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HomeMy WebLinkAbout2004-02-05 Stormwater Peer Review tipv 19 03 04:34p Eggleston Environmental 9704439262 p. 1 RECEIVED NQ 12003 FAx TRANSMISSION NORTH ANDOVER E+GGLES-.rONENVIRONMENTAL CONSERVAT16 COMMISSION 65 Old Coach Road Sudbury, MA 01776 Tel/Fax: (978)443-9262 To: Julie Parrino, Date: November 19, 2003 N.Andover Cons. Coordinator Fax#: (978)688-9542 Pages: 9, including this cover sheet. From: Lisa D. Eggleston,P.E. Subject: Eaglewood review See attached. hov 19 03 04:.35p Eggleston Environmental 9704439262 p. 2 EGGLESTON ENHRONMENTAL November 19, 2003 North Andover Conservation Commission 27 Charles Street North Andover,MA 01845 Attn, Julie Parrino RE: Stormwater Management Review Eaglewood Shops Retail Development Dear Julie and Commission Members: Per your request, I have conducted an initial technical review of the Notice of Intent (NOI) submittal package for the proposed Eaglewood Shops Retail Development in North Andover with respect to stormwater management. The materials I have received and reviewed to date include the following: f ■ Notice of Intent with Attachments A through F, Eaglewood Shops Retail Development,prepared for Eaglewood Properties,LLC by VHB/Vwiasse Hangen Brustlin, Inc. and dated 9/26/03. ■ Design Plans entitled "Eaglewood Shops,Turnpike St. (Route 114),North Andover MA", 11 sheets (C-1 through C-8 and SV-1),prepared by VI-IB/Vanasse Hangen Brustlin, Inc. and revised through 9/25/03. My primary focus in this initial review is on the overall stormwater management approach and design concepts used in the project, as well as its compliance with the stormwater management and flood storage standards (Section IV) of the North Andover Wetlands Bylaw and with the Massachusetts Wetlands Protection Act and Stormwater Management Policy. My comments are outlined below. Overall Stormwater Management Approach_and S stemDesi n The project site, located on Route 114 near its intersection with Waverly Road, is approximately 13.3-acres in size and in its current state is largely undeveloped and wooded. The triangular shaped parcel slopes from the southeast toward the northwest, with a total elevation drop of approximately 100 feet and an average slope of 6.5 percent. There is a forested wetland in the northwest corner of the site, to which most of the surface drainage flows. (I would presume that subsurface drainage on this site flows toward this wetland as well.) Flow through the wetland discharges through a culvert under Waverly Road and ultimately to the'Shawsheen River. 55 OLD COActI ROAD SuoBuRrMA 01776 rEVrAx 978.443.9262 Hav 19 03 04: 35p Eggleston Environmental 9704439262 p. 3 E,joleNvood Shops, Technical RwvicN:v November 19, 2003 The proposed project, a retail development comprised of three buildings (10 to 12 stares} and associated parking, driveways, landscaping, and utilities would encompass most of the upland portion of the project site. As proposed, all of titre stormwater drainage from the development would be conveyed through a closed drainage system to a stormwater detention basin located just upgradient of the 25-foot no-disturbance zone associated with the wetland. The basin-is intended to attenuate peak flow rates from the development, such that the peak runoff rates discharged from the site do not exceed pre-development rates. Water quality treatment would be provided through a combination of street/pavement sweeping, deep suinp hooded catchbasins, a sediment forebay and extended detention in the basin. As proposed, a foot of storage in the basin below the outlet elevation would store and infiltrate the required recharge volume from the site. My comments on the overall stormwater management approach and drainage system design are outlined below: 1. As proposed, all of the runoff from the developed portions of the site would be routed through a single large detention basin for groundwater recharge and surface discharge. No segregation of roof runoff from pavement runoff is proposed,nor has any attempt been made to distribute the recharge throughout the site to better replicate existing conditions. ' 2. The proposed dual use of the detention basin for groundwater recharge and for extended detention is not compatible nor is it consistent with the DEp design guidelines for extended detention basins. The sediment removal levels achieved by extended detention are accomplished through increased settling of solids in the basin, which is in direct conflict with the promotion of infiltration through the bottom of the basin. 3. The proposed detention basin would be excavated from approximately 2 to 11 feet below existing grade on a relatively steep (>7 percent) slope, and seems likely to intercept subsurface groundwater flow (particularly if it is perched). Site specific testing to determine soil infiltration rates, depth to groundwater and depth to bedrock in the vicinity of the detention basin is needed and any potential groundwater seepage into the basin needs to be factored into the design. 4. The HydroCAD model of the post-developi-nent site treats the entire developed portion as one drainage area. In order to more accurately reflect the rate of delivery of flow from the different portions of the site to and through the basin, the post-development model should be broken out into several subareas. Roof areas and individual drainage networks should be inodeled separately. 5. Existing drainage patterns on the site need to be clarified. Based on the topography shown on Sheet SV-1,it appears that there is some sort of drainage channel or swale(behind the property owned by Victor Hatein) that intercepts a portion of the runoff from the southern end of the site and conveys it in a westerly. Nov 19 03 04: 35p Eggleston Environmental 9794439262 p. 4 Noveniber 19, 2003 direction offsite, My concern would be that there might be downgradient resource areas that would be impacted by the project. 6. On the proposed grading plans, there are several locations where drainage is directed onto adjacent properties. A portion of the northern-most driveway (accessing Building 1) drains onto Route 114, with no provision made for the collection of this drainage. A portion of the site along, Route 114 appears to drain onto the sidewalk, and another portion drains to a new catchbasia tied into the highway drainage system. (I presume MHD permission will be needed, but who will maintain this structure?) The embankment behind the bank property extends to the property lime in places and will direct drainage onto the bank property. In addition, the embankment located along the northwestern edge of the site slopes directly onto the adjacent property, It is not clear how the runoff from this embankment would be directed toward the wetland as modeled. 7. More catchbasins are needed in the proposed parking areas and driveways. There are several locations, e.g. the driveway behind Buildings 2 and 3 and the parking lot in front of Building 1 where the overland distance exceeds typical design standards. Also, it appears that a portion of the runoff down the driveway behind Building 1 would pool at the base of the loading dock. 8. The site plans show several reserved parking areas between Retail Building 2 and the detention basin, but these areas have not been factored into the drainage system design, nor has the grading to accommodate these parking facilities been shown. 9. The 6 to 15-foot berm and modular block retaining wall impounding the detention basin would subject to jurisdiction by the Massachusetts Office for Dam Safety. The design of the embankments and spillways must meet the applicable state regulations'(302 GMR 10,00). 10, It is not clear what the purpose of the Turfstone interlocking pavers in the southernmost overflow parking area is, or-how they are treated in the drainage calculations. 11. It is also not clear what function, if any, the depressed landscape islands in the upper parking lot provide with respect to stormwater management. My specific comments on the project as they relate to the project's compliance with the nine North Andover and State Stormwater Standards follow. Standard#1. Untreated Stormwater Standard #1 prohibits any new discharges of untreated stormwater to wetland resource areas of the Town of North Andover, whereby treated stormwater is defined to the Wov 19 03 04: 35p Eggleston Environmental 9784439262 p. 5 L1. Englewood SIw1�S. `Technical Review November 19. 2003 stormwater that meets the requirements in Standards 2 through 9, As currently proposed, all of the runolT flows from the developed areas of the project site will undergo treatment in the extended detention basin prior to discharge, with pretreatment provided by deep sump catchbasins and a sediment forebay, The adequacy of the treatment provided is addressed under Standard #4. Standard#f2.Post-Development Peak Discharge Rates The North Andover regulations require that post-development peak discharge rates for the 1, 10 and 100-year storm events do not exceed pre-development peak discharge rates. The state standards require this of the 2 and 10-year 24-hour storm events, with evaluation to determine that the 100-year event does not cause increased flooding impacts offsite. The North Andover regulations also call for a sub-watershed delineation of the site, including the peak flow rate, time of peak flow and the volume of runoff at each discharge point,to be used as a basis for the hydrologic analyses. The NOI package includes a hydrologic analysis based on modeling conducted using the HydroCAD 6.10 model for the 2, 10 and I00-year design storms which indicate that the peak rate of runoff to the wetlands will not exceed pre-development rates. I have the following comments on the hydrologic analysis: ' 1, The analysis does not include the I-year storm event required by the local bylaw, nor does it address impacts to the timing of peak flow and the volume of runoff discharged to the wetland for each of the design storms. 2. As indicated above, the post-development model should be broken out into several subareas to more accurately reflect the rate of delivery of flow from the different portions of the site to and through the basin. Roof areas and individual drainage networks should be modeled separately. Portions of the developed site that would drain to adjacent properties or to the.drainage system in Route 114 should also be modeled separately, 3. Figure 4-5 (Proposed Drainage Areas) seems to include a portion of the pavement along the northern end of the property in Subcatchment PR-2,yet there is no impervious area listed in this subeatchment in the model. This needs further clarification. 4. Further clarification is also needed of the post-development flow paths from Subcatchment PR-2. 5. Storage capacity in the detention basin below the outlet invert should not be included in the model unless it can be demonstrated that this portion of the basin will be emptied (e.g. through exfiltration) within 48 to 72 hours after a storm event. Nov 19 03 04: 36p Eggleston Environmental 9704439262 p, 6 E�E'100N-ood itcts;s, `1'ealtFtical Rev;ew November 19' 200'1 6. Under post-development 100-year storm conditions, the peals water level in the detention pond exceeds the emergency spillway elevation by 0.7 feet and is within 0.5 feet of the top of the be= I recommend a more conservative design that provides a rniiiimum of I foot of freeboard above the 100 year level, and does not utilize storage in the pond above the spillway elevation to achieve the required flow attenuation. Standard ##3. Rechar e to Groundwater Standard 43 requires that the annual groundwater recharge from the post-development site should approximate the annual recharge from the pre-development site, based on pre- development soil conditions. The NOI submittal includes infiltration volume calculations based on 6.7 acres of net :impervious area being added to the site in areas of HSG B and C soils, The calculated recharge volume is 3,957 cubic feet. This volume is more than exceeded by the 12,922 retention volume provided at. the bottom of the detention basin however, as indicated above, I do not believe that infiltration through the bottom of the proposed extended detention basin is consistent with its design as a water quality BMP. In addition, I offer the following comments: 1. Wherever the recharge facilities are located on the site, soil testing data will be needed to confirm infiltration rates, depth to groundwater, depth to bedrock, and general suitability for infiltration, 2. The applicant needs to provide calculations demonstrating that recharge facilities will be totally dewatered within 72 hours following a storm event. Standard#4. 80%TSS Removal Standard 94 stipulates that stormwater management systems be designed to remove 80% of the average annual load of total suspended solids (TSS) from the post-development site. It is presumed to be met when suitable BMPs are implemented, sized appropriately to treat the prescribed runoff volume, and properly maintained. The stormwater management system proposed for this project would utilize a combination of street sweeping and deep sump catchbasins with outlet hoods followed by treatment through a sediment forebay and an extended detention basin to reduce the total suspended solids (TSS) load from pavement nwoff on the site_ My comments are as follows: 1. It is not clear why the water quality volume calculations use a net impervious area of 5.87 acres while the infiltration volume calculations use 6.7 acres and the model input uses a net increase in.impervious area of 6.8 acres. N6v 19 03 04: 36p Eggleston Environmental 9764439262 p. 7 E�tglev,;c�i�d Shctias: Tec:ktnicai l:evEceti 6 2. The DEP Stormwater Policy states that granting 10 percent TSS removal credit for pavement sweeping is discretionary on the part of the Commission. At a mH mum the frequency of sweeping should be increased from that proposed in the vacuum manual. I would suggest weekly sweeping with a vacuu sweeper from March through November to achieve this removal rate. Alternatively, I would encourage the applicant to incorporate other means of TSS removal in the project design. 3. The 12-inch pipe draining the driveway to the rear of retail buildings 2 and 3 and the roof drainage from both buildings discharges to the detention pond directly and does not undergo pretreatment in the sediment forebay. The outlet of this pipe should be moved further away from the outlet of the extended detention basin in order to prevent short-circuiting of the basin. While much of the flow from this pipe is clean roof drainage, the pavement runoff'needs to either be segregated and re-routed through the sediment forebay or undergo some other form of pretreatment. It is not clear whether this is what is intended by the "water quality inlet"labels on catchbasins CBAI l and CBA8. Do these relate to the Stormceptor inlet units shown on Detail sheet C-67 If so, this should be included in the TSS removal calculations and design calculations for the Stormceptors provided. Per my previous comment,additional inlets are needed in this area as well. 4. Additional information is needed to demonstrate that the proposed detention basin would provide adequate detention to achieve the stated pollutant removals. Specifically, the basin should provide a minimum of 24 hours detention for the range of storms that would occur over a year and should empty within.a 48 to 72- hour period following a storm to provide storage capacity for the next event. A low flow charrnel should be, incorporated in the basin design and the flow path through the basin should be maximized. In addition, a multi-stage outlet structure should replace the single 12-inch outlet pipe proposed. Standard #5. Hi her Potential Pollutant Loads The proposed project is a commercial development with higb-intensity use; and therefore constitutes a land use with higher potential pollutant loads as defined by the Stormwater Management Policy. Provided all pavement runoff undergoes pretreatment, the proposed BMPs are suitable for use in this application. Standard#6. Protection of Critical Areas The project site is not in a critical area as defined by the Stormwater Management Policy, Standard 07. Redeveio rnent The proposed project is not a redevelopment project as defined in the Stormwater Management Standards. N'ov 19 03' 04: 36p Eggleston Environmental 9704439262 p, g i~"glewood S1171Is. TOr.4�ni4a1 Standard 98. Erosion and Sediment Control Erosion and sediment control measures to be undertaken during project construction are preliminarily addressed in the NOl submittal and depicted on Sheets C-3A, C-3B and C- 3C of the design plans. 1. Given the amount of regrading that would be required on this site, the Commission may want to request that the applicant provide cut and fill calculations. The transport and stockpiling of material on tine site should also be addressed. 2. As indicated in the NOI, the proposed project will be'subject to NPDES permit compliance and will require preparation of a construction Stormwater Pollution Prevention Plan (SWPPP). The Commission should be provided the opportunity to review and approve the S WPPP as it is developed, including locations and sizing of temporary sediment basins. Provision for construction monitoring of the site should also be established, Standard#9. Operation and Maintenance Plan ` The applicant has submitted an O&M plan outlining measures for maintaining the structural water quality controls on the site. The plan identifies the owner and party responsible for O&M as being Eaglewood Properties LLC. 1. The current design plans do not provide suitable access to the detention basin and sediment forebay for maintenance purposes. 2. The O&M plan should include periodic removal of sediments from the extended detention basin and the sediment forebay. 3. The O&M plan references sorbent pillows to be placed in each catchbasin to absorb hydrocarbons. These should be shown on the design detail sheet. Proper disposal of petroleum hydrocarbons removed from the catchbasins (e.g. by a hazmat contractor) should be addressed in the O&M Plan. 4. Maintenance of the Stormceptor units, if they are an intended component of the stormwater management system should also be addressed. 5. The areas designated for snow storage on Sheet C-2 need to be clarified—are they on the parking lot surface (in which case parking spaces will be lost) or on the landscaped aprons? I recommend that the snow be stockpiled in closer proximity to onsite drainage structures to minimize icing on the pavement surfaces. Provision should also be made for removal of snow from the site if the designated storage capacity is exceeded. A description of the proposed snow management Nov 19 03 04:37p Eggleston Environmental. 9784439262 p. 9 �ltlt el[li)c l '9' 2001, procedures for the site in accordance with the DEP Bureau of Resource Protection snow disposal guidelines should be included in the O&M Plan. Additio al C rnrnents 1. Design details are needed for the detention pond berm, spillways and outlet control and for the proposed retaining walls shown on the site plans. Top and bottom elevations for the rctaining walls should also be shown on the plans. 2. it is not clear why the drain manhole detail shown on sheet C-6 has a hooded outlet. 3. There is a design detail for a double-grated catchbasins — where are they located on the plan? These units should be equipped with separate grates to facilitate .access and maintenance. 4. There is a design detail for a Stormceptor inlet unit. Where is this unit located on the plan? 5. The drainage system design calculations provided in Appendix P indicate excessively high velocities in some structures. The system should be designed to maintain velocities through the system between 2.5 and 10 fps, Minimum S mittal Re uir rnents The NOI submittal package is lacking the following information required by the North Andover Wetlands Protection Bylaw: • Test pit data indicating seasonal high groundwater elevations • Analysis of peak flow rates for 1-year 24-hour storm • Analysis of project impacts on discharge volume and time of concentration for all design storms • Design criteria for extended detention basin I appreciate the opportunity to assist the North Andover Conservation Comrnission.with the review of this project, and hope that this information is suitable for your needs. Please feel free to contact me if you or the applicants have any questions regarding the issues addressed berein. Sincerely, EGCrLESTON ENVIRONMENTAL Lisa D.Eggleston,P.E.