Optimal Stormwater Management Plan Alternatives: A Demonstration Project in Three Upper Charles River Communities Final Report December 2009 Prepared for: United States Environmental Protection Agency – New England One Congress Street, Suite 1100 Boston, MA 02114 and Massachusetts Department of Environmental Protection One Winter Street Boston, MA 02108 Prepared by: Tetra Tech, Inc. 10306 Eaton Place, Suite 340 Fairfax, VA 22030 Optimal Stormwater Management Plan Alternatives in Three Upper Charles River Communities ii Optimal Stormwater Management Plan Alternatives in Three Upper Charles River Communities Contents Executive Summary.1 2 Data for Developing HRUs and Management Categories.3 Design Specifications of BMPs.2 Biofiltration and Bioinfiltration.3 Water Quality Swales.6 Retention/Detention Ponds.4 Costs of BMPs.12 3 Developing Hydrologic Response Units (HRUs).1 Generating HRU Maps.2 Estimating HRU Loading Rates.3 Generating HRU Time Series. 16 4 Developing Management Categories.1 Design Requirements for BMPs.5 Water Quality Swales (Wet).2 Developing Management Categories.19 5 Optimizing BMP Implementation Alternatives.1 Tabulating HRUs into Management Categories.2 BMP Setup without Optimization.3 The Optimization Problem.1 Refined Optimization Setup.4 BMP Optimization Scenario I.3 Required Level of Treatment for Scenario I.5 BMP Optimization Setup Scenario II.2 Scenario II Setup.3 Scenario II Results.4 Required Level of Treatment for Scenario II.6 BMP Optimization Setup Scenario III.1 Scenario III Setup.2 Scenario III Results.3 Required Level of Treatment for Scenario III.54 iii Optimal Stormwater Management Plan Alternatives in Three Upper Charles River Communities 5.7 Summary and Conclusions. HRU Maps in the Three Charles River Communities.
Management Category Maps in the Three Upper Charles River Communities. Summary of area and imperviousness of the three communities (Charles River portion) selected for the pilot project. Design parameters for infiltration type BMPs. Design parameters for biofiltration.
Design parameters for water quality swales. The design parameters for porous pavement. The design parameters for the gravel wetland. Design parameters for a wet retention pond.
Construction cost information for several BMPs. Summary of HRU groups to be generated for the three Upper Charles River communities. Phosphorus load export rates for Bellingham, Franklin, and Milford. Site restrictions for potential BMPs.
Categorizing management categories on the basis of site conditions. Summary of phosphorus removal for various BMP sizing schemes in Bellingham. Summary of phosphorus removal for various BMP sizing schemes in Franklin. Summary of phosphorus removal for various BMP sizing schemes in Milford.
Tabulation of impervious HRUs into management categories in Bellingham for Scenario I setup (Unit: acres). Tabulation of impervious HRUs into management categories in Franklin for Scenario I setup (Unit: acres). Tabulation of impervious HRUs into management categories in Milford for Scenario I setup (Unit: acres). Summary of optimal solutions identified for Scenario I in the three communities.
The level of treatment needed in Bellingham for Scenario I. The level of treatment needed in Franklin for Scenario I. The level of treatment needed in Milford for Scenario I. Tabulation of impervious HRUs into onsite and neighborhood management categories in Bellingham for Scenario II setup (Unit: acres).
Tabulation of impervious HRUs into onsite and neighborhood management categories in Franklin for Scenario II setup (Unit: acres). Tabulation of impervious HRUs into onsite and neighborhood management categories in Milford for Scenario II setup (Unit: acres).43 iv Optimal Stormwater Management Plan Alternatives in Three Upper Charles River Communities Table 5-14. Summary of optimal solutions identified for Scenario II in all three communities. The level of treatment needed in Bellingham for Scenario II.
The level of treatment needed in Franklin for Scenario II. The level of treatment needed in Milford for Scenario II. Near-optimal solutions identified for Scenario III as compared to those for Scenario II in the three communities. The level of treatment needed in Bellingham for Scenario III.
The level of treatment needed in Franklin for Scenario III. The level of treatment needed in Milford for Scenario III. Summary of scenario setups in the three Upper Charles River communities 58 Table 5-23. Summary of total costs for the BMP scenarios.
The general concept of the pilot project. Imperviousness in the three Upper Charles River communities of Bellingham, Franklin, and Milford. Land uses in the three Upper Charles River communities of Bellingham, Franklin, and Milford. Soils in the three Upper Charles River communities of Bellingham, Franklin, and Milford.
Typical cross sections for infiltration type of BMPs. Typical cross sections for biofiltration. Typical designs for the water quality swale. Typical cross-sectional design for porous pavement.
Cross-sectional design for the gravel wetland. The design for a wet retention pond. Routing of HRU to management category and Scenario I setup in the Upper Charles River communities. BMPDSS optimization results for Scenario I setup in Bellingham.
BMPDSS optimization results for Scenario I setup in Franklin. BMPDSS optimization results for Scenario I setup in Milford. The HMU subbasins in the communities of Bellingham, Franklin, and Milford. Scenario II setup in the three Upper Charles River communities.
BMPDSS optimization results for Scenario II setup in Bellingham. BMPDSS optimization results for Scenario II setup in Franklin. BMPDSS optimization results for Scenario II setup in Milford. Schematic for Scenario III setup in the three Upper Charles River communities.
BMPDSS optimization results for Scenario III setup in Bellingham. BMPDSS optimization results for Scenario III setup in Franklin. BMPDSS optimization results for Scenario III setup in Milford.53 v Optimal Stormwater Management Plan Alternatives in Three Upper Charles River Communities Executive Summary The Lower Charles River Phosphorus Total Maximum Daily Load (TMDL) sets stormwater phosphorus load reduction targets for communities in the Charles River watershed, Massachusetts. With the upcoming renewal of the National Pollutant Discharge Elimination System (NPDES) permits for municipal separate storm sewer systems (MS4 permits), it is anticipated that each community will need to develop stormwater management plans to meet its respective stormwater phosphorus load reduction requirements.
Managing stormwater runoff from large urban/suburban landscapes is a complex process in which managers must consider numerous factors, including site conditions, source areas, space limitations, and the widely varying pollutant removal efficiencies of available best management practices (BMPs). One way to systematically consider the many important factors when developing a stormwater management plan is by using optimization techniques. This project is a demonstration study of using optimization techniques to help identify cost-effective solutions to meet the phosphorus TMDL reduction targets in three Upper Charles River communities: Bellingham, Franklin, and Milford. The project involved extensive geographic information system data analysis and regular interaction with representatives from the three communities.
Hydrologic response units (HRUs) were generated to derive runoff and water quality time series from a variety of source areas that represent different land use and soil conditions. Runoff time series were routed to management categories, which correspond to BMPs that are applicable to certain estimated site conditions. The communities provided valuable insights into the probability of locating neighborhood BMPs and better understanding of locally known site constraints. Three scenarios were developed in conjunction with local officials to make the scenarios as real world as possible for each community.
Such efforts included quality checking of land use data, site constraints, management concepts, hydrologic management units, and scenario setup. The Best Management Practices Decision Support System (BMPDSS) program was used to set up and optimize three BMP implementation alternatives. In Scenario I, runoff from all impervious HRUs was completely treated by onsite BMPs. In Scenario II, runoff from the public right-of-way and highly constrained parcels deemed unlikely for onsite BMPs was treated by neighborhood BMPs, and runoff from the remaining impervious areas was still treated by onsite BMPs.
In Scenario III, runoff from the public right-of-way was treated by neighborhood BMPs, and runoff from both pervious and impervious HRUs was treated by onsite BMPs. For comparison purposes, a benchmark scenario with no optimization was also set up, and all BMPs in that scenario were sized to provide a fixed level of treatment to the inflow (called the uniform sizing strategy). Overall the scenarios made no differentiation between regulatory mechanisms, and phosphorus loadings from both the MS4 and the privately owned sources were taken into account. In addition, only structural BMPs were used for the analysis in this project.
The optimization processes helped identify the most cost-effective BMP implementation alternative for each of the three BMP setup scenarios in each community. The BMP construction costs were used during the optimization process. For all three communities, the near-optimal BMP implementation alternative identified through the optimization vi Optimal Stormwater Management Plan Alternatives in Three Upper Charles River Communities process was able to significantly reduce the total project cost for meeting the TMDL reduction targets when compared to the uniform sizing strategy. This was consistently observed for all three BMP setup scenarios in each community.
For example, the uniform-sizing-strategy-estimated costs for the three communities were about two to three times those of the Scenario III near-optimal BMP implementation alternative total costs. Overall, the results demonstrate that the optimization techniques are able to help identify more cost-effective BMP implementation alternatives in a community, and there could be significant reductions in project costs by adopting the optimization techniques during TMDL implementation. The optimization results also show that BMPs with higher efficiencies in phosphorus removal, placed in areas of high phosphorus loads, tend to have larger sizes in the near-optimal BMP implementation scenario. The resulting sizes of the different BMPs identified in the near-optimal BMP implementation scenario also provides a starting point for developing a trading framework for phosphorus-reduction credits.
vii Optimal Stormwater Management Plan Alternatives in Three Upper Charles River Communities 1 Introduction The Lower Charles River Phosphorus Total Maximum Daily Load (TMDL) (MassDEP and USEPA 2007) was developed for reducing algae levels in the Lower Charles River and for attaining Massachusetts Surface Water Quality Standards. The TMDL implementation plan provides estimations of existing phosphorus loads and necessary load reductions by land use categories, as well as the overall reduction needed by each community in the Charles River watershed. When implementing the TMDL, each community is faced with the key question of how to achieve the needed reductions with available best management practice (BMP) technologies given the distribution of land use, impervious cover, and soil type within the community. Developing an answer to that question requires analysis of land characteristics, source areas, site constraints, BMP effectiveness, and BMP costs, the combinations of which would be difficult to numerate.
For example, phosphorus loadings from different source areas and the pollutant-removal effectiveness of different BMPs are known to vary considerably. Meanwhile, the optimization techniques can account for the many aforementioned variables in a community and efficiently search through the TMDL implementation plan alternatives, resulting in more cost-effective choices. The goal of this project was to investigate cost-effective stormwater management alternatives for a community to achieve needed phosphorus reductions. The communities need insight into what is the optimal mix of BMP technologies and level of control for their portion of the Charles River watershed.
As a demonstration study, the project objectives were to develop optimized, planning-level-scale stormwater management alternatives for the communities of Bellingham, Franklin, and Milford, Massachusetts, and to identify the overall level of stormwater control in each community for meeting the Lower Charles River Phosphorus TMDL targets. The primary tools employed in this project include the ArcGIS geographic information system (GIS); the U. Environmental Protection Agency’s (EPA’s) Stormwater Management Model (SWMM) (Rossman 2007); and the Prince George’s County, Maryland’s Best Management Practice Decision Support System (BMPDSS) model (Tetra Tech 2005). The BMPDSS model had been previously calibrated and validated using monitored data from the University of New Hampshire Stormwater Center (Tetra Tech 2008).
A general concept of the project is presented in Figure 1-1. As shown, in each community, the watershed data of land use, imperviousness, and soils information are used to categorize the community into various hydrologic response units (HRUs). Each HRU has its unique flow and water quality time series, which was generated using the SWMM. Management categories were developed in each community on the basis of BMP design specifications and the watershed data of imperviousness, soil type, depth to bedrock, depth to water table, and available space to install a BMP.
