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DEI’S RESPONSES TO ALL OUTSTANDING COMMENTS Outstanding comments from VHB (Ken Staffier) in his letter dated 1/16/17.

4. The plans show two different details for the accessible curb ramps. The plans should clearly label the type of accessible curb ramp to be used for each location. The accessible curb ramp adjacent to Building C does not appear to provide adequate clearance at the top of the ramp. The plan should be revised to provide adequate clearance consistent with the Massachusetts Architectural Access Board Regulations and the ADA (whichever is more stringent).

The stairs have been adjusted to provide the landing area needed.

9. Recommend that additional grading detail be added at these locations that sufficiently demonstrate that runoff from the site will not be discharged onto the abutting properties. The proposed grading is in close proximity to the property line, recommend the proposed swale be shifted to the north to prevent potential grading impacts to the abutting property.

The grading has been adjusted to clearly indicate that any water traveling in the area will be collected in the onsite drainage system within the property mimicking the existing conditions.

10. The width of the parallel spaces should be added to the plans.

The width has been added to the plans and is more than adequate to provide access to vehicles for parking.

12. The mounding analysis has been updated to incorporate the suggested variables. The applicant should clearly label each of the calculations. The analysis should also include calculations for determining the recharge rate (volume of runoff to be infiltrated) and a simple schematic showing the overall dimensions of the infiltration basins for the three scenarios; the centroid of the systems should be clearly delineated.

The calculations have been provided.

29. The hydrologic analysis has been updated to reflect the infiltration rates as recommended. The analysis indicates that there is no discharge from the infiltration system during the 100-year storm event, however, the water surface elevation within the infiltration system exceeds the invert elevation of the outlet. It is expected this would generate some discharge during the 100-year storm event. The applicant should explain this discrepancy.

The 12-inch outlet pipe of the underground infiltration system is set at elevation 126.60, however, the outlet control is the downstream emergency overflow device, CB #209, that has a rim elevation of 130.0.

The analysis also indicates a 60” x 60” outlet from P-4; the inlet structure detail on Sheet C- 5.10 calls for a 24” cover. The detail should be updated to match the hydrologic model.

The detail has been updated.

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The detail should also be updated to reflect the size of the rectangular orifice (14” x 9”). There is also a discrepancy regarding the size of the outlet pipe from the inlet structure between the HydroCAD model and the site plans. This discrepancy should be addressed.

The detail has been updated.

33. Hydraulic sizing calculations were not included with the Stormwater Report. Please provide. The hydraulic analysis should also include calculation demonstrating that the 25” x 12” equalizer culvert has adequate capacity to allow unimpeded flow between the two infiltration chambers.

The culvert has been revised to be a standard 24” x 24” box culvert. Rational Method calculations will be provided under separate cover.

38. The sewer line from Building B to SMH 300 does not meet the minimum velocity.

The system has been adjusted and the spreadsheet has been updated.

79. The STOP sign at the site driveway and North Avenue should be relocated to the back of sidewalk.

Sign has been moved as requested.

80. The revised plans show snow storage within the parking area immediately adjacent to the utility shed serving the septic system. At a minimum, an access aisle/clear pathway should be maintained for access to the utility shed.

An access pathway has been illustrated.

81. Recommend a trash rack/grate and 4-foot sump be added to the inlet device.

A 5-foot sump has been added to the inlet device.

82. Provide invert elevations for all inlet pipes to the infiltration system.

Invert elevations for all inlet pipes have been added.

83. The grading and drainage plan call for 14 - ConSpan 14 x 9 Units. However, the detail and HydroCAD model call for StormTrap Double Trap Units. The plans should be updated accordingly. In addition, there is a discrepancy between the infiltration system detail and the HydroCAD model. The detail calls out two different StormTrap unit sizes while the HydroCAD model call for 9’-0” model. The applicant should address the discrepancy.

The discrepancies have been corrected.

84. Additional grading detail should be added in the vicinity of the overflow structure (CB-209) to prevent water from discharging onto the abutting property (263 North Avenue).

The grading has been adjusted to clearly indicate any water traveling in the area will be collected in the onsite drainage system within the property mimicking the existing conditions.

85. There is a pipe conflict between sewer service to Building B and the outlet pipe from CB-210.

The conflict has been rectified.

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86. The applicant should provide formal responses to comments received from Richard Sweeney, PE Weston DPW via email dated 1/4/2017.

See responses below.

Outstanding Comments from VHB (Kathleen Lynch) in her letter dated 12/30/16

(Note: The balance of the comments in this letter are addressed by Terraink in a separated document.)

1. Recommend clear indication on the Site Preparation Plan of which trees within the site and along the property line are to be protected and remain, typically shown by X-ing out trees to be removed, and circling trees to remain. The note on the Drawing related to identification of trees to remain, and stating that the significant trees to remain will be further identified on the Landscape plan still leaves many gray areas. A site preparation contractor will not necessarily look at the final planting plans. And while the dashed boundary of the wastewater field and related note on the Site Preparation plan, and the text of the memorandum from Beveridge and Diamond, state that all trees at the front of the site will be removed, and all trees at the back will remain, there are trees outside of the dashed wastewater boundary, including along the property lines and in areas not disturbed by grading that ideally would remain. Specifically:

A. There are several trees near the upper end of the eastern haybale line, outside of the dashed wastewater line but in an area undisturbed by grading. These large trees ideally would be protected and remain. These are a 30” tree, 2x6” trees, and a 12” tree.

The site preparation plan has been revised to indicate which trees are to be removed using an “X”. The plan also includes trees that are to receive protection in the area of the septic field. These are marked with an “O”. It is understood that the area up the hill from the diversion swale will only be accessed during construction by the septic system installer and that no staging or other work will occur in that area. It was discussed that additional tree protection around the trees not immediately affected by the septic system installation would be required.

B. The proposed ‘Diversion Swale’ between the wastewater system and the developed area is routed through the boundary indicating trees that will remain. There are several existing large trees in this area, especially along the 146 contour, that would ideally remain, and that are indicated as remaining on Drawing L1.0. But all are not within the dashed waste water boundary, and it is not clear what disturbance the diversion swale will create. Is it cutting into the grade, or formed on top of it? Clarify treatment of trees within the swale.

The swale has been re-aligned to better conform to the proposed limits of excavation work and the trees affected have been identified with an “X” or “O”.

2. Tree protection detail: This detail does not seem adequate to address protection of trees to remain, especially since the detail appears to indicate a tree protection fence at the drip line, but none is

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called out or referred to, and many of the trees do not have a wide canopy to define a protection zone. The detail does not indicate any protective layer between the tree trunk and boards, or how to hold vertical protection boards in place. Even with appropriate attachment methods added, the detail may provide trunk protection, but doesn’t provide the more critical root protection. We’d recommend a line of snow fence generally protecting the zone of the trees to remain, a minimum of 10’ from the trunk, as well as more information on how the trees will be protected during installation of the waste water system with an airspade.

The plan and detail have been revised as discussed during a meeting with VHB. Snow fence and burlap have been added to the detail. In addition, the limit of work has been pulled away as much as possible from trees along the property lines. Also, see response to Comment #1 above.

Comments from Weston DPW in its email dated 1/4/17.

1. There is a plan for 269 North Ave., dated 2011, on which there was a test pit with test pit log and it is indicated that the test pit was done on the abutting property. There was mottling found at 8.0-ft., elevation 123.00, which is higher than the current bottom of the infiltration systems proposed. This test pit was used for design of an infiltration system for 269 North Ave. at the time. We know there were recent test pits done on site and no mottling was found, but as you know, mottling can be difficult to see in sand. It is very possible that the ESHGW is higher than the Applicant is considering; it may or may not affect the design of the systems, but we maintain that a couple of monitoring wells make sense.

The proposed stormwater design uses information collected from 15 test pits conducted in accordance with Massachusetts DEP requirements on 269 North Avenue for the design of the proposed system. The low point on the property is at 127, a groundwater elevation of 123 would put groundwater 4-feet below grade and likely at the elevation of the neighboring property basements.

DEI conducted 15 test pits; test pits 1 and 2 in October 2013, test pits 5, 6, 7 and 8 in May of 2015 and test pits 9,10 and 11 in April of 2016. Mottles were found in TP# 11 up on the hill, the mottles were encountered immediately on top of the bedrock confirming that water is flowing just on top of the rock. The aforementioned test pits were conducted during the “wet season”, as required for soil testing, and not during a certified drought. Test pits 12 through 14 were conducted in September 2016 to dig deeper to find bedrock and no mottles or bedrock were encountered. Those test pits and reports have all been previously submitted.

2. The Town of Weston Stormwater & Erosion Control Regulations state that at a minimum, all projects shall comply with the performance standards of the most recent version of the Massachusetts Stormwater Standards and Handbook. Since a Stormwater Management Permit Application was filed through the ZBA, the requirements should be met, which include the typical setbacks for drainage facilities, especially the infiltration facilities. The setbacks should apply regardless. These drainage facilities should not be a couple of feet from any property line or building. The stormwater management system is not in compliance with the State or Local Regulations.

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The infiltration basin at the front of the property that was close to the property line has been removed.

3. At the 8/31/2016 meeting at the Weston DPW with you, Bill Doyle, the 269 North Ave. owner, GPR Engineer, Steve Fogg., and myself present, it was determined and agreed upon that the infiltration rate in the existing conditions would be 2.41 in./hour at a minimum. With that rate and conditions, there is no overflow into North Ave. from the existing site even without the previous pipe. It appears that that infiltration rate has changed back to 1.02 inches/hour (sandy loam?), and the Applicant is indicating there is overflow into North Ave. in the 100-yr. storm event. We believe that there should be no runoff leaving the existing site at North Ave. even without the previous 18” existing pipe. The soil is the same sandy soil as they are basing their 8.27 in./hr. in the proposed conditions on, so 2.41 in./hr. It does not appear that using 1.02 in./hr. is conservative when determining any flooding on the north side of the site.

The infiltration rate used for the calculations was determined by VHB based on the sensitivity analysis with parameters set by VHB.

4. The structure should not be next to the sidewalk regardless, especially as an overflow structure. If an overflow is needed, it should be located it away from the road and sidewalk and abutters. Based on a brief review, the latest plans do not appear to be consistent with the latest HydroCAD model.

Upon revisions to the grading on the side of 263, we have located the structure at the existing low point and set its elevation at 130.0, this will mimic any discharge that may occur.

5. The Town of Weston Stormwater & Erosion Control Regulations, Section 7.0-A.1 state that at a minimum, all projects shall comply with the performance standards of the most recent version of the Massachusetts Stormwater Standards and Handbook. The project stormwater drainage system is not in compliance with the Massachusetts Stormwater Handbook or Weston Stormwater & Erosion Control Regulations as setbacks are not met. General accepted engineering principles typically include meeting required setbacks. Any infiltration system, whether an above ground system or a subsurface system, there is a minimum of a 10-ft. setback to building foundations or property lines. Depending on the system, the setback can be 20-ft. to a building or property line.

The infiltration basin in the front of the property has been removed and all of the buildings are slab-on grade without foundations. The system complies with the state regulations.

6. The comment was not regarding the infiltration rates, it was regarding the area for infiltration. The wetted perimeter is the area being used for infiltration in the infiltration system. As noted in the comment above, the structures only have bottom open area. A conservative design should only consider infiltration through the bottom of the structures.

The use of this system was recommended by VHB. The system is set in an envelope of gravel that is considered significantly permeable and will act as the wetted perimeter.

7. The existing drainage path and drainage pattern at and from 263 North Ave. is being changed, with impacts to 263 North Ave. Runoff from most of the northerly side of the existing property at 263 North Ave. is directed towards property line and 269 North Ave. in the current existing conditions. The proposed site and proposed grading is blocking this existing drainage path, and will create a

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pond on the property line. The ponding will extend onto 263 North Ave. property. DEI has indicated that they added one foot contours, which only makes the issue more clear.

The existing drainage path and drainage pattern at and from 263 North Avenue has not been altered. There is no change to the grading and drainage on 263 North Avenue. The drainage system within 269 North Avenue has been developed to retain the volume of water within the underground infiltration basins with an outlet on the property that is set to mimic the existing conditions.

8. Based on the proposed grading, the runoff from Subcatchment P-3 does not appear to be able to get to the catch basin CB-204 with rim elevation at 131.9 or into the infiltration system. The proposed grading is actually directing the runoff down the property line and into a portion of 263 North Ave. adding to the ponding as indicated above.

The existing drainage path and drainage pattern at and from 263 North Avenue has not been altered. There is no change to the grading and drainage on 263 North Avenue. The grading and drainage system within 269 North Avenue has been developed to capture and retain the volume of water within the underground infiltration basins with an outlet on the property that is set to mimic the existing conditions.

9. The latest calculations are not consistent with the latest plans so it is no known yet if the functions adequately. The State and Town Regulations are still not being met.

The calculations and plans are consistent, the project meets or exceed the state standards for stormwater mitigation.

10. The only catch basin detail provided is the catch basin Stormceptor. Are all the catch basins intended to be Stormceptors?

Yes. Comments from Cambridge Water Department identified in their letter dated November 1, 2016.

1. TSS removal calculation worksheet lists leaching catch basins and subsurface infiltration systems for the treatment BMPs. However, the plans and report text indicate that the treatment train consists of deep sump hooded catch basins, water quality inserts, and subsurface infiltration systems. The calculation sheet should be updated to reflect the actual treatment onsite.

The revised TSS calculation sheet and the Stormceptor worksheets are included in the drainage report.

2. TSS removal calculation sheet is missing for the catchment P-3, the area downstream of the infiltration basins.

All of the stormwater generated from the property is captured in the underground retention basin via catch basins fitted with Stormceptor inlets. The revised TSS calculation sheet and the Stormceptor worksheets are included in the drainage report.

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3. Text describing catchment P-3 references a detention basin east of Building A. This detention basin was not shown on the plans provided.

This basin has been removed from the design.

4. The Utilities plan references a septic system design plan titled “Subsurface Sewage Disposal System – New Construction, 269 North Ave., Weston, MA.” CWD does not have a copy of this plan which is needed to verify distance to groundwater from the septic system.

The septic system design has been provided under separate cover.

5. Stormwater Management Standard 6 is relevant to the site given the potential for reconnecting the 18” drainage pipe and the outfall from North Ave into Stony Brook. The text in section 3.0 of the Post-Construction Stormwater Management Report should be updated accordingly. Given that the site discharges to an Outstanding Resource Water, CWD requests that the long term management plan for the site comply with Stormwater Management Standard 6 and prohibit the use of sodium- based deicers. Sand, calcium chloride, or a sand/calcium chloride mix are examples of preferred deicing compounds. Regardless of the deicer used, the amount of material applied should be minimized to protect water quality.

The system is designed to remove greater than 98% TSS through proprietary catch basin inlets and infiltration basins. Furthermore, all stormwater is discharged to an infiltration system. The project could be conditioned to not use sodium based deicers.

6. Section 3.0 of the above mentioned report (Stormwater Standard 9) says that an Operations and Maintenance Plan (O & M) was included with the report. However, CWD did not receive a copy of the plan to review.

The Operation and Management Plan is included with this submittal.

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