USGS Publications Warehouse

Abstract

A study was done of the effects of a closed landfill on the quality of water and streambed sediment and the benthic macroinvertebrate community of an unnamed stream and its tributary that flow through Blue Ridge Parkway lands in west-central Virginia. The primary water source for the tributary is a 4-inch polyvinyl chloride (PVC) pipe that protrudes from the slope at the base of the embankment bordering the landfill. An unusual expanse of precipitate was observed in the stream near the PVC pipe. Stream discharge was measured and water and streambed sediment samples were collected at a nearby reference site and at three sites downstream of the landfill in April and September 1999. Water samples were analyzed for major ions, nitrate, total and dissolved metals, total dissolved solids, total organic carbon, and volatile and semivolatile organic compounds, including organochlorine pesticides and polychlorinated biphenyls (PCBs). Streambed sediment samples were analyzed for total metals, total organic carbon, percent moisture, and volatile and semivolatile organic compounds, including organochlorine pesticides and PCBs. The benthic macroinvertebrate community within the stream channel also was sampled at the four chemical sampling sites and at one additional site in April and September. Each of the five sites was assessed for physical habitat quality. Water collected periodically at the PVC pipe discharge between November 1998 and November 1999 was used to conduct 48-hour acute and 7-day chronic toxicity tests using selected laboratory test organisms. Two 10-day chronic toxicity tests of streambed sediments collected near the discharge pipe also were conducted. Analyses showed that organic and inorganic constituents in water from beneath the landfill were discharged into the sampled tributary. In April, 79 percent of inorganic constituents detected in water had their highest concentrations at the site closest to the landfill; at the same site, 59 percent of inorganic constituents detected in streambed sediments were at their lowest concentration. The low dissolved-oxygen concentration and relatively low pH in ground water from beneath the landfill probably had a direct effect on the solubility of metals and other constituents, resulting in the high concentration of inorganic constituents in water, low concentration in sediment, and the development of the precipitate. Most constituents in water in April were progressively lower in concentration from the landfill site downstream. The highest concentrations for 59 percent of constituents detected in sediment were at the farthest downstream site, suggesting that the inorganic constituents came out of solution as the stream water was exposed to the atmosphere. In September, 52 percent of inorganic constituents detected in water were at their highest concentrations at the site nearest the landfill. Of inorganic constituents detected in streambed sediments in September, 60 percent were at their highest concentrations near the landfill. A storm that occurred a few days prior to the September sampling probably affected the preceding steady-state conditions and the distribution of constituents in sediment along the stream. Concentrations of many inorganic constituents in water remained elevated at the farthest downstream site in comparison to the reference site in April and September, indicating that concentrations did not return to background concentrations. In April and September, most of the 17 organic compounds detected in water, including volatile organic and semivolatile organic compounds, were collected in samples near the landfill, and most concentrations were below their respective reporting limits. Probably because of their volatility, few organic compounds were detected at sites downstream of that site. A total of 17 discrete organic compounds were detected in sediment samples in either April or September, including trichloroethene and tetrachloroethene along with their degradation products, 1, 1 dichloroethane and 1,2-dichloroethene; and 4, 4' DDT. All benthic macroinvertebrate community metrics indicated significantly better conditions at the reference site in comparison to the site nearest the landfill. At the reference site and at three other sites, the taxa collected included several macroinvertebrates that would normally be found under good stream-quality conditions; those collected at the site near the landfill comprised primarily very tolerant macroinvertebrates, including snails, oligochaetes, and a pollution-tolerant dipteran. The reaction of test organisms to samples of the water discharged from the PVC pipe showed acute toxicity in 10 out of 11 independent tests from November 1998 to November 1999. Organism mortality was observed in every acute test at 100-percent sample strength, and a 48-hr LC50 (the lethal concentration that causes 50-percent mortality of the test organisms after a defined period of exposure) was exceeded 89 percent of the time. Chronic toxicological impairment was reported for Ceriodaphnia dubia with survival and reproduction impaired at 50- and 25-percent concentration of the sample water, respectively. No impairment occurred at 12.5-percent concentration. Overall, the three most notable factors indicating stressed and (or) impacted conditions in the stream near the landfill consisted of (1) the layer of fine metal oxide precipitate in the streambed at and below the site nearest the landfill; (2) the significantly depressed numbers of benthic macroinvertebrate fauna, particularly of sensitive or pollution-intolerant groups; and (3) the consistent acute toxicity of water to Ceriodaphnia dubia.