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SWMU Demo Dud Area (DD) Area Closure Report

Section 1 - Introduction

On May 5, 1999 an Administrative Consent Order was issued to Camp Stanley Storage Activity (CSSA) pursuant to §3008(h) of the Solid Waste Disposal Act (SWDA), as amended by the Resource Conservation and Recovery Act (RCRA), and further amended by the Hazardous and Solid Waste Amendments (HSWA) of 1984. In accordance with the RCRA Facility Investigation (RFI) requirements of the Consent Order, an RFI report for Solid Waste Management Unit (SWMU) Demo Dud (DD) Area was completed in May 2002 to document the environmental condition of the site and site closure requirements, and recommend further investigation. This Closure Report includes by reference the information presented in the SWMU DD Area RFI Report.

The SWMU DD Area RFI Report recommended excavation and disposal of waste at the site. Results for three borings sampled at SWMU DD Area indicated above background levels of copper, lead, mercury, zinc, and toluene in soils. The report suggested that additional sampling be done to determine the extent of the contamination, and remediation was to follow the results. This report documents the closure activities at SWMU DD Area.

The closure work was performed by Parsons under the U.S. Air Force Environmental Remediation and Construction (ENRAC) Contract F41624‑01‑D‑8544, Task Order 19 (TO 0019). The Air Force Center for Environmental Excellence (AFCEE) provided technical oversight for the delivery order. Based on the project statement of work (SOW), a set of work plans to govern the fieldwork was established. These include:

Work Plan Overview

(Volume 1-1, TO0019 Addendum);

Site‑Specific Work Plan

(Volume 1-2, SWMU DD Area);

Field Sampling Plan

(Volume 1‑4, TO 0019 Addendum); and

Health and Safety Plan

(Volume 1‑5, TO 0019 Addendum).

Closure activities at SWMU DD Area were conducted from December 2003 through May 2004. As recommended in the TO 0019 Work Plan, excavation and disposal activities were conducted. Approximately 1,630 cubic yards (CY) of soil were excavated from the site during the closure activities. This soil was disposed along with soil stockpiled at the site during excavation activities conducted in 1997 (see Section 1.4.1). Confirmation sampling was conducted to verify that contaminant concentrations met closure requirements.

For this closure report, Section 1 provides the Site‑specific background and closure standard. Section 2 describes the closure actions and the closure evaluation. Section 3 summarizes the findings, evaluates attainment of data quality objectives (DQOs), and certifies the site closure. References cited in this report can be found in the Bibliography (Volume 1‑1 of the Environmental Encyclopedia).

1.1 - Closure Standard

As described in Section 4.3 of the Risk Assessment Technical Approach Document (Volume 1‑6), CSSA has opted to pursue closure of many of its sites under the Risk Reduction Rules (RRR) (30 Texas Administrative Code [TAC] §335). A notification of intent to close sites identified to date (including SWMU DD Area) was sent to the Texas Commission on Environmental Quality (TCEQ) on July 12, 1999 in accordance with the RRR. TCEQ acceptance of this notification was received on October 5, 1999.

Following the RRR guidelines, if site concentrations are at or below background, and all waste and waste residue have been removed, the site can then be closed under Risk Reduction Standard 1 (RRS1). CSSA background levels are the RRS1 criteria for metals concentrations, and laboratory reporting limits (RLs) are the RRS1 criteria for organic compounds. Based on the RFI sampling results at SWMU DD Area, CSSA opted to clean the site to background levels and pursue closure under RRS1. If closure requirements under RRS1 are attained and approved by the TCEQ Executive Director, then the owner is released from the deed recordation requirement.

Due to the presence of waste at the site, as well as metals concentrations above background levels, removal of waste and waste residue was recommended to meet RRS1 requirements.

1.2 - Background and Site Description

1.2.1   CSSA

General information regarding the history and environmental setting of CSSA is provided in the CSSA Environmental Encyclopedia (Volume 1‑1, Background Information Report). In that report, detailed data regarding the geology, hydrology, and physiography are also available for reference.

1.2.2   SWMU DD Area

1.2.3   Site Description

The SWMU DD Area consists of approximately 1.71 undeveloped acres in the southern Inner Cantonment area of CSSA (Figure DD‑1, SWMU DD Area RFI Report). Prior uses of the site are unknown; however, the area was posted with “Demolition Dud Area” warning signs. Investigation of the site commenced with a sweep for surface UXO. During this work, a disposal trench measuring 250 feet long and up to 5 feet deep was identified. The actual SWMU is approximately 450 feet long by 250 feet wide.

The site is mostly level and covered with sparse vegetation and a thin soil profile. Except for cattle and wildlife grazing, no other activities currently take place at SWMU DD Area. There are no utilities at the site. As shown in Figure DD‑5, the southern portion of the site contains numerous Live oak (Quercus fusiformis) and Ashe juniper (Juniperus ashei, locally called “cedar”) trees.

Background information regarding the location, size, and known historical use of the SWMU DD Area is provided in the CSSA Environmental Encyclopedia (Volume 1-2, SWMU DD Area). Volume 1‑2 also includes a Chronology of Actions and a Site‑Specific Work Plan Addendum for the SWMU DD Area.

1.2.4   Potential Sources of Contamination

The potential source of contamination at the SWMU DD Area is buried waste consisting primarily of fuses, Stokes mortars, and scrap metal. Excavation activities performed at the site in 1997 identified the presence of buried metal debris and small amounts of UXO. There are no records available to confirm possible waste disposed at the site.

1.2.5   Site Location

The SWMU DD Area is located in the south‑central portion of the Inner Cantonment (Figure DD‑5). The SWMU is approximately 2,000 feet north of the southern boundary of the facility. SWMU B‑12 is approximately 900 feet north of SWMU DD Area, and SWMU F‑14 is approximately 950 feet to the northeast. Range Management Unit 2 (RMU 2) is approximately 1,200 feet southwest, and AOC‑54 is approximately 1,500 feet northwest of SWMU DD Area. A gravel road forms the southwestern boundary of the site and a paved road, F‑11, is the northern boundary.

1.3 - Site Environmental Setting

A detailed description of the site environmental setting is provided in the CSSA Background Information Report (Volume 1‑1) and the SWMU DD RFI Report (Parsons, 2002) and a summarized description is provided in the paragraphs below.

1.3.1   Site Soils and Topography

The elevation of the site is approximately 1,265 to 1,285 feet above sea level (Figure DD‑2 in the SWMU DD RFI Report). The site is located on a topographic saddle, with the ground surface gently sloping to the east and west. Because the site is located closer to the western edge of the saddle, surface runoff from the site drains primarily to the west toward an unnamed intermittent creek approximately 1,150 feet to the west. A small portion of runoff may drain to the east to Salado Creek, which is about 2,000 feet to the east of SWMU DD Area.

The SWMU DD Area lies in the Brackett soils with 12‑30 percent slopes (Figure DD‑2 in the SWMU DD RFI Report). These loamy and clayey soils are very shallow (about 4 inches thick), grayish‑brown, and strongly calcareous. Laying within and on the surface layer are gravel and cobblestones up to 6 inches in diameter. The soils develop over soft limestone and are underlain by hard limestone, which gives the slopes a stairstep appearance. Detailed descriptions of the CSSA soil types are provided in the CSSA Environmental Encyclopedia (Volume 1‑1, Background Information Report, Soils and Geology). The SWMU DD Area appears to be fairly typical, with silty clay observed down to 4.5 feet bgs, underlain by limestone and packstone.

1.3.2   Geology

Throughout the CSSA, the uppermost geologic stratum is the Upper Glen Rose Formation, as shown in Figure DD‑6. The Upper Glen Rose, estimated to be up to 128 feet thick at CSSA, consists of beds of blue shale, limestone, and marly limestone, with occasional gypsum beds. The Upper Glen Rose is underlain by the Lower Glen Rose, averaging 320 feet thick beneath CSSA. The Lower Glen Rose is underlain by the Bexar Shale (regionally known as the Hensell Shale, averaging 60 feet thick), and the Cow Creek Limestone (averaging 76 feet thick). The geologic strata dip approximately 10 to 12 degrees to the south‑southeast at CSSA. Additional information on structural geology at CSSA can be found in the Environmental Encyclopedia (Volume 1‑1, Background Information Report, Soils and Geology).

1.3.3   Hydrology

At CSSA, The uppermost hydrogeologic layer is the unconfined Upper Trinity Aquifer, which consists of the Upper Glen Rose Limestone. Locally at CSSA, low‑yielding perched zones of groundwater can exist in the Upper Glen Rose. Transmissivity values are not available for the Upper Glen Rose. Groundwater flow is thought to be enhanced along the bedding contacts between marl and limestone; however, the hydraulic conductivity between beds is thought to be poor. This interpretation is based on the observation that static well levels in adjacent wells completed at approximately the same elevation are discordant. Principal development of solution channels is limited to evaporite layers in the Upper Glen Rose Limestone. Groundwater discharge occurs predominantly via natural springs, seeps, and pumping.

The Middle Trinity Aquifer is unconfined and functions as the primary source of groundwater at CSSA. It consists of the Lower Glen Rose Limestone, the Bexar Shale, and the Cow Creek Limestone. The Lower Glen Rose Limestone outcrops north of CSSA along Cibolo Creek and within the central and southwest portions of CSSA. Principal recharge into the Middle Trinity Aquifer is via precipitation infiltration at outcrops. At CSSA, the Bexar Shale is interpreted as a confining layer, except where it is fractured and faulted, therefore allowing vertical flow from the up‑dip Cow Creek Limestone into the overlying, but down‑dip Lower Glen Rose Limestone. Fractures and faults within the Bexar Shale may allow hydraulic communication between the Lower Glen Rose and Cow Creek Limestones. In general, groundwater at CSSA flows in a north to south direction with some seasonal fluctuations. However, local flow gradient may vary depending on rainfall, recharge, and possibly well pumping.

The nearest on‑site water well is Well CS‑9, located approximately 4,250 feet northwest of the SWMU DD Area. Well CS‑9 is currently part of CSSA’s water supply system, along with Well CS‑10. The nearest on‑site monitoring wells are CS‑MW11A‑LGR and CS‑MW11B‑LGR, located approximately 3,400 feet southwest of the site. The nearest off‑site water well is Well CS‑1, located approximately 2,700 feet southeast of the SWMU DD Area. Groundwater levels within Well CS‑1 typically range from 100 to 115 feet bgs, but have exceeded 200 feet bgs during periods of drought. Additional information regarding the water wells at CSSA is presented in the Environmental Encyclopedia (Volume 5, Groundwater Monitoring).

The nearest surface water body is a small unnamed tributary of Salado Creek located approximately 500 feet southeast of SWMU DD Area. This tributary merges with Salado Creek approximately 2,100 feet southeast of the SWMU DD Area, immediately upstream of the point where Salado Creek exits CSSA. Another small tributary is located approximately 1,150 feet west of the SWMU DD Area. This stream exits CSSA at the southwest corner of the site.

1.3.4   Cultural Resources

Cultural resources are prehistoric and historic sites, structures, districts, artifacts, or any other physical evidence of human activity considered important to a culture, subculture, or community for scientific, traditional, or religious purposes. World War I‑era “foxhole” trenches, located approximately 3,500 feet to the north and northeast, are the nearest historic sites.

Another site of potential archeological significance is the two‑story stone house at Comanche Spring, just outside the southeast boundary of CSSA, approximately 3,400 feet to the southeast of the SWMU DD Area. This house was built around 1847. Former cantonments were also located within 1,300 feet to the northwest of the site, circa 1925. Additionally, all of the structures on the installation are considered historical resources

1.3.5   Potential Receptors

A land use survey describing local current and possible future uses of groundwater and surface water, a water well survey, and sensitive environmental areas at CSSA was completed during December 15 and 16, 1999. Results of this survey, along with results from a more in‑depth survey to identify potential receptors, points of human exposure, and possible constituent pathways is presented in Section 3 of the Technical Approach Document for Risk Assessment (Volume 1‑6). Land uses on the facility are not anticipated to change in the foreseeable future.

The majority of land within 0.25 mile of SWMU DD Area is classified as “Commercial and Services.” To the south, a small portion within the 0.25‑mile radius is classified as “Evergreen Forest Land.” Several storage igloos are located within 0.25 mile, but no water supply wells are within this distance. The closest well is water supply Well CS‑1, which is approximately 2,900 feet to the southeast of the site. The nearest residential area, Hidden Springs Estates, is over 0.75 mile south of the site, and the nearest school, Fair Oaks Elementary School, is over two miles northwest of the site.

A small herd of cattle, maintained on CSSA by the USDA ARC, roam freely throughout selected areas of the North Pasture. CSSA also manages wild game species for hunting purposes. White‑Tailed deer, Axis deer, and wild turkey all roam freely throughout CSSA. A map of deer hunting stands that overlook mechanical feeders and planted food plots is located in Figure 5.2 of the Technical Approach Document for Risk Assessment (Volume 1‑6). SWMU DD Area is located within an area where hunting is allowed. The closest deer blind (#8) is located approximately 750 feet northeast of SWMU DD Area.

The nearest potential habitats for local endangered species (Figure 11, Volume 1‑1, Background Information Report) are 3,500 feet to the northeast (Black‑capped vireo) and 100 feet to the east (Golden‑cheeked warbler).

1.4 - Previous Investigations

The SWMU DD Area RFI Report outlined initial closure actions performed, such as excavation/sifting of soil to remove UXO and scrap metal, and collection of surface and subsurface soil samples to determine the extent of the contamination. In addition to the RFI, interim measures were also taken at the site, in accordance with the Consent Order, to address stockpiled sifted soil at the site. Results of sampling associated with the interim measures are also described in the RFI Report because they are important for site characterization. However, plans for treatability studies associated with these soils are discussed in the Soil Pile Disposition Assessment Report.

1.4.1   UXO Clearance and Magnetometer Survey

UXO identification and removal activities were conducted between February 4 and May 30, 1997. The initial intent of the work was to determine if UXO was a potential concern at the site. During initial surface sweeps in February and March 1997, potentially live ordnance items were identified and Schonstedt magnetometers indicated buried metal at the site.

Due to the presence of buried metal at the site, sifting was identified as a cost‑effective method for removing buried UXO and other metal debris. The sifting operation commenced on May 20, 1997 and continued until May 30, 1997. Magnetometers indicated the presence of a trench containing metallic waste. Material in this trench was excavated with a backhoe. The trench was excavated until no additional solid waste material (UXO, scrap metal, etc.) was encountered on the bottom or in each of the walls of the trench. The trench was situated adjacent to the paved road to the north, and was approximately 250 feet long by eight feet wide. The trench was up to five feet deep. Based on visual observation and the presence of older/mature live oak trees, it does not appear that any additional trenches were located at the site.

As material was sifted, discharged soil was stockpiled on site. At the conclusion of sifting operations at the site, a total of approximately 600 cubic yards of soil were stockpiled in one pile at the site. All metal scrap found at the site was placed into roll‑off containers and later transported to Newell Recycling in San Antonio, Texas. All UXO found at the site was segregated and later detonated at SWMU B‑20 on September 25, 1997. Because the trench was located adjacent to an active road, it could not be left unfilled; therefore, the site was graded and backfilled with native soils in adjacent embankments at the conclusion of the UXO removal activities.

1.4.2   Subsurface Samples

To characterize the subsurface soils near the trench, three soil borings were advanced at SWMU DD Area on March 31, 2000. The borings, SB01, SB02, and SB03 (Figure DD‑4 in the SWMU DD Area RFI Report), were advanced to depths of 10, 13, and 11 feet below ground surface (ft bgs), respectively. Samples were collected from the surface, middle, and terminus of each boring. The subsurface samples (bedrock) were collected using a decontaminated core barrel.

A total of six subsurface samples were collected and submitted for analysis of explosives, VOCs, and metals.

Analytical results from the subsurface samples indicate all analytes were below the RLs or background concentration for Glen Rose Limestone with the exception of cadmium and methylene chloride. Cadmium was detected at 0.20 mg/kg in SB03 (4.5‑5.0 ft bgs). The background concentration for cadmium is 0.1 mg/kg. Methylene chloride was detected at 0.0054 mg/kg in SB01 (9.5‑10.0 ft bgs), slightly above the RL (0.005 mg/kg). Since methylene chloride was also detected in the laboratory blank, it is believed to be a laboratory artifact and not representative of soil conditions at the site.

1.4.3   Surface Soil Samples

Surface soil samples were collected at the SWMU DD Area during the soil boring activities to assess surface soil conditions near the trench. Surface soil samples were collected from the 0‑0.5‑foot depth intervals from SB01, SB02, and SB03 (Figure DD‑4 in the SWMU DD Area RFI Report).

Three surface soil samples, SB01 (0.0‑0.5 ft bgs), SB02 (0.0‑0.5 ft bgs), SB03 (0.0‑0.5 ft bgs), and one field duplicate sample, SB03 (0.0‑0.5 ft bgs), were submitted for explosives, VOCs, and metals analysis.

Results of the surface soil sampling indicate that metals and VOCs were present above background concentrations. Metals detected above background concentrations include copper, lead, mercury, and zinc. Copper was detected above background (23.2 mg/kg) in SB02 (38.17 mg/kg), SB03 (61.15 mg/kg), and the SB03 field duplicate sample (63.28 mg/kg). Lead was detected above background (84.5 mg/kg) in SB01 (162.36 mg/kg), SB02 (749.06 mg/kg), SB03 (445.63 mg/kg), and the SB03 field duplicate sample (427.04 mg/kg). Mercury was detected above background (0.77 mg/kg) in SB03 (2.80 mg/kg) and the SB03 field duplicate sample (2.54 mg/kg). Finally, zinc was detected above background (73.2 mg/kg) in SB03 (111.09 mg/kg) and the SB03 field duplicate sample (122.29 mg/kg).

The VOCs detected above background (RLs) were toluene and methylene chloride. Toluene was detected above background (0.005 mg/kg) in SB01 (0.0205 mg/kg), SB02 (0.0100 mg/kg), SB03 (0.0213 mg/kg), and the SB03 field duplicate sample (0.0055 mg/kg). Methylene chloride was detected above background (0.005 mg/kg) in SB01 (0.0063 mg/kg). Methylene chloride is a common laboratory contaminant and was also detected in the laboratory blank sample. Therefore, the presence of methylene chloride in the soil sample is believed to be a laboratory artifact and not representative of soil conditions at the site.

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