Evaluating the Performance of over 110 Distributed Source Control Projects: Challenges, Methods, and Results

Status In 2019, ALCOSAN adopted a Clean Water Plan (CWP) to improve and protect the water quality of the region's streams and rivers by controlling separate and combined sewer overflows (CSOs). The CWP resulted from a Federal Consent Decree (CD) to comply with the Clean Water Act and the United States Environmental Protection Agency's (EPA's) CSO Control Policy. The CWP is made up of several 'pillars,' distinct programs of differing scope to meet the goals of the CWP. One pillar includes the prevention of excess water from entering the sewer system through its green stormwater infrastructure and source control (GSI/SC) program. ALCOSAN supports GSI/SC in the region through its award-winning $100M Green Revitalization of Our Waterways (GROW) grant program. GROW covers up to 85% of the costs of eligible source control projects completed by municipalities. Eligible source project types include GSI, infiltration/ inflow reduction, direct stream inflow removal, sewer separation, and system optimization. To ensure awards are provided to the most cost-effective projects, ALCOSAN completes a rigorous application review process. This includes detailed hydrologic and hydraulic (H&H) modeling with EPA's Storm Water Management Model (SWMM) to estimate the volume and sewer overflow reduction benefits of the projects. Awarded projects are also monitored before and after construction to evaluate the actual performance of the funded projects (Figures 1 and 2). Since 2016, 88% of ALCOSAN's customer municipalities have participated in the GROW program. GROW has awarded $77 million in grant funding towards approximately 203 projects throughout their service area (Figure 3). Based on a comparison with pre-CWP conditions, these projects are anticipated to reduce sewer overflows by 240 million gallons per year. Currently, 114 projects (and counting) are complete, and new projects continue to be evaluated as they are completed. Methodology ALCOSAN performs a rigorous performance evaluation process of completed projects based on as-built drawings, photos, pipe videos, rainfall and flow monitoring results and analyses, regional groundwater levels, H&H modeling, calculations, and scaling and extrapolation procedures (Figures 4-7). The flow reduction achieved by each project in the typical year is estimated, and the reliability of that estimate is assessed as either low, medium, or high. The reliability categories are based on multiple factors, including the quality, duration, location, and timing of the flow monitoring; climatological, groundwater, and rainfall characteristics during the pre-and post-construction monitoring periods; the results of flow data analyses; the reasonableness of the estimated performance in relation to the scale of the project; and engineering judgment (Table 1). As part of its regulatory compliance, the CD requires that ALCOSAN report a summary of the flow reductions achieved by completed GROW projects to all its customer municipalities every 60 days. ALCOSAN must also request any new information on SC projects from its customer municipalities every year from 2020 to 2025 and develop an annual report documenting and summarizing the information received, including an assessment of the flow reduction achieved by the SC projects submitted. This presentation will describe the GROW grant program, review the performance evaluation process in detail including an example evaluation for each GSI/SC project type, outline the challenges in estimating performance under extremely variable pre- and post-construction monitoring conditions, and provide a summary of the estimated performance of over 110 GROW projects including project types that perform most efficiently for flow and sewer overflow reduction. The paper and presentation will also discuss lessons learned for applicability in helping to address wet weather issues in other communities.

Findings Highlights of the results are summarized below and in the following figures.
• The most significant issues evaluating project performance include: o changes in the monitoring area apart from those made for the GROW project (e.g., development/redevelopment and additional sewer infrastructure/repair work), o a monitoring area that is too large to adequately distinguish project impacts, o inadequate or deficient monitoring data (e.g., too short, too far apart, not synoptic) o significantly different climatic conditions between the pre- and post-construction monitoring periods, and o difficulties extrapolating to typical/average year conditions.
• The performance evaluation has found that: o 89% of the completed projects are estimated to be overperforming or performing as anticipated (+/- 25%) based on the review of the grant application (Table 2) o I/I and DSIR projects dominate in terms of cost efficiency from a flow reduction standpoint, with average costs of $0.03 and $0.02/gal/yr, respectively (Figure 8). o SS and DSIR projects dominate in terms of cost efficiency from an sewer overflow (CSO and SSO) reduction perspective, with average costs of $0.10 and $0.12/gal/yr, respectively (Figure 9). o In total, the projects are estimated to be removing over 1.2 billion gallons per year and reducing overflows by over 225 million gallons per year. o Cumulatively through the end of 2025, the projects removed an estimated 7.4 billion gallons of extraneous flow, enough to fill over 11,000 Olympic-size pools (Figure 10).