The URL can be used to link to this page

Home My WebLink AboutCorrespondence - 158 COACHMANS LANE 7/2/2003 CEV D j l i_ 23 2005 NORTH ANDOVER PLANNING DEPARTMENT GROUNDWATER RECHARGE CALCULATIONS A.F. WATSON GENERAL CONTRACTING 3 EDGEMONT STREET DERRY, NEW HAMPSHIRE 03038 OBERT C , P.E. MERRIMACK ENGINEERING SERVICES, Inc. 66 Park Street Andover, Massachusetts 01810 planners 40 engineers • surveyors TABLE OF CONTENTS ACCOMPANYING APPLICATION FOR WATERSHED SPECIAL PERMIT • U.S.G.S. TOPO MAP • SOILS MAP • NARRATIVE • CALCULATIONS FOR RETENTION BASIN DESIGN • SITE PLAN ILL Gra N. mon; C e m Q) 40 O �TF- It kW, 4.) RESI- �j 0 "M We--- L (lRE-sue, ESS5EA COLIN I Y, MASSACr sL 1 16, NUK I HLKIV I'AN I — SHEE I NUIV113LH 30 C PcE PcE — - - StB C COB C In G PbD PaD I StC COD StB C oC CmC PaB PaD PaC I CrC� CO StC F WsB 0 aq R dA RIB Fp Go �tp GFO �0 m LeA WrB L A K E Wh cae PbB CmC /N(0g Wh \�� C O IC H I C H E W I C K StB PaB CDE 03 CaB \ CoC COC wp ; StC �eP Ws6 0 Sub ° UD CmC w COD SuC Wg StB B PbD WtC CoC � PbB oO StA w w ' G StC RIA R/e CSC Sub RIBS�e CoD StC SUB � PbC COD RIB SuC / sS p < Q StB UD G°G w ti Cm8 PaB 9 PaD �� Q I N� �C StB SUB Qf$ COB Pb , V *� CaC� CmB p� CmD StA G MG �G ) oQ SUB StB \ Ur Wh I TV StB CaC O SUB I H S f 1 G Cm StB °C) U � StC RIB. .. S T V 6 m WsD `r+�, v� � StB Sub � CoD -\ WSC CaD �° I o� Stevens t C< � PbD ... C OQ SUB �. CmC 3 Pond Pg MmC S'B GO G RIB Ca Co4 Wg \. 3� F G MC Cob RIB Se PbD 2 n? CrD % _�' -~ LeB UD:'U) MmD SuC C MC mC Q 01 D Wh r B StB Ur VOO C � O MD 1 m CoD LeB 7� A S ap Sfe C rD U RoD MD CoC �'OS 4 Wh �0 Le@ G Se ° MC CbC G SuB CrC G<G StB \. CoD C Gcc r A CaL. �. i \ �i0 .L� p CoD� \ LeB• t � CoD w G t'j � `)2- -�• MC CrC - CbC MC StC SUB Cm6 36) SrB ) vJ� CrD MC GaC o o er oW :' )Se COC Se y1- d eP cde Y RIB 60 SUB 3w :E SrB y MmD Cr!iB — Jre i MC CaC .V 6C C6O PcE W •� 0 / \Ir •. CbC � 3� StA E 6� JO Sfe...` HfC J StB St8 SUB CbC \ Std CbC / �y e E UD PaC Cm8 �c \jy S U CbD Se PcE \ 6 Q 3 MmB d9 GB MD WtC Goo co O COQ j Cob CbC PbD PbC CbC hh RIB PaD PaD / St AEG he ��6) HOW RM SUB Pb8 Ws8 WSC � \\ \\ Se Rd6 .'�StA Gg m s, RIA \ PbD PcE CoC Grog PaC WrC Q �•�/ U M COB PaC� rn 06 ( COC MC G 1Q f PbC MD CbC PaD ro R/g 0 GbC U SUB \ CrC Sub 3 \• Q UD' RIB RIB 1 Sub Pats WSB �r Cab CbD RIB d� SuB \ �� r WrA w) �c Cb' CbC wrn. / PcE r/ ROD U Sh6 �... w Rae Wh CbC r A / PaB Sub PbD \ IpbO Shy PbD SgC SUB \ 1 1 \ CoC MC I \\' PcE CbC ��h v 60 Wh CrD Mills RIB 0 Cb8 �� HfB � PaB Hill Sg6 � 60 - Sa —� 11///f \ �\ SrB \... Sr\ SrA ° S. �/ t RdA C` � '• \ �p d SUB w 9 s q M HfC d /. Q N O CbB CbC �q PQi)>.ucli'. P D ShC RIB y hg \ SrA Se S<P �! HfA Y PbC Sh6 _ Pe SrB HfB NARRATIVE The project site is located at#158 Coachmans Lane in North Andover. This location is within the General Zone of the established Watershed Protection District as delineated on the North Andover Zoning Map. The subject property is serviced by Town water and sewerage systems. Gas service is also provided. The house is situated at a lower elevation than the roadway. The proposed addition is a one-story family room with a basement for storage below and a screened-in porch attached to the family room. .Also, in front of the house, a proposed new enlarged entry is proposed. Refer to the Architectural Drawings for plans, elevations and additional information. There are no proposed changes to the existing roof dainage system of gutters and downspouts. However, should it be convenient or feasible to interconnect the existing roof drainage to the proposed roof drainage system, it is suggestive to make this transition at that time. The proposed roof drainage system will collect runoff from the roof area of the new addition. The new entry will not have gutters. A small retention or infiltration basin is proposed to provide the desired groundwater recharge volume of stormwater runoff which will be generated from the new impervious roof surface areas. This basin will also intercept surface runoff from the land surfaces between the roadway and the proposed drainage swale and basin. The detained volume of collected runoff will fill the basin to its maximum capacity on a periodic basis,based on rainfall intensity and ground conditions at any given time of year. The basin will have an overflow berm which will discharge any excess runoff volume toward the wetland. The overflow will be a rip-rap swale to prevent any long term erosion potential. The actual depth of detained water in the basin will be a maximum of 0.7' or 8.4" for a short duration after the storm runoff has ended. There will be no standing or detained water within the proposed rip-rapped swale leading to the basin. CALCULATIONS FOR RETENTION BASIN DESIGN I. SOIL TYPES ON SUBJECT PROPERTY @#158 COACHMANS LANE Based on Natural Resource Conservation Service (N.R.C.S.) Soils Map, the property has MC-Medisaprists and Sub—Sutton series soil types. These soils are in the Hydrologic Soil Group `B" category. These soils are generally comprised of a fine sand loam textural classification. For Standard#3 —Recharge to Groundwater, the required minimum volume to be recharged is calculated, based on`B" Soils. V= 0.25"X Total Impervious Area The impervious area is based on the additions to the building and entry way. The net increase in impervious surface area has been determined from the Site Plan to be 680 square feet, approximately, as follows. New front porch roof and steps = 55 sq. ft. New family room addition = 396 sq. ft. New screened-in porch = 234 sq. ft. TOTAL ADDITIONAL IMPERVIOUS AREA = 685 sq. ft. IL REQUIRED RECHARGE VOLUME CALCULATIONS 0.25"x 685 sq. ft. = 14.3 cu. ft. III. The total recharge volume provided by the proposed retention basin is calculated Elev Area Volume (sq. ft) (cubic feet) Incremental - - Cumulative *165.6 -0- -0- -0- 166.0 23' x 4' =92' 18.4 18.4 **166.3 26' x5' = 130' 33.3 51.7 166.6 30' x7' =210 51 102.7 *Bottom of Retention Basin ** Invert Elevation at Overflow Rip Rap Weir IV. CONCLUSION With 51.7 cubic feet provided for within the small retention basin, which exceeds the Required Recharge Volume of 14.2 cubic feet,this design is in compliance with the intent of the North Andover Zoning By-Law associated with permitted uses and activities within the Watershed Protection District (per Section 4.136)