[SWMU B-12]

TO0019 Work Plan Addendum, Solid Waste Management Unit B-12

December 2003

Site Description and History

SWMU B-12 is a one-acre site that was reportedly used for disposal of scrap metal and various weapons.  Vegetation at the site is sparse and consists of grassy patches (Figure B12-2).  The southwestern portion of the site consists of an embankment while the northeastern area is flat and slopes gently toward the embankment. The area periodically contains standing water.

Based on interviews and historical research, SWMU B-12 was reportedly used for the disposal of large pieces of scrap metal and various weapons.  Scrap metal, including the tailfins of dummy practice rounds, clay pipe fragments, and ceramic and porcelain shards were observed embedded in the embankment during a field visit in 1995.  Prior to waste disposal at this site, this area may have been excavated to provide soil for the nearby earthen-covered magazines.

Summary of Previous Investigation Results

Geophysical Survey

In May 1995, an EM geophysical survey was conducted on the flat lying area of the site.  No anomalies were detected.  The embankment was not included in this survey due to the abundance of surface metallic debris, the steep slope of the embankment, and the presence of thick vegetation along the embankment.

Soil Borings

In August and September of 2000, four soil borings were drilled at SWMU B-12 at the base of the embankment where scrap and debris have been observed.  Eight subsurface samples and four surface soil samples were collected, along with three field duplicates.  These samples were analyzed for metals, VOCs, SVOCs, and explosives.

Metals concentrations above RRS1 closure standards were detected in all borings.  Most of these concentrations did not significantly exceed RRS1 standards, except at RW‑B12-SB04 (0 to 0.5 ft bgs) where lead was detected at 773.2 mg/kg, mercury was detected at 0.65 mg/kg, and zinc was detected at 182.5 mg/kg.  Other metals exceeding RRS1 criteria at the site include barium, copper, and nickel.

Fluoranthene was present in the surface soil sample collected from RW-B12-SB04 (0 to 0.5 ft bgs) in a concentration of 0.75 mg/kg, which only slightly exceeds the reporting limit (RL) for this sample of 0.70 mg/kg.

Bis(2-ethylhexyl)phthalate was detected above the RRS1 closure standard in seven out of fifteen samples retained from the borings.  However, as explained in the SWMU B-12 RCRA Facility Investigation Report, due to the absence of any other SVOCs, bis(2-ethylhexyl)phthalate is excluded from closure considerations as it likely associated with sampling equipment.  There are no records of bis(2-ethylhexyl)phthalate use or disposal at CSSA.

SVOCs, explosives, and all other VOCs were reported below RRS1 closure standards.

Closure Plan and Sampling Recommendations

Closure of SWMU B-12 under RRS1 requires removal of waste visible in the embankment at the site and delineation and subsequent remediation or removal of contaminated soil at the site.  The waste must be removed from CSSA for off-post disposal to pursue RRS1 closure with respect to the soil unit at SWMU B-12.  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.

Excavated material should be characterized with TPH and TCLP metals (Texas Eleven) analyses prior to disposal.  The estimated volume of waste material and waste residue present at SWMU B-12 is approximately 1,300 CY.  This estimate is based on an assumed length of 200 ft.  In addition, it is assumed that waste material is present throughout the height of the 20-foot embankment, and it extends back 8 ft from the embankment wall.  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 barium, nickel, copper, and zinc (SW-6010B), lead (SW-7421), mercury (SW-7471A), and fluoranthene (SW-8270C), based on results of the RFI soil boring samples.  Samples will be collected at a frequency of one per 100 linear ft of sidewall, with a minimum of one sample per wall.  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 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).

Evaluation of the current boundary of SWMU B-12 should also be made at this time, and if any adjustments are necessary, the boundary of the site should be re-surveyed with a GPS unit.  The current boundary of the site appears to include too much area to the east, and possibly not enough area to the west.  Following excavation of waste and waste residue, any resulting trenches should be backfilled with clean fill and the site restored.

Summary Of Planned Work

  1. Excavate waste and waste residue in embankment and at the base of the embankment.  Surface soil metals concentrations in each of the RFI soil borings exceeded background criteria, so soil at the base of the embankment must also be excavated for disposal.  If practical, separate metal debris for recycling.

  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 SWMU B-12 waste.  It is estimated that approximately 1,300 CY of waste and contaminated soil will require disposal.

  3. Collect samples of the excavation sidewalls and bottom.  Samples will be analyzed for fluoranthene, barium, copper, lead, mercury, nickel, and zinc; these parameters exceeded RRS1 criteria in the samples collected at the site in 2000.

  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 SWMU B-12.