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HomeMy WebLinkAboutMiscellaneous - 1679 OSGOOD STREET 9/20/2011 Eggleston Environmental l August 16, 2010 North Andover Planning Board 1600 Osgood Street North Andover, MA 01845 Attn: Judy Tymon, Town Planner RE: Stormwater Management Review 1679 Osgood St. &Bradford St. Dear Ms. Tymon and Board Members: Per your request, I have conducted an initial technical review of the Definitive Subdivision application packet for the 1679 Osgood Street & Bradford Street site. The materials I have received and reviewed to date include the following: ■ Bound copy of Definitive Subdivision Application Package, for GMZ Realty Trust, Route 125 &Bradford Street, prepared by Jones&Beach Engineers, Inc. and dated July 16, 2010. ■ Drainage Analysis, Sediment and Erosion Control Plan and Stormwater Pollution Prevention Plan, GMZ Realty Trust, 1679 Osgood St, prepared by Jones&Beach Engineers, Inc. and dated July 12, 2010. ■ Definitive Subdivision Plan(Sheets 1-19 of 21) for Tax Map 61, Lots 16 &34, 1679 Osgood St. &Bradford St,prepared by Jones&Beach Engineers, Inc. and dated July 14, 2010.The focus of my review is on the proposed stormwater management aspects of the project. My comments are as follows: It is my understanding that a Notice of Intent (NOI) application for the project has been filed concurrently with the Conservation Commission, and that my review is intended to assist both the Planning Board and the Conservation Commission in their respective reviews of the project. My primary focus in this initial review is therefore on the overall stormwater management approach and design concepts used in the project, as well as its compliance with the Rules and Regulations Governing the Subdivision of Land in Town of North Andover, the Massachusetts Wetlands Protection Act Regulations (310 CMR 10.0), and the North Andover Wetlands Protection Bylaw (Ch. 178) and Regulations, specifically with respect to drainage. The approximately 14.4-acre project site, located between Osgood Street and Bradford Street, is presently occupied by four dwelling units on Osgood Street, but is otherwise wooded and undeveloped. The site slopes, and drains, in a westerly direction toward Osgood Street. There is an onsite wetland system that appears to drain from east to west across the site, and a similar wetland just to the north of the project site. 55 Old Coach Road Sudbury MA 01776 tet 508.259.1137 fax 866.820.7840 1679 Osgood Street, 'Technical Review 2 August 16, 2010 The proposed project is an 8-lot subdivision with access via a 1,062-ft roadway off Bradford Street. As proposed, runoff from the roadway would be collected in a closed drainage system with deep sump catchbasins and routed through a sediment forebay to one of two onsite infiltration basins. Runoff from three of the house lots would also drain to the infiltration basins. The proposed basins are designed to capture and infiltrate the required recharge and water quality volumes, with excess flow discharged overland toward the northwest. Runoff from most of the remaining five house lots would be drained to three onsite wet detention ponds, with discharge toward the west. As proposed, I believe that the project design has the potential to significantly alter the hydrology of the site, andkarticularly the wetland resources on an adjacent o the site. I a so a leve that the project design could make better use of Low Impact Development (LID) techniques to dis erse, treat and infiltrate runoff flows throu o --the site, ra er than relying on larger structural best management practices (BMPs) that require a relatively large area of disturbance and potentially burden the Town with long-term maintenance needs. My specific comments follow: 1. In accordance with submission requirements of the Subdivision regulations (Appendix V), the Applicant should identify the principal vegetation types on the property, and provide detailed descriptions of the impacts to vegetation, site hydrology and water quality associated with the proposed project. 2. The submittal packet includes HydroCAD analyses and a tabular summary of the peak flow rates under pre- and post-development conditions for the 2, 10, 25, 50 and 100-yr design storms. It does not, however, address changes in the volume of runoff that would result from the project. The Subdivision regulations, DEP Stormwater Standards and the Wetlands Bylaw all require evaluation of the impacts on the volume of runoff discharged from the site as well as to the wetland resource areas on or adjacent to the site. The Subdivision regulations and Wetlands Bylaw require that impacts to groundwater flow also be addressed. Based on what I was able to extract from the HydroCAD analysis submitted.the total volume of runoff discharged from the project site under 10-year storm con rtions would increase a o percent un er pos eve opment conditions, which means that dlschargil':s om t e sitewou as onger than r pL� underesent conditions an cou exa o acer e ownstream omg i ere are restrictions. The ow to t e onsite wet an s was no mo, e , owe�ver'it appears to me that much of the runoff(as well as groundwater flow) that currently drains and/or is recharged to both the onsite and offsite wetlands would be diverted through the proposed drainage system and discharged offsite. _ 3. In order to fully assess the impacts on runoff volume, the hydrologic analysis should be run for a time span of 0 to 30 hours. 4. The North Andover Wetlands Bylaw also requires analysis of runoff from the 1-yr storm event. 1679 Osgood Street, Technical Review 3 August 16, 2010. 5. Hydraulic calculations demonstrating that the storm drain piping and grate inlets are designed to convey a 25-yr event are needed, per the Subdivision regulations. 6. The Subdivision regulations also require a nitrogen and/or phosphorus loading rem to assess the impacts on all receiving water systems on the site. This was not included in the materials reviewed. I suggest that such a study should be focused on phosphorus, as that tends to be the limiting nutrient in freshwater systems. 7. Section 7.0 of the North Andover Wetlands Bylaw regulations stipulates that storage capacities in detention/retention basins shall be based on the volume of active storage above the estimated seasonal high ground water level (ESHGW). Based on the test pit data provided, virtually all of the active storage in Wet Ponds 44 and#5 would be below this level. While the proposed design may maintain the available storage above the outlet inverts, it would do so by intercepting and draining off seepage into the ponds, hence diverting groundwater flow away-rom the onsi e we an s. 8. Per DEP requirements, exfiltration from the proposed infiltration basins should be modeled at the Rawls rate of 2.41 in/hr used in the recharge calculations, not 3 in/hr as was used in the analysis. 9. The HydroCAD modeling of the proposed pond outlets as individual small- diameter culverts is not reflective of the design shown on the plans. Each outlet control structure should be modeled as a compound outlet, with the 12-inch culvert routed to the primary outlet, and each orifice routed to the culvert as a secondary device. Except where the detention ponds are in series, the ponds should also be modeled as having free discharge instead of dynamic tailwater. 10. The outlet control structure for Wet Pond #3 (Pond 21P) is modeled with 3-in orifice at el. 80.20,but the plan calls for a 4-in orifice. 11.Based on the HydroCAD analysis submitted, the peak water depth in Wet Pond #5 would exceed the four foot maximum allowed by the Subdivision Regulations during the 100-yr storm event. 12. I note that the total drainage area modeled under post-development conditions is about 0.6 acre larger than under pre-development conditions, as it includes drainage from two frontage lots that currently drain onto Bradford Street. If flow from Bradford Street is to drain onto the subdivision roadway, an additional catchbasin should be added at the corner to collect it. 13. The plans do not address how roof runoff from the proposed houses would be handled. The flow has been me u e m e runoff calculations, but no roof eY aders are shown. To the maximum extent possible, roof runoff should be 1.679 Osgood Street, Technical Review 4 August 16, 2010 recharged onsite, either through drip trenches around the foundations or subsurface infiltration structures. 14.The proposed project calls for the infiltration BMPs to attenuate large storm flows (10-yr and larger), therefore the DEP standards require that a moundinu analvciS be performed since the separation to seasonal high groundwater is less than 4 feet. 15.Based on the grading plans, the driveway runoff from lot 16-3 would not drain to any of the proposed treatment BMPs, and the driveway runoff from Lot 16-1 would drain to Infiltration Basin #1 directly without undergoing pretreatment through the sediment forebay. 16.The project design calls for treatment of runoff from the impervious areas on five of the lots in the three proposed wet ponds, however the design of the wet ponds (particularly#3 and #5) is not consistent with DEP design criteria with respect to the volume and depth of the permanent pool, total surface area, and length:width ratio, all of which impact the effectiveness of treatment in the ponds. In addition, the bottom of Wet Pond # 3 is less than a foot below ESHGW. Given the small drainage area and highly permeable soils, it is not clear that a permanent pool can be maintained in this location. 17. The DEP regulations call for infiltration basins to have a minimum setback of 50 ft from slopes greater than 15 percent. Neither of the proposed infiltration basins meets this requirement. ^x,,:_18. The DEP stormwater regulations also call for a 50-ft setback to MY soil absorption system for both infiltration basins an wet detention ponds. The proposed septic field on Lot 16-4 is located upgradient and within 50 feet of both Wet Pond 43 and Infiltration Basin#2. 19. The design detail on Sheet D4 should list the ESHGW at each BMP location. The pond outlets should be screened to prevent blockage (particularly of the small orifices proposed),and the orifice plate should have an overflow weir. 20.As required by both the Subdivision regulations and DEP standards, reinforced emergency spillways are needed on the infiltration basins and wet ponds to protect the integrity of the berms. 21.The infiltration basins should have a valved underdrain or some other means of dewatering if needed. 22.Additional information is needed on the proposed vegetation in the infiltration basins and wet ponds. 1679 Osgood Street, Technical Review 5 August 16, 2010 23. The proposed design includes a box culvert under the common driveway to Lots 16-5 and 16-6 connecting the onsite wetlands. Based on its 10 percent slope, this culvert has the capacity to convey flows at a relatively high rate that is not reflected in the HydroCAD analysis since it was not modeled as a free discharge. A stone splash pad or plunge pool at the outlet may be warranted. 24.The DEP Stormwater Standards require a Long Term Pollution Prevention Plan outlining pollutant source control measures to be employed on the site. This was not included in the material I reviewed. 25.The proposed invert of FES #6 is below existing grade. 26. Sheet D3 shows a design detail for a pervious concrete paver; it is not clear where this feature is proposed. 27. The Drainage Report includes a narrative description of the Sediment & Erosion Control practices to be employed on the site, and design details and additional narrative are provided on Sheet E1. In addition, the project is subject to the requirements of the EPA Construction General Permit, and a draft Construction Stormwater Pollution Prevention Plan(SWPPP) is included in the drainage report. Temporary stockpile locations are shown on Sheet C6 of the plan set. Sheet C6 also shows what I believe to be the location of silt fence and/or haybales along the western edge of the project, however it is not labeled and there is no siltation barrier shown around the onsite wetlands or between the project site and the offsite wetland to the north. I suggest that the Erosion& Sediment Control/SWPP Plan be put on a separate sheet that also shows the locations of temporary sedimentation ponds, runoff detention structures and other interim control measures called for in the Construction SWPPP. 28. The Erosion & Sediment Control Plan/Construction SWPPP should call for the proposed infiltration basins to be kept off-line until the tributary drainage areas are fully stabilized, and should identify alternative measures to control the rate and quality of runoff from the site during construction. 29. The stone for the stabilized construction entrance should be 2"-3" coarse aggregate, not 1"-2"as shown on Sheet D 1. 30.The Conservation Commission should have the opportunity to review the Construction SWPPP as it is finalized prior to construction, and to request updates as the project proceeds through construction. 31. I have the following comments on the O&M Plan included with the Drainage Report: ■ Short term construction-related activities should be removed from the O&M plan and incorporated into the Erosion & Sediment Control/Construction Period Pollution Prevention Plan. 1679 Osgood Street,Technical Review 6 August 16, 2010 ■ The proposed project does not include any vegetated swales stone check dams or rock riprap; these elements should be taken out of the O&M plan. Instead, the plan should address the maintenance requirements of the BMPs proposed for the project site, including the deep sump catchbasins, sediment forebays, wet ponds, and infiltration basins. Note #17 on Sheet P1 regarding detention pond maintenance should be incorporated in the O&M Plan. ■ The Applicant has indicated that the proposed road will be a Town road, and that the maintenance of the drainage structures will therefore assumed by the Town. Consideration should be given to whether it makes sense to have the Town maintain e m i tration asins and wet onds or whether these should be main ame y a private contractor funded through a homeowners association. ■ Access to t e wet ponds and in i tration asms or the regular maintenance required needs to be addressed. Drainage easements are shown on Sheets A4 and A5, however the drainage structures and proposed grades are not, so it is difficult to determine whether they provide adequate access for maintenance of the outlet structures and sediment forebays. It is clear that the drainage easement on Lot 16-3 does not provide adequate access since it intersects the right of way at a point. ■ An estimated O&M budget and an O&M schedule and log form(for long-term maintenance tasks))are required per the DEP regulations. 32. Under Standard#10 of the DEP Stormwater Checklist the Applicant has indicated that an Illicit Discharge Statement will be submitted prior to the discharge of any stormwater to post-construction BMPs. This should be included in the Order of Conditions. I appreciate the opportunity to assist the North Andover Planning Board 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 herein. Sincerely, EGGLESTON ENVIRONMENTAL 55 Lisa D. Eggleston, P.E. C: Jennifer Hughes,North Andover Conservation Commission - Eggleston [Enver onrne W December 6, 2010 North Andover Planning Board 1600 Osgood Street North Andover, MA 01845 Attn: Judy Tymon, Town Planner RE: Stormwater Management Review 1679 Osgood St. &Bradford St. Dear Ms. Tymon and Board Members: I am writing this letter in follow-up to my August 16, 2010 review letter on the above- referenced project. Since that time I met with the Applicant's engineers and town staff on September 10, 2010 to discuss my comments, and have received and reviewed the November 11, 2010 response letter, November 12, 2010 revised plans (22 sheets), and November 11, 2010 revised drainage analysis from Jones &Beach Engineers, Inc. In response to the review comments received and the discussions at our September 10th meeting, the revised plans reflect a substantial re-design of the drainage proposed for the project. As currently proposed, the runoff from impervious surfaces on the individual house lots would be treated and/or infiltrated onsite; with the roof drainage directed to subsurface infiltration structures and runoff from the driveways draining to biofiltration "rain gardens" located on each lot. The two basins receiving runoff from the subdivision roadway have been moved closer to the roadway, and one of the basins is now proposed as a gravel wetland. In general, the project as currently proposed would adequately maintain the hydrology of the site and provide improved access for maintenance of the two drainage basins. My specific comments, once again aimed at assisting both the Planning Board and the Conservation Commission in their respective reviews of the project, are as follows: 1. As stated in the revised drainage report, the proposed project would result in increased rates of runoff at several of the locations where runoff leaves the property and decreases at others, with a net decrease in the total rate of runoff. Although not specifically called out, the drainage analysis also indicates that the volume of discharge would increase at some locations and decrease at others, with a net decrease in volume leaving the site during small storms (due to increased recharge), and an increase of up to about 18 percent in the total volume leaving the site during the larger 100-year design storm. Since the rate of delivery would be attenuated, the closed drainage system in Osgood St/Route 125 should be able to handle the increase in volume, provided there are no significant flow restrictions in the system downstream. The one concern I have is with the projected increase in both the rate and volume of runoff discharged through the existing stone swale in the northwest corner of the site (Analysis Point #5) under 55 Old Coach Road Sudbury MA 01776 tel 508.259.1137 fax 866.820.7840 1679 Osgood Street, Technical Review 2 December 6, 2010 all design storm conditions, since it does appear to drain across an abutter's property between the site and Osgood Street. The impact of an increase in discharge at this location needs to be assessed. 2. The response letter (comment #14) indicates that a mounding analysis for the proposed infiltration basin was included in the revised submittal; however I was unable to locate one in the materials I reviewed. 3. Jones & Beach's response letter indicates that they are seeking relief from the DEP setback requirement of 50-ft from a slope in excess of 15 percent for the proposed infiltration basin. Given its proximity, I do have some concern that there is potential for breakout along the downgradient slope of the infiltration basin, since it extends approximately four feet below the bottom of the basin. In lieu of a greater setback, I recommend that an impermeable barrier be placed inside the fill slope to prevent seepage. 4. The proposed vegetation in the infiltration basin and the surrounding berm is not detailed on the plans. Vegetation should be non-woody and easily maintained. 5. Inverts of the emergency spillways should be identified on the plans. 6. The elevation of the high flow outlet of the gravel wetland should be lowered to provide one foot of freeboard below the emergency spillway. 7. The design should provide some means of draining out the gravel wetland if needed for maintenance, e.g. through a removable plug in the outlet weir wall that would provide access for pumping. 8. The grading of the rain garden on Lot 16-1 needs labeling. Also, I believe that the labels for the temporary stockpile area and the rain garden on that lot are reversed (Sh. C5 and C6). 9. There are only two temporary stockpile areas shown on Sheet C6, and both are just upgradient of proposed rain gardens. The sequence of construction should ensure that the stockpiles are removed prior to the installation of the rain gardens. I believe that other stockpile locations, and possibly dewatering basins, will be needed—this should be addressed in the Construction SWPPP. 10. I recommend substituting several inches of pea stone for the geotextile fabric underlying the rain gardens, as it will be less prone to clogging. 11. The proposed rain gardens are an integral part of the drainage design for the subdivision, therefore there needs to be some way of ensuring that they will not be filled or re-graded and that they will continue to be maintained by the individual homeowners. 1679 Osgood Street, Technical Review 3 December 6, 2010 12. The maintenance checklists and inspection forms included with the O&M Plan pertain primarily to the inspections that will occur during the construction phase of the project, not the long term maintenance of the stormwater BMPs. The DEP regulations call for an O&M schedule, budget and log form for the long-term maintenance tasks. 13. The notes on Sheet D4 regarding inspection and maintenance of the gravel wetland should be incorporated in the O&M Plan. 14. Catchbasins and sediment forebays should be cleaned a minimum of once per year. 15. In addition to the forebays, the infiltration basin and gravel wetland berm will likely also need periodic mowing. 16. While the revised plans provide improved access to the basins, I still question whether it makes sense to have the Town maintain the infiltration basin and gravel wetland once the road is accepted, or whether these should be maintained by a private contractor funded through a homeowners association. Once again, I appreciate the opportunity to assist the North Andover Planning Board 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 herein. Sincerely, EGGLESTON ENVIRONMENTAL Lisa D. Eggleston,P.E. C: Jennifer Hughes, North Andover Conservation Commission 6 Eggleston Environmental January 27, 2011 North Andover Planning Board 1600 Osgood Street North Andover, MA 01845 Attn: Judy Tymon, Town Planner RE: Stormwater Management Review 1679 Osgood St. &Bradford St. Dear Ms. Tymon and Board Members: I am writing this letter in follow-up to my August 16, 2010 and December 6, 2010 review letters on the above-referenced project. Since that time I have received and reviewed the January 10, 2011 response letter, revised plans, and drainage analysis from Jones & Beach Engineers, Inc. The revised submission addresses a number of the issues expressed in my previous letters, and incorporates several design modifications to the gravel wetland and infiltration basin. My comments, again aimed at both Planning Board and Conservation Commission review, are as follows: 1. The modifications to the gravel wetland include a small increase in storage capacity and a reduction in the outlet orifice to further attenuate the rate of flow. However, since the gravel wetland is in groundwater and therefore is lined, the discharge cannot be totally eliminated. The discharge from the gravel wetland is directed toward a private property owned by Carey Storage and, while the flow is relatively small, it does still represent an increase over existing conditions under the 1, 2 and 10-yr design storm conditions. (There is currently no discharge to the downgradient property in the 1-yr and 2-yr design storms). I do not believe any increase should be allowed without the permission of the downgradient property owner. 2. The hydrologic analysis does not take into account the outlet control structure overflow at el. 103, or the emergency spillway at elevation 103.5. Both would be exceeded during the 100-yr storm, hence the rate of discharge from the gravel wetland would be higher than what is projected by the model. 3. Both the gravel wetland and the infiltration pond should have at least a foot of freeboard below the emergency overflow elevation in the 100-yr storm. Neither one currently meets this criterion. 4. The drainage plan should reference the details shown on Sheet El. 55 Old Coach Road Sudbury MA 01776 tel 508.259.1137 fax 866.820.7840 1679 Osgood Street, Technical Review 2 January 27, 2011 5. The response letter states that a homeowner's association will be responsible for the long-term maintenance of the gravel wetland and the infiltration basin; however that is not reflected in the O&M Plan. The O&M Plan should clearly indicate which long-term maintenance tasks and inspections are to be conducted by the town, and which by the homeowners association or, (in the case of the rain gardens), by the homeowners themselves. The maintenance schedule and logs should address these tasks, not the short-term, construction related ones. 6. Maintenance of the rain gardens should be included in the O&M Plan. In addition, some other means of making future property owners aware that the rain gardens cannot be re-graded and need to be maintained is needed, e.g. through drainage easements or the homeowners association. I do not believe that the note added to the design plans is sufficient. 7. The O&M Plan should call for catchbasins to be cleaned, not just inspected, at least once per year. Once again, I appreciate the opportunity to assist the North Andover Planning Board 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 herein. Sincerely, EGGLESTON ENVIRONMENTAL Lisa D. Eggleston, P.E. C: Jennifer Hughes, North Andover Conservation Commission Eggleston Environmental August 2, 2011 North Andover Planning Board 1600 Osgood Street North Andover, MA 01845 Attn: Judy Tymon,Town Planner RE: Stormwater Management Review 1679 Osgood St. &Bradford St. Dear Ms. Tymon and Board Members: In follow-up to my January 27, 2011 and previous review letters on the above-referenced project, I have received and reviewed the July 8, 2011 response letter, June 30, 2011 revised plans (Sheets Al, A4, C4, C5, C6, and 134) and June 30, 2011 revised Drainage Analysis, Sediment and Erosion Control Plan and Stormwater Pollution Prevention Plan from Jones&Beach Engineers, Inc. The revised submission addresses a number of the issues expressed in my previous letters, and incorporates an additional "outlet pond" infiltration basin in the design to reduce the discharge from the gravel wetland to below pre-development levels. It also includes the addition of Lot 31 to the subdivision design, and provides drainage for that lot. I am at this time satisfied that all of my previous comments regarding the drainage system design have been adequately addressed. My remaining comments, focused on construction and maintenance issues, are outlined below: 1. Note 10 on Sheet Al states that the homeowner's association (HOA) will be responsible for the long-term maintenance of all drainage structures outside of the roadway ROW, and that all lots are to have deed restrictions stating this fact. The revised O&M Plan, however, indicates that the Town will be responsible for maintaining the gravel wetland, infiltration basins, sediment forebays and vegetated areas of the development, and the proposed deed language only addresses the bioretention systems. Both the O&M Plan and the proposed deed language should be revised to be consistent with Note 10. 2. Note 14 on Sheet Al, prohibiting filling or re-grading of the bioretention systems/rain gardens, should also be included in the deed restriction. The language currently proposed only addresses maintenance of the basins. 3. While it may be appropriate for individual homeowners to maintain the roof infiltration systems and rain gardens, I believe that the maintenance of the gravel wetland, infiltration ponds and sediment forebays should be conducted by professionals under contract to the HOA. The Board should ensure that such contracts are in place prior to bond release. 32 Old Framingham Rd Unit 29 Sudbury MA 01776 tel 508.259.1137 fax 856.820.7840 1679 Osgood Street, Technical Review 2 August 2, 2011 4. As indicated previously, this project entails the disturbance of more than one acre of land and is therefore subject to the Construction General Permit issued by EPA. The Applicants have provided a draft Construction Stormwater Pollution Prevention Plan (SWPPP) in one of the earlier submittals. It is expected that the SWPPP will be finalized when a contractor has been selected and an NOI is filed for coverage under the permit, and updated as construction progresses. I recommend a pre-construction meeting between representatives of the Planning Board and Conservation Commission and the contractor to discuss implementation of the SWPPP. The Board should also consider requiring an independent Environmental Monitor for the project. 5. The June 30, 2011 revised Drainage Analysis, Sediment and Erosion Control Plan and Stormwater Pollution Prevention Plan should be treated in the record as a supplemental document and not to replace the July 12, 2010 version in its entirety. Several important items, including design calculations and the draft SWPPP, are not included in the copy of the June 30th revisions that I received. Once again, I appreciate the opportunity to assist the North Andover Planning Board 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 herein. Sincerely, EGGLESTON ENVIRONMENTAL Lisa D. Eggleston, P.E. C: Jennifer Hughes,North Andover Conservation Commission Eggleston Environment= August 16, 2010 North Andover Planning Board 1600 Osgood Street North Andover,MA 01845 Attn: Judy Tymon, Town Planner RE: Stormwater Management Review 1679 Osgood St. &Bradford St. Dear Ms. Tymon and Board Members: Per your request, I have conducted an initial technical review of the Definitive Subdivision application packet for the 1679 Osgood Street & Bradford Street site. The materials I have received and reviewed to date include the following: ■ Bound copy of Definitive Subdivision Application Package, for GMZ Realty Trust, Route 125 &Bradford Street, prepared by Jones&Beach Engineers, Inc. and dated July 16, 2010. ■ Drainage Analysis, Sediment and Erosion Control Plan and Stormwater Pollution Prevention Plan, GMZ Realty Trust, 1679 Osgood St, prepared by Jones&Beach Engineers, Inc. and dated July 12, 2010. ■ Definitive Subdivision Plan(Sheets 1-19 of 21) for Tax Map 61, Lots 16&34, 1679 Osgood St. &Bradford St,prepared by Jones&Beach Engineers, Inc. and dated July 14, 2010.The focus of my review is on the proposed stormwater management aspects of the project. My comments are as follows: It is my understanding that a Notice of Intent (NOI) application for the project has been filed concurrently with the Conservation Commission, and that my review is intended to assist both the Planning Board and the Conservation Commission in their respective reviews of the project. My primary focus in this initial review is therefore on the overall stormwater management approach and design concepts used in the project, as well as its compliance with the Rules and Regulations Governing the Subdivision of Land in Town of North Andover, the Massachusetts Wetlands Protection Act Regulations (310 CMR 10.0), and the North Andover Wetlands Protection Bylaw (Ch. 178) and Regulations, specifically with respect to drainage. The approximately 14.4-acre project site, located between Osgood Street and Bradford Street, is presently occupied by four dwelling units on Osgood Street, but is otherwise wooded and undeveloped. The site slopes, and drains, in a westerly direction toward Osgood Street. There is an onsite wetland system that appears to drain from east to west across the site, and a similar wetland just to the north of the project site. 55 Old Coach Road Sudbury MA 01776 tel 508.259.1137 fax 866.820.7840 1679 Osgood Street,Technical Review 2 August 16, 2010 The proposed project is an 8-lot subdivision with access via a 1,062-ft roadway off Bradford Street. As proposed, runoff from the roadway would be collected in a closed drainage system with deep sump catchbasins and routed through a sediment forebay to one of two onsite infiltration basins. Runoff from three of the house lots would also drain to the infiltration basins. The proposed basins are designed to capture and infiltrate the required recharge and water quality volumes, with excess flow discharged overland toward the northwest. Runoff from most of the remaining five house lots would be drained to three onsite wet detention ponds, with discharge toward the west. As proposed, I believe that the project design has the potential to significantly alter the hydrology of the site, and particularly the wetland resources on and adjacent to the site. I also believe that the project design could make better use of Low Impact Development (LID) techniques to disperse, treat and infiltrate runoff flows throughout the project site, rather than relying on larger structural best management practices (BMPs) that require a relatively large area of disturbance and potentially burden the Town with long-term maintenance needs. My specific comments follow: 1. In accordance with submission requirements of the Subdivision regulations (Appendix V), the Applicant should identify the principal vegetation types on the property, and provide detailed descriptions of the impacts to vegetation, site hydrology and water quality associated with the proposed project. 2. The submittal packet includes HydroCAD analyses and a tabular summary of the peak flow rates under pre- and post-development conditions for the 2, 10, 25, 50 and 100-yr design storms. It does not, however, address changes in the volume of runoff that would result from the project. The Subdivision regulations, DEP Stormwater Standards and the Wetlands Bylaw all require evaluation of the impacts on the volume of runoff discharged from the site as well as to the wetland resource areas on or adjacent to the site. The Subdivision regulations and Wetlands Bylaw require that impacts to groundwater flow also be addressed. Based on what I was able to extract from the HydroCAD analysis submitted, the total volume of runoff discharged from the project site under 10-year storm conditions would increase by about 200 percent under post-development conditions, which means that discharges from the site would last longer than under present conditions and could exacerbate downstream flooding if there are restrictions. The flow to the onsite wetlands was not modeled, however it appears to me that much of the runoff(as well as groundwater flow) that currently drains and/or is recharged to both the onsite and offsite wetlands would be diverted through the proposed drainage system and discharged offsite. 3. In order to fully assess the impacts on runoff volume, the hydrologic analysis should be run for a time span of 0 to 30 hours. 4. The North Andover Wetlands Bylaw also requires analysis of runoff from the 1-yr storm event. 1679 Osgood Street, Technical Review 3 August 16, 2010 5. Hydraulic calculations demonstrating that the storm drain piping and grate inlets are designed to convey a 25-yr event are needed, per the Subdivision regulations. 6. The Subdivision regulations also require a nitrogen and/or phosphorus loading report to assess the impacts on all receiving water systems on the site. This was not included in the materials reviewed. I suggest that such a study should be focused on phosphorus, as that tends to be the limiting nutrient in freshwater systems. 7. Section 7.0 of the North Andover Wetlands Bylaw regulations stipulates that storage capacities in detention/retention basins shall be based on the volume of active storage above the estimated seasonal high ground water level (ESHGW). Based on the test pit data provided, virtually all of the active storage in Wet Ponds #4 and#5 would be below this level. While the proposed design may maintain the available storage above the outlet inverts, it would do so by intercepting and draining off seepage into the ponds, hence diverting groundwater flow away from the onsite wetlands. 8. Per DEP requirements, exfiltration from the proposed infiltration basins should be modeled at the Rawls rate of 2.41 in/hr used in the recharge calculations, not 3 in/hr as was used in the analysis. 9. The HydroCAD modeling of the proposed pond outlets as individual small- diameter culverts is not reflective of the design shown on the plans. Each outlet control structure should be modeled as a compound outlet, with the 12-inch culvert routed to the primary outlet, and each orifice routed to the culvert as a secondary device. Except where the detention ponds are in series, the ponds should also be modeled as having free discharge instead of dynamic tailwater. 10. The outlet control structure for Wet Pond #3 (Pond 21P) is modeled with 3-in orifice at el. 80.20, but the plan calls for a 4-in orifice. 11. Based on the HydroCAD analysis submitted, the peak water depth in Wet Pond #5 would exceed the four foot maximum allowed by the Subdivision Regulations during the 100-yr storm event. 12. I note that the total drainage area modeled under post-development conditions is about 0.6 acre larger than under pre-development conditions, as it includes drainage from two frontage lots that currently drain onto Bradford Street. If flow from Bradford Street is to drain onto the subdivision roadway, an additional catchbasin should be added at the corner to collect it. 13. The plans do not address how roof runoff from the proposed houses would be handled. The flow has been included in the runoff calculations, but no roof leaders are shown. To the maximum extent possible, roof runoff should be 1679 Osgood Street, Techfiiea.I Review 4 August 16, 2010 recharged onsite, either through drip trenches around the foundations or subsurface infiltration structures. 14. The proposed project calls for the infiltration BMPs to attenuate large storm flows (10-yr and larger), therefore the DEP standards require that a mounding analysis be performed since the separation to seasonal high groundwater is less than 4 feet. 15. Based on the grading plans, the driveway runoff from lot 16-3 would not drain to any of the proposed treatment BMPs, and the driveway runoff from Lot 16-1 would drain to Infiltration Basin #1 directly without undergoing pretreatment through the sediment forebay. 16. The project design calls for treatment of runoff from the impervious areas on five of the lots in the three proposed wet ponds, however the design of the wet ponds (particularly 43 and #5) is not consistent with DEP design criteria with respect to the volume and depth of the permanent pool, total surface area, and length:width ratio, all of which impact the effectiveness of treatment in the ponds. In addition, the bottom of Wet Pond # 3 is less than a foot below ESHGW. Given the small drainage area and highly permeable soils, it is not clear that a permanent pool can be maintained in this location. 17. The DEP regulations call for infiltration basins to have a minimum setback of 50 ft from slopes greater than 15 percent. Neither of the proposed infiltration basins meets this requirement. 18. The DEP stormwater regulations also call for a 50-$ setback to any soil absorption system for both infiltration basins and wet detention ponds. The proposed septic field on Lot 16-4 is located upgradient and within 50 feet of both Wet Pond#3 and Infiltration Basin#2. 19. The design detail on Sheet D4 should list the ESHGW at each BMP location. The pond outlets should be screened to prevent blockage (particularly of the small orifices proposed), and the orifice plate should have an overflow weir. 20. As required by both the Subdivision regulations and DEP standards, reinforced emergency spillways are needed on the infiltration basins and wet ponds to protect the integrity of the berms. 21. The infiltration basins should have a valved underdrain or some other means of dewatering if needed. 22.Additional information is needed on the proposed vegetation in the infiltration basins and wet ponds. 1679 Osgood Street; Technical Revie\v 5 August 16, 2010 23. The proposed design includes a box culvert under the common driveway to Lots 16-5 and 16-6 connecting the onsite wetlands. Based on its 10 percent slope, this culvert has the capacity to convey flows at a relatively high rate that is not reflected in the HydroCAD analysis since it was not modeled as a free discharge. A stone splash pad or plunge pool at the outlet may be warranted. 24. The DEP Stormwater Standards require a Long Term Pollution Prevention Plan outlining pollutant source control measures to be employed on the site. This was not included in the material I reviewed. 25. The proposed invert of FES #6 is below existing grade. 26. Sheet D3 shows a design detail for a pervious concrete paver; it is not clear where this feature is proposed. 27. The Drainage Report includes a narrative description of the Sediment & Erosion Control practices to be employed on the site, and design details and additional narrative are provided on Sheet E1. In addition, the project is subject to the requirements of the EPA Construction General Permit, and a draft Construction Stormwater Pollution Prevention Plan(SWPPP) is included in the drainage report. Temporary stockpile locations are shown on Sheet C6 of the plan set. Sheet C6 also shows what I believe to be the location of silt fence and/or haybales along the western edge of the project, however it is not labeled and there is no siltation barrier shown around the onsite wetlands or between the project site and the offsite wetland to the north. I suggest that the Erosion& Sediment ControVSWPP Plan be put on a separate sheet that also shows the locations of temporary sedimentation ponds, runoff detention structures and other interim control measures called for in the Construction SWPPP. 28. The Erosion & Sediment Control Plan/Construction SWPPP should call for the proposed infiltration basins to be kept off-line until the tributary drainage areas are fully stabilized, and should identify alternative measures to control the rate and quality of runoff from the site during construction. 29. The stone for the stabilized construction entrance should be 2"-3" coarse aggregate, not 1"-2"as shown on Sheet D 1. 30.The Conservation Commission should have the opportunity to review the Construction S WPPP as it is finalized prior to construction, and to request updates as the project proceeds through construction. 31. I have the following comments on the O&M Plan included with the Drainage Report: ■ Short term construction-related activities should be removed from the O&M plan and incorporated into the Erosion & Sediment Control/Construction Period Pollution Prevention Plan. 1679 Osgood Street, 'Technical Review 6 August 16, 2010 ■ The proposed project does not include any vegetated swales, stone check dams or rock riprap; these elements should be taken out of the O&M plan. Instead, the plan should address the maintenance requirements of the BMPs proposed for the project site, including the deep sump catchbasins, sediment forebays, wet ponds, and infiltration basins. Note #17 on Sheet P1 regarding detention pond maintenance should be incorporated in the O&M Plan. ■ The Applicant has indicated that the proposed road will be a Town road, and that the maintenance of the drainage structures will therefore assumed by the Town. Consideration should be given to whether it makes sense to have the Town maintain the infiltration basins and wet ponds, or whether these should be maintained by a private contractor funded through a homeowners association. ■ Access to the wet ponds and infiltration basins for the regular maintenance required needs to be addressed. Drainage easements are shown on Sheets A4 and A5, however the drainage structures and proposed grades are not, so it is difficult to determine whether they provide adequate access for maintenance of the outlet structures and sediment forebays. It is clear that the drainage easement on Lot 16-3 does not provide adequate access since it intersects the right of way at a point. ■ An estimated O&M budget and an O&M schedule and log form (for long-term maintenance tasks) are required per the DEP regulations. 32. Under Standard#10 of the DEP Stormwater Checklist the Applicant has indicated that an Illicit Discharge Statement will be submitted prior to the discharge of any stormwater to post-construction BMPs. This should be included in the Order of Conditions. I appreciate the opportunity to assist the North Andover Planning Board 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 herein. Sincerely, EGGLESTON ENVIRONMENTAL Lisa D. Eggleston, P.E. C: Jennifer Hughes, North Andover Conservation Commission 1.1 Bioretention Systems. With the approval of the Massachusetts Department of Environmental Protection and the Town of North Andover, bioretention systems shall be installed on Lots 16-1, 16-2, 16-3, 16-4, 16-5, 16-6, 16-7, 16-8 and 31. The purpose of this section of the Declaration is to notify future lot owners of these lots of the bioretention systems, and to establish the allowed uses and required maintenance of the bioretention basins. 1.1.1 The Declarant hereby declares the following notice and perpetual obligations for the owners of Lots 16-1, 16-2, 16-3, 16-4, 16-5, 16-6, 16-7, 16-8 and 31: 1.1.2 A bioretention system (also called a"rain garden") is a type of stormwater filtration system designed to collect and filter moderate amounts of stormwater runoff using conditioned planting soil beds, gravel beds, and vegetation within shallow depressions. 1.1.3 The location of the bioretention systems on each lot is shown on the subdivision engineering plans approved by and filed with the Town of North Andover, Massachusetts. Any Lot releasing any excess water shall be responsible for any downstream damage caused by excess stormwater released due to lack of maintaining the bioretention system. Design, construction and maintenance of downstream culverts, swales or other stormwater management systems to handle normal upstream releases shall be the responsibility of the Lot upon which the downstream stormwater management system is located. 1.1.4 The proposed rain gardens are an integral part of the drainage design for the subdivision and should therefore not be filled or re-graded and should continue to be maintained by the respective homeowners. 1.1.5 Lot owners are initially responsible for the maintenance of the bioretention systems. The Association is ultimately responsible for the maintenance of the bioretention systems if the Lot owners fail to maintain them. Maintenance shall be as follows: 1.1.5.1 The systems shall be maintained with 2"to 3" of well aged shredded bark mulch, and may be planted with native, non-invasive plants that are specifically suited to surviving well in the occasionally wet by normally dry conditions of a rain garden. The systems shall not be compacted or grassed over. 1.1.5.2 The systems should be inspected at least twice annually, and following any rainfall event exceeding 2.5 inches in a 24 hour period, with maintenance or rehabilitation conducted as warranted by such inspection. 1.1.5.3 Pretreatment measures (if any) should be inspected at least twice annually, and cleaned of accumulated sediment as warranted by inspection, but not less than once annually. 1.1.5.4 Trash and debris should be removed at each inspection. 1.1.5.5 At least once annually, systems should be inspected for drawdown time. If the bioretention system does not drain within 48 hours following a rainfall event, then a qualified professional should assess the condition of the facility to determine measures required to restore filtration function or infiltration function (as applicable), including but not limited to removal of accumulated sediments or reconstruction of the filter media. 1.1.5.6 Vegetation should be inspected at least annually, and maintained in healthy condition, including pruning,removal and replacement of dead or diseased vegetation, and removal of invasive species. 1.1.5 Lot owners and the Association shall maintain the bioretention systems in compliance with MA Department of Environmental Protection(MADEP). 1.1.6 The Association is obligated to enforce and the MADEP and the Town of North Andover are authorized to enforce compliance with this Declaration but in no case shall any of the entities be responsible for any costs. The Association, MADEP and the Town of North Andover may record enforcement orders in the registry of deeds that shall run with the land and be binding on subsequent lot owners. The Association shall have the right of access onto Lots 16-1, 16-2, 16-3, 16-4, 16-5, 16- 6, 16-7, 16-8 and 31 for the purpose of maintaining and repair of the bioretention systems. The lot owners shall be responsible for any and all costs of the maintenance, repair, and replacement of the bioretention systems. If the Lot owner fails to maintain the bioretention system and the Association expends funds repairing or maintaining the system, the Association shall issue a special assessment against the Lot for the cost of maintenance.