Water Effect Ratio Study

Water Effect Ratio Study


Enthalpy supported the consulting firm contracted by the pulp and paper mill to determine if metal limits presented in the draft wastewater discharge permit were scientifically sound. The biggest concerns that needed to be addressed were the low limits for copper, cadmium, zinc, and lead, which would have been challenging for the discharger to meet.  As part of the assessment, the firm required bioassay data to determine the toxicity of each metal on aquatic organisms.  The specific bioassay study selected, known as a Water Effect Ratio (WER), entails concurrent testing with metals spiked into subsamples of receiving water as well as into specially formulated laboratory water for comparison of results.  This allows for assessment of the potential difference in outcomes between organisms exposed to the metal of concern in the laboratory environment and native waters, and ultimately provides data for development of site-specific criteria when the ambient environment can tolerate a higher metals load than typical permit limits.


Not only was it necessary to conduct concurrent bioassays in receiving water and lab water, the WER study also required these parallel bioassays be run seasonally during high and low flow river conditions.  In this case, it took analysis of 16 bioassays during each of three collection events over a two-year period to provide the necessary toxicological data. To capture an effective dose response, up to seven test treatments per metal were utilized, resulting in more than 2,000 unique metals samples (total and dissolved) per collection event. The scope of the project required extensive coordination between the project management and field team, as sample collection was dependent on flow conditions and a lack of precipitation. The laboratory could provide transport of approximately 500 gallons of surface water for each testing event and initiate assays within the 36-hour hold time.


Our team and labs have extensive experience performing WER studies using several metals, and routinely work with the target test species as part of their Whole Effluent Toxicity program. The laboratory is equipped with dual ICP-MS for performing metals analysis, allowing for near real-time evaluations of sample metals content. Additionally, the laboratory provides refrigerated sample transport of large volumes of surface waters and has sufficient on-site cold storage to maintain upwards of 800 gallons of surface water at temperature. Enthalpy’s expertise with the test organism, clean metals sampling techniques, and thorough metals analysis ensured successful outcomes of all the bioassays and <1% error rate on metals spiking and analysis.  The results ultimately demonstrated that the drafted metal limitations were too conservative for actual river conditions which led to an easing of permit limitations and an avoidance of expensive fines and technological upgrades to the treatment system at the paper mill.

By clicking “Accept” or continuing to use this site, you agree to the use of cookies, as described in our Privacy Notice and Cookie Notice, where and as permitted by law.
Let's Chat
Contact us >