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[SWMU B-2]

SWMU B-2 RFI Work Plan Addendum
August 1999

Soils: Tarrant Association, gently undulating (east) and Lewisville silty clay.

Known: SWMU B-2 was historically used as a small arms ammunition burn area (two trenches). The two trenches and three more anomalies were verified during geophysical survey, for a total of five anomalies. Approximately 2.5 acres in size, SWMU B-2 is located north of Well 16 and east of SWMU B-1.

Previous Investigations: Under Order 67, five geophysical anomalies were observed during an EM geophysical survey (14 February 1995). A GPR survey indicated ground disturbances, verifying the EM survey results (1 and 2 March 1995).

Also under Order 67, five soil borings were completed on 2 through 7 March 1995. Groundwater samples were collected from SB3 and SB5 on 6 and 7 March 1995. Butylbenzyl phthalate, di-n-butyl phthalate, toluene, chromium, copper, lead and nickel were detected in the soil/rock samples. Cadmium, chromium, lead and nickel were detected in the groundwater samples from SB3. Chemical constituents detected in the soil and groundwater are listed in Table B2-1 and Table B2-2, respectively. An additional boring was completed on 12 June 1995. There was insufficient water in the boring to collect a groundwater sample.

A soil gas survey was conducted on 26 and 27 June 1995. PCE was detected in the samples in concentrations less than 1 ug/L.

Under RL33, potential UXO items at the site were investigated in September 1997. Two trenches were excavated, but no UXO items were identified at the site. The trenches remain open, and soil from the trenches is in two mounds adjacent to the trenches.

Data Needs: Analytical data, including groundwater and subsurface soils/rock analyzed for VOCs, SVOCs, and metals, are needed for verification and clarification of previous data.

Rationale for Analytical Programs: Based on previous analytical results and past usage, chemicals of potential concern include VOCs, SVOCs, and metals. Toluene was the only VOC contaminant, phthalates were the only SVOC contaminant detected, and chromium was the only metal detected significantly above background levels in soil during previous investigations. Therefore, sample analysis will be limited to toluene, phthalates and chromium.

Closure Activities: The following activities constitute an additional investigation at SWMU B-2. This work will be completed as part of the requirements under the RCRA 3008(h) Order, but it is not currently included in any delivery orders.

  1. Soils excavated from the trenches during UXO investigation activities will be placed back in the trenches to prevent accidents during the RFI. Grass seed will be spread at the close of investigation activities to prevent erosion.

  2. Four soil borings will be advanced to further characterize the subsurface soils surrounding the area. The four borings will be completed in the approximate locations of borings SB1, SB3, SB4, and SB5. Three soil/rock samples will be collected from each boring; one at the surface, one at the middle of the boring and one at the total depth. The total depth of each boring will be approximately 30 feet. Each sample will be analyzed for toluene, phthalates and any metals which historically exceeded background concentrations. QA/QC samples will be collected as described in Section 2.4 of the FSP.

  3. If water is discovered in any of the soil borings, all borings will be sampled and may be 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 cadmium and lead, which were historically detected at concentrations above RRS2 GW standards. QA/QC samples will be collected as described in Section 2.4 of the FSP.

  4. IDW will be handled as specified in the FSP.

  5. If the results of the above work indicate that the site can be closed under RRS1 without any further investigation and/or remediation, a technical/closure report will be prepared and submitted in accordance with TNRCC closure requirements. If the site does not meet RRS1 requirements, a technical report describing the results of the investigation and recommended additional investigation and/or remediation will be prepared.