HomeMy WebLinkAbout2013-04-02 Planning Board Supplemental Materials (140)
March 25, 2013
North Andover Planning Board
1600 Osgood Street
North Andover, MA 01845
Attn: Judy Tymon, Town Planner
Re: 1018 Osgood Street
JFJ Holdings, LLC
Sub: Plan
Revisions based on
March 7, 2013 meeting
Dear Ms. Tymon and Board Members:
Please find enclosed revised plans and supporting documentation regarding the above referenced project located
at 1018 Osgood Street.
As you know, MHF Design Consultants met with yourself, Jennifer Hughes and Ms. Eggleston on March 7, 2013 to review the additional comments from Eggleston
Environmental relative to the above referenced project. The attached plans and revised Drainage Report incorporate revisions based on the design options discussed at that meeting.
Specifically we have revised the plans as follows:
1. The roof drainage has been redirected into infiltration system #2 and the pavement area in the lower parking lot has been redirected
to other systems; a portion going to infiltration system#1 and another portion going to the sand filer located at the front portion of the site. This has allowed us to raise the bottom
of infiltration system #2 to elevation 144.00 which provides for a greater separation from the estimated seasonal high water table. Two test pits in the area of infiltration system
#2 indicated a variation in the depth of the seasonal high water table from none observed at 120" (1112-4) at the west end of the site to 48" faint (1112-4) on the east end of the
site. It was also discussed that this seasonal high water table elevation at this location is potentially created as a result of runoff from the roof not being controlled and creating
this condition. It would be reasonable to assume that the average seasonal high water table would be approximately at a depth of 6 feet or at elevation 142+/-. This is substantiated
by other test pits in the immediate vicinity and shown on the revised plans (113-2 and 113-3). Using this estimated seasonal high water table elevation would provide a 2 foot separation
from the bottom of the proposed infiltration system #2.
2. A portion of the site's lower parking area has been intercepted thru the use of a trench drain that will capture the
pavement runoff and direct it to infiltration system #1. This runoff had gone to infiltration system # 2 in the previous design. Additionally, some runoff from the lower area will
also be captured and be directed into the proposed sand filter located at the front of the site.
3. Both infiltration systems have been enlarged to provide as much storage as possible
to reduce the volume of flow from the site.
4. Included in the report are exhibits which provide for documentation regarding the issue of additional volume from the site as a result of the development See Appendix D. Based
on these exhibits and our documentation and calculations, the additional volume from the site that will be directed to the wetland thru the Osgood Street drainage system is an additional
1,523 cf. Based on the ponded area of the wetland that is at the outlet of this drainage system being 80,000 sf , the additional volume represents an increase of this ponded wetland
area of only 0.019 feet or 0.22 inches . Additionally, we were conservative in the calculation of the area at the outlet and restricted it to just the observed ponded area, Based
on the aerial photo, the wetland area associated with the outlet of this drainage system is much larger, approximately 3 times the size that we calculated for the ponded area of the
existing outlet, which would suggest an even smaller increase.
Based on the revised plans and documents, we feel that we have addressed the comments in both the previous review
letters and the March 7, 2013 meeting.
Please contact our office if you have any comments or questions.
Sincerely,
MHF Design Consultants, Inc.
Mark Gross, P.E.
Principal
cc:
Lisa Eggleston, Eggleston Environmental
Jennifer Hughes, Conservation Commission Agent
Greg Nolan, JFJ Holdings, LLC