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HomeMy WebLinkAboutConsultant Review - 940 GREAT POND ROAD 9/10/2012 /1 s � � Enright, � From: Lisa Eggleston [l nlanhaioon] Sent: yWonday, . 2O121:41 PKU To: Tymon, Judy � Cc: Hughes, Jennifer; Jack Sullivan � Subject: 0 Great Pond Road � ]udy, Just letting you know that I've received and reviewed the 9/5/12 revised plans and calculations for 0 Great Pond Road, and it appears that all of my previous comments have been satisfactorily addressed. I do recommend that the � � confirmatory soil testing to verify soil suitability in the vicinity of the porous pavement driveway be included as a condition of approval, as should the ongoing maintenance requirements for the pervious pavement and the restrictions on landscaping chemicals. Please feel free to contact meif you have any questions orconcerns. Lisa D. Eggleston, P.E. Eggleston Environmental 32 Old Framingham Rd./ Unit #29 Sddbury, M/\ 01776 te1508.25q,1137 | | fax 866.820.7840 Please note the Massachusetts Secretary of State's office has determined that most emails to and from municipal offices and officials are public records.For more information please refer to: Please consider the environment before printing this email. 1 Eggleston Envirounental August 20, 2012 North Andover Planning Board 1600 Osgood Street North Andover, MA 01845 Attn: Judy Tymon, Town Planner RE: Watershed Special Permit Review 0 Great Pond Road Dear Ms. Tymon and Board Members: Per your request, I have conducted a technical review of the August 7, 2012 Watershed Special Permit Application packet for the above-referenced project, prepared by Sullivan Engineering Group, LLC on behalf of David and Corliss Paolino. The proposed project entails the construction of a single family home on a presently undeveloped lot, a portion of which is in the Non-Disturbance Zone of the Watershed District since it is within 100 it of a wetland resource area within the watershed. The lot was created prior to October 24, 1994. My comments on the application are outlined below: 1. The only soil data included with the application was the log fiom a single test pit excavated at the proposed roof drywell location, which indicated that the subsurface soil is a sandy loam. The design of the infiltration structures should therefore be based on the hydraulic conductivity characteristic of sandy loam, or abort 1.02 in/hr per the DEP Storrnwater Handbook and 1982 "Rawls" table. Percolation tests tend to underestimate the saturated hydraulic conductivity and should not be used to design stormwater systems. 2. Additional soil tests will be needed in the vicinity of the porous pavement driveway prior to installation to verify soil suitability in that location, and the area where the old stone foundation is to be removed will need to be filled with suitable subgrade material. 3. The stone surround for the drywell should be modeled as a 12'D x 4'H cylinder, not a 12' x 12' x 4' bed. 4. The proposed roof drywell is to be set partially in fill, and is less than 10 feet away from a 3.5 foot drop in grade at the retaining wall. The design plans should specify the nature of the fill material to be used, and a means to prevent breakout of infiltrated flow. 5. Filter fabric should be used on the top and sides only of the roof infiltration system. Placement of the fabric on the bottom of the excavation can lead to system failure. 32 Old Framingham Rd Unit, 29 Sudbury MA 01776 tel 508.159.1137 fax 866.820.7840 0 Great Pond Rd, Technical Revie\v 2 Amaist 20, 2012 6. The application indicates that the roof drainage from the front portion of the house will be directed to the stone reservoir beneath the porous pavement, and that is how the system is modeled. However there is no roof drain connection shown on the plans and it is not clear how this roof drainage would be distributed within the driveway subbase. 7. The limit of work, including vegetation clearing, should be shown on the site plan per the Special Permit requirements, and the proposed landscaping should be described. I recommend that the creation of new lawn area be limited to that which is absolutely necessary, and that any new landscape area be constructed in such a manner as to minimize the maintenance that is required, e.g. the soil should be well aerated, it should have a minimum of 6-inches of topsoil and, where possible, native vegetation should be planted to minimize the need for fertilizer and watering. As with similar projects permitted within the Watershed Protection District, both the limits of approved clearing and the restriction on lawn care products should be permanently recorded on the deed to the property. 8. The porous asphalt should specify polymer modified performance grade asphalt binder(PGAB). 9. The O&M Plan for the porous pavement should call for regular (e.g. annual vacuuming) in order to prevent clogging. It should also specifically prohibit sealcoating. 10. In order to preserve the infiltration capacity of the porous asphalt driveway and provide stormwater management during construction, I recommend that the sequencing plan developed by the UNH Stormwater Center be utilized. This would entail installing the driveway subbase with a two-inch overfill at the outset of construction, then removing the overfill (and the sediment and fines trapped within it) once the site is stabilized. The subbase should then be inspected for compaction and infiltrative capacity and, if necessary, scarified to the depth required prior to placement of the porous asphalt layer. I appreciate the opportunity to assist the North Andover Planning Board with the review of this project, and hope that this information is suitable for your needs. Please feel free to contact me if you or the applicants have any questions regarding the issues addressed herein. Sincerely, EGGLESTON ENVIRONMENTAL Lisa D. Eggleston, P.E. Sullivan Engineering Group, LLC Civi/Engineers&Land Development Consultants September 5, 2012 Town of North Andover Planning Board c/o Judith Tymon-Town Planner 1600 Osgood Street North Andover, MA 01845 Re: Watershed Special Permit Application 0 Great Pond Road, North Andover Tax Map 103 Parcel 128 Ms. Tymon; Based on the Planning Board comments, Conservation Commission comments, and Eggleston Environmental (review consultant)comments the following plan changes have been made; 1) The proposed drywell to handle the rear roof runoff has been resized to a 1,000 gallon concrete drywell with 54 inches of stone surrounding. The need to resize the system was based on the drywell being modeled with a 1.02 in/hr hydraulic conductivity instead of the field percolation rate. The drywell sizing has capacity to store and infiltrate the 100 year storm event(HydroCAD calculations attached). 2) A note has been added to Sheet 1 of the design plan requiring the design engineer to conduct a deep observation soil test in the proposed driveway location prior to installation of the crushed stone subbase. Additionally, a note has been added for clean sand to be placed in the area of the old foundation following demolition/removal. 3) The stone surround for the drywell has been modeled as a cylinder. 4) On Sheet 2 a note has been added to the drywell construction detail that septic sand shall be provided as fill in the drywell area and 5 feet surrounding. Additionally, a 40 mil HPDE barrier is proposed between the drywell and proposed retaining wall to prevent breakout. 5) The proposed filter fabric for the drywell construction has been revised to be placed on the sidewalls and top of the system only. 6) A roof drain connection detail has been provided on Sheet 2. 7) The limit of work and limit of vegetation clearing have been labeled on the plan. Both limits are consistent with the proposed erosion control barrier for the site. 8) A note has been added to the cross-section of the Porous Pavement construction on Sheet 2 calling out that the porous asphalt shall be Polymer Modified Performance Grade Asphalt Binder. 9) The Operation and Maintenance requirements for the Porous Pavement on Sheet 2 now reflect annual vacuuming and prohibiting sealcoating. 10)A note has been added on Sheet 1 (see Note 8) for 6 inches of loam to be spread in all grassed areas. 11)The majority of the limit of work line has been moved away from the wetlands to leave a natural wooded buffer to the wetland resource areas. The Conservation Commission expressed concerns with invasive species growth in some of the wooded area to remain. The applicant is willing to work with the Commission to remove invasives beyond the limit of work as needed. 22 Mount Vernon Road ... Boxford,Massachusetts 01921 — (978)352-7871-Phone — 978352-7871 -Fax 12)The Planning Board asked for a composite plan of the 4 parcels of land under the Paolino's ownership. This detail has been added on Sheet 2. 13)Setbacks have been added from the proposed house to the wetland line. Please note that that the hardscape features on the plan(walkways, driveway, retaining wall) represent the full extent of hardscape landscaping for the site. The majority of the site will be loamed/seeded (proposed grassed areas have been labeled) and there may be some mulch beds in the front of the house with typical landscape plantings. If you should have any questions or require additional information please feel free to contact me. Very Truly Yours, Jack Sullivan, P.E. Cc: Conservation Commission David + Corliss Paolino, Owners 22 Mount Vernon Road — Boxford,Massachusetts 01921 — (978)352-7871-Phone — 978 352-7871 -Fax C3 Rear Ro f Areas A 1 , 000 Gallon Drywell w/ 5411 stone surrroundin g Subcat Reach on Link Drainage Diagram for 940 Great Pond Road,NA Prepared by Sullivan Engineering Group,LLC 9/5/2012 HydroCAD®7.00 s/n 001433 ©1986-2003 Applied Microcomputer Systems 940 Great Pond Road, NA Type Ill 24-hr 2 Year Storm Rainfall=3.10" Prepared by Sullivan Engineering Group, LLC Page 2 HydroCADO 7.00 s/n 001433 ©1986-2003 Applied Microcomputer Systems 9/5/2012 Time span=5.00-20.00 hrs, dt=0.05 hrs, 301 points Runoff by SCS TR-20 method, UH=SCS Reach routing by Stor-Ind+Trans method - Pond routing by Stor-Ind method Subcatchment 3S: Rear Roof Areas Runoff Area=1,442 sf Runoff Depth=2.68" Tc=6.0 min CN=98 Runoff=0.10 cfs 0.007 of Pond 2P: 1,000 Gallon Drywell w/54"stone surPeak Elev=90.68' Storage=200 cf Inflow=0.10 cfs 0.007 of Outflow=0.00 cfs 0.003 of Total Runoff Area = 0.033 ac Runoff Volume = 0.007 of Average Runoff Depth = 2.68" 940 Great Pond Road, NA Type ///24-hr 2 Year Storm Rainfall=3.10" Prepared by Sullivan Engineering Group, LLC Page 3 HydroCADO 7.00 s/n 001433 ©1986-2003 Applied Microcomputer Systems 9/5/2012 Subcatchment 3S: Rear Roof Areas Runoff = 0.10 cfs @ 12.09 hrs, Volume= 0.007 af, Depth= 2.68" Runoff by SCS TR-20 method, UH=SCS, Time Span= 5.00-20.00 hrs, dt= 0.05 hrs Type III 24-hr 2 Year Storm Rainfall=3.10" Area (sf) CN Description 1,442 98 Portion of Bldg Roof+ Rear Porch Roof Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 6.0 Direct Entry, Subcatchment 3S: Rear Roof Areas Hydrograph 0.105" O Runoff 0.10 cfs 0.095 Type III 24-hr-2 Year Storm 0.09_ -- Rainfall-3.1.0" 0.085- 0.08 -Runoff Area=1;442 sf 0.075- - - 0.07 Runoff Volume=0.007 of 0.065 0.06 Runoff Depth=2.68" v 0.055- Tc=6.0-min 0 0.05 , LL 0.045 - CIV=98 0.04- 0.035_ 0.03-- 0.025 0.02-:. 0.015 0.01- 0.005' 0. 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Time (hours) 940 Great Pond Road, NA Type Ill 24-hr 2 Year Storm Rainfall=3.10" Prepared by Sullivan Engineering Group, LLC Page 4 HydroCAD®7 00 s/n 001433 ©1986-2003 Applied Microcomputer Systems 9/5/2012 Pond 2P: 1,000 Gallon Drywell w/ 54" stone surrrounding Inflow Area= 0.033 ac, Inflow Depth = 2.68" for 2 Year Storm event Inflow = 0.10 cfs @ 12.09 hrs, Volume= 0.007 of Outflow = 0.00 cfs @ 9.15 hrs, Volume= 0.003 af, Atten= 97%, Lag= 0.0 min Discarded = 0.00 cfs @ 9.15 hrs, Volume= 0.003 of Routing by Stor-Ind method, Time Span= 5.00-20.00 hrs, dt= 0.05 hrs Peak Elev= 90.68' @ 15.87 hrs Surf.Area= 177 sf Storage= 200 cf Plug-Flow detention time= 174.8 min calculated for 0.003 of(43%of inflow) Center-of-Mass det. time= 67.9 min (806.8 -738.9 ) _ # Invert Avail Storage Storage Description 1 88.20' 427 cf 15.00'D x 7.00'H Vertical Cone/Cylinder 1,237 cf Overall - 170 cf Embedded = 1,067 cf x 40.0%Voids _ 2 89.20' 170 cf 6.00'D x 6.00'H Vertical Cone/Cylinder Inside#1 597 cf Total Available Storage # Routing Invert Outlet Devices 1 Discarded 0.00' 0.001000 fpm Exfiltration over entire Surface area Qiscarded OutFlow Max=0.00 cfs @ 9.15 hrs HW=88.27' (Free Discharge) 1=Exfiltration (Exfiltration Controls 0.00 cfs) Pond 2P: 1,000 Gallon Drywell w/ 54" stone surrrounding Hydrograph - 0 Inflow - 0.1 cfs O Discarded - 0 0.105. 0.1 - Inflow Area=0.033 ac 0.095 - - 0.09. Peak Elev=90.68' 0.085-: 0.08- Storage=200 cf 0.075 - - _ - 0.07= 0.065- 0.06= 0.055= - 0 0.05 - gr 0.045. 0.04 0.035. 0.03' 0.025-_ < 0.02 0.015 y 0.01: 0.00 cfs " 0.005- r 0- 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Time (hours) 940 Great Pond Road, NA Type 111 24-hr 10 Year Storm Rainfall=4.50" Prepared by Sullivan Engineering Group, LLC Page 5 H droCADO 7.00 s/n 001433 ©1986-2003 Applied Microcomputer Systems 9/5/2012 Time span=5.00-20.00 hrs, dt=0.05 hrs, 301 points Runoff by SCS TR-20 method, UH=SCS Reach routing by Stor-Ind+Trans method - Pond routing by Stor-Ind method Subcatchment 3S: Rear Roof Areas Runoff Area=1,442 sf Runoff Depth=3.96" Tc=6.0 min CN=98 Runoff=0.14 cfs 0.011 of Pond 2P: 1,000 Gallon Drywell w/54"stone surPeak Elev=92.20' Storage=334 cfIn Ofl w=0.00 cfs 0.003 of Total Runoff Area=0.033 ac Runoff Volume = 0.011 of Average Runoff Depth = 3.96" 940 Great Pond Road, NA Type 111 24-hr 10 Year Storm Rainfall=4.50" Page 6 Prepared by Sullivan Engineering Group, LLC 9/5/2012 Hydro AM 7.00 s/n 001433 ©1986-2003 Applied Microco mputer Systems Subcatchment 3S: Rear Roof Areas Runoff = 0.14 cfs @ 12.09 hrs, Volume= 0.011 af, Depth= 3.96" Runoff by SCS TR-20 method, UH=SCS, Time Span= 5.00-20.00 hrs, dt= 0.05 hrs Type III 24-hr 10 Year Storm Rainfall=4.50" Area (sD CN Descri tion 1,442 98 Portion of Bldg Roof+ Rear Porch Roof Tc Length Slope Velocity Capacity Description min feet ft/ft ft/sec cfs Direct Entry, 6.0 Subcatchment 3S: Rear Roof Areas Hydrograph FO Runoff 0.15 0.14 cfs Type III 24-hr 10 Year Storm 0.14. 0.13= Rainfal1=4.50" 0.12- Runoff Area=1,442 sf 0.11 Runoff Volume=0.011 of 01= Runoff Depth=3.96" 0.09 _ Tc=6.0 min 3 o.os: CN=98 ll. 0.07- 0.06_ 0.05- „ 0.04= _ 0.03 0.02= 0.01- 0 , 5 6 7 „6 9 10 11 12 (hours)3 14 15 16 17 T 18 19 20 940 Great Pond Road, NA Type 11124-hr 10 Year Storm Rainfall=4.50" Prepared by Sullivan Engineering Group, LLC Page 7 HydroCAM 7.00 s/n 001433 ©1986-2003 Applied Microcomputer Systems 9/5/2012 Pond 2P: 1,000 Gallon Drywell w/ 54" stone surrrounding Inflow Area = 0.033 ac, Inflow Depth = 3.96" for 10 Year Storm event Inflow = 0.14 cfs @ 12.09 hrs, Volume= 0.011 of Outflow = 0.00 cfs @ 7.80 hrs, Volume= 0.003 af, Atten= 98%, Lag= 0.0 min Discarded = 0.00 cfs @ 7.80 hrs, Volume= 0.003 of Routing by Stor-Ind method, Time Span= 5.00-20.00 hrs, dt= 0.05 hrs Peak Elev= 92.20' @ 17.36 hrs Surf.Area= 177 sf Storage= 334 cf Plug-Flow detention time= 188.2 min calculated for 0.003 of(31% of inflow) Center-of-Mass det. time= 44.9 min ( 780.6 -735.8 ) # Invert Avail.Storage Storage Description 1 88.20' 427 cf 15.00'D x 7.00'H Vertical Cone/Cylinder 1,237 cf Overall - 170 cf Embedded = 1,067 cf x 40.0%Voids 2 89.20' 170 cf 6.00'D x 6.00'H Vertical Cone/Cylinder Inside#1 597 cf Total Available Storage # Routing Invert Outlet Devices 1 Discarded 0.00' 0.001000 fpm Exfiltration over entire Surface area Qiscarded OutFlow Max=0.00 cfs @ 7.80 hrs HW=88.27' (Free Discharge) 1=Exfiltration (Exfiltration Controls 0.00 cfs) Pond 2P: 1,000 Gallon Drywell w/ 54" stone surrrounding Hydrograph - _ E Inflow 0.14 cfs IM Discarded 0.15-: - - Inflow Area=0.033 ac 0.14= 0.13= = Peak Elev=92.20' 0.12- � 0.11 Storage=334 cf 0.1= F 0.09= 3 0.08 LL 0.07- ; 0.06= 0.05- , 0.04- 0.03- 0.02- y f 0.01= 0 00 cfs Wo 0 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Time (hours) 940 Great Pond Road, NA Type 11124-hr 25 Year Storm Rainfall=5.50" Prepared by Sullivan Engineering Group, LLC Page 8 HydroCADO 7.00 s/n 001433 ©1986-2003 Applied Microcomputer Systems 9/5/2012 Time span=5.00-20.00 hrs, dt=0.05 hrs, 301 points Runoff by SCS TR-20 method, UH=SCS Reach routing by Stor-Ind+Trans method - Pond routing by Stor-Ind method Subcatchment 3S: Rear Roof Areas Runoff Area=1,442 sf Runoff Depth=4.87" Tc=6.0 min CN=98 Runoff=0.17 cfs 0.013 of Pond 2P: 1,000 Gallon Drywell w/54"stone surPeak Elev=93.36' Storage=435 cf Inflow=0.17 cfs 0.013 of Outflow=0.00 cfs 0.003 of Total Runoff Area= 0.033 ac Runoff Volume = 0.013 of Average Runoff Depth =4.87" 940 Great Pond Road, NA Type ///24-hr 25 Year Storm Rainfall=5.50" Prepared by Sullivan Engineering Group, LLC Page 9 HydroCAD®7.00 s/n 001433 ©1986-2003 Applied Microcomputer Systems 9/5/2012 Subcatchment 3S: Rear Roof Areas Runoff = 0.17 cfs @ 12.09 hrs, Volume= 0.013 af, Depth= 4.87" Runoff by SCS TR-20 method, UH=SCS, Time Span= 5.00-20.00 hrs, dt= 0.05 hrs Type III 24-hr 25 Year Storm Rainfall=5.50" Area(sf) CN Description 1,442 98 Portion of Bldg Roof+ Rear Porch Roof Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 6.0 Direct Entry, Subcatchment 3S: Rear Roof Areas Hydrograph 0.19: 0.18' 7 cfs 0.17 - Type III 24-hr 25 Year Storm 0.16 Rainfall=5.50" 0.15- 0.14 Runoff Area=1,44-2-sf 0.13_ - s Runoff Volume=0.013 af- 0.12 -- -- — - - 0.11 Runoff Depth=4.87" 0.1. Tc=6.0 min `0 0.09 0.08- CN=98 0.07 0.06- - 0.05 0.04 0.03- - 0.02- 0.01 0' 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Time (hours) 940 Great Pond Road, NA Type 111 24-hr 25 Year Storm Rainfall=5.50" Prepared by Sullivan Engineering Group, LLC Page 10 HydroCADO 7.00 s/n 001433 ©1986-2003 Applied Microcomputer Systems 9/5/2012 Pond 2P: 1,000 Gallon Drywell w/ 54" stone surrrounding Inflow Area = 0.033 ac, Inflow Depth = 4.87" for 25 Year Storm event Inflow = 0.17 cfs @ 12.09 hrs, Volume= 0.013 of Outflow = 0.00 cfs @ 7.00 hrs, Volume= 0.003 af, Atten= 98%, Lag= 0.0 min Discarded = 0.00 cfs @ 7.00 hrs, Volume= 0.003 of Routing by Stor-Ind method, Time Span= 5.00-20.00 hrs, dt= 0.05 hrs Peak Elev= 93.36' @ 18.10 hrs Surf.Area= 177 sf Storage=435 cf Plug-Flow detention time= 202.9 min calculated for 0.003 of(26% of inflow) Center-of-Mass det. time= 35.5 min ( 770.1 -734.6 ) # Invert Avail.Storage Storage Description 1 88.20' 427 cf 15.00'D x 7.00'H Vertical Cone/Cylinder 1,237 cf Overall - 170 cf Embedded = 1,067 cf x 40.0%Voids 2 89.20' 170 cf 6.00'D x 6.00'H Vertical Cone/Cylinder Inside#1 597 cf Total Available Storage # Routing Invert Outlet Devices 1 Discarded 0.00' 0.001000 fpm Exfiltration over entire Surface area Discarded OutFlow Max=0.00 cfs @ 7.00 hrs HW=88.27' (Free Discharge) t1=Exfiltration (Exfiltration Controls 0.00 cfs) Pond 2P: 1,000 Gallon Drywell w/ 54" stone surrrounding Hydrograph I Inflow 0.19 0.17 CfS EEl Discarded 0.18= Inflow Area=0.033 ac 0.17' 0.16: Peak Elev=93.36' 0.15: 0.14= r Storage=435 cf 0.13-- 0.12- 0.11- 0.1_ y 0 0.09- 0.08- - 0.07- e; 0.06= 0.05-- , 0.04 0.03 0.02_ 0.01: 0.00 cfs MW/10 W11.1 0= 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Time (hours) 940 Great Pond Road, NA Type 111 24-hr 100 Year Storm Rainfall=6.40" Prepared by Sullivan Engineering Group, LLC Page 11 HydroCADO 7.00 s/n 001433 ©1986-2003 Applied Microcomputer Systems 9/5/2012 Time span=5.00-20.00 hrs, dt=0.05 hrs, 301 points Runoff by SCS TR-20 method, UH=SCS Reach routing by Stor-Ind+Trans method - Pond routing by Stor-Ind method Subcatchment 3S: Rear Roof Areas Runoff Area=1,442 sf Runoff Depth=5.69" Tc=6.0 min CN=98 Runoff=0.20 cfs 0.016 of Pond 2P: 1,000 Gallon Drywell w/54"stone surPeak Elev=94.44' Storage=530 cf Inflow=0.20 cfs 0.016 of Outfl0w=0.00 cfs 0.004 of Total Runoff Area= 0.033 ac Runoff Volume = 0.016 of Average Runoff Depth = 5.69" 940 Great Pond Road, NA Type 111 24-hr 100 Year Storm Rainfall=6.40" Prepared by Sullivan Engineering Group, LLC Page 12 HydroCADO 7.00 s/n 001433 ©1986-2003 Applied Microcomputer Systems 9/5/2012 Subcatchment 3S: Rear Roof Areas Runoff = 0.20 cfs @ 12.09 hrs, Volume= 0.016 af, Depth= 5.69" Runoff by SCS TR-20 method, UH=SCS, Time Span= 5.00-20.00 hrs, dt= 0.05 hrs Type III 24-hr 100 Year Storm Rainfall=6.40" Area (sf) CN Description 1,442 98 Portion of Bldg Roof+ Rear Porch Roof Tc Length Slope Velocity Capacity Description min) (feet) (ft/ft) (ft/sec) (cfs) 6.0 Direct Entry, Subcatchment 3S: Rear Roof Areas Hydrograph 0.22- ❑Runoff 0.21_ 0.20 cfs 0.2'- r I Type III 24-hr 100 Year Storm 0.19- 0.18- 0.17: 0.16= Runoff Area=1,442 sf 0.15 _ Runoff Volume=0.016 of 0.14- a ; Z,, 0.13- - _ Runoff Depth=5.69 - Tc=6.0 min .S 0.12- 3 0.11= 0 0.1_ CN=98 0.09_ 0.08- 0.07- 0.0s 0.0s _ - 0.04- 0.03- 0.02= 0.01 0" 5 6 7 8 9 10 11 12 13 14 15 16 17 18 ' '1,9. . . . 20 Time (hours) 940 Great Pond Road, NA Type 111 24-hr 100 Year Storm Rainfall=6.40" Prepared by Sullivan Engineering Group, LLC HydroCAD®7.00 s/n 001433 ©1986-2003 Applied Microcomputer Systems Page 13 9/5/2012 Pond 2P: 1,000 Gallon Drywell w/54" stone surrrounding Inflow Area = 0.033 ac, Inflow Depth = 5.69" for 100 Year Storm event Inflow = 0.20 cfs @ 12.09 hrs, Volume= 0.016 of Outflow = 0.00 cfs @ 6.45 hrs, Volume= 0.004 af, Atten= 99%, Lag= 0.0 min Discarded = 0.00 cfs @ 6.45 hrs, Volume= 0.004 of Routing by Stor-Ind method, Time Span= 5.00-20.00 hrs, dt= 0.05 hrs Peak Elev= 94.44' @ 19.56 hrs Surf.Area= 177 sf Storage= 530 cf Plug-Flow detention time= 217.2 min calculated for 0.004 of(22% of inflow) Center-of-Mass det. time= 30.3 min ( 764.2 - 733.9 ) # Invert Avail.Stora e Storage Description 1 88.20' 427 cf 15.00'D x 7.00'H Vertical Cone/Cylinder 1,237 cf Overall - 170 cf Embedded = 1,067 cf x 40.0% Voids 2 89.20' 170 cf 6.00'D x 6.00'H Vertical Cone/Cylinder Inside#1 597 cf Total Available Storage # Routing Invert Outlet Devices 1 Discarded 0.00' 0.001000 fpm Exfiltration over entire Surface area Discarded OutFlow Max=0.00 cfs @ 6.45 hrs HW=88.27' (Free Discharge) Z 1=Exfiltration (Exfiltration Controls 0.00 cfs) Pond 2P: 1,000 Gallon Drywell w/54" stone surrrounding Hydrograph 0.22- 0.20 ®inflow 0.21 M Discarded 0.2- , Inflow Area=0.033 ac 0.19 0.18: , 0.17_ Peak Elev=94._44' 0.16' 0.15- storage-530 cf , 0.14= - w 0.13 0.12= c 0.11 L 0.1: 0.09- 0.08 0.07 0.06- 0.05. 0.04= 0.03. , 0.02- 0.00 0.01- cfs 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Time (hours)