The Sacramento Branch is pleased to present:
Assessing the Use of Dry Wells as an Integrated LID Tool for Reducing Stormwater Runoff While Protecting Groundwater in Urban Watersheds:
The Elk Grove Dry Well Project
Ecotoxicology Program at the Office of Environmental Health Hazard Assessment at Cal/EPA
Dry wells, also known as recharge wells or underground injection control systems (UICs), are stormwater infiltration devices that are deeper than they are wide. Typically they are constructed of a pipe about 3 feet wide and 20 – 50 feet deep; containing holes through much of the length. They are particularly useful to quickly infiltrate runoff, especially in areas with clay soils, and to recharge the aquifer. However, many are concerned that releasing stormwater close to the aquifer could compromise groundwater quality. The purpose of this project was to assess the risk of groundwater degradation associated with the use of recharge wells. The project involved construction of two dry well systems with pretreatment in a residential neighborhood (at a detention basin; SDB) and a large bus fleet servicing/parking area (at Elk Grove’s Corporation Yard; CY). Both stormwater and groundwater (vadose zone and water table) were monitoring for key classes of contaminants, including PAHs, VOCs, pesticides, and metals, for two years. Infiltration rates were assessed. Vadose zone and groundwater modeling was conducted to estimate the fate and transport of contaminants. A review of the scientific literature was also performed. Monitoring results suggested that the vegetated pretreatment feature removed approximately 50% of suspended sediment and associated pollutants. Semi-volatile and volatile organics were rarely identified in runoff; when identified, they were present in trace amounts, usually below the reporting limits. Pyrethroids (typically found at concentrations less than 50 ng/L) and metals (most less than 100 µg/L) were the most common contaminants identified. Oil and grease was present at the CY as well. A single metal, aluminum, was detected in CY runoff as it entered the dry well at levels that exceeded the MCL of 1 ppm. Vadose zone modeling performed by UC Davis groundwater hydrologists, suggests that aluminum would not reach the aquifer for hundreds of years, likely because it is strongly sorbed by clay and silt, which composes major portions of the vadose zone. The literature on dry wells is small and contains few peer-reviewed articles. However, the materials reviewed do not report groundwater quality issues associated with dry wells use, in one case for as long as 50 years after dry wells were first constructed. Lastly, a review of UIC programs in other states, where tens of thousands of dry wells have been used for over a decade, was performed. Considering the results of the Elk Grove study, the review of the scientific literature, and the vadose zone modeling, dry well appear to be a valuable tool to reduce stormwater runoff and increase aquifer recharge with little risk to groundwater quality.
Barbara Shayne Washburn, Ph.D, is the lead scientist with the Ecotoxicology Program at the Office of Environmental Health Hazard Assessment at Cal/EPA. She has a PhD in nutritional biochemistry from UC Davis, conducted post-doctoral research at the U. of Miami Marine School, and was on the faculty of the U. Texas El Paso before moving to OEHHA 17 years ago. Her work focuses on developing tools to support ecological risk assessment. Her most recent project, the Elk Grove Dry Well study, evaluated the risks associated with infiltrating stormwater through dry well. Barbara also serves on the Board of the Laguna Creek Watershed Council and is a member of the Valley Foothills Watershed Collaborative, one of the partners in the development of a regional stormwater resources plan.
ANNOUNCING SCHOLASTIC SPONSORSHIP OPPORTUNITIES:
All Proceeds to Benefit Science Students
GRA Sacramento Branch has a history of supporting university-level science students. Our Scholastic Sponsorship Program is an opportunity to publicize your business while contributing toward a good cause. The cost is minimal; if interested, please contact Scott Furnas at (916) 638-7301 or you can email Scott at firstname.lastname@example.org.
THIS MONTH'S SPONSOR:
EDR provides environmental risk information/due diligence solutions related to commercial real estate across multiple industries, working directly with Scientists, Engineers, Chief Credit Officers, Attorneys, Corporate Environmental Managers, and C-level executives. Solutions include environmental database mapping reports, commercial real estate screening platforms and other software platforms which streamline business processes for environmental professionals, banks and corporations.
COST & RSVP:
Costs and menu are shown below. GRA is unable to assure food and room for you without an RSVP. Using GRA's automated RSVP process is quick and painless!
Usual great food, including two meat entrées, salad, rice, potatoes, vegetable and Iced Tea. A No-host beer and wine bar will be available.
If you RSVP by Noon on Monday, November 7th the meeting costs are:
*Retired professionals receive a 10% (rounded to the nearest dollar) discount on any meal.
If you RSVP after Noon on Monday, November 7th, or walk-in, a $3.00 surcharge will be added to the meeting costs. Cancellations must be made by Noon on Monday, November 7th.