Description

This report documents an evaluation of chemical contaminants in, and toxicity of, sediments collected from impoundments created by dams on the Haw River in Alamance and Chatham Counties, central North Carolina. Eighteen wholesediment samples from within the impounded reaches of Swepsonville Dam, Saxapahaw Dam, Bynum Dam, and B. Everett Jordan Dam were collected in June 2008. All samples were analyzed for elemental contaminants and polycyclic aromatic hydrocarbons. All samples were also assessed with a battery of toxicity tests. Elemental contaminant concentrations in wholesediments were below those of toxicological significance. One or more sediment PAHs with freshwater sediment threshold effects screening values exceeded the screening values at 17 of the 18 sites, but no samples exceeded the probable effects concentrations. Survival of Hyallela azteca freshwater amphipod exposed to sediments from one of five sites in the Bynum Dam impounded reach was 80 and statistically lower than controls in 28d toxicity tests; amphipod growth was not affected at this or any other site. Whole sediments had no significant effect on survival or growth in 10d tests with Chironomus dilutus freshwater midge at any of the 18 sites. Results indicate the contaminants associated with the wholesediment samples were not chronically toxic to amphipods or midge. In 2d sediment elutriate waterextractable fraction tests with Ceriodaphnia dubia freshwater cladoceran, statisticallysignificant reductions in survival occurred in four of the 18 exposures two from the five samples taken from within the Bynum Dam impounded reach, one from the flooded portion of Big Alamance Creek, and one in the headwaters of Jordan Lake. Chromium in pore water at one of five sites in the Saxapahaw Dam impoundment was 119 gL; the State standard for chromium is 50 gL. Copper, lead, and zinc in the elutriate and pore water samples exceeded State standards infrequently but most commonly in sediments from the Saxapahaw Dam impoundment. This is an indication that aggressive resuspension of sediments like those tested could temporarily impair surface water quality. These data and surveys of sediment physical characteristics, volume, and likelihood of movement can be used together to infer the impacts the different types of sediments disturbing activities on shortterm water column chemistry. In particular, data regarding the modeled or measured sediment resuspension caused by specific sediment disturbing activities e.g., dredging, dam alterations, dam removal, etc. will help put the elutriate test results in context for a range of sediment management practices.

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