Leveraging the Natural Environment as Treatment for Highway Runoff within the Lake Tahoe Basin

摘要

After many years struggling to agree on the best approach for improving water quality within the Lake Tahoe Basin, the California Department of Transportation (Caltrans) and the Lahontan Regional Water Quality Control Board have developed a process to evaluate and prioritize water quality needs within the Basin that is based on low impact development (LID) principles and source control methods. This collaborative effort is documented in the Natural Environment As Treatment (NEAT) Study. Prior to the NEAT Study, both agencies believed the best way to address water quality within the Basin was to capture and treat all storm water runoff. However, many studies completed industry wide indicated that LID and the reliance on vegetation for treatment most likely provide a greater benefit to water quality for less cost.The NEAT Study identified locations where the natural environment serves as acceptable treatment for storm water runoff generated from Caltrans' Right of Way (ROW); locations where minor modifications (LID type); and areas where a structural treatment device may be required to control pollutant discharges. Thirty-eight miles of highway within the Tahoe Basin in El Dorado and Placer Counties were evaluated in the NEAT Study. This effort resulted in the categorization of the highway into:1. NEAT (Natural Environment as Treatment) - a segment of roadway where pollutants that would be transported by storm water runoff are adequately addressed by the natural environment. This may be accomplished through infiltration and/or absorption by vegetation.2. MEAT (Modified Environment as Treatment) - a segment of roadway where minor modifications, similar to low impact type improvements, or source controls measures could be implemented in order to treat highway runoff. These areas exhibit much of the same characteristics as NEAT areas, but require some improvement to meet all criteria.3. TREAT (Treated Environment as Treatment) - a segment of highway where factors such as proximity to a receiving water, lack of vegetation, visible erosion, and/or significant amounts of impervious surface would indicate that storm water runoff should be collected and treated prior to discharge.The final product is a GIS based tool that allows Caltrans and Regional Board staff to utilize NEAT mapping and supporting information when designing a project. The tool allows for a consensus based approach that will allow project's to be delivered more quickly and for less cost.