HomeMy WebLinkAbout2000-02-24 Response Comments i
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r MH1= Design~ Consultants, Inc. 12_g Manor Parkway• Salem. h�3i 43�73 � l'EL (603) 893-0720- FAX (603}893-0739
January S, 2000
Rjohelle Martin
Forth Andover Conservation Commission
7 Charles St_
f orth Ajrdover, MA 0 t 845
Re: DRAINAGE & SITE PLAID: 4 Y"LL[1WSTRLLT
Dear Ms. Martin,
In response to the review letter by Cc & Colationio dated December 23, 1999 we of`cr
the following information and revisions (labeled sari-espondingly to letter):
Wetlands Bylaw
1_ 1 hcr(,as the lot preexisted the Riverfi-onl Protection Act, It is our understanding
that the project sloes riot have,to imet the Perfornrarice Staudards for Riverfront
Areas.
Beeause of site constraints, we are requesting pprmission to grade a small area
along the perimeter of the parking into the No-Disturbance Zone_ A rcqucst for a
waiver has been submitted to-the NAC C. (see attached)
tormwat r Management Standa.rd.s
3_ The roof material is specified on the rchitect€ ia3 Plans (asphalt shingle).
4, It would be unpractical to design thc infiltration System for the I00-year storm-
Therefore, we have provided an overflow-pipe, which would route stormwater h,
ceps of[lie recharge capacity of the Infiltrator toward the catch.basin. M
sugaeAed, we have recalculated the drainage system to account for the, runoff
from the roof going into our proposed system-
5- Du ly noted. The Storm water lVManagement calculations lave been modified as
requested_
TS5 removal rates have been rccalc€ulated such that wc are no longer applying a
10% credit Cor s e(i)ing, and the pours is redesigned as a Detention Basins with
Forebay -with associated TSS reAnoval rates calculated-
7- As stated above, the pond is no larger a "Wct Pond" and is not calculated to store
alay water below the invert. Water quality volumixc are includcd in revised
torm ater'Managemert 1{orrn calculations_
8-1 1- Duly noted,
12, The Wetland Resource Area setbacks are shown on the Ex i sti ng Conditions Plan.
13,14, Addressed below.
MUM
1
MHF Deeign Cansultants, Inc.
15. DOy noted-
Add itioijal D3i-aina .-Co- r ments
Paragraph 1:
Thp, flood elevation rcfined to is indicated oil the Plain it, note 4 sheet 3, and
graphically depicted on sheets -6.
back.watel' flooding the sight dc-ainage system; it is the &signet's
4 c ►rditsg possibly
opinion that whereas the peak now rate to the proposed detention bmi11 recurs alMOSt
two Hours earlier than the peak 11aw to the existing ditcltichannel outlet tx�tytroI Str Ciriic
there would be a positive flow through the system Piping toward the chanrYel outlet -
which would prevent backwater to inttude into out' system. A-nd the frioposed detention
arcs is ci-eafing more storage volume for flooding than existed prior to developtnent-
Consi�giwntly there would lac a reductiorn in overall flooding impacts Qoynpaccd to
predevelopment. Therel'orc, a€though tire, pi-ecise elevation! may be higher than the 236-74
indicated in prev]aus ood studies, the extent oCflooding would be similar i11 pre& post
development uonditiomi,
Paragraph 2:
Tn paragraph I it was requested that we show a flood plain elevatiopl of 236.74, We Have
Qamplied with this. As reco€lZrC3endcd, we (rave raised the bottom of the Detention Bamn
and the top of the berm. we are not propomng fit ling in the,Flood Plain;therefare IYo
Compensatory storage 1s required, And as indicated above, a at'e providing additio�mal
%forage compared to picdcvelopment, which should improve flooding con sitt ions
-
-Paragraph 3:
e have revised our calculatiolrs with the reQotnineiided curve numbers.
As rogi}ested,
Paragraph 4:
The calculations have been revised to include the channel known as Mosquito i3rool<-
Paragraph 5:
tilt calculations have been expanded to inchide all pertinent input/output
r s recluesteci,
data.
Paragraph
As requested, the ocotlet. invert has been raised to 34.5, And as discusser) ire item�7
above, the pond is fro Ianger ca "Wet Potld-"
Paragraph 7:
s suggested, no storage below .34-5 is included in the !'cvisecl C#ilc laftolms-
T'aragr ph 8: MHF Design Consultants, Inc.
As suggested, the berm leas bean raised, Providivrg 1.7 feet of fteeboaid dwing the 100-
year storm event.
Paragraph 9:
The top of the berm aTound the pond has been revised to the rNuested S' width and
should provide suffi6ent access to the detection facility from the parking area.
Paragraph 10.
Pis previously discumed, the pond is not to be a "Wet Pond-" Therefore, the poild Should
be seeded with "?dew England �.rosion t;ontrof lestoraEion �1ii -��
Additional Oqq T p ts-
Whereas it was suggested in Item #6 ahove that sweeping should not be crediLed to the
T S 8 removal system, e aro no propwing any sweeping lit the Operation and
Main ((ranee Fran.
sediment removal from the Ford & forebay was included in the Operallon and
Maintenance flan.
} 'rhe rcde,6gned pond would now drain to the bottom.
7
The grading at the foundation leas been t-aisecl - to decrease the amount oC exposed
foundation This design has been discussed with the Building Inspector and verbally
approved.
We hope the Inc laded plans and report address all of the reviewer's comments Please
review theIit at.your W11VCnicj1ce. We wouId be pleased to answcr any questions at the
r. coritrtnuat.ion of the public hearing.
Thank you Cor your attention.
Sincemly,
NfFTF Design Consul#ants, Inc.
Aadrew zava-Kovats, Dte6gnei'
eiic.
Cc: Dutton & Garfield, John Chessia- Coler& Col anton.io