Narrative, Location Map, and Soils Map Bethel BHF 0241(38)

Attachment 1: Narrative, Location Map, and Soils Map Bethel BHF 0241(38)

1. Introduction Clough Harbour & Associates, LLP is writing on behalf of Vermont Agency of Transportation to apply for a State Stormwater Discharge Permit for the above referenced project.

2. Project Description Bethel BHF 0241(38) involves the removal of existing Bridge 38 over Gilead Brook, installation of a new bridge on a new alignment shifted 34 ft west of the existing bridge, and related approach and channel work. The bridge is located on VT Route 12 approximately 4.04 miles north of the intersection at VT Route 107. There will be one residence and seven properties outside of the current ROW that will be impacted. The project will be accessed from the existing VT Route 12 as well as the local roads Spring Hollow Road and Gilead Brook Road. There will be several phases to the project which restrict earth disturbance to 2 acres or less. The project requires permit coverage under jurisdiction of stormwater management rules – Environmental Protection Rules, Chapter 18.

3. Existing Condition The topography of the area is generally rolling, mostly wooded with occasional open areas. There are some surrounding commercial and residential buildings. The bridge spans over a large valley containing Gilead Brook. Gilead Brook is the only water source on the project site. The stream bed consists of gravel, cobbles and boulders. Drainage through the project area consists primarily of overland flow which collects in grassed swales that run parallel with VT Route 12. Runoff from the bridge collects in two drop inlets at the south end of the bridge, both connect to pipes that drain away from the current bridge. The runoff throughout the project site flows down the valley walls into Gilead Brook.

4. Proposed Stormwater System: i) Description of Impervious Area: Approximately 0.59 acres of VT Route 12 will be redeveloped and is not considered jurisdictional because it is less than one acre. An additional 0.72 acres of impervious area will be included in the project as expansion for a total of 0.72 acres of impervious area. ii) Site Balancing: Stormwater treatment for the new impervious area north of Bridge 38 has been deemed impractical due to topographical and historical constraints on the project. An additional 0.12 acres of existing impervious area at the southern limit of the project will be treated to account for the un-treated expansion north of Bridge 38. Grass channels on either side of VT Route 12 have been extended to collect and convey the additional stormwater to its respective discharge points. iii) Receiving Body: Gilead Brook iv) Fish Habitat Designation for Receiving Water: Cold v) Description of compliance with each of the five Unified Sizing Criteria in the 2002 VSMM Vol. I including the treatment practices or credits/waivers used to meet each of the following standards: (a) Water Quality Treatment Standard (WQv): 1. S/N 001: Grass channel approximately 600’ long with a modified curve number of 93 pertaining to WQv = 1475 cf. The channel outlets into a drop inlet and flows into a Dry swale approximately 85’ long with a modified curve number of 93 pertaining to a total WQv = 2075 cf. The dry swale will have a 4’ width and consist of 30” permeable soil, 6” gravel and a 4” underdrain pipe. The minimum length requirement according to the Vermont Stormwater Management Manual Volume I – Stormwater Treatment Standards 2002 was found to be approximately 70’.

2. S/N 002: Grass channel approximately 760’ long with a modified curve number of 88 pertaining to a total WQv = 2759 cf. The minimum length requirement according to the Vermont Stormwater Management Manual Volume I – Stormwater Treatment Standards 2002 was found to be approximately 360’.

(b) Groundwater Recharge Treatment Standard: [This is a site wide standard, describe how it is met or waived for the entire site, including which discharge points it is being met in] 1. S/N 001: S/N 001: Grass channel that treats a WQv of 1475 cf and therefore Rev (399 cf) for the grass channel is automatically met. Dry Swale that infiltrates the total WQv of 2075 cf and therefore Rev (563 cf) is automatically met.

2. S/N 002: Grass channel that treats a WQv of 2759 cf and therefore Rev (91 cf) is automatically met.

(c) Channel Protection Standard (CPv): 1. S/N 001: Expansion project involves less than or equal to one (1) acre of impervious cover and therefore, CPv waiver was applied.

2. S/N 002: Expansion project involves less than or equal to one (1) acre of impervious cover and therefore, CPv waiver was applied.

(d) Overbank Flood Protection Standard (Qp10) : 1. S/N 001: The site directly discharges to a large reservoir, lake or stream with a drainage area greater than 10 square miles and therefore, Qp10 waiver was applied.

2. S/N 002: The site directly discharges to a large reservoir, lake or stream with a drainage area greater than 10 square miles and therefore, Qp10 waiver was applied.

(e) Extreme Flood Protection Standard (Qp100) : 1. S/N 001: The site directly discharges to a large reservoir, lake or stream with a drainage area greater than 10 square miles and therefore, Qp100 waiver was applied.

2. S/N 002: The site directly discharges to a large reservoir, lake or stream with a drainage area greater than 10 square miles and therefore, Qp100 waiver was applied.

The following items are attached for review:

· Complete NOI form · Attachment 1: Narrative: Narrative, Location Map and Soils Map. · Attachment 2: Worksheets: Schedule A’s, waivers and BMP worksheets- grouped by discharge point. · Attachment 3: Modeling: Runoff modeling and calculations demonstrating compliance with the applicable treatment standards. · Attachment 4: Plans: Pertinent plan sheets with all required information outlined in Part 5 of the General Guidance Document. Location Map PROJECT LOCATION

Project Location Map

Vermont Route 12 Over Gilead Brook – Bridge No. 38 (Bethel) Scale 1" = 2000' CHA File No: 23825 Bethel, Windsor County, VT Randolph and Bethel USGS Quads Soils Map Soil Map—Orange County, Vermont, and Windsor County, Vermont (aoi_a_aoi[1]) 72° 46' 43'' W 72° 38' 6'' W

679000 680000 681000 682000 683000 684000 685000 686000 687000 688000 689000 43° 55' 27'' N 43° 55' 27'' N 4866000 4865000 4865000 4864000 4864000 4863000 4863000 4862000 4862000 4861000 4861000 4860000 4860000 4859000 4859000 43° 51' 24'' N 43° 51' 24'' N 679000 680000 681000 682000 683000 684000 685000 686000 687000 688000 689000 690000

Map Scale: 1:52,700 if printed on A landscape (11" x 8.5") sheet. Meters 72° 38' 6'' W

72° 46' 43'' W N 0 500 1000 2000 3000 Feet 0 2500 5000 10000 15000 Map projection: Web Mercator Corner coordinates: WGS84 Edge tics: UTM Zone 18N WGS84

Natural Resources Web Soil Survey 11/8/2016 Conservation Service National Cooperative Soil Survey Page 1 of 6 Soil Map—Orange County, Vermont, and Windsor County, Vermont (aoi_a_aoi[1])

MAP LEGEND MAP INFORMATION

Area of Interest (AOI) Spoil Area The soil surveys that comprise your AOI were mapped at 1:20,000. Area of Interest (AOI) Stony Spot Please rely on the bar scale on each map sheet for map Soils measurements. Very Stony Spot Soil Map Unit Polygons Source of Map: Natural Resources Conservation Service Wet Spot Soil Map Unit Lines Web Soil Survey URL: http://websoilsurvey.nrcs.usda.gov Other Coordinate System: Web Mercator (EPSG:3857) Soil Map Unit Points Special Line Features Maps from the Web Soil Survey are based on the Web Mercator Special Point Features projection, which preserves direction and shape but distorts Water Features Blowout distance and area. A projection that preserves area, such as the Streams and Canals Albers equal-area conic projection, should be used if more accurate Borrow Pit Transportation calculations of distance or area are required. Clay Spot Rails This product is generated from the USDA-NRCS certified data as of Closed Depression the version date(s) listed below. Interstate Highways Gravel Pit US Routes Soil Survey Area: Orange County, Vermont Survey Area Data: Version 18, Sep 25, 2015 Gravelly Spot Major Roads Soil Survey Area: Windsor County, Vermont Landfill Local Roads Survey Area Data: Version 19, Sep 25, 2015 Lava Flow Background Your area of interest (AOI) includes more than one soil survey area. Marsh or swamp Aerial Photography These survey areas may have been mapped at different scales, with a different land use in mind, at different times, or at different levels Mine or Quarry of detail. This may result in map unit symbols, soil properties, and Miscellaneous Water interpretations that do not completely agree across soil survey area boundaries. Perennial Water Soil map units are labeled (as space allows) for map scales 1:50,000 Rock Outcrop or larger. Saline Spot Date(s) aerial images were photographed: Jul 10, 2011—Oct 8, Sandy Spot 2011

Severely Eroded Spot The orthophoto or other base map on which the soil lines were compiled and digitized probably differs from the background Sinkhole imagery displayed on these maps. As a result, some minor shifting Slide or Slip of map unit boundaries may be evident.

Sodic Spot

Natural Resources Web Soil Survey 11/8/2016 Conservation Service National Cooperative Soil Survey Page 2 of 6 Soil Map—Orange County, Vermont, and Windsor County, Vermont aoi_a_aoi[1]

Map Unit Legend

Orange County, Vermont (VT017)

Map Unit Symbol Map Unit Name Acres in AOI Percent of AOI TbC Tunbridge-Woodstock rocky 0.5 0.0% fine sandy loams, 8 to 15 percent slopes TrD Tunbridge-Woodstock very 1.4 0.0% rocky fine sandy loams, 8 to 25 percent slopes TwE Tunbridge-Woodstock 8.0 0.1% complex, 25 to 50 percent slopes Subtotals for Soil Survey Area 9.9 0.1% Totals for Area of Interest 8,367.0 100.0%

Windsor County, Vermont (VT027)

Map Unit Symbol Map Unit Name Acres in AOI Percent of AOI 2B Belgrade silt loam, 3 to 8 4.7 0.1% percent slopes 8A Agawam fine sandy loam, 0 to 3 20.1 0.2% percent slopes 8B Agawam fine sandy loam, 3 to 8 51.8 0.6% percent slopes 9B Ninigret fine sandy loam, 0 to 8 24.8 0.3% percent slopes 10C Marlow fine sandy loam, 8 to 15 24.8 0.3% percent slopes 10D Marlow fine sandy loam, 15 to 5.8 0.1% 25 percent slopes 11D Marlow fine sandy loam, 15 to 36.7 0.4% 35 percent slopes, very stony 11E Marlow fine sandy loam, 35 to 304.9 3.6% 60 percent slopes, very stony 12C Tunbridge-Lyman complex, 8 to 673.9 8.1% 15 percent slopes, very rocky 12D Tunbridge-Lyman complex, 15 1,779.5 21.3% to 35 percent slopes, very rocky 12E Tunbridge-Lyman complex, 35 727.2 8.7% to 60 percent slopes, very rocky 14B Hinckley sandy loam, 0 to 8 7.9 0.1% percent slopes 14E Hinckley sandy loam, 25 to 50 4.3 0.1% percent slopes 17B Peru, Skerry, and Colonel soils, 64.5 0.8% 3 to 8 percent slopes

Natural Resources Web Soil Survey 11/8/2016 Conservation Service National Cooperative Soil Survey Page 3 of 6 Soil Map—Orange County, Vermont, and Windsor County, Vermont aoi_a_aoi[1]

Windsor County, Vermont (VT027)

Map Unit Symbol Map Unit Name Acres in AOI Percent of AOI 17C Peru, Skerry, and Colonel soils, 108.5 1.3% 8 to 15 percent slopes 17D Peru, Skerry, and Colonel soils, 173.1 2.1% 15 to 25 percent slopes 18B Peru, Skerry, and Colonel soils, 55.8 0.7% 3 to 8 percent slopes, very stony 18C Peru, Skerry, and Colonel soils, 407.9 4.9% 8 to 15 percent slopes, very stony 18D Peru, Skerry, and Colonel soils, 628.6 7.5% 15 to 35 percent slopes, very stony 19D Vershire-Dummerston 21.4 0.3% complex, 15 to 25 percent slopes, rocky 19E Vershire-Dummerston 0.1 0.0% complex, 25 to 60 percent slopes, rocky 20D Glover-Vershire complex, 15 to 36.6 0.4% 35 percent slopes, very rocky 20E Glover-Vershire complex, 35 to 3.5 0.0% 60 percent slopes, very rocky 21D Shelburne fine sandy loam, 15 1.9 0.0% to 25 percent slopes 24 Podunk fine sandy loam, 0 to 3 37.2 0.4% percent slopes, occasionally flooded 25C Buckland loam, 8 to 15 percent 43.2 0.5% slopes 25D Buckland loam, 15 to 25 percent 14.6 0.2% slopes 26C Buckland loam, 8 to 15 percent 8.0 0.1% slopes, very stony 26D Buckland loam, 15 to 35 percent 33.4 0.4% slopes, very stony 26E Buckland loam, 35 to 60 percent 8.2 0.1% slopes, very stony 29A Grange very fine sandy loam, 0 2.2 0.0% to 3 percent slopes 30B Cabot silt loam, 0 to 8 percent 21.4 0.3% slopes 30C Cabot silt loam, 8 to 15 percent 4.8 0.1% slopes 31B Cabot silt loam, 0 to 8 percent 59.9 0.7% slopes, very stony 31C Cabot silt loam, 8 to 15 percent 31.7 0.4% slopes, very stony

Natural Resources Web Soil Survey 11/8/2016 Conservation Service National Cooperative Soil Survey Page 4 of 6 Soil Map—Orange County, Vermont, and Windsor County, Vermont aoi_a_aoi[1]

Windsor County, Vermont (VT027)

Map Unit Symbol Map Unit Name Acres in AOI Percent of AOI 33 Rumney fine sandy loam, 0 to 3 15.1 0.2% percent slopes, frequently flooded 41 Saco silt loam, 0 to 2 percent 2.8 0.0% slopes, frequently flooded 42D Lyman-Rock outcrop complex, 37.8 0.5% 15 to 35 percent slopes 42F Lyman-Rock outcrop complex, 49.2 0.6% 35 to 60 percent slopes 47 Pondicherry and Wonsqueak 51.5 0.6% mucks, ponded 48 Pits, Sand, and Pits, gravel 7.3 0.1% 49B Vershire-Buckland complex, 3 4.7 0.1% to 8 percent slopes 49C Vershire-Buckland complex, 8 20.6 0.2% to 15 percent slopes 49D Vershire-Buckland complex, 15 10.3 0.1% to 25 percent slopes 54B Tunbridge-Lyman complex, 3 to 6.4 0.1% 8 percent slopes, rocky 54C Tunbridge-Lyman complex, 8 to 103.2 1.2% 15 percent slopes, rocky 54D Tunbridge-Lyman complex, 15 187.5 2.2% to 25 percent slopes, rocky 56 Bucksport muck, ponded 9.1 0.1% 58C Berkshire-Tunbridge complex, 123.1 1.5% 8 to 15 percent slopes, very stony 58D Berkshire-Tunbridge complex, 1,030.3 12.3% 15 to 35 percent slopes, very stony 58E Berkshire-Tunbridge complex, 326.0 3.9% 35 to 50 percent slopes, very stony 59E Rawsonville-Houghtonville 345.3 4.1% complex, 35 to 60 percent slopes, rocky 60D Glebe-Stratton complex, 15 to 4.1 0.0% 35 percent slopes, very stony 60F Glebe-Stratton complex, 35 to 151.3 1.8% 70 percent slopes, very stony 61D Ricker-Londonderry-Stratton 39.6 0.5% complex, 15 to 35 percent slopes, very rocky 61F Ricker-Londonderry-Stratton 0.5 0.0% complex, 35 to 70 percent slopes, very rocky

Natural Resources Web Soil Survey 11/8/2016 Conservation Service National Cooperative Soil Survey Page 5 of 6 Soil Map—Orange County, Vermont, and Windsor County, Vermont aoi_a_aoi[1]

Windsor County, Vermont (VT027)

Map Unit Symbol Map Unit Name Acres in AOI Percent of AOI 62C Hogback-Rawsonville complex, 13.1 0.2% 8 to 15 percent slopes, very rocky 62D Hogback-Rawsonville complex, 17.6 0.2% 15 to 35 percent slopes, very rocky 62E Hogback-Rawsonville complex, 125.5 1.5% 35 to 60 percent slopes, very rocky 63C Berkshire and Monadnock fine 7.8 0.1% sandy loams, 8 to 15 percent slopes, very stony 63D Berkshire and Monadnock fine 20.8 0.2% sandy loams, 15 to 35 percent slopes, very stony 63E Berkshire and Monadnock fine 37.4 0.4% sandy loams, 35 to 60 percent slopes, very stony 64B Colton fine sandy loam, 3 to 8 37.0 0.4% percent slopes 64E Colton fine sandy loam, 25 to 60 2.7 0.0% percent slopes 68C Berkshire and Monadnock fine 17.6 0.2% sandy loams, 8 to 15 percent slopes 71B Croghan and Sheepscot fine 16.0 0.2% sandy loams, 0 to 8 percent slopes 82 Udifluvents, cobbly, frequently 99.7 1.2% flooded W Water 3.1 0.0% Subtotals for Soil Survey Area 8,357.1 99.9% Totals for Area of Interest 8,367.0 100.0%

Natural Resources Web Soil Survey 11/8/2016 Conservation Service National Cooperative Soil Survey Page 6 of 6 StreamStats 4.0 Page 1 of 2

StreamStats Report Region ID: VT Workspace ID: VT20160803060958105000 Clicked Point (Latit... 43.87358,-72.64727 Time: 2016-08-03 08:16:09 -0400

Basin Characteristics Parameter Code Parameter Description Value Unit

DRNAREA Area that drains to a point on a stream 13.1 square miles

EL1200 Percentage of basin at or above 1200 ft elevation 77.8 percent

LC06STOR Percentage of water bodies and wetlands determined from the NLCD 2006 0.96 percent

PRECPRIS10 Basin average mean annual precipitation for 1981 to 2010 from PRISM 50.1 inches

OUTLETX Basin outlet horizontal (x) location in state plane coordinates 488165 State plane coordinates

OUTLETY Basin outlet vertical (y) location in state plane coordinates 152605 State plane coordinates

CENTROIDX Basin centroid horizontal (x) location in state plane coordinates 482755.4 State plane coordinates

CENTROIDY Basin centroid vertical (y) location in state plane units 153976.6 State plane coordinates

LC11IMP Average percentage of impervious area determined from NLCD 2011 impervious dataset 0.14 percent

LC11DEV Percentage of land-use from NLCD 2011 classes 21-24 1.64 percent

http://streamstatsags.cr.usgs.gov/streamstats/ 8/3/2016 Version 2-2015 Vermont Stormwater Discharge Permit Application Schedule A Fill out one Schedule A for each discharge point. For each Standard Treatment Practice (STP), Credit or Waiver specified, a STP, Credit, and/or Waiver worksheet must also be included.

Line General Discharge Point Information

1 Project name Þ»¬¸»´ ÞØÚ ðîìïøíè÷

2 Discharge point serial number (e.g. S/N 001) ÍñÒ ððï

3 Name of receiving water Ù·´»¿¼ Þ®±±µ

4 Latitude & Longitude of discharge point (Decimal Degree format with 6 digits to the right of the decimal): ìíòèéíêïí óéîòêìéïéè 5 Site area draining to discharge point (acres) = impervious + disturbed pervious ïòëì 6

On-site impervious area included for permit coverage (Round to nearest 0.01 acre)

7 New Impervious area contributing stormwater runoff to discharge point (acres) ðòëì 8 Redeveloped impervious area* contributing stormwater runoff to discharge point (acres) ðòðð 9 Existing Impervious area* contributing to stormwater runoff to discharge point (acres) ðòðè 10 Total ðòêî *DO NOT include impervious area unless it has met the Vermont Stormwater Treatment Standards 2002. If using the site balancing procedure refer to General Guidance Document.

Water Quality (0.9 inches) Treatment Standard (WQ)

11 STP used (e.g. Grass Channel O-3) Ü®§ Í©¿´» øÑóï÷

12 Voluntary Stormwater Management Credits applied (e.g. Grass Channel Credit 3.5) Òñß

Groundwater Recharge Treatment Standard (Re) 13 Criterion applicable? (Yes or No) If No, indicate waiver applied Ç»

14 STP used (e.g. Grass Channel O-3) Ü®§ Í©¿´» øÑóï÷

15 Voluntary Stormwater Management Credits applied (e.g. Grass Channel Credit 3.5) Òñß

Channel Protection (1-year) Treatment Standard (CP) 16 Criterion applicable? (Yes or No) If No, indicate waiver applied Ò± Ô» Ì¸¿² Ñ²» ß½®»

17 Warm or Cold Fish Habitat Designation (see Vermont Water Quality Standards)

18 STP used (e.g. Wet Pond P-2)

Overbank (10-year) Flood Protection Treatment Standard (Qp10)

19 Criterion applicable? (Yes or No) If No, indicate waiver applied Ò± Î»½»·ª·²¹ É¿¬»® â ïð Í¯«¿®» Ó·´»

20 STP used (e.g. Dry Detention Pond LA-1)

21 Pre-development peak discharge rate (cfs)

22 Pre-routed, post-development peak discharge rate (cfs)

23 Routed, post-development peak discharge rate (cfs)

Extreme (100-year) Flood Protection Treatment Standard (Qp100)

24 Criterion applicable? (Yes or No) If No, indicate waiver applied Ò± Î»½»·ª·²¹ É¿¬»® â ïð Í¯«¿®» Ó·´»

25 STP used (e.g. Dry Detention Pond LA-1)

26 Pre-development peak discharge rate (cfs)

27 Pre-routed, post-development peak discharge rate (cfs)

28 Routed, post-development peak discharge rate (cfs) DrySwale_WQV_flow.xls

Page 1 of 2 Version: 9/06 For the area draining to*: Gilead Brook Located in drainage area for S/N: SN001 WQ Volume and Modified Curve Number Calculation for Water Quality Treatment in Flow-Based Practice

Use this worksheet to calculate your WQv if you need to determine the Peak Q for the WQ storm (i.e. designing a grass channel, flow-splitter or other flow based practice) and you are not using any of the site design credits in section 3 of the 2002 VSWMM. See page 2 for "Calculating Peak WQ Discharge Rate (0.9" storm) using the Modified Curve Number." Please note that in the case of grass channels you must include any off-site area draining to the practice as this will affect the peak discharge rate which will ultimately affect the hydraulics, and thus residence time, in your channel.

Water Quality Volume Calculations Line value/calculation units 1 Area draining to practice A= 1.54 acres 2 Impervious area 0.62 acres 3 Percent Impervious Area = [(line 2/line 1) * 100] = I = 40.26 % (whole #) 4 Precipitation P = 0.9 inches 5 Runoff coefficient calculation = (0.05 + (0.009*I)) Rv = 0.412 6 WQ Volume (in watershed inches) Calculation =( P * Rv) = 0.371 Qa (watershed inches, a.k.a. inches of runoff) 1 7 Minimum WQ Volume 0.2 watershed inches 8 Enter the greater of line 6 or line 7 WQv = 0.371 watershed inches 9 WQ Volume Calculation = (line 8 *A)/12 = WQv = 0.048 ac. ft. 10 WQ Volume Calculation = (line 9 * 43560) = WQv = 2075 cu. ft.

Notes: 1: Sites with low impervious cover ( ~19%) but that do not employ a significant use of the stormwater design credits in Section 3 of the VSWMM are required to treat the minimum water quality volume of 0.2 watershed inches. Sites that have a significant portion of their impervious cover addressed via the stormwater credits (section 3 of the VSWMM) will be able to reduce this WQv and will only be required to treat the volume calculated on the "WQ Volume (with credit reduction)" worksheet which will be less than the 0.2 watershed inches.

* Enter the name of the STP (both type and label) which has been designed to treat this particular WQv (e.g. Wet Pond #2) DrySwale_WQV_flow.xls

Page 2 of 2

Version: 9/06 For the area draining to*: Gilead Brook Located in drainage area for S/N: SN001 Calculating Peak WQ Peak Discharge Rate (0.9" storm) using the Modified Curve Number Because NRCS methods underestimate the peak discharge for rainfall events of less than 2", simply plugging in 0.9" of rainfall into your hydrologic model with the standard curve numbers will not produce the correct peak discharge during the WQv storm, nor will it produce a volume of runoff equivalent to that which you have calculated using the WQv formula (WQv = P*Rv*A/12). In order to calculate the peak discharge for the 0.9" storm, a modified curve number must be calculated. This modified curve number is based on the runoff (in inches) calculated using the short cut method formula (WQv = P*Rv) that is also the basis of the familiar WQv calculations provided in the 2002 VSWMM (and on the WQv calculation worksheets). Essentially, the curve number that is calculated using the methods below is the curve number that will generate the volume of runoff calculated using the WQv formula.

Above, you should have calculated the WQv in watershed inches draining to the facility/practice for which you need to calculate the WQ- peak discharge. As provided in the guidance listed on the grass channel worksheet, please remember that the WQv calculation should include runoff from on-site as well as off-site area draining to the grass channel since this will have an impact on the channel hydraulics and thus the velocity and residence time.

Steps: 1. Transfer information from WQv calculation worksheets.

Enter the Qa ( line 8 from WQv sheet ) Qa = 0.371 inches

Enter the area (site +off-site draining to practice) used in calculating the percent impervious (I) A = 1.5 acres

2. Use the following equation to calculate a corresponding curve number where P = 0.9 inches

CN = 1000/(10 +(5*P)+(10*Qa) - (10*(Qa^2 + (1.25*Qa*P))^0.5))

CN = 92.9

3. If you are using hand hydrologic runoff calculations, use the computed CN above along with your calculated time of concentration and the drainage area (A) to calculate the peak discharge (Qwq) for the water quality storm using the TR-55 Graphical Peak Discharge Method.

3. If you are using a computer aided hydrologic model, simply revise the curve number for your subwatershed(s) draining to the practice using the curve number calculated above; the computed curve number should be applied to the total area (A) used in the WQv calcuation. As a check, you should note that now when you run the 0.9" storm, your runoff depth should be roughly equal to Qa (WQ runoff in inches) and your total runoff volume roughly equal to your WQv (in ac. ft.). If this is not the case, make sure that the time span for your modelling run is long enough to capture the entire storm. Small variations are likely due to having to round your computed CN to a whole number. Remember that for storms larger than 2", you do not need to use the modified curve number and you should calculate your composite curve number based on the accepted values for different types of land-use (see TR-55).

* Enter the name of the STP (both type and label) which has been designed to treat this particular WQv (e.g. Wet Pond #2) DrySwale_RechargeWorksheet.xlsx

Version: 2/12 For the area draining to*: Bethel BHF 0241(38) Gilead Brook Located in drainage area for S/N: S/N 001 Groundwater Recharge Treatment Standard - Calculation & Waiver Worksheet The average annual groundwater recharge rate for the prevailing hydrologic soil group(s) (HSG) must be maintained in order to preserve existing water table elevations. Recharge is determined as a function of annual predevelopment recharge for a given HSG, the average annual rainfall and the amount of impervious surface at the site. The Groundwater Recharge Treatment Standard can be met by using one or both of the following methods: volume method and/or percent area method. See Table 2.2 in the VSMM - Volume I for a list of acceptable STPs or credits that satisfy this requirement. Use NRCS's Web Soil Survey to obtain specific soil data at your site, available at: http://websoilsurvey.nrcs.usda.gov/app/HomePage.htm

Site Information value/calculation units Site Area (impervious + disturbed pervious) A= 1.54 acres Impervious area 0.62 acres Percent Impervious Area = [(line 2/line 1)] = I = 0.40 % (decimal percent)

Composite Recharge Factor Calculation Enter site acreage of each HSG draining to POI or S/N value/calculation HSG A 0.00 acres HSG B 1.54 acres HSG C 0.00 acres HSG D 0.00 acres Total Site Area yes Composite Recharge Factor 0.250

0.013 acre feet ReV (Percent Volume Method) 563 cubic feet

The percent volume method is commonly used to meet recharge. Designers must demonstrate that a proposed STP allows at least the Rev to enter the ground. The Rev is contained within the WQv. So, if a practice is infiltrating the entire WQv, then Rev is automatically met. Please use the applicable STP worksheets to verify the Groundwater Recharge Treatment Standard has been met. Note that not all STPs can be used to meet this standard.

0.155 acres ReA (Percent Area Method) 6752 square feet

The percent area method is used when meeting recharge via nonstructural design credits(disconnection of rooftop/non-rooftop surfaces, stream buffer, grass channel credit, or ESRD). In this case, the designer must demonstrate that stormwater runoff from a portion of the new impervious area, equivalent to the area calculated under the percent area method, drains into a nonstructural design credit practice.

Additional notes: *Recharge is one of the unified sizing criteria that can be achieved site wide, rather than at each point of interest (POI) or discharge point (S/N), assuming the receiving water is the same for each discharge point.

* Enter the name of the STP (both type and label) which has been designed to treat this particular Rev or Rea. Version: 4/10 Project Name: BETHEL BHF0241(38) Discharge Point: S/N 001 Dry Swale (O-1) Dry Swale #1

Line Treatment Standards Indicate the treatment standards met for the site area draining to this practice: 1 WQv ¨ 2 Rev ¨ This practice automatically meets Rev if you have met the WQv treatment standards 3 Cpv ¨ 4 Qp10 ¨ { Dry swales are not typically appropriate to provide Cpv, Qp10 or Qp100 except under ideal conditions. 5 Qp100 ¨

Water Quality Volume (WQv) WQv (Cubic Feet)

6 Provide the WQv for the site area draining to this swale (from WQv worksheets) 2075

Feasibility (2.7.5.A) Response Attachment location BHF_0241(38)_Attachment3- Is the maximum longitudinal slope of the swale 4% or less? 7 YES Modeling.pdf

Conveyance (2.7.5.B) Response Attachment location BHF_0241(38)_Attachment3- Is the peak velocity for the 1-year storm non-erosive? 8 YES Modeling.pdf BHF_0241(38)_Attachment3- Are the design side slopes less than or equal to the 2:1 maximum? 9 YES Modeling.pdf BHF_0241(38)_Attachment3- Does the practice safely convey the 10-year storm with a minimum of 6 inches of freeboard? 10 YES Modeling.pdf BHF_0241(38)_Attachment4- Has the swale been designed with an underdrain system? 11 YES Plans.pdf

Pretreatment (2.7.5.C) Response Attachment location BHF_0241(38)_Attachment3- Has pre-treatment been provided for non-rooftop runoff? 12 YES Modeling.pdf

Treatment (2.7.5.D) Channel Width (Feet) 13 What is the bottom width of the channel? (no greater than 8 feet, but no less than 2 feet) 4

Response Attachment location BHF_0241(38)_Attachment3- Is the swale designed to accommodate a portion of the WQv through surface ponding? 14 YES Modeling.pdf BHF_0241(38)_Attachment3- Is the swale bottom designed to drain the WQv in less than 40 hours? 15 YES Modeling.pdf BHF_0241(38)_Attachment3- Does the swale design release the WQv over a minimum of 30 minutes? 16 YES Modeling.pdf BHF_0241(38)_Attachment3- Is the average head (height of water above the bottom of the swale) below 12 inches? 17 YES Modeling.pdf BHF_0241(38)_Attachment3- Does the soil media meet the open vegetated swale specifications? 18 YES Modeling.pdf 19 What infiltration rate (if any) is used for exfiltration (in/hour)? N/A -

Cold Climate Design Considerations (2.7.5.G) Response Attachment location

20 Have the potential impacts of Vermont's severe winter climate been addressed in your design? NO -

DrySwale_O-1.xls Dry Swale: Cpv, Qp10 and Qp100 Page 2

Channel Protection Treatment Standard (Cpv) Response

21 Check which detention time standard must be used, based on the fisheries designation of the receiving water: ¨ 12 hours for cold water

¨ 24 hours for warm water

Response Attachment location

22 Did you use the Storage Volume Estimation Method? If yes, skip to Line 26.* yes / no *Please review the guidance sheet "Channel Protection Storage Volume Estimation" and attach the specified information. This method is not appropriate if more than a one subwatershed drains to the practice. Using the center of mass detention time calculated by a hydrologic model that accounts for pond routing is the preferred method.

23 What storage volume (cubic feet) necessary to meet the Channel Protection Standard?

24 What is the calculated average release rate (cfs)?

25 What is the controlled peak release rate (cfs) during the 1-year storm as indicated by the model?

Overbank Flood Protection Treatment Standard (Qp10) Response Attachment location

26 Have you demonstrated that Qp10 post is less than or equal to Qp10 pre at the discharge point?* yes / no *Please include runoff and routing calculations of the 10-year storm event.

Extreme Flood Protection Treatment Standard (Qp100) Response Attachment location

27 Have you demonstrated that Qp100 post is less than or equal to Qp100 pre at the discharge point?* yes / no *Please include runoff and routing calculations of the 100-year storm event.

A dry swale is a volume-based treatment channel. Check dams, weirs or coir logs are encouraged to promote ponding. Convey larger storms through overflow weirs or outlet control structures. See VSMM-Vol. II, Appendix D7 for guidance about maintaining non-erosive conditions. Attachment location: Please indicate the specific location (i.e. appendix, page, plan sheet) where the requisite support documentation has been provided within the application.

DrySwale_O-1.xls Ð®·²¬ Ú±®³

Project Name: Þ»¬¸»´ ÞØÚ ðîìï øíè÷ Discharge Point: ÍñÒððï Channel Protection Standard Treatment Standard Waiver Worksheet

Fill out this worksheet for each discharge point in which use of this waiver is sought.

Channel Protection Standard Treatment Standard (CPv) Waiver (check only one):

ì 1. Expansions involving less than or equal to one (1) acre of impervious cover.

Enter the new/expanded impervious area (acres): ðòêî

2. A site where the pre-routed, post-development discharge is less than 2 cubic feet per second (cfs).

Enter the total pre-routed post development discharge rate (cfs): Guidance: Pre-routed post development flow is the runoff from the site area without detenon provided. However, this runoff flow should include all post-development conveyance. The site is equal to the disturbed area. When examining whether or not the site qualifies for this waiver, off-site runoff does not need to be considered. Please aach the runoff calculaons/hydrologic modeling for the pre-routed, post-development during the 1-year, 24-hour storm event.

3. A site that directly discharges to a waterbody with a drainage area equal or greater than 10 square miles, and upstream boundary.

Name of Receiving Water at Discharge Point:

Drainage Area of Receiving Water at Discharge Point (square miles):

Guidance: means that the runoﬀ from the project does not reach any water of the State before discharging to the waterbody with a equal or greater than 10 square mile watershed. If the discharge point deﬁnion is unclear, refer to the Schedule A document and/or contact the Stormwater Program.

These waivers are applied per receiving water. For example, if discharge point S/N 001 drains directly to the Winooski River (greater than 10 square miles), but discharge point S/N 002 drains to a small tributary of the Winooski River, then S/N 001 could be waived from the Channel Protecon Treatment Standard using waiver 3, but S/N 002 could not. However, S/N002 may be eligible for the other waivers.

For addional informaon please go to the Vermont Stormwater Management Manual, Volume 1, Secon 1.1.2, Page 1-6 Ð®·²¬ Ú±®³

Project Name: Þ»¬¸»´ ÞØÚ ðîìïøíè÷ Discharge Point:ÍñÒððï Overbank Flood Protection Standard Treatment Standard Waiver Worksheet

Fill out this worksheet for each discharge point in which use of this waiver is sought.

Overbank Flood Protection Standard Treatment Standard (Qp10) Waiver (check only one): ì 1. The site directly discharges to a large reservoir, lake or stream with a drainage area greater than or than 10 square miles.

Name of Receiving Water at Discharge Point: Ù·´»¿¼ Þ®±±µ

Drainage Area of Receiving Water at Discharge Point (square miles): ïíòï

2. The site is smaller than 5 acres and the channel has adequate capacity to convey the post-development 10-year discharge downstream to the point of the 10% rule; and downstream conveyances have adequate capacity to convey the 10 year storm.

Is the site area less than ﬁve (5) acres? Yes No

Has adequate conveyance from the site to the discharge point been veriﬁed? Yes No

Has supporting informaon (e.g. narrave descripon, calculaons, modeling) been included? Yes No

These waivers are applied per receiving water. For example, if discharge point S/N 001 drains directly to the Winooski River (greater than 10 square miles), but discharge point S/N 002 drains to a small tributary of the Winooski River, then S/N 001 could be waived from the Overbank Flood Protecon Standard Treatment Standard using waiver 1, but S/N 002 could not. However, S/N002 may be eligible for the other waiver.

For addional informaon please go to the Vermont Stormwater Management Manual, Volume 1, Secon 1.1.2, Page 1-10 Ð®·²¬ Ú±®³

Project Name: Þ»¬¸»´ ÞØÚ ðîìïøíè÷ Discharge Point:ÍñÒððï Extreme Flood Protection Standard Treatment Standard Waiver Worksheet

Fill out this worksheet for each discharge point in which use of this waiver is sought.

Extreme Flood Protection Standard Treatment Standard (Qp100) Waiver (check only one): ì 1. The site directly discharges to a large reservoir, lake or stream with a drainage area greater than or than ten (10) square miles.

Name of Receiving Water at Discharge Point: Ù·´»¿¼ Þ®±±µ

Drainage Area of Receiving Water at Discharge Point (square miles): ïíòï

2. The impervious area is less than or equal to ten (10) acres.

Enter the new/expanded impervious area (acres):

Guidance: The ten (10) acre treatment requirement applies to only new impervious created since July 4, 2005.

3. A downstream analysis is conducted that indicates extreme ﬂood control is not necessary for the site.

Has adequate conveyance from the site to the discharge point been veriﬁed? Yes No

Has supporng informaon (e.g. narrave descripon, calculaons, modeling) been included? Yes No

Note: These waivers are applied per receiving water.

For addional informaon please go to the Vermont Stormwater Management Manual, Volume 1, Secon 1.1.2, Page 1-11 Version 2-2015 Vermont Stormwater Discharge Permit Application Schedule A Fill out one Schedule A for each discharge point. For each Standard Treatment Practice (STP), Credit or Waiver specified, a STP, Credit, and/or Waiver worksheet must also be included.

Line General Discharge Point Information

1 Project name Þ»¬¸»´ ÞØÚ ðîìïøíè÷

2 Discharge point serial number (e.g. S/N 001) ÍñÒ ððî

3 Name of receiving water Ù·´»¿¼ Þ®±±µ

On-site impervious area included for permit coverage (Round to nearest 0.01 acre)

7 New Impervious area contributing stormwater runoff to discharge point (acres) ðòðê 8 Redeveloped impervious area* contributing stormwater runoff to discharge point (acres) ðòðð 9 Existing Impervious area* contributing to stormwater runoff to discharge point (acres) ðòðì 10 Total ðòïð *DO NOT include impervious area unless it has met the Vermont Stormwater Treatment Standards 2002. If using the site balancing procedure refer to General Guidance Document.

Water Quality (0.9 inches) Treatment Standard (WQ)

11 STP used (e.g. Grass Channel O-3) Ù®¿ Ý¸¿²²»´ øÑóí÷

12 Voluntary Stormwater Management Credits applied (e.g. Grass Channel Credit 3.5) Òñß

Groundwater Recharge Treatment Standard (Re) 13 Criterion applicable? (Yes or No) If No, indicate waiver applied Ç»

14 STP used (e.g. Grass Channel O-3) Ù®¿ Ý¸¿²²»´ øÑóí÷

15 Voluntary Stormwater Management Credits applied (e.g. Grass Channel Credit 3.5) Òñß

Channel Protection (1-year) Treatment Standard (CP) 16 Criterion applicable? (Yes or No) If No, indicate waiver applied Ò± Ô» Ì¸¿² Ñ²» ß½®»

17 Warm or Cold Fish Habitat Designation (see Vermont Water Quality Standards)

18 STP used (e.g. Wet Pond P-2)

Overbank (10-year) Flood Protection Treatment Standard (Qp10)

19 Criterion applicable? (Yes or No) If No, indicate waiver applied Ò± Î»½»·ª·²¹ É¿¬»® â ïð Í¯«¿®» Ó·´»

20 STP used (e.g. Dry Detention Pond LA-1)

21 Pre-development peak discharge rate (cfs)

22 Pre-routed, post-development peak discharge rate (cfs)

23 Routed, post-development peak discharge rate (cfs)

Extreme (100-year) Flood Protection Treatment Standard (Qp100)

24 Criterion applicable? (Yes or No) If No, indicate waiver applied Ò± Î»½»·ª·²¹ É¿¬»® â ïð Í¯«¿®» Ó·´»

25 STP used (e.g. Dry Detention Pond LA-1)

26 Pre-development peak discharge rate (cfs)

27 Pre-routed, post-development peak discharge rate (cfs)

28 Routed, post-development peak discharge rate (cfs) SouthwestGrassChannel_WQV_Flow.xls

Page 1 of 2 Version: 9/06 For the area draining to*: Gilead Brook Located in drainage area for S/N: SN 002 WQ Volume and Modified Curve Number Calculation for Water Quality Treatment in Flow-Based Practice

Water Quality Volume Calculations Line value/calculation units 1 Area draining to practice A= 3.80 acres 2 Impervious area 0.10 acres 3 Percent Impervious Area = [(line 2/line 1) * 100] = I = 2.63 % (whole #) 4 Precipitation P = 0.9 inches 5 Runoff coefficient calculation = (0.05 + (0.009*I)) Rv = 0.074 6 WQ Volume (in watershed inches) Calculation =( P * Rv) = 0.066 Qa (watershed inches, a.k.a. inches of runoff) 1 7 Minimum WQ Volume 0.2 watershed inches 8 Enter the greater of line 6 or line 7 WQv = 0.200 watershed inches 9 WQ Volume Calculation = (line 8 *A)/12 = WQv = 0.063 ac. ft. 10 WQ Volume Calculation = (line 9 * 43560) = WQv = 2759 cu. ft.

* Enter the name of the STP (both type and label) which has been designed to treat this particular WQv (e.g. Wet Pond #2) SouthwestGrassChannel_WQV_Flow.xls

Page 2 of 2

Version: 9/06 For the area draining to*: Gilead Brook Located in drainage area for S/N: SN 002 Calculating Peak WQ Peak Discharge Rate (0.9" storm) using the Modified Curve Number Because NRCS methods underestimate the peak discharge for rainfall events of less than 2", simply plugging in 0.9" of rainfall into your hydrologic model with the standard curve numbers will not produce the correct peak discharge during the WQv storm, nor will it produce a volume of runoff equivalent to that which you have calculated using the WQv formula (WQv = P*Rv*A/12). In order to calculate the peak discharge for the 0.9" storm, a modified curve number must be calculated. This modified curve number is based on the runoff (in inches) calculated using the short cut method formula (WQv = P*Rv) that is also the basis of the familiar WQv calculations provided in the 2002 VSWMM (and on the WQv calculation worksheets). Essentially, the curve number that is calculated using the methods below is the curve number that will generate the volume of runoff calculated using the WQv formula.

Steps: 1. Transfer information from WQv calculation worksheets.

Enter the Qa ( line 8 from WQv sheet ) Qa = 0.200 inches

Enter the area (site +off-site draining to practice) used in calculating the percent impervious (I) A = 3.8 acres

2. Use the following equation to calculate a corresponding curve number where P = 0.9 inches

CN = 1000/(10 +(5*P)+(10*Qa) - (10*(Qa^2 + (1.25*Qa*P))^0.5))

CN = 88.1

* Enter the name of the STP (both type and label) which has been designed to treat this particular WQv (e.g. Wet Pond #2) SouthwestGrassChannel_RechargeWorksheet.xlsx

Version: 2/12 For the area draining to*: Bethel BHF 0241(38) Gilead Brook Located in drainage area for S/N: S/N 002 Groundwater Recharge Treatment Standard - Calculation & Waiver Worksheet The average annual groundwater recharge rate for the prevailing hydrologic soil group(s) (HSG) must be maintained in order to preserve existing water table elevations. Recharge is determined as a function of annual predevelopment recharge for a given HSG, the average annual rainfall and the amount of impervious surface at the site. The Groundwater Recharge Treatment Standard can be met by using one or both of the following methods: volume method and/or percent area method. See Table 2.2 in the VSMM - Volume I for a list of acceptable STPs or credits that satisfy this requirement. Use NRCS's Web Soil Survey to obtain specific soil data at your site, available at: http://websoilsurvey.nrcs.usda.gov/app/HomePage.htm

Site Information value/calculation units Site Area (impervious + disturbed pervious) A= 3.80 acres Impervious area 0.10 acres Percent Impervious Area = [(line 2/line 1)] = I = 0.03 % (decimal percent)

Composite Recharge Factor Calculation Enter site acreage of each HSG draining to POI or S/N value/calculation HSG A 0.00 acres HSG B 3.80 acres HSG C 0.00 acres HSG D 0.00 acres Total Site Area yes Composite Recharge Factor 0.250

0.002 acre feet ReV (Percent Volume Method) 91 cubic feet

0.025 acres ReA (Percent Area Method) 1089 square feet

* Enter the name of the STP (both type and label) which has been designed to treat this particular Rev or Rea. Ð®·²¬ Ú±®³

Project Name: Þ»¬¸»´ ÞØÚ ðîìï øíè÷ Discharge Point: ÍñÒððî Channel Protection Standard Treatment Standard Waiver Worksheet

Fill out this worksheet for each discharge point in which use of this waiver is sought.

Channel Protection Standard Treatment Standard (CPv) Waiver (check only one):

ì 1. Expansions involving less than or equal to one (1) acre of impervious cover.

Enter the new/expanded impervious area (acres): ðòïð

2. A site where the pre-routed, post-development discharge is less than 2 cubic feet per second (cfs).

3. A site that directly discharges to a waterbody with a drainage area equal or greater than 10 square miles, and upstream boundary.

Name of Receiving Water at Discharge Point:

Drainage Area of Receiving Water at Discharge Point (square miles):

For addional informaon please go to the Vermont Stormwater Management Manual, Volume 1, Secon 1.1.2, Page 1-6 Ð®·²¬ Ú±®³

Project Name: Þ»¬¸»´ ÞØÚ ðîìïøíè÷ Discharge Point:ÍñÒððî Overbank Flood Protection Standard Treatment Standard Waiver Worksheet

Fill out this worksheet for each discharge point in which use of this waiver is sought.

Name of Receiving Water at Discharge Point: Ù·´»¿¼ Þ®±±µ

Drainage Area of Receiving Water at Discharge Point (square miles): ïíòï

Is the site area less than ﬁve (5) acres? Yes No

Has adequate conveyance from the site to the discharge point been veriﬁed? Yes No

Has supporting informaon (e.g. narrave descripon, calculaons, modeling) been included? Yes No

These waivers are applied per receiving water. For example, if discharge point S/N 001 drains directly to the Winooski River (greater than 10 square miles), but discharge point S/N 002 drains to a small tributary of the Winooski River, then S/N 001 could be waived from the Overbank Flood Protecon Standard Treatment Standard using waiver 1, but S/N 002 could not. However, S/N002 may be eligible for the other waiver.

For addional informaon please go to the Vermont Stormwater Management Manual, Volume 1, Secon 1.1.2, Page 1-10 Ð®·²¬ Ú±®³

Project Name: Þ»¬¸»´ ÞØÚ ðîìïøíè÷ Discharge Point:ÍñÒððî Extreme Flood Protection Standard Treatment Standard Waiver Worksheet

Fill out this worksheet for each discharge point in which use of this waiver is sought.

Name of Receiving Water at Discharge Point: Ù·´»¿¼ Þ®±±µ

Drainage Area of Receiving Water at Discharge Point (square miles): ïíòï

2. The impervious area is less than or equal to ten (10) acres.

Enter the new/expanded impervious area (acres):

Guidance: The ten (10) acre treatment requirement applies to only new impervious created since July 4, 2005.

3. A downstream analysis is conducted that indicates extreme ﬂood control is not necessary for the site.

Has adequate conveyance from the site to the discharge point been veriﬁed? Yes No

Has supporng informaon (e.g. narrave descripon, calculaons, modeling) been included? Yes No

Note: These waivers are applied per receiving water.

For addional informaon please go to the Vermont Stormwater Management Manual, Volume 1, Secon 1.1.2, Page 1-11 Version: 4/10 Project Name: Bethel BHF 0241(38) Discharge Point: S/N002 Grass Treatment Channel (O-3) Grass Treatment Channel #1

Line Treatment Standards Indicate the treatment standards met for the site area draining to this practice: 1 WQv ¨ 2 Rev ¨ This practice automatically meets Rev if you have met the WQv treatment standards 3 Cpv ¨ 4 Qp10 ¨ { Grass channels are not typically appropriate to provide Cpv, Qp10 or Qp100 except under ideal conditions. 5 Qp100 ¨

Modified Curve Number Modified CN*

6 What is the modified curve number (CN) for both on and off-site areas draining to this facility? 88

Water Quality Volume (WQv) WQv (Cubic Feet)

7 Provide the WQv for both on and off-site area draining to this facility (from WQv worksheets)? 2759

WQ Peak (Cfs)

8 What is the peak discharge rate associated with the WQ storm? 0.9

Feasibility (2.7.5.A) Response Attachment location BHF_0241(38)_Attachment3- 9 Is the maximum longitudinal slope of the channel 4% or less? YES Modeling.pdf

Conveyance (2.7.5.B) Response Attachment location BHF_0241(38)_Attachment3- 10 Is the peak velocity for the 1-year storm non-erosive? YES Modeling.pdf

BHF_0241(38)_Attachment3- 11 Are the channel slopes less than or equal to the 2:1 maximum? YES Modeling.pdf BHF_0241(38)_Attachment3- 12 Does the channel safely convey the 10-year storm with a minimum of 6 inches of freeboard? YES Modeling.pdf BHF_0241(38)_Attachment3- 13 Was the Manning's n value adjusted for the depth of water in the channel for larger storm events? YES Modeling.pdf

Pretreatment (2.7.5.C) Response Attachment location BHF_0241(38)_Attachment3- 14 Has pre-treatment been provided for non-rooftop runoff? YES Modeling.pdf

Treatment (2.7.5.D) Channel Width (Feet) 15 What is the bottom width of the channel? (no greater than 8 feet, but no less than 2 feet) 4

Response Attachment location BHF_0241(38)_Attachment3- 16 Is the average residence time of the WQv peak discharge at least 10 minutes? YES Modeling.pdf BHF_0241(38)_Attachment3- 17 Is the velocity of the WQv peak discharge less than 1 foot/second? YES Modeling.pdf BHF_0241(38)_Attachment3- 18 Is the depth of the WQv peak discharge 4 inches or less? YES Modeling.pdf BHF_0241(38)_Attachment3- 19 Were check dams used to meet the requisite treatment design criteria? NO Modeling.pdf

Cold Climate Design Considerations (2.7.5.G) Response Attachment location

20 Have the potential impacts of Vermont's severe winter climate been addressed in your design? NO N/A

SouthwestGrassChannel_O-3.xls Grass Channel: Cpv, Qp10 and Qp100 Page 2

Channel Protection Treatment Standard (Cpv) Response

21 Check which detention time standard must be used, based on the fisheries designation of the receiving water: ¨ 12 hours for cold water

¨ 24 hours for warm water

Response Attachment location

22 Did you use the Storage Volume Estimation Method? If yes, skip to Line 25.* yes / no *Please review the guidance sheet "Channel Protection Storage Volume Estimation" and attach the specified information. This method is not appropriate if more than a one subwatershed drains to the practice. Using the center of mass detention time calculated by a hydrologic model that accounts for pond routing is the preferred method.

23 What storage volume (cubic feet) necessary to meet the Channel Protection Standard?

24 What is the calculated average release rate (cfs)?

25 What is the controlled peak release rate (cfs) during the 1-year storm as indicated by the model?

Overbank Flood Protection Treatment Standard (Qp10) Response Attachment location

25 Have you demonstrated that Qp10 post is less than or equal to Qp10 pre at the discharge point?* yes / no *Please include runoff and routing calculations of the 10-year storm event.

Extreme Flood Protection Treatment Standard (Qp100) Response Attachment location

26 Have you demonstrated that Qp100 post is less than or equal to Qp100 pre at the discharge point?* yes / no *Please include runoff and routing calculations of the 100-year storm event.

*Grass channels provide rate-based treatment and must be designed to provide 10 minutes of residence time for the peak WQ discharge (a 0.9 inch storm). Traditional methods underestimate the volume and rate of runoff for storms of less than 2 inches. Modified curve numbers must be used. Because this practice is rate-based, both on and off-site water reaching the grass channel must be included in the calculations. This additional water will affect the velocity and residence time of the water in the channel. The average residence time for the peak discharge corresponds to the residence time calculated at the peak/maximum velocity, which is reported as the minimum residence time. Attachment location: Please indicate the specific location (i.e. appendix, page, plan sheet) where the requisite support documentation has been provided within the application.

SouthwestGrassChannel_O-3.xls BETHEL BHF 0241(38)

DRY SWALE

1/16/2017

Spreadsheet Design Compute Water Quality Volume, WQv ( )( )( ) = 12 P = 0.9 90% rainfall event (0.9 inches across VT) Rv = 0.412 Volumetric runoff coefficient equal to: [0.05 + 0.009(I)] A = 1.54 Site area (ac) MSTN LEVEL 22 + MSTN LEVEL 16 Imp Area 0.62 (ac) MSTN LEVEL 23 + MSTN LEVEL 17 I = 40.26 Whole number percent of impervious cover at the site Qa = 0.371 Min WQv 0.2 Standard Min Greater of Qa or Min WQv = 0.371 WQv = 0.048 Water quality volume (ac-ft) WQv = 2075 Water quality volume (cu. ft)

Recharge Volume, Rev Volume Based: ( )( )( ) = 12 HSG A = 0 AC HSG B = 1.54 AC HSG C = 0 AC HSG D = 0 AC

F = 0.25 Recharge factor (inches) A = 1.54 Site area (ac) I = 0.40 Site imperviousness (decimal percent) Fc = 0.250 Composite F determined from the percentages of HGCs

Rev = 0.013 ac-ft Rev = 563 cu. ft

Area Based: =( )( )( ) F = 0.250 Rechage factor (inches) A = 1.54 Site area (ac) I = 0.40 Site imperviousness (decimal percent)

Rea = 0.155 acres Rea = 6752 acres

Qa = 0.371 A = 1.54 AC P = 0.9 in CN = 92.9 EXISTING IMPERVIOUS AREA = 0.54 AC MSTN LEVEL 24 + MSTN LEVEL 15

EXISTING PERVIOUS AREA = 0.88 AC MSTN LEVEL 25 + MSTN LEVEL 16

PROPOSED IMPERVIOUS AREA = 0.62 AC MSTN LEVEL 26 + MSTN LEVEL 17

0.91 AC MSTN LEVEL 27 + MSTN LEVEL 18

NET INCREASE IN IMPERVIOUS AREA = 15 %

Compute Water Quality Volume, WQv

( )( )( ) = 12 P = 0.9 90% rainfall event (0.9 inches across VT) Rv = 0.41 Volumetric runoff coefficient equal to: [0.05 + 0.009(I)] A = 1.54 Site area (ac) I = 40.26 Whole number percent of impervious cover at the site

WQv = 0.05 Water quality volume (ac-ft) Channel Size Based on Water Quality Volume Storm DESIGN 1 YR 10 YR

Assumed tc (10 mins Table 2.1 VT Stormwater Treatment Standards) tc = 0.17 hr tc = 0.17 tc = 0.17 hr Rainfall, in inches - 90% rainfall event (0.9 inches across VT) P = 0.9 in P = 2.3 hr P = 3.7 in Drainage Area A = 1.54 ac A = 1.54 in A = 1.54 ac Impervious cover at the site IMP = 0.62 ac IMP = 0.62 ac IMP = 0.62 ac I, Whole Number Percentage I = 40.26 I = 40.26 ac I = 40.26 Rv, Volumetric runoff coefficient equal to: [0.05 + 0.009(I)] Rv = 0.41 Rv = 0.41 Rv = 0.41 Runoff volume in inches Qa = 0.371 in Qa = 0.948 in Qa = 1.524 in Minimum Qa Qa = 0.200 in Qa = 0.200 in Qa = 0.200 in Design Qa Qa = 0.371 in Qa = 0.948 in Qa = 1.524 in Curve number CN = 93 CN = 84 CN = 76 Corresponding initial abstraction from TR-55 (Table 4-1) Ia = 0.151 Ia = 0.381 Ia = 0.632 Compute Ia/P Ia/P = 0.17 Ia/P = 0.17 Ia/P = 0.17 Read unit peak discharge (VT Stormwater Mgmt Manual Appendix D6 (Fig. D.11) qu = 790 qu = 790 qu = 790 Qwq calculation (Qwq = qu x A x Qa/640) Qwq = 0.7 cfs Qwq = 1.8 cfs Qwq = 2.9 cfs

Base width b = 4.00 ft b = 4.00 ft b = 4.00 ft Side slope (1:__) z = 2.00 ft z = 2.00 ft z = 2.00 ft Channel Slope S = 4.0% S = 4.0% S = 4.0% Peak discharge Q = 0.7 cfs Q = 1.8 cfs Q = 2.9 cfs Velocity V = 0.7 ft/s V = 1.0 ft/s V = 1.3 ft/s Wetted perimeter P = 5.04 ft P = 5.63 ft P = 6.05 ft Cross sectional area A = 1.04 sf A = 1.73 sf A = 2.25 sf Hydraulic radius R = 0.21 ft R = 0.31 ft R = 0.37 ft Depth y = 0.23 ft y = 0.37 ft y = 0.46 ft Manning's n (VT Stormwater Mgmt Manual Appendix D7, Figure D.14) n = 0.15 * n = 0.13 n = 0.12 *assume n = .15 first *V must be <1 ft/s *design+6in

WQv = 2075 cf 49.0 min Soil Depth = 2.5 ft Gravel Depth = 0.5 ft

df = 3 ft

hf = 1 ft k (sand) = 3.5 ft/day

tf = 1.67 days

Minimum swale surface area (WQv)(df)/[(k)(hf+df)(tf)] A = 266.2 sq ft Determine minimum channel length (L = A / b) L = 67 ft BETHEL BHF 0241(38)

SOUTHWEST GRASS LINED CHANNEL

1/17/2017

Spreadsheet Design Compute Water Quality Volume, WQv ( )( )( ) = 12 P = 0.9 90% rainfall event (0.9 inches across VT) Rv = 0.07 Volumetric runoff coefficient equal to: [0.05 + 0.009(I)] A = 3.8 Site area (ac) MSTN LEVEL 7 + MSTN LEVEL 1 Imp Area 0.10 (ac) MSTN LEVEL 8 + MSTN LEVEL 2 I = 2.63 Whole number percent of impervious cover at the site Qa = 0.066 Min WQv 0.2 Standard Min Greater of Qa or Min WQv = 0.2 WQv = 0.063 Water quality volume (ac-ft) WQv = 2759 Water quality volume (cu. ft)

Recharge Volume, Rev Volume Based: ( )( )( ) = 12 HSG A = 0 AC HSG B = 3.8 AC HSG C = 0 AC HSG D = 0 AC

F = 0.25 Recharge factor (inches) A = 3.8 Site area (ac) I = 0.03 Site imperviousness (decimal percent) Fc = 0.250 Composite F determined from the percentages of HGCs

Rev = 0.002 ac-ft Rev = 91 cu. ft

Area Based: =( )( )( ) F = 0.250 Rechage factor (inches) A = 3.8 Site area (ac) I = 0.03 Site imperviousness (decimal percent)

Rea = 0.025 acres Rea = 1089 acres 1089.009

Qa = 0.2 A = 3.8 AC P = 0.9 in CN = 88.1 EXISTING IMPERVIOUS AREA = 0.16 AC MSTN LEVEL 3 + MSTN LEVEL 9

EXISTING PERVIOUS AREA = 3.65 AC MSTN LEVEL 4 + MSTN LEVEL 10

PROPOSED IMPERVIOUS AREA = 0.19 AC MSTN LEVEL 5 + MSTN LEVEL 11

PROPOSED PERVIOUS AREA = 3.61 AC MSTN LEVEL 6 + MSTN LEVEL 12

NET INCREASE IN IMPERVIOUS AREA = 19 %

Compute Water Quality Volume, WQv

( )( )( ) = 12 P = 0.9 90% rainfall event (0.9 inches across VT) Rv = 0.10 Volumetric runoff coefficient equal to: [0.05 + 0.009(I)] A = 3.80 Site area (ac) I = 5.00 Whole number percent of impervious cover at the site

WQv = 0.03 Water quality volume (ac-ft) Channel Size Based on Water Quality Volume Storm DESIGN 1 YR 10 YR

Assumed tc (10 mins Table 2.1 VT Stormwater Treatment Standards) tc = 0.17 hr tc = 0.17 hr tc = 0.17 hr Rainfall, in inches - 90% rainfall event (0.9 inches across VT) P = 0.9 in P = 2.3 in P = 3.7 in Drainage Area A = 3.8 ac A = 3.8 ac A = 3.8 ac Impervious cover at the site IMP = 0.10 ac IMP = 0.10 ac IMP = 0.10 ac I, Whole Number Percentage I = 2.63 I = 2.63 I = 2.63 Rv, Volumetric runoff coefficient equal to: [0.05 + 0.009(I)] Rv = 0.07 Rv = 0.07 Rv = 0.07 Runoff volume in inches Qa = 0.063 in Qa = 0.170 in Qa = 0.274 in Minimum Qa Qa = 0.200 in Qa = 0.200 in Qa = 0.200 in Design Qa Qa = 0.200 in Qa = 0.200 in Qa = 0.274 in Curve number CN = 88 CN = 64 CN = 51 Corresponding initial abstraction from TR-55 (Table 4-1) Ia = 0.273 Ia = 1.125 Ia = 1.922 Compute Ia/P Ia/P = 0.30 Ia/P = 0.49 Ia/P = 0.52 Read unit peak discharge (VT Stormwater Mgmt Manual Appendix D6 (Fig. D.11) qu = 760 qu = 430 qu = 400 Qwq calculation (Qwq = qu x A x Qa/640) Qwq = 0.9 cfs Qwq = 0.5 cfs Qwq = 0.7 cfs

Base width b = 4.00 ft b = 4.00 ft b = 4.00 ft Side slope (1:__) z = 2.00 ft z = 2.00 ft z = 2.00 ft Channel Slope S = 2.0% S = 2.0% S = 2.0% Peak discharge Q = 0.9 cfs Q = 0.5 cfs Q = 0.7 cfs Velocity V = 0.6 ft/s V = 0.5 ft/s V = 0.5 ft/s Wetted perimeter P = 5.45 ft P = 5.03 ft P = 5.25 ft Cross sectional area A = 1.51 sf A = 1.03 sf A = 1.28 sf Hydraulic radius R = 0.28 ft R = 0.20 ft R = 0.24 ft Depth y = 0.32 ft y = 0.23 ft y = 0.28 ft Manning's n (VT Stormwater Mgmt Manual Appendix D7, Figure D.14) n = 0.15 * n = 0.15 n = 0.15 *assume n = .15 first *V must be <1 ft/s *design+6in

Determine minimum channel length (L = V x t) L = 358 ft