Eng. & WR Report- 2024-02 Chanhassen Civic Campus Site Plan & Prelim Plat Memorandum To: Eric Maass, Planning Director From: Erik Henricksen, Project Engineer Joe Seidl, Water Resources Engineer CC: Charles Howley, Public Works Director/City Engineer George Bender, Assistant City Engineer Jamie Marsh, Environmental Resource Specialist Charlie Burke, Public Works Operations Manager Date: 3/11/2024 Re: Chanhassen Civic Campus Preliminary Plat and Site Plan Review – Planning Case No. 2024-02 EASEMENTS The City of Chanhassen is proposing the preliminary plat “Chanhassen Civic Campus” which will re-plat Schneider Park Second Addition, as well as a city owned parcel to the east (PIN 250122100), into four (4) lots, Block 1 Lots 1-4, while also dedicating approximately 13,500 square feet of right-of-way along Kerber Boulevard and Laredo Drive. It is recommended that another parcel owned by the city abutting the preliminary plat to the east of Lot 2, PIN 250122010, be incorporated into the preliminary plat and be dedicated as public right-of-way (Market Boulevard). The lots are configured to accommodate the build-out of the Chanhassen Civic Campus project which includes a new City Hall, park pavilion, pickleball court and performance stage. Existing structures to remain include the Chanhassen Fire Station and the Chanhassen Library. The configuration of the preliminary plat meets Chanhassen City Code; adequate public drainage and utility easements are provided, and each lot will accommodate one primary structure. GRADING & DRAINAGE The Chanhassen Civic Campus is located in the northeast intersection of West 78th Street and Kerber Boulevard. The site is bound by Market Blvd to the east and City Center Park to the North. The existing site is developed with several buildings and associated parking lots. The site contains a significant amount of green spaces including the ball fields located north of City Hall. Drainage from the existing Civic Campus area is picked up in storm sewer throughout the site and routed to trunk storm sewer systems within Kerber Boulevard, West 78th Street and Market Boulevard. Trunk lines from the three adjacent roadways all combine into one trunk storm sewer line which continues south down Market Boulevard until it discharges into a large existing stormwater wet pond located just west of Market Boulevard and north of the Trunk Highway 5. In the proposed condition the site will be mass graded to facilitate the construction of the Civic Campus build out. The Library will remain unchanged but the rest of the site will be reconfigured. During Phase 1 of the construction the new City Hall Building will be built at the southeast corner of the site to allow the current City Hall to remain during construction. In Phase 2 the old City Hall building will be removed to allow the construction of the park gathering spaces. In the proposed condition drainage from the Civic Campus site will continue to be picked up in storm sewer and will connect into the same trunk storm sewer lines as it does under existing conditions. Drainage will continue to be routed to the existing stormwater pond west of Market Boulevard and north of Trunk Highway 5. Overall proposed drainage patterns onsite remain relatively consistent with existing conditions. The proposed design shows a small net increase in impervious area (0.07 acre). The existing storm sewer is anticipated to have capacity for the connections currently proposed. / The majority of the stormwater runoff generated by the site will be treated by a large regional Best Management Practice (BMP) facility that is being designed to treat stormwater generated by the Civic Campus Project, 24-01 Pavement Rehabilitation Project, and Market Boulevard Reconstruction Project. See the Storm Water Management section of the report for more information. While the stormwater treatment needs are anticipated to be met with the Regional BMP approach, staff is working with the Civic Campus designers to implement smaller BMP’s onsite such as rain gardens and filtration swales. The regional BMP facility is currently being designed by the engineering firm Kimley-Horn who was hired by the City to design the Market Boulevard Reconstruction Project. City Staff has collaborated with the engineers at Kimley-Horn and the Riley Purgatory Bluff Creek Watershed District (RPBCWD) to plan the regional BMP approach. A concept plan was presented to the RPBCWD board on January 25th and received support from the district’s board of managers during the meeting. EROSION CONTROL The proposed development will impact one (1) acre of disturbance and will, therefore, be subject to the General Permit Authorization to Discharge Stormwater Associated with Construction Activity Under the National Pollution Discharge Elimination/State Disposal System (NPDES Construction Permit). The applicant has prepared and submitted a Surface Water Pollution Prevention Plan (SWPPP) which was submitted as part of the preliminary plat application. The SWPPP is a required submittal element for final site plan review along with the Erosion and Sediment Control Plan (ESCP) in accordance with Section 19-145 of City Ordinance. No earth disturbing activities may occur until an approved SWPPP is developed. This SWPPP shall be a standalone document consistent with the NPDES Construction Permit and shall contain all required elements of the permit. The SWPPP will need to be updated as the plans are finalized, when the contractor and their sub-contractors are identified, and as other conditions change. All erosion control shall be installed and inspected prior to initiation of site grading activities. STREETS The Chanhassen Civic Campus project does not propose the addition or extension of any public or private streets. However, the dedication of public right-of-way along Kerber Boulevard is necessary to accommodate the proposed improvements associated with the project. Along Kerber Boulevard, the project is proposing additional street parking, relocation of the existing sidewalk, and the addition of a crosswalk enhancement at the intersection of Kerber Boulevard and West Village Heights shopping center entrance. Additionally, there are relatively minor street impacts along W 78th, Market Boulevard, and Chan View to accommodate the build-out of the new City Hall as the site improvements are directly abutting the streets, as well as the relocation of a trunk water main. No impacts to Laredo are proposed as part of this project. Lastly, the city initiated a Downtown Chanhassen Traffic Study in 2023 in conjunction with on-going city projects (e.g., the Market Boulevard Reconstruction Project #25-02). The study evaluated existing conditions, conducted traffic forecasts, and reviewed multiple build conditions and future improvements for the Chanhassen’s downtown. The study included the Chanhassen Civic Campus project in its traffic forecasting and analysis. Due to the intensification of the redevelopment, which includes additional public amenities and public spaces, the study increased the existing volume counts at the entry points to the Chanhassen Civic Campus project by 10% (the north leg of W 78th Street and Market Boulevard, and the west leg of Kerber Boulevard and the North City Center Drive). If there are significant changes to the uses or redevelopment of the campus based on City Council direction, such as the addition or intensification of public amenities that would drive higher traffic volumes, it is strongly recommended that the city update the traffic study to accurately account for such changes. SANITARY SEWER AND WATERMAIN Due to the eventual total redevelopment of the Civic Campus area, a majority of the utilities abutting and internal to the development are proposed to be removed and/or relocated. The utility plans account for the required sanitary sewer and water services necessary to facilitate the build-out. These plans have already been reviewed by staff and were let for bidding as “Bid Pack 1”. The city received competitive and favorable bid pricing as bids were lower than the engineer’s estimate by over one million dollars. Construction activities associated with the underground utilities, including sanitary sewer and watermains, are scheduled to begin in the summer of 2024. Permits from the appropriate regulatory agencies will have to be obtained, including but not limited to the MPCA, NPDES, Minnesota Department of Health, Riley Purgatory Bluff Creek Watershed District. STORM WATER MANAGEMENT Article VII, Chapter 19 of City Code describes the required storm water management development standards. Section 19-141 states that “these development standards shall be reflected in plans prepared by developers and/or project proposers in the design and layout of site plans, subdivisions and water management features.” These standards include abstraction of runoff and water quality treatment resulting in the removal of 90% total suspended solids (TSS) and 60% total phosphorous (TP). The proposed project is located within the Riley Purgatory Bluff Creek (RPBCWD) and is therefore subject to the watershed’s rules and regulations. A RPBCWD permit will be required for final plat approval. A Stormwater Management Report is required to be submitted for review to confirm all applicable stormwater management requirements are being met. This includes rate control, volume abstraction and water quality requirements among others. The site is proposing to meet stormwater management requirements through the use of a proposed regional BMP facility which will be used to irrigate the green spaces proposed as part of the Civic Campus reconstruction including the existing ball fields located within City Center Park. The regional water reuse system will draw stormwater from the large existing stormwater pond that the Civic Campus Site discharges to west of Market Boulevard and north of Trunk Highway 5. Stormwater will be treated with a UV system and pumped by a lift station back to the Civic Campus Site for irrigation through a force main that will run south to north along the Market Boulevard corridor. The regional stormwater reuse system is proposed to provide treatment for other public improvement projects in addition to the Civic Campus including the 24-01 Pavement Rehabilitation Project, and the Market Boulevard Reconstruction Project. A permit application for the regional BMP’s design will be submitted as part of the 24-01 Pavement Rehabilitation Project which is anticipated to be submitted by March 15th, 2024. All comments from RPBCWD will need to be addressed. The applicant shall provide final versions of all modeling (HydroCAD and MIDS) and Stormwater Management Report to address remaining comments and confirm rate, volume and water quality requirements are met as part of the final plat approval. The concept of the regional BMP design is that larger more regional treatment strategies can provide better treatment at lower capital and maintenance costs than smaller individual practices. Regional BMP designs are encouraged by the City of Chanhassen’s Local Surface Water Management Plan. This specific design is especially encouraging as it will provide water quality benefits that exceed what the individual projects could accomplish while also reducing the water consumption from the City’s irrigation system. The regional BMP system is anticipated to be completed and brought online in 2025 when the Marketplace Boulevard Project is constructed. As outlined in the City’s Surface Water Management Plan adopted in December 2018, the City requires at least 3 feet of freeboard between a building elevation and adjacent ponding features’ high water levels. Currently there are no onsite BMPs identified on the plans with high water levels noted to confirm freeboard requirements against. If onsite BMPs are added to the plans, freeboard requirements will need to be confirmed to be met. The proposed BMPs are to be publicly owned and maintained. A maintenance plan for all proposed BMPs will be required and should include the maintenance schedule, responsible party, and include information on how the system will be cleaned out as necessary. A maintenance declaration with the RPBCWD will be required to ensure that the City property maintains the site’s stormwater infrastructure. ASSESSMENTS As the project will be conducted by the city, no assessment or fees will be charged. RECOMMENDATION ENGINEERING: All sanitary sewer and watermains will be publicly owned and maintained after acceptance of the public improvements by the City Council. The city shall ensure that permits are received from all other agencies with jurisdiction over the project (i.e. Army Corps of Engineers, DNR, MnDOT, Carver County, Riley Purgatory Bluff Creek Watershed District, Board of Water and Soil Resources, MPCA, etc.). WATER RESOURCES: The applicant shall secure a signed permit from the RPBCWD prior to the start of construction activities. The applicant shall update the models (HydroCAD and MIDS) per City and any watershed district comments and submit updated computations and models in their native forms with the final plat submittal. Prior to the final plat submittal, the applicant shall work with staff to revise and optimize the design of any onsite BMPs and/or stormwater infrastructure. An Operations and Maintenance plan for all proposed BMPs including the inspection frequency, maintenance schedule, and responsible party shall be submitted for review with the final plat application. The applicant shall enter into an Operations and Maintenance Declaration with the RPBCWD for all proposed stormwater facilities which shall be completed concurrently with the final plat. A Stormwater Management Plan is required noting how all stormwater management requirements are proposed to be met. These requirements include volume abstraction, water quality and rate control among others shall be included in the final plat application. References to the Regional BMP design and permit application are anticipated. If onsite BMPs are added to the plans, information on the proposed HWLs shall be noted on the plans and documentation provided to confirm the City’s freeboard requirements are being met.