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Home My WebLink About240920_2nd_HW_SWPeerReview_BoatLaunch - - 0 GREAT POND ROAD %�. Horsley Wiften Group 0 SLIStainable, Ehvirownental Solutions 112 W'at r `tr t-61 Floor-Boston,MBA 02109 .......... 5 -2 1 ho,r 1 ten September 20, 2024 Ms. Jean Enright, Planning Director North Andover Planning Board 120 Main Street North Andover, Massachusetts 01845 Ref: 2nd Stormwater Peer Review North Lake Cochichewick Boat Launch North Andover, Massachusetts Dear Ms. Enright and Board Members: The Horsley Witten Group, Inc. (HW) is pleased to provide the North Andover Planning Board with this letter report summarizing our second review of the Stormwater Report and plan set for the proposed redevelopment of the North Lake Cochichewick Boat Launch (Boat Launch), located across the street from 1939 Great Pond Road, North Andover, MA. The plans and Stormwater Report were prepared by Environmental Partners on behalf of the Town of North Andover (Applicant). The redevelopment project proposes to reconstruct the existing boat launch, add a new block retaining wall, install a permeable access drive and parking lot, and install two bioretention areas to manage stormwater. The proposed redevelopment includes reducing the total impervious area from 5,253 square feet (sf) to 483 sf, which includes eliminating the 5,074 sf of existing gravel parking areas considered impermeable and installing 9,991 sf of permeable pavers with crushed stone. The entire site is within the 150-foot Watershed Protection District Non-Disturbance Zone of Lake Cochichewick, with proposed work within Bordering Vegetated Wetlands (BVW), inland Bank, Land Under Waterbodies and Waterways (LUWW), Bordering Land Subject to Flooding (BLSF), and the 25-foot, 50-foot, and 100-foot Buffer Zones to the BVW. The project is under the jurisdiction of the North Andover Conservation Commission. The boat launch ramp is located within the 100-year floodplain, identified as Zone A on the most recent Flood Insurance Rate Map (FIRM). The Applicant has noted the Top of Bank JOB) at approximate elevation 113 and the Observed High Water (OHW) at approximate elevation 114. By modifying the grades along the bank and reducing the slope of the new ramp, the proposed project increases the flood storage volume by 100 cubic feet (cf) below elevation 114. The following additional documents were received by HW in response to our initial review: • Letter to North Andover Planning Board, regarding North Lake Cochichewick Boat Launch — RE: Initial Stormwater Peer Review, prepared by Environmental Partners, dated September 11, 2024 (7 pages) with the following attachments: 0 2. Permeable Paver Detail, dated September 8, 2024 (6 pages); 0 3. HydroCAD Stage Storage Tables, North Lake Cochichewick Boat Launch, Town of North Andover, MA, prepared by Environmental Partners, printed September 9, 2024 (2 pages); r � [f n. t- I, " ii tte n G ro u p �IM Horsley W'Itten Group, [iris. Town of North Andover September 20, 2024 Page 2of8 o 4. Revised TSS Worksheets, North Lake Cochichewick Boat Launch, Town of North Andover, MA, prepared by Environmental Partners dated September 9, 2024 (3 pages); o 5. North Andover Design and Performance Criteria with Attachments (2 pages); ■ Stormwater Model Report (Existing and Proposed), North Lake Cochichewick Boat Launch, Town of North Andover, MA, prepared by Environmental Partners, dated September 11, 2024 (111 pages); and o 6. BMP Location Map, North Lake Cochichewick Boat Launch, Town of North Andover, MA, prepared by Environmental Partners, dated August 21, 2024 (1 page). Stormwater Management Design Peer Review HW offers the following comments concerning the stormwater management design as per the Massachusetts Stormwater Handbook (MSH) dated February 2008, and the North Andover Chapter 165 Stormwater Management and Erosion Control Bylaw (Bylaw), and the Chapter 250 Stormwater Management and Erosion Control regulations (Stormwater Regulations) adopted June 21, 2022. In accordance with Article 195-4.19.C (4)5 "All construction in the Watershed Protection District shall comply with best management practices for erosion, siltation, and stormwater control in order to preserve the purity of the groundwater and the lake; to maintain the groundwater table; and to maintain filtration and purification functions of the land." The stormwater best management practices have been reviewed in accordance with the most recent version of the Massachusetts Stormwater Standards as well as the North Andover Stormwater Management and Erosion Control Bylaws. We have used the Massachusetts Stormwater Standards as the basis for organizing our comments. However, in instances where the additional criteria established in §250-22 of the North Andover Code requires further recommendations; we have referenced these as well. The following comments correlate with our initial review letter dated August 26, 2024. Follow up comments are provided in bold font. 1. Standard 1: No new stormwater conveyances (e.g., outfalls) may discharge untreated stormwater directly to or cause erosion in wetlands or waters of the Commonwealth. a. The Applicant has analyzed the pre- and post-development stormwater runoff at one Design Point 1 (DP1), Lake Cochichewick. i) Under existing conditions, there are no stormwater practices to manage the runoff. The project area has been divided into 2 subcatchment areas. (1) Subcatchment 1 S flows towards the southwest edge of the project area into the lake via sheet flow. (2) Subcatchment 2S flows towards the southeast edge of the project area into the lake via sheet flow. ii) Under proposed conditions the Applicant has subdivided the project area into four subcatchment areas. ° a' ml ae', iii � �� "III�� iii.�� . �. iii��.. �.�III III�� IIL �. ..�IIL ...�.�iii�� III III �. �.iii.�� .��' �� iii�� III �iii�l��..��iii.�. IIL '�.t III l l iii�.�!ii .� Town of North Andover September 20, 2024 Page 3of8 (1) Subcatchment 1 S flows towards the southwest edge of the project area into the lake via sheet flow. Permeable pavers have been proposed to allow some of the runoff to infiltrate into the ground before discharging into the Lake. (2) Subcatchment 2S flows towards the southeast edge of the project area into the lake via sheet flow. Permeable pavers have been proposed to allow some of the runoff to infiltrate into the ground before discharging into the Lake. (3) Subcatchment 3S, includes a large portion of the permeable pavers as well as a section of Great Road that flows onto the site. The runoff is directed into a (Bioretention Area 2). Bioretention Area 2 is piped into Bioretention Area 1. (4) Subcatchment 4S, includes a large portion of the permeable pavers, as well as a section of Great Road that flows onto the site. The runoff is directed into a bioretention area (Bioretention Area 1). Bioretention Area 1 outlets via a riprap channel towards the Lake. iii) The Applicant has provided the velocity of the riprap channel documenting that the proposed discharge should not cause erosion into the BVW or the Lake. September 20, 2024: No further action requested. 2. Standard 2: Stormwater management systems shall be designed so that post-development peak discharge rates do not exceed pre-development peak discharge rates. a. HW has reviewed the Pre-Development and Post-Development Drainage Plans and the HydroCAD model. The subcatchment areas, surface materials, curve numbers (CN), times of concentrations, depths of precipitations, and flow patterns appear reasonable. A CN of 80 was used for the permeable interlocking concrete pavement based on the Manufacturer recommended CN value. HW recommends that the Applicant provide a plan view detail of the permeable interlocking concrete pavement with paver dimensions, and the placement of the 1/4-inch crushed stone in openings for clarity. September 20, 2024: The Applicant has provided images and a Typical Cross Section for the concrete permeable pavers in Attachment 2 of its response letter. No further action requested. b. HW recommends that the Applicant clarify the stone to be placed beneath the concrete pavers. Specifications for the process gravel backfill and the crushed stone bedding would be beneficial to confirm the permeable interlocking concrete pavement will function as anticipated. HW recommends that the Applicant confirm if an underdrain is applicable and update the details as necessary. September 20, 2024: The Applicant has provided a Typical Cross Section for the concrete permeable pavers in Attachment 2 of its response letter. No further action requested. c. HW recommends that the Applicant specify the filter fabric and clarify if the intent is to install the filter fabric under all the pavers to create an impermeable liner. HW notes that the Applicant has not included exfiltration or storage beneath the pavers in the HydroCAD model. September 20, 2024: The Applicant has noted that the filter fabric proposed is . � I�. . �II .� �� .�i �.�I �� i ° � � �� i�� . Town of North Andover September 20, 2024 Page 4 of 8 designed to act as a permeable membrane. HW has no issue with the proposed filter fabric. No further action requested. d. The Applicant has used an exfiltration rate of 0.17 inches per hour (iph) for the Bioretention Areas, which is comparable to a sandy clay loam for hydrologic soil group (HSG) C. Three borings were conducted within the project area which support the exfiltration rate used. HW notes that the test pits are not within the footprints of the bioretention areas. The value appears reasonable. However, prior to construction additional soil testing should be conducted within the footprints to confirm the soil texture as well as the depth to estimated seasonal high ground water (ESHGW). September 20, 2024: The Applicant has noted under comment 3.a. that additional soil testing will be conducted by the contractor. The Planning Board may choose to require receipt of the soil logs as well as confirmation from a professional engineer that the design presented does not need to be adjusted as a Condition of Approval. e. The water table for the three borings was noted to be 6.5 feet below ground surface (bgs). Based on boring B1 the ESHGW is at approximately elevation 110.75. The bottom surface of the bioretention areas is elevation 115.0 and 115.5 with approximately 4.5 feet of planting soil and crushed stone below, to elevation 110.5 and 111.0. HW recommends that the Applicant conduct additional soil testing to document that the ESHGW is lower than elevation 110.5 or raise the bottom of the systems. September 20, 2024: The Applicant has noted that additional test pits will be incorporated into the final design. As noted above the Planning Board may choose to require receipt of the soil logs as a Condition of Approval. f. In accordance with §250-22 B. (6) a summary of pre- and post-development peak rates and volumes of stormwater demonstrating no adverse impacts should be provided as part of the narrative. The Applicant has provided the peak flows but has not provided the peak volumes for the 2-year, 10-year, and 100-year 24-hour storm events. HW recommends that the Applicant provide a volume comparison table as required. September 20, 2024: The Applicant provided the HydroCAD model for each subcatchment area. HW has provided a summary table comparing the peak flows and peak volumes as required per §250-22 B. (6) of the North Andover Stormwater Regulations. Storm Event Existing Peak Proposed Peak Existing Peak Proposed Peak Flow(cfs) Flow(cfs) Volume(cf) Volume(cf) 2-yr, 24 hour 1.47 0.74 4517 2288 10-yr, 24 hour 2.90 1.58 8820 6458 25-yr, 24 hour 4.23 3.17 12900 10460 100-yr,24 hour 6.83 6.44 21169 18615 mIII . � ii �� . �� III � i�� .� ii �� II � �i � �� . Town of North Andover September 20, 2024 Page 5 of 8 3. Standard 3 requires that the annual recharge from post-development shall approximate annual recharge from pre-development conditions. a. The Applicant has reduced the total impervious surface. The annual recharge from post- development is greater than the pre-development conditions. The Applicant has further provided recharge calculations. However, as noted above HW recommends that additional soil testing is conducted to confirm the exfiltration rate and the ESHGW. HW recommends that the Applicant provide the stage storage HydroCAD worksheet for the two bioretention areas to confirm the storage volume listed in the calculations (1,432 cubic feet (cf) for Bioretention Area #1 and 1,239 cf for Bioretention Area #2). September 20, 2024: The Applicant has agreed to add test pits to confirm the ESHGW and exfiltration rate in its final design. The Applicant has provided the HydroCAD Stage-Area-Storage sheets for Bioretention Areas as suggested. As noted above the Planning Board may choose to require receipt of the soil logs as a Condition of Approval . b. Per §250-23 C. (1)(b) redevelopments sites are required to retain the volume of runoff equivalent to 0.8 inch multiplied by the total post-construction impervious surface or meet a combination of retention and treatment that achieves the above standards listed under§250-23 C. (1). HW notes that the HydroCAD model indicates that the Applicant is retaining the 2-year storm event within the bioretention areas. HW further notes that the proposed Bioretention Areas are managing the runoff from a portion of Great Pond Road. HW has no further comment. September 20, 2024: No further action requested. 4. Standard 4 requires that the stormwater system be designed to remove 80% Total Suspended Solids (TSS) and to treat 1-inch of volume from the impervious area for water quality. a. The Applicant has provided a TSS worksheet that states the Bioretention Areas have a TSS Removal Rate of 90%. In accordance with the MSH, Volume 1, Chapter 1, page 11 90% credit is allowed when combined with adequate pretreatment. HW recommends that the Applicant clarify what the pretreatment practice is. September 20, 2024: The Applicant has provided a detailed explanation of the proposed treatment trains and updated TSS worksheets. HW agrees that the requirement to remove 80% of TSS has been met. No further action requested. b. HW further notes that including 90% pretreatment from Bioretention Area 2 prior to Bioretention Area 1 is not realistic considering the additional surface area captured by Bioretention Area 1 that does not go through Bioretention Area 2 first. September 20, 2024: The Applicant has provided a detailed explanation of the proposed treatment trains and updated TSS worksheets. HW agrees that the requirement to remove 80% of TSS has been met. No further action requested. 5. Standard 5 is related to projects with a Land Use of Higher Potential Pollutant Loads (LUHPPL). a. The proposed use is not considered a LU H PPL, therefore Standard 5 is not applicable. No further action requested. a ml ae', µ iii � � �� "III�� iii.�� . �. iii��.. �.�III III�� IIL �. ..�IIL ...�.�iii�� III III �. �.iii.�� .��' �� iii�� III �iii��..��iii.�. IIL '�.�III l �iii�.�1 i .� Town of North Andover September 20, 2024 Page 6of8 September 20, 2024: No further action requested. 6. Standard 6 is related to projects with stormwater discharging into a critical area, a Zone Il, or an Interim Wellhead Protection Area of a public water supply. a. The proposed development is discharging into an Outstanding Water Resource, listed as Zone A and Zone B public surface water supply. HW notes that in accordance with the MSH Volume 1, Chapter 1, page 18, "Unless essential to operation of a public water system, stormwater BMPS are prohibited within the Zone A."HW understands that the proposed redevelopment is a boat launch for the Town of North Andover and is an improvement over the existing condition. HW further notes that exfiltrating Bioretention Areas are considered an accepted infiltration practice for stormwater discharges to outstanding resource waters. It is HW's understanding that MassDEP has stated that porous pavement is not suitable within a Zone I or a Zone A. The practice can be lined with an underdrain. The underdrain must employ a practice to provide for shut down and containment if there is a spill on the surface. HW recommends that the Applicant review the permeable pavement design and confirm it meets MassDEP's requirements. September 20, 2024: The permeable paver detail provided by the Applicant describes the usage of paving stones, a type of porous pavement listed by MassDEP. The usage of porous pavement in regards to Standard 6 is described as "not suitable especially within Zone Its or Zone A's of public water supplies" in Volume 2, Chapter 2, page 118 of the MSH. HW understands that a redevelopment project is required to meet this standard to the maximum extent practicable. HW also notes that Lake Cochichewick does not allow any gasoline or diesel-powered engines, so the risk of oil getting into the water supply is diminished. The Boat Launch appears to be primarily used for kayaks and canoes. HW agrees that the project will be an improvement over existing conditions, therefore HW accepts the use of permeable pavement if the Applicant is able to obtain a Section 401 WQC from MassDEP. 7. Standard 7 is related to projects considered Redevelopment. a. The Boat Launch project is considered a redevelopment because it has reduced the total impervious area. Per the MSH, a redevelopment project is required to meet the following Stormwater Management Standards only to the maximum extent practicable: Standard 2, Standard 3, and the pretreatment and structural best management practice requirements of Standards 4, 5, and 6. Existing stormwater discharges shall comply with Standard 1 only to the maximum extent practicable. A redevelopment project shall also comply with all other requirements of the Stormwater Management Standards and improve existing conditions. HW concurs that the Applicant will improve existing conditions. September 20, 2024: No further action requested. b. HW notes that the North Andover Stormwater Management and Erosion Control Bylaws have specific requirements for redevelopment projects that are more stringent than the MSH. HW recommends that the Applicant clearly demonstrate that it complies with the local regulations. September 20, 2024: The Applicant mentions "project compliance with the . � I�. . �II .� i�� ..�ii �.�I � �� i ° � � �� i�� . Town of North Andover September 20, 2024 Page 7of8 performance criteria as identified in Section 250-27". However, §250-27 relates to the O&M Plan, while §250-23 relates to redevelopment projects. Attachment 5 provided by the Applicant (North Andover Design and Performance Criteria with Attachments) illustrates how the project complies with Standard 2, but it does not directly reference the stormwater requirements in §250-23. Specifically, §250-23C provides specific requirements for redevelopment sites such as reducing total phosphorus. HW suggests that the Applicant confirm it is complying with §250-23. 8. Standard 8 requires a plan to control construction related impacts including erosion, sedimentation, or other pollutant sources. a. The proposed project will be disturbing less than one acre of land. Therefore, a Stormwater Pollution Prevention Plan (SWPPP) is not required by EPA. September 20, 2024: No further action requested. b. The Applicant has provided a detail for Sedimentation Control at Catch Basins Silt Sacks. However, the location for the silt sacks is not obvious on the Erosion Control and Dewatering Plan. HW recommends that the Applicant install silt sacks in all catch basins within 100 feet of the construction entrance. September 20, 2024: The Applicant has clarified the location of a silt sack to be installed at the catch basin downslope of the project site and will indicate it on final design drawings. No further action requested. c. The Applicant has provided an Erosion Control and Dewatering Plan, that includes a 12- inch filter sock and silt fence within the project area. The Applicant has also proposed a turbidity curtain and cofferdam to be located within the Lake along the Limit of Work. HW recommends that the Construction Entrance be a minimum of 30 feet long. September 20, 2024: The Applicant confirmed that the construction entrance on Sheet C-2 of the permit drawings is at least 30 feet long. However, on Sheet CD-1 the construction entrance detail is shown as 15 feet long. HW recommends that the Applicant confirm that the plan and construction detail are consistent. d. There appear to be 16 trees proposed to be removed and 15 native trees to be installed. HW recommends that the Applicant confirm that it is necessary to remove all the trees proposed to be cut and list the size and types of trees to be installed. September 20, 2024: Standard 8 applies to impacts from land disturbances, which includes tree clearing. HW defers to the North Andover Planning Board and Conservation Commission for approval of the proposed tree clearing. 9. Standard 9 requires a Long-Term Operation and Maintenance (O & M) Plan to be provided. a. The Applicant included an O&M Plan in Attachment 8 of the Stormwater Report. The O&M Plan is for the Bioretention Areas only. HW recommends that the Applicant include the routine inspections and maintenance of the permeable pavers as well as the riprap aprons and lined swale. September 20, 2024: In accordance with §250-27 A. An operation and maintenance plan (O&M Plan) for the permanent stormwater management system is required at a' ml ae', µ iii � � �� "III�� iii.�� . �. iii��.. �.�III III�� IIL �. ..�IIL ...�.�iii�� III III �. �.iii.�� .��' �� iii�� III �iii��..��iii.�. IIL '�.�III l �iii�.�1 i .� Town of North Andover September 20, 2024 Page 8of8 the time of application for all projects that include the structural and nonstructural stormwater BMPs. The Applicant has provided a BMP location map and O&M Plan for the Bioretention Areas only. However, an O&M Plan is required for all structural and nonstructural stormwater BMPs, which includes permeable pavers, riprap aprons, and the lined swale. HW recommends that the Applicant provide the O&M Plan for long term functionality of the proposed stormwater system. b. HW further recommends that the Applicant include a simple maintenance schedule, with a simple sketch to illustrate where the practices are located on the site, as well as a budget, so that the property owner understands what to expect. September 20, 2024: In accordance with MSH Standard 9, "the Long-Term Operation and Maintenance Plan shall at a minimum include: ... 3. The routine and non-routine maintenance tasks to be undertaken after construction is complete and a schedule for implementing those tasks; ... 6. An estimated operations and maintenance budget". HW recommends that the Applicant include the information noted above to confirm the Town fully understands what is expected for long term maintenance. 10. Standard 10 requires an Illicit Discharge Compliance Statement be provided. a. The Applicant has provided an Illicit Discharge Compliance Statement signed by the engineer. The Planning Board may choose to require receipt of a statement signed by the Property Owner prior to land disturbance. September 20, 2024: HW recommends that the Planning Board require receipt of a signed statement by the Property Owner prior to land disturbance as a Condition of Approval. Conclusions HW recommends that the Planning Board require that the Applicant provide a written response to address the few outstanding comments as part of the Board's review process. The Applicant is advised that provision of these comments does not relieve him/her of the responsibility to comply with all Town of North Andover Codes and By-Laws, Commonwealth of Massachusetts laws, and federal regulations as applicable to this project. Please contact Janet Bernardo at 508-833-6600 or at jbernardo@horsleywitten.com if you have any questions regarding these comments. Sincerely, HORSLEY WITTEN GROUP, INC. y III ^a ..... +'"" ,hV fi 4 Janet Carter Bernardo, P.E. Principal III I � ii . � III I ..v ii I.tI l Ll n �ii d .II Ii n° �� I�� i�� .