Application of Ultraclean Sampling and Analytical Techniques to an Investigation of the Impact of Power-Plant Derived Heavy Metals on Groundwater, Riverwater, Bottom Sediments and Benthic Organisms

As utility companies refit their oil-fired power stations for use with coal, they are attracting the attention of a concerned public. It becomes especially important, when operating under such close scrutiny, to conduct thoughtful environmental investigations with accurate analytic techniques. In one case, at a Massachusetts, U.S.A., power station, the routine trace metal analyses provided by private water-quality laboratories gave the impression that metal levels in stream and groundwaters adjacent to the plant were alarmingly high. This data, released by the utility company itself, resulted in extensive public criticism and costly effort for the utility and State of Massachusetts regulatory agencies. The problem, however, was more perceived than real, as the present study, conducted later, showed. This investigation brought together ultra-clean sampling and handling techniques (borrowed from geochemical oceanographic practices) and interpretive concepts from aquatic geochemistry. Levels of metal enrichment in stream waters were revealed to be in fact much lower (eg. Cu, 2 µg/l) than implied by the evidently investigator-contaminated samples (eg. Cu, 20 µg/l) from previous work, underlining the importance of employing difficult but uncompromising procedures when dealing with metals in the aquatic environment. Furthermore, with accurate analyses at hand, the geochemist's “mixing diagram” concept allowed interpretation of the fate of the power-plant derived excess metals in the cooling-water discharge; excess dissolved copper, for instance, disappeared not due to reactions with particles, but rather due to simple and rapid dilution in the effluent-river mixing zone. Examination of the relationships between various trace metal concentrations and parameters reflecting major processes controlling metal distributions (sediment grain size, labile iron and manganese concentrations) for bottom sediments from the adjacent Connecticut River revealed that natural processes largely explained the distribution of Cd, Cr, Cu, Fe, Mn, Ni, Pb, and Zn associated with the acid leachable fraction of the sediments in all locations. While no anomalous metal concentrations were recognized amongst sediments, oligochaete worms living in the sediments beneath the cooling-water plume appeared to have accumulated more metal than those elsewhere. Because tissue metal levels were unrelated to sediment metal levels, it seems that the worms may respond more to the dissolved metal load than to the sediment burden. Tight correlations are evident between metal concentrations determined by the author's techniques and a measure of the redox poise (COD) in groundwaters near fly ash settling ponds. Relationships between parameters determined by the routine water-qua1ity laboratories on duplicate samples, on the other hand, are characterized by the lack of correlations, suggesting that in the latter case sample handling methods were inappropriate, leading to unrepresentative concentration estimates. The correlations that appeared with the author's data, however, indicate that metal levels in the groundwater are controlled more by spatial variations in the redox poise than by pollutant (leachate) source strength.