Long-Term Recovery of PCB-Contaminated Surface Sediments at the Sangamo-Weston/Twelvemile Creek/Lake Hartwell Superfund Site

Abstract

Natural recovery of contaminated sediments relies on burial of contaminated sediments with increasingly clean sediments over time (i.e., natural capping). Natural capping reduces the risk of resuspension of contaminated surface sediments, and it reduces the potential for contaminant transport into the food chain by limiting bioturbation of contaminated surface or near-surface sediments. This study evaluated the natural recovery of surface sediments contaminated with polychlorinated biphenyls (PCBs) at the Sangamo-Weston/Twelvemile Creek/Lake Hartwell Superfund Site (Lake Hartwell), Pickens County, SC. The primary focus was on sediment recovery resulting from natural capping processes. Total PCB (t-PCB), lead-210 (210Pb), and cesium-137 (137Cs) sediment core profiles were used to establish vertical t-PCB concentration profiles, age date sediments, and determine surface sedimentation and surface sediment recovery rates in 18 cores collected along 10 transects. Four upgradient transects in the headwaters of Lake Hartwell were impacted by historical sediment releases from three upgradient sediment impoundments. These transects were characterized by silt/ clay and sand layering. The highest PCB concentrations were associated with silt/clay layers (1.8-3.5% total organic carbon (TOC)), while sand layers (0.05-0.32% TOC) contained much lower PCB concentrations. The historical sediment releases resulted in substantial burial of PCB-contaminated sediment in the vicinity of these four cores; each core contained less than 1 mg/kg t-PCBs in the surface sand layers. Cores collected from six downgradient Lake Hartwell transects consisted primarily of silt and clay (0.91-5.1% TOC) and were less noticeably impacted by the release of sand from the impoundments. Vertical t-PCB concentration profiles in these cores began with relatively low PCB concentrations at the sediment-water interface and increased in concentration with depth until maximum PCB concentrations were measured at approximately 30-60 cm below the sediment-water interface, ca. 1960-1980. Maximum t-PCB concentrations were followed by progressively decreasing concentrations with depth until the t-PCB concentrations approached the detection limit, where sediments were likely deposited before the onset of PCB use at the Sangamo-Weston plant. The sediments containing the maximum PCB concentrations are associated with the period of maximum PCB release into the watershed. Sedimentation rates averaged 2.1 +/- 1.5 g/(cm2 yr) for 12 of 18 cores collected. The 1994 Record of Decision cleanup requirement is 1.0 mg/kg; two more goals (0.4 and 0.05 mg/kg t-PCBs) also were identified. Average surface sedimentation requirements to meet the three goals were 1.4 +/- 3.7, 11 +/- 4.2, and 33 +/- 11 cm, respectively. Using the age dating results, the average recovery dates to meet these goals were 2000.6 +/- 2.7, 2007.4 +/- 3.5, and 2022.7 +/- 11 yr, respectively. (The 95% prediction limits for these values also are provided.) Despite the reduction in surface sediment PCB concentrations...

Reduction of PCB Contamination in an Arctic Coastal Environment: A First Step in Assessing Ecosystem Recovery after the Removal of a Point Source

“…Biotic recovery trends observed in this study differ from the biotic trends reported at Lake Hartwell, where largemouth and hybrid bass have not measurably responded to decreases in surface sediment PCB concentrations (33). The time lag between surface sediment PCB concentrations and the response of indicator species at Lake Hartwell appears to be far greater than that observed at Saglek Bay.…”

Processes, Assessment and Remediation of Contaminated Sediments

“…Natural deposition of clean material can result in contaminant concentrations that approach or achieve cleanup levels and reduce risks to human health and the environment Brenner et al, , 2004.…”

Foodweb modeling for polychlorinated biphenyls (PCBs) in the Twelvemile Creek Arm of Lake Hartwell, South Carolina, USA

“…In 1991, PCBs were undetected in the study area at detection limits ranging from 0.49 to 2.0 g/L and in 1992, PCBs were undetected at detection limits of 1.2 or 1.3 g/L AQUATOX assumes that all PCB in sediment is associated with the detritus, which was modeled in AQUATOX as organic matter. The initial PCB concentration of sedimented detritus in the lake was calculated from data reported by Brenner et al (2004): 2 mg PCB per kg dry sediment, divided by 0.03 kg total organic carbon (TOC) per kg dry sediment, divided by 1.9 (standard AQUATOX conversion from TOC to organic matter) = 35 mg PCB/mg sediment organic matter. PCB load for inflow detritus was set based on yearly observed sediment concentrations at the sample site directly upstream of the USGS gage (Site SD002); the AQUATOX model conducts linear interpolation between the yearly values.…”

“…PCBs in sediments and aquatic fauna have been monitored since 1995 to gauge the effectiveness of Monitored Natural Recovery in lowering PCB concentrations in sediments and aquatic fauna (Georgia DNR, 2006). Brenner et al (2004) demonstrated that PCB concentrations in TCA sediments in 2001 and 2002 were in the range of 1 ppm, the recovery goal for sediments (U.S. EPA, 1994). The recovery goal for PCBs in fish tissue is 2.0 ppm, which is the current federally specified level for fish consumption (U.S. EPA, 1994).…”

“…The recovery goal for PCBs in fish tissue is 2.0 ppm, which is the current federally specified level for fish consumption (U.S. EPA, 1994). Although some tissue data show that concentrations are declining in some species over time, data for largemouth bass (Micropterus salmoides), a primary sport-fish in the TCA, show that PCB levels remain above the recovery goal (Brenner et al, 2004). In order to understand the patterns of contamination in Lake Hartwell fish, it is necessary to understand the sources and pathways for PCBs into fishes at higher trophic levels and the residence times of PCBs in the Lake Hartwell foodweb.…”