Use of an integrated monitoring approach to determine site‐specific effluent metal limits

Abstract

ABSTRACT: An integrated monitoring approach was implemented for an overland‐flow wastewater facility over a 1‐year period to determine whether the effluent caused water quality impairment in the receiving system (X‐Trib) and appropriate metal effluent limits. The Rapidan Service Authority (Gordonsville, Va.) wastewater effluent comprises approximately 98% of the X‐Trib flow under 7Q10 conditions. Aquatic life in both X‐Trib and South Anna River, downstream of the discharge, were previously recorded as heavily impacted prior to the addition of overland‐flow treatment. Three forms of monitoring were implemented at this facility: chemical‐specific analyses of effluent samples, whole effluent chronic toxicity tests, and stream bioassessments. Two reference streams in the area were also sampled to determine the types of fauna capable of inhabiting the receiving stream. Chemical data suggested elevated levels of copper, cadmium, and lead instream compared to U.S. EPA criteria and Virginia Standards. Chronic toxicity tests, however, often indicated no effects on sensitive EPA indicator species. Stream bioassessments suggested that both habitat and benthic substrate quality were limiting for aquatic biota in the X‐Trib. Benthic grab samples and fish sampling suggested ecological impairment due to the effluent. However, introduced benthic substrate studies in the fall and spring indicated no impairment. Thus, the adverse impact observed in benthic samples appeared to be an historical effect of the effluent prior to upgrade, and not an indication of present effluent quality. The biological results indicated that the upgraded plant was in compliance with the goals of the Clean Water Act despite elevated metal levels. High effluent total organic carbon (TOC) was at least partly responsible for this result since even occasional high levels of dissolved metals did not cause toxicity. Our results suggest that following a truly integrated monitoring approach can yield appropriate effluent metal limits on a site‐specific basis without necessarily relying on criteria or standards modification studies; state standards for metals, even based on the dissolved fraction, may, in some cases, be overly stringent where other factors are present that reduce the bioavailability of those metals; and setting appropriate standards for effluent‐dominated streams requires consideration of effluent characteristics which may affect the bioavailability of pollutants.