In 2012, the City of Elk Grove and its team of engineers and scientists, applied for and was awarded a Proposition 84 Stormwater Grant from the California State Water Resources Control Board for approximately $500,000 to study the risks to groundwater quality associated with the use of dry wells with Low Impact Development (LID) features. Together with in-kind contributions from the City of Elk Grove and Office of Environmental Health Hazard Assessment (OEHHA), Cal EPA, the total project cost is estimated to be $825,000. The City was officially awarded the grant in January, 2013, and began work on this study in the spring of 2013.
Watershed urbanization can result in degraded water quality and increased flood risk due to hydromodification (larger peak runoff volume and shorter watershed residence time). Low Impact Development (LID) techniques can help reduce these impacts. However, in many areas throughout California, the use of LID practices is challenging due to poor infiltrative capabilities associated with clay soils. One solution to bypass these low-permeability clay zones is to use dry wells with associated pre-treatment designed to trap sediment and other pollutants. This approach can recharge the groundwater and provide biofiltration to store and treat runoff and release it at a controlled rate to reduce the adverse impacts of hydromodification on waterways. This conjunctive use to capture stormwater and recharge the aquifer can also potentially reduce localized flooding and could meet numerous water resource management needs.
The purpose of the study is to address data gaps from previous studies in California (i.e. Modesto and Los Angeles studies) and gain additional knowledge of the risks and benefits of dry well use. The City of Elk Grove and its partners are conducting a 3-year study to evaluate the potential for using dry wells, in combination with Low Impact Development (LID) practices, to infiltrate stormwater runoff, alleviate localized flooding, and recharge groundwater without negatively impacting groundwater quality.
The project will construct two dry wells with vegetated and structure pre-treatment features (LID) in a residential and light industrial area of Elk Grove (Figure 1). A network of shallow and deep monitoring wells will also be established near the dry wells for monitoring of stormwater which will be collected and sampled 3 – 4 times a year. Monitoring efforts will analyze a wide range of contaminants, including volatile and semi-volatile organics, pyrogenic PAHs, metals, and pesticides. In addition, as part of the study, estimates of recharge capacity will also be made to determine percent of stormwater captured.
Results of this study shall provide additional information for decision makers on the safety and efficacy of using dry wells with LID features to manage stormwater runoff and reduce localized flooding in the Sacramento region and throughout the State of California. Figure 1. Aerial photograph showing the two study sites and their associated watersheds. The photograph shows the City of Elk Grove, California and surrounding area. The City of Elk Grove is situated about 15 miles south of Sacramento.