Metal-based coagulant effect on sediment slurry for the Lake Combie Reservoir Sediment and Mercury Removal Project, Grass Valley, CA

This study was conducted to assist Nevada Irrigation District (NID) in the analysis of a sediment and mercury removal treatment process at the Lake Combie Reservoir, Grass Valley CA. Part of the removal process consisted of administering metal-based coagulants to promote the sedimentation of fine grain materials. Field-scale tests resulted in process effluent below regulatory criteria for total metal concentrations including mercury (Hg), chromium (Cr), iron (Fe), magnesium (Mg), molybdenum (Mo), nickel (Ni), and zinc (Zn). Additional sediments from future sites (Combie Lake and Greenhorn Creek) and alternative coagulants (LBP-2101 and Clar+Ion 5057) were tested in the sedimentation process. Furthermore, prediction models for continuous real time total mercury (THg) and filtered mercury (fHg) concentrations during the sedimentation treatment process are presented. The models use the parameters; total suspended solids (TSS), total dissolved solids (TDS), and ultraviolet absorbance (A254) as proxies for THg and fHg concentrations. The multivariate regression models had R2 values of 0.97 and 0.85 for the prediction of THg and fHg, and p-values 0.0001. Continuous monitoring of these proxies at pre- and post-treatment locations coupled with the predictive capabilities of the models suggest that full scale implementation of the sediment and mercury removal process at Lake Combie Reservoir can operate within regulatory criteria with the ability to identify an exceedance before effluent is released.