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OBJECTIVE

The primary objective for additional work efforts for the B-20 remedial investigation is removal of contaminated soils, scrap metal, and unexploded ordnance (UXO) in the 5-acre grid area in the northern portion of the B-20 site (as shown in Figure 1). Contaminated soils will be excavated, stabilized (if necessary), and disposed off-site. Scrap metal and UXO will be removed through use of a sifter. UXO found at the site will be detonated, and scrap metal will be sent to a metal recycling facility. The approach for accomplishing these tasks is described below.

APPROACH

Waste disposal and sifting operations at the B-20 site will focus on the 5-acre grid area in the northern portion of the site. The two types of areas which will be addressed are the small ammunition disposal areas and the grid areas. Two of the three small ammunition disposal areas are situated within the grid areas. The approach which will be taken for completing each of the main tasks is described in detail below.

Small Ammunition Disposal Areas

I. As shown in Figure 1, two small ammunition disposal areas are situated within the grid area. A third ammunition disposal area at B-20 (B-21, located on the east side of the site) will also be addressed in the same manner as the two within the grid area. The disposed ammunition and associated sand (i.e., the waste material) will be excavated and placed on plastic sheeting at an appropriate location within the B-20 boundary. The material, as much as possible, will be located on level terrain which is easily accessible by heavy equipment.

II. Previous analytical results indicate that this material would be considered hazardous waste. The material will be sampled after it is stabilized for disposal. The hazardous waste stabilization and sampling effort will be described after the waste disposal subcontractors have been identified and consulted.

III. After the ammunition and sand have been excavated, soils from underneath that material will be overexcavated and stockpiled for disposal. Analytical results from previous investigations indicate that lead in the ammunition has leached; therefore, this overexcavation is necessary to remove contaminated soils. At least one sample will be collected from the bottom of each excavation to determine if all of the contaminated material has been removed. The bottom samples will be analyzed for lead (SW-7421). This overexcavated material will also be disposed of, but stabilization is not anticipated to be necessary. Waste disposal and characterization sampling will be described after waste disposal subcontractors have been identified and consulted.

IV. Overexcavation and stockpiling at the ammunition disposal areas will continue until lead levels reach risk reduction standard 1 (RRS1) criteria. As shown in Figure 2, two soil types occur within the grid area. The RRS1 level for lead in Brackett Tarrant soils is 128 mg/kg, and 133 mg/kg in Crawford and Bexar soils. For this effort, the target cleanup level will be 133 mg/kg. When lead levels reach 133 mg/kg or below, overexcavation will be considered to be complete.

Grid Areas

I. The top 6 inches of soils will be removed from the grid areas and stockpiled within the B-20 boundary for sifting operations. Although soils in this portion of the B-20 site are relatively deep (ranging from 4 to approximately 10 feet deep), most waste material has been found to occur within the top 6 inches. To ensure that no UXO remains at greater depths, the area will be swept with a magnetometer after the top 6 inches have been removed and stockpiled. Earth-moving equipment will be used to stockpile the soils. Craters will be cleared of UXO and leveled to facilitate the soil stockpiling effort.

II. Once the sifter and conveyor belt assembly are mobilized to the site, the stockpiled soil will be loaded onto the conveyor belt, which will feed the soils into the sifter. The sifter will be equipped with a screen capable of removing all debris greater than 3/4 inch in diameter. A rotating assembly on top of the sifter will break the clayey soil up before it is sifted. To verify that this material is not contaminated, composite samples of the sifted soils will be collected at a frequency of one per 500 yd³ and will be analyzed for lead (SW-7421). Soil will be collected from the output of the sifter and composited for each sample. Previous sampling at the site has shown lead to be the only contaminant occurring in grid area surface soils at levels exceeding RRS1 criteria.

Based on previous sampling at the site, these soils are not expected to contain lead levels above background. However, since there is some lead contamination in this portion of the site, these additional samples will ensure that the site meets RRS1 levels, and will provide data for future site closure. The 500 yd³ lots will be redistributed in the grid area if soils are found to meet background levels.

Lab analysis will identify what, if any, additional work on the redistributed soils is necessary:

1. If total lead results for the 500-yd³-lot are greater than 133 mg/kg, the soil will be considered potentially hazardous.

1. Three additional samples will be collected from the subject 500 yd³ lot (one composite sample per 100 yd³) and analyzed for total lead (SW-7421).

2. Sample lots which contain greater than 133 mg/kg total lead will be segregated. Depending on the quantity of soils which exceed background, this material will either be disposed of (no stabilization necessary) or left on site for future on-site remediation.

2. Soils which are below 133 mg/kg, identified through lab analysis, will be left within the grid areas. Based on previous surface soil analytical results, it is anticipated that most, if not all, of the sifted soils will contain lead levels below background.

SAMPLE ANALYSIS

The following table identifies the anticipated number of samples required and analysis method expected from the work efforts.

Sample collection and handling techniques will follow the Sampling Analysis Plan (SAP) for SWMU Closures at Camp Stanley Storage Activity (Parsons ES, 1996). Analytical techniques will follow procedures described in Test Methods for Evaluating Solid Waste, U.S. Environmental Protection Agency, SW-846 and the HQ AFCEE QAPP (AFCEE, 1996).

As described in the Amendment to Project Plans for Remedial Investigation at B-20 Former Open Burn/Open Detonation Area (Parsons ES, 1997a), four types of field QC samples will be collected during the investigative effort. QC samples to be collected include equipment blanks, field duplicate samples, and MS/MSD samples. Sample descriptions, identifications, and frequencies required are described in detail in the SAP (Parsons ES, 1996a).

The results of these additional activities at B-20 will be documented in an addendum to the B-20 Remedial Investigation Report (Parsons ES, 1995d). A detailed description of the sifting operation and its results will be included, as well as sampling results which verify that the ammunition disposal areas have been completely removed. Photographs of the sifting operation and waste disposal activities will also be included.