Dry storage of coal combustion wastes (CCW) can negatively impact the surrounding environment. CCW leachates are characterized by low pH and high conductivity and are often enriched with metals and metalloids that threaten nearby ecosystems. In the present study, a quarterly series of whole effluent toxicity (WET) tests were completed on facility-treated discharge samples from three Maryland CCW disposal facilities. Priority metals and major ions were measured over time and concurrently with bioassays. Chronic toxicity was identified at all three locations at varying frequencies. The wastewaters were consistently high in total dissolved solids (TDS) with high conductivities, evidence that major ion toxicity could be contributing to the effects. Traditional Phase I Toxicity Identification Evaluation methods do not address these issues. Therefore, the present study evaluated the toxicity associated with major ion imbalances using mock effluents and a weight-of-evidence approach in order to identify the primary causative ions.