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TO0019 Work Plan Addendum, Area of Concern 50

Site Description and History

AOC-50 is a one-acre tract that is located in the southeastern portion of the inner cantonment area.  The site is approximately 100 ft south of SWMU B-29 and 200 ft south of SWMU B-30.  SWMU I-1 is located approximately 200 ft northwest of AOC-50 and the CSSA perimeter fence, which borders Leon Springs Villa Mobile Home Park, is approximately 400 ft south of the site.

AOC-50 consists of undeveloped wooded land.  The site is irregularly shaped and approximately 450 ft at its widest point, which is oriented in an east-west direction (Figure AOC50-2).  In the north-south direction, AOC-50 is approximately 200 ft at its widest point.  A dirt road enters the site’s boundary in the northwestern corner and exits the boundary in the far northeastern portion of the AOC.  The site was identified in March 1996 during the field efforts that were conducted at nearby SWMUs B-29 and B‑30.  During the initial site visit in March 1996, seventeen distinct areas of suspected waste were identified.  The suspected areas consist of rust-colored material at the ground surface and in near-surface soils.  During a site inspection in December 1999, potential UXO and other munitions scrap were located at the AOC.  The remaining metal carcass of a 100-pound practice bomb was removed from the site prior to the site inspection.

The potential sources of contamination at AOC-50 include the areas of rust-colored material on the surface, the trash-filled trench, spent munitions, and potential UXO.  The rust-colored material was identified as metal waste generated from ordnance maintenance operations conducted in Building 90.  This waste material consisted of metal particles and was thought to contain nickel penetrant.  However, recent information from personnel working in Building 90 indicates that this waste was generated from the Wheelabrator blast cleaning operations and does not contain nickel penetrant.  Because of the metallic nature of the waste, metals are the primary COC.  VOCs are also COCs because they are frequently associated with waste management activities and explosives are included as COCs because spent munitions and potential UXO were discovered at the site.

Summary of Previous Investigation Results

Geophysical Survey

EM and GPR geophysical surveys were conducted at AOC-50 in December 2001.  Prior to collecting EM or GPR data, a grid system was established at the site that encompassed the areas of suspected ground disturbance.  These grids consisted of staked locations separated by intervals ranging from 10-50 ft, depending on the size of the area and the amount of obstructions, if any.  The AOC-50 geophysical survey grid is illustrated in Figure AOC50-2.

The EM survey revealed evidence of one subsurface anomaly related to past waste disposal activities.  This anomaly was found to be a household trash trench.  There was little variation in the data that were recorded during the EM survey, which can be interpreted as homogenous and consistent soil and bedrock profiles throughout the AOC.  The GPR surveys were conducted to further investigate the information obtained by the EM survey.  The GPR also revealed no evidence of subsurface anomalies.  The geophysical survey results are displayed on Figure AOC50-2.

Surface/Subsurface Soil Samples and Waste Excavation Activities

Surface soil samples were first collected at AOC-50 in December 1999.  Two samples were collected, one where noticeable Wheelabrator waste was present (AOC50 NP-1) and another six inches directly below the Wheelabrator waste (AOC50‑1).  All metals were below background levels.

In September 2000, one waste characterization sample (AOC50 NP-1) was collected to determine the recyclability of the Wheelabrator waste.  This sample was analyzed for total metals.  This sample’s iron concentration was high enough for recycling but Newell Recycling does not accept military wastes; therefore, the waste was disposed of at Covel Gardens Landfill.

A field crew mobilized to the site on March 12, 2001 for excavation activities at AOC-50.  Prior to the initiation of excavation activities, the site was swept by a Parsons UXO avoidance team using handheld magnetometers.  The only items found were two spent rifle grenades.  All visible Wheelabrator blast cleaning operations waste was also marked for removal during the comprehensive sweep of the area.  Eagle Construction and Environmental Services (Eagle) over-excavated approximately 200 CY of soil and Wheelabrator blast cleaning operations waste.  During the activities, a backfilled trench was discovered at the southeast corner of the excavation area.  The visible contents included banding material, horseshoes, glass, and soil.  Eagle excavated and stockpiled the contents of the trench during April 9, 2001.  During that excavation, additional buried Wheelabrator waste was discovered.  Eagle was de-mobilized from the site until proper modifications to the project SOW could be implemented to address these new findings.

On April 12, 2001, two waste characterization samples were collected from the stockpiles soils after the excavation activities to confirm that the soil was non-hazardous and acceptable for disposal in a landfill.  One more waste characterization sample was taken of a deeper Wheelabrator waste horizon.  The three waste characterization samples (AOC50‑COMP1, AOC50-COMP2 and AOC50-NP01) were analyzed for VOCs and metals.  The three waste characterization samples were analyzed for VOCs and metals.  All were determined to be non-hazardous by both state and federal criteria.  In addition to the surface soil sampling, subsurface soil samples were also collected at three locations in the bottom of the excavated trench.  These samples were analyzed for metals and VOCs.  None of the samples had metals concentrations above background and all VOC detections were below RLs.

Using a backhoe, CSSA and Parsons personnel excavated test pits to determine the lateral extent of the additional Wheelabrator blast cleaning operations waste.  The reconnaissance trenching indicated that the extent of the additional buried Wheelabrator waste was limited to less than 50 CY.  Based on the analytical results discussed in the previous paragraph, the stockpiled soil and the additional Wheelabrator waste were disposed of offsite as non-hazardous waste.

In August 2001, 10 subsurface soil samples were collected to determine the extent of contamination at AOC-50 after the trench was backfilled.  These samples were analyzed for VOCs, metals and explosives.  No VOCs or explosives were detected above their respective RLs.  Background levels for cadmium, lead, chromium, copper, and zinc were exceeded.  All of the background level exceedances for metals occurred in four samples: AOC50-SS02, AOC50-SS03, AOC50-SS05, and AOC50-SS06.

Closure Plan and Sampling Recommendations

Closure of AOC-50 under RRS1 would require excavation and proper disposal of the contaminated soil.  Surface soil in the vicinity of SS02, SS03, SS05, and SS06 significantly exceed background metals concentrations.  The horizontal extent of contamination has been delineated to the east and west, but not to the north and south.  In addition, the vertical extent of contamination is not known.  Therefore, initially, the top two ft of soil in the vicinity of SS02, SS03, SS05, and SS06 will be excavated.  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 between 1,600 to 3,200 CY of material will need to be removed.

Prior to backfilling the excavated areas with clean fill, confirmation samples should be collected from the trench 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 cadmium (SW-7131A), lead (SW-7421), and chromium, copper, and zinc (SW-6010); these compounds were detected at concentrations above RRS1 criteria during previous sampling efforts.

A waste profile currently exists for this site.  Additional waste characterization samples may be necessary depending on the volume of material removed.  After excavation has been completed, the site will be regarded, and clean fill will be brought in if necessary.

Summary Of Planned Work

  1. Excavate top two ft of soil in the vicinity of samples SS02, SS03, SS05, and SS06.

  2. Dispose of soils exceeding CSSA background levels at Covel Gardens Landfill under waste profile CG‑25591.  Additional waste characterization samples (for TPH and TCLP Texas Eleven Metals) may be necessary depending on the volume of soil excavated.

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

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

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

  6. Validate data and prepare Closure Report for AOC-50.