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RL33 Work Plan Addendum
SWMU B-24, May 2000

Soils: Krum Complex and Tarrant Association, gently undulating

Known: The B-24 site covers approximately 5 acres in the north pasture of CSSA. This site was identified in the field during the 1993 environmental assessment (ES, 1993). Spent ammunition and small spent rockets were observed there. Results from a geophysical survey conducted in 1995 indicated that there are several disposal trenches at the site, as shown in Figure B24-1.

Preliminary UXO identification work was initiated at the site in March 1997. Anomalies B and C were excavated in preparation for sifting activities which will be conducted to remove UXO and scrap metal. Anomaly A actually consists of two side-by-side trenches which trend north-south. Both of these trenches are approximately 250 feet long, 20 feet wide, and 15 feet deep. The trench contaminating anomalies B and C trench is approximately 400 feet long, 50 feet wide, and 15 feet deep. A fourth trench, measuring approximately 100 feet by 15 feet deep, is located south of the trenches containing anomaly A. Waste material encountered in the soil matrix consists primarily of rifle cartridges. The waste material may have been burned using gasoline as fuel. A small number of 20 mm projectiles (UXO) have also been identified at the site.

A preliminary soil sample was collected at the site in June 1997 to identify potential contaminants at the site. This sample was collected from soils excavated from the trenches at anomaly B. Preliminary results indicate that copper, lead, and zinc occur at above-background (RRS1) levels. Of the metals, only the lead concentration exceeds the RRS2 soil air ingestion concentration. In addition, the sample contained 7.65 mg/kg of 2,4-dinitrotoluene (2,4-DNT) and 0.476 mg/kg of 2,6-DNT.

Due to heavy rains this spring, the trenches filled with water. A sample of this water was also collected in June 1997. None of the metals levels in this sample exceeded maximum contaminant levels (MCLs).

Previous Investigations: As described above, a geophysical survey was conducted at the site in 1995. Three isolated anomalies were identified at the site.

Data Needs: Analytical data on subsurface soils and shallow groundwater (if it occurs at the site). Potential UXO items at the site need to be identified and removed.

Closure Activities: The following field activities will be performed to gather data for potential TNRCC closure submittal of SWMU B-24.

Each trench consists of waste scrap metal and a minor amount of UXO mixed in a soil matrix. This material will be excavated and sifted to remove the metal scrap to the greatest extent possible. In addition, a trailer-mounted electromagnet will be pulled over the excavated material to remove scrap metal. The sifter may be equipped with a smaller screen for this site.

The sifted soil will be sampled to ensure that it meets background (RRS1) criteria. Samples will be collected at a rate of one per 500 cubic yards. Each sampled lot of 500 cubic yards will be delineated in the field in case analytical results indicate that the soil does in fact exceed background. Each of these samples will be analyzed for the parameters listed in the table below.

To determine if each trench bottom meets RRS1 criteria, two to three samples will be collected from the bottom of each trench and analyzed for the parameters listed in the table above.

Sifted soil that has been identified as meeting RRS1 criteria will be placed back into the trench and the site will be regraded. Sifted soil that exceeds RRS1 criteria will be left in mounds on the surface for future decontamination. The soil mounds will be fenced with silt barriers.

If trench bottom and sifted soil samples indicate that chemical contamination exists at the site, five soil borings will be drilled to characterize the subsurface soils surrounding the trenches. Two soil samples will be collected from each boring; one near the middle of the boring and one at the total depth. The total depth of each boring will be 20 feet (five feet below the bottom of the waste management unit). Each sample will be analyzed for VOCs, SVOCs, explosives, and metals, as listed in the table above. Tentative boring locations are shown in Figure B24-1.

Water is not expected to be encountered at the site. However, if water is discovered in any of the soil borings, all five borings will be sampled and potentially completed as groundwater monitoring wells as detailed in Section 2.4.1 of the Work Plan Overview. Groundwater will be sampled, where present, and each sample will be analyzed for VOCs, SVOCs, explosives, and metals identified in the soil samples.

IDW will be handled as specified in agreed procedures identified by TNRCC letter dated 12 August 1996.

If the results of the above work indicate that the site can be closed under RRS1 without any further decontamination, a technical/closure report will be prepared in accordance with state closure requirements. However, preliminary results suggest that RRS1 closure may not be possible without soil disposal/treatment or decontamination.