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Area of Concern 67

TO0019 Work Plan Addendum

Site Description and History

AOC-67 is located along the east side of Building 90-1, in the southwestern portion of CSSA (Figure AOC67-2). The site consists of a north-south drainage ditch and a three-sided (open on one side with a base) concrete storage area that was built into the slope between the drainage ditch and Building 90-1. A concrete pad with a covered structure is located between the slope and Building 90-1, but this covered structure and concrete pad are not included as part of AOC-67. According to staff personnel associated with Building 90-1, the three-sided concrete storage area measures approximately four ft by ten ft (ten foot dimension parallel to Building 90-1) was used to store a temporary container for collecting liquid waste generated in Building 90-1. Site personnel indicated that piping ran from the building to the storage tank. When the fluid level was at capacity, the tank was moved to another storage area at CSSA and replaced with an empty tank. There are no records of spills or overfills at this tank, but due to the proximity of groundwater contamination, this site is considered an area of concern. In order to further investigate the site, the four-sided concrete structure will need to be removed and soil samples will be collected from the surrounding soils.

Building 90 is used for ordnance maintenance and Building 90-1 is used for ordnance materials bluing operations. The AST, removed in approximately 1997, was used to contain cleaning fluids and rinsate from both buildings. Potential sources of contamination at AOC-67 include liquid solvents, such as PCE and TCE, which were used during operations at Buildings 90 and 90-1. PCE and TCE were formerly used at CSSA to clean weapons and were stored in a metal vat located inside Building 90. The most recently used vat was removed from operation in 1995. The use of chlorinated solvents in Building 90 was discontinued in 1995 and an alternative citrus-based cleaner replaced PCE and TCE at CSSA.

Another potential source of contamination is a PCE plume identified in soil, soil gas, and shallow (up to 35 ft deep) monitoring well samples around Buildings 90 and 90-1 (Soil Gas Survey Technical Report, Parsons ES, 2001, and AOC-65 RFI Investigation Report). The perimeter of the PCE soil gas plume is approximately 35 ft west of AOC-67.

Summary of Previous Investigation Results

Soil Gas Survey

A soil gas survey was performed in January and February 2001 (Soil Gas Survey Technical Report) to address AOC-57, AOC-65, and AOC-67. Sampling was performed on a grid that covered the AOCs, with grid spacing ranging from 25 to 100 ft, depending on the detection of VOCs within the area of the survey. Samples were analyzed for TCE, PCE, DCE, trans-1,2-DCE, BTEX, vinyl chloride (VC), toluene, o-xylene, and m,p-xylene, and benzene. Approximately 40 samples were collected within a 200-foot radius of AOC-67.

No VOCs were detected in samples collected within the boundaries of AOC-67; however, PCE, TCE, cis-1,2-DCE, and trans-1,2-DCE were all detected within 200 ft of AOC-67. The soil gas sampling grid within AOC-67 was not tightened to less than 25-foot spacing since no contamination was indicated in any samples collected within AOC-67. PCE and TCE soil gas plumes were identified in the vicinity of AOC-65.

A localized TCE soil gas plume with a diameter of approximately 80 ft was identified approximately 200 ft southwest of AOC-67. The plume is located on the west side of Building 90 and had a maximum detected concentration of 8.56 �g/L. In addition, a PCE soil gas plume was identified underneath and around Building 90, within 35 ft of AOC-67. PCE was detected in 23 of the 40 samples collected within 200 ft of AOC-67. The highest reported concentration of 24,800 �g/L occurred under the former metal vat area in AOC-65, which is approximately 200 ft from AOC-67. The concentrations of the samples nearest to AOC-67 were all less than 1 �g/L.

Surface/Subsurface Soil Samples

Two composite surface soil samples were collected from within AOC-67 on January 2, 2002, following some utility work that trenched through AOC-67. Sample AOC67-1 was a composite of four soil samples northeast of the concrete pad at AOC-67 and sample AOC67-2 was a composite of four samples collected just northwest of the concrete pad. Samples were analyzed for barium, cadmium, chromium, copper, lead, and zinc. AOC67-1 exceeded the CSSA soils background concentration for lead (84.5 mg/kg) with a reported concentration of 240 mg/kg. AOC67-2 did not exceed background metals levels. The results for these samples may only be used for screening, but seem to indicate that metals contamination extends northeast of the concrete pad and not northwest of the pad.

Three soil borings were advanced at AOC-67 during April 2001 (Figure AOC67‑2). Borings were advanced to 35 ft. One surface soil sample was collected from each boring within 3 ft bgs. The second sample from each boring was chosen based on PID readings and structural/geological features. Barring the absence of any additional zones of potential contamination, the final sample was retained from the borehole terminus.

Metals concentrations from surface soil samples AOC67-SB1 (0-0.6 ft bgs) and AOC67-SB3 (0-0.6 ft bgs) exceeded CSSA metals background concentrations (RRS1). Chromium was detected at 50.0 mg/kg and lead was detected at 252.35 mg/kg in AOC67‑SB1 (0-0.6 ft bgs). These values exceed RRS1 concentrations of 40.2 mg/kg and 84.5 mg/kg for chromium and lead, respectively. AOC67-SB3 (0 to 0.6 ft bgs) and its field duplicate sample revealed concentrations of chromium (47 mg/kg and 52.9 mg/kg), zinc (108.77 mg/kg and 148.08 mg/kg), and lead (342.56 mg/kg and 324.45 mg/kg) in excess of respective background concentrations: 40.2 mg/kg, 73.2 mg/kg, and 84.5 mg/kg. The duplicate sample barium concentration (218.26 mg/kg) exceeded background (186 mg/kg), but the normal sample concentration (82.5 mg/kg) was less than background. For copper, the normal sample exceeded background (23.2 mg/kg) with a reported concentration of 31.77 mg/kg, whereas the duplicate sample concentration of 11.65 mg/kg was less than background.

AOC67-SB3 (30 to 30.5 ft bgs) had a reported chromium concentration of 8.8 mg/kg, slightly exceeding the Glen Rose background concentration of 8.1 mg/kg. Nickel also exceeded background with a concentration of 11.28 mg/kg. Glen Rose background for nickel is 6.8 mg/kg.

One VOC was detected above RRS1. Sample AOC67-SB3 (30 to 30.5 ft bgs) exceeded the RL (0.005 mg/kg) for methylene chloride with a reported concentration of 0.0093 mg/kg. Methylene chloride, a common laboratory contaminant, was not used at CSSA. Because only a very low concentration was detected in only one sample, this one exceedance is attributed to laboratory contamination. No other soil/rock sample concentrations exceed RLs for VOCs. No SVOCs exceeded RRS1 criteria.

Closure Plan and Sampling Recommendations

Soil sampling at AOC-67 has revealed metals contamination. Borings completed at the site encountered bedrock within 3 ft of ground surface. Since the soil profile is relatively shallow at AOC-67, it is recommended that the soils be excavated. Confirmation sampling should be performed after excavation to ensure that all contamination is removed from the site. Samples should be collected every 100 ft along the excavation sidewalls and one sample per 100 yd2 should be collected at the base of the excavation. Samples collected from the excavation base may be composited at a maximum of five locations per composite sample. Confirmation samples will be analyzed for VOCs, SVOCs, and metals (arsenic, barium, chromium, copper, nickel, zinc, cadmium, lead, and mercury). The waste generated from the excavation will be characterized by collecting samples from the waste and analyzing them for TPH and TCLP metals.

Closure of AOC-67 under RRS1 would require excavation and proper disposal of the contaminated soil. Surface soil in the vicinity of SB1, SB2, and SB3 exceeds background metals concentrations. The three-sided concrete pad and surrounding surface soils will be excavated for off-site disposal. Soil samples will then be collected from the excavation sidewalls and bottom to determine if all waste residue has been removed. Depending on soil thickness and depth of contamination, it is estimated that approximately 100 CY of material will need to be removed.

Prior to backfilling the excavated areas with clean fill, confirmation samples should be collected from the excavation bottoms and sidewalls to verify that waste residue has been removed. Samples will be collected at a frequency of one per 100 linear ft of sidewall, with a minimum of one sample per sidewall. If the bottom of the excavation is bedrock, bottom samples will be collected at a frequency of one per 20,000 ft2 of bottom surface area, with a minimum of two samples per excavation area. If the bottom of the excavation is soil, bottom samples will be collected at a frequency of one per 100 ft (100-ft grids). Samples will be analyzed for lead (SW-7421); barium, chromium, copper, and zinc (SW-6010); and VOCs (SW-8260B); these compounds were detected at concentrations above RRS1 criteria during previous sampling efforts.

After excavation has been completed, the site will be regarded, and clean fill will be brought in if necessary.

Summary Of Planned Work

  1. Remove concrete pad and excavate contaminated soil in the vicinity of the pad.

  2. Collect samples of excavated soils for waste characterization purposes. One composite sample consisting of five aliquots will be collected per 1,000 CY of soil. Analyze samples for TPH and TCLP antimony, arsenic, barium, beryllium, cadmium, chromium, lead, mercury, nickel, selenium, and silver. Dispose of any soils exceeding CSSA background criteria at Covel Gardens Landfill under waste profile CG-25591. The profile will be amended to include AOC-67 waste. It is estimated that approximately 100 CY of waste and contaminated soil will require disposal.

  3. Collect samples of the excavation sidewalls and bottom. Samples will be analyzed for barium, chromium, copper, lead, zinc, and VOCs.

  4. Continue excavation until RRS1 soil criteria or competent bedrock, whichever comes first, is reached.

  5. Re-grade the site with clean fill and reseed.

  6. Validate data and prepare Closure Report for AOC-67.