Central Valley Clean Water Association Freshwater Mussel Collaborative Study for Wastewater Treatment Plants

RBI is currently serving as the prime consultant for a multi-agency collaborative study developed by the Central Valley Clean Water Association (CVCWA) to evaluate the presence or absence of freshwater mussels in Central Valley POTW receiving waters.  In 2013, the U.S. Environmental Protection Agency (USEPA) promulgated new ammonia criteria for freshwater ecosystems, which incorporated new toxicity data developed for unionid freshwater mussels, non-pulmonary snails, and other freshwater organisms not available at the time the previous 1999 ammonia criteria were developed.  This study, which is being implemented in several phases, was undertaken in response to a California Water Code Section 13267 information request issued by the Central Valley Regional Water Quality Control Board to facilitate application of the 2013 ammonia criteria in NPDES permits for POTWs, based on the presence or absence of freshwater mussels in their receiving waters.

Phase I of the study included the preparation of a State of Knowledge report to summarize the current understanding of the biology, ecology, and distribution of freshwater mussels occurring in the Central Valley.  In addition, a Field Study Guidance and Methodology report was prepared to guide the approach, methods, and interpretation of results for mussel surveys that some POTWs may elect to implement under a later phase of the study.  This report compared and contrasted the most widely used traditional mussel survey methods with the use of environmental DNA (eDNA), an emerging and highly effective methodology for unobtrusively determining presence and absence of rare and cryptic aquatic organisms, such as freshwater mussels.  A series of policy and permitting discussions were held under Phase I with the Regional Water Quality Control Board, USEPA, U.S. Fish and Wildlife Service, California Department of Fish and Wildlife, and regional mussel experts to explore various approaches for implementing the new 2013 ammonia criteria that would provide reasonable protection of aquatic life beneficial uses in POTW receiving waters, while simultaneously maximizing the ability of Central Valley POTWs to cost-effectively comply with the criteria.

The use of the eDNA methodology, which allows for detection of specific aquatic organisms by analyzing surface water samples for the presence of their DNA, was identified under Phase I as the most cost-effective and reliable method for determining the presence or absence of freshwater mussels.  Phase IIa of the study consisted of a pilot study to evaluate the use of eDNA for making defensible determinations of mussel presence/absence in Central Valley water bodies using four individual study elements.  The first study element validated the effectiveness of the eDNA methodology by successfully detecting the presence of all mussel taxa that were confirmed present in the Pit River through snorkel surveys.  The second study element tested the used of eDNA methodology in two representative Central Valley receiving waters where mussel presence/absence was not known.  Under the third study element, eDNA samples were collected at ten locations throughout the tidally influenced waters of the Delta to determine if mussels were present and, if so, to characterize their distribution.  The fourth study element was designed to determine the attenuation rate of eDNA by analyzing samples collected downstream of a cage containing 20 individual mussels in a reach of the Pit River where mussels were absent.  The results of the Phase IIa eDNA Pilot Study demonstrated that the eDNA methodology is a valid and cost-effective method for making scientifically defensible presence/absence determinations for freshwater mussels in the receiving waters of POTW in the Central Valley.

Additional work to be performed under this study includes an expansion of the eDNA attenuation study, refinement of the eDNA sampling protocol for non-wadeable water bodies (e.g., the Delta and large rivers), and additional policy and permitting discussions with the resource agencies to further develop and refine the permitting approach for implementing the 2013 ammonia criteria within the NPDES program.