The former open burn/open detonation SWMU B-20 is a 33.5-acre field surrounded by a wooded area in the northeastern portion of CSSA. B-21 is a small area located immediately adjacent to B-20. Due to the close proximity and similar usage of SWMUs B-20 and B-21, they are collectively referred to as B-20 for this report. According to a memorandum on file at CSSA, the B-20 area was first used for demolition activities in 1946. The B-20 operations included detonation of conventional explosive ordnance and other ordnance items, static downward firing of one rocket motor nose, disposal of scrap metal from detonation activities, and disposal of small arms ammunition. Based on the nature of its operation, the B-20 site is considered a thermal treatment unit by federal regulators and is referred to as Unit 05 on CSSA�s Notice of Registration (NOR). As a hazardous waste treatment unit, the B-20 site is regulated under both federal and state regulations. The U.S. Environmental Protection Agency (EPA), Region VI, RCRA Enforcement, Texas Section, issued a Compliance Order to CSSA on June 30, 1993. This order required CSSA to immediately cease operations of the unit and prepare a closure plan in accordance with applicable regulations. After the closure plan was prepared and approved, a Remedial Investigation (RI) was conducted. The objectives of the RI were to assess the effect of past waste disposal actions on the environment and to recommend a standard to be applied for site closure. The RI also included several phases of unexploded ordnance (UXO) removal.

The Remedial Investigation Report for B-20 Former Open Burn/Open Detonation Area (Parsons ES, 1995) presented several recommendations for additional work at the B-20 site to prepare it for future closure. Metals levels in surface soils over a large area at the site (approximately 10 acres) were found to exceed background concentrations. The RI report recommended that treatability studies be conducted to determine the most technically appropriate and cost-effective remediation technology for the site.

One of the remediation methods chosen for a treatability study was physical treatment by use of a soil washing technique to separate lead particulates from the soil matrix. This physical treatment method, referred to as density separation, uses water to separate heavy metals from the soil matrix, as traditionally used in mining operations. Physically treated soils were to be advanced to an evaluation of acid leaching. However, soils at the site were found to have a high pH (alkaline); therefore acid leaching was considered too cost prohibitive and technically inappropriate. This finding was further substantiated by the acidification portion of the Electrokinetic Treatability Study at SWMU O-1 (see Electrokinetics Treatability Study report) as well a similar soil washing treatability study at Lackland AFB, which is located approximately 20 miles from CSSA in an area with similar alkaline limestone-based clayey soils. Therefore the focus of this study report is on the physical separation technique (soil washing). In order to assess the ability of soil washing to remove contaminants from SWMU B-20 soils, a benchscale study was performed by Brice. During this study, density treatment techniques were used to remove lead projectiles from B-20 surface soils. The analyses performed, methodologies, and results from this study form the basis of this report.

This report is prepared by Parsons Engineering Science (Parsons ES) under contract to the U.S. Air Force Air Mobility Command (AMC) Contract F11623-94-D0024, delivery order RL33.

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