Printing Facility, Karst Terrain, Eastern Tennessee

After discovery of contaminated soil under a former drum storage area, ground water was found to be contaminated by PCE up to 11.6 mg/l. Contaminated soil was removed from the source area. Subsequently, three years of ground water monitoring showed the ground water concentrations had not attenuated. Cl-out aerobic bioremediation was implemented in the ground water under the source area. After three years of Cl-out aerobic bioremediation, the contaminant concentrations throughout the two-acre plume were reduced nearly to drinking water standards.

Site Summary:

With an increase in production goals, an industrial facility decided to add onto to their current building. During the construction planning, soil and ground water contamination by chlorinated solvents was discovered. To keep with the construction schedule, a portion of the contaminated soil was excavated. The ground water contamination was addressed after the construction of the building addition.

Geology

The geologic structure of the region is characterized by northeast-southwest trending parallel low ridges and valleys, which are formed by the eastward dipping low angle thrust sheets. The bedrock underlying the site is the Knox Dolomite which is a thick-bedded siliceous dolomite. The Knox Dolomite is susceptible to karst development with associated features such as sinkholes, solution channels, and caves.

The significance of the karst setting became evident during the subsurface investigation when several zones of clay-filled solutions channels, voids without water, and fracture zones were found. These zones were grouped into an upper dry fracture and a void layer as well as a lower water-bearing fracture and void layer with a relatively competent bedrock in between and below. The bedrock became more competent with the depth and the frequency of solution channels or solution enlarged fractures diminished with depth. Sinkholes bottoms were at about the same elevation as the upper dry fracture and void zone.

Hydrogeology

The ground water depth was approximately 110 feet below the ground surface in the lower void and fracture system. While the individual fractures and voids were discontinuous, the hydraulic zone appeared to be continuous. The hydrology was characterized by underground drainage through bedrock fractures and joints widened by solution.

Soil and Ground Water Contamination

Tetrachloroethylene (PCE) and its breakdown constituents were found in soil around a former solvent storage area. The highest concentration found in shallow soils was 99 mg/kg of PCE at less than one foot deep. The contaminated soil was removed for off-site disposal to facilitate the immediate construction of a building addition. The extent of soil excavation was limited by the presence of the existing building to the south. To keep the integrity of the structure, residual contaminated soil was left underneath the building.

Ground water directly under the source had a maximum contaminant level of PCE at 11.6 mg/L. At two of the monitoring wells, the ratio of parent to daughter compounds showed that natural breakdown was occurring. At one of these wells, the concentration of cis-1,2-Dichloroethene (DCE) was more than half the concentration of PCE. In the second well, the proportions of PCE and Trichloroethylene (TCE) were less than DCE.

Remediation Design

Only the ground water was treated with CL-Out in the source area, and the ground water conditions were monitored downgradient. From January 2000 to 2003, CL-Out was injected on a monthly injection basis. From 2003 to 2004, CL-Out was added on a quarterly basis.

The bioaugmentation treatment consisted of 110 gallons of the CL-Out and dextrose slurry into one monitoring well. While the evidence showed that natural breakdown was occurring, the bioaugmentation added a consortium of organisms known to degrade the contaminants without significant production of vinyl chloride.

Results

Quarterly sampling was implemented during remediation. The first sampling event, which was taken one quarter after the first treatment, showed the PCE level in one monitoring well decreased from 11,000 µg/L to 64 µg/L. The concentration of TCE decreased from 1,450 to 800 µg/L. However, the cis-1,2 DCE and the vinyl chloride concentrations increased from 1,800 to 4,200 µg/L and from 35 to 200 µg/L, respectively.

The Federal MCLs were attained sporadically in 2003, but were not maintained for successive quarterly sampling because of the residual contaminated soil left to keep the integrity of the structures on the site. Since the treatment, the site owner has petitioned for closure and is waiting for a response.