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Home My WebLink About11/17/2016 - Eggleston Environmental Response - - 1210 Osgood Street uuuuuu Vumum"'It u uumm IlVuluul ��n uuuuuu Ipumll I IV"uu o IlVuull puu°lu m Iluuum Vuuuo "'It u uuuuu glululu ll� g gi �I""IlllllluomuuuIIII "IIIIIIIIIuI �u dull °°°u*��wav�rrrrra��aum�ulllp111111A111))�� November 17, 2016 North Andover Planning Board 1600 Osgood Street North Andover, MA 01845 Attn: Rebecca Oldham, Staff Planner RE: Stormwater Review Princeton at North Andover, 1210 Osgood Street Dear Ms. Oldham and Board Members: In follow-up to my October 28, 2016 review comments on the above-referenced project and subsequent email exchanges with the Applicant's engineer, I have received and reviewed the October 31, 2016 response letter, November 1, 2016 revised Stormwater Report (note: the Stormwater Report is incorrectly dated 10-1-16) and November 1, 2016 Site Plans (31 Sheets) submitted by Hancock Associates. I also received a copy of the November 4, 2016 Notice of Intent for the project prepared by Epsilon Associates. As with previous design revisions, a number of my previous comments have been satisfactorily addressed by this revised submittal; however, I do still have several concerns with the design as currently proposed. My specific comments are outlined below: 1. The October 31 St response letter references several items that are being worked on by Hancock Associates but have yet to be provided; specifically the offsite topography within 50 feet of the property, the locations of the most recent soil tests to be shown on the Existing Conditions plan, and documentation that the BayFilter treatment units are effective in treating oil and grease. This last element is needed to demonstrate compliance with Stormwater Standard 5 since the project proposes using the filters to treat runoff from the commercial area of the project, a Land Use with Higher Potential Pollutant Loads (LUHPPL) with the potential to generate moderate to higher concentrations of oil and grease. 2. In response to my 10/28 Comment #6 Hancock has added cleanouts at the inlets to the ADS closed pipe detention systems, and revised the O&M Plan to call for removing the sediment directly beneath the inlets as necessary and at least every 5 years. I question whether cleaning the pipes only at the inlets will be adequate — the detention systems are designed retain the entire one-inch water quality volume until it slowly drains through the filters and will likely function like sediment forebays, with sedimentation occurring throughout the closed pipes. Over time the sediment buildup may reduce both the detention capacity and the volume of water that is retained in the systems and directed through the filters. I recommend that inspection ports be added to the systems so that they can be monitored for �w ��„ I�� '"� IIIIY"°°' I� I' d 'u 'II �" III� �"�I�IP""" �'��II WI IIII IIIII 'IIpV II° II��II�� iiii �iiii��iiii iiii °III iiii�� iii��I�� I�� :��ii��:iiiiiI �I�� 1 ',IIIII ��II�� °��IIII�1�1�1��IIII � '��III� �� 'IIIIIII I III''I .III "..I1 Po....°ppp��u.�:.��i!I'M��I'M...ull1O I��V 1'��L.�'i��h�„IVY�IIIiP��ll" wV.�.."uiib 12".1...0 Osgood ,. IVY...... 2 .,,ppOpppl.., sediment accumulation, and that some means of access be provided to clean the systems in their entirety should it become necessary. 3. The revised hydrologic analysis is still overestimating the storage in infiltration system #35. The model assumes the bottom of stone at 147.75 and the bottom of system at 148.5, while the plan (Sh. 25) calls for the bottom of stone to be at 149.25 and the bottom of the chambers at 150. 4. The revised plan gives the invert of the three 8-in orifices at OS-10 as 148.75 (Sh. 14); this is inconsistent with the model which assumes an invert for the three orifices of 149.25. The model also treats the orifices as a primary outlet rather than a device on the 15-in culvert. 5. The model assumes that the weir in OS-11 has a 3-in orifice at el. 147.4; the plan (Sh. 14) does not call for any orifice. 6. The bottom of the chambers in system#21 is modeled as 134.75; the plan (Sh. 24) specifies the bottom at 135.0. 7. The overflow weir in OS-34 is modeled as invert 146.3; the plan (Sh. 16) specifies an invert of 145.8. The model also treats the 3-in orifice as a primary outlet rather than a device on the 12-in culvert. 8. The invert given on the plan (Sh. 15) for the roof drain out of Building 3 (154.5) is below the inlet invert to IS-3 8B (154.6). 9. Per my 10/28 comment #11, the manifold invert at IS-21 is more than a foot higher than the overflow outlet at DMH-23, which means that excess flow to the Isolator Row would back up and bypass the system altogether instead of being distributed to the remaining infiltration chambers. This was not addressed on the 11/1 revised plans. 10. In response to my 10/28 comment #12 the inlet manifold at System #21 B has been lowered on the revised plan, however the inverts given for the 12-in inlets to the chamber system at IS -21 A and IS-21 B are still 3.5 feet higher than the manifold and would actually be above the top of the chambers. The invert of the manifold and the inlets to all four rows of chambers should all be the same in order to better distribute flow within the system and maximize infiltration. 11. Per my 10/28 comment #14, the outlet structure details on Sheets 19 (MC-3500 Outlet) and 20 (MC-4500/SC-3 10) should be revised to show the 15-in manifold as an inlet to the OCS, not an outlet, and located on the other side of the weir. This was not addressed on the 11/1 revised plans. 111[1 1 '"L. 1Illi''4. O' IIII,,.. III .iM 3 .pppppp11 1,..du'Illllr�� I'M.��I'M,.�.I'M ��ii�'.I'M� .�... ,dull 0 1 1„„, 12. The revised plans include an outlet structure detail for the ADS closed systems, however a separate detail may be needed for OS-34 to show the connection from DMH 27 on the downgradient side of the weir. 13. As currently proposed the overflow outlet from systems #10 and #11 is at el. 144.2, almost two feet below the existing grade shown on the plan. Additional detail may be needed to show that all of the grading for the outlet and the 8 x 16-ft stone apron will be outside of the 50-ft wetland buffer. 14. The 11-1-16 revised O&M Plan addresses some, but not all of my previous comments. My comments at this time are as follows: ■ The BayFilter treatment units should be inspected/maintained on a semi- annual (2 times/yr) basis, not biannually (once every two years). ■ As indicated above, provision should be made for periodic cleaning of the ADS Solid Pipe Systems in their entirety. ■ The Long Term Pollution Prevention Plan should address deicing and snow management. The snow storage locations on the revised Layout and Materials Plan do not appear to be adequate for the site. ■ If the commercial and residential portions of the site are to have different owners separate plans may be required. ■ The subsurface storage/infiltration systems should be fully drained within 72 hours following a large storm event. If they are not, corrective action must be taken. ■ The plan should also include a checklist of long-term inspections and maintenance tasks and a simple figure showing the locations of all stormwater BMPs to be maintained and the designated snow storage locations. The stormwater checklist is not the same as that developed as part of the SWPPP — the latter will list O&M tasks specific to the construction phase of the project. Once, 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