2017 CASQA Award Winner - Outstanding Stormwater Research Project: The Elk Grove Dry Well Project
Stormwater managers face multiple requirements for the management of urban runoff. There is a need for hydromodification management tools to reduce urban runoff volumes and the pollutants they carry to achieve stormwater goals. This can be challenging especially in the presence of clay soils. Managers are also faced with capturing and reusing stormwater for aquifer recharge. One BMP that has the potential to address these demands are dry wells. However, considerable skepticism regarding their use and potential for contaminating groundwater has impeded widespread use, especially in northern California. The Elk Grove dry well study was designed to identify the risks associated with dry well use for managing urban runoff.
A two year study was performed at two sites in Elk Grove: 1) at a water quality basin in a residential neighborhood, and 2) at the City’s Corporation Yard, the bus fleet parking and servicing area. Two dry wells with pretreatment features as well as a groundwater monitoring network were constructed. Stormwater and groundwater samples were collected during and after 5 rain event for the 2014-16 water years. Water samples were analyzed for over 200 contaminants. This data was analyzed using non-parametric statistical methods, comparing stormwater before and after pretreatment, in the vadose zone, and in upgradient and downgradient water table wells. Fate and transport vadose zone modeling was also performed, using a 3000 year timeframe. Contaminants, such as aluminum and bifenthrin that were detected at elevated concentrations in stormwater were present in low concentrations or not found in groundwater. In many cases, the concentrations of pollutants were no different in upgradient and downgradient wells, suggesting that the dry wells were not the source of the contaminant. In contrast, pollutants present at elevated concentrations in groundwater, such as chromium or arsenic, were very low or not detected in stormwater. Vadose zone modeling found that most contaminants would not be quantifiable within the modeling timeframe. Exceptions were two water soluble pesticides, imidacloprid and fipronil, that were modeled but not analyzed during the study. Unlike metals and most organic contaminants, these pesticides are sequestered in the vadose zone. Lastly, an extensive review of the scientific literature and government reports found little evidence to suggest that the use of dry wells led to systematic contamination of the aquifer. These three lines of evidence pointed to the same conclusions: with appropriate siting, design, and maintenance, dry wells pose little risk to groundwater quality.
Information gained from this study can be directly used by stormwater managers for complying with NPDES requirements and IRWM Programs. A discussion of lessons learned from the project, including design of dry wells, siting issues, monitoring recommendations, and maintenance needs, can be used by conference attendees along with how dry wells are used for managing stormwater runoff for adaptation practice in response to drought and climate change.
The presentation will be informal and with an interactive approach to engage the audience. Previous presentations given by the project team have resulted in lively conversations and exchanges of ideas. In California, there is a significant discrepancy between dry well use in northern and southern California. This presentation will promote a dialog with stormwater managers from both regions of the state with the goal of learning from the experiences of others.
The conference theme “Building Bridges for Water” will be directly addressed in this presentation. Dry wells provide one of the clearest links between wise use of stormwater and groundwater sustainability, between protection of surface and groundwater, and a useful tool for achieving integrated water management. This study supports the thoughtful use of dry wells to manage both stormwater and groundwater.
Connie Nelson has over 30 years of planning and engineering experience developing a wide variety of program and projects. She has serviced in both the Public and Private sector. Connie brings a depth of understanding to the political, regulatory and procedural aspects of issues faced by local government staff. Her program and projects have required extensive coordination with local, county, State and federal agencies, residents, and other key stakeholders. She has knowledge and an ecological vision to work towards more sustainable and environmentally friendly stormwater solutions that integrate multiple objectives including flood protection, water quality, habitat protection, watershed stewardship.
Barbara Washburn serves as lead scientist of the Ecotoxicology Program at the Office of Environmental Health Hazard Assessment (OEHHA), where she has worked for the past 17 years. Her work involves developing tools and technical resources to support environmental risk assessment, with an emphasis on watershed assessment and water resource protection. The Elk Grove Dry Well Project evolved from the knowledge that LID practices, including dry wells, are important tools for protecting urban aquatic ecosystems.