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Final Phytoremediation Treatability Study
Section 2 - Site and Study Background
CSSA is located in northwestern Bexar County, approximately 19 miles northwest of downtown San Antonio in south-central Texas. The installation consists of 4,004 acres immediately east of State Highway 3351 (Ralph Fair Road), and is approximately 0.5 mile east of Interstate Highway 10.
Generalized facts regarding this history and environmental setting of CSSA are located in the CSSA Environmental Encyclopedia (Volume 1-1; Background Information Report). In the Background Information Report, data regarding the geology, hydrology, and physiography are available for reference.
2.2 - Site Background and History
As noted in the introduction, the former OB/OD SWMU B-20 is a 33.5-acre field surrounded by wooded areas in the northeastern portion of CSSA. According to a 1950 memorandum on file at CSSA, approximately 200 tons per year of ammunition were destroyed at the site from 1946 to 1950. Additional explosives were detonated in 1984, 1986, and 1987. There were no reported detonations at the site from 1951 to 1983, in 1985, or after 1987.
According to the USDA Soil Conservation Service (SCS) soil survey for Bexar County, Texas, soil types at the B-20 site include Brackett-Tarrant association, Crawford and Bexar stony soils, and the Krum complex (USDA, 1966).
The Brackett-Tarrant association soils occur on the hills in the west-central and northern portions of the B-20 site. The Crawford and Bexar stony soils occur in the north-central and southeastern portions of the B-20 site on broad, level to gently undulating areas. The Krum complex soils are located in infrequently flooded streambeds such as those in the eastern and northeastern areas of B-20. A site location map is shown as Figure 1 within the CSSA Environmental Encyclopedia (Volume 1-1, Background Information Report). A soils classification map is included as Figure 4 in Volume 1-1, Background Information Report of the CSSA Environmental Encyclopedia.
A description of the B-20 geology is included in Volume 1-1, Background Information Report, of the CSSA Environmental Encyclopedia.
2.5 - Statistical Evaluation of Background Metals Concentrations
Background concentrations of metals in the soil types that occur at CSSA were statistically calculated and initially reported in the Evaluation of Background Metals Levels (Parsons ES, 1996a). The statistical approach was revised, and the Revised Evaluation of Background Metals Concentrations (Parsons ES, 1997) was submitted. The revised evaluation, which is included in Volume 2 of the Environmental Encyclopedia, was approved by the Texas Natural Resources Conservation Commission (TNRCC) on September 23, 1997. Much of the data used in the document was generated by Intertek Testing Services (ITS). In 1998, concerns regarding the quality of data analyses conducted by ITS were identified. Therefore, in 1999, CSSA background samples previously analyzed by ITS were recollected and analyzed by APPL Laboratory in Fresno, California. A draft second revision to the Evaluation of Background Metals concentrations has recently been prepared (Parsons ES, 2001). Because this report is a draft and has not yet been approved by the TNRCC, the approved 1997 values are used in this report.
2.6 - Summary of Prior Investigation Results
A brief summary of results obtained from previous investigations are provided behind the B-20/21 tab in Volumes 1-2 and 3-1 of CSSA�s Environmental Encyclopedia. An overview of the results of previous investigations is provided below. A chronology of environmental investigations at B-20 is included in Appendix A.
A total of 43 surface soil samples were collected during the Phase I Remedial Investigation of B-20 in November 1994 (Parsons ES, 1995). These samples consisted of 21 judgmental samples and 22 random systematic samples. An additional 16 surface soil samples were collected in September 1995 during the Phase II Remedial Investigation (Parsons ES, 1996b). All surface soil samples were collected at a depth of approximately 0.5-foot. Analytical techniques followed procedures described in Test Methods for Evaluating Solid Waste, USEPA, SW-846, November 1986 (USEPA, 1986). Terra Laboratories in League City, Texas performed all metal analyses for the remedial investigations at B-20.
Results of these investigations concluded that approximately 30 percent of the surface soils were contaminated with heavy metals, including arsenic, barium, cadmium, lead, and mercury at concentrations above Risk Reduction Standards 1 (RRS1), or background levels. Subsurface soils were generally not contaminated with heavy metals. Additional details of the results of B-20/21 investigations are available in CSSA�s Environmental Encyclopedia (Volume 3-1, B-20/21 Remedial Investigation).
Explosive residue was detected at low concentrations in extremely localized areas. For instance, soil samples collected immediately under �chunks� of raw TNT contained explosive residue, as might be expected. However, soil samples collected as little as 3 to 4 inches away did not contain any explosives. In addition, a total of 812 UXO items were removed from the site and its perimeter areas (Parsons ES, 1996b). Most UXO found at the site has consisted of explosive residue encased in a portion of the original metal housing of the ordnance item. The focus of this report is on the ability of phytoextraction to remediate heavy metals from surface soils at CSSA and does not address UXO or explosive residue.
During 1997, UXO items were removed from approximately 6 acres of surface soils located in the northern portion of the site. Initially, these items were removed during a �mag and flag� UXO identification operation. However, the large amount of buried metallic debris in this portion of the sites made this effort extremely labor intensive. Each individual metallic item identified by a magnetometer had to be flagged and hand-dug. Many of these items were found to be nails and other non-UXO debris. Therefore, in 1997, a sifting operation was initiated to remove the UXO and other metal debris. The top 6 inches of soil in the B-20 site was excavated, stockpiled, and sifted in the second phase of the remedial investigation to remove UXO and scrap metal. The sifted soils were then characterized and compared against background (RRS1) criteria for lead. These samples were only analyzed for lead because, as shown in Figure 2.1, lead was the only metal in this portion of the site which exceeded background levels. Samples were collected at a rate of one per 500 cubic yards. Analytical results indicate that the sifted soils exceeds background criteria for lead. Intertek Testing Services (ITS) laboratory analyzed the samples collected during the sifting operations. Because of issues concerning the quality of any data generated from the ITS laboratory, the data were determined to be questionable, and only usable as screening or qualified data. The ITS qualified data however, complements the existing data collected during the previous phases of remedial investigations, although the lead levels are higher than previously observed.
The results of these investigations indicate that both the sifted soil piles from the northern 6 acres of the site and the approximately 10 acres of soil which remains in situ in the central portion of the site will require remediation of metals to close under RRS1 (background).
2.7 - Media and Contaminants of Concern
A discussion of the media and contaminants of concern is located in CSSA�s Environmental Encyclopedia (Volume 1-2, B-20/21) and in the Remedial Investigation Report for SWMU B-20 (Parsons ES, 1995). Results obtained from additional samples taken during the second phase of investigation at B-20 are discussed in the Conclusions section of the Addendum to Remedial Investigation Report for SWMU B-20 (Parsons ES, 1996b). A brief overview of the contaminants of concern is discussed below.
Results of the surface soil analytical data indicated areas within the SWMU B-20 boundary where metals concentrations exceeded RRS1 levels (1997 background). Metals exceeding background over an approximate 10-acre area include arsenic, barium, cadmium, lead, and mercury.
The primary contaminant of concern in the sifted soil piles is lead. The phytoextraction treatability study was performed on the sifted soil piles. Therefore, the focus of this treatability study report is for the treatment of lead contaminated soils specifically generated from the sifted soils located at SWMU B-20/21.
2.8 - Determination of Cleanup Levels
The TNRCC promulgated the Texas Risk Reduction Program (TRRP) under Chapter 30 of the Texas Administrative Code (TAC), Section 350 (30 TAC �350) in September 1999. The effective date of the TRRP rule is May 1, 2000. However, in the interim, the regulated community has the right to choose whether the response action is reviewed under the TRRP or under the former Risk Reduction Rule (30 TAC �335). CSSA submitted letters of closure notification to the TNRCC on February 20, 1996 and July 19, 1999 indicating their intent to close the site under 30 TAC �335, Subchapter S, Risk Reduction Standard 1. Under the TRRP, CSSA still maintains the same decision of closing SWMU B-20/21 under RRS1.
As specified in 30 TAC �335, Subchapter S, closure under RRS1 requires all contaminant concentrations be remediated or removed and must not exceed determined background concentration levels for metals or practical quantitation limits (PCL) for other contaminants of concern. Background lead concentration for soils within the sifted soil area of SWMU B-20/21 has been determined to be 133 milligrams per kilogram (mg/kg) for Crawford and Bexar soils, and 128 mg/kg for the Brackett-Tarrant soils. Additional information regarding background concentration levels of metals of concern are included in CSSA�s Environmental Encyclopedia (Volume 2, Background Metals Level).