LOW IMPACT DEVELOPMENT (LID) STORMWATER INFILTRATION PROJECT REVIEW
Since becoming ULARA Watermaster in January 2009, this Watermaster has been reviewing information and reports from various private engineers and/or owners in regard to Standard Urban Stormwater Mitigation Plan (SUSMP) requirements for all proposed developments and re-developments of existing properties within those portions of the City of Los Angeles that overlie the San Fernando and Sylmar basins. Note that, in May 2012, the City of Los Angeles implemented a Low Impact Development Ordinance (LID) that expanded/revised the original SUSMP requirements; hence, SUSMP projects are now referred to as LID projects. The background of LID projects and the role of the Watermaster in the LID approval process are summarized below.
The State Regional Water Quality Control Board-Los Angeles Region (RWQCB-LA) promulgated its National Pollutant Discharge Elimination System (NPDES) permit process in 1990 to help minimize the impacts of stormwater and urban runoff on the receiving water bodies in its sphere of influence (i.e., local rivers and the Pacific Ocean). The goal of their NPDES process was to minimize the impacts on the river, and ultimately to the ocean, by reducing the amount and improving the quality of surface water runoff from each storm event. For the ULARA region, the main receiving waters are the Los Angeles River and the Pacific Ocean.
Several years after the implementation of the NPDES process, the City of Los Angeles, Department of Public Works, Bureau of Sanitation - Watershed Protection Division (LAWPD), promulgated a series of guidelines intended to increase onsite infiltration of stormwater at all proposed developments and re-developments throughout the City. These guidelines established the requirements and limitations for infiltration (and recharge) of onsite stormwater and also specified an order of preference (via a set of Best Management Practices---BMPs) for providing LID improvements at each development and/or re-development site in the City.
The specific order of the BMP preference list was established by the LAWPD to collect and provide basic "treatment" of onsite stormwater runoff, and to help increase the amount of infiltration (i.e., deep percolation) from the initial 3/4-inch of rainfall from each storm event at all new development and re-development sites in the City. The end result is intended to reduce the volumes of stormwater runoff that enter the storm drain system (from each new storm event) and simultaneously help reduce the volume and enhance the quality of the runoff that enters the Los Angeles River and ultimately the Pacific Ocean. Potential urban-derived contaminants and turbidity in the captured runoff could be reduced by the "treatment" effects of the various stormwater infiltration systems proposed via the BMPs. From a hydrogeologic perspective, and in the opinion of this Watermaster, whenever and wherever deep percolation (infiltration) of "treated" stormwater can be appropriately enhanced, then recharge to the local groundwater basin can be beneficially increased.
Per the LID Information Guidelines of the LAWPD, the five BMP options, in order of preference, are:
1. Infiltration Systems (design based on the volume of stormwater);
2. Bio-Filtration/Retention Systems (design based on flow of stormwater);
3. Stormwater Capture and Re-Use (optional; subject to County Health Department approval);
4. Mechanical/Hydrodynamic Units;
5. Combination of any of the above.
More information is available from the Los Angeles Stormwater Protection Program Website http://wwww.lastormwater.org.