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Third CSG RESPONSE - RPBCWD Permit 2022-007 GAYLE MORIN SUBDIVSION -Completeness Review and comments 5-18-22From:Don Giacchetti To:Al-Jaff, Sharmeen Subject:Request RESTORATION of May 18th email (Pavek-to-Sobiech) into Public Record and on City Website Date:Friday, July 8, 2022 8:05:52 AM Attachments:Third CSG RESPONSE - RPBCWD Permit 2022-007 GAYLE MORIN SUBDIVSION -Completeness Review and comments 5-18-22.pdf Sharmeen, Thank you for your voicemails late yesterday on the issues with the City’s website and the associated external Laserfiche® website the City uses for public viewing and downloading of the project documents. As we have previously discussed over the past several weeks, there continues to be “technical” difficulties in trying to get public access to the documents on the Laserfiche website….but I kept trying and eventually got into such website last night. There are other neighbors that have complained to me about the same difficulties. This is a real hassle and should be fixed immediately by the City IT dept and/or Laserfiche. It is an “inconvenient” time to have these technical issues occurring when the public is trying to review these important documents before some critical decision meetings that are on the immediate horizon (ie. the July 19th City Planning Commission Meeting and the August 8th City Council Meeting). I was able to see that the recent “folder” submission by Civil Site Group with several embedded files was eliminated and now those individual files are instead included in the top level of the document listing which now shows 33 document files. While confusing why this change took place, I think I see what happened. HOWEVER, there is one file that I believe to be now missing from the Laserfiche document website that was previously part of the files which the public was able to view and download. Not sure exactly when this document file was removed, perhaps in this latest folder elimination situation….just do not know. Nevertheless, it is a very important part of the public record since it documents an interchange of responses in “red” from Matt Pavek (Civil Site Group) to outstanding questions in “blue” from Scott Sobiech (Barr Engineering) regarding the water issues on the Morin Development Project. Of particular note are the several “Remains an open comment” designation on such outstanding questions meaning such water related issues have not been adequately addressed… Given the above, I have attached such 7-page May 18th email document for your reference. I request that both my email herein and the attached 7-page May 18th document file be placed into the public record on the City’s website and Laserfiche document website. Please acknowledge that you have received this email from me with the attached PDF file of referenced document and that this email and such attachment will be made public on the City of Chanhassen’s website associated external Laserfiche® website both related to the Morin Development Project [ Gayle Morin Addition -- Rezoning and Subdivision with Variances project (Case# 2022-03) ]. Thank you and regards…DON Don J. Giacchetti TACT Solutions, Inc. c#: 612-328-2853 website: www.tactsolutions.com Don J. Giacchetti TACT Solutions, Inc. c#: 612-328-2853 website: www.tactsolutions.com Civil Site Group, PC • 5000 Glenwood Avenue • Golden Valley • Minnesota • 55422 www.CivilSiteGroup.com • (612) 615-0060 Memorandum TO: Scott Sobiech Barr Engineering 4300 Market Pointe Drive Suite 200 Minneapolis, MN 55435 FROM: Matt Pavek Civil Site Group DATE: 5/18/2022 RE: Gayle Morin Subdivision Scott, Below are your written comments regarding the Gayle Morin Subdivision project, in Chanhassen. I have included my response below each question in bold red. Matt Pavek Civil Site Group mpavek@civilsitegroup.com 612-615-0060 Additional Riley Purgatory Comments Shown in blue CSG RESPONSES SHOWN IN BOLD RED BELOW Civil Site Group, PC • 5000 Glenwood Avenue • Golden Valley • Minnesota • 55422 www.CivilSiteGroup.com • (612) 615-0060 Because the site layout changed from prior submittals, please confirm the following information is correct for the re-design of the site: CSG RESPONSE: Project Site Information Area (acres) Total Site Area 4.84 4.62 acres Existing Site Impervious 0.29 Correct Disturbed Site Impervious Area 0.0 (0%) Correct Proposed Site Impervious Area 0.44 0.43 acres Change in Site Impervious Area 0.14 (48% increase) Correct Total Disturbed Area 0.4 Correct Because the project will involve 0.4 acres of land-disturbing activity, the project must conform to the requirements set forth by the RPBCWD Rule C - Erosion Prevention and Sediment Control. To conform to the RPBCWD Rule C, the following revisions are needed before the application will be considered complete: C1. Identification of the name, address and phone number of the individual who will remain liable to the District for performance under this rule and maintenance of erosion and sediment control measures from the time the permitted activities commence until vegetative cover is established (per Rule C, Subsection 4.3a). Remains an open comment, but this can be provided after the RPBCWD Board considers the permit application and will be included as a recommended condition for Board consideration. This information will be needed before the permit is released. CSG RESPONSE: Noted. Because there are wetlands downgradient of the activities, Rule D, Subsections 2.1a and 3.1 require buffer along the downgradient edge of the wetlands. To conform to the RPBCWD Rule D the following revisions are needed: D1. The restoration plan should be amended to incorporate the following: a. standard notes from Rule D for the buffer areas disturbed during construction: i. Buffer areas disturbed must be planted with native vegetation and maintained to retain natural resources and ecological value. Remains an open comment (note not found on L1.0). b. Outdated restoration hatching and linework is shown on L1.0. Please update CSG RESPONSE: Buffer area note added and hatching and linework updated appropriately. Civil Site Group, PC • 5000 Glenwood Avenue • Golden Valley • Minnesota • 55422 www.CivilSiteGroup.com • (612) 615-0060 D2. Before any work subject to District permit requirements commences, buffer areas and maintenance requirements must be documented in a declaration recorded after review and approval by RPBCWD in accordance with Rule D, Subsection 3.4. Remains an open comment, but this can be provided after the RPBCWD Board considers the permit application and will be included as a recommended condition for Board consideration. CSG RESPONSE: Noted. Because the project will involve 0.4 acres of land-disturbing activity, the project must conform to RPBCWD’s stormwater management rule as described in Rule J, Subsection 3. The criteria listed in Subsection 3.1 will apply to the disturbed portion of the project site because the project will increase the imperviousness of the entire site by approximately 48% percent (Rule J, Subsection 2.3). To conform to the RPBCWD Rule J, the following revisions are needed before being considered complete: J1. While soil borings indicate clay soils, additional information is needed to support a restricted site determination. RPBCWD require on-site infiltration testing to verify the infiltration capacity of the soils because substantial variation has been observed by other applicant with clay soils on their site. a. Measured infiltration rates at the proposed stormwater management facility locations and completed by a state-licensed soil scientist, geologist, or engineer needs to be submitted. Infiltrometer tests of the site are needed to determine the presence or absence of soil conditions more suitable for abstraction, assess if there are site restrictions limiting the abstraction required, and to help verify the selected hydrologic curve numbers used in the stormwater modeling of the site. Remains an open comment but will be included as a recommend condition of approval for the Board’s consideration. CSG RESPONSE: Noted. b. Additional information was provided by Sharmeen Al-Jaff, with the City from adjacent property owners concerning the Morin Subdivision- 1441 Lake Lucy Road (Gayle Morin Addition) Rezoning and Subdivision with Variances on 5/4/22. The information indicates that on 4-29-22 one of the borings was not compeltely filled in afterwards and contained standing water about 2.5 feet below ground level at that location (believe to be SB-1). This suggest that high groundwater might exist on the site. Please collect additional information such as observations and measurement of the groundwater elevation observed in the boring which was not completely backfilled. Please review the soils information and revise the design to ensure a minimum of three feet of separation between groundwater and redoximorphic soils. Civil Site Group, PC • 5000 Glenwood Avenue • Golden Valley • Minnesota • 55422 www.CivilSiteGroup.com • (612) 615-0060 CSG RESPONSE: Between the date borings were taken on February 15, 2022 and water was observed on April 29, 2022 approximately 6-inches of precipitation fell during the 73-day stretch, in addition to snow blowing and snowmelt draining into the open hole. We recognize the professional geotechnical engineer’s opinion that groundwater was not encountered onsite and that they “do not anticipate that groundwater will be encountered during construction.” J2. In our experience, draintile installed directly in topsoil with fabric socks are prone to clogging. You may want to consider design changes to promote long-term effectiveness of the BMP. CSG RESPONSE: Noted. J3. Outdated restoration hatching and linework is shown on L1.0. Please update plan sheet L1.0, as incomplete linework/hatching does not allow for a complete review of the design. CSG RESPONSE: Sheet L1.0 has been updated appropriately. J4. Conflicting design/model inputs for the biofiltration basin: a. Plan view of the biofiltration basin shows rim elevation = 970.0, but storm manhole detail shows rim elevation = 974.3, which is correct? The HydroCAD model uses rim elevation 974.0, but the MIDs model uses 974.3. CSG RESPONSE: The grate of the outflow structure will be at elevation 974.00, and details have been updated to reflect that. b. Plan view of the biofiltration basin shows berm overflow elevation = 975.10, but EOF elevation is listed as 975.0. HydroCAD model uses 974.99. Which is correct? CSG RESPONSE: The berm overflow will be at 975.10 and instances have been updated appropriately. J5. The Wetland Protection (Treatment of runoff to wetlands) requirements based on RPBCWD Rule 3.10b have not been met. Discharge from regulated disturbed areas to a protected wetland must be treated to meet: Remains an open comment. a. The Wetland Protection criteria (Rule J Subsection 3.10b) requires all direct discharge to a medium value wetland to meet at least 60% TP and 90% TSS removal efficiency. Please provide modeling and a summary table showing the runoff entering Wetland A has been treated to these criteria because the submitted MIDs model shows 66% TP and 86% TSS removal efficiencies. Civil Site Group, PC • 5000 Glenwood Avenue • Golden Valley • Minnesota • 55422 www.CivilSiteGroup.com • (612) 615-0060 CSG RESPONSE: Our project meets the wetland protection criteria via the abstraction requirement of 1.1 inch from the regulated impervious surface in Rule J 3.1b.i. J6. A HydroCAD model output was provided containing existing and proposed conditions for the site. The following are comments that should be addressed: Remains open a. The Wetland A watershed is missing in both the existing and proposed HydroCAD models. Please add this watershed to the models based on the information provided in the Stormwater Report (existing/proposed models). CSG RESPONSE: Wetland A watershed is represented in both proposed and existing models. It is represented by “EX1B, EX1C, and OFFSITE B” in the existing model and “PR1B, PR1C, PR1D, and OFFSITE B” in the proposed model for approx. 3.3 acres. The subwatershed is constrained by existing stormwater infrastructure on Lake Lucy Road to the North, Pointe Lake Lucy on the East, and a natural drainage swale on the West. b. A subwatershed labeled “Offsite Wetland B watershed” is input in the HydroCAD model, but no supporting information is provided in the Stormwater Report (existing/proposed models). Please either: i. Show the subwatershed divide and corresponding impervious/pervious/total areas on your watershed map OR ii. Show that the total watershed area tributary to Wetland B in the HydroCAD model matches the area listed in the PCSWMM model CSG RESPONSE: PCSWMM model provided: 12.87 ac, 16.4% imperious (2.11 ac imp, 10.76 ac perv). The HydroCAD models were updated to reflect provided data in the “Existing” model. The drainage areas tributary to Wetland B (all subwatersheds excluding PR1A) in the existing model now show a drainage area of 12.87 acres with 16.4% impervious equal to the provided PCSWMM model. Civil Site Group, PC • 5000 Glenwood Avenue • Golden Valley • Minnesota • 55422 www.CivilSiteGroup.com • (612) 615-0060 c. The impervious and pervious areas input for watershed PR2 do not match the impervious and pervious areas listed in the stormwater report. Please revise either the table in the stormwater report to match the HydroCAD model or vice-versa (proposed model). CSG RESPONSE: Stormwater report table has been corrected. d. Conflicting design/model inputs for the biofiltration basin (proposed model): i. Plan view of the biofiltration basin shows rim elevation = 970.0, but storm manhole detail shows rim elevation = 974.3, which is correct? The HydroCAD model uses rim elevation 974.0, but the MIDs model uses 974.3. Update HydroCAD model with correct rim elevation. ii. Plan view of the biofiltration basin shows berm overflow elevation = 975.10, but EOF elevation is listed as 975.0. HydroCAD model uses 974.99. Which is correct? Update HydroCAD model with correct berm overflow elevation. CSG RESPONSE: Details have been updated appropriately where the grate/top of outlet structure is at 974.00 and the top of the berm is at 975.10. J7. The following are comments relative to the MIDs modeling provided: a. The incorrect zip code was entered resulting in an inaccurate annual precipitation depth (-0.3 inches). Please update the zip code. CSG RESPONSE: MIDS model has been updated to the correct zip code. b. Please update the pervious area to correctly reflect the existing and restored site vegetation (e.g., a portion of disturbed area will be seeded with turf grass). CSG RESPONSE: The MIDS model is used to model abstraction volume. Any additional abstraction by pervious areas not modeled in BMPs are not required to meet the regulated impervious abstraction volume. c. Conflicting design/model inputs for the biofiltration basin (proposed model): i. Plan view of the biofiltration basin shows rim elevation = 970.0, but storm manhole detail shows rim elevation = 974.3, which is correct? The HydroCAD model uses rim elevation 974.0, but the MIDs model uses 974.3. Update MIDs model with correct rim elevation  overflow depth CSG RESPONSE: Details have been updated appropriately where the grate/top of outlet structure is at 974.00 and the top of the berm is at 975.10. Civil Site Group, PC • 5000 Glenwood Avenue • Golden Valley • Minnesota • 55422 www.CivilSiteGroup.com • (612) 615-0060 ii. Biofiltration basin detail shows a total media depth = 2.6’, but the MIDs model uses 2.74’, which is correct? Update MIDs model with correct media depth. CSG RESPONSE: The MIDS model reflects 2.5’ media depth consistent with the biofiltration detail, and 0.24’ below the tile drain invert. 0.24’ below the tile drain invert reflects the 48-hr drain down volume maximum in Type D soils at an infiltration rate of 0.06 in/hr stored in the 0.6’ underground rock section with 40% void space, also depicted in the biofiltration detail. iii. The MIDs model used Media Mix C for the topsoil; however, the biofiltration basin detail calls out “70% homogenous construction sand + 30% organic compost” for the media, which does not accurately represent Media Mix C. Please update the specified media mix on the plan sheets or update the Media Mix type in the MIDs model. Additional information on media mixes can be found here: Engineered (bioretention) media mixes for stormwater applications - Minnesota Stormwater Manual (state.mn.us) CSG RESPONSE: Biofiltration detail has been updated to reflect Media Mix C. J8. Permit applicant must provide a maintenance and inspection declaration. A maintenance declaration template is available on the permits page of the RPBCWD website (http://www.rpbcwd.org/permits/). A draft declaration must be provided for District review prior to recording. Remains an open comment but this information does not need to be provided prior to making a recommendation to the RPBCWD Board. CSG RESPONSE: Noted.