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[SWMU B-33 ]

TO0019 Work Plan Addendum

Solid Waste Management Unit B-33

Site Description and History

SWMU B-33 consists of bedding material for an approximately 325-foot section of water supply pipe that leads from a cutoff valve north to Building 45. The water supply pipe taps into a larger 6-inch water main which trends east-west through an empty field. Sand containing projectiles from the Building 90 test range was used as bedding material for the water supply pipe at SWMU B-33. Sand and spent projectiles were uncovered in areas along the pipe. Sand and spent ammunition jackets were also present at the surface where the water supply line entered Building 45. Figure B33-2 is an aerial photograph from 2003, showing the location of SWMU B-33. During a waste removal effort in 1997, most of the waste and waste residue was removed from this site. However, a small amount (2 to 3 CY) of contaminated backfill material, inaccessible to a backhoe, still remains near the foundation of Building 45.

Summary of Previous Investigation Results

Geophysical Survey

An EM geophysical survey was conducted in 1996 at SWMU B-33. Four anomalies were found. However, two of these anomalies were associated with buildings, a third with railroad tracks, and the fourth with the 6-inch metal water supply line. Thus, no anomalies related to past waste management activities were discovered during the geophysical survey.

Excavation Activities

In 1997, approximately 180 CY of lead-contaminated sand was excavated from SWMU B-33. The waste was then stabilized by solidification with Portland cement for disposal as non-hazardous Class 2 waste. While the excavation was open and water line diverted, four confirmation soil samples (B33-T1, B33-T2, B33-T3, and B33-T4) were collected and analyzed for metals in order to determine if all shot and lead-contaminated soils had been removed from all accessible areas. However, the analyses of the subsurface samples collected in 1997 were conducted by ITS Laboratories and deemed invalid by EPA in 1999. Replacement of these test pit samples was not performed to avoid damage to the active water line. Instead, collection of subsurface soil boring samples was performed.

Soil Borings

Subsurface and surface samples were retained from borings advanced prior to the excavation activities. However, these samples had to be recollected because the data was rejected by the EPA. When the borings were re-advanced in 2000, the contaminated soil had already been excavated and the trench backfilled; therefore, samples are representative of post-remediation conditions. This soil boring sampling at SWMU B-33 was biased toward sources for potential soil contamination related to leachate migration into soils adjacent to the trench. Each sample collected from three soil borings was analyzed for metals and explosives. No explosives were detected at concentrations exceeding applicable RRS1 criteria.

Analytical results indicated contaminations in exceedance of RRS1 criteria for Glen Rose Limestone, but not for soils. Barium, chromium, nickel, zinc, cadmium, and lead in one subsurface sample (B33-SB01 and B33-SB03) each exceeded background levels. All other metals concentrations reported were below the RRS1 closure standard criteria.

Closure Plan and Sampling Recommendations

Closure of SWMU B-33 under RRS1 requires removal of remaining projectile-laden sand (estimated to be 2-3 CY of material) and 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-33. 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.

The remaining projectile-laden sand is located at the junction of the water supply pipe to Building 45. This material could not be excavated with a backhoe in 1997 due to the proximity of active utility lines in the area. Therefore, these utility lines should be taken out of service temporarily while the excavation is conducted. Due to the proximity of utilities, the remaining material will likely have to be excavated by hand with a shovel.

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-33 is less than 20 CY. This waste may require PIMS stabilization prior to disposal.

Confirmation samples should be collected following removal/remediation to verify that no contamination remains. Analysis should include barium, chromium, nickel, and zinc (SW-6010B); cadmium (SW-7131A), and lead (SW-7421), based on results of the historic sample analyses. Since the area to be excavated is very small, one sample will be collected per sidewall and on the bottom of the excavated area.

Summary Of Planned Field Work

  1. Temporarily divert or take out-of-service any utilities in the vicinity of the remaining projectile-laden fill material.

  2. Manually excavate soils in the vicinity of the water utility pipe and Building 45, where projectile-laden fill material remains. A very small amount (less than 20 CY) of projectile-laden sand remains.

  3. 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. Stabilize waste with PIMS material, if necessary, prior to disposal.

  4. Dispose of waste and contaminated soils at Covel Gardens Landfill under waste profile CG-25591. The profile will be amended to include waste from SWMU B-33.

  5. Collect samples of the excavation sidewalls and bottom. Samples will be analyzed for barium, cadmium, chromium, lead, nickel, and zinc.

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

  7. Re-grade the site with clean fill and reseed. Restore any diverted or out-of-service utilities to Building 45.

  8. Validate data and prepare Closure Report for SWMU B-33.