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HomeMy WebLinkAboutConsultant Review - 250 CLARK STREET 4/9/2013 Eggleston Environmental April 9, 2013 North Andover Planning Board (a 1600 Osgood Street North Andover, MA 01845 APR 10 2013 Attn: Judy Tymon,Town Planner NORTH ANDOVER RE: Stormwater Review CONSERVATION COMMISSION 250 Clark Street Dear Ms. Tymon and Board Members: In follow-up to my previous comments on March 13, 2013 on the proposed expansion of the Flight Landata facility at 250 Clark Street, I have received and reviewed the April 3, 2013 response from Williams & Sparages Engineers, including the following: • April 3, 2013 letter to North Andover Planning Board from Peter Blaisdell, Jr., of Williams & Sparages re: Response to Stormwater Review by Eggleston Environmental • Site Plan in North Andover, MA, Sheets 1-4 of 4, prepared by Williams & Sparages, dated February 7,2013 and revised through March 26, 2013. ® Comparative Drainage Analysis, Flight Landata, 250 Clark Street, North Andover, prepared by Williams& Sparages and revised through March 26, 2013. Notice of Intent, 250 Clark Street, prepared by Williams & Sparages and dated February 7, 2013. I've also discussed my comments and the proposed revisions with the project engineer. The revised submission satisfactory addresses the issues identified in my March 13tH letter with respect to the drainage design. I do have just a few comments at this time: 1. The proposed plan calls for a siltation fence erosion control barrier. Additional measures (e.g.hay bales or silt socks) may also be needed. 2. It appears that the proposed project may entail the disturbance of an acre or more of land. If so, it will also be subject to the EPA Construction General Permit and require filing of a Notice of Intent under that program, and implementation of a Construction Stormwater Pollution Plan (SWPPP) in accordance with EPA guidelines. 3. The Pollution Prevention Plan included with the NOI addresses short-term construction related measures aimed at the site contractors. Per DEP requirements, a Long-Term Pollution Prevention Plan is still needed. As with the O&M Plan, this would be aimed at the parties responsible for maintaining the site 32 Old Framingham Rd Unit 29 Sudbury MA 01776 tel 508.259.9137 fax 866.820.7840 250 Clark Street, Stormwater Review 2 April 9, 2013 over the long term and should address snow storage locations, pavement sweeping, spill control and good housekeeping measures to be employed on the site in order to minimize pollutant exposure to stormwater. Given the nature of the operations on the site, the storage and use of potentially hazardous materials as well as any vehicle(or airplane)washing, deicing, etc. should also be addressed. Once again, I appreciate the opportunity to assist the North Andover Planning Board and Conservation Commission 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 t j Lisa D. Eggleston,P.E. C: Jennifer Hughes, Conservation Coordinator Project No.NAND-0020 11 V El j April 10,2013E L 13 NORTH ANDOVER WILLIAMS North Andover Planning Board CONSERVATION COMMISSION SPARAGES North Andover Conservation Commis Et7GWEEAS PUNwFRS SURdEY00.5 1600 Osgood Street North Andover,MA 01845 Subject: Response to Stormwater Review by Eggleston Environmental 250 Clark Street(Flight Landata,Inc.) DEP File No. 242-1584 Dear Members of the Planning Board and Conservation Commission, The purpose of this letter is to respond the few remaining comments that we received yesterday afternoon from Eggleston Environmental(EE)regarding the proposed expansion of the Flight Landata facility located at 250 Clark Street. The comments provided by Eggleston Environmental are shown in italics below,and,our responses are in the bold text that follows. I. The proposed plan calls for a siltation fence erosion control barrier. Additional measures (e.g.hay bales or silt socks)may also be needed, In the Erosion&Sediment Control Plan included in our original Notice of Intent package dated February 7,2013,under Erosion and Sediment Control Device,please see the following statement starting in the middle of the second line... "It is important for the owner, builder, and/or site contractor to have access to a supply of haybales should the need arise for additional erosion and sediment control measures." We have added this text to the notes (Note 8)found on the revised site plan to ensure that this is emphasized during construction activities. 2. It appears that the proposed project may entail the disturbance of an acre or more of land. If so,it will also be subject to the EPA Construction General Permit and require a Notice of Intent under that program, and implementation of a Construction Stormwater Pollution Prevention Plan (SWPPP)in accordance with the EPA guidelines, The amount of proposed disturbance is approximately 37,000 square feet,which is less than the minimum required land disturbance of 1 acre required for a filing with the EPA. 3. The Pollution Prevention Plan included with the NOI addresses short-terns construction related measures aimed at the site contractors. Per DEP requirements,a Long-Term Pollution Prevention Plan is still needed. As with the O&M Plan, this would be aimed at the parties responsible for maintaining the site in order to minimize the pollutant exposure to stormwater. Given the nature of the operations on the site,the storage and use of potentially hazardous materials as Well as any vehicle (or airplane)washing,deicing, etc. should be addressed. i 191 South Main Street, Suite 103 Middleton, MA 01949 Tel: (978) 539-8088 Fax: (978) 767-8579 i I Response to Stormwater Review 250 Clark Street North Andover, MA April 10, 2013 i We have attached a revised Operation&Maintenance Plan that is to be used for the post construction period naming Flight Landata,Inc.as the party responsible for the operation and maintenance of the stormwater management system. We have also noted that if Flight Landata,Inc,were no longer the tenant the responsibility would revert back to the Leasehold Owner,Michael Florence. We have also attached a revised Inspection and Maintenance form to be used in the Long-Term which requires inspections twice per year, spring and fall,or within a 24 hours of a storm event with 2 year storm intensity or greater,i.e. 3.1 inches of rainfall within a 24 hour period. We have also shown designated snow storage areas that are currently being utilized by the property which are all up-gradient of the wetlands. We have spoken with Mr. Scott Stetson of KEYW Corporation(the parent company of Flight Landata,Inc.)and they do have an aircraft spill-kit located in their hanger,in the unlikely event of an aircraft leak. As presented by Attorney Jill Mann at the April 2,2013 Planning Board hearing,the,aircraft are not fueled at this location. In addition,they do not wash or de-ice the planes at this location according to Mr. Stetson. Therefore,there is no danger of contaminating the wetland resource areas with wash water runoff. We trust that you will find the responses above adequately address these last few comments made by the technical review agent and will allow you to close the hearing for the proposed expansion of the Flight Landata,Inc.facility. If you have any questions,please do not hesitate to contact me directly. Very truly yours, i Peter M.Blaisdell,Jr.,P.E.,P.L.S. Project Engineer PMB: CPS Enclosures cc: Attorney Jill Mann Scott Stetson/KEYW Corporation Lisa Eggleston,P.E. i I i Operation&Maintenance Plan C E [l 1 E "250 Clark Street" 250 Clark Street,North Andover,MA 01845 A;' February 7,2013 NORTH ANDOVER Revised: March 26,2013 CONSERVATION COMMISSION Revised: April 9,2013 i This Operation&Maintenance Plan has been prepared to comply with the provisions set forth in the Massachusetts Department of Environmental Protection(DEP)Stormwater Management Standards. Structural Best Management Practices (BMPs)require periodic maintenance to insure proper function and efficiency in pollutant removal from stormwater discharges that would otherwise reach wetland resource areas untreated. Maintenance schedules found below are as recommended in Department of Environmental Protections Massachusetts Stormwater Handbook and as recommended in the manufacturer's specifications. The following BMPs shall be utilized for project at 250 Clark Street for pollutant removal from stormwater discharge as well as providing additional groundwater recharge on site: ® Parking Lot Sweeping ® Biofilters with stone diaphragms '... ® Stone Trench for roof runoff '.. I The responsible party for following the Operation&Maintenance Plan long-term after construction f has been completed will be Flight Landata,Inc. Should Flight Landata,Inc.not be the tenant of the I facility in the future,the responsibility will revert back to the Leasehold Owner,Michael Florence. See attached Inspection Log. Parking Lot Sweeping; ® We recommend that the parking lot be swept at a minimum of once per year in the spring. Biofilters: • Inspect and remove trash year monthly throughout the year. • Remove and replace dead vegetation annually in the spring. • Prune the shrubs annually in the spring. • Remove any sediment from the top of the stone diaphragms and from the pretreatment sideslope annually in the spring. • Mow the pretreatment sideslopes once a month during the growing season. ® When areas of erosion are identified,repair areas of erosion and revegetate as needed as soon as possible. • Inspections shall be performed at least twice a year,or after a major storm event which is defined as a storm that is equal to or greater than the 2-year storm event. Operation&Maintenance Plan 250 Clark Street, North Andover, MA 01845 Revised:April 9,2013 ® During these inspections,record and map the following information: -The presence of accumulated trash and/or debris, -The presence of dead vegetation and/ or invasive species (invasives must be removed), -Stability of the sideslopes and berms, -Accumulation of sediment, -Survival rate of plantings(dead plantings must be replaced) Stone Trench for roof recharge: ® Leaf screens shall be installed in the gutters to prevent debris from reaching the trench. i ® Install three (3)inspection ports to be located at the beginning,middle and end of trench. ® Should standing water be present in bottom of system during a routine inspection or more than twenty-four(24)hours after the end of a rainfall event,it may be as a result of the stone bed layer being clogged. The amount of elapsed time required for the water to infiltrate completely should be recorded. If after seventy-two (72)hours from the end of a rainfall event there is still standing water in the bottom of the trench,the affected area should be excavated and the stone replaced with clean stone. i I ® We recommend the following schedule for system maintenance Monthly in first year of service: -Check inlets for clogging and remove any debris as necessary -Check for depressions in areas over and surrounding the system Spring and fall in the second year service: -Check inlets for clogging and remove any debris as necessary -Check for depressions in areas over and surrounding the system One year after commissioning and every year following: -Check inlets for clogging and remove any debris as necessary -Inspect the interior of the trench via inspection ports and measure sediment or depth of standing water -Check for depressions in areas over and surrounding the system -Confirm that no unauthorized modifications have been performed to the site ® It should be noted that most failures that occur in subsurface systems are due to inadequate pre-treatment which leads to clogging. However,this system shall only receive roof runoff from the roof,which is considered clean by DEP and does not require pre-treatment. Therefore,we do not expect there to be any adverse impacts to the system due to debris accumulation. 2 Eggleston Envi ron mental March 13, 2013 North Andover Planning Board 1600 Osgood Street North Andover, MA 01845 Attn: Judy Tymon, Town Planner RE: Stormwater Review 250 Clark Street Dear Ms. Tycoon and Board Members: Per your request, I have conducted a technical review of the February 15, 2013 Special Permit Application packet submitted by Mann & Mann, P.C. for the construction of a 9,280 sf addition and associated alterations to the property at 250 Clark Street in North Andover. Included in the materials I received and reviewed were the following: • Special Permit — Site Plan Review Application, Flight Landata, Inc. 250 Clark Street North Andover, ■ Site Plan in North Andover, MA, Sheets 1-4 of 4, prepared by Williams & Sparages, dated February 7, 2013 and revised February 15, 2013. • Stormwater Report, 250 Clark Street, North Andover, prepared for Flight Landata Inc. by Williams & Sparages and dated February 7, 2013. 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 Town of North Andover's zoning requirements for Site Plan Review, the Massachusetts Department of Environmental Protection (DEP) Stormwater Management Standards and Regulations, and the North Andover Wetlands Bylaw. It is my understanding that a Notice of Intent (NOI) application for the project has been filed concurrently with the Conservation Commission. My review is aimed at assisting both the Planning Board and the Conservation Commission in their respective reviews of the project. The project site is a 27,027 sf(proposed) lease parcel on the Lawrence Municipal Airport property located in North Andover. It is currently occupied by a 9,525 commercial building and associated parking and driveways. There are no stormwater management structures on the existing site; runoff from the property drains overland toward wetlands located to the west,north and east of the lease parcel. The proposed project includes construction of a new 9,680 sf building, 19 new parking spaces, relocation of the septic system serving the facility, and two rain gardens (bioretention areas) for stormwater treatment of runoff from the new paved areas and portion of the roof areas. 32 Old Framingham Rd Unit 29 Sudbury MA 01776 tel 508.259.1137 fax 866.820.7840 250 Clark Street, Stormwater Review 2 March 13, 2013 My comments on the proposed plan are outlined below: 1. It appears from the plans and available aerial photography that runoff from the project area currently drains to three different wetland areas; however it is not clear to what degree the three are hydrologically connected. In order to evaluate impacts on the hydrologic regime of the three wetlands as well as any potential downstream flooding the drainage analysis needs to be broken out on a subwatershed basis, with control points at each resource area. In accordance with the North Andover Wetlands Bylaw Regulations, the analysis should evaluate the volume of runoff discharged to each control point as well as the peak rate of flow. The local wetlands regulations also require analysis of the 1-year storm. 2. The proposed rain gardens are intended to exfiltrate captured runoff flow in order to provide the required groundwater recharge and water quality treatment (via filtration and pollutant uptake) of runoff flow. However, due to the shallow groundwater table on the site, in conjunction with the shallow depth (0.25 ft) of the proposed rain gardens, their capacity to provide either effective recharge or filtration of the recharge will be minimal to non-existent during periods of high groundwater, and may also be diminished during periods of lower groundwater. Based on the soil tests conducted, the surface elevation of Rain Garden #1 will intercept the groundwater table during high groundwater conditions, and in Rain Garden #2 the ESHGW elevation is less than a foot below the surface, within the soil media layer. Per the DEP Stormwater Handbook, rain gardens designed to exfiltrate must ensure two feet of vertical separation from the seasonal high groundwater table to the bottom of the bioretention cell (e.g. the bottom of the filtration media). 3. The dead storage volume in the rain gardens, e.g. for calculating water quality or recharge volume should only include that which is above the ESHGW elevation. During high groundwater conditions, there may be as little as 0.05 ft (0.6 in) of storage between the pool/groundwater elevation and the overflow weir of Rain Garden#1. 4. Since the proposed project calls for the infiltration BMPs to attenuate large storm flows (10-yr and larger) and the separation to seasonal high groundwater beneath the systems is less than 4 feet, the DEP Stormwater Standards require that a mounding analysis be performed to demonstrate that the systems will be fully dewatered within 72 hours. Per my comments above, the proposed design provides little to no separation to groundwater, hence a mounding analysis is unlikely to provide any benefit. I would suggest instead that the hydrologic analysis be run without any exfiltration from the basins in order to fully account for impacts to the rate and volume of runoff. 5. As they are currently designed, the proposed rain gardens are to be mulched areas with clustered grasses and shrubs. Frequent inundation and overflow of the 250 Clark Street, Stormwater Review 3 March 13, 2013 basins, particularly Rain Garden#1, has the potential to wash the mulch out of the basin and into the adjacent wetlands. Consideration should be given to vegetating the entire bottom of the basins and letting them function more as vegetated bioswales. This would both eliminate the potential for mulch washout and provide filtration/water quality enhancement of the runoff that is not infiltrated. 6. The design detail for the proposed rain gardens on Sheet 4 of 4 calls for a 6-inch ponding depth however, based on the spillway elevations, the effective ponding depth is only 3 inches. 7. Based on the plans, overflows from Rain Garden #1 will drain approximately 50 feet overland to the adjacent wetland. It is unclear, however, where the discharge from Rain Garden #2 will go, particularly as there is a stone wall immediately downgradient of the proposed overflow weir and a paved road immediately to the north. 8. The surface area of the proposed rain gardens should be treated as impervious areas in the HydroCAD analysis in order to avoid double-counting of the infiltration capacity. 9. Based on the plans the existing building has roof downspouts that appear to discharge to the ground around the building, with the runoff flow then draining across the pavement. It is not clear how the roof drainage from the proposed building will be handled. Given that the proposed rain gardens will be limited in the amount of groundwater recharge they can provide, it may be possible to direct some of the roof runoff to drip trenches or a shallow infiltration trench(e.g. in the vegetated area to the southeast of the new building) to provide the needed recharge. 10.Additional information is needed on the proposed roofing material for the new building. Unless they are coated or sealed, galvanized metal roofs can leach significant quantities of zinc into the runoff stream. The discharge from such roofs should not be infiltrated or discharged to wetland a resource area. 11. While it is appropriate to combine the Long-term Pollution Prevention Plan with the O&M plan for the permanent BMPs on the site, short-term construction- related pollution prevention measures should be incorporated in a separate Erosion & Sediment Control Plan for use by the site contractor. The Long-term Pollution Prevention/O&M Plan should be aimed at the facility manager and should address site specific good housekeeping measures such as pavement sweeping, pesticide and fertilizer use, deicing and snow storage locations for the project site, as well as the locations and maintenance of the permanent BMPs. Given the nature of the operations on the site, the storage and use of potentially hazardous materials as well as any vehicle (or airplane) washing, deicing, etc. should also be addressed. 250 Clank Street, Stormwater Review 4 March 13, 2013 I appreciate the opportunity to assist the North Andover Planning Board and Conservation Commission 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, Conservation Coordinator Eggleston Environmental April 9, 2013 V 1600 Osgood Street , North Andover Planning Board E North Andover, MA 01845 A PR 10 2C)13 Attn: Judy Tymon, Town Planner NORTH ANDOVER RE: Stormwater Review CONSERVATION COMMISSION LL�l 250 Clark Street Dear Ms. Tymon and Board Members: In follow-up to my previous comments on March 13, 2013 on the proposed expansion of the Flight Landata facility at 250 Clark Street, I have received and reviewed the April 3, 2013 response fi-om Williams & Sparages Engineers, including the following: ■ April 3, 2013 letter to North Andover Planning Board from Peter Blaisdell, Jr., of Williams & Sparages re: Response to Stormwater Review by Eggleston Environmental • Site Plan in North Andover, MA, Sheets 1-4 of 4, prepared by Williams & Sparages, dated February 7, 2013 and revised through March 26, 2013. ■ Comparative Drainage Analysis, Flight Landata, 250 Clark Street, North Andover, prepared by Williams &Sparages and revised through March 26, 2013. ■ Notice of Intent, 250 Clark Street, prepared by Williams & Sparages and dated February 7, 2013. I've also discussed my comments and the proposed revisions with the project engineer. The revised submission satisfactory addresses the issues identified in my March 13tH letter with respect to the drainage design. I do have just a few comments at this time: 1. The proposed plan calls for a siltation fence erosion control barrier. Additional measures (e.g. hay bales or silt socks) may also be needed. 2. It appears that the proposed project may entail the disturbance of an acre or more of land. If so, it will also be subject to the EPA Construction General Permit and require filing of a Notice of Intent under that program, and implementation of a Construction Stormwater Pollution Plan (SVvTPP) in accordance with EPA guidelines, 3. The Pollution Prevention Plan included with the NOI addresses short-term construction related measures aimed at the site contractors. Per DEP requirements, a Long-Term Pollution Prevention Plan is still needed. As with the O&M Plan, this would be aimed at the parties responsible for maintaining the site 32 Old I- 250 Clark Street, Stormwater Review 2 April 9. 2013 over the long term and should address snow storage locations, pavement sweeping, spill control and good housekeeping measures to be employed on the site in order to minimize pollutant exposure to stormwater. Given the nature of the operations on the site, the storage and use of potentially hazardous materials as well as any vehicle (or airplane) washing, deicing, etc. should also be addressed. Once again, I appreciate the opportunity to assist the North Andover Planning Board and Conservation Commission 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 ._1 Lisa D. Eggleston, P.E. C: Jennifer Hughes, Conservation Coordinator Project No. NAND-0020 C� , (c,' �} I A ril 3,2013 North Andover Planning Board & WILLIAMS North Andover Conservation Commis ERVA N,aN(;Oiq_ i SPARAGES 15C(3VATION COMMICION ENGINEERS . PLANNERS . SURVEYORS 1600 Osgood Street North Andover,MA 01845 Subject: Response to Stormwater Review by Eggleston Environmental 250 Clark Street(Flight Landata,Inc.) DEP File No. 242-1584 Dear Members of the Planning Board and Conservation Commission, The purpose of this letter is to respond to technical review comments that we received in a letter addressed to the Planning Board from Eggleston Environmental (EE) dated March 13, 2013 for the proposed expansion of the Flight Landata facility located at 250 Clark Street. We have spoken with Lisa Eggleston regarding the comments and have communicated on how we intend to address them. The comments provided by Eggleston Environmental are shown in italics below, and,our responses are in the bold text that follows. 1. It appears from the plans and available aerial photography that runoff from the project area currently drains to three different watershed areas,hozvever it is not clear to zvhat degree the three are hydrologically connected. In order to evaluate impacts on the hydrologic regime of the three zvetlands as well as any potential downstream flooding the drainage analysis needs to be broken out on a subzvatershed basis, with control points at each resource area. In accordance with the North Andover Wetlands Bylaw Regulations, the analysis should evaluate the volume of runoff discharged to each control point as zvell as the peak rate of flow. The local zvetlands regulations also require analysis of the 1-year storm. The first topic was discussed at our presentation to the Conservation Commission on March 27,2013. The two wetland resource areas to the north and west of the existing building are joined at approximately 150'to the northwest of the existing edge of pavement and are tributary to an unnamed stream that ultimately reaches the Merrimack River. The wetland resource area to the southeast of the existing building is tributary to a different unnamed stream which passes under Holt Road and also reaches the Merrimack River. We have split the flows into three directions in our revised calculations to compare the flows to the wetland resource areas to the north,west and to the southeast as requested. A Volume Comparison Table was included in the initial Comparative Drainage Analysis on page 3 and will be updated to reflect the results of the revised calculations. We have included an analysis of the 1-year storm in the revised calculations. As discussed with Lisa Eggleston,we have revised the title of the structures known as Rain Garden#1 and Rain Garden #2 to Biofilter#1 and Biofilter#2 respectively. 191 South Main Street, Suite 103 • Middleton, MA 01949 • Tel: (978) 539-8088 • Fax: (978) 767-8579 Response to Stormwater Review 250 Clark Street North Andover, MA 2. The proposed rain gardens are intended to exfiltrate captured runoff flow in order to provide the required groundwater recharge and water quality treatment (via filtration and pollutant uptake) of runoff flow. However, due to the shallow groundwater table on the site, in conjunction with the shallow depth (0.25 ft) of the proposed rain gardens, their capacity to provide either effective recharge or filtration of the recharge will be minimal to non-existent during periods of lower groundwater. Based on the soil tests conducted, the surface elevation of Rain Garden #1 will intercept the groundwater table during high groundwater conditions,and in Rain Garden #2 the ESHGW elevation is less than afoot below the surface, within the soil media layer. Per the DEP Stormwater Handbook, rain gardens designed to exfiltrate mush ensure two feet of vertical separation from the seasonal high groundwater table to the bottom of the bioretention cell (e.g. the bottom of the filtration media). As discussed with EE,the presence of shallow groundwater is an existing condition that we must work around. For example,the surface elevation of the edge of pavement where we are proposing additional parking spaces ranges between 134.54 to 134.06 (average=134.3). The estimated seasonal high groundwater table (ESHGWT) was observed at 133.2,only 1.1 feet below the average pavement grade in this area. We agree with EE's comment,but our position is that we have to make our best attempt to improve the water quality of the stormwater runoff even if it does not exactly fit into the criteria of the DEP Stormwater Handbook. If this were a new project,we could design a system that met each criteria,but as an expansion of an existing facility this option is not available to us. We agree with EE's comment regarding the requirement of 2-foot of separation from the high groundwater elevation,however,DEP does recognize that for sites comprised of hydrologic soil groups "C" and"D"and bedrock at the land surface,proponents are required to infiltrate the required recharge volume only to the maximum extent practicable (see Volume 1,Chapter 1 pages 6 &7 of the Stormwater Handbook). Our site is comprised solely of"C" soils and it is our belief that based on the existing conditions that we have to work with...we are infiltrating to the maximum extent practicable. We have raised the level of the bottom of Biofilter#1 in the revised calculations to elevation 133.2 in order to provide additional storage during periods of high groundwater. 3. The dead storage volume in the rain gardens,e.g.for calculating water quality or recharge volume should only include that which is above the ESHGWelevation. During high groundwater conditions, there nuuy be as little as 0.05 ft (0.6 in) of storage between the pool/groundwater elevation and the overflow weir of Rain Garden #1. As mentioned in our previous response,we have raised the bottom of Biofilter#1 to match the ESHGWT and therefore,will be able to count the volume below the spillway towards dead storage. The ESHGWT observed at Biofilter#2 was at elevation 129.1 and is approximately 0.9 feet below the proposed bottom of the biofilter at elevation 133.0 and no change to the provided dead storage will be required. Response to Stormwater Review 250 Clark Street North Andover, MA 4. Since the proposed project calls for the infiltration BMPs to attenuate large storm flows (10-yr and larger) and the separation to seasonal high groundwater beneath the systems is less than four feet, the DEP Stormwater Standards require that a mounding analysis be performed to demonstrate that the systems will be fidly deivatered within 72 hours. Per my comnients above, the proposed design provides little to no separation to groundwater, hence a mounding analysis is unlikely to provide any benefit. I would suggest that the hydrologic analysis be run without any exfiltrationftont the basins in order to fully account far the impacts to the rate and volume of runoff. We agree with EE's comment regarding the requirement of a mounding analysis and came to the same conclusion. We also removed the rate of exfiltration through the bottom of the biofilters as suggested by EE in the revised calculations to show the difference between providing for no exfiltration and providing some limited exfiltration. There will be many times during the year where some infiltration will occur. 5. As they are currently designed, the proposed rain gardens are to be mulched areas with clustered grasses and shrubs. Frequent inundation and overflow of the basins, particularly Rain Garden #1, has the potential to wash the mulch out of the basin and into the adjacent wetlands. Consideration should be given to vegetating the entire bottom of the basins and letting them function more as vegetated biosivales. This would both eliminate the potential for mulch washout and provide filtration/water qualihj enh ancenrent of the runoff that is not infiltrated. We have revised the detail to specify that the bottoms of the Biofilters will be seeded with "New England Wetmix" or a suitable alternative. 6. T]w design detail for the proposed rain gardens on Sheet 4 of 4 calls for a 6-inch ponding depth however, based on the spillway elevations, the effective ponding depth is only 3 inches. See the revised calculations. 7. Based on the plans, overflows from Rain Garden #1 will drain approximately 50 feet overland to the adjacent wetland. It is unclear, however, where the discharge from Rain Garden #2 will go, particularly as there is a stone wall immediately down gradient of the proposed overflow weir and a paved road immediately to the north. The overflow from Biofilter#2 will discharge via stone spillway at elevation 133.25 and then flow overland across the existing lawn towards the utility pole and the lower grades at the existing limit of disturbance. Runoff from this lawn area then flows east, southeast away from the paved roadway towards the existing wetland system tributary to the unnamed stream flowing under Holt Road mentioned previously. 8. The surface area of the proposed rain gardens should be treated as impervious areas in the HydroCAD analysis in order to avoid double-counting of the infiltration capacity. We have revised the bottom of the Biofilters to be treated as impervious surfaces in the revised calculations. We have discussed this with EE and agree that there will be some exfiltration occurring through the bottoms at certain times of the year. Response to Stormwater Review 250 Clark Street North Andover, MA 9. Based on the plans the existing building has roof downspouts that appear to discharge to the ground around the building, with the runoff flow then draining across the pavement. It is not clear hozv the roof drainage front the proposed building will be handles. Given that the proposed rain gardens will be limited in the amount of groundwater recharge they can provide, it may be possible to direct some of the roof runoff to drip trenches or a s1U71107V infiltration trench (e.g. in the vegetated area to the southeast of the nezv building) to provide the needed recharge. We have added a 157'long,4'wide and 2' deep stone-filled trench to distribute the southern half of the proposed roof runoff evenly over the length of the building,which will provide storage volume for the 2 year storm event and then overflow across the lawn area towards the southeast. We felt it prudent not to add a similar trench on the other side of the proposed building as there is not a lot of room between it and the existing building. On this side of the building,roof runoff will continue to be directed to the surface and the land between the buildings will be graded to allow surface water to flow out to the west. 10. Additional information is needed on the proposed roofing material for the new building. Unless they are coated or sealed,galvanized metal roofs can leach significant quantities of zinc into the runoff stream. The discharge from such roofs should not be infiltrated or discharged to a wetland resource area. According to the project architect,Mr. David Barsky,the roof shall be constructed of a patented sheet steel product having an acrylic coating of corrosion-resistant material applied to the steel sheets. 11. While it is appropriate to combine the Long-term Pollution Prevention Plan with the O&M plan for the permanent BMPs on the site, short-term construction-related pollution prevention measures should be incorporated in a separate Erosion &Sediment Control Plan for use by the site contractor. The Long-term Pollution Prevention/O&M Plan should be aimed at the facilihj manager and should address site specific good housekeeping measures such as pavement sweeping,pesticide and fertilizer use, deicing and snow storage locations for the project site, as well as the locations and maintenance of the permanent BMPs. Given the nature of the operations of the site, the storage and use of potentially hazardous materials as well as any vehicle (or airplane) washing, deicing, etc, should also be addressed. Please see the Erosion and Sediment Control Plan dated February 7,2013 included in the Notice of Intent (NOI) submittal package as well as an Operation &Maintenance Plan with the same date which will address the comment made by EE. A copy of the NOI package has been provided to EE. Response to Stormwater Review 250 Clark Street North Andover, MA We trust that you will find the responses above adequately address the comments made by the technical review agent and will allow you to approve the proposed expansion of the Flight Landata facility. If you have any questions, please do not hesitate to contact me directly. Very truly yours, , Peter M. Blaisdell,Jr., P.E.,P.L.S. Project Engineer PMB:CPS Enclosures cc: Attorney Jill Mann Scott Stetson/KEYW Corporation Lisa Eggleston,P.E. Project No. NAND-0020 April 10,2013 & North Andover Planning Board � WILLIAMS SPARAGES North Andover Conservation Commission ENGINEERS PUNNERS � suevF oas 1600 Osgood Street North Andover,MA 01845 Subject: Response to St rm p o water Review by Eggleston Environmenta 250 Clark Street(Flight Landata,Inc.) r•14 DEP File No. 242-1584 smart NORTH ANDOVER Dear Members of the Planning Board and Conservation Commission, CONSERVATION COMMISSION The purpose of this letter is to respond the few remaining comments that we received yesterday afternoon from Eggleston Environmental (EE) regarding the proposed expansion of the Flight Landata facility located at 250 Clark Street. The comments provided by Eggleston Environmental are shown in italics below,and,our responses are in the bold text that follows. 1. The proposed plan calls for a siltation fence erosion control barrier. Additional measures (e.g. hay bales or silt socks) may also be needed. In the Erosion &Sediment Control Plan included in our original Notice of Intent package dated February 7,2013,under Erosion and Sediment Control Device,please see the following statement starting in the middle of the second line... "It is important-for the owner, builder, and/or site contractor to have access to a supply of haybales should the need arise for additional erosion and sediment control measures." We have added this text to the notes (Note 8) found on the revised site plan to ensure that this is emphasized during construction activities. 2. It appears that the proposed project may entail the disturbance of an acre or more of land. If so, it will also be subject to the EPA Construction General Permit and require a Notice of Intent under that program, and implementation of a Construction Stormzvater Pollution Prevention Plan (SWPPP) in accordance with the EPA guidelines. The amount of proposed disturbance is approximately 37,000 square feet,which is less than the minimum required land disturbance of 1 acre required for a filing with the EPA. 3. The Pollution Prevention Plan included zvith the NOI addresses short-term construction related measures aimed at the site contractors. Per DEP requirements,a Long-Term Pollution Prevention Plan is still needed. As zvith the O&M Plan, this zvould be aimed at the parties responsible for maintaining the site in order to minimize the pollutant exposure to stormzvater. Given the nature of the operations on the site, the storage and use of potentially hazardous materials as zvell as any vehicle (or airplane) zvashing, deicing, etc. should be addressed. 191 South Main Street, Suite 103 • Middleton, MA 01949 • Tel: (978) 539-8088 • Fax: (978) 767-8579 Response to Stormwater Review 250 Clark Street North Andover, MA April 10, 2013 We have attached a revised Operation &Maintenance Plan that is to be used for the post construction period naming Flight Landata,Inc. as the party responsible for the operation and maintenance of the stormwater management system. We have also noted that if Flight Landata, Inc.were no longer the tenant the responsibility would revert back to the Leasehold Owner,Michael Florence. We have also attached a revised Inspection and Maintenance form to be used in the Long-Term which requires inspections twice per year, spring and fall, or within a 24 hours of a storm event with 2 year storm intensity or greater,i.e. 3.1 inches of rainfall within a 24 hour period. We have also shown designated snow storage areas that are currently being utilized by the property which are all up-gradient of the wetlands. We have spoken with Mr. Scott Stetson of KEYW Corporation(the parent company of Flight Landata, Inc.) and they do have an aircraft spill-kit located in their hanger,in the unlikely event of an aircraft leak. As presented by Attorney Jill Mann at the April 2,2013 Planning Board hearing,the aircraft are not fueled at this location. In addition,they do not wash or de-ice the planes at this location according to Mr. Stetson. Therefore,there is no danger of contaminating the wetland resource areas with wash water runoff. We trust that you will find the responses above adequately address these last few comments made by the technical review agent and will allow you to close the hearing for the proposed expansion of the Flight Landata,Inc.facility. If you have any questions,please do not hesitate to contact me directly. Very truly yours, &a* Z4041�;? I? Peter M. Blaisdell,Jr.,P.E.,P.L.S. Project Engineer PMB:CPS Enclosures cc: Attorney Jill Mann Scott Stetson/KEYW Corporation Lisa Eggleston,P.E. Operation &Maintenance Plan "250 Clark Street " 250 Clark Street, North Andover, MA 01845 February 7, 2013 Revised: March 26, 2013 Revised: April 9, 2013 This Operation&Maintenance Plan has been prepared to comply with the provisions set forth in the Massachusetts Department of Environmental Protection(DEP) Stormwater Management Standards. Structural Best Management Practices (BMPs) require periodic maintenance to insure proper function and efficiency in pollutant removal from stormwater discharges that would otherwise reach wetland resource areas untreated. Maintenance schedules found below are as recommended in Department of Environmental Protections Massachusetts Stormwater Handbook and as recommended in the manufacturer's specifications. The following BMPs shall be utilized for project at 250 Clark Street for pollutant removal from stormwater discharge as well as providing additional groundwater recharge on site: • Parking Lot Sweeping • Biofilters with stone diaphragms • Stone Trench for roof runoff The responsible party for following the Operation&Maintenance Plan long-term after construction has been completed will be Flight Landata,Inc. Should Flight Landata,Inc.not be the tenant of the facility in the future,the responsibility will revert back to the Leasehold Owner,Michael Florence. See attached Inspection Log. Parking Lot Sweeping_ • We recommend that the parking lot be swept at a minimum of once per year in the spring. Biofilters • Inspect and remove trash year monthly throughout the year. • Remove and replace dead vegetation annually in the spring. • Prune the shrubs annually in the spring. • Remove any sediment from the top of the stone diaphragms and from the pretreatment sideslope annually in the spring. • Mow the pretreatment sideslopes once a month during the growing season. • When areas of erosion are identified,repair areas of erosion and revegetate as needed as soon as possible. • Inspections shall be performed at least twice a year, or after a major storm event which is defined as a storm that is equal to or greater than the 2-year storm event. Operation & Maintenance Plan 250 Clark Street, North Andover, MA 01845 Revised: April 9, 2013 • During these inspections, record and map the following information: -The presence of accumulated trash and/or debris, -The presence of dead vegetation and/ or invasive species (invasives must be removed), -Stability of the sideslopes and berms, -Accumulation of sediment, -Survival rate of plantings (dead plantings must be replaced) Stone Trench for roof recharge: • Leaf screens shall be installed in the gutters to prevent debris from reaching the trench. • Install three (3) inspection ports to be located at the beginning,middle and end of trench. • Should standing water be present in bottom of system during a routine inspection or more than twenty-four (24) hours after the end of a rainfall event,it may be as a result of the stone bed layer being clogged. The amount of elapsed time required for the water to infiltrate completely should be recorded. If after seventy-two (72)hours from the end of a rainfall event there is still standing water in the bottom of the trench,the affected area should be excavated and the stone replaced with clean stone. • We recommend the following schedule for system maintenance Monthly in first year of service: -Check inlets for clogging and remove any debris as necessary -Check for depressions in areas over and surrounding the system Spring and fall in the second year service: -Check inlets for clogging and remove any debris as necessary -Check for depressions in areas over and surrounding the system One year after commissioning and every year following: -Check inlets for clogging and remove any debris as necessary -Inspect the interior of the trench via inspection ports and measure sediment or depth of standing water -Check for depressions in areas over and surrounding the system -Confirm that no unauthorized modifications have been performed to the site • It should be noted that most failures that occur in subsurface systems are due to inadequate pre-treatment which leads to clogging. However,this system shall only receive roof runoff from the roof,which is considered clean by DEP and does not require pre-treatment. Therefore,we do not expect there to be any adverse impacts to the system due to debris accumulation. 2 INSPECTION AND MAINTENANCE REPORT FORM 250 CLARK STREET, NORTH ANDOVER, MA TO BE COMPLETED TWICE PER YEAR (SPRING & FALL) OR WITHIN 24 HOURS OF A 2 YEAR STORM EVENT (3.1 INCH OR GREATER WITHIN A 24 HOUR PERIOD) Name of Inspector: Date: Inspector's Company/Affiliation: Days Since Last Rainfall: Amount of Last Rainfall: w,_�. � . _.t : S#ruc���a� Coh�io�sR.StQrmwater�111��,� e,�ment�ireas _ Sfiori�nvua�elr��l�.hagetnent Ca�,���ro� Qf Hoyir Much Sediment How tVluGh Sedimen#�u�l�i Area-lde ��l�c�tt�on � j Sidee5lopes Buils� up in �as�n up at the Outlet 3 FF 3, s - ��Q��t9C`�� minor/moderate/major Bat��lt�r�2 �y minor/moderate/major WWII minor/moderate/major NoteChlt�cond��0orofP , �tot�e Rai . r is ,. MEW minor/moderate/major minor/moderate/major Maintenance Required: To Be Performed By: On of Before: Project No. NAND-0020 . ; April 17,2013 Louis Napoli,Chairman WILLIAMS Conservation Commission W-4 SPA:RAGES Town of North Andover ENGINEERS . PLANNERS SURVEYORS 1600 Osgood Street-Suite 2-36 North Andover,MA 01845 U ` rju Subject: Revised Plans v C5 AP 250 Clark Street-DEP File No. 242-1584 R 5 1 / ?01J Dear Mr. Chairman&Members of the Commission, �pNS INA 11 pN OM814 MISS/p� At the last Conservation Commission meeting on April 10,2013,there were some additional questions raised by the Commission members and staff that required minor changes to the plans and to the Operation and Maintenance Plan for the site. The following discussion describes the questions raised and how they have been addressed. 1) Snow Storage Areas-There was some concern regarding snow storage areas and the proximity of these areas to wetland resources and the stormwater management areas. The plan has been revised to show a wooden guardrail along the new parking spaces along the west side of the site. Two signs are also proposed with the words,"No Snow Storage or Salt Use." These measures are intended to prevent snow from being plowed into the proposed biofilter BMP area. In addition,snow storage areas are now limited to the area along the northern edge of the access driveway,the lawn area located in the northwestern section of the site,and the lawn area just east of the new parking field near the entrance to the site. 2) Operation&Maintenance Plan-The language describing parking lot sweeping and inspecting for trash has been revised to clarify the frequency of the maintenance schedule. 3) Area of Disturbance-Both staff and the members were concerned about an area of lawn in the northwest corner of the site that was disturbed during this past winter. We have not been able to determine who or what caused this disturbance,even after checking in with representatives at Flight Landata,Inc. and the leasehold owner,Michael Florence. This area is outside the lease area for Flight Landata,Inc.,however,Flight Landata has agreed to restore the disturbance as soon as the site work begins at their facility. A note has been added to the plans describing that the disturbed area will be restored with the 4-inches of loam and seed. 4) Aircraft Fueling and De-icing-In our response letter dated April 10,2013 and during our presentation before the Planning Board of April 2,2013 and later before the Conservation Commission both our office and attorney Jill Mann have represented that fueling of aircraft and washing/ de-icing of aircraft does not occur on the subject property. During the Conservation Commission hearing on April 10,2013,members asked where the aircraft is fueled and/or washed/ de-iced if it does not occur on site. 191 South Main Street, Suite 103 • Middleton, MA 01949 • Tel: (978) 539-8088 - Fax: (978) 767-8579 Following the April 10,2013,we contacted representatives of Flight Landata, Inc. and the leasehold owner Michael Florence and asked again about fueling and washing/ de-icing. According to the persons we spoke with,aircraft is fueled at one of the designated fuel farms at the airport,not on site. In addition,washing/ de-icing does not occur on site. In fact, de- icing is not done at all for the aircraft operated by Flight Landata. This is because it is not needed. If the weather is bad,the aircraft do not fly. In addition, since the aircraft at Flight Landata is kept in a hangar in close proximity to the runway....if there is light winter precipitation,de-icing is not needed because it is a very short trip from the hangar to the runway. Attached to this letter are nine (9) copies of the revised site plan and a revised Operation& Maintenance Plan. We look forward to meeting with the Commission again on April 24,2013. In the meantime,please do not hesitate to contact me directly with any questions of the Commission members or staff. Very truly yours, C Ps Principal Enclosures cc: Jill Mann Scott Stetson i I i III i | � � � Hughes, Jennifer � From: Lisa Eggleston |eatonem�nnnmen�dcon� . r~~x�~uuO5OA� ^ Smm� . 2013 1 : To: Hughes, Jennifer Subject: RE: 25OClark � � Sony, it was tucked into an email I sent you regarding the Merrimack College review: I've reviewed the April loth response from Williams&Sparages on 250 Clark St and arn more or less okay with it. | had � tried to get them to add some language about good housekeeping measures to the O&M Plan but had only minimal � success. Perhaps you can include in your OOC that they take steps to minimize pollutant exposure to stormwater and that all aircraft maintenance operations be kept under cover. � � Let rne know if you need anything more. [jBa D. Foo\8stoM/ P.E. Eggleston Env@ronimental 32 Old Framingham Rd., Unit #29 Sudbury, M/\ 01776 � � tel 508.259.1137 � fax 866.820.7840 From: Hughes,Jennifer � Sent: Tuesday/ April 23, 2013 10:10 AM To: 'Lisa Eggleston' Subject: 250 Clark Lisa, Have you done a final review of this one? I am writing their order and do not see a final sign off from you after their last submittal on April 17.Thanks. Jennifer A. Hughes Conservation Administrator Town of North Andover 16OO Osgood Street,Suite 2035 North Andover,MA 01845 Phone 978.688.9530 Fax 978.588.9556 Email Web