environmental impacts from this sewer main extension, as the City of Bozeman Wastewater Treatment Plant has adequate capacity for this extension. 8 OPERATION AND MAINTENANCE Sewer mains will be owned, operated, and maintained by the City of Bozeman.