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[SWMU B-28]

RL33 Work Plan Addendum
SWMU B-28, June 1997

Soils: Krum Complex and Tarrant Association (Gently Undulating)

Known: Area in inner cantonment where small arms ammunition and metal ammunition parts were disposed in two trenches. Some scrap metal appears to have melted and cooled, indicating that waste material may have been burned in the trenches.

Previous Investigations: Previous investigations at the site include a geophysical survey, a soil gas survey, and drilling and sampling of soil borings. The geophysical survey indicated that there are two northwest-southeast trending trenches (shown in Figure B28-1) containing buried metal. The northern trench is approximately 300 feet long and 15 feet wide. The southern trench is approximately 100 feet long and 15 feet wide. The trenches are shallow (less than 5 feet deep) as evidenced by field observations where the northern trench intersects the drainage ditch.

A soil gas survey was conducted at the site in 1995. In soil gas, PCE was detected at a maximum concentration of 0.70 ug/L. Six surface soil samples were collected at the site in 1995. Low levels of phthalates were detected in two of the surface soil samples. None of the metals levels exceeded background (RRS1) levels.

A total of six soil borings were drilled and sampled at the site. No VOCs were detected in the samples. Phthalates, probably laboratory contaminants, were detected in three samples. Chromium was detected in three borings at concentrations exceeding background (RRS1) levels; however, these concentrations were all less than the background concentration for the overlying soil. Results are summarized in Table B28-1. One groundwater grab sample was collected from B28-SB3; none of the analytes exceeded groundwater standards, as shown in Table B28-2.

In March 1997, UXO identification work was initiated at the site. As part of this effort, the trenches were excavated so that the material could be sifted to remove scrap metal and UXO. These sifting operations commenced in June 1997. A sample of the sifted soil was collected on June 19, 1997 to identify potential contaminants of concern at the site. As described in the paragraphs above, previous results had indicated that neither metals nor organics occur at elevated concentrations. However, the sample of the sifted soil indicate that barium, cadmium, copper, mercury, and zinc occur at above-background (above RRS1) concentrations.

Data Needs: Verification that no UXO is present in the trenches was needed. Analytical data to verify that soil matrix in and below trenches meets RRS1 criteria is necessary.

Closure Activities: The following field activities have been or will be performed to gather data for TNRCC closure submittal of SWMU B-28.

Each trench consisted of waste scrap metal and a minor amount of UXO mixed in a soil matrix. This material was excavated and sifted primarily to remove UXO but also to remove the metal scrap to the greatest extent possible. In addition, a trailer-mounted electromagnet was pulled over the excavated material to remove scrap metal.

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 and analyzed for the parameters listed in the following table. 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. If a lot does exceed background, three additional samples will be collected from that lot, and analyzed for the exceeding contaminant, to identify the portion of the lot exceeding background.

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.

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.