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HomeMy WebLinkAboutAppendix H - Preliminary Engineering Design Report 4-9-2021 t dhengineering.com 406.586.0277 tdhengineering.com 234 East Babcock Street Suite 3 Bozeman, MT 59715 JOB NO B16-089 SEPTEMBER 2020 CLIENT EAST LAKE PROFESSIONAL CENTER, LLC ENGINEER TD&H ENGINEERING Mr. Randy Scully 5073 Patterson Road Bozeman, MT 59718 Alex Edwards, P.E. 234 E. Babcock St., Suite 3 Bozeman, MT 59715 EASTLAKE PROFESSIONAL CENTER PRELIMINARY ENGINEERING DESIGN REPORT DRAFT DESIGN GUIDELINES t dhengineering.com 1 EASTLAKE PROFESSIONAL CENTER 1 INTRODUCTION The following information is provided to present preliminary infrastructure considerations to direct design of the development over the phased buildout of the project. Utility infrastructure designed for the Eastlake Professional Center (EPC) is designed in accordance with Montana Department of Environmental Quality (DEQ) requirements, City of Bozeman (COB) design standards, and Montana Public Works (MPW) construction specifications. Sequential individual site plans for specific areas within the master site plan will be submitted to the department following approval of the master site plan. Each application for site plan approval will be consistent with the approved master site plan and subject to the review criteria of Section 38.230.100.A of the Bozeman Municipal Code. 2 GENERAL The Eastlake Professional Center is a planned 4 lot Minor Subdivision located on the southeast corner of North 27th and Valley Center Road in Bozeman Montana. The project legal description is defined as Section 26, Township 1 South, Range 5 East, Lot 1A, Gallatin County, Montana. The existing 7.65 acre lot is proposed to be developed by subdivision into 4 lots for commercial use. The property is designated as Community Commercial in the Community Plan and is zoned B-2 (Community Business District). Proposed site improvements, at full buildout, include improvements to North 27th, full construction of Honor Lane from the east property boundary to North 27th, internal paved roads and parking lots, shared use trail connections, water and sewer main infrastructure, commercial service installations, stormwater management facilities, and commercial buildings. The project will be constructed in phases and is being submitted as a COB Master Site Plan (MSP). 3 INFRASTRUCTURE IMPROVEMENTS Construction proposed for phase 1 will include municipal road and trail improvements, one primary access road through the site, 16” and 8” water mains with 2” service sizes provided to each lot, 8” sewer main with 4” services to each lot, internal primary pedestrian access routes, and required signage and site lighting. All infrastructure installed in phase 1 will be sized to handle subdivision flows at full buildout. The following sections describe system design methodology for planned phase 1 construction and proposed future development. 3.1 WASTEWATER COLLECTION SYSTEM EXISTING FACILITIES There is currently no sanitary sewer collection system available at the site. Design for development of the neighboring property to the west is currently under review, and it is anticipated that sewer main infrastructure will be built to the west side of North 27th Avenue prior to phase 1 construction. Wastewater flows generated from EPC will flow west into the new sewer main in North 27th where it will be conveyed through the new Billings clinic campus and continue to the Davis Lift Station. The flows will then be treated at the COB wastewater treatment plant. DRAFT DESIGN GUIDELINES t dhengineering.com 2 EASTLAKE PROFESSIONAL CENTER DESIGN FLOWS New sewer mains are sized to flow below 75-percent capacity at peak hour conditions for the full build out of the Subdivision. Sewer flow rates are projected based on COB design standards, table V-1 “Zoned Undeveloped Areas” for B-2 zoning. An infiltration rate of 150 gallons/acre/day was added to the design flow to account for inflow and infiltration across the site. A peaking factor was calculated for analysis of flow at each pipe segment based on the following formula: 𝑄௠௔௫ 𝑄௔௩௘ =18 +√𝑃 4 +√𝑃 An equivalent population/thousands of 0.14 was estimated for the commercial development resulting in a peaking factor of 4.21 for the entire subdivision. The equivalent population was determined utilizing the COB design standard of 89 gallons/person/day compared to the 2,000 gallons/acre/day for B-2 zoning found in table V-1 of the COB design standards, resulting in an equivalent population of 22.5 people/acre. Table 3-1 summarizes the projected flow conditions for the development. TABLE 3-1 WASTEWATER FLOWS Sewer Segment Contributing Area (Acre) Total Flow (gpm) Peaking Factor Infiltration (gpm) Peak Flow (gpm) Required Pipe Dia. (in.) LOT 1 0.74 1.03 4.21 0.08 4.40 8 LOT 2 1.28 1.78 4.21 0.13 7.62 8 LOT 3 2.06 2.86 4.21 0.21 12.23 8 LOT 4 1.93 2.67 4.21 0.20 11.45 8 TOTAL 6.01 8.34 4.21 0.63 35.70 8 OFFSITE CAPACITY The City of Bozeman engineering department will be relied upon for determination of the current capacity of the wastewater treatment plant. Based on the current COB wastewater collection facilities plan, the Davis lift station has been sized to accept 4,800 gpm. A capacity letter will be requested from the City for approval of new proposed flows into the wastewater plant. CONSTRUCTION New sewer mains shall be constructed of SDR-35 PVC pipe and 48” diameter precast sewer manholes constructed according to COB specifications. A maximum manhole spacing of 400 feet is used and 4” PVC services are proposed for future commercial development. A 4 inch sewer service line constructed at a 2% grade can convey approximately 110 gpm at 75% capacity. Peak flows from individual lots are anticipated to fall below the 75% capacity flow rate. DRAFT DESIGN GUIDELINES t dhengineering.com 3 EASTLAKE PROFESSIONAL CENTER The individual lot services will connect to an 8” PVC main utilizing in-line gasketed wyes. The main will have the capacity to route the peak flow from all the individual sites at or below 75% capacity. The manholes along the sanitary main will be located within a paved road for maintenance access. The sanitary sewer main will be constructed to the extents of the east and south property boundary in order to allow suitable development of adjacent properties. The alignment of the main will be constructed so that there is a minimum of 10 feet of horizontal separation from the water main. The vertical alignment will have a minimum depth of cover of 4’. CONCLUSION Based on proposed development layout and corresponding flow calculations, the proposed wastewater system for the Eastlake Professional Center provides adequate service to meet the flows generated from the proposed development at full buildout. Subsequent reports will be completed for review by the City of Bozeman and DEQ for final approval prior to construction. 3.2 WATER SYSTEM EXISTING FACILITIES There is currently no water infrastructure in place to serve the Eastlake Professional Center. Design for development of the neighboring property to the west is currently under review, and it is anticipated that water main infrastructure will be built to the west side of North 27th Avenue prior to phase 1 construction. A connection will be made to the main extension on the east side of Billings Clinic and routed through the EPC site to allow services to all the proposed lots. The main will be routed through the site and will connect to the future 16” water main located in East Valley Center Road. The connection in East Valley Center Road will ensure that the main is looped. WATER DEMANDS The proposed water main extension will service 4 lots that will each be comprised of future commercial development. The lots are being developed to accommodate a broad range of building layouts and various building sizes to meet prospective business owner needs. All buildings will follow the COB site plan approval process and will be constructed in accordance with building code. The approximate size and layout of each future building is unknown at this time. The water distribution system is designed to meet the maximum peak hour demand plus fire flow for the development. Table 3.8 of the 2017 Water Facility Plan was referenced for the average domestic on the site. The table suggests a demand of 815 gallons/acre/day for regional commercial development. Estimated fire flow demands were generated using the guidelines as determined by the Insurance Services Office. With the individual sites not yet designed, projected fire flow demands are based on conservative building footprints and class 1 building frames at full buildout. The class 1 building frames require the highest fire demands. The occupancy factors were assumed to be 1.0 for unknown sites. It is also assumed that each building will have a sprinkler system and no exposure/communications factors were utilized. DRAFT DESIGN GUIDELINES t dhengineering.com 4 EASTLAKE PROFESSIONAL CENTER Irrigation demand for the Subdivision is estimated based on an assumed irrigation rate of 14 inches (1.16 ft) per year which is slightly above average annual rainfall. The rate is distributed daily for the duration of the watering season, approximately 90 days. A conservative estimate of approximately 25% of the land area on site is used for irrigation area. Irrigation flow result in a total of 4.38 gpm. 𝐼𝑟𝑟𝑖𝑔𝑎𝑡𝑖𝑜𝑛 = 65449 𝑠𝑓 × ଵ.ଵ଺௙௧ ଽ଴ ௗ௔௬௦ × 7.48 ௚௔௟ ௖௙ = 6,310 ௚௔௟௟௢௡௦ ௗ௔௬ or 6,310 𝑔𝑎𝑙𝑙𝑜𝑛𝑠 𝑑𝑎𝑦× 1 𝑑𝑎𝑦 24 ℎ𝑜𝑢𝑟𝑠× 1 ℎ𝑜𝑢𝑟 60 𝑚𝑖𝑛𝑢𝑡𝑒𝑠= 4.38 𝑔𝑎𝑙𝑙𝑜𝑛𝑠 𝑚𝑖𝑛𝑢𝑡𝑒 Table 3.2 summarizes the estimated demand for lots within the Subdivision including estimated flows for irrigation demand and fire flow. Table 3-2 Water Demands Segment Contributing Area (Acre) Irrigation Demand (gpm) Avg. Domestic use (gal/day) Fire Flow (gpm) Peak Flow (Avg. Day x 3 + NFF) (gpm) LOT 1 0.74 0.54 605 2900 2902 LOT 2 1.28 0.93 1045 4050 4053 LOT 3 2.06 1.50 1680 1150 1155 LOT 4 1.93 1.40 1570 3190 3192 The subtotal for domestic use and irrigation demands for the subdivision is 7.78 gpm. The maximum peak flow demand is 11,302 gpm. CONSTRUCTION The proposed water main extension will serve individual lots within the subdivision. It is anticipated that the site to the east will be developed in the future. The proposed 16” water main loop will allow for suitable development of the adjoining un-developed land. The main is sized in the COB 2017 Water Facility Plan and therefore is assumed to be adequately sized for all development in the area. The main will be constructed at a minimum depth of cover of 6.5’ below finished grade. The alignment will keep 10’ of horizontal separation between the sanitary main and will have a minimum of 18” vertical separation between sanitary and storm sewer crossings. CONCLUSION Based on proposed development layout and projected water demands, the proposed potable water system for the Eastlake Professional Center is designed with adequate capacity to serve the proposed development at full buildout. Subsequent reports will be completed for review by the City of Bozeman and DEQ for final approval prior to construction. DRAFT DESIGN GUIDELINES t dhengineering.com 5 EASTLAKE PROFESSIONAL CENTER 3.3 STORM SEWER SYSTEM EXISTING CONDITIONS The existing property is undeveloped and previously used for agriculture. The area surrounding the Subdivision is also currently undeveloped. In general, the site is separated in the center of the lot from north to south by a gentle ridgeline. The site naturally slopes to the north towards a swale that travels along the north side of the property. Soil information for the area is available through the Natural Resources Conservation Service (NRCS). The site resides on 100% Blackdog silt loam with 0 to 4 percent slopes. SITE IMPROVEMENTS The proposed site for development is currently comprised of 1 lot that will be subdivided for commercial use. Four lots will be devoted to commercial development with stormwater runoff being treated on each individual site. The buildings will range from 6,000 to 9,000 S.F. footprints. The lots will be accessed by a 24’ wide paved road with access points along Honor Lane to the south and North 27th Avenue to the west. A shared use asphalt trail will be constructed along East Valley Center Road that will connect to the proposed concrete sidewalks throughout the development. Stormwater runoff from North 27th Avenue and Honor Lane improvements will be treated within the North 27th R-O-W. The remaining lots will provide individual detention/retention ponds to treat the stormwater runoff on each individual lot. Temporary retention will be provided, if necessary, on each site to treat the runoff from the internal roads and sidewalks that will be constructed in each phase of construction. Table 3.3 summarizes flows for each of the lots within the development for the internal roads and sidewalks (assuming the individual site is not yet constructed). Each lot will make provision for adequate storage of run-off in subsequent site plan submittals. TABLE 3-3 STORMWATER RUNOFF ESTIMATES Segment Contributing Area (Acre) Pre. Dev. Q10 (cfs) Post. Dev. Q10 (cfs) 10-year Retention Volume (CF) LOT 1 0.74 0.11 0.67 303 LOT 2 1.28 0.20 1.60 714 LOT 3 2.06 0.32 0.39 299 LOT 4 1.93 0.27 0.27 0 N. 27TH 1.93 1.88 3.58 829 DRAFT DESIGN GUIDELINES t dhengineering.com 6 EASTLAKE PROFESSIONAL CENTER 4 PHASING CONSTRUCTION SEQUENCING The site is anticipated to be developed in a maximum of 5 phases, however phases may be combined if individual site design schedules overlap. The 1st stage of construction will include the improvements to North 27th Ave, North 27th stormwater retention pond, Honor Lane, water and sanitary main extensions, internal pedestrian access and partial construction of internal private roads. Once stage 1 items are in place, the individual lots will be furnished with the necessary infrastructure to begin construction any time thereafter. Phase 2, 3, 4 and 5 may all be independent phases for individual site construction. PHASING CONTINGENCIES Each lot within the subdivision has adequate space for staging as well as storage locations for topsoil, spoils, and construction materials. In the event the development requires a different build sequence than what has been proposed on the master site plan, the proposed staging and storage locations will be relocated to a different lot. Preferably, it will be located on the last lot to be developed.