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HomeMy WebLinkAboutResponse to DRC 2 Eng. Comments 04-24-2020 1091 Stoneridge Drive • Bozeman, Montana • Phone (406) 587-1115 • Fax (406) 587-9768 www.chengineers.com • E-Mail: info@chengineers.com Civil/Structural Engineering and Surveying April 23, 2020 Sarah Rosenberg City of Bozeman Planning Department 20 E. Olive Street Bozeman, MT 59718 RE: Response to DRC 2 Engineering Comments – Norton East Ranch Subdivision, Phase 5 DRC Comments (#18278) Dear Ms. Rosenberg: This letter is to provide a narrative response to the DRC comments from November 5, 2019: Engineering Division, Griffin Nielsen, gnielsen@bozeman.net, (406) 582-2280 1. All existing utilities must be shown on the preliminary plat. The existing public utilities to the north of the Phase 5 are not shown. • All existing utilities have been shown on the preliminary plat. 2. The Norton Ranch area is known to have high groundwater. The applicant indicated that seasonal high groundwater measurements can be up to 2 feet below existing grade, however the applicant has not provided sufficient data demonstrating the seasonal maximum and minimum groundwater levels. Groundwater data must be provided. • Groundwater monitoring information is included in Appendix C of this submittal. 3. The applicant must provide a surface water exhibit that shows all identified surface water, the temporary detention pond (Along West Babcock Street, Phase 5A), and the drain tile system. • The surface water exhibit showing all identified surface water, the temporary retention pond, and the drain tile has been included in Appendix E of this submittal. 4. The Surface Water section of the Plat supplements notes the extension of a trench from along the northwester edge of Norton East property to the Aajker Creek to prevent overland flow of surface across the home sites on Norton East and Valley West. The trench may be subject to water course setback requirements, however future review of the sites surface water is required. • This ditch is currently being reviewed by the USACE for a Jurisdictional Status Civil/Structural Engineering and Surveying Determination. It is anticipated that the final determination will state that the ditch is non-jurisdictional as the ditch was installed a couple years back to prevent overland flow from Norton Ranch into the Lakes at Valley West subdivision. If this is the case, the ditch will be filled in and will no longer exist. If the ditch is determined to be jurisdictional, all associated permits will be obtained prior to construction of the phases that the ditch occupies (5B and 5D). The Surface Water section of the plat supplements is updated to include information relating to this ditch. 5. Currently, Norton Ranch Phase 3 conveys stormwater directly north to a temporary detention pond located on the southwest corner of the proposed Phase 5A development. The following must be provided in order for continued review. a. The relevant sections of the Norton Ranch Phase 3 stormwater report which identify the offsite drainage which must be accounted for in the Phase 5 subdivision design must be provided. b. Include the offsite drainage basin within the stormwater report’s Drainage Area Exhibit. c. Include the offsite flows into the 25-year conveyance capacity analysis. • The Norton Ranch Phase 3 stormwater design report has been included as an appendix within the Phase 5 stormwater design report included in Appendix B of this submittal. The phase 3 report includes a drainage area map showing all drainage areas currently contributing to the temporary retention pond that is being filled in with this project. The proposed detention pond and all stormwater infrastructure accounts for this additional drainage from phase 3. 6. The Surface Water section of the plat supplements note the extension of a trench from along the northwester edge of Norton East property to the Aajker Creek to prevent overland flow of surface across the home sites on Norton East and Valley West. An analysis of the existing trench and basin must be included in the stormwater report along with the proposed design accommodate the water course and trench. There is no indication that the proposed subdivision design accounts for the existing trench. • The final determination of this ditch is currently being processed. It is anticipated that the final determination will state that the ditch is non-jurisdictional as the ditch was installed a couple years back to prevent overland flow from Norton Ranch into the Lakes at Valley West subdivision. If this is the case, the ditch will be filled in and will no longer exist. Per the recommendation of Barb Vaughn, this is what the applicant is planning at the moment. If the ditch is determined to be jurisdictional, all associated permits will be obtained prior to construction of the phases that the ditch occupies (5B and 5D). The Surface Water section of the plat supplements is updated to include information relating to this ditch. 7. The stormwater conveyance system must be located above the seasonal high groundwater level (SHGWL). Capacity of the conveyance system may not be occupied by groundwater at any time of the year, and the subdivision design must be based off of clearly defined measurements of the SHGWL. Current site conditions indicate that a stormwater conveyance system cannot be located at a depth to satisfy the City’s depth requirement, per DSSP Section IV.D.4.a. The applicant needs to design a stormwater system that satisfies City design standards and functions Civil/Structural Engineering and Surveying correctly. • The entire subdivision will be raised approx. 2 feet from existing grade. In some areas of the subdivision, the SHGWL can be a couple of inches below the existing ground surface. These elevations are based off of C&H’s observations of the groundwater during the spring of 2018. This was an extreme year of precipitation and groundwater levels. The applicant has raised the stormwater system as high as possible while maintaining a minimum of 2’ of cover over storm pipes. There are a few areas that will be no more than 3” below the groundwater level during the peak levels, but will be above the SHGWL for 11+ months of the year. All stormwater ponds are located above the SHGWL. The Stormwater Design Report is updated to illustrate the relationship between the stormwater system and groundwater in the area. A profile of this system showing the relationship between groundwater and the detention pond is included in Appendix E of the Stormwater Design Report (page 83). 8. The applicant must provide the full traffic impact study (TIS) which includes traffic data, traffic assignment, and evaluation for engineering to complete a comprehensive review. A cursory review of the TIS provided resulted in the following comments: a. The TIS must provide an analysis on the intersection of Laurel Parkway and West Babcock. Without this intersection analysis the City will recommended that the intersection be constructed to its full buildout condition at or before the design year for the subdivision. b. b. The TIS states that traffic counts were taken during the summer of 2017. A number schools are located within the study area and are not in session during the summer months. Schools have a significant impact on peak-trips generated. If the traffic impact data that was used in the analysis occurred when the schools were not in session, the applicant must update the TIS to include trips generated from the schools prior to future review. • Traffic control needs at this intersection are addressed in the new April 2020 TIS for Norton East Ranch Phase 5. The TIS recommends configuring this intersection as a four-way STOP to meet future traffic demands. This analysis can be found in Appendix F. • The data used in the 2020 TIS Update is from a variety of sources. With the level of construction occurring in this area over the last several years it has been difficult to collect new reliable data for the area roadways. New traffic data was collected at the intersection of Durston Road and Laurel Parkway in September 2019 which recorded school traffic at that time. Peak-hour turning movement count data for the intersections of Durston Road & Cottonwood Road was obtained from the 2017 Bozeman Transportation Master Plan. Traffic data collected during the summer of 2017 was used for analysis of the intersections on Cottonwood Road south of Durston Road only. The Cottonwood Road intersections south of Durston Road will be minimally affected by traffic from the recent schools north on Durston Road and only during the morning peak hour. New data for these intersections would obviously be preferable with the roadway improvements which are set to go online in 2020. 9. The applicant must provide the centerline alignment data for all streets for engineering department to determine if the proposed street alignments meet the City’s horizontal geometry requirements outlined in the DSSP. Civil/Structural Engineering and Surveying • An exhibit showing all centerline alignment data for the streets is included in Appendix F of this submittal. 10. Boomtown Road must be constructed to the western edge of the property boundary. • The applicant does not intend to extend the road to the western edge of the property. There is a conservation easement on the property to the west and the road will most likely never continue to the west. The applicant has dedicated a 60’ right of way to the western edge of the property in the small chance that the conservation easement is removed and the road continues. 11. El Dorado Avenue must be constructed to the western edge of the property boundary. • The applicant does not intend to extend the road to the western edge of the property. There is a conservation easement on the property to the west and the road will most likely never continue to the west. The applicant has dedicated a 60’ right of way to the western edge of the property in the small chance that the conservation easement is removed and the road continues. 12. Gooseberry Lane must align with intersection of the Lakes at Valley West Phase 5 alley. The distance between the intersections is less than the City’s minimum distance of 125 feet. • The applicant has revised the road layout for this subdivision. The new layout extends the alley/woonerf section from Lakes to intersect with Gooseberry Drive within Norton Ranch Phase 5. 13. The intersection of South Reliance/Blue Lagoon and Gooseberry Drive/Blue Lagoon do not meet the City’s minimum distance requirement of 125 feet. • Blue Lagoon Road has been removed with the updated layout to address this comment. 14. A cursory review of the TIS shows that the intersection of Laurel Parkway and Durston will not meet the City’s level-of-service requirement at the design year. The TIS does not provide a complete analysis of what improvements (signal or roundabout) are required to meet an acceptable level-of-service at the design year. The applicant must provide a complete analysis and receive approval from the engineering department prior to infrastructure submittal. • Using the updated traffic count numbers, the intersection of Laurel Parkway and Durston will meet the City’s future LOS requirement. This topic is discussed in detail in Section H of the April 2020 TIS update. Civil/Structural Engineering and Surveying 15. A cursory review of the TIS shows Laurel Parkway must be constructed from Durston to West Babcock with the first phase of the subdivision as there is no indication within the TIS when the connection is required. A cursory review of the TIS shows the intersection of Fallon Street and Cottonwood Road acts a primary route for the development and will deteriorate to a level-of-service grade D by the design year. The TIS does not provide a complete analysis of what improvements are required to meet an acceptable level-of- service at the design year. The applicant must provide a complete analysis and receive an approval from the engineering department prior to infrastructure submittal. An alternative analysis discussed with the TIS noted that a signal at the intersection of Babcock and Cottonwood increases the functionality of the intersection of Fallon and Cottonwood. Currently, the Babcock and Cottonwood intersection is in the processes of being upgraded and must be reflected in the analysis. • With the planned traffic signal at the intersection of Babcock Street and Cottonwood Road we do not expect LOS issues at the intersection of Fallon Road from the Norton East Ranch Phase 5. Additional information can be found in Appendix F. 16. The applicant must provide a local street connection that spans from Laurel Parkway east to the western property boundary within the northern portion of the Phase 5 development to satisfy block length standards as well as provide for future street connectivity. The northern east-west connection must be named Cascade Street. The engineering department doesn’t support the increase in block length. • The applicant cannot extend a street from Laurel Parkway east to the western property boundary because there is an existing Covenant of Dedication located within the park area just west of Laurel Parkway. The applicant has worked with the City engineering department and has come to an agreement on the shown road layout. 17. A ten foot utility easement (power, gas, communication, etc.) along the developments property northern frontage of Vaughn Drive must be provided. Required stormwater infrastructure many not be located in the easement. • The 10’ utility easement has been added along the northern property line. No stormwater infrastructure is located within the easement. 18. Wastewater generated in the Norton Ranch subdivision currently flows to the Norton Ranch Lift Station and is pumped via force main into the gravity collection system. Wastewater entering the gravity collection system from the Norton Ranch force main flows into the Baxter Meadows Lift station service area. Currently, the Baxter Meadows Lift station is fully allocated and does not have the capacity to accommodate an increase in sanitary sewer flows from Norton Ranch. The City has allowed the development to utilize the Baxter Meadows Lift station in the short-term as identified long-term capital improvement projects such as the Davis Lane Lift Station and Norton East Ranch Diversion Interceptor get funded and ultimately constructed. The applicant has indicated the exists of a “Norton Ranch Wastewater Collection System Agreement”, a copy of the agreement must be provided. Civil/Structural Engineering and Surveying With that being said, the Davis Lane Lift Station and Norton East Ranch Diversion Interceptor must be constructed prior to final plat approval to accommodate sanitary sewer flows from the proposed development. Otherwise, an interim upgrade to the Baxter Meadows Lift Station may be considered to accommodate future flows from Norton Ranch. The applicant must elect which option the subdivision will use prior to adequacy. • The applicant is working with Lance Lehigh with the City Engineering department to come up with a desirable configuration for the Norton Ranch Lift Station. C&H Engineering is updating the Norton Ranch Lift Station design report with the demand from Phase 5 as well as future developments planned to be routed to this lift station. This lift station will be upgraded prior to final plat approval. • A copy of the Norton Ranch Wastewater Collection System Agreement is included Appendix B. 19. The sanitary sewer along the northern property boundary must be constructed in the City standard alignment (5.5ft from the south curbline) in Vaughn Drive, per the Section V.D.3.a of the City’s Design Standard and Specification Manual. • The proposed sewer main runs within the open space located within the Lakes and Valley West. The applicant has worked with the owner of the Lakes and it has been agreed upon to run the sewer main in this location with a public utility easement. This sewer main will connect to the Norton Ranch Lift station rather than connecting to the sewer main within the Lakes, which is part of a different system. An existing sewer serving The Lakes at Valley West Phase 5 and Phase 6 is currently located in Vaughn Drive. We ask that this comment be reconsidered due to the existing water and sewer currently located in Vaughn Drive. 20. The Norton Ranch development resides in the City’s Northwest pressure zone. The 2015 water facility plan update recommended changing the hydraulic grade line (HGL) in the zone from 4980 to 4975. The HGL changes for the Northwest zone have been implemented. Therefore, the water design report must be updated to reflect the new 4975 HGL changes prior to infrastructure submittal. • The applicant is working with Erin Shane to acquire the updated data with the new hydraulic grade line. The water design report will be updated with new hydrant data representing the new HGL prior to infrastructure design. Engineering Final Plat Comments: The following comments must be addressed prior to final plat approval. 1. Street names must be reviewed and approved by the County geographic information systems and City Engineering Department prior to final plat approval. The applicant must submit written approval from both entities with the final plat application. Civil/Structural Engineering and Surveying • Street names will be coordinated and finalized prior to final plat approval. 2. The Norton Ranch Lift Station has been designed to be reconfigured to allow for phased development of the Norton Ranch Subdivision. The exact configuration is dependent on the phase and number of dwelling units to be served. Currently, there are three pumps at the lift station with a single principal pump that can operate under different hydraulic conditions that the station experiences, specifically column separation after pumping cycles. DEQ Circular 2 requires that multiple pumps must be provided and of the same size. Units must have capacity such that, with any unit out of service, the remaining units will have capacity to handle the design peak hour flow. The station does not satisfy DEQ firm capacity requirements. The lift station must be upgraded prior to final plat approval. • The applicant is working with Lance Lehigh with the City Engineering department to come up with a desirable configuration for the Norton Ranch Lift Station. 3. The proposed stormwater discharge from the detention pond on the northwest corner of the development is located off-site. The applicant must obtain an easement from the adjacent property owner for the off-site discharge prior to final plat approval. • The owner finalized this easement with the property owner to the west in 2017. A copy of the filed deed/easement is included in Appendix B. 4. The subdivision is responsible for maintaining the stormwater system. A stormwater maintenance plan must be reviewed and approved with the infrastructure submittal. The approved plan must then be incorporated into the property owner’s association (POA)/home owner’s association (HOA) documents and demonstrate inclusion in the documents prior to final plat approval. • The stormwater maintenance plan will be incorporated into the HOA documents prior to final plat approval. 5. The applicant must contact the City Engineering Department (Brian Heaston) for an analysis of CIL of water rights and pay any CIL of water rights due prior to final plat approval. • This project will use a portion of the CILWR credit for the Norton Ranch Subdivision. This portion has been coordinated with Brian Heaston. This payment will be provided with the final plat application. Recommended Conditions of Approval: The following are recommended conditions of approval. 1. If not already filed, the applicant must provide and file with the County Clerk and Recorder's office executed Waivers of Right to Protest Creation of Special Improvement Districts (SID’s) for the following: Civil/Structural Engineering and Surveying a. Street improvements to Cottonwood Road including paving, curb/gutter, sidewalk, and storm drainage b. Street improvements to Laurel Parkway including paving, curb/gutter, sidewalk, and storm drainage c. Street improvements to West Babcock including paving, curb/gutter, sidewalk, and storm drainage d. Street improvements to Durston Road including paving, curb/gutter, sidewalk, and storm drainage e. Street improvements to Gooch Hill Road including paving, curb/gutter, sidewalk, and storm drainage f. Intersection improvements to Laurel Parkway and Durston g. Intersection improvements to Laurel Parkway and West Babcock Street h. Intersection improvements to Laurel Parkway and Huffine Lane i. Intersection improvements to Cottonwood Road and Huffine Lane j. Intersection improvements to Cottonwood Road and West Babcock Street The document filed must specify that in the event an SID is not utilized for the completion of these improvements, the developer agrees to participate in an alternate financing method for the completion of said improvements on a fair share, proportionate basis as determined by square footage of property, taxable valuation of the property, traffic contribution from the development, or a combination thereof. The applicant must provide a copy of the filed SID waiver prior to final plat approval. • The waiver of right to protest SIDs will be finalized and recorded prior to final plat. A draft copy is included in Section 3 of this submittal. 2. A 1 foot “No Access” strip shall be placed along the West Babcock frontage for the full length of the development. • A 1 foot “No Access” strip has been provided along the full frontage of W. Babcock Street. 3. A 1 foot “No Access” strip shall be placed along the Laurel Parkway frontage Block 16 of the development. • A 1 foot “No Access” strip has been provided along the Block 16 frontage of Laurel Parkway. 4. The applicant must include a note on the plat as follows, “This is a known area of high groundwater. No crawl spaces or basements may be constructed. Sump pumps are not allowed to be connected to the sanitary sewer system. Sump pumps are not allowed to be connected to the drainage system. Water from sump pumps may not be discharged onto streets, such as into the curb and gutters where they create a safety hazard for pedestrians and vehicles. • This note is included under “General Notes” on page 3. 5. Due to the high groundwater and increased rate of corrosion associated with clay soils all water mains must be zinc coated. This condition may be met if the applicant can demonstrate to the engineering department that the additional cathodic protection is not required. Civil/Structural Engineering and Surveying • All water mains will be zinc coated. This will be coordinated during infrastructure design. Fire Department, Scott Mueller, smueller@bozeman.net, (406) 582-2353 1. My only conditions are that fire hydrants are installed along North section on Laurel Parkway, mid-block along North section of S Reliance Ave, and removal of mid-block South section on Westgate Ave and Gooseberry Dr. • The fire hydrant layout has been revised to reflect Scott’s request. Future Impact Fees - Please note that future building permit applications will require payment of the required transportation, water, sewer and fire impact fees according to the City of Bozeman adopted impact fee schedule in place at the time of building permit issuance. If you desire an estimate of the required impact fees according to current rates please contact the Department of Community Development and/or visit. Note: During preparation of the staff report for future applications, additional conditions of approval may be recommended based on comments and recommendations provided by other applicable review agencies involved with the review of the project. If you require any further information, please give me a call at (406) 587-1115. Sincerely, Luke Stein, E.I.