T3 PM Aquatic Ecotoxicology (Part 2)
Tuesday, 15 November 2005: 1:50 PM - 5:30 PM in Ballroom 3

(BAI-1117-851009) Evaluation of impacts and benefits associated with discharge of treated effluent to the Santa Clara River Estuary.

Bailey, H¹, Stransky, B¹, Magier, S¹, Kamman, G², Pfeifer, D³, ¹ Nautilus Environmental, San Diego, California, United States² Kamman Hydrology and Engineering, Inc., San Rafael, California, United States³ City of San Buenaventura, Ventura, California, United States

ABSTRACT- The objective of this study was to evaluate impacts and benefits associated with discharge of treated wastewater to the Santa Clara River Estuary. The estuary is located in a semi-arid region of California that has been subjected to intensive habitat and water development over time, and currently supports a number of species of regulatory interest, including the federally listed tidewater goby (Eucyclogobius newberryi). The analysis included evaluation of effluent toxicity and sediment quality, as well as investigations of ecological and hydrological function. The frequency and magnitude of toxicity in samples from the estuary was minimal, and not related to the discharge. In addition, the sediment quality investigation indicated that contaminants of concern were not accumulating in estuary sediments, and that the intermittent adverse effects observed in sediment toxicity tests were largely due to grain size effects. The ecological investigation relied on extensive historical information, including maps, aerial photographs, and anecdotal accounts from a variety of sources. Most changes in flora and fauna could be attributed to changes in land use that resulted in a decrease in estuary size of approximately 90% between the late 1800s and 2003. The hydrological analysis used historical data, anecdotal evidence, and modeling to develop estimates of flows that would be present in the absence of upstream diversions. This analysis showed that the discharge accounts for a portion of the river flows that would have historically reached the estuary, but which have been diverted for other uses upstream. Overall, the analysis demonstrated that the discharge has no demonstrable negative impacts on the estuary, and supports beneficial uses by maintaining water quality and habitat. In a broader perspective, this study is an example of a robust approach that integrates several environmental disciplines to evaluate the extent of impacts (both positive and negative) to a given receiving environment.

Key words: effluent, impacts, beneficial uses, estuary