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HomeMy WebLinkAbout2012-06-19 Stormwater Peer Review Eggleston Environmental March 8, 2012 North Andover Planning Board 1600 Osgood Street North Andover, MA 01845 Attn: Judy Tymon, Town Planner North Andover Conservation Commission 1600 Osgood Street North Andover, MA 01845 Attn: Jennifer Hughes, Conservation Coordinator RE: Stormwater Management Review 26 Main Street Dear Ms, Tymon and Ms. Hughes: Per your request, I have conducted an initial technical review of the Notice of Intent application packet, for the proposed "Pondview" condominium development at 26 Main Street. Included in the materials I received and reviewed were the following: • Stormwater Report, "Pondview", 26 Main Street, North Andover, prepared for Jeffco, Inc. by Andover Consultants, Inc. and dated January 19, 2012. • Site Design Plan Set, (Sheets 1-4 of 4), "Pondview", 26 Main Street, North Andover, prepared for Jeffco, file. by Andover Consultants, Inc. and dated January 19, 2012, It is my understanding that the project is also subject to permitting by the North Andover Planning Board, 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 review is therefore on the overall storniwater 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 Wetlands Protection Act (WPA), the North Andover Wetlands Bylaw, and the Massachusetts Department of Environmental Protection (DEP) Stormwater Management Standards and Regulations. The project site is all approximately 0.6-acre parcel on the east side of Main Street, behind the existing buildings at 22-24 Main and 28-30 Main St and adjacent to Sutton Pond and its associated bordering vegetated wetlands. It is presently occupied by two wood fiame garages and approximately 10,000 sf of pavement, much of which is in deteriorated condition. Drainage oil the site is overland, in a northeasterly direction toward Sutton Pond. The proposed plan calls for the removal of the existing garages and pavement, and construction of eight attached townhouse condominiums, with associated driveways, walkways and parking areas. Drainage from the rear portion of the buildings would be collected and discharged to a 32 Old Framingham Rd Unit 29 Sudbury MA 01776 tel 508.259.1137 fax 866.820.7840 26 Main Street, Technical Review 2 March 8, 2012 500-gallon subsurface drywell. Overland flow fi•om the remaining impervious areas (roof and pavement), as well as from several properties to the south of the site, would be routed through a Stormceptor 900 treatment unit and discharged through a level spreader toward the wetlands and Sutton Pond. My comments are outlined below: 1. The proposed project qualifies as a redevelopment project under Standard 7 of the DEP Stormwater Standards, since no net increase in impervious area is proposed. A redevelopment project is required to meet Standards 2, 3, and the pretreatment and structural stormwater best management practice (BMP) requirements of Standards 4, 5, and 6 to the maximum extent practicable, i.e. reasonable effort must be made to comply fully with these standards and the project should be implementing the highest practicable level of stormwater management. It must fully comply with the remaining Stormwater Standards. For the reasons outlined below, I do not believe that the project design currently proposed meets these requirements. 2. The proposed drywell is sized to infiltrate only the recharge volume(0.35 in) from half of the building roof, or 20 percent of the post-development impervious area. There is nothing in the Stormwater Report documenting why the project cannot comply fully with the recharge requirement of Standard 3, e.g. by infiltrating the entire recharge volume for the post-development site, as is warranted under the "maximum extent practicable" requirement for a redevelopment project. 3. The TSS removal calculations are based on 77 percent TSS removal by the proposed Stormceptor unit. As is indicated in the supporting documentation submitted, the Stormceptor units are currently certified by the NJCAT (New Jersey Corporation for Advanced Technology) through the TARP (Technology Acceptance and Reciprocity Partnership) Tier 1 program for a TSS removal rate of 50 percent, not 77 percent. The proposed treatment train, consisting of a deep sump catchbasin followed by the Stormceptor, therefore does not meet the 80 percent TSS removal requirement of Standard 4. 4. It is not clear where the roof drainage fi•om the fi•ont of the building will go, although it appears this flow was included in the area tributary to the Stormceptor unit. To the maximum extent possible, roof downspouts should be directed away from impervious areas to enhance infiltration of the clean roof runoff and minimize the flow across the pavement. 5. Based on the log for Test Pit TP-1, at the proposed drywell location, the entire 10-foot excavation was in fill, possibly associated with the old railroad bridge abutment. Evidence of trash disposal and layers of ash were also noted. Not only is this material unsuitable for infiltration, but it may suggest the need for further investigation of the site for potential hazardous wastes. Test Pit TP-2 had significantly less fill and may be a more suitable location for infiltration. I note that while three test pits are shown on the plan, the log for Test Pit TP-3 was not included in the Stormwater Report. 26 Main Street, Technical Review 3 March 8, 2012 6. The proposed drywell location is also only about 12 ft from a steep embankment. For most subsurface infiltration structures, the DEP Handbook calls for a minimum setback of 50 ft from slopes greater than 15 percent to prevent breakout of the infiltrated flow. While 50 ft may be more than is needed for a small shallow drywell, I believe that 12 ft is inadequate. 7. It is not clear from the design detail whether the drywell cover is to be solid or grated. If grated, I recommend a beehive grate to prevent clogging. 8. The design detail for the level spreader indicates that the upgradient area is to be grassed. The flared end section should be sized in accordance with the projected discharge velocities onto the turf, and a design detail provided on the plan. 9. I have the following comments on the O&M Plan: ■ The plan should include a schedule and log form listing the long-term maintenance tasks, and should be a stand-alone document separate from the Construction Period O&M/Sediment Control Plan. I find it useful to include a simple sketch plan showing the locations of the BMPs to be maintained. ■ Item #3 in the O&M Plan should be re-worded to say that the catchbasins should be cleaned when the sediment level is within two feet of the outlet pipe; this is easier to measure than the depth of sediment accumulated. ■ The Stormceptor unit should also be cleaned a minimum of once per year, with a vacuum truck. ■ Periodic inspection of the drywell and the outlet sump and level spreader should be included in the O&M plan. 10. The Long-Term O&M Plan indicates that snow will be plowed to just off the edge of pavement. Based on the site configuration, it appears that much of the snow would get plowed off the eastern end of the parking area, within the wetland buffer zone and downgradient of the treatment processes. Snow storage in this area should be specifically prohibited, and alternative locations on the site designated. 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. Eggleston Environmental April 10, 2012 North Andover Planning Board 1600 Osgood Street North Andover, MA 01845 Attn: Judy Tyrnon, Town Planner North Andover Conservation Commission 1600 Osgood Street North Andover, MA 01845 Attn: Jennifer Hughes, Conservation Coordinator RE: Stormwater Management Review 26 Main Street .Dear Ms. Tymon and Ms. Hughes: I am writing this letter in follow-up to my March 8, 2012 review letter on the above-referenced project. Since that time I have received and reviewed the March 19, 2012 revised plans and calculations from Andover Consultants, Inc. My comments on the response are outlined below: 1. As has been agreed, the proposed project is subject to the DEP Stormwater Standards to the maximum extent practicable. Per the requirements of the Massachusetts Stormwater Handbook(V.1,Ch.l,p.3): Project proponents seeking to demonstrate compliance with some or all of the Stormwater Management Standards to the maximum extent practicable shall demonstrate that: 1) They have made all reasonable efforts to meet each of the Standards; 2) They have made a complete evaluation of possible stormwater management measures, including environmentally sensitive site design,low impact development techniques that minimize land disturbance and Impervious surfaces, structural stormwater best management practices, pollution prevention, erosion and sediment control,and proper operation and maintenance of stormwater best management practices:and 3) If full compliance with the Standards cannot be achieved,they are implementing the highest practicable level of stormwater management. Standard 7(VA Ch.1.p.21)also requires that redevelopment projects improve existing conditions. As currently proposed, the project will provide no groundwater recharge as is called for under Standard 3. Given that the existing pavement on the site will be removed and replaced, and the test pits indicate that the soils beneath the site are well suited for infiltration, it does not appear that all reasonable efforts to comply fully with Standard 3 have been made. As is explained further under Comment #2, the proposed project also does not fully comply with the 80 percent TSS removal requirement of Standard 4, and there is no indication in the application materials that low impact alternatives (e.g. pervious pavement or bioretention) that would meet Standard 4 have been evaluated. 32 Old Framingham Rd Unit 29 Sudbury MA 01776 tel 508.259.1137 fax 866.820.7840 26 Main Street, Technical Review 2 April 10, 2012 Finally, since the proposed project does not propose any increase in groundwater recharge and does not provide sufficient water quality treatment to even mitigate the impact of the pollutant sources being added to the site, I do not believe that it meets the requirement of Standard 7 to improve existing conditions. 2. I fully recognize that the project is located in Massachusetts, not New Jersey. However, the applicant should be aware that the Massachusetts STEP fact sheet used as the basis for design was recalled by the Massachusetts DEP on January, 2011, as part of its transition to a stormwater performance rating system using the Technology Acceptance Reciprocity Partnership (TARP) field studies (see attached notice). The TARP program was established in 2000 as a standardized method of evaluating the performance of stormwater treatment technologies, and Massachusetts is one of eight states participating in the program. Per the notice, MassDEP intends to use the results and findings of other states from field studies conducted using the TARP protocol to evaluate how products meet relevant state stormwater standards. MassDEP has yet to formally assign a TSS removal efficiency to the Stormceptor units (or any hydrodynamic separators) under this program, therefore the Stormwater Handbook (V.2, ChA) calls for Conservation Commissions to consider other performance evaluations conducted using TARP protocol. Through the New Jersey Department of Environmental Protection (NJDEP) and the New Jersey Corporation for Advanced Technology (NJCAT), New Jersey is the only state currently reviewing and certifying technologies under the TARP protocol, which is why it is appropriate that the Conservation Commission use their data. I have not included the full 41-page verification report issued by NJDEP on 9/9/2004 and updated 7/2010, but I have attached a copy of the 8/31/2011 certification letter establishing the certified removal rate for the Stormceptor units as 50 percent. It is important to note that the certification is based on anticipated performance in the field, whereas the TARP Tier 1 testing that indicated higher removal rates was based on laboratory studies. 3. I reiterate my previous comment that, to the maximum extent possible, roof downspouts should be directed away from impervious areas to enhance infiltration of the clean roof runoff and minimize the flow across the pavement. It should be possible for the roof drainage from the front of the buildings to recharged onsite, e.g. in subsurface structures beneath the parking lot. 4. While I acknowledge that the maintenance schedule provided by the manufacturer calls for less frequent inspections and/or cleaning of the Stormceptor unit, experience has shown that the units are more likely to be maintained if they are cleaned on a regular schedule, e.g. yearly. The O&M Plan calls for the catchbasins to be cleaned at least once a year as well; therefore it makes sense to combine the two. If the inspections of the Stormceptor unit during the first year indicate that it accumulates 8 inches of sediment in less time the frequency of cleaning should be adjusted accordingly. 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 26 Main Street, Technical Review 3 April 10, 2012 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, Eggleston Environ mental May 1, 2012 North Andover Planning Board 1600 Osgood Street North Andover, MA 01845 Attn: Judy Tycoon, Town Planner North Andover Conservation Commission 1600 Osgood Street North Andover, MA 01845 Attn: Jennifer Hughes, Conservation Coordinator RE: Storrawater Management Review 26 Main Street Dear Ms. Tycoon and Ms, Hughes: In follow-tip to iny previous comments, I have received and reviewed the April 24, 2012 revised plans and calculations fi-orn Andover Consultants, Inc. on the proposed "Pondview" development at 26 Main Street, The revised design incorporates a Subsurface infiltration systern to replace the Storinceptor unit originally proposed in order to provide groundwater recharge as well as water quality treatment of infiltrated flows. My comments on the revised submittal are outlined below: I. Soils at the site are mapped as FISG "B", and two of the three test pits indicate the soils to be sands and loam suitable for infiltration (the third test pit was conducted in fill). I do note, however, that a "fine to medium platy structure" that may inhibit the rate of flow was observed near the bottom of both pits. The closest test pit was also located approximately 30 feet from the proposed infiltration system. Additional soil testing within the proposed infiltration area will therefore be needed prior to system installation to verify that the soil conditions in that area are consistent with the design parameters. (This can be made a condition of approval.) 2. Roof drainage from the front of the buildings should be piped directly to the infiltration system, instead of draining across the parking lot. This will reduce the Volume of flow through the catchbasin and enhance settling of solids. 3. The catchbasin detail should specify the double grate. 4. The infiltration system should be equipped with at least one inspection port to facilitate monitoring. The O&M Plan should specify that the system should empty within 72 hours after a storm event, and should identify corrective actions to be taken in the event that it is not draining properly. 32 0[d Framingham Rd Unit 29 Sudbury MA 01776 tel 508.259.1137 fax 866.820.7840 26 Main Street,Technical Review 2 May 1. 2012 5. It is not clear why the "Grasspave" cells are proposed at the outlet of the flared end section, since they are typically used as pervious pavers (e.g. to enhance infiltration Where structural integrity/loading is required). However, since the projected discharge velocities from the FES are relatively low, the Grasspave cells should work fine in that location, and will provide another opportunity for infiltration of the rLinoff. The plan should specify that the pavers be installed with sod (the manufacturer's specifications call for either sod or seed) in order to stabilize the area. In accordance with the manufacturer's specifications, the O&M plan should also call for periodic mowing of the grassed pavers and should specifically prohibit soil aeration in that area. 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, EGGI.I STON ENViRONmrNTAL p Lisa D. Eggleston, P.E.