PROJECT: UIC Management Plan

Portland, Oregon

GSI worked with the City of Portland and another consulting firm in development of the Evaluation and Response guidelines portion of the UIC Management Plan. Specifically, GSI worked with the City to prepare the guideline for demonstrating groundwater protectiveness. Subsequently, GSI developed the groundwater protectiveness demonstration framework document, which provides a consistent, streamlined decision making framework for evaluating potential impacts to groundwater associated with the discharge of urban stormwater to UICs. As part of the demonstration, GSI developed a groundwater protectiveness demonstration tool (GWPD Tool) consisting of a fate and transport analysis model. Because a simplified method for modeling pollutant transport from stormwater entering UICs had not previously been developed, this approach and tool were developed in close coordination with the Oregon Department of Environmental Quality (DEQ) to ensure the effort met potential agency concerns. The groundwater protectiveness demonstration was used to obtain a No Further Action determination from DEQ for four noncompliant UICs because of concentration exceedances, and for more than 300 UICs where the GWPD Tool was used to demonstrate that UICs with a separation distance between 5 and 10 feet are protective of groundwater given the range of concentration detected in stormwater based on the UIC stormwater compliance monitoring. In addition, the GWPD framework has been used to demonstrate protectiveness of drinking water wells near UICs. Development of the GWPD involved compiling site-specific geologic, precipitation, stormwater flow, UIC infiltration rates, stormwater pollutant quality, site-specific pollutant mobility, and degradation parameters.