Stormwater Analysis Report

Transcription

1 Stormwater Analysis Report Solar Panel Array Temple Street (Rt. 14) West Boylston, MA February 24, 216 SITE Prepared for: West Boylston Municipal Lighting Plant 4 Crescent Street West Boylston, MA 1583 Prepared by: Whitman & Bingham Associates, LLC 51 Mechanic Street Leominster, MA 1453 Tel. (978) Fax (978)

2 TABLE OF CONTENTS 1.) Drainage Narrative 1.1) Introduction 1.2) Method of Analysis 1.3) Soils 1.4) Curve Numbers 1.5) Design Criteria 1.6) Hydrologic Descriptions 1.6.1) Pre-Development Conditions 1.6.2) Post-Development Conditions 1.7) Conclusions 2.) Hydrological Calculations Figures Figure 1 Soils Maps Figure 2 Pre-Development Watershed Delineation Figure 3 Post-Development Watershed Delineation

3 1. DRAINAGE NARRATIVE

4 1. NARRATIVE 1.1 INTRODUCTION On behalf of West Boylston Municipal Lighting Plant, Whitman & Bingham Associates, LLC has prepared this stormwater analysis for a proposed Solar Panel Array Development on Temple Street (Rt. 14) in West Boylston, MA. The Site is located in the eastern section of West Boylston on Temple Street (Rt. 14), south of Oak Avenue. The project Site is 15. acres. The site is the location of a capped landfill. The proposed plans include the development of a Solar Panel Array, approximately 1.5 MW AC in size, on the existing capped landfill. The purpose of this stormwater analysis is to compare the predevelopment conditions to the post development conditions resulting from the change in surface conditions. The stormwater pre- and post-construction is tributary to a system of wetlands and a stream to the south of the site and to the existing drainage in Temple Street to the north of the site. The stormwater calculations have been completed to comply with the intent of Massachusetts DEP s Stormwater Management Policy guidelines, and with the criteria of the local permitting agencies of the Town of West Boylston.

5 1.2 METHOD OF ANALYSIS The enclosed hydrologic calculations utilize the runoff estimating techniques developed by the USDA Soil Conservation Service (SCS). The following publications were used in the preparation of this report: 1. Urban Hydrology for Small Watersheds 1 2. National Engineering Handbook, Hydrology, Section 4 (NEH-4) 2 Using SCS publications and other texts on surface water hydrology, in conjunction with drainage software HydroCAD developed by Applied Microcomputer Systems 3, Whitman & Bingham Associates, LLC has calculated stormwater hydrographs, which provide the peak rates of runoff, for the Site. The drainage software program HydroCAD calculates runoff hydrographs using the same basic methodology as the TR-2 program entitled Computer Programs for Project Formulations Hydrology, Technical Release Number 2 developed by SCS. The total Site area was subdivided into two subwatersheds for both the existing conditions and the proposed conditions. For each subwatershed a series of hydrologic parameters were estimated and entered into the HydroCAD program. For this application of HydroCAD the times of concentration (Tc) were computed by using the Upland Method which calculates the Tc utilizing land use and slope in conjunction with other land use variables. The Tc for a specific sub-watershed represents the time required for a droplet of water to travel from the most hydraulically distant point of the subwatershed to the design point. It is computed by summing the times it takes the water to travel through the different components of the subwatershed drainage system. As a result of urbanization of an area (i.e., increase of impervious area), the time of concentration will be decreased since velocity of overland flow will be increased. As the time of concentration is decreased for a subwatershed, the peak flow rate will be increased for that particular subwatershed. The "upland method" estimates more accurate Tc s than other available methods.

6 1.3 SOILS As part of the Soil Conservation Service s (SCS) hydrologic methodology, soils are classified as categories A through D, with A being very pervious (i.e. gravels, etc.) and D being very impervious (i.e. clays, muck, peat, etc.). The four (4) soil classifications as defined by SCS are: Group A Group B Group C Group D Generally have low runoff potential and have high infiltration rates. This group includes mainly sands and gravels consisting of deep, well to excessively drained media (sand, loamy sand, or sandy loam). Soils in this classification have moderate infiltration rates and contain well drained soils with moderately fine to moderately coarse textures (silt loam or loam). These soils have low infiltration rates and generally consist of a soil layer that prevents downward movement of water to the water table (sandy, clay, loam). Soils under this group have high runoff potential since they are chiefly clay soils with high expansive capability. High water table, clay layers, nearly impervious material are all associated with this classification (clay loam, silty clay loam, sand clay, silty clay, or clay). Soils throughout the Site were classified by the Soil Conservation Service (SCS) as the following soil groups: Soil Group/Symbol Hinckley loamy sand/245c & 245D Windsor loamy sand/255b & 255C Hydrologic Class A A

7 1.4 RUNOFF CURVE NUMBERS There are several primary factors that affect the volume of runoff that is generated from a particular land use. These include surface treatment, cover type, and antecedent runoff condition, or how wet the soils are prior to the start of the rainfall event. Hydraulic condition represents the effects of cover type and treatment on infiltration and runoff. Density of plant cover and forest litter heavily influences this condition. Good hydraulic condition indicates a low run-off potential due to heavy ground cover while poor hydraulic condition indicates poor cover (i.e. bare soil, etc.) and is indicative of comparatively high runoff potential. The SCS uses a curve number (CN) in the calculations to represent the combination of hydraulic condition and soil type. As the curve number increases the amount of expected runoff is also increased. A curve number of 3 indicates a low potential for runoff while a number of 9 indicates a high potential. Curve numbers were selected for the various soil types and land uses found on the site in accordance with the following table. Weighted curve numbers for each sub-watershed were determined by land area of the different soil types. The SCS runoff curve numbers used in all watershed modeling contained in this report are based upon the following Hydrologic Soil Group and their following land uses: SURFACE TYPE HYDROLOGICAL SOIL GROUP A B C D CURVE NUMBERS Pavement/Roofs/Impervious Surfaces Pasture (Good) Wooded (Good) Meadow Gravel Diveway/Road Orchard (25% Tree Coverage) Residential 1 Acre Lots (2% Imp.) Row Crops, straight row

8 1.5 DESIGN CRITERIA This stormwater system analysis was developed utilizing as the design storm s rainfall distribution a Type III, 24-hour tropical storm as developed by SCS. Type III represents Gulf of Mexico and Atlantic Coastal areas where tropical storms yield large 24-hour rainfall amounts. The storm frequencies and the corresponding rainfall depths were compiled from "Technical Paper No.4, Rainfall Frequency Atlas of the United States for Duration s from 3 minutes to 24 hours and Return Periods from 1 to 1 years." The specific storm depths that apply to the West Boylston area are as follows: Storm Frequency (years) Rainfall Depth Rainfall-runoff-routing calculations were completed for the 2, 1, 25 and 1 -year, 24-hour storms and the results are provided in Section 2..

9 1.6 HYDROLOGICAL DESCRIPTIONS PRE-DEVELOPMENT As mentioned previously, the subject site is the location of a capped landfill. The site is bounded by Temple Street (Rt. 14) to the east, Pierce Street to the north, property of the New England Power Company to the west, and property of the Department of Conservation and Recreation to the south. The topography of the portion of the subject Site where the development is proposed ranges from 482 (along the northern project boundary) to 436 (adjacent to the southwest corner of array). The majority of the site drains towards the south towards the wetland system and existing stream on the abutting property of the Department of Conservation and Recreation. The remainder of the site drains to the north towards the drainage in Templet Street (Rt. 14). For purpose of this analysis, the Site was analyzed as two watersheds. The watersheds as outlined below, and can be located on the attached plan labeled Pre-Development Watershed Delineation. Subcatchment 1S: Subcatchment 2S consists of 1.98± acres of land tributary to the north to the drainage in Temple Street (Rt. 14), of which.32± acres is impervious,.16± acres is gravel, 1.46± acres is meadow, and.4± acres is wooded. Subcatchment 2S: Subcatchment 2S consists of 9.17± acres of land tributary to the wetlands and existing stream to the south of the subject site, of which.14± acres is impervious,.1± acres is gravel, 8.12± acres is meadow, and.81± acres is wooded POST-DEVELOPMENT The proposed project consists of the construction of an approximate 1.5 Mw AC Solar Panel Array which will utilize a gravel driveway off of Temple Street (Rt. 14) for access. The panels' racking system will be supported by ballasts that will sit on top of the capped landfill. The supports will create an increase in impervious surface cover which will create a negligible increase in the peak rate of runoff. No alteration to the existing topography is proposed as part of the development. The post-development watersheds are tributary to the same design points as described above. (Refer to Post-Development Watershed Delineation plan for the proposed improvements and sub-watersheds.)

10 1.7 CONCLUSIONS The proposed stormwater analysis was completed to meet the series of design objectives or criteria established for this location. The peak rates of runoff at the selected design points are outlined below: Peak Rate of of Subcatchment 1S Storm Event Existing Conditions Proposed Conditions 2 yr. storm 1 yr. storm 25 yr. storm 1 yr. storm Peak Rate of of Subcatchment 2S Storm Event Existing Conditions Proposed Conditions 2 yr. storm 1 yr. storm 25 yr. storm 1 yr. storm As shown in the tables above, the stormwater analysis has been completed so that no negative impact, relative to the marginal increase in peak runoff rates, will occur to abutting properties.

11 2. HYDROLOGICAL CALCULATIONS

12 1S-Pre 1S-Post Area Trib. to North (Pre) Area Trib. to North (Post) 2S-Pre 2S-Post Area Trib. to South (Off-site Wetlands) (Pre) Area Trib. to South (Off-site Wetlands) (Post) Subcat Reach Pond Link Drainage Diagram for West Boylston Landfill Solar Array

13 West Boylston Landfill Solar Array Type III 24-hr 2-Year Storm Event Rainfall=3." Page 2 span=.-3. hrs, dt=.5 hrs, 61 points by SCS TR-2 method, UH=SCS Reach routing by Dyn-Stor-Ind method - Pond routing by Dyn-Stor-Ind method Subcatchment 1S-Post: Area Trib. to North (Post) Area=86,379 sf Depth=.2" Flow Length=446' Tc=18.6 min CN=45 =.1 cfs.4 af Subcatchment 1S-Pre: Area Trib. to North (Pre) Area=86,379 sf Depth=.2" Flow Length=446' Tc=18.6 min CN=45 =.1 cfs.4 af Subcatchment 2S-Post: Area Trib. to South (Off-site Wetland Area=399,391 sf Depth=." Flow Length=698' Tc=18.4 min CN=33 =. cfs. af Subcatchment 2S-Pre: Area Trib. to South (Off-site Wetlands Area=399,391 sf Depth=." Flow Length=698' Tc=18.4 min CN=32 =. cfs. af Total Area = ac Volume =.8 af Average Depth =."

14 West Boylston Landfill Solar Array Type III 24-hr 2-Year Storm Event Rainfall=3." Page 3 Subcatchment 1S-Post: Area Trib. to North (Post) = hrs, Volume=.4 af, Depth=.2" by SCS TR-2 method, UH=SCS, Span=.-3. hrs, dt=.5 hrs Type III 24-hr 2-Year Storm Event Rainfall=3." Area (sf) CN Description 14, Paved parking & roofs 6, Gravel roads, HSG A 63,65 3 Meadow, non-grazed, HSG A 1,11 3 Woods, Good, HSG A Ballasts 86, Weighted Average Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) Sheet Flow, Grass: Dense n=.24 P2= 3." Shallow Concentrated Flow, Shallow Concentrated Flow, Total Subcatchment 1S-Post: Area Trib. to North (Post) Hydrograph.6.1 cfs Flow Type III 24-hr 2-Year Storm Event Rainfall=3." Area=86,379 sf Volume=.4 af Depth=.2" Flow Length=446' Tc=18.6 min CN=

15 West Boylston Landfill Solar Array Type III 24-hr 2-Year Storm Event Rainfall=3." Page 4 Hydrograph for Subcatchment 1S-Post: Area Trib. to North (Post)

16 West Boylston Landfill Solar Array Type III 24-hr 2-Year Storm Event Rainfall=3." Page 5 Subcatchment 1S-Pre: Area Trib. to North (Pre) = hrs, Volume=.4 af, Depth=.2" by SCS TR-2 method, UH=SCS, Span=.-3. hrs, dt=.5 hrs Type III 24-hr 2-Year Storm Event Rainfall=3." Area (sf) CN Description 14,74 98 Paved parking & roofs 6, Gravel roads, HSG A 63,74 3 Meadow, non-grazed, HSG A 1,652 3 Woods, Good, HSG A 86, Weighted Average Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) Sheet Flow, Grass: Dense n=.24 P2= 3." Shallow Concentrated Flow, Shallow Concentrated Flow, Total Subcatchment 1S-Pre: Area Trib. to North (Pre) Hydrograph.6.1 cfs Flow Type III 24-hr 2-Year Storm Event Rainfall=3." Area=86,379 sf Volume=.4 af Depth=.2" Flow Length=446' Tc=18.6 min CN=

17 West Boylston Landfill Solar Array Type III 24-hr 2-Year Storm Event Rainfall=3." Page 6 Hydrograph for Subcatchment 1S-Pre: Area Trib. to North (Pre)

18 West Boylston Landfill Solar Array Type III 24-hr 2-Year Storm Event Rainfall=3." Page 7 Subcatchment 2S-Post: Area Trib. to South (Off-site Wetlands) (Post) =. hrs, Volume=. af, Depth=." by SCS TR-2 method, UH=SCS, Span=.-3. hrs, dt=.5 hrs Type III 24-hr 2-Year Storm Event Rainfall=3." Area (sf) CN Description 3, Paved parking & roofs 7, Gravel roads, HSG A 379,812 3 Meadow, non-grazed, HSG A 8, Ballasts 399, Weighted Average Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) Sheet Flow, Grass: Dense n=.24 P2= 3." Shallow Concentrated Flow, Shallow Concentrated Flow, Shallow Concentrated Flow, Total 1 Subcatchment 2S-Post: Area Trib. to South (Off-site Wetlands) (Post) Hydrograph Flow Type III 24-hr 2-Year Storm Event Rainfall=3." Area=399,391 sf Volume=. af Depth=." Flow Length=698' Tc=18.4 min CN=33. cfs

19 West Boylston Landfill Solar Array Type III 24-hr 2-Year Storm Event Rainfall=3." Page 8 Hydrograph for Subcatchment 2S-Post: Area Trib. to South (Off-site Wetlands) (Post)

20 West Boylston Landfill Solar Array Type III 24-hr 2-Year Storm Event Rainfall=3." Page 9 Subcatchment 2S-Pre: Area Trib. to South (Off-site Wetlands) (Pre) =. hrs, Volume=. af, Depth=." by SCS TR-2 method, UH=SCS, Span=.-3. hrs, dt=.5 hrs Type III 24-hr 2-Year Storm Event Rainfall=3." Area (sf) CN Description 5, Paved parking & roofs 4, Gravel roads, HSG A 35,224 3 Woods, Good, HSG A 353,729 3 Meadow, non-grazed, HSG A 399, Weighted Average Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) Sheet Flow, Grass: Dense n=.24 P2= 3." Shallow Concentrated Flow, Shallow Concentrated Flow, Shallow Concentrated Flow, Total 1 Subcatchment 2S-Pre: Area Trib. to South (Off-site Wetlands) (Pre) Hydrograph Flow Type III 24-hr 2-Year Storm Event Rainfall=3." Area=399,391 sf Volume=. af Depth=." Flow Length=698' Tc=18.4 min CN=32. cfs

21 West Boylston Landfill Solar Array Type III 24-hr 2-Year Storm Event Rainfall=3." Page 1 Hydrograph for Subcatchment 2S-Pre: Area Trib. to South (Off-site Wetlands) (Pre)

22 West Boylston Landfill Solar Array Type III 24-hr 1-Year Storm Event Rainfall=4.5" Page 11 span=.-3. hrs, dt=.5 hrs, 61 points by SCS TR-2 method, UH=SCS Reach routing by Dyn-Stor-Ind method - Pond routing by Dyn-Stor-Ind method Subcatchment 1S-Post: Area Trib. to North (Post) Area=86,379 sf Depth=.3" Flow Length=446' Tc=18.6 min CN=45 =.18 cfs.49 af Subcatchment 1S-Pre: Area Trib. to North (Pre) Area=86,379 sf Depth=.3" Flow Length=446' Tc=18.6 min CN=45 =.18 cfs.49 af Subcatchment 2S-Post: Area Trib. to South (Off-site Wetland Area=399,391 sf Depth=.1" Flow Length=698' Tc=18.4 min CN=33 =.2 cfs.7 af Subcatchment 2S-Pre: Area Trib. to South (Off-site Wetlands Area=399,391 sf Depth=." Flow Length=698' Tc=18.4 min CN=32 =.1 cfs.2 af Total Area = ac Volume =.17 af Average Depth =.6"

23 West Boylston Landfill Solar Array Type III 24-hr 1-Year Storm Event Rainfall=4.5" Page 12 Subcatchment 1S-Post: Area Trib. to North (Post) = hrs, Volume=.49 af, Depth=.3" by SCS TR-2 method, UH=SCS, Span=.-3. hrs, dt=.5 hrs Type III 24-hr 1-Year Storm Event Rainfall=4.5" Area (sf) CN Description 14, Paved parking & roofs 6, Gravel roads, HSG A 63,65 3 Meadow, non-grazed, HSG A 1,11 3 Woods, Good, HSG A Ballasts 86, Weighted Average Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) Sheet Flow, Grass: Dense n=.24 P2= 3." Shallow Concentrated Flow, Shallow Concentrated Flow, Total Subcatchment 1S-Post: Area Trib. to North (Post) Hydrograph Flow cfs Type III 24-hr 1-Year Storm Event Rainfall=4.5" Area=86,379 sf Volume=.49 af Depth=.3" Flow Length=446' Tc=18.6 min CN=

24 West Boylston Landfill Solar Array Type III 24-hr 1-Year Storm Event Rainfall=4.5" Page 13 Hydrograph for Subcatchment 1S-Post: Area Trib. to North (Post)

25 West Boylston Landfill Solar Array Type III 24-hr 1-Year Storm Event Rainfall=4.5" Page 14 Subcatchment 1S-Pre: Area Trib. to North (Pre) = hrs, Volume=.49 af, Depth=.3" by SCS TR-2 method, UH=SCS, Span=.-3. hrs, dt=.5 hrs Type III 24-hr 1-Year Storm Event Rainfall=4.5" Area (sf) CN Description 14,74 98 Paved parking & roofs 6, Gravel roads, HSG A 63,74 3 Meadow, non-grazed, HSG A 1,652 3 Woods, Good, HSG A 86, Weighted Average Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) Sheet Flow, Grass: Dense n=.24 P2= 3." Shallow Concentrated Flow, Shallow Concentrated Flow, Total Subcatchment 1S-Pre: Area Trib. to North (Pre) Hydrograph Flow cfs Type III 24-hr 1-Year Storm Event Rainfall=4.5" Area=86,379 sf Volume=.49 af Depth=.3" Flow Length=446' Tc=18.6 min CN=

26 West Boylston Landfill Solar Array Type III 24-hr 1-Year Storm Event Rainfall=4.5" Page 15 Hydrograph for Subcatchment 1S-Pre: Area Trib. to North (Pre)

27 West Boylston Landfill Solar Array Type III 24-hr 1-Year Storm Event Rainfall=4.5" Page 16 Subcatchment 2S-Post: Area Trib. to South (Off-site Wetlands) (Post) = hrs, Volume=.7 af, Depth=.1" by SCS TR-2 method, UH=SCS, Span=.-3. hrs, dt=.5 hrs Type III 24-hr 1-Year Storm Event Rainfall=4.5" Area (sf) CN Description 3, Paved parking & roofs 7, Gravel roads, HSG A 379,812 3 Meadow, non-grazed, HSG A 8, Ballasts 399, Weighted Average Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) Sheet Flow, Grass: Dense n=.24 P2= 3." Shallow Concentrated Flow, Shallow Concentrated Flow, Shallow Concentrated Flow, Total Flow Subcatchment 2S-Post: Area Trib. to South (Off-site Wetlands) (Post) Type III 24-hr 1-Year Storm Event Rainfall=4.5" Area=399,391 sf Volume=.7 af Depth=.1" Flow Length=698' Tc=18.4 min CN= Hydrograph cfs

28 West Boylston Landfill Solar Array Type III 24-hr 1-Year Storm Event Rainfall=4.5" Page 17 Hydrograph for Subcatchment 2S-Post: Area Trib. to South (Off-site Wetlands) (Post)

29 West Boylston Landfill Solar Array Type III 24-hr 1-Year Storm Event Rainfall=4.5" Page 18 Subcatchment 2S-Pre: Area Trib. to South (Off-site Wetlands) (Pre) = hrs, Volume=.2 af, Depth=." by SCS TR-2 method, UH=SCS, Span=.-3. hrs, dt=.5 hrs Type III 24-hr 1-Year Storm Event Rainfall=4.5" Area (sf) CN Description 5, Paved parking & roofs 4, Gravel roads, HSG A 35,224 3 Woods, Good, HSG A 353,729 3 Meadow, non-grazed, HSG A 399, Weighted Average Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) Sheet Flow, Grass: Dense n=.24 P2= 3." Shallow Concentrated Flow, Shallow Concentrated Flow, Shallow Concentrated Flow, Total Flow Subcatchment 2S-Pre: Area Trib. to South (Off-site Wetlands) (Pre) Type III 24-hr 1-Year Storm Event Rainfall=4.5" Area=399,391 sf Volume=.2 af Depth=." Flow Length=698' Tc=18.4 min CN= Hydrograph cfs

30 West Boylston Landfill Solar Array Type III 24-hr 1-Year Storm Event Rainfall=4.5" Page 19 Hydrograph for Subcatchment 2S-Pre: Area Trib. to South (Off-site Wetlands) (Pre)

31 West Boylston Landfill Solar Array Type III 24-hr 25-Year Storm Event Rainfall=5.3" Page 2 span=.-3. hrs, dt=.5 hrs, 61 points by SCS TR-2 method, UH=SCS Reach routing by Dyn-Stor-Ind method - Pond routing by Dyn-Stor-Ind method Subcatchment 1S-Post: Area Trib. to North (Post) Area=86,379 sf Depth=.54" Flow Length=446' Tc=18.6 min CN=45 =.46 cfs.89 af Subcatchment 1S-Pre: Area Trib. to North (Pre) Area=86,379 sf Depth=.54" Flow Length=446' Tc=18.6 min CN=45 =.46 cfs.89 af Subcatchment 2S-Post: Area Trib. to South (Off-site Wetland Area=399,391 sf Depth=.7" Flow Length=698' Tc=18.4 min CN=33 =.8 cfs.54 af Subcatchment 2S-Pre: Area Trib. to South (Off-site Wetlands Area=399,391 sf Depth=.5" Flow Length=698' Tc=18.4 min CN=32 =.5 cfs.38 af Total Area = ac Volume =.271 af Average Depth =.15"

32 West Boylston Landfill Solar Array Type III 24-hr 25-Year Storm Event Rainfall=5.3" Page 21 Subcatchment 1S-Post: Area Trib. to North (Post) = hrs, Volume=.89 af, Depth=.54" by SCS TR-2 method, UH=SCS, Span=.-3. hrs, dt=.5 hrs Type III 24-hr 25-Year Storm Event Rainfall=5.3" Area (sf) CN Description 14, Paved parking & roofs 6, Gravel roads, HSG A 63,65 3 Meadow, non-grazed, HSG A 1,11 3 Woods, Good, HSG A Ballasts 86, Weighted Average Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) Sheet Flow, Grass: Dense n=.24 P2= 3." Shallow Concentrated Flow, Shallow Concentrated Flow, Total Subcatchment 1S-Post: Area Trib. to North (Post) Hydrograph Flow cfs Type III 24-hr 25-Year Storm Event Rainfall=5.3" Area=86,379 sf Volume=.89 af Depth=.54" Flow Length=446' Tc=18.6 min CN=

33 West Boylston Landfill Solar Array Type III 24-hr 25-Year Storm Event Rainfall=5.3" Page 22 Hydrograph for Subcatchment 1S-Post: Area Trib. to North (Post)

34 West Boylston Landfill Solar Array Type III 24-hr 25-Year Storm Event Rainfall=5.3" Page 23 Subcatchment 1S-Pre: Area Trib. to North (Pre) = hrs, Volume=.89 af, Depth=.54" by SCS TR-2 method, UH=SCS, Span=.-3. hrs, dt=.5 hrs Type III 24-hr 25-Year Storm Event Rainfall=5.3" Area (sf) CN Description 14,74 98 Paved parking & roofs 6, Gravel roads, HSG A 63,74 3 Meadow, non-grazed, HSG A 1,652 3 Woods, Good, HSG A 86, Weighted Average Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) Sheet Flow, Grass: Dense n=.24 P2= 3." Shallow Concentrated Flow, Shallow Concentrated Flow, Total Subcatchment 1S-Pre: Area Trib. to North (Pre) Hydrograph Flow cfs Type III 24-hr 25-Year Storm Event Rainfall=5.3" Area=86,379 sf Volume=.89 af Depth=.54" Flow Length=446' Tc=18.6 min CN=

35 West Boylston Landfill Solar Array Type III 24-hr 25-Year Storm Event Rainfall=5.3" Page 24 Hydrograph for Subcatchment 1S-Pre: Area Trib. to North (Pre)

36 West Boylston Landfill Solar Array Type III 24-hr 25-Year Storm Event Rainfall=5.3" Page 25 Subcatchment 2S-Post: Area Trib. to South (Off-site Wetlands) (Post) = hrs, Volume=.54 af, Depth=.7" by SCS TR-2 method, UH=SCS, Span=.-3. hrs, dt=.5 hrs Type III 24-hr 25-Year Storm Event Rainfall=5.3" Area (sf) CN Description 3, Paved parking & roofs 7, Gravel roads, HSG A 379,812 3 Meadow, non-grazed, HSG A 8, Ballasts 399, Weighted Average Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) Sheet Flow, Grass: Dense n=.24 P2= 3." Shallow Concentrated Flow, Shallow Concentrated Flow, Shallow Concentrated Flow, Total Flow Subcatchment 2S-Post: Area Trib. to South (Off-site Wetlands) (Post) Type III 24-hr 25-Year Storm Event Rainfall=5.3" Area=399,391 sf Volume=.54 af Depth=.7" Flow Length=698' Tc=18.4 min CN= Hydrograph.8 cfs

37 West Boylston Landfill Solar Array Type III 24-hr 25-Year Storm Event Rainfall=5.3" Page 26 Hydrograph for Subcatchment 2S-Post: Area Trib. to South (Off-site Wetlands) (Post)

38 West Boylston Landfill Solar Array Type III 24-hr 25-Year Storm Event Rainfall=5.3" Page 27 Subcatchment 2S-Pre: Area Trib. to South (Off-site Wetlands) (Pre) = hrs, Volume=.38 af, Depth=.5" by SCS TR-2 method, UH=SCS, Span=.-3. hrs, dt=.5 hrs Type III 24-hr 25-Year Storm Event Rainfall=5.3" Area (sf) CN Description 5, Paved parking & roofs 4, Gravel roads, HSG A 35,224 3 Woods, Good, HSG A 353,729 3 Meadow, non-grazed, HSG A 399, Weighted Average Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) Sheet Flow, Grass: Dense n=.24 P2= 3." Shallow Concentrated Flow, Shallow Concentrated Flow, Shallow Concentrated Flow, Total Subcatchment 2S-Pre: Area Trib. to South (Off-site Wetlands) (Pre) Hydrograph.55.5 cfs Flow Type III 24-hr 25-Year Storm Event Rainfall=5.3" Area=399,391 sf Volume=.38 af Depth=.5" Flow Length=698' Tc=18.4 min CN=

39 West Boylston Landfill Solar Array Type III 24-hr 25-Year Storm Event Rainfall=5.3" Page 28 Hydrograph for Subcatchment 2S-Pre: Area Trib. to South (Off-site Wetlands) (Pre)

40 West Boylston Landfill Solar Array Type III 24-hr 1-Year Storm Event Rainfall=6.6" Page 29 span=.-3. hrs, dt=.5 hrs, 61 points by SCS TR-2 method, UH=SCS Reach routing by Dyn-Stor-Ind method - Pond routing by Dyn-Stor-Ind method Subcatchment 1S-Post: Area Trib. to North (Post) Area=86,379 sf Depth=1.5" Flow Length=446' Tc=18.6 min CN=45 =1.21 cfs.174 af Subcatchment 1S-Pre: Area Trib. to North (Pre) Area=86,379 sf Depth=1.5" Flow Length=446' Tc=18.6 min CN=45 =1.21 cfs.174 af Subcatchment 2S-Post: Area Trib. to South (Off-site Wetland Area=399,391 sf Depth=.28" Flow Length=698' Tc=18.4 min CN=33 =.44 cfs.216 af Subcatchment 2S-Pre: Area Trib. to South (Off-site Wetlands Area=399,391 sf Depth=.23" Flow Length=698' Tc=18.4 min CN=32 =.3 cfs.179 af Total Area = ac Volume =.743 af Average Depth =.4"

41 West Boylston Landfill Solar Array Type III 24-hr 1-Year Storm Event Rainfall=6.6" Page 3 Subcatchment 1S-Post: Area Trib. to North (Post) = hrs, Volume=.174 af, Depth= 1.5" by SCS TR-2 method, UH=SCS, Span=.-3. hrs, dt=.5 hrs Type III 24-hr 1-Year Storm Event Rainfall=6.6" Area (sf) CN Description 14, Paved parking & roofs 6, Gravel roads, HSG A 63,65 3 Meadow, non-grazed, HSG A 1,11 3 Woods, Good, HSG A Ballasts 86, Weighted Average Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) Sheet Flow, Grass: Dense n=.24 P2= 3." Shallow Concentrated Flow, Shallow Concentrated Flow, Total Subcatchment 1S-Post: Area Trib. to North (Post) Hydrograph 1.21 cfs Flow 1 Type III 24-hr 1-Year Storm Event Rainfall=6.6" Area=86,379 sf Volume=.174 af Depth=1.5" Flow Length=446' Tc=18.6 min CN=

42 West Boylston Landfill Solar Array Type III 24-hr 1-Year Storm Event Rainfall=6.6" Page 31 Hydrograph for Subcatchment 1S-Post: Area Trib. to North (Post)

43 West Boylston Landfill Solar Array Type III 24-hr 1-Year Storm Event Rainfall=6.6" Page 32 Subcatchment 1S-Pre: Area Trib. to North (Pre) = hrs, Volume=.174 af, Depth= 1.5" by SCS TR-2 method, UH=SCS, Span=.-3. hrs, dt=.5 hrs Type III 24-hr 1-Year Storm Event Rainfall=6.6" Area (sf) CN Description 14,74 98 Paved parking & roofs 6, Gravel roads, HSG A 63,74 3 Meadow, non-grazed, HSG A 1,652 3 Woods, Good, HSG A 86, Weighted Average Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) Sheet Flow, Grass: Dense n=.24 P2= 3." Shallow Concentrated Flow, Shallow Concentrated Flow, Total Subcatchment 1S-Pre: Area Trib. to North (Pre) Hydrograph 1.21 cfs Flow 1 Type III 24-hr 1-Year Storm Event Rainfall=6.6" Area=86,379 sf Volume=.174 af Depth=1.5" Flow Length=446' Tc=18.6 min CN=

44 West Boylston Landfill Solar Array Type III 24-hr 1-Year Storm Event Rainfall=6.6" Page 33 Hydrograph for Subcatchment 1S-Pre: Area Trib. to North (Pre)

45 West Boylston Landfill Solar Array Type III 24-hr 1-Year Storm Event Rainfall=6.6" Page 34 Subcatchment 2S-Post: Area Trib. to South (Off-site Wetlands) (Post) = hrs, Volume=.216 af, Depth=.28" by SCS TR-2 method, UH=SCS, Span=.-3. hrs, dt=.5 hrs Type III 24-hr 1-Year Storm Event Rainfall=6.6" Area (sf) CN Description 3, Paved parking & roofs 7, Gravel roads, HSG A 379,812 3 Meadow, non-grazed, HSG A 8, Ballasts 399, Weighted Average Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) Sheet Flow, Grass: Dense n=.24 P2= 3." Shallow Concentrated Flow, Shallow Concentrated Flow, Shallow Concentrated Flow, Total Flow Subcatchment 2S-Post: Area Trib. to South (Off-site Wetlands) (Post) Hydrograph.44 cfs Type III 24-hr 1-Year Storm Event Rainfall=6.6" Area=399,391 sf Volume=.216 af Depth=.28" Flow Length=698' Tc=18.4 min CN=

46 West Boylston Landfill Solar Array Type III 24-hr 1-Year Storm Event Rainfall=6.6" Page 35 Hydrograph for Subcatchment 2S-Post: Area Trib. to South (Off-site Wetlands) (Post)

47 West Boylston Landfill Solar Array Type III 24-hr 1-Year Storm Event Rainfall=6.6" Page 36 Subcatchment 2S-Pre: Area Trib. to South (Off-site Wetlands) (Pre) = hrs, Volume=.179 af, Depth=.23" by SCS TR-2 method, UH=SCS, Span=.-3. hrs, dt=.5 hrs Type III 24-hr 1-Year Storm Event Rainfall=6.6" Area (sf) CN Description 5, Paved parking & roofs 4, Gravel roads, HSG A 35,224 3 Woods, Good, HSG A 353,729 3 Meadow, non-grazed, HSG A 399, Weighted Average Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) Sheet Flow, Grass: Dense n=.24 P2= 3." Shallow Concentrated Flow, Shallow Concentrated Flow, Shallow Concentrated Flow, Total Subcatchment 2S-Pre: Area Trib. to South (Off-site Wetlands) (Pre) Hydrograph Flow cfs Type III 24-hr 1-Year Storm Event Rainfall=6.6" Area=399,391 sf Volume=.179 af Depth=.23" Flow Length=698' Tc=18.4 min CN=

48 West Boylston Landfill Solar Array Type III 24-hr 1-Year Storm Event Rainfall=6.6" Page 37 Hydrograph for Subcatchment 2S-Pre: Area Trib. to South (Off-site Wetlands) (Pre)

49 FIGURES

50 FIGURE 1 SCS SOIL MAP

51 71 46' 7'' W Hydrologic Soil Group Worcester County, Massachusetts, Northeastern Part (Temple Street, West Boylston) 71 45' 48'' W 42 21' 12'' N ' 12'' N 42 2' 54'' N 42 2' 54'' N ' 7'' W N Map Scale: 1:2,7 if printed on A portrait (8.5" x 11") sheet. Meters Feet Map projection: Web Mercator Corner coordinates: WGS84 Edge tics: UTM Zone 19N WGS ' 48'' W Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 2/4/216 Page 1 of 4

52 Hydrologic Soil Group Worcester County, Massachusetts, Northeastern Part (Temple Street, West Boylston) MAP LEGEND MAP INFORMATION Area of Interest (AOI) Area of Interest (AOI) Soils Soil Rating Polygons A A/D B B/D C C/D D Not rated or not available Soil Rating Lines A A/D B B/D C C/D D Not rated or not available Soil Rating Points A A/D B B/D C C/D D Not rated or not available Water Features Streams and Canals Transportation Rails Interstate Highways US Routes Major Roads Local Roads Background Aerial Photography The soil surveys that comprise your AOI were mapped at 1:2,. Warning: Soil Map may not be valid at this scale. Enlargement of maps beyond the scale of mapping can cause misunderstanding of the detail of mapping and accuracy of soil line placement. The maps do not show the small areas of contrasting soils that could have been shown at a more detailed scale. Please rely on the bar scale on each map sheet for map measurements. Source of Map: Natural Resources Conservation Service Web Soil Survey URL: Coordinate System: Web Mercator (EPSG:3857) Maps from the Web Soil Survey are based on the Web Mercator projection, which preserves direction and shape but distorts distance and area. A projection that preserves area, such as the Albers equal-area conic projection, should be used if more accurate calculations of distance or area are required. This product is generated from the USDA-NRCS certified data as of the version date(s) listed below. Soil Survey Area: Worcester County, Massachusetts, Northeastern Part Survey Area Data: Version 1, Sep 28, 215 Soil map units are labeled (as space allows) for map scales 1:5, or larger. Date(s) aerial images were photographed: 28, 214 Sep 12, 214 Sep The orthophoto or other base map on which the soil lines were compiled and digitized probably differs from the background imagery displayed on these maps. As a result, some minor shifting of map unit boundaries may be evident. Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 2/4/216 Page 2 of 4

53 Hydrologic Soil Group Worcester County, Massachusetts, Northeastern Part Temple Street, West Boylston Hydrologic Soil Group Hydrologic Soil Group Summary by Map Unit Worcester County, Massachusetts, Northeastern Part (MA613) Map unit symbol Map unit name Rating Acres in AOI Percent of AOI 12C Chatfield-Hollis-Rock outcrop complex, 3 to 15 percent slopes 245C Hinckley loamy sand, 8 to 15 percent slopes 245D Hinckley loamy sand, 15 to 25 percent slopes 255B 255C Windsor loamy sand, 3 to 8 percent slopes Windsor loamy sand, 8 to 15 percent slopes B..2% A % A % A % A % Totals for Area of Interest % Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 2/4/216 Page 3 of 4

54 Hydrologic Soil Group Worcester County, Massachusetts, Northeastern Part Temple Street, West Boylston Description Hydrologic soil groups are based on estimates of runoff potential. Soils are assigned to one of four groups according to the rate of water infiltration when the soils are not protected by vegetation, are thoroughly wet, and receive precipitation from long-duration storms. The soils in the United States are assigned to four groups (A, B, C, and D) and three dual classes (A/D, B/D, and C/D). The groups are defined as follows: Group A. Soils having a high infiltration rate (low runoff potential) when thoroughly wet. These consist mainly of deep, well drained to excessively drained sands or gravelly sands. These soils have a high rate of water transmission. Group B. Soils having a moderate infiltration rate when thoroughly wet. These consist chiefly of moderately deep or deep, moderately well drained or well drained soils that have moderately fine texture to moderately coarse texture. These soils have a moderate rate of water transmission. Group C. Soils having a slow infiltration rate when thoroughly wet. These consist chiefly of soils having a layer that impedes the downward movement of water or soils of moderately fine texture or fine texture. These soils have a slow rate of water transmission. Group D. Soils having a very slow infiltration rate (high runoff potential) when thoroughly wet. These consist chiefly of clays that have a high shrink-swell potential, soils that have a high water table, soils that have a claypan or clay layer at or near the surface, and soils that are shallow over nearly impervious material. These soils have a very slow rate of water transmission. If a soil is assigned to a dual hydrologic group (A/D, B/D, or C/D), the first letter is for drained areas and the second is for undrained areas. Only the soils that in their natural condition are in group D are assigned to dual classes. Rating Options Aggregation Method: Dominant Condition Component Percent Cutoff: None Specified Tie-break Rule: Higher Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 2/4/216 Page 4 of 4

55 FIGURE 2 PRE-DEVELOPMENT WATERSHED DELINEATION

56

57 FIGURE 3 POST-DEVELOPMENT WATERSHED DELINEATION

58

59 1 Urban Hydrology for Small Watersheds (Technical Release Number 55); Engineering Division, United States Dept. of Agriculture, Soil Conservation Service (Jan. 1975). 2 National Engineering Handbook Section 4-Hydrology ; United States Dept. of Agriculture, Soil Conservation Service (March 1985) 3 HydroCAD Drainage software developed by Applied Microcomputer, Page Hill Road, Chocorua, NH; Tel. (63) 927- RAIN Copyrights (version 7.1)