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[SWMU B-2]

SWMU B-2 TO0019 Work Plan Addendum
December 2003

Site Description and History

The area that encompasses Solid Waste Management Unit (SWMU) B-2 is relatively flat and is covered by native grasses, with some small trees and brushy areas. SWMU B-2 is approximately 2.6 acres and is bounded by a dirt road to the northeast and trees to the east and west (Figure B2-1). A fence is present to the west, between SWMU B-2 and closed SWMU B-1.

Based on historical records, SWMU B-2 was used as a small arms ammunition burn site during 1954. Aerial photograph analysis revealed two nearly parallel trenches oriented from east to west at SWMU B-2. The presence of these trenches was confirmed during a field visit in 1995. At this time, munition canister lids (57 millimeter guns), an unidentified munition, and bricks were observed at SWMU B-2. Soil mounds are present at both ends of the northern trench, and at the west end of the southern trench. An additional soil mound is present north of both trenches. In August 2003, a third subsurface disposal area was identified immediately to the north of the previously-identified trenches. These trenches were presumably used to dispose of burned small arms ammunition. 

Summary of Previous Investigation Results

Previous investigations conducted at SWMU B-2 included two geophysical surveys, subsurface soil and groundwater sampling, a soil gas survey, and excavation activities conducted to identify and investigate potential unexploded ordnance (UXO) at SWMU B-2.

Geophysical Survey

In February and March 1995, ground penetrating radar (GPR) and electromagnetic (EM) surveys were conducted at the site. The EM survey identified five anomalies. Three of the anomalies (labeled A, B, and D) were caused by the two linear trenches, and two additional anomalies (labeled C and E) were situated to the north of the trenches where the third disposal area was recently identified. These five anomalies are presented in Figure B2-1. Although anomalies A and D appear to be south of the southern trench, this offset is associated with less exact measuring techniques during the 1995 survey. The GPR survey results indicated two disturbed areas corresponding to the two linear trench areas.

Soil Borings

Five borings were advanced to 30 feet (ft) below ground surface (bgs) each at SWMU B-2 in March 1995 (Figure B2-1). The borings were drilled on the edges of the two trenches known at the time to determine the extent of potential contamination and any potential releases associated with the trenches. In all of these borings, except B2-SB04 which was drilled in the trench area, limestone was encountered at a depth of only one foot. Surface soil, subsurface rock, and two borehole groundwater samples were collected for analysis of metals, volatile organic compounds (VOCs), and semivolatile organic compounds (SVOCs).

Borings B2-SB01 and B2-SB02 were advanced on either side of the southern trench at SWMU B-2. SB01 was advanced adjacent to a geophysical anomaly. None of the samples from these borings contained contaminants of concern (COCs) in concentrations above Risk Reduction Standard 1 (RRS1) standards.

The remaining three borings were advanced adjacent to the northern trench. Thin metal wire was recovered from a shallow depth (less than 6 ft bgs) in boring B2-SB04, located adjacent to one of the geophysical anomalies and north of the eastern end of the northern trench. At this boring, lead, chromium, and nickel concentrations in the shallow bedrock sample (1.8 to 3 ft bgs) exceeded RRS1 standards for the Glen Rose Limestone. At B2-SB03 and B2-SB05, toluene was reported in excess of the RRS1 closure standard in bedrock samples collected from 29 to 30 ft bgs. 

Phthlalates were reported in two soil and two bedrock samples. However, as discussed in the SWMU B-2 RCRA Facility Investigation Report, the presence of pthlalates is excluded from closure considerations because they were also detected in the associated equipment blank. 

Grab groundwater samples were collected from open borings B2-SB03 and B2‑SB05. Lead and cadmium were detected at 0.05 milligrams per liter (mg/L) and 0.01 mg/L, respectively, in the grab sample collected at B2-SB03, exceeding the 0.015 mg/L action level for lead and the 0.005 mg/L maximum contaminant level (MCL) for cadmium. Shallow groundwater is very rarely encountered at CSSA, and wells installed at shallow depths in the past have commonly been dry. Occasionally, shallow groundwater is encountered after precipitation events; therefore, shallow wells were not installed at SWMU B-2, and instead grab groundwater samples were collected. Due to the sampling conditions, these grab groundwater samples can only be used as an indication of possible contaminants in the soil at the site. 

Soil Gas Survey

In June 1995, a soil gas survey for VOCs was conducted at SWMU B-2 with 20 sample points arranged in a grid within the B-2 boundary. Numerous soil gas samples were collected from the area associated with each of the geophysical anomalies. Tetrachloroethene (PCE) was the only VOC detected. It was present at concentrations less than 1.0 microgram per liter (mg/L) throughout the site, with a peak concentration of 0.32 mg/L in central portion of the northern trench. Due to the very low concentrations detected in soil gas, the proximity of the groundwater PCE plume associated with SWMUs B-3 and O-1, and the lack of PCE detections in soil borings at the site, these low PCE concentrations detected in soil gas at SWMU B-2 are presumed to be associated with groundwater contamination in the vicinity of Well CS-MW16. 

Unexploded Ordnance Survey and Excavations

In September 1997, the two linear trenches at SWMU B-2 were excavated by UXO specialists. The lateral extent of the disturbed area to be excavated was determined based on previous investigations and the use of a Schonstedt metal detector. A brick burn box and associated brick pad were identified between the two trenches during site inspection. The southern and northern trenches were identified to be approximately 215 ft and 250 ft in length, respectively. The two linear disposal trenches were approximately 12 ft wide. The northern trench was only approximately five ft deep, and the southern was about 12 ft deep. 

UXO specialists examined all waste as it was excavated from the trench to determine whether any UXO was present. No UXO was found, however ordnance and explosives (OE) scrap, including munitions, firearms, and associated materials were found in the southern trench. The excavated materials were stored within SWMU B-2 in two stockpiles, one north and one south of the southern trench. The northern and southern stockpiles are 500 and 1,000 cubic yards (CY) respectively and contain metal debris, limestone cobble, and soil. The munitions and OE scrap are contained in the larger, southern stockpile.

Closure Plan

Waste and waste residue remaining at the site must be removed to meet RRS1 closure requirements. Because there is a potential for UXO at the site, the material must be carefully screened for OE prior to off-site disposal. Material excavated from the two linear trenches will be sifted and carefully monitored by UXO specialists. Any UXO encountered will be detonated by Fort Sam Houston. All other metal debris will be segregated for recycling. In addition, the third trench will also be excavated and the material screened for UXO.

After the waste has been screened for UXO and metal debris has been removed, the excavated soil will be sampled for waste characterization purposes, and analyzed for total petroleum hydrocarbons (TPH) and toxicity characteristic leaching procedure (TCLP) Texas 11 metals. One composite sample will be collected per 1,000 CY of material. Each composite sample will consist of five aliquots collected at random locations. The soil will then be removed and disposed at an appropriate landfill based on their waste characterization. 

After the stockpiles and mounds have been removed, confirmation samples will be collected from the bottom and sidewalls of the excavated areas to ensure that all contaminated media has been removed. Confirmation samples will be analyzed for chromium and nickel (SW-6010B); cadmium (SW-7131); lead (SW-7421); toluene (SW-8260B); and explosives (SW-8330). All of these analytes, with the exception of explosives, were detected above RRS1 standards during investigation activities at the site. None of the previous samples were analyzed for explosives. Prior to collecting any trench bottom samples, soil and silt that has eroded into the trenches, which have been open since 1997, will be removed and added to the stockpiles already on-site to ensure that representative confirmation samples of the sidewalls and trench-bottoms are collected. 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 square feet (ft2) of bottom surface, 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). 

After sample analysis confirms that all waste and waste residue have been removed from the site, the excavated areas will be backfilled with clean fill material, and the site will be re-graded and seeded.

Summary Of Planned Work

  1. Sift material previously excavated from the two linear trenches to remove any UXO.

  2. Excavate third subsurface disposal area (located to the north of the linear trenches), and sift material excavated from it.

  3. Detonate any UXO found, and render OE scrap unidentifiable. Recycle all metal scrap.

  4. Collect samples of the sifted soil for waste characterization purposes. 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-2 waste.

  5. Excavate soils and sediment that have eroded into the trenches that have been open since 1997. Collect samples of the trench/excavation sidewalls and bottom. Analyze for cadmium, chromium, lead, nickel, toluene, and explosives.

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

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

  8. Validate data and prepare Closure Report for SWMU B-2.