Regional Solutions for Treating Stormwater in Los Angeles County: A Macrofeasibility Study.

by Brown and Caldwell, 2001

EXECUTIVE SUMMARY

New regulations in Los Angeles County require onsite treatment of stormwater runoff in areas that are undergoing new development or redevelopment. This smaller-scale on-site approach, however, is less effective in controlling water quality than larger scale regional, watershed-based approaches.

This Macrofeasibility Study, authored by Brown and Caldwell and sponsored by the Construction Industry Coalition on Water Quality (CICWQ), evaluates the potential for achieving stormwater quality improvements through effective regional approaches. These regional solutions would employ comprehensive best management practices to treat urban runoff from new development sites, as well as surrounding sites that have already been developed. Many groups in the Los Angeles area are interested in applying these regional, watershed-based approaches to achieve comprehensive, long-term water quality solutions.

THE OPPORTUNITY

Municipalities, industry and the general public face new challenges in managing water quality as a result of evolving environmental regulations. Recent amendments to Los Angeles County’s municipal stormwater permits require stricter controls on runoff from new land development and significant redevelopment projects. Additional controls on urban runoff could also result from Total Maximum Daily Load (TMDL) limits for pollutants, which are being developed to improve the quality of impaired waters.

Given these pressures, there is a significant window of opportunity for the region to make real improvements in water quality instead of taking a piecemeal, on-site approach. Over the next several years, developers will be required to spend millions of dollars to address stormwater runoff from new development and redevelopment sites. Instead of spending money on thousands of individual, dispersed facilities—which may or may not be effective over the long term and will treat only small pieces of the overall problem—these funds could support broad, regional solutions and effective, long-term mechanisms that improve water quality cost-efficiency over larger areas.

REGIONAL ADVANTAGES

The amended Los Angeles County stormwater permit relies on Standard Urban Stormwater Mitigation Plans (SUSMPs) to control runoff, on a site-by-site basis, from most new development and redevelopment areas. On-site controls, or SUSMPs, are required regardless of the location of the project, environmental effectiveness, availability of land for treatment, environmental sensitivity or cost.

The SUSMPs must capture, treat or infiltrate runoff from individual sites from a 0.75-inch storm event. SUSMP facilities typically rely on water quality inlet filter devices, oil/water separators or localized hydrodynamic separators. These are often proprietary devices with limited long-term effectiveness in removing pollutants.

Moreover, on-site controls, such as SUSMPs, may work in certain situations, but they are not uniformly effective, especially in treating many toxic pollutants restricted by TMDLs. Much more effective and reliable are regional stormwater facilities, which use infiltration, wetlands or “treatment trains,” employing several mechanisms in a series to remove pollutants.

Unfortunately, the amended Los Angeles County stormwater permit does not encourage regional approaches. Regulatory authorities appear to recognize the merits of watershed-based, regional solutions, but in practice they discourage such strategies. Regional solutions require special approval by the Regional Board Executive Officer. In addition, they must meet many additional requirements above and beyond those for SUSMPs. As a result, unless a viable alternative is found, developers will construct on-site controls that may not work well and are not cost-effective to implement.