SWMU B-20/21 RL33 Work Plan

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RL33 Work Plan Addendum

SWMUs B-20 and B-21, March 1998

Soils: Crawford and Bexar stony soils, Krum Complex, and Brackett-Tarrant association

Known/Previous Investigations: Investigations at the B-20 former open burn/open detonation (OB/OD) area have taken place over several phases since November 1994. The initial scope of these investigations was based on the Partial Facility Closure Plan (ES, 1994a). Additional tasks were conducted under three amendments to the closure plan (Parsons ES, 1995f, 1995g, and 1997a). Results of these phases of work are described in the Remedial Investigation Report (Parsons ES, 1995d) and an Addendum to the Remedial Investigation Report (Parsons ES, 1996b).

The B-20 SWMU is a 33.5-acre field surrounded by wooded areas in the northeastern portion of CSSA. 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. B-21 is a small arms ammunition disposal area which is situated immediately adjacent to the B-20 site. Due to its proximity to B20, it has been combined with B-20 for the purposes of this plan. A chronology of events at the site, including environmental investigation activities and findings, is listed on the following page.

During previous investigations at the site, a total of 812 UXO items were identified within the site boundaries and in the perimeter areas (Parsons ES, 1996b). Fourteen of these items were found outside of the area that was systematically swept, in what are called the north and east extensions. Three items were as far as approximately ¼ mile north of the site. Most of the UXO found at the site has consisted of explosive residue encased in a portion of the original metal housing of the ordnance item. However, several chunks (approximate diameter of up to 1 inch) of bulk trinitrotoluene (TNT) were also found on the site.

The following chronology lists relevant activities at the B-20 unit since the first known use of the site in 1946.

1946- 1987	CSSA periodically used the B-20 area for ordnance OB/OD activities.
June 1993	EPA issued a Compliance Order for the B-20 site for unpermitted treatment of hazardous waste and for failure to have a closure plan.
January 1994	Red River Army Depot (RRAD) collected preliminary samples to provide an estimation of the nature and extent of contamination for environmental investigation planning purposes.
March 1994	Partial Facility Closure Plan for B-20 closure/remedial investigation (Parsons ES, 1994a) submitted to EPA Region VI.
Nov - Dec 1994	First phase of closure/remedial investigation conducted. Investigation consisted of the following activities: - Surface soil, subsurface soil, surface water, and sediment sampling; - UXO sweeping within original site boundary; and - Geophysical surveys to identify anomalies in craters.
June 1995	Final Remedial Investigation Report (Parsons ES, 1995d) submitted. Report recommended additional sampling and UXO clearing activities.
September 1995	Amendment to Project Plans (Parsons ES, 1995f) submitted to regulatory agencies, and second phase of RI initiated. Investigation included the following activities: - Subsurface soil sampling near three first phase RI borings; and - Surface soil sampling in south-central portion of site.
October 1995	CSSA received concurrence letter from U.S. Fish and Wildlife Service (USFWS) for planned vegetation clearing activities at the site.
December 1995-March 1996	Second Amendment to Project Plans (Parsons ES, 1995g) submitted to regulatory agencies, and subsequently, field activities were conducted. Investigation included the following activities: - Vegetation clearing to facilitate UXO identification; - Control-burned brush piles (Controlled burn of entire site was intended, but weather did not permit); - Systematic sweep of surface for UXO with magnetometers within original site and perimeter; - Excavation and removal of buried UXO in craters; - Excavation and removal of buried UXO in northern "disturbed" portion of site; and - Collection and disposal (via recycler) of scrap metal scattered over the surface of the site.
January 31, 1996	All UXO items found on site to date (365 items) were detonated after receiving approval from TNRCC on January 29, 1996.
May 8, 1996	UXO items identified since January 31 (447 items) were detonated on site.
June 1996	Addendum to the Remedial Investigation Report (Parsons ES, 1996b) submitted. Report recommended additional UXO clearing activities.
January 17, 1997	Prescribed burn conducted at B-20.
January 1997- May 1997	Third Amendment to Project Plans for Remedial Investigation at B-20 Former Open Burn/Open Detonation Area (Parsons ES, 1997a) submitted, and subsequently, field activities were conducted. East extension to B-20 was cleared of vegetation and systematically swept. In addition, sifting operations were initiated to remove buried UXO and scrap metal from the site.

Data Needs: Buried UXO at the site had to be identified and removed. In addition, shot and lead-contaminated sand existing at both B-20 and B-21 must also be removed.

Closure Activities: The top 6 inches of soil in the northern portion (grids A1-B4) of the B-20 site (Figure B20-1) have been sifted to remove UXO and scrap metal. The removed material from the sifting operation (i.e., rock and metal debris) were spread over an area and metal debris was further removed by a trailer mounted electromagnet.

The sifted soil was sampled to determine if it meets background (RRS1) criteria. Samples were collected at a rate of one per 500 cubic yards. Each sampled lot of 500 cubic yards was delineated into separate lots. Analytical results indicate that the soil does in fact exceed background concentrations. Three additional samples were collected from each lot, and analyzed for the exceeding contaminant (lead), to identify the portion of the lot exceeding background. Results indicate that a majority of the sifted soils exceed background criteria for lead, but none of the sifted soils have been found to be hazardous. These soils will be remediated or disposed of as described in the waste disposal technical approach.

There are approximately 80 cubic yards of shot and lead-contaminated sand in the northern portion of B-20, and approximately 20 cubic yards of material at B-21. Toxicity characteristic leaching procedure (TCLP) analytical results of one sample of the B-20 overexcavated material will be used to determine potential disposal options.