Infiltration and Recharge: Addressing Surface Water Quality Impairments Caused by Urban Runoff in Los Angeles

Several Total Maximum Daily Loads (TMDLs) are being implemented in the Los Angeles area to address surface water quality impairments in the Ballona Creek and Los Angeles River watersheds. These TMDLs include wasteload allocations for metals, bacteria, and toxics, applicable to urban runoff under dry and wet weather conditions. As required, the City of Los Angeles (City) has submitted to regulators TMDL Implementation Plans (IPs) that describe the City’s approach for achieving compliance. The IPs rely on an integrated water resource management approach that addresses TMDL requirements and supports regional needs to increase water conservation through stormwater harvesting (e.g., through infiltration and recharge). These outcomes will be achieved, in part, through implementation of structural Best Management Practices (BMPs).

Increased infiltration of urban runoff is planned through the development of multiple regional (> 100 acre drainage area) and distributed (typically 10-50 acre drainage area) structural BMPs. Regional BMPs can provide benefits beyond stormwater infiltration, including creation of open space for parks. Distributed BMP implementation will focus on development of “green street” projects, which retrofit residential streets with bioretention facilities to minimize surface runoff from the local area.

Central to harvesting stormwater is the assumption that infiltration and recharge do not create new water quality concerns. To support this assumption, the City has partnered with a number of agencies to implement a multi-year phased Water Augmentation Study to evaluate potential water quality impacts from stormwater infiltration. Studies completed to date demonstrate that the City’s plan to use infiltration as a key element to manage urban runoff will not cause water quality concerns in groundwater.

This presentation will provide an overview of surface water quality concerns in the Los Angeles area and describe how these concerns are being addressed in part through stormwater harvesting and groundwater recharge.