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Eng. Comments - 22-04 10500 and 10520 Great Plains Blvd Conceptual PUD Memorandum To: MacKenzie Young-Walters, Associate Planner From: Erik Henricksen, Project Engineer Joe Seidl, Water Resources Engineer CC: Charles Howley, Public Works Director/City Engineer George Bender, Assistant City Engineer Joe Seidl, Water Resources Engineer Charlie Burke, Public Works Operations Manager Date: 2/18/2022 Re: 10500 and 10520 Great Plains Boulevard Conceptual PUD Review – Planning Case No. 2022-04 EASEMENTS The preliminary plat provided with the Conceptual PUD materials, dated 12/4/2018 and produced by James R. Hill, Inc., illustrates typical 10 foot public drainage and utility easements (DUE) along all property lines. Additional public DUEs will be required over public utilities (only watermain at this phase) extended into the property as discussed under the “Sanitary Sewer and Watermain” section of this report. The dimensions of the DUE must be adequate to properly repair and maintain the utility; the minimum for watermains is typically 20 feet wide, centered over the main, due to their typical installation depth of 7.5 feet, however additional DUE may be required depending on the plans that will be provided. Any and all existing easements must be vacated prior to recording of the final plat. Based on Carver County property information there appears to be two parcels abutting the preliminary plat’s western property lines that are listed as “Parcel ID: Gap”. It is unclear if these parcels are being considered in the lot combination of the Conceptual PUD, or if they are being considered a part of the adjacent lot to the west (PID #250361300). Clarification regarding the status of “Parcel ID: Gap” in conjunction with the proposed plat will be required prior to recording of the final plat from either the County or the applicant. The preliminary plat abuts and gains access from Carver County right-of-way. Thus, the applicant must coordinate with Carver County regarding any additional considerations and potential conditions associated with easements for the property as well as any requirements associated with ingress/egress and construction activities such as during grading and hauling operations. EXISTING CONDITIONS SURVEY The existing condition survey, dated 1/28/2022 and produced by James R. Hill, Inc., will need to be updated upon resubmittal to incorporate the following information, as necessary: · Topographic data 100 feet beyond the property boundary · Illustration of existing features that would impact the site’s ingress/egress (e.g. the full extents of Flying Cloud Drive which includes the median near the site’s entrance) · Utilities on or adjacent to the property, including location, size and invert elevation of storm sewers, catch basins and manholes; location and size of water mains (including casings) and hydrants; location of gas mains, high pressure lines, fire hydrants, electric and telephone lines, and street lights. The direction, distance to, and size of such facilities shall be indicated. · Wetlands · Bluff impact zones · Sewage treatment systems and associated conveyance systems · Existing easements and associated recording document numbers · Property information within 150 feet of the property’s boundary · Retaining wall elevations WETLANDS A study completed by Kjolhaug Environmental Services in 2021 shows there are no wetlands within the project site. City records show there is one wetland just south of the project site located in the drainage ditch along County Road 101 (Great Plains Blvd). This wetland has been classified as a manage type 2 wetland in the City’s Surface Water Management Plan. A 1992 delineation report indicates the source of water as surface water runoff and the route of outflow is a culvert to the Minnesota River. The preliminary plans submitted with the Conceptual PUD show grading in close proximity to the wetland which is near the proposed access to the site. Article VI, Chapter 20 of City Code describes buffer strip and setback requirements. For example a 10 to 30 foot buffer strip with an average of 20 foot width for manage type 2 wetlands. There is also a 30-foot setback from the buffer strip so the building setback should be from 40 to 60 feet averaging 50 feet away from the edge of a manage type 2 wetland. The wetland buffer and wetland setback should be shown on the grading plan and stacked in the field prior to construction. The preliminary plans appear meet the wetland buffer and setback requirements. BLUFFS There is a steep slope located on the west side of the property; the bottom generally follows the 750 contour of the property and the top of the follows the 772 -774 contours. The steep area is called out in the preliminary plans as a bluff, however because this area was created from grading completed as part of a development project in 1996 it is not a natural slope and therefore does not meet the City's definition of a bluff. The Lower Minnesota River Watershed District (LMRWD) also regulates steep slopes within their jurisdiction. The applicant will need to coordinate with the watershed district to confirm if the project triggers any regulations as defined in Rule F – Steep Slopes. RETAINING WALLS Preliminary plans provided with the Conceptual PUD submittal indicate that retaining walls may be required for the development. These walls are shown around the northern and western portions of the property. Portions of the retaining walls illustrated are shown to be located within public drainage and utility easements along the western property lines. An encroachment agreement would be required for any retaining walls located within public easements. Portions of the retaining walls are illustrated to be either close to or directly over the western property line. Due to the proximity to the property line, the construction of these walls would require construction activities to occur on the abutting property. The construction of any improvements that impact or require access to abutting properties must have the appropriate right-of-entry agreements and/or temporary construction easements prior to construction operations commencing. Retaining walls over 4 feet in height shall be constructed in accordance with plans prepared by a registered engineer and shall be constructed of a durable material (smooth face concrete, masonry/mortared, railroad ties and timber are prohibited). It should be noted that the height of any retaining wall is measured from the top of the wall to the bottom of the footing (not to the top of grade adjacent to the bottom of the wall). ACCESS Access to the site is currently had from Flying Cloud Drive (CSAH 61) and is located near the western property line. The preliminary plans indicate that the current access will remain and no additional accesses to the surrounding Carver County rights-of-way are proposed. The development will be required to construct a commercial driveway access in accordance with City Standards. Any comments or conditions by Carver County associated with impacts to their rights-of-way must be adhered to and all permits required must be obtained prior to construction activities commencing. It appears no turnaround is provided in the preliminary plans. In accordance with Section 20- 1122 of City Code a turnaround is required when access is had from a state highway, county road or collector roadway. As access is being had from CSAH 61 a turnaround will be required that can adequately facilitate the turning movement of the largest anticipated design vehicle for the site or the City’s largest fire truck, whichever is greater. GRADING AND DRAINAGE The existing conditions plansheet and drainage maps included in the Conceptual PUD submittal show an existing building near the center of the property with access to Great Plains Boulevard provide by an asphalt parking area and gravel driveway. Stormwater runoff general flows from north to south down the slope of the site where it enters a drainage swale along Flying Cloud Drive. The drainage swale conveys stormwater from west to east. Stormwater leaves the site by way of an existing 48” culvert under Flying Cloud Drive which conveys the stormwater to the South through Bluff Creek and ultimately outleting to the Minnesota River. The preliminary plans provided with the Conceptual PUD submittal show a significant amount of grading. The design steepens the hill on the northeast side of the site to create a flat area conducive for the four proposed buildings with access and parking. The proposed design uses combination of drainage swales and stormwater infrastructure to collect and convey stormwater into a Best Management Practice (BMP) located on the southwest corner of the property. The design shows stormwater being conveyed from the proposed BMP to the existing swale along Flying Cloud Blvd through an outlet control structure. Any impacts to Carver County’s right-of- way must be approved and permitted by the County prior to construction activities. The overall design of the stormwater infrastructure mimics the flow path of the existing condition and acts to convey stormwater runoff from impervious surfaces through water quality BMPS. A more detailed analysis of stormwater volumes and rates may be required to show the wetland onsite is not negatively impacted by the proposed design. EROSION PREVENTION AND SEDIMENT CONTROL The proposed development will exceed 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 preliminary Surface Water Pollution Prevention Plan (SWPPP) and generally appears feasible. The SWPPP is a required submittal element for preliminary plat review. 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 as listed in Parts III and IV 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. SANITARY SEWER AND WATERMAIN Currently, municipal sanitary sewer and potable water services are not available to the site. During the build-out of the Highway 101 Realignment project, which was substantially completed in 2021, public sanitary sewer mains and water mains were extended along the corridor. However, these newly extended utilities are not fully active nor ready for operation to service properties, as such the site does not have adequate public sanitary and water to fully serve the development’s needs. In 2014, a Highway 61 corridor study was conducted in response to several near and long-term infrastructure projects at the time (e.g. Highway 101 Realignment, CSAH 61 reconstruction, flood mitigation projects, etc.) which prompted the City to investigate the feasibility of extending public utilities to the southern portion of the City. The study, known as “County Road 61 Corridor Plan”, conducted by SRF in association with Hoisington Koegler Group, Inc., determined that utility extensions were feasible within the study area. The image below, taken from Figure 3.1 of the City’s 2040 Comprehensive Plan, depicts the City’s existing and planned sanitary sewer in this area (planned water system build-out generally adheres to the same areas and alignments). The proposed development falls within the southcentral region of sanitary subdistrict LB-1 (the Lower Bluff Creek District). The 2014 study estimated costs and fee revenue associated with extending City utilities to the study area, along with estimated utility assessments per acre, which are shown in Tables 1 and 2. With a lack of adequate city utilities in the area, the development will be required to provide private utility services (sanitary sewer and potable water) to adequately meet the needs of the development. The City has preliminarily agreed to allow the development to tap into the public watermain which was extended with the Highway 101 Realignment project, but only to service the development’s fire suppression needs. At this time there is not sufficient demand along the extended watermain to supply water to the quality standards that the City requires for consumption. This is important to note because the preliminary plans provided indicate the existing well on-site is proposed to be abandoned. If the site will have any fixtures requiring the use of water other than for fire suppression needs, a private source of water supply must be used for those fixtures. The preliminary plans indicate tapping of the existing public watermain for fire suppression needs at the southwest corner of the property. As shown on the preliminary plans this would be infeasible as the watermain was housed in a casing at the location, and would be required to be extended further west to facilitate the connection. Regardless, the development will be required to extend the public watermain to the western property line, and the extension into the site must be along or near the improved private access to allow for reasonable access for future repair and maintenance. Adequate public drainage and utility easements will be required over the public main as it extends into the site. Private fire laterals can then be tapped from the public main as necessary. The property and potential future properties associated with this developable area will be specially assessed for the extension of the public sanitary sewer when they connect. STORM WATER MANAGEMENT The project site is located within the Lower Minnesota River Watershed District (LMRWD). The LMRWD is the LGU that administers NPDES Construction Permits for stormwater management. The proposed development will exceed the one (1) acre of new impervious area and will therefore require permanent stormwater BMPs to be constructed as part of this project and maintained by the owner. The project will be subject to stormwater regulations outlined under LMRWD Rule D including rate, volume, and water quality. The City of Chanhassen also regulates the design, construction, and maintenance of stormwater infrastructure. 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.” A stormwater maintenance agreement and associated operations and maintenance plan is required for all private stormwater BMPs. Preliminary plans provided with the Conceptual PUD submittal show stormwater treatment and rate control from a wet pond with an incorporated filtration bench BMP located on the southwest corner of the property. The stormwater BMP appears to be properly sized for the impervious surface proposed in the plans. The design of the BMP is highly dependent on soil types and infiltration rates of the underlying soils. Soil borings, infiltration testing and an associated geotechnical report will be needed to confirm the design of the stormwater BMP. No geotechnical report was included as part of the Conceptual PUD submittal. The City’s water resources engineer reviewed the preliminary plans provided with the Conceptual PUD. Specific comments regarding the design of stormwater infrastructure and BMPs were provided to the applicant. STORM WATER MANAGEMENT FEES In 2005 a Stipulation of Settlement (Court File No. 10-CV-05-48) between PCH Development, LLC and the City of Chanhassen was agreed to regarding the park dedication fees and surface water management fees surrounding the subdivision of the “Paws Claws and Hooves Addition” subdivision (PC #2003-04 and the property of this Conceptual PUD). The surface water management fee was reduced to $9,900.00 and was paid on 7/25/2005. The settlement agreement states, “If all or any part of the property is changed to a different principal use or further subdivided, the property shall be subject to payment of additional park dedication and surface water management fees based upon the rates in effect at that time applicable to the proposed use and type of municipal approval requested.” However, as the stipulation was between the property owner and the City and was not required to be memorialized against the property, if the property owner changes from PCH Development, LLC no stormwater fees will be required if the PUD is approved. If the property is subdivided in the future, stormwater fees will be collected at the rate in affect at the time of platting, minus the $9,900.00 already paid.