1. Modeling the Benefits of LID Stormwater Techniques for Developable Parcels in the Nashoba Brook Subwatershed Bob Hartzel, CLM, CPESC Senior Water Resources Scientist

2.  Project funded through:  Provide planning to aid 5 subwatershed towns in promoting LID as part of master planning, project permitting and development of bylaws. Organization for the Assabet River Project Overview / Goals

3.  Develop model to evaluate the suitability and priority of developable parcels in the Nashoba Brook subwatershed for LID stormwater techniques.  Estimate the benefits and costs of LID stormwater management compared to “conventional” stormwater management. Vine Brook Nashoba Brook

4. Low Impact Development (LID) An ecosystem-based approach to land development and stormwater management. Goal: Mimic pre-development site hydrology

7. Conventional Development Centralized Pipe and Pond Control

8. LID Development Disconnected Decentralized Distributed Conservation Minimization Soil Amendments Open Drainage Infiltration BMPs Vegetative BMPs Rain Barrels Pollution Prevention Multiple Systems

9. LID Subdivision Cluster Only Subdivision Conventional Subdivision Pre-development Watershed LID Cluster Non-LID Cluster Non-LID Non-Cluster Undeveloped Effectiveness of Environmental Site Design Modeling: Model Scenarios Partridgeberry Place Case Study (Ipswich, MA)

10. Effectiveness of Environmental Site Design Development Comparison Results Compared to Pre-development Watershed: LID/Cluster Subdivision: 2 to 11 % more runoff Cluster Subdivision: 3 to 18 % more runoff Conventional Subdivision: 13 to 45 % more runoff Partridgeberry Place Case Study (Ipswich, MA)

11. Residential LID Site

12. LID Stormwater Controls Rain Garden Treatment Train Approach Raingarden Cell Storm Drain System Raingarden Cell Flow Path Grass Swale Grass Filter Strip

13. Low Impact Development Stormwater Controls Bioretention Raingardens/barrels Porous surfacesBioretention

14. Raingardens A bowl-shaped garden designed to capture and absorb stormwater.

15. Bioretention Cell Similar to raingarden, more highly engineered: underdrain/riser pipe gravel bed engineered soils

16. Street Edge Alternatives (SEA) Functional Landscape Reduced Impervious Area 98% Stormwater volume reduction for 2-year storm

17. “SEA” Street: Maximized space for filtration, recharge and landscape elements

20. Watershed Communities Town % of watershed Acton43% Westford35% Littleton14% Carlisle5% Concord3%

21. Subwatershed Delineation

22. A. “Developable Parcel” Inventory / Map (Not Retrofits) Unimproved lots > minimum lot size requirement Municipally owned property that is for sale. Parcels protected though open space preservation, deed restrictions, etc. = Not Developable Any portion of a parcel within wetlands = Not Developable Task 1: Evaluate Parcels Most Suitable for LID Inventory developed with 5 town planning departments

23. Developable Parcels Map  198 Parcels  11% of land in watershed  Summary Statistics: Size Range: 0.3 – 150 acres 50% of land comprised by largest 8% of parcels 178 residential parcels 12 commercial parcels 8 industrial parcels

24. Task 1: Evaluate Parcels Most Suitable for LID B. Develop Model to Rank Site Suitability / Priority S = Soils D = Distance to Receiving Water B = Shallow Bedrock Imp = Impervious Cover Analysis PWS = Lands Critical to Public Water Supply Quality and Quantity LID Priority Ranking = 2 (S) + 1 (D) + 1 (Imp) - 1 (PWS) – 1 (B)

25. “…with proper design and maintenance, LID stormwater techniques can be used successfully at many sites with less than ideal initial conditions.”  Soil Amendments  Underdrains  Steep Slope Designs (Terraces, etc.)  “Not Enough Space”

26. A newly planted bioretention cell installed in the Dudley Pond watershed (Wayland, MA).

27. Lake Shirley Bioretention Cell

28. Lesson: Small is beautiful!

29. Terraced bio-infiltration system (Plymouth, MA) Lesson: Sloped areas can be put to work!

30. Soils A: Sand, loamy sand or sandy loam soils. High infiltration rates! B: Silt loam or loam. Moderate infiltration when fully wetted. C: Sandy clay loam. Poor infiltration when thoroughly wetted. D: Clay loam, silty clay loam, sandy clay, silty clay or clay. Highest runoff potential, very low infiltration when fully wetted. Hydrologic Soil Groups

31. Shallow Bedrock

32. Impervious Cover Assessment Total Subwatershed Imperviousness = 12.1%

33. Impervious Cover Assessment Total Subwatershed Imperviousness = 12.1%

34. Range = 5.9% - 20.2% Impervious Cover Assessment

35. Public Water Supply Protection  Public Water Supply Wells  Interim Wellhead Protection Areas  Zone 2 Wellhead Protection Areas Water quantity Drinking water quality concerns

36. Parcel Ranking

38. Parcel Ranking…Wetlands

39. Next Steps: Evaluate the Relative Benefits of LID Techniques A. Create “Standardized” Development Scenarios  LID  Conventional Development  Cluster / Open Space Development (Residential parcels only) B. Compare LID vs. Traditional Stormwater Mgt.  Water Quality / Quantity Benefits  Cost

40. Review Existing Municipal By-Laws and Regulations Review of bylaws and regulations:  Identify existing conflicts/overlaps relative to stormwater mgt.  Identify areas of recommended modification / revisions Review LID by-laws (and similar bylaws, regulations and policies) which have passed in MA and neighboring states.

41. Parcel Statistics: Choosing a “Representative” Parcel Median (50 th Percentile) Values:  Size: 0.9 Acres  % IMP: 8.4%

42. Examples: “Representative” Residential Parcels Size: ~0.9 acres Imperviousness: ~8%

43. Examples: “Representative” Commercial/Industrial Parcels Size: ~1.3 acres Imperviousness: ~30%

44. PRECIPITATION STORAGE INFILTRATION RUNOFF EVAPORATION SWMM (VOLUME) EVENT MEAN CONCENTRATION (QUALITY) LOAD = RUNOFF VOLUME X EMC Quantifying LID Benefits: Infiltration and Load Reduction

45. Modeling Hydrologic Budget: EPA’s SWMM INPUTS Precipitation: 57 years of Boston rainfall data Evaporation: data obtained from MassGIS Subwatersheds based on surface types: roofs, pavement, lawn, wooded, etc. Infiltration BMPs: drywells, bioinfiltration OUTPUTS Runoff totals from subwatersheds Precipitation/Runoff statistics

46. Event Mean Concentration: Total Suspended Solids (TSS)

47. Event Mean Concentration: Total Phosphorus (TP) !

48. Single Family Lot vs. Residential Subdivision Parcels with 1-4 buildable lots = “Single Family Lots” (138 parcels, 285 ac.) Parcels with 5+ buildable lots = “Residential Subdivisions” (40 parcels, 920 ac.)

49. Conceptual Single Family Lot: Conventional Development Runoff: 8.9 in/yr Infiltration: 28.1 in/yr TSS: 213 lb/ac/yr TP: 0.72 lb/ac/yr

50. Conceptual Single Family Lot: Low Impact Development Runoff: 1.9 in/yr Infiltration: 35.2 in/yr TSS: 68 lb/ac/yr TP: 0.27 lb/ac/yr Runoff: -7.0 in/yr Infiltration: +7.1 in/yr TSS: -145 lb/ac/yr (-68%) TP: -0.44 lb/ac/yr (-63%)

51. Conceptual Residential Subdivision: Conventional Development Runoff: 11.8 in/yr Infiltration: 25.2 in/yr TSS: 330 lb/ac/yr TP: 0.92 lb/ac/yr

52. Conceptual Residential Subdivision: Low Impact Development Runoff: 0.7 in/yr Infiltration: 36.5 in/yr TSS: 38.4 lb/ac/yr TP: 0.06 lb/ac/yr Runoff: -11.1 in/yr Infiltration: +11.3 in/yr TSS: -292 lb/ac/yr (-88%) TP: -0.86 lb/ac/yr (-93%)

53. Conceptual Commercial/Industrial: Conventional Development Runoff: 16.3 in/yr Infiltration: 20.8 in/yr TSS: 415 lb/ac/yr TP: 1.73 lb/ac/yr

54. Conceptual Residential Subdivision: Low Impact Development Runoff: 1.1 in/yr Infiltration: 36.5 in/yr TSS: 24 lb/ac/yr TP: 0.07 lb/ac/yr Runoff: -15.2 in/yr Infiltration: +15.7 in/yr TSS: -391 lb/ac/yr (-94%) TP: -1.66 lb/ac/yr (-96%)

55. LID Benefits: Infiltration The added infiltration from LID being applied to developable parcels may be as high as: … for the population of Acton, Littleton, and Westford (~51,500 people) 22 gal/person/day

56. 2 extra toilet flushes (1.6 gal each) per person per day… … for the population of Acton, Littleton, and Westford (~51,500 people) 1 5-minute shower (10 gal) per person per day… 1 dishwasher load (8 gal) per person per day… 22 gal/person/day = approximately… LID Benefits: Infiltration

57. LID Benefits: TSS … entering Nashoba Brook The reduction in weight of TSS from LID being applied to developable parcels may be as high as: 190 tons/year

58. LID Benefits: TSS 140 cubic yards of sand/sediment… entering Nashoba Brook each year 190 tons = approximately…

59. LID Benefits: TP … entering Nashoba Brook The reduction in weight of TP from LID being applied to developable parcels may be as high as: 1190 lbs/year

60. 1190 lbs/year of TP = approximately… ….growing per year in Nashoba Brook (and tributary ponds) *assuming 1 lb P : 1026 lb wet Phytoplankton, density Phytoplankton ~ density H 2 0 14,760 cu. ft. of algae

61. COST: LID vs. Conventional Stormwater

62. Thank you for your time!

63. Conventional Design Low Impact Design UnitsUnit Cost Qty.Total Qty.Total LANDSCAPING Item: Tree Removal 1 ac$9,150 0.8$7,320 0.3$2,745 Clearing/Grubbing 1 ac$7,500 0.9$6,750 0.38$2,850 Grass Seed/Sod 1 sy$6 3900$23,400 1328$7,968 Native Trees/Shrubs 1,2 ea$30 0$0 5$150 Soil Amendment 2 cy$51 0$0 12$627 Raingarden/Bioretention 2,3 sf$11 0$0 770$8,470 INFRASTRUCTURE/CONVEYANCE/STORAGE Item: Standard Asphalt Driveway 2 sy$10 94$940 0$0 Porous Pavement Driveway 2,3 sy$108 0$0 94$10,152 Drywell - (including inst.) 2 ea$1,500 0$0 1$1,500 TOTAL $38,410 $34,462 -10.3% Notes: Construction/Material costs only. Does not include maintenance or property values. 1. From PA DOT construction cost spreadsheet (ftp://ftp.dot.state.pa.us/public/Bureaus/design/Pub2 87/Pub%20287.pdf) 2. Geosyntec cost estimate data, past projects 3. "Evaluation of LID Best Management Practices (BMPs) Opportunities," Charles River Watershed Association Single Family Home

64. Residential Subdivision Conventional Design Low Impact Design UnitsUnit Cost Qty.Total Qty.Total LANDSCAPING Item: Tree Removal 1 ac$9,150 0.8$7,320 3.6$32,940 Clearing/Grubbing 1 ac$7,500 0.9$6,750 4.6$34,500 Grass Seed/Sod 1 sy$6 46800$280,800 15936$95,616 Native Trees/Shrubs (for bioretention areas) 1,2 ea$30 0$0 200$6,000 Soil Amendment 2 cy$51 0$0 148$7,525 Raingarden/Bioretention 2,3 sf$11 0$0 19100$210,100 INFRASTRUCTURE/CONVEYANCE/STORAGE Item: Standard Asphalt Driveway 2 sy$10 1130$11,300 0$0 Standard Asphalt Roadway 2 sy$20 4670$93,400 3090$61,800 Porous Pavement Driveway 2,3 sy$108 0$0 1130$122,040 Drywell - (including inst.) 2 ea$1,500 0$0 12$18,000 Catch Basins 1,2 ea$3,000 7$21,000 0$0 CPP Storm Drain Pipe 1 lf$75 1710$128,250 180$13,500 Vegetated Swale 2 sf$2 0$0 1840$3,680 Detention Pond 2,4 cy$15 2450$36,750 0$0 Outlet Structure 2 ea$1,500 1 0$0 TOTAL $587,070 $605,701 3.2%

65. Commercial / Industrial Conventional Design Low Impact Design Units Unit Cost Qty.Total Qty.Total LANDSCAPING Item: Tree Removal 1 ac$9,150 1.1$10,065 0.8$7,320 Clearing/Grubbing 1 ac$7,500 1.1$8,250 0.8$6,000 Grass Seed/Sod 1 sy$6 3390$20,340 1940$11,640 Native Trees/Shrubs (for bioretention areas) 1,2 ea$30 0$0 24$720 Soil Amendment 2 cy$51 0$0 18$916 Raingarden/Bioretention 2,3 sf$11 0$0 1800$19,800 INFRASTRUCTURE/CONVEYANCE/STORAGE Item: Standard Asphalt Parking 2 sy$10 1475$14,750 1100$11,000 Porous Pavement Parking 2,3 sy$108 0$0 370$39,960 Drywell - (including inst.) 2 ea$1,500 0$0 1$1,500 Catch Basins 1,2 ea$3,000 3$9,000 0$0 CPP Storm Drain Pipe 1 lf$75 325$24,375 0$0 Vegetated Swale 2 sf$2 0$0 470$940 Detention Pond 2,4 cy$15 340$5,100 0$0 Outlet Structure 2 ea$1,500 1 0$0 TOTAL $93,380 $99,796 6.9%

66. Costs: Literature Review Comparison