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Home My WebLink About021 Sanitary Sewer ReportSANITARY SEWER REPORT The Cottonwood Apartments – BLOCK 1, LOTS 1 & 2 The Cottonwood Apartments – Phase 2, Bozeman, Montana 59718 Block 1 – Lots 1 and 2, Cottonwood Subdivision (Site Plan Packages F & G) Prepared For: Roundhouse Attn: Patrick Boel Director of Development & Construction 1100 West Idaho Street, Ste 630 Boise, ID 83702 Prepared By: Cushing Terrell 411 E. Main Street, Ste. 101 Bozeman, MT 59715 www.cushingterrell.com Cushing Terrell Project No. Cottonwood_P2 December 18, 2024 Adam Schlegel, PE Sanitary Sewer Report The Cottonwood Apartments – Block 1, Lots 1 & 2 and Block 2, Lot 1 Project No. Cottonwood_P1 cushingterrell.com i TABLE OF CONTENTS 1.0 INTRODUCTION ................................................................................................................................................. 1 1.1 Zoning ............................................................................................................................................................... 3 1.2 Existing Ground Cover and Vegetation ................................................................................................ 3 1.3 Topographic Features, and Slopes ......................................................................................................... 4 1.4 FEMA Floodplain Classification................................................................................................................ 4 1.5 Wetlands .......................................................................................................................................................... 4 1.6 Geologic Features and Geotechnical Data .......................................................................................... 4 2.0 SANITARY SEWER DESIGN ............................................................................................................................. 4 2.1 Pipe Capacity Analysis – 8” Sanitary Sewer Main Extension ......................................................... 4 2.2 Flow Analysis .................................................................................................................................................. 5 3.0 CONCLUSION ..................................................................................................................................................... 6 LIST OF FIGURES Figure 1.1: Overall Location Map .............................................................................................................................. 2 Figure 1.2: Project Map ................................................................................................................................................ 3 LIST OF TABLES Table 2.1: SS Main Extension Flows ........................................................................................................................ 5 Table 2.2: Package E Flows ......................................................................................................................................... 5 APPENDICES Appendix A: Geotechnical Report Excerpts Appendix B: Cottonwood Subdivision Sanitary Sewer Report Excerpts Appendix C: Cottonwood Phase 1 Sanitary Sewer Report Appendix D: Loyal Garden Lift Station Analysis Excerpts Appendix E: Calculations and Back-Up Data Sanitary Sewer Report The Cottonwood Apartments – Block 1, Lots 1 & 2 and Block 2, Lot 1 Project No. Cottonwood_P1 cushingterrell.com 1 1.0 INTRODUCTION Roundhouse Development Group proposes a multifamily housing development on Lots 1 and 2 of Block 1 and Lot 1 of Block 2 of the Cottonwood Subdivision, Phase 2, generally located east of Cottonwood Road and south of Huffine Lane. The housing development will utilize the previously approved and installed public water and sewer utilities (EQ#20-1840). Additionally, the housing development will utilize the existing subdivision stormwater detention facilities and connect to the existing stormwater infrastructure in Stafford Avenue and along the north side of the property boundary. The development has been separated into three different site plan packages (E, F, and G). Site plan package E covers Lot 1, Block 2. Package F covers Lot 1, Block 1. Package G covers Lot 2, Block 1. The following figures show the boundaries of the different site plan packages and project location. The intent and purpose of this report is to request a public sewer main extension to service Building #19 - #23 within in Block 1, as it is not practical to service the buildings from the adjacent streets with traditional services. Additionally, the report will provide an update to overall wastewater flows for the subdivision to account for the actual proposed development. This report will reference the previously approved subdivision engineering reports prepared by Madison Engineering titled “WASTEWATER SYSTEM DESIGN REPORT FOR: COTTONWOOD SUBDIVISION BOZEMAN, MT” dated March 2020 and by Cushing Terrell titled “SANITARY SEWER REPORT The Cottonwood Apartments – Block 3, Lots 1 & 2” dated December 23, 2020. See Appendix B and C for original report excerpts. It is important to note that buildings 15 and 18 within Package E will be served by existing sanitary sewer stubs from Stafford Ave. Buildings 16 and 17 within Package E will not contain water/wastewater facilities. The following references were used in the design of the sanitary sewer main extension. • EQ# 20 -1840 • Wastewater System Design Report – For: Cottonwood Subdivision, Bozeman, MT. Prepared by: Madison Engineering. Dated: March 2020. See Appendix B. • Sanitary Sewer Report The Cottonwood Apartments – Block 3, Lots 1 & 2” dated December 23, 2020. See Appendix C. • Loyal Garden Lift Station Analysis Report – For: Cottonwood Subdivision, Bozeman, MT. Prepared by: Madison Engineering. Dated: March 2020. See Appendix D. • COB Design Standards and Specifications Policy, 2004. Addendum #6 (DSSP) • COB Modifications to Montana Public Works Standard Specifications (MPWSS), Addendum #3 • City adopted MPWSS and Adopted Addenda • COB Wastewater Facility Plan, 2015 • WQB Circular No. 2 • City of Bozeman Zoning Map Sanitary Sewer Report The Cottonwood Apartments – Block 1, Lots 1 & 2 and Block 2, Lot 1 Project No. Cottonwood_P1 cushingterrell.com 2 Figure 1.1: Overall Location Map Sanitary Sewer Report The Cottonwood Apartments – Block 1, Lots 1 & 2 and Block 2, Lot 1 Project No. Cottonwood_P1 cushingterrell.com 3 Figure 1.2: Project Map 1.1 Zoning The subject properties are zoned R5: Residential Mixed-Use High-Density District. This zoning matches the zoning assumed in the original engineering report. 1.2 Existing Ground Cover and Vegetation The subject properties are serviced by the existing subdivision streets and City utilities (water, sewer, and storm). Internal lot areas are stripped of topsoil and have various stockpile locations as a result of the construction of the off-site infrastructure. Sanitary Sewer Report The Cottonwood Apartments – Block 1, Lots 1 & 2 and Block 2, Lot 1 Project No. Cottonwood_P1 cushingterrell.com 4 1.3 Topographic Features, and Slopes Blocks 1 & 2 slope from the east to the west towards S Cottonwood. Significant topographic features on site include stockpiles reaching heights of 15’ as a result of construction during phase 1 of this development. Stockpiles and excess dirt in these lots will be removed during the construction of phase 2. 1.4 FEMA Floodplain Classification Per FEMA FIRM Panel #30031C0811D, there are no FEMA determined floodplains on or near the subject property. 1.5 Wetlands Wetlands were previously located within the subdivision but have since been mitigated as part of the subdivision infrastructure work (Corps No. NWO-2017-02234-MTH, Type: NWP 29). 1.6 Geologic Features and Geotechnical Data See Appendix A for the geotechnical investigation excerpts from the report prepared by Allied Engineering Services, Inc. titled, “Cottonwood Subdivision Southeast Side of Huffine Ln/Cottonwood Rd Bozeman MT” dated January 2019. The full report can be provided upon request. 1.6.1 Soils Overall, the report indicates the soils in the area consist of topsoil in the upper ten inches, underlain by eight inches of native silt/clay, underlain by approximately ten feet of a native sandy gravel. Borehole logs and an excerpt on subsurface conditions are located in Appendix A. 1.6.2 Groundwater The report does indicate the presence of groundwater in the project area. The borehole logs indicate varying levels throughout the site from 3.7’ to 5.1’ below the ground surface. See Appendix A for excerpts. 2.0 SANITARY SEWER DESIGN 2.1 Pipe Capacity Analysis – 8” Sanitary Sewer Main Extension The proposed 371 linear foot 8” main extension will slope to the south with an approximate slope of 0.4% and connect to an existing stub that extends north from the W Garfield Street 8” main. Assuming a 0.4% slope, 8” diameter pipe, roughness coefficient of 0.013, and 75% full flow capacity the proposed extension will have an approximate capacity of 0.70 cfs or 316 gpm. The proposed main extension has adequate capacity to convey the proposed peak hour flow of 0.08 cfs. Sanitary Sewer Report The Cottonwood Apartments – Block 1, Lots 1 & 2 and Block 2, Lot 1 Project No. Cottonwood_P1 cushingterrell.com 5 2.2 Flow Analysis The following table indicates the expected flows required to be conveyed by the proposed extension. The total approximate average daily flow required to be conveyed by the extension is 13,416 GPD (9.32 gpm or 0.16 cfs). Table 2.1: SS Main Extension Flows Table 2.2: Package E Flows The City approved Loyal Garden Lift Station Analysis Report prepared for Cottonwood Subdivision indicated approximately 76,778 gpd was available for use by the Cottonwood Subdivision. Additionally, the report estimated an average daily flow of 55,900 gpd for the Cottonwood Subdivision (400 units at full build) and excess lift station capacity of 20,878 gpd to be utilized on a first come, first serve basis. Roundhouse has paid for the additional capacity available. CONTRIBUTING BUILDINGS # OF UNITS DENSITY (PERSONS /UNIT) POPULATION (PERSONS) AVG. DAILY UNIT FLOW RATE (GPD PER CAPITA) ADF (GPD) 1BUILDING #19 - TYPE C 24 2.17 52 64.4 3,354 1BUILDING #20 - TYPE A 12 2.17 26 64.4 1,677 1BUILDING #21 - TYPE C 24 2.17 52 64.4 3,354 1BUILDING #22 - TYPE A 12 2.17 26 64.4 1,677 1BUILDING #23 - TYPE C 24 2.17 52 64.4 3,354 96 208 TOTAL ADF =13,416 COTTONWOOD APARTMENTS | SANITARY SEWER USAGE - SITE PLAN PACKAGES F & G 1AVERAGE DAILY FLOW IS BASED ON THE UNIT DEMAND OF 64.4 GAL./PERSON/DAY AND 2.17 PERSONS PER HOUSEHOLD. THIS INFORMATION IS PROVIDED ON PAGE OF 2015 WASTEWATER COLLECTION FACILITIES PLAN UPDATE. CONTRIBUTING BUILDINGS # OF UNITS DENSITY (PERSONS /UNIT) POPULATION (PERSONS) AVG. DAILY UNIT FLOW RATE (GPD PER CAPITA) ADF (GPD) 1BUILDING #15 - TYPE C 12 2.17 26 64.4 1,677 1BUILDING #18 - TYPE A 24 2.17 52 64.4 3,354 36 78 TOTAL ADF =5,031 COTTONWOOD APARTMENTS | SANITARY SEWER USAGE - SITE PLAN PACKAGE E 1AVERAGE DAILY FLOW IS BASED ON THE UNIT DEMAND OF 64.4 GAL./PERSON/DAY AND 2.17 PERSONS PER Sanitary Sewer Report The Cottonwood Apartments – Block 1, Lots 1 & 2 and Block 2, Lot 1 Project No. Cottonwood_P1 cushingterrell.com 6 3.0 CONCLUSION To conclude this report, updated estimated subdivision wastewater flows are provided below. The proposed sanitary sewer main extension has adequate capacity to convey the proposed flows from Block 1 – Lots 1 and 2. Additionally, the downstream 0.4% sloped 8” sanitary sewer mains have adequate capacity to carry flows from this extension as well as from the additional flows from site plan E. See Appendix E for calculations. Cottonwood Sub - Average Day Flow =13,416 GPD (SS Main Extension in package F & G) + 5,031 GPD (Flows from site plan E) + 36,376 (Total ADF from Phase 1) = 54,823 GPD or 0.08 cfs • Note: Previous estimate showed 55,900 GPD. Peaking Factor = 3.87. See Appendix D for calculation. Cottonwood Sub - Peak Hour Flow = 3.87 * 54,823 GPD + 150 gal/day/acre * 28.09 acres (4,214 GPD) = 216,379 GPD or 0.33 cfs. • Note: Previous estimate showed 218,870 GPD or 0.34 cfs. cushingterrell.com Appendix A: Geotechnical Report Excerpts Cottonwood Subdivision Huffine Lane / Cottonwood Road – Bozeman, MT Project: 17-170 January 9, 2019 Allied Engineering Services, Inc. Page 6 Soil Conditions The site can simply be characterized as being underlain by good, dense, clean sandy gravel beginning at depths of 1.5 to 2.5 feet across the entire property. The gravels in this part of Bozeman are expected to extend at least 100 feet deep and were confirmed to the 50-foot depth during the borehole drilling that was conducted at the Bozeman Health Ambulatory Care Facility. The presence of the shallow gravel is not surprising and has been pretty consistent in the other nearby areas we have recently investigated, including the Town Pump site to the north, the Bozeman Health ACF to the northwest, and the Cottonwood Road corridor to the north of Huffine Lane. Based on the eight test pits, the gravels have a “clean” and sandy composition and are relatively small in size. Most of the gravel is a 3” to 4”-minus material, but it does contain scattered cobbles up to 6 to 8 inches. The gravels were uniform through- out the 10 to 11-foot test pit depths. See Figure 4 for the distribution of gravel depth across the site. No random/foreign surface fill material was found in any of the test pits. All soils were native and in- place. The site is blanketed by 9 to 12 inches of organic topsoil. Underlying the topsoil and overlying the sandy gravel is a thin, intermediate layer of silt/clay. In most locations, the silt/clay was stiff to very stiff and the lowermost 0.5-foot of the silt/clay contained some scattered small gravels (as the interface with the alluvial sandy gravel was neared). Really, the only anomalies were found in TP-7, which was located on the south side of the site. At this location, the same soil stratigraphy is present, but the topsoil was more gravelly and the silt/clay was not only more gravelly, but very moist and much less stiff. Provided in Table 3 is a summary of the soil conditions that were observed in the eight test pits. The material descriptions and soil depths in the table match the data shown on the logs. Table 3. Summary of Soil Conditions in Test Pits 1 - 8 TP # TP LOCATION NATIVE TOPSOIL NATIVE SILT/CLAY NATIVE SANDY GRAVEL 1 N1/2 of Site, NW Corner 0.0’ - 1.0’ 1.0’ - 1.7’ 1.7’ - 10.0’ 2 N1/2 of Site, NE Corner 0.0’ - 0.8’ 0.8’ - 2.0’ 2.0’ - 11.0’ 3 N1/2 of Site, Center 0.0’ - 0.8’ 0.8’ - 1.8’ 1.8’ - 11.0’ 4 Middle of Site, Center 0.0’ - 0.8’ 0.8’ - 1.5’ 1.5’ - 11.0’ 5 Middle of Site, East Side 0.0’ - 0.8’ 0.8’ - 2.2’ 2.2’ - 11.0’ 6 S1/2 of Site, SE Corner 0.0’ - 1.0’ 1.0’ - 2.3’ 2.3’ - 10.0’ 7 S1/2 of Site, South Side 0.0’ - 1.0’ 1.0’ - 2.0’ 2.0’ - 10.0’ 8 S1/2 of Site, West Side 0.0’ - 0.8’ 0.8’ - 2.2’ 2.2’ - 10.0’ Notes: 1) All soil measurements are depths below existing ground. 2) The native silt/clay is an unsuitable bearing material and shall be removed from under all footing locations. 3) The “target” bearing material for all foundation elements is the dense, native sandy gravel starting at 1.5’ to 2.5’. 4) Generally, the lower 0.5-foot of silt/clay (in all test pits) contained some scattered, small gravels. 5) In TP-7, the silt/clay was more gravelly, more moist, and less stiff (as compared to the other seven pits). 6) PVC monitoring wells were installed in TP-1 through TP-8 for future groundwater monitoring purposes. Cottonwood Subdivision Huffine Lane / Cottonwood Road – Bozeman, MT Project: 17-170 January 9, 2019 Allied Engineering Services, Inc. Page 7 Provided below is a general description of the soil conditions encountered in the test pits. Following each soil description is a statement regarding foundation bearing potential for the particular soil type. • Native Topsoil: Generally consists of moist; medium stiff; black to dark brown; organic clayey SILT with abundant roots.  The native topsoil is an unsuitable foundation bearing material that must be removed from under all footings. In addition, all organic topsoil must be stripped/removed from building footprints, utility trench locations, and under exterior slabs and asphalt areas. • Native Silt/Clay: Generally consists of moist; stiff to very stiff; brown to orangish brown; sandy SILT to sandy lean CLAY. The lower six inches (+/-) of silt/clay directly above the underlying sandy gravel contains some scattered gravels. This transitional zone does not constitute clean sandy gravel. In most pits, the silt/clay was on the dry side (due to relatively deep groundwater) and consequently these soils were in a stiff to very stiff condition. Really the only exception was in TP-7, which is located on the south side of the property and closest to the Farmers Canal. At this location, the silt/clay was very moist and hence less stiff (ie. little softer than other areas).  The native silt/clay is an unsuitable foundation bearing material that must be removed from under all footings. • Native Sandy Gravel: Generally consists of slightly moist to wet; dense; brown; clean sandy GRAVEL with abundant 3” to 4”-minus gravels and scattered 6” to 8”-minus cobbles. The on-site gravel is a very good reserve of high-quality, sandy pitrun gravel and can be re-used as granular structural fill under buildings or as sub-base gravel under asphalt areas.  The native, clean sandy gravel is the “target” foundation bearing material for all footings, including perimeter, interior, and exterior footings. Groundwater Conditions During our test pits in January, groundwater was encountered at depths of 7.0 to 9.0 feet in the north, central, and eastern parts of the site. Two pits (TP-7 and TP-8) were dug in the southwest portion of the property where the surface terrain appeared to be a little lower. In both of these pits, the groundwater table was shallower and found at 5.0 feet. The depth of the water relative to the top of the native sandy gravel was generally 5.0 to 7.0 feet below the gravel in most areas, but decreased to 2.8 to 3.0 feet in the southwest corner. See Figure 5 for the distribution of groundwater depth across the site. Provided in Table 4 (on the following page) is a summary of the groundwater measurements in each of the test pits, along with its positon relative to the top of the sandy gravel. As stated previously, all test pits were backfilled with PVC monitoring wells. The approximate casing height of each well is also listed in the table. DEPARTMENT OF THE ARMY CORPS OF ENGINEERS, OMAHA DISTRICT HELENA REGULATORY OFFICE 10 WEST 15TH STREET, SUITE 2200 HELENA, MONTANA 59626 REPLY TO ATTENTION OF Printed on Recycled Paper January 19, 2018 Regulatory Branch Montana State Program Corps No. NWO-2017-02234-MTH Subject: TKO Enterprises (Vaughn Environmental Services) - Cottonwood Subdivision - Farmer's Canal - (Gallatin County) Tyson Olsen TKO Enterprises Po Box 10303 Bozeman, Montana 59719 Dear Mr. Olsen: We are responding to your request for Nationwide Permit (NWP) verification for the above-mentioned project. The project is located at Latitude 45.665522°, Longitude -111.101588°, on or near Farmers Canal, within Section 15, Township 2 S, Range 5 E, Gallatin County, Montana. Specifically, you requested authorization for the following work in waters of the U.S.: Work Item Description a. Approximately 1,095 cubic yards (cy3) of native fill, 361 cy3 of 6-inch minus of uncrushed subbase course, 123 cy3 of 1.5-inch crushed gravel and 96 cy3 of asphalt will be used to fill 0.307 acre of jurisdictional wetland in preparation to develop are for a residential subdivision. In addition, a 30-inch reinforced concrete culvert will be placed across Cottonwood road and will be extended 22 linear feet. Based on the information you provided, the proposed activity, permanently affecting approximately 0.307 acre of jurisdictional Wetlands, is authorized by NWP 29, found in the January 6, 2017, Federal Register (82 FR 1860), Reissuance of Nationwide Permits. Enclosed is a fact sheet that fully describes this NWP and lists the General and Regional Conditions that must be adhered to for this authorization to remain valid. Please note that deviations from the original plans and specifications of your project could require additional authorization from this office. In addition to conditions referenced above, the following special conditions apply: Condition Description 1. Compensatory mitigation will be required for the 0.307 acre of unavoidable impacts to the wetlands adjacent to Farmers Canal. It has been determined that a practicable alternative to compensate for the aquatic resource functions that will be lost as a result of the permitted activity is mitigation by a third party provider. You have selected the Upper Missouri Mitigation Bank (SRI Missouri Headwaters, -2- Printed on Recycled Paper LLC and Eco-Asset Management, LLC) as the party or parties responsible for the implementation, performance, and long-term management of the compensatory mitigation project (332.3[l][1]) and so the following specific provisions apply: 1. Credits must be secured from a third party provider authorized by the U.S. Army Corps of Engineers to provide the mitigation; 2. Credits must come from the same service area as the permitted impacts, as specified in the authorized third party provider’s mitigation strategy or executed Banking Agreement; and The applicant must use the authorized third party provider’s credit multipliers in determining the amount of credits to be purchased (for Upper Missouri Mitigation Bank the multipliers are the same as for the Omaha District) namely (i) released credits are secured on a 1:1 ratio (1 impact debit to 1 mitigation credit), and (ii) after-the-fact credits are secured on a 1:1.5 ratio. In this case 0.307 acres of wetland mitigation credits will be required prior to working in Waters of the U.S., provide this office with documentation of completion of the transaction for securing credits. This can be a letter from the third party provider stating its acceptance of responsibility for the specified mitigation. You are responsible for ensuring that all work is performed in accordance with the terms and conditions of the NWP. If a contractor or other authorized representative will be conducting work on your behalf it is strongly recommended that they be provided a copy of this letter and the enclosed conditions. Failure to comply with the General and Regional Conditions of this NWP, or the project-specific special conditions of this authorization, may result in the suspension or revocation of your authorization and may be subject to appropriate enforcement action. The Montana Department of Environmental Quality has provided the enclosed CWA Section 401 water quality certification for this NWP which includes General Conditions, all of which must be complied with for that certification to remain valid. This does not eliminate the need to obtain other permits that may be required by that agency. This verification is valid until March 18, 2022, when the existing NWPs are scheduled to be modified, reissued, or revoked. Furthermore, if you commence or are under contract to commence this activity before the date that the relevant NWP is modified, reissued or revoked, you will have twelve (12) months from the date of the modification, reissuance or revocation of the NWP to complete the activity under the present terms and conditions unless discretionary authority has been exercised on a case-by-case basis to modify, suspend, or revoke the authorization in accordance with 33 CFR 330.4(e) and 33 CFR 330.5 (c) or (d). Project specific special conditions listed in this letter continue to remain in effect after the NWP verification expires, unless the district engineer removes those conditions. Activities completed under the authorization of an NWP which was in effect at the time the activity was completed continue to be authorized by that NWP. In compliance with General Condition 30, we have enclosed a "compliance certification" form, which must be signed and returned within 30 days of completion of the project, including -3- Printed on Recycled Paper any required mitigation. Your signature on this form certifies that you have completed the work in accordance with the terms and conditions of the NWP. The Omaha District, Regulatory Branch is committed to providing quality and timely service to our customers. In an effort to improve customer service, please take a moment to complete our Customer Service Survey found on our website at: http://corpsmapu.usace.army.mil/cm_apex/f?p=regulatory_survey. If you do not have Internet access, you may call and request a paper copy of the survey that you can complete and return to us by mail or fax. Please refer to identification number NWO-2017-02234-MTH in any correspondence concerning this project. If you have any questions, please contact Timothy McNew at Helena Regulatory Office 10 West 15 Street, Suite 2200 Helena, Montana 59626, by email at Timothy.M.McNew@usace.army.mil, or telephone at (406) 441-1375. Sincerely, Todd N. Tillinger P.E. Montana Program Manager Enclosures: Compliance Certification NWP 29 Fact Sheet with Regional Conditions Montana DEQ CWA Section 401 Water Quality Certification cc: Barb Vaughn via e-mail: bvaughn@montana.com -4- Printed on Recycled Paper COMPLIANCE CERTIFICATION Corps File Number: NWO-2017-02234-MTH Permit Type: NWP 29 Name of Permittee: Tyson Olsen County: Gallatin County, Montana Date of Issuance: January 18, 2018 Corps Project Manager: Timothy McNew Upon completion of the activity authorized by this permit and any mitigation required by the permit, sign this certification and return it to the following address: US Army Corps of Engineers Omaha District Helena Regulatory Office 10 West 15 Street, Suite 2200 Helena, Montana 59626 Please note that your permitted activity is subject to a compliance inspection by a U.S. Army Corps of Engineers representative. If you fail to comply with the conditions of this permit, you are subject to permit suspension, modification, or revocation. - - - - - - - - - - - - - - - - - - - - - - - - - - - I hereby certify that the work authorized by the above referenced permit has been completed in accordance with the terms and conditions of the said permit, and required mitigation was completed in accordance with the permit conditions. _______________________________________ Signature of Permittee ___________________ Date cushingterrell.com Appendix B: Cottonwood Subdivision Sanitary Sewer Report Excerpts Cottonwood Subdivision Wastewater Design Report Page 1 of 5 COTTONWOOD SUBDIVISION WASTEWATER SYSTEM DESIGN REPORT A. General This report will give an overview of the proposed wastewater collection system for the development of the Cottonwood Subdivision, located at the intersection of Cottonwood Road and Loyal Drive in Bozeman. The 28.09-acre subdivision is zoned R-5 (Residential Mixed-Use High Density District) and will consist of multi-residential units. The proposed improvements are anticipated to be phased, with the first phase being constructed in 2021. Included in this report is a description of the proposed wastewater collection system and design parameters. Once the wastewater system is constructed and approved, the system will become a part of the City of Bozeman system. The following references were used in the wastewater facilities design and capacity analysis: a. COB Design Standards and Specifications Policy, 2004. Addendum #6 (DSSP) b. COB Modifications to Montana Public Works Standard Specifications (MPWSS), Addendum #3 c. City adopted MPWSS and Adopted Addenda d. COB Wastewater Facility Plan, 2015 e. WQB Circular No. 2 f. City of Bozeman Zoning Map The procedures and parameters outlined in the COB Design Standards and Specifications Policy (DSSP) were used in the design of the sewer infrastructure for the proposed development. This project will require the approval of the City Engineer and the Montana Department of Environmental Quality (MDEQ). A.1. Site Conditions Soil conditions on site consist of a native topsoil to a depth of approximately 12 inches, which is underlain by a thin, intermediate layer of stiff, silt/clay. Beginning at depths of 1.2 to 2.5 feet is an alluvial deposit of clean, sandy gravel that underlies much of the Bozeman area at relatively shallow depths. This clean, sandy gravel extended to the bottom of all 10 to 11 foot test pits. Groundwater depths on site are, on average, to a depth of 7 to 9 feet in the north, central, and east sides of the property, but at a shallower 5-foot depth on the south and southwest sides. Groundwater levels were monitored during the spring and summer of 2018. The highest groundwater levels were recorded in mid-April and showed shallow water conditions across the site. Throughout most of the site, the seasonal high-water depths ranged from 3 to 4 feet, but rose to as high as 1.0 to 2.5 feet below the ground surface in the site’s southwest corner. Water flows on site in a northwesterly direction. Buoyancy calculations can be found in Appendix 6 of this report. Although groundwater is highest in the southwestern most area of the site, there are no manholes proposed in that area and so buoyancy calculations were performed on the southernmost manhole (SSMH#15). Buoyancy calculations were based on the highest groundwater elevation of 1-foot depth because this is an incredibly conservative estimate for all manholes in the entire site. Cottonwood Subdivision Wastewater Design Report Page 2 of 5 No basements are advised on site. Crawl spaces are only recommended if the depth is limited below existing site grades, in-filling the crawl space up to the top of footings with a clean crushed rock layer, and installing subsurface drainage measure. Otherwise, at-grade slabs with perimeter footings and frost wall are recommended. The site is in an “Area of Minimal Flood Hazard” per the FEMA Panel 30031C0811D. A.2. Environmental Impacts Potential environmental impacts could include affecting the soil, groundwater, waterways, and wetlands on or off site. Cumulative and secondary impacts have been taken into consideration and minimized through design and permitting processes. Impacts to the soil, groundwater, and waterways will be minimized and mitigated through directing all stormwater runoff from on site into retention and detention basins that will allow any contaminants and sediment to settle before being discharged. Wetland impacts on site have been fully permitted. B. Capacity Analysis The proposed wastewater system will provide service to Cottonwood Subdivision as well as 16.71 acres of future development to the east. The 16.71 acres to the east is currently in Gallatin County, so it was assumed that it will be zoned as R-4 (Residential High Density District) when it is annexed into the City of Bozeman. The wastewater demand was estimated on a per capita basis for Cottonwood Subdivision and on a per acre basis for the future 16.71 acres of future development to the east (see Tables 2 & 3). The City of Bozeman's Design Standards do not specify an average daily flow rate for R-5 zoning, so the flow rates were calculated using the proposed number of units (400 units) and the updated residential daily flow of 64.4 gal./person/day combined with the value of 2.17 persons per household. This information is not published in the City Design Standards, but rather found on page 5 of the 2015 Wastewater Collection Facilities Plan Update (see Appendix 7). It has been confirmed with the City of Bozeman Engineering Department that these updated figures should be used for design of sanitary sewers and not the values of 89 gal./person/day and 2.11 person per household published in the design standards. The Standards specify an average daily flow rate of 1,950 gal/acre/day for R-4 development, obtained from Table V-1. This value is used to estimate flows from the adjacent 16.71-acre future development to the east. Inflow and Infiltration (I&I) were estimated based on the City Standard 150 gallons per acre per day (see Table 1). The proposed sewer mains have been sized to flow at no more than 75-percent of full capacity at peak hour conditions of full build out, and a Manning coefficient of 0.013 was used for PVC pipe. Cottonwood Subdivision Wastewater Design Report Page 3 of 5 Table 1: I & I Estimates for Cottonwood Subdivision and future development to the east Sewer System I & I (gal/acre/day) Area (acres) Total I & I (gal/day) Cottonwood Subdivision 150 28.09 4,214 Future Development to the East 150 16.71 2,507 Total 6,721 Table 2: Sanitary Sewer Flow Estimates for Cottonwood Subdivision Sewer System Proposed no. of units Density (Persons /unit) Total no. of people Avg. Daily Flow Rate (gpd) Peaking factor Peak Flow Rate (gpd) Peak Flow Rate + I&I (gpd) Peak Flow Rate + I&I (cfs) Cottonwood Subdivision 400 2.17 868 55,900 3.84 214,656 218,870 0.34 Table 3: Sanitary Sewer Flow Estimates for future development to the east Sewer System Wastewater Loading (gpd/acre) Area Served (acres) Avg. Daily Flow Rate (gpd) Peaking Factor Peak Flow Rate (gpd) Peak Flow Rate + I&I (gpd) Peak Flow Rate + I&I (cfs) Future Development to the East 1,950 (assumed) 16.71 (assumed) 32,585 4.03 131,318 133,825 0.21 The calculated peaking factors are included in Appendix 5 of this report. The peak flow rate anticipated from the development was calculated by multiplying the average daily flow rate by the peaking factor and then adding the I &I. The peak flow rate was then converted from gallons per day (gpd) to cubic feet per second (cfs). Adding the peak flow rate from Cottonwood Subdivision of 0.34 cfs to the peak flow rate from the future development to the east of 0.21 cfs yields a design peak flow rate value of 0.55 cfs. The sewer main sizes for the all streets will be 8-inch based on minimum required pipe size and slope. An 8-inch PVC sewer main at 0.40% slope has a capacity of 0.64 cfs at 75% of full flow capacity, which has adequate capacity for the proposed peak flows. Calculations are provided in Appendix 1 of this report. Cottonwood Subdivision Wastewater Design Report Page 4 of 5 C. Proposed Collection System With the extension of local streets within the subdivision, 48-inch manholes (spaced a maximum of 400-feet apart) with 8-inch sanitary sewer main will be installed to serve the proposed lots. All 8-inch sanitary sewer mains within the subdivision will drain to the west into the existing 15-inch sanitary sewer main in Cottonwood Road. This 15-inch main in Cottonwood Road drains to the Loyal Garden lift station. The lift station capacity is discussed in the following section D of this report. PVC pipe meeting COB specifications will be used for all sewer mains. The sewer main will maintain a minimum separation of 10-feet horizontally and 18-inches vertically from any proposed or existing public water mains. D. Downstream Capacity Analysis The sanitary sewer mains were designed in conformance with the City of Bozeman Wastewater Improvement Plan. Cottonwood Subdivision will be served by the Loyal Garden Subdivision Lift Station until sewer main improvements are installed in Cottonwood Road per the Facility Plan. These improvements include a sewer main in Cottonwood Road from the intersection of Durston Road to approximately 460 feet south of Huffine Lane. The original Loyal Garden lift station was designed to serve Loyal Garden Subdivision and an "additional 140 acres" located to the south and to the east of Loyal Garden. The 28.09-acre Cottonwood Subdivision falls within this “additional 140-acre” area and is therefore intended to be served by the Loyal Garden lift station. In 2019, the City of Bozeman Engineering Department decided that the remaining capacity in the Loyal Garden lift station would be allocated on a first- come first-served basis. A capacity analysis of the lift station was performed by Madison Engineering during the winter of 2019-2020. As of this writing (March 2020), that report is under review at the City of Bozeman Engineering Department. The analysis found that adequate capacity is available in the Loyal Garden lift station to serve the entirety of Cottonwood Subdivision. The lift station analysis report is included in Appendix 8 of this report. It should be noted that the 16.71 future development to the east of Cottonwood Subdivision was only included in the calculations for the Cottonwood Subdivision sanitary sewer design to ensure adequate capacity of the 8-inch pipes within the subdivision. This 16.71-acre area was not included in the lift station capacity analysis. If ever developed, the 16.71-acre area to the east will be required to determine the remaining capacity of the lift station and if capacity does not exist, then be required to install the sanitary sewer upgrade in Cottonwood Road from intersection of Durston Road to approximately 460 feet south of Huffine Lane. LOYAL DRIVE COTTONWOOD RD HUFFINE LANETOWN PUMPLOYALGARDENSUBDIVISIONW GARFIELD STALPHA DRIVECOTTONWOOD SUBDIVISION28.09 ACRESCOUNTY16.71 ACRES1 inch =0SCALE300 feet600'150'300'SS1.0MADISON ENGINEERING895 TECHNOLOGY BLVD, BOZEMAN, MT 59718PHONE (406) 586-0262COTTONWOOD SUBDIVISIONSANITARY SEWER DRAINAGE BASINSBOZEMAN, MT LP LOYAL GARDEN SUBDIVISION ALPHA DRIVE HUFFINE LANE COTTONWOOD ROADSTAFFORD AVEGARFIELD ST RESORT DRPARK BLVD LOY A L D R LOT 2 BLOCK 2 LOT 2 BLOCK 1 LOT 1 BLOCK 1 LOT 1 BLOCK 2 LOT 1 BLOCK 3 LOT 2 BLOCK 3 LOT 1 BLOCK 5 LOT 1 BLOCK 6 PUBLIC PARK PUBLIC PARK PUBLIC PARK PUBLIC PARK TOWN PUMP -EXT'G-STAFFORD AVE(FUTURE)1 inch = 0 SCALE 200' 400'100'200' EXHIBIT AMADISON ENGINEERING 895 TECHNOLOGY BLVD, SUITE 203 BOZEMAN, MT 59718 PHONE (406) 586-0262 COTTONWOOD ROAD IMPROVEMENTS SEWER AND WATER MAIN EXHIBIT BOZEMAN, MT cushingterrell.com Appendix C: Cottonwood Phase 1 Sanitary Sewer Report cushingterrell.com Appendix D: Loyal Garden Lift Station Analysis Excerpts Loyal Garden Lift Station Capacity Analysis Report Page 1 of 4 LOYAL GARDEN SUBDIVISION LIFT STATION CAPACITY ANALYSIS REPORT A. General This report will give an overview of the analysis of the capacity of the existing Loyal Garden Subdivision Sanitary Sewer Lift Station. The purpose of this analysis is to determine the actual flow to the lift station and determine how much additional capacity remains for the future development of the 28-acre Cottonwood Subdivision (Lot 3A-1, Minor Subdivision 454C) located to the east of Loyal Garden Subdivision. The lift station was designed for the sanitary sewer flows within Loyal Garden Subdivision and an additional 140 acres in the surrounding area to the east and south (including future Cottonwood Subdivision). As of this writing (March 2020), only one development within the 140 acres outside of Loyal Garden Subdivision has utilized the lift station; Lot 1, Minor Subdivision 454B (Town Pump). Given the size and density of the proposed Cottonwood Subdivision, the City of Bozeman Engineering Department has requested a capacity analysis of the lift station prior to allowing Cottonwood Subdivision to utilize it for their development. The following references were used in this capacity analysis: a. COB Design Standards and Specifications Policy, 2004. Addendum #6 (DSSP) b. COB Modifications to Montana Public Works Standard Specifications (MPWSS), Addendum #3 c. City adopted MPWSS and Adopted Addenda d. COB Wastewater Facility Plan, 2015 e. City of Bozeman Zoning Map f. City of Bozeman GIS Infrastructure viewer B. Capacity Analysis It was originally intended to meter the sanitary sewer flow at four different manholes within the subdivision; capturing all the contributing drainage basins to the lift station. For various reasons discussed below, this method was abandoned and a multi-faceted approach was agreed upon between Madison Engineering and the City of Bozeman Engineering Department for the capacity analysis. These methods included: • Flow metering of two manholes (M0615 and M0617) within Loyal Garden Subdivision (see Sheet EX1.0 in Appendix A for the location of these manholes within the subdivision), • Water consumption data provided by City of Bozeman Utility Billing Department, • Proportional estimation of flow per single family home based on flow metering data from M0615, and • Sewage Calculation Memorandum from CTA Group for West Bozeman Ambulatory Surgery Center (ASC) dated April 24, 2019. Flow metering TD&H Engineering provided the metering and data collection services for this project in collaboration with the City of Bozeman Water and Sewer Department. The original plan of Loyal Garden Lift Station Capacity Analysis Report Page 2 of 4 monitoring four separate manholes for a duration that captured three rainfall storm events was abandoned in February 2020. Multiple technical issues with the flow meters and the time of year during which monitoring needed to take place made capturing three rainfall storm events impractical and overly time consuming. Also, the manholes that drain from Lot 11, Block 1 (Golden Gate Condos) had sub-optimal pipe in/out angles to accurately meter the flow. Flow data from M0615 was collected for one week between 11/20 and 11/28/2019. The average daily flow to this manhole was 234 gallons per day (gpd). M0615 receives flow from seven single family homes in Loyal Garden Subdivision (see Sheet EX1.0, Drainage Basin 2). Flow data from M0617 was collected for two weeks between 02/19 and 03/05/2020. The average daily flow to this manhole was 13,170 gpd. M0617 receives flow from the majority of lots in Loyal Garden Subdivision (see Sheet EX1.0, Drainage Basin 3). The flow metering data captures data points once per minute which resulted in over 10,000 data points per manhole. The excel files containing this data are too large to share in the appendix of this report and are available upon request from Madison Engineering. The data has been averaged and summarized in Appendix B. Water consumption data Water consumption data provided by the City of Bozeman Utility Billing Department was used to determine the sanitary sewer flows from Lot 11, Block 1 (Golden Gate Condos) and Lot 1, Minor Subd. 454B (Town Pump). Data was collected from the previous two years to determine an average daily flow. This is considered to be a conservative estimate of sanitary sewer flows from these two lots because if any water consumption was used for landscape irrigation, it is included in these figures even though it does not drain directly to the sanitary sewer. The average daily flow from Golden Gate Condos is 5,066 gpd and from Town Pump it is 3,862 gpd. See Appendix B for a summary of the water consumption data and Appendix E for the original data provided by the City of Bozeman Billing Department. Proportional estimation of flow Eight lots within Block 3 of Loyal Garden Subdivision fall outside of the manholes that were monitored. Since these lots contain single family homes, similar to the seven lots that drain to M0615, the flow per lot per day was calculated and applied to these unmonitored lots in Block 3. The average daily flow from these eight lots in Block 3 is 268 gpd (see Sheet EX1.0, Drainage Basin 1). See Appendix B for calculations. Sewage Calculation Memorandum from CTA Group for West Bozeman ASC At the time of this writing the West Bozeman ASC is under construction on Lot 1A of Block 1, Loyal Garden Subdivision. CTA Group provided a memorandum with sewage calculations for the proposed site development to the City of Bozeman Engineering Department on April 24, 2019. Their calculations show that the ASC will result in 4,095 gpd of sanitary sewer flow to the lift station. A summary table of the average daily sanitary sewer flows to Loyal Garden Subdivision Lift Station is included on Sheet EX1.0 in Appendix A. Loyal Garden Lift Station Capacity Analysis Report Page 3 of 4 C. Discussion of Inflow & Infiltration In order for Cottonwood Subdivision to be developed, the remaining capacity of the Loyal Garden Lift Station needed to be determined. Given the timing of the start of construction of Cottonwood Subdivision (estimated summer 2020) and the need for the manhole flow metering to include a time period that receives three rainfall events, the Inflow and Infiltration (I & I) was estimated using the Bozeman DSSP standard of 150 gpd/acre. This was agreed upon as an acceptable solution for performing the lift station capacity analysis during the winter of 2019-2020 between Madison Engineering and the City of Bozeman Engineering Department. It is assumed that given the time of year of the flow metering at M0615 and M0617 (November and February/March, respectively) that no significant I & I was captured during those periods. Therefore, 150 gpd/acre was applied to the entire 75-acre Loyal Garden Subdivision, the 3.06-acre Lot 1 of Minor Subd. 454B (Town Pump) and the 28.09-acre Lot 3A-1 of Minor Subd. 454C (Future Cottonwood Subd.) to estimate the I & I. This is considered a conservative estimate because the Loyal Garden sanitary sewer system is relatively new PVC SDR 35 (constructed in 2007) and I & I is a far less common of an issue in newer PVC systems. All I & I flow values cancel out because the lift station was originally designed using the same 150 gpd/acre standard in 2006. D. Summary of original lift station design The Loyal Garden Lift Station was designed in 2006 by TD&H Engineering. It was calculated that the average daily flow from Loyal Garden Subdivision would be 28,080 gpd with an additional 11,250 gpd allocated for I & I (see excerpt of original TD&H design report in Appendix D). The analysis presented herein, shows that the original design figure of 28,080 gpd was conservative. The actual estimated flow to the lift station from Loyal Garden Subdivision is 22,833 gpd. Because our analysis did not monitor I & I, the same value of 11,250 gpd was used, which cancels out. Therefore, 5,247 gpd of lift station capacity remains unused within the Loyal Garden Subdivision. The original estimation provided in the lift station design report (see Appendix D) of daily flow from the additional 140 acres was 80,640 gpd. With the development of Town Pump in 2016 on Lot 1, Minor Subd. 454B, 3.06 acres of the 140 acres were used. Using the water consumption data for Town Pump, our analysis shows an average daily flow of 3,862 gpd. This means that for the additional 140-acre area originally specified in the Loyal Garden lift station design report, a sanitary sewer capacity of 76,778 gpd remains available for use by the Cottonwood Subdivision. In 2019, the City of Bozeman Engineering Department decided that the remaining capacity in the Loyal Garden lift station would be allocated on a first-come first-served basis. The sanitary sewer design report for Cottonwood Subdivision estimates an average daily flow of 55,900 gpd (see excerpts from Cottonwood Subd. sanitary sewer report in Appendix E). Therefore, adequate capacity exists in the Loyal Garden Lift Station for the entirety of Cottonwood Subdivision. A summary table comparing the original lift station design with the flow analysis and the future Cottonwood Subdivision is presented below in Table 1. Loyal Garden Lift Station Capacity Analysis Report Page 4 of 4 Table 1. Original design and capacity analysis summary Area Original design avg. daily flow (gpd) Capacity analysis avg. daily flow (gpd) Difference between original and actual (gpd) Loyal Garden Subd. 28,080 22,833 5,247 surplus Add’l 140 acres 80,640 59,762 20,878 surplus Total 108,720 82,595 26,125 surplus In summary, the Loyal Garden lift station has adequate capacity to serve the full build out of the future 28-acre Cottonwood Subdivision and still has 20,878 gpd available for the future development of adjacent lots within the original “additional 140-acre” district. Also, there is 5,247 gpd of unused lift station capacity within Loyal Garden Subdivision, which equates to a total of 26,125 gpd of available capacity. Appendices A. Exhibit 1.0 – Drainage Basin Map B. Summary of flow data, water usage and I & I C. Sewage flow calculation memo by CTA Group for West Bozeman ASC D. Excerpts from original Loyal Garden Lift Station Design Report E. Excerpts from Cottonwood Subdivision sewer design report F. Water usage data for Golden Gate Condos and Town Pump cushingterrell.com Appendix E: Calculations and Back-Up Data Channel Report Hydraflow Express Extension for Autodesk® Civil 3D® by Autodesk, Inc.Sunday, Dec 20 2020 <Name> Circular Diameter (ft) = 0.67 Invert Elev (ft) = 100.00 Slope (%) = 0.40 N-Value = 0.013 Calculations Compute by: Known Depth Known Depth (ft) = 0.50 Highlighted Depth (ft) = 0.50 Q (cfs) = 0.706 Area (sqft) = 0.28 Velocity (ft/s) = 2.49 Wetted Perim (ft) = 1.40 Crit Depth, Yc (ft) = 0.40 Top Width (ft) = 0.58 EGL (ft) = 0.60 0 1 Elev (ft)Section 99.75 100.00 100.25 100.50 100.75 101.00 Reach (ft) 256 + 96 =352 Population = 352 units * 2.17 persons/household = 764 persons Peaking Factor = ((18+.764^.5)/(4+.764^.5)) = 18.87/4.87 = 3.87 COTTONWOOD SUBDIVISION - PEAKING FACTOR UPDATE Phase 1 & Phase 2 Unit Count =