Known: The oxidation pond (SWMU O-1) was an evaporation pond constructed in 1975 for the disposal of waste liquids and sludges from the bluing operation. The pond was lined with a plastic liner and reportedly measured about 42 feet by 60 feet with a depth of 2.5 feet. In 1982, an estimated 24,000 gallons were contained in the oxidation pond. In 1985, the pond was filled in with surrounding soil and the liner system was reportedly destroyed during excavation activities.

Chlorinated hydrocarbons were detected in Well 16 in 1991 at concentrations above drinking water standards, prompting several investigations aimed at identifying possible source areas that could have contributed to the contamination. Well 16 is located less than ¼ mile north of SWMU O-1. Investigations performed to date on SWMU O-1 identified the chlorinated solvent PCE, and the metals cadmium and chromium exceeding the TNRCC risk reduction standard 2 groundwater protection criteria (RRS2-GWP). The site is depicted in Figure O1-1.

Previous Investigations: The Environmental Assessment verified the site location and that the pond had been bulldozed and graded to land surface in 1984. In 1995, CSSA decided to initiate field work at seven potential sources of groundwater contamination under the work plan for AL/OEB contract F33615-89-D-4003, order 67. A geophysical survey using EMI and GPR techniques was performed in March 1995. The apparent ground conductivity, shown in Figure O1-2, indicates the extent of the oxidation pond while the in-phase EMI data did not reveal any metal debris underneath the ground surface. The increase in conductivity values indicates that the ground has been disturbed. The GPR confirmed the results of the EMI survey, indicating the site to be roughly 75 feet in diameter and less than 5 feet deep.

Drilling and sampling were also conducted at the site in March 1995 under order AL/OEB 67. The analyses were conducted by Chemron Incorporated (Chemron) laboratory located in San Antonio. The field investigation revealed that the site contained weathered limestone and caliche at the surface with little vegetation. Sample OX-SB3 contained 2 feet of fill, and OX-SB2 contained 4 feet of fill material. The fill consisted of clay, limestone fragments, sand, and waste material. Results indicated the presence of PCE, and the metals cadmium and chromium, above RRS2-GWP criteria (see Figure O1-2).

A surface water sample contained toluene at a concentration of 0.034 mg/l. The MCL for toluene, as promulgated under the Safe Drinking Water Act, is 1.0 mg/l, which is above the level detected in the surface water sample. During a 1995 soil gas survey, both PCE and TCE were detected at the oxidation pond. The detected concentrations of PCE correspond with the results of the soil samples and form contours approximating the dimensions of the pond (see Figure O1-3). The results of investigations indicated that the highest concentrations are found where the pond was deepest. The high levels of PCE indicate residual saturation of PCE in the soil which could persist as a source of groundwater contamination. This area of contoured soil-gas concentrations is referred to as a "hot spot". Further soil-gas survey efforts to define the size of the "hot spot" were conducted in November and December 1995. The preliminary evaluation of the data indicated that the highest concentrations are in the south central area of the O-1 unit.

An investigation into the integrity of the remaining liner was initiated in 1996. Soil samples were collected within the excavated areas where the liner material was located. Chemron performed the analyses with results indicating significant levels of PCE and the metals chromium and cadmium (see Figure O1-4). The investigation continued with the excavation of approximately 80 cubic yards of fill material within the SWMU O-1 unit. This was done primarily to determine if any fractures of the underlying limestone were visible. Results of the investigation found that the liner material was indeed destroyed, as no piece larger than 5 feet in diameter was found intact. Additionally, no visible fractures of the bedrock beneath the soil layer were observed. The excavated soils were replaced and an additional soil gas survey performed in August of 1996 (see Figure O1-5).

During 1997, Parsons ES identified potential technologies that would remediate solvents and metals at SWMU O-1. These technologies included electrokinetic remediation; low temperature thermal desorption; stabilization/solidification; soil vapor extraction; soil washing/roasting/leaching; and landfilling. Electrokinetic remediation, an emerging and innovative remedial technology, was chosen for its potential ability to remove both solvents and heavy metals from contaminated soil. Lynntech Inc., located in College Station, TX, conducted a treatability study on the potential use of electrokinetic remediation at SWMU O-1. The primary tasks performed as part of the electrokinetic treatability study are briefly outlined below.

Initial efforts were made to identify an acceptable location for the field pilot study area and to provide soil from that area for a laboratory benchscale test. Soil samples were collected to assess the contaminant levels from three potential areas within SWMU O-1. The chemical analyses were performed by ITS.

SWMU O-1 soil from the selected area of the field pilot study was collected for the benchscale test. The soil was evaluated using batch tests to determine the optimum extractant for removing chromium from SWMU O-1 soils, the valence state of chromium after removal, and the appropriate tests to control soil swelling. The chemical and physical analyses conducted during the benchscale test were performed by Lynntech’s Analytical Laboratory and by EnviroTech Mid-Atlantic Laboratories located in Blacksburg, VA.

Soil samples collected during construction of the pilot scale field test unit in July 1997 were used to establish baseline conditions of the chosen area. ITS conducted the chemical analyses for PCE.

Construction of the field test unit was completed on 15 August 1997. The field test operations began with an effort to acidify the soils within the area using a mixture of citric and hydrochloric acid.

Initial operations for contaminant removal commenced 26 September 1997. Soil samples were collected to provide data on contaminant levels present in "control zones" between the anode and cathode wells. The chemical analyses conducted during the fieldscale test were performed by Lynntech’s Analytical Laboratory and by EnviroTech Mid-Atlantic Laboratories located in Blacksburg, VA.

Lynntech coordinated periodic monitoring and testing of the system.

The system operation was shut down 23 December 1997 and soil samples were collected to assess the operation of the unit. The electrokinetic field test unit was operated for 89 days. DHL Analytical performed the chemical analyses.

The limitations of the study include a shortened electrokinetic operation schedule, limited qualified PCE analytical data, and no data regarding complexation of metals with the citric and hydrochloric acids used in acidifying SWMU O-1 surface soils.

Soil samples were collected for initial (before the treatability study) and final (after the treatability study) site conditions at SWMU O-1. ITS generated the initial site characterization analytical data. DHL Analytical generated the final site conditions analytical data. Because of issues concerning the quality of any data generated from the ITS Richardson laboratory, the ITS data were determined to be questionable, and only usable as screening or qualified data.

The ITS qualified data is comparable to the analytical data generated by Chemron. Results of chemical analytical data from Chemron indicate that SWMU O-1 contained average concentrations of PCE and chromium of 57.3 mg/l and 169.7 mg/l, respectively. ITS qualified analytical data reported average concentrations of PCE and chromium of 1.7 mg/l and 272.6 mg/l, respectively. The PCE data generated by Chemron were collected prior to and during the liner investigation, and as such the levels of PCE were higher because of volatilization effects from investigation. DHL data were generated to determine the effectiveness of the treatability study, rather than to provide site characterization data such as the previous data generated by Chemron and ITS. Conclusions of the treatability study were drawn primarily from the data generated during the treatability study and the final site conditions analytical data generated by DHL.

ITS data did not affect the findings of the treatability testing relating to electrokinetic remediation effectiveness, operability, or cost determinations. The primary goal of the treatability study at SWMU O-1 was to test the efficacy of electrokinetic remediation on contaminated soils at CSSA, specifically at SWMU O-1. The conclusions drawn from the study indicate that electrokinetic treatment of the soils at SWMU O-1 is not cost effective due to the high buffering capacity exhibited in the soils. Since it is unnecessary to replicate the treatability study performed on
SWMU O-1 as the study accomplished its goals, rework data collection is not warranted.