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SITE CHARACTERIZATION OF A CHROMIUM SOURCE AREA AT THE USCG SUPPORT CENTER, ELIZABETH CITY, NC
Citation:
Paul*, C J., F A. Khan*, AND R W. Puls*. SITE CHARACTERIZATION OF A CHROMIUM SOURCE AREA AT THE USCG SUPPORT CENTER, ELIZABETH CITY, NC. Presented at 2002 Intl. Ground Water Symposium, IAHR, & IAHS, ASCE, and AGU, Berkeley, CA, 03/01/2002.
Description:
The chrome source area is located beneath an old electroplating shop at the United States Coast Guard Support Center near Elizabeth City, NC . This electroplating shop was in
use for approximately 30 years until 1984 and was the source of discharges of chromic and sulfuric acid wastes though a hole in the concrete floor of the plating shop. These wastes infiltrated into the soils and ground water beneath the shop. Initial site characterization was conducted beneath the plating shop by the National Risk Management Research Laboratory (NRMRL), U.S. EPA, in 1990 and 1991 to determine the extent of soil and aquifer contamination. In general, the highest concentrations of total chromium in the soils beneath the shop were detected in the shallow soils 0.91 - 1.22 m above the water table, with a maximum concentration of 14,500 mg/kg at 0.91 m below land surface (bls). It was initially felt the chromium in the soils would remain immobile and did not present potential risk; therefore, initial remedial efforts focused on treating the diffuse chromium plume which was moving toward the Pasquotank River by installing a permeable reactive barrier (PRB) in 1996.
However, a subsequent rupture of a subsurface fire suppression water line adjacent to the former electroplating shop occurred in 1994. Chromate salts were discovered and identified on the surface rocks within the shop in August 1995. This water main break is suspected to have caused an artificial rise in the water table which likely solubilized some of the chromate in the remaining soils/sediments and redistributed contaminants into the fill material, gravel and ground water below the shop. Historical data for monitoring well MW12 (installed in 1991) inside the plating shop shows Cr(VI) concentrations increased from 1.41 mg/L in June 1993 to 28.0 and 27.0 mg/L in June 1994 and May 1995 respectively (Table 1). Sulfate levels also increased from 86 mg/L to 140 and 120 mg/L during the same time period. Although Cr(VI) levels subsequently decreased, levels still remained approximately three times greater than before the water main break. This suggested a continual release of Cr(VI) into the mobile contaminant plume being treated by the PRB.