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HomeMy WebLinkAbout21212 Soccoccia Minor Sub PA Eng. Comments MMI Narrative MEMORANDUM ------------------------------------------------------------------------------------------------------------ TO: Susana Montana, Planner III FROM: Karl Johnson, Engineer I RE: Application #21212 – Saccoccia Subsequent Minor Sub of 407C PA DATE: June 30, 2021 ----------------------------------------------------------------------------------------------------------- ENGINERING REQURIED CODE CORRECTIONS: General 1. Engineering is not in support of the following requested waivers. a. Groundwater b. Streets, Roads, and Alleys – TIS Study Acknowledged. 2. Due to the known high groundwater conditions in the area no basements will be permitted with future development of the site. No crawl spaces will be permitted with future development of the site, unless a professional engineer registered in the State of Montana certifies that the lowest point of any proposed structure is located above the seasonal high groundwater level and provide supporting groundwater data prior to the release of building permit. In addition, sump pumps are not allowed to be connected to the sanitary sewer system or the drainage system unless capacity is designed into the drainage system to accept the pumped water. Water from sump pumps may not be discharged onto streets, such as into the curb and gutters where they may create a safety hazard for pedestrians and vehicles. Acknowledged. Easements 1. BMC 38.410.060 - All Easements indicated below must be provided on city standard easements templates. Drafts must be prepared for review and approval by the city with preliminary plat submittal. Signed hard copies of the easements must be submitted to the city and recorded easement numbers must be shown on the final plat. The applicant may contact the reviewing engineer to receive standard templates. a. The applicant must provide a ten foot utility easement (power, gas, communication, etc.) along the developments property frontage. A 10’ PUE has been granted on the Preliminary Plat. See the attached Plat located in the Plans folder for details. b. The applicant must provide the proposed shared access easement. A shared access easement was provided to the City of Bozeman as part of the HOME-2 Suites Hotel, COB#: 19394 project. See the document titled (Easement - EX C - Shared Access Easement 080119.pdf) in the Documents folder for detail. Also provided with the HOME-2 Site Plan were a Pedestrian Easement and a Public Utility Easement (files labeled Easement - EX D - Pedestrian Easement 080119.pdf and Easement - EX A - NWE easement 080119.pdf in the Documents folder). These Easements were submitted to the City of Bozeman, and to date have not been filed at the Clerk and Recorders office. c. The applicant must provide a drainage easement for the prosed storm sewer crossing multiple lots. See the preliminary plat in the Plans folder for details. Water Rights 1. BMC Section 38.23.180 states: the transfer of water rights or the payment of cash-in-lieu (CIL) of water rights shall be provided. The applicate should contact Griffin Nielsen, with the City of Bozeman Engineering Department, for determination of payment. The Cash-in-Lieu of water rights for this property was paid with the original Saccoccia Minor Subdivision. Please see the document titled Ta CIL Water Rights 051207.pdf and Tb Email From Brian Heaston CIL Water Rights 072321.pdf in the Appendices folder for details. Paybacks 1. The subject property is located within the N 19th and Baxter Intersection Payback. If the subject property did not participate in the original cost of construction of improvements and will be assessed a payback charge. The subject property did participate in the original cost of the construction N 19th and Baxter Intersection improvements. Stormwater 1. Stormwater drainage crossing multiple lots must be contained within a drainage easement. See the preliminary plat in the Plans folder for details. 2. It appears the applicant is proposing to utilize the Arrowleaf detention pond. This pond is nonfunctioning as it has long-term standing water. If this detention pond will be utilized by the proposed project it must be brought into conformance with current City of Bozeman Standards. Furthermore the applicant must provide the original design report showing capacity for the proposed subdivision in the detention facility. Per our call on 7/20/21, we have gathered the design information for the existing pond that was built with the LOWES’s HIW improvements in 2006. Per the Bozeman LOWE’s HIW, Inc Basis of Design Report (located in the Appendices folder - Kd Original LOWE's Storm Water Report 121206.pdf), the stormwater for all lots In the Saccoccia Minor Subdivision is directed to a regional detention pond located in the northeast corner of the subdivision. The pond was sized and constructed as part of the Lowe’s HIW PUD, accounting for all the land within the Saccoccia Minor Subdivision in the design of the detention pond associated with this PUD. The intent was for the individual lots to capture stormwater by grading to catch basins or sheet draining directly to swales that will be conveyed either though piping or open channels to the regional detention pond. The Saccoccia Minor Subdivision currently utilizes this detention pond to attenuate the increase from pre-development to post-development flows prior to discharging into the Walton’s Stream/Ditch. In order to simplify the phasing of the planned unit development, the entire detention pond was built during the first phase of construction. By building out the entire pond at one time, disturbance of the detention area can be avoided during the final phasing of the development. The detention pond was sized according to the City of Bozeman Design Standards and Specifications Policy. The modified rational method was used to compare the predevelopment and post development runoff rates using the formula Q = CiA. The post development runoff rate for the subdivision was calculated using a conservative composite C of 0.76. The detention pond was sized by subtracting the total basin release volume from the allowable pre-development runoff at different storm durations. For the entire subdivision, the required storage volume was designed to be 44,860 cf (see the Saccoccia Minor Subdivision Basis of Design Report for calculations - attached). From the design report for the LOWE’s HIW project, you can see from the 4th / 5th page of the report that: . Therefore, you can see that the pond was designed and permitted through the USACE to be a pond / wetland. The stormwater detention volume was designed to function above the pond / wetland / water levels. Also in the Appendices folder is the Record Drawings for the pond construction showing the elevations (Ke LOWE's Detention Pond Plan Sheet 121206.pdf). So the long-term standing water in the pond is how it was initially designed. It should also be noted that the LOWE’s site, the Rocky Mountain Credit Union site and the proposed HOME-2 site all drain to this existing pond. Along with this, the approved HOME-2 design accounted for the area that will be Lot 2A2 see the Basin Map exhibit in the Appendices folder that was part of the approved HOME-2 Design Report (Kf HOME-2 Basin Exhibit 050320.pdf) Per our call on 9/28/21 – we discussed adding a Pretreatment Forebay to the existing wet pond. This stormwater feature could be added to the existing channel leading to the pond at the location shown on the Record Drawing (Ke LOWE's Detention Pond Plan Sheet 121206.pdf). It is also our understanding that the Arrowleaf multi-family project to the south of the existing pond does not drain to the pond. Therefore, this opens up a lot of capacity in the existing pond since it was originally designed for the entire Saccoccia Minor Subdivision. 3. DSSP II.C.3 - Basins serving multiple lots shall be located in common open space owned by a Homeowners or Property Owners Association. Locating a basin within an easement on a lot will not be permitted unless approved by the governing body. See the answer above. 4. A stormwater drainage and treatment grading plan and maintenance plan for a system designed to remove solids, silt, oils, grease, and other pollutants must be provided to and approved with the preliminary plat application. The plan must demonstrate adequate site drainage (including sufficient spot elevations), storm water detention/retention basin details (including basin sizing and discharge calculations, and discharge structure details), storm water discharge destination, and a storm water maintenance plan. See the storm water maintenance plan located in the Appendices folder for details (Kc StormWater Maintenance Plan 030320.pdf). Utilities 1. The applicant is advised that due to the known high groundwater and soil conditions within the proposed area of development an increased rate of corrosion has been observed with ductile iron water mains, thus decreasing the longevity of publicly owned and maintained infrastructure. The applicant must provide corrosion protection for all future water mains within the development and identify how the mains will be protected with future infrastructure submittal. Acceptable protection methods include zinc coated ductile iron or v-bio enhanced polyethylene encasement of the main. Corrosion protection can be waived, if the applicant can demonstrate that corrosion protection is not applicable for the proposed development. Typically, in order for a waiver to be granted, the applicant must consult the latest American Water Works Association and Ductile Iron Pipe Research Association (DIRPA) documentation for testing\evaluation procedures and provide an analysis demonstrating that corrosion protection is not needed throughout the entire development. See the Geotech Report located in Appendices folder for details (D Rawhide Geotech Report 102821.pdf). Transportation 1. The existing access on to Baxter Lane does not meet spacing standards. The traffic impact study must analyze this access and address the requirements of BMC 38.400.090-H.3. Attached in Appendices folder, Section L is a Trip Generation Analysis (La TIS Memo Saccoccia- Minor_Trip-Gen-Comparison 071921.pdf) for this Minor Subdivision. Also attached is an email from our Traffic Engineer Tom Eastwood dated 7/27/21 (Lc Email from Traffic Engineer 072721.pdf) detailing how the previously approved deviation (Lb 2015 access deviation approval traffic data 040815.pdf) is still valid because the proposed trip generation numbers are less that what was originally assumed for this subdivision. N:\2927\012 - Minor Sub 407C PreApp\04 Design\Platting\PRE-Plat\21212 Soccoccia Minor Sub PA Eng. Comments - 6-30-21 MMI Narrative.docx