HomeMy WebLinkAbout01/15/2018 - Hancock Associates Peer Review Response Comments - - 1210 Osgood Street H,,A"N"COCK,.
SS I T S
January 5, 2018.
North Andover Nanning Board
120 Main Street
North Andover, MA 01845
John Simons,, Chair
S u bj e . Proposed Mixed Use Development pme for
Princeton Development LLC and Forgetta Development LLC
Update to,Peer Rew*ewResponse Comments(era email),
Dear Mr., Chairman and Members he Board:
Hancock Associates,, acting on behalf of Princeton Properties and Forgetta Development respectfully
submit the oll ingl; response,to letter from Eggleston it men l dated 1-12-18.
E,g lest n Commients
Comment The treatment train currently proposed provides,a more effective and more easily
maintained means:oftreatling the runoff before it eaters the Ralristore3 infiltration ham rs-, hence the
revised design, adequately addresses my concern regarding the ongoing maintenance of the Riainstore3
systems. Based on the data, presented in the Storm water ater Report, the Isolator Rows have been
adequately sized to treat the water quality volume minimum),will be directed to the Isolator Rows
without pu ass ng. 'Ire particular,, I note that Systems .2, 3 n .2 have smaller differential In inverts
between thile inlet to the isolator Rotes and the overflow lime to her Ralnstiore3 structures than the offer
infiltration systems.
RESPONSE: any of the Isolator,Rows have larger inner differentials than necessary.Stormtech
recommends that the overflow be located' between the top ofthe chamber and its midpoint.
Therefore Isolator Rows using the SC310 chambers should have a minis aum differential of 0.,66,feet
and the SC1740 cham eirs should have a minimum differential of,11.25 "feet.The systems have been
adjusted to conformthis guideline.Some of the systems were designed to have a 2 foot,differential
through the inlet manhole configuration.
Comment in addition of infiltration Systems 2.4 and 2.5 provide somewhat better distribution f
the proposed gr n w a r recharge, however there is still relatively little recharge in the up gradient
arcs relative to exis in cond11
itions.This has the potential to reduce the a it a ili of the
groundwater flow to, the wetlands ands during periods of extended drought.The, lower grades e urr n l
proposed' preclude subsurface infiltration in the furthest up gradientarea of the site nt to:
Osgood Street, however their theire are several l r areas where i believe sufficient fill is being proposed to
allows for additional subsurface recharge. l discussed this with,, e Pezriola in a telephone,conversation
ye "er , and we agreed that are additional infiltration system could be added in the area between
rw arnaer i al Building 3 and resi ' n i al' Building C to, recharge roafrunoff from �n r both of these
aril in , and that the roof recharge from Building E (currently discharged to System! .3) could be
movecIto a separate infiltration system to the north of System 1.3. With the addition of these two
systems discussed I believe the drainage design would l r vid better distribution of the groundwater
r h r e provided and wouldmieetthe criterion for replicating the existing hydrology to the rn a irn m
extent practicable,.
Page 1 1
Municipal Review Response HANCOCK
Princeton, r —Mixed Use Development A,SSOC71ATES
RESPONSE: Systems,2.6 aind 2.7 ha been:added to accept roof runoff from Building 3 and
Building C. Minor reductions havebeen made own r dien systems., Attempts were, acle ,
routs the east sides ofBuildings and C to Systems 2.4 and2.6 but grades along the east id
these building r l d .These slides of the pitchedroofs will be routed around the buildings to the
Systems,on the west s1 de as shown. 'There is suff i1clent elevation from they back the buildings
�route,given the current cles,jigned roof dr in inver s.The, longest path from the center of the east side
to the rood drain is approximately 36 "feet. At 0.0,05 slope results. in less than a 2 foot drop.The
invert of the, � 'drain at Building B has been lowered to .4,to,insure sufficient drop.
Comment 3 In response to my previous Comment#7,, Hancock has added a schedule l Sheet
listing the number of RaInstore3 chambers per system, in terms,of the numbers columns and the
number of rows. AccordIng to the manufacturer's literature however,the RaInstore3 systern cores in
u p s 12 ' x 3.2 ' x " high, each unit having 36 columns.Since the number of columns listed on sheet
17 for most not all) the proposed infiltration systems i not entirely divisible by 36, 1 question
whether Hancock its suggesting tha" the prefabricated units supplied by the manufacturer would have to
cut.
RESPONSE: The terra "column" on the table on sheet ' re rs,to,one 3. '8'x 3.28'x "unit.,Thus
11 c luulmn would be the equivalent 5 square"feet. T , rm "row" refers to the height
system,so if 3 units were stacked on,,top of each other,there would be 3, r ws. a are not proposing
to cut any of the uruni s.
Comment Sheet 19 of the Site Plan shows the outlet from System _3 as,an 8-in pipe atinv. 148.3.
Based on both the model el and the size of the pipe downgradient the outlet should e inches.
RESPONSE,,., The,outlet has been a fed 6—inches.
Comment 5: An additional access manhole is needed e " the terminus ofthe Isolator Row on the west
side of Systems 1.213.
RESPONSE: Are access manhole has beenadded to,the,west side of system .
Comment 6 Inspection ports locations for both ties Isolator Rows and the Rainstore3 systerns,should
e shown on the, plains.
ES S The,pleas have been revised to show inspection ports on all the Isolator Rows,and
maintenance ports on gull!the Rainstore3 systems.
ru s.
H'anclock Associates believes Ms. g1e n's comments have been sufficiently addressed and would
respectfully request the Board act on the proposed modification,.,
Sincerely,
Hancock Also *, , s�.� ill,w- „H
Joseph Pezno,la, PE
Director of Engineering
CPrinceton Properties
Eggleston Environmental
Page 2