NET ECOLOGICAL BENEFIT ASSOCIATED WITH THE CREATION OF AN EFFLUENT DEPENDENT AQUATIC ECOSYSTEM IN SOUTHERN CALIFORIA

The California Lahontan Regional Water Quality Control Board (LRWQCB) (Region 6) plans to establish site-specific beneficial uses for surface waters receiving discharge from the Lancaster, California County Sanitation District No. 14 Water Reclamation Plant (WRP). The discharge creates a significant effluent-dependent ecosystem in normally dry ephemeral waterbodies in an arid region. In preparation for LRWQCB action, the County Sanitation Districts of Los Angeles County completed a study to identify existing and reasonably attainable beneficial uses in Amargosa Creek, Paiute Ponds and Rosamond Dry Lake, and evaluate if there is a net ecological benefit associated with the created effluent-dependent ecosystem.To support project goals, an analysis was conducted using the ecological benefits comparison principles established by the U.S. Environmental Protection Agency (EPA) Region 9 (EPA 1992, 1993). This approach evaluates the benefits and detriments associated with effluent-created habitats and provides an objective means to evaluate whether the created habitat provides a net ecological benefit to a local region. Findings from this analysis have been used to support the establishment of site-specific water quality objectives for ammonia and may be used to support establishment of other site specific water quality objectives in the future.Eight ecological concerns were identified as potential benefits or detriments associated with the created Paiute Ponds ecosystem. Examples of potential benefits included use of the ponds as aquatic habitat by threatened and endangered species and use of the ponds as an outdoor environmental classroom for students. Examples of potential detriments included impacts from effluent on local groundwater and downstream waters. An objective analysis of each concern was conducted using available physical, chemical and biological data from the study area. The results of the ecological benefits comparison indicate that a net ecological benefit exists as a result of the discharge of treated effluent. In addition, the study identified three existing and/or reasonably attainable beneficial uses in the three evaluated waterbodies: Warmwater freshwater habitat (WARM), wildlife habitat (WILD), and non-contact water recreation (REC-2).