ENV-11-08 Water Conservation, Total Dissolved Solids, and Whole-Effluent Toxicity Testing

Description:

Total dissolved solids (TDS) in water has become an increasingly important topic as competition for water supply sources and the intensity of use both increase. This paper uses the case study of a refinery to present a TDS balance for a facility, and then reviews each water source and the ability to alter the TDS. Next, TDS mitigation alternatives are reviewed, showing that there are no treatment methods, only very expensive, unproven disposal processes, thus making TDS a dilemma with little technical flexibility. Although bioassay failures are a real driver, potential failures would be due to TDS concentration, not mass. Consequently, bioassays become a de facto concentration standard that sets the limit for the intensity of water use and the amount of water conservation possible for a facility. Since failing bioassays and being out of compliance with a facility’s NPDES wastewater permit is not an option, the only reasonable course of action would be to reduce the intensity of water conservation and thereby lower the TDS concentration. Such an approach would reduce the amount of conservation and intensity of water use, which is counterproductive to water conservation goals. A second companion paper deals with the impact of TDS on NPDES-required bioassays, and conflicting regulations dealing with the application of mixing zones and anti-degradation policies that can prevent water conservation and actually result in the unintended consequence of causing more water use.