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SWMU B-26 - TO0019 Work Plan Addendum
December 2003
Site Description and History
SWMU B-26 contains a trench identified during a review of a 1966 aerial photograph. Field investigations revealed wooden pallets next to the trench but no waste materials. There is no known prior documentation of the trench or its usage by CSSA. However, because of presence of the trench, SWMU B-26 is a suspected waste management site.
SWMU B-26 is a rectangular area covering approximately 0.4 acres (Figure B26-2). A three-foot deep, 20-foot wide, 185-ft long trench runs north-south down the center of SWMU B‑26. A five-foot high circular soil pile is present at either end of the trench. These soil piles were most likely generated from materials excavated from the trench. Three linear soil piles run parallel to each side of the trench. These linear soil piles are less than an inch high and approximately one foot wide. The site boundaries are defined such that the site contains the soil piles and trench.
Summary of Previous Investigation Results
An EM geophysical survey was conducted at SWMU B-26 in March 1996. Two anomalies were revealed by the survey in the northwest and central portions of the site. The northwestern anomaly, shown on Figure B26-2, was interpreted as potentially related to past waste-management activities. It is suspected that this anomaly is caused by buried metal because it was identified by both the in-phase and quadrature components of the EM survey. The second anomaly, located along the trench, was only identified by the quadrature component of the EM survey, and therefore was not caused by buried metal.
Three surface soil samples and three soil borings were advanced in 2000 and analyzed for metals, volatile organic compounds (VOCs), and semivolatile organic compounds (SVOCs). Sample SS01 was collected in the location of the geophysical anomaly. Sample SS02 was collected within the trench. Sample SS03 was collected from the soil pile adjoining the northern end of the trench. None of the soil samples contained contaminants of concern in concentrations above RRS1 closure standards.
A soil boring was advanced in the trench (SB02), another adjacent to the geophysical anomaly (SB01), and the final boring was located between the trench and the geophysical anomaly (SB03). Two samples were retained from each boring, one from approximately mid-way down the boring, and one from the terminus of the boring. No waste material or evidence of subsurface disturbance was encountered in any of the borings.
The majority of metal analyses results for subsurface soil samples were less than the associated background concentrations, with the exception of slight zinc exceedances at SB01 (12.5 to 13 ft), SB02 (9.5 to 10 ft), SB03 (6 to 6.5 ft), and SB03 (12.5 to 13 ft). Concentrations in these samples ranged from 11.9 to 17.5 mg/kg, and the zinc background level for Glen Rose Limestone is 11.3 mg/kg. However, all of these exceedances are below the Texas-specific median background concentration (30 TAC 350.51(m)) of 30 mg/kg.
Chromium was detected at 9.7 mg/kg in SB01 (12.5 to 13 ft), slightly exceeding the RRS1 standard for Glen Rose Limestone of 8.1 mg/kg. This concentration is below the Texas-specific median background level of 30 mg/kg.
Closure Plan and Sampling Recommendations
The site contains a trench and excavated soil material in two soil piles. Based on the results of the geophysical survey and the drilling program, it appears that the trench may not have been used for intended waste management activities. However, the small anomaly located in the northwest portion of the site warrants excavation to determine if it is associated with past waste management activities. Stockpiled soil present at the site can be used to regrade the site if sample analysis confirms that it meets RRS1 criteria.
Closure of SWMU B-26 under RRS1 requires removal of waste and waste residue at the site. Although geophysical survey results indicate that there is no buried metal within the trench, test pits will be excavated within the trench area to confirm that no other waste has been disposed of in the trench. A test pit will also be excavated at the location of the small anomaly in the northwest portion of the site. All waste encountered must be removed from CSSA for off-post disposal to pursue RRS1 closure with respect to the soil unit at SWMU B-26. Groundwater and competent bedrock will be addressed as part of the groundwater operable unit. The soil excavation will extend to the depth that waste or waste residue is encountered or to bedrock, whichever comes first.
If no waste material is encountered, any excavated soil should be backfilled into the excavation because RFI soil results showed no RRS1 exceedances. The estimated volume of waste material and waste residue present at SWMU B-26 could be up to 300 CY, if the trench or anomaly location does contain waste. Based on waste at most other SWMUs at CSSA, it is likely that this waste is non-hazardous. Confirmation samples should be collected following removal/remediation to verify that no contamination remains. Analysis should include chromium and zinc (SW-6010B), based on sample results from 2000. 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).
Following excavation of waste and waste residue, any resulting trenches will be backfilled with clean fill and the site restored.
Summary Of Planned Field Work
Amend CSSA’s Waste Profile using B-26 RFI data. RFI data indicates that the material at this site meets nonhazardous Class 2 criteria.
Collect one sample from each soil mound to determine if concentrations meet RRS1 criteria. Each sample should be analyzed for arsenic, barium, cadmium, chromium, copper, lead, mercury, nickel, and zinc. If this material meets RRS1 criteria, it can be used as backfill for any site excavations.
Excavate test pits at the anomaly and within the trench to determine if there is any buried waste. Remove all waste for disposal, and if practical, separate metal debris for recycling. If no waste is encountered, backfill excavation. Dispose of any waste encountered and soils exceeding CSSA background levels at Covel Gardens Landfill under waste profile CG-25591 C-5.
If waste is encountered, collect samples of the excavation sidewalls and bottom. Samples will be analyzed for chromium and zinc, based on the results of samples collected at the site in 2000.
Continue excavation until RRS1 soil criteria or competent bedrock, whichever comes first, is reached.
Re-grade the site with clean fill and reseed.
Validate data and prepare Closure Report for SWMU B-26.