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Drainage Report#1A 24 NATIVE DRIVE–CONCEPT DRAINAGE REPORT-2/18/19 In response to the Town of Queensbury request for a Storm water management calculation for the impact of the Tenant required Site Plan Modifications for the existing 24 Native Drive Site , a drainage plan review assessment was prepared for the proposed less than an acre area of disturbance review. The Proposed Sheet Labels Inc. is a proposed isolated area fit up review of roughly 28,000 SF within the existing 115,892 SF PEMB shell at 24 Native Drive, situated on existing Site Plan of 14.28 Acre Site for proposed minor dock and parking driveway improvements . The post development (.4 ac) storm area of the proposed northeastern side Site Entrance and parking area currently drains via an existing CB network to the designated front SWM area of the existing site. The Pre-development runoff area of can be protected with Sediment Erosion Structure Inlet Controls of the existing CB’s, and silt fence at all adjacent affected contours, and propose no change in sheet flow as an area volume of review . Although the existing gravel driveway area is to be paved , by commercial standards, the same sheet flow overland flow is conducted via previously paved pad areas surrounding each catch basin. The proposed 19,098 SF area of disturbance currently drains to the existing CB /SWM network so no re-sizing of the SWM area, or impacts to the side entrance is anticipated. The proposal will have a negligible impact on the area , other than improving what is proposed to satisfy the demand of an otherwise vacant building , by the applicant and proposed Tenant. On the proposed area of exterior of workon the west side , to comply with the Tenant request for graded dock doors and drive –in truck area, the Site requires 23, 645 SF of disturbance review to re-align the existing gravel fire lane and also proposes (3) isolated Drywells to take the Dock runoff at the west rear location of the Site. Since the front SWM pond discharge design points are more remote, the (3) Drywells are proposed independent to the existing front drainage network . The Drywells are proposed to be interconnected with an 8” equalizer pipe , each having an internal volume of 698 CF of storage . These Drywells should address the immediate proposed graded are to accomplish the Tenant dock area plan . The new SWM DW inlet protections and proposed silt fence containing the area of work are proposed on (SP-1) and Site Details and profiles of the DW’s on (SD-1 & SD-2) . The Goal#1 of proposed review will retain the calculated 2,094 CF volume of accumulated Site Are Storage Volume at the west side site work . SWM storage from runoff determined from the Fire lane upland, as well as the drive door ramp and dock area pervious sheet flow drainage ,being channeled to the improved fire lane contour elevation 384 to 380 inlet of the (3) Drywells . The 8” PVC connector pipes will equalize flow and accumulate and transfer runoff thru and to the (3) DW’s to receive the total proposed infiltration system of the 2,094 CF Volume of Storage . Although the whole site area is (14.28 AC) , the western and eastern areas of work are isolated at the rear and analyzed independently within a disturbed area review of less than an acre combined between the west side and the east side . The West Rear Dock drainage area is analyzed separately as it’s own discharge point to the 2,094 CF Volume of Drywell storage . The SWM design point, having a disturbed area review of 23,645 sf: The longest time of drainage concentration was selected for the gravel Driveway approach and Area along with the Fire lane and dock Grading Area, since grading will be analyzed, assuming a gravel driveway with asphalt pads to remain. The existing property Pre-Development area depicts the west (.54 Ac) site area draining the area of proposed work , while the east draining with approximately ( .44 acres) . The areas are relatively flat , although the west side fire lane is proposed to drain (-4’) change in height in approximately 148 lf horizontal gravel fire lane (2.7% slope) at the West Site. The existing fire lane at the East side is to be resurfaced with no grading cut required , which is 2 Ft drop in 40 Ft horizontal , or 5% existing fire lane grade.The Site Post Construction is proposed to be improved with a re-alignment of the fire lane around the proposed docks on the west side and re-surface pavements at the existing gravel fire lane on the East. post construction all disturbed areas proposed with stabilized lawn slopes . The Pre & Post Development areas are calculated for the Time of Concentration (Tc) analysis review for 25 year and 100 year storm events. The purpose of this report is to establish an on-site storm water design which is reasonable and consistent with the storm water management goals of the Town Of Queensbury, to limit discharge within the site areas and preserve the existing downstream slopes/ site from any erosion during development. Calculations analyzing Pre-development and Post-development for a 25 year storm analysis are offered as a basis design . Goal #2 analyzes Water Quality The Site is also noted to pass the Standard 1.5 gals /SF disturbed area calculation Review. The longest West sideTime of Concentration analyses for Pre (Tc=8 Min.) was determined to be the west site area drainage path and Post Development improved to (Tc=4.5 Min.) were utilized, assuming the developer maintains the agreement to install an assumed graveldriveway . Similarly, longest East sideTime of Concentration analyses for Pre (Tc=7.5 Min.) was determined to be the east site area drainage path , after a paved condition, quickens the and Post Development improved to (Tc=5.5 Min.) were utilized.. The methodology of the rational formula calculations and the New York State charts are attached . Existing Site West side Docks-25 yr (Pre) : -Pre-developed- Site (Dock Area) is 152 LF of 4’(elevation 384 -380) over gravel slope =2.7% (Tc=8 minutes off chart) C=.8 analysis for overland flow: -Therefore Tc= 8 minutes existing site, where -coefficient total (c) =.8, undisturbed -Drainage Dock Site Area Disturbance = 23,645 SF(.54ac) -25 year storm tc off chart, I=4.7 inches/hour -Q25 pre(Dock) Fire lane Site Existing =CIA=(.8)(4.7)(.54)=2.03 CFS Drainage Site- Pre Development Post Development 25 Yr.(Post): -Post-developed-Dock Area, pervious sheet flows , improved storm control areas , (.54 acre) site drainage area to 380 CF SWM basin to be controlled . C= Drive analysis, localized grading review toward DW’s , 23,645 SF(.54 ac) -Drainage path Fire Lane (Tc=4.5 ) minutes . -Most remote Tc tracked driveway site travel is 4.5 minutes -Therefore Tc= 4.5 minutes proposed for revised graded driveway site analyzed for the disturbed area. Rainfall Intensity is 5.3 inches /hour off 25 Hour Rainfall Chart . -1162 SF Asphal t Paved Apron (.024 ac), Site Gravel drive resurfaced (.516) -25 year storm tc off chart =4.5 minutes Dock Area Drive Site, I=5.3 inches/hour -Q25 post (Gravel Lane ) Dock Area Proposed =CIA=(.8) (5.3) (.516)=2.188 CFS -Q25 post (Paved Apron ) Dock Area Proposed =CIA=(.9) (5.3) (.024)=.1145 CFS -Sum of CFS at West Side Dock =2.3 CFS Storage Volume Analysis is the difference between the existing and proposed 25 year runoff volume Qv pre=64(2.03 ) 60/2= 3,898 CF Volume pre- development 25 year –to Dock Area Qv post=64(2.3)60/2= 4,416 CF Volume of post development 25 year-Dock Area – with Paved Apron The Delta Post Development Volume of Storage is 4,416 CF-3,898 CF=518 CF. Volume of Storage is accommodated with the build out with the 1162 SF paved apron at the (3) DW’s, , so the design runoff is addressed . Each 8Ft effective drywell with the stabilized 5.5 minute perc rate , drains down in 528 minutes or 8.8 hours. The deep test pit depth by the Contractor was made early in October anticipating the use of Drywells to satisfy the Tenant requirement for additional Docks to inspect soils at a depth of 18 Ft to the bottom of the proposed DW system Pit where no ground water was found . No additional drainage storage proposed outside of the Drywell combined volume need be analyzed required beyond the 2,094 CF is proposed as a reasonable management solution, to address the 25 yr storage requirement . Therefore, Goal #1 is addressed if Volume of Storage for infiltration SWM Drywells at 5.5 min/inch is utilized to improve the Post Development Volume of Storage of 2,094 CF at the West Side Dock Area, is actually more than the Pre- Development condition of 518 CF requirement storage for 25 year analysis . Existing Site East Side Fire lane (Pre) : -Pre-developed- Site (Dock Area) is 118 LF of ’(elevation 385 -383) over gravel slope =1.7% (Tc=7.5 minutes off chart) C=.8 analysis for overland flow: -Therefore Tc= 7.5 minutes existing site, where -coefficient total (c) =.8, undisturbed -Fire lane Site Area Disturbance = 19,098 SF(.44ac) -25 year storm tc off chart, I=4.75 inches/hour -Q25 pre East side Fire lane Site Existing =CIA=(.8)(4.75)(.19)=.722 CFS Drainage Site- Pre Development -Q25 pre East side lawn buffer Site Existing =CIA=(.3)(4.75)(.25)=.356 CFS Drainage Site- Pre Development -Sum of Pre-CFS 25 Yr. =1.078 CFS Post Development (Post): -Post-developed-East side Fire Lane Area, pervious sheet flows , improved storm control areas , (.44 acre) site drainage area to catch basin to be controlled . C= Drive analysis, localized grading review toward , 19,098 SF(.44 ac) -Drainage path Fire Lane (Tc=5.5 ) minutes . -Most remote Tc tracked fire lane site travel is 5.5 minutes -Therefore Tc= 5.5 minutes proposed for revised graded driveway site analyzed for the disturbed area. Rainfall Intensity is 5.1 inches /hour off 25 Hour Rainfall Chart . -12,763 SF Asphal t & Concrete Dr. pad (.293 ac), Site Gravel drive resurfaced with Pavement -25 year storm tc off chart =5.5 minutes Fire lane Site, I=5.1 inches/hour -Q25 post (Paved) Fire lane Area Proposed =CIA=(.9) (5.1) (.29)=1.33 CFS -Q25 post (Lawn Buffer ) Fire lane Proposed =CIA=(.3) (5.1) (.145)=.22 CFS -Sum of CFS at East Side Fire Lane =1.55 CFS Storage Volume Analysis is the difference between the existing and proposed 25 year runoff volume Qv pre=64(1.078 ) 60/2= 2,070 CF Volume pre- development 25 year –to East SideArea Qv post=64(1.55)60/2= 2,976 CF Volume of post development 25 year-Fire lane Area –with Pavements The Delta Post Development Volume of Storage is 2,976 CF less 2,070CF=906 CF.Volume of Storage is accommodated with the build out with pavement at the fire lane . Since the original design runoff area has not changed , and was previously designed for pavement , no improvements , other than new landscaping in the buffer is being proposed .Although drywells were not tested on the east side, if (2) 8Ft effective drywells were proposed , assuming the tested same stabilized 5.5 minute perc rate , an additional 1396 CF Volume of Storage could be proposed within the area of the diagonal parking to address the increase in pavement at the area of improvement, additional 906 CF determined Volume of Storage , or additional grading within the already sized SWM Basin could be proposed as mitigation , but seems contrary to what had already been designed which exists . No additional drainage storage proposed outside of the preexisting SWM basin is proposed as a reasonable management solution. Although the Contractor may consider scraping (.33’) or 4” off of the bottom of the existing 3616 SF SWM Basin which would offset the Drainage Volume By 1,194 CF > 906 CF required (which should also address the 50yr. Therefore, Goal #1 at the east side Fire Lane is to improve with pavement with no additional SWM infiltration . , Analysis Goal #2 summary is as follows: If Goal #2 is required with a Water Quality (WQv to be reviewed. WQv=CPA/12, where .8 runoff coefficient was established within the statistic for gravel drive impacts, where the regional target 90% rule rainfall is (1”) , where the disturbed area is (23,645-.54 ac’s). Therefore WQv={(.8)(1)(23,645)}/12=1576 CF . The current rear yard infiltration SWM design is 2,094 CF +- ,which is greater than 1576 CF , WQv for the West Side Dock Area Review . No additional improvements for water quality other than continued maintenance and landscaping is proposed on the East side Fire lane . See supplemental handout for Eastside Fire Lane. Lastly, proposed SWM Basin Sizing proposed on application as a Standard for Warren County Region , being generally accepted is 1.5 Gals/SF Area of Disturbed Impervious Calculated. Assuming West Side dock area is partially paved around the (3) Drywells the 1162 SF Impact X 1.5 Gals=1743 Gals Min. Volume/ 7.48 Gals /CF=233 CF Minimum Storage Volume For the proposed west side development. The Provided Volume Of Storage for the Project is 2,094 CF , At the West side Dock Area , having mostly reserve potential given the other scenario reviews that were explored for this project, all passing . Given the tests for a stabilized less than .5 minute percolation rate of the soil for drywells , each drywell at the 8Ft depth (96 inches )X .5 minutes =48minutes/ 60 =.8 hours to drain . No additional improvements for water quality other than continued maintenance and landscaping is proposed on the East side Fire lane at this time , unless the Contractor is required to remove up to 12” of existing SWM Basin and Reseed until stabilized . . See supplemental handout for Eastside Fire Lane. ,Warren County having pond sizing review for less 1 acre disturbance review should not require any further protection to accommodate drainage discharge for the developed site areas . If analyzed 50 Yr. Storm per Chazen Comments : Existing Site West side Docks-50 yr (Pre) : -Pre-developed- Site (Dock Area) is 152 LF of 4’(elevation 384 -380) over gravel slope =2.7% (Tc=8 minutes off chart) C=.8 analysis for overland flow: -Therefore Tc= 8 minutes existing site, where -coefficient total (c) =.8, undisturbed -Drainage Dock Site Area Disturbance = 23,645 SF(.54ac) -50 year storm tc off chart, I=6.2 inches/hour -Q50 pre(Dock) Fire lane Site Existing =CIA=(.8)(6.2)(.54)=2.68 CFS Drainage Site- Pre Development Post Development Westside Docks-50 Yr.(Post): -Post-developed-Dock Area, pervious sheet flows , improved storm control areas , (.54 acre) site drainage area to 380 CF SWM basin to be controlled . C= Drive analysis, localized grading review toward DW’s , 23,645 SF(.54 ac) -Drainage path Fire Lane (Tc=4.5 ) minutes . -Most remote Tc tracked driveway site travel is 4.5 minutes -Therefore Tc= 4.5 minutes proposed for revised graded driveway site analyzed for the disturbed area. Rainfall Intensity is 5.6 inches /hour off 50Hour Rainfall Chart . -1162 SF Asphal t Paved Apron (.024 ac), Site Gravel drive resurfaced (.516) -50 year storm tc off chart =4.5 minutes Dock Area Drive Site, I=5.6 inches/hour -Q50 post (Gravel Lane ) Dock Area Proposed =CIA=(.8) (5.6) (.516)=2.31 CFS -Q50 post (Paved Apron ) Dock Area Proposed =CIA=(.9) (5.6) (.024)=.12 CFS -Sum of CFS at West Side Dock =2.43 CFS Storage Volume Analysis is the difference between the existing and proposed 25 year runoff volume Qv pre=64(2.68 ) 60/2= 5,146 CF Volume pre- development 50 year –to Dock Area Qv post=64(2.43)60/2= 4,666 CF Volume of post development 50 year-Dock Area – with Paved Apron Storage Volume Analysis is the difference between the existing and proposed 50 year runoff volume. Volume Post is actually less than pre-Development , but the Storage Volume delta is 480 CF. The Storage Volume of the proposed Drywells is 2,094 CF If analyzed 50 Yr. Storm per Chazen Comments : Existing Site East Side Fire lane (Pre) : -Pre-developed- Site (Dock Area) is 118 LF of ’(elevation 385 -383) over gravel slope =1.7% (Tc=7.5 minutes off chart) C=.8 analysis for overland flow: -Therefore Tc= 7.5 minutes existing site, where -coefficient total (c) =.8, undisturbed -Fire lane Site Area Disturbance = 19,098 SF(.44ac) -50 year storm tc off chart, I=5.65 inches/hour -Q50 pre East side Fire lane Site Existing =CIA=(.8)(5.65)(.19)=.859 CFS Drainage Site- Pre Development -Q50 pre East side lawn buffer Site Existing =CIA=(.3)(5.65)(.25)=.424 CFS Drainage Site- Pre Development -Sum of Pre-CFS 25 Yr. =1.28 CFS Post Development (Post): -Post-developed-East side Fire Lane Area, pervious sheet flows , improved storm control areas , (.44 acre) site drainage area to catch basin to be controlled . C= Drive analysis, localized grading review toward , 19,098 SF(.44 ac) -Drainage path Fire Lane (Tc=5.5 ) minutes . -Most remote Tc tracked fire lane site travel is 5.5 minutes -Therefore Tc= 5.5 minutes proposed for revised graded driveway site analyzed for the disturbed area. Rainfall Intensity is 6.05 inches/hour off 50 Hour Rainfall Chart . -12,763 SF Asphal t & Concrete Dr. pad (.293 ac), Site Gravel drive resurfaced with Pavement -50 year storm tc off chart =5.5 minutes Fire lane Site, I=6.05 inches/hour -Q50 post (Paved) Fire lane Area Proposed =CIA=(.9) (6.05) (.29)=1.58 CFS -Q50 post (Lawn Buffer ) Fire lane Proposed =CIA=(.3) (6.05) (.145)=.263 CFS -Sum of CFS at East Side Fire Lane =1.84 CFS Storage Volume Analysis is the difference between the existing and proposed 50 year runoff volume Qv pre=64(1.28 ) 60/2= 2,458 CF Volume pre- development 50 year –to East SideArea Qv post=64(1.84)60/2= 3,532 CF Volume of post development 50 year-Fire lane Area –with Pavements Storage Volume Analysis is the difference between the existing and proposed 50 year runoff volume. Volume Post is greater than pre-Development , (3532-2458) Storage Volume delta is 1,074 CF. The Storage Volume of the Original Pond Scrape down and seed 12”. (3617 SF X FT=3617 CF)