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SWMU Demo Dud Area (DD) Area RCRA Facility Investigation Report

Section 1 - Introduction

On May 5, 1999 an Administrative Consent Order was issued to CSSA pursuant to §3008(h) of SWDA, as amended by RCRA, and further amended by the HSWA of 1984. In accordance with the RFI requirements of the Consent Order, this report was prepared to document the environmental condition and site closure requirements of the SWMU Demolition Dud (DD) Area and to recommend further investigation, if necessary, or to provide documentation necessary for site closure. The main objectives of the SWMU DD Area investigation are to determine if the site meets TNRCC requirements for closure, as described in Section 1.4, and to meet requirements of the Consent Order.

This specific RFI was performed by Parsons under the U.S. Air Force AMC Contract F11623-94-D0024, Delivery Order RL33. AFCEE provided technical oversight for the delivery order. Based upon the RL33 SOW, a set of work plans to govern the fieldwork was established. These include:

Work Plan Overview

(Volume 1-1, RL33 Addendum);

Site-Specific Work Plan

(Volume 1-2, Demolition Dud Area);

Field Sampling Plan

(Volume 1-4, RL33 Addendum); and

Health and Safety Plan

(Volume 1-5, RL33 Addendum).

For this RFI report, Section 1 provides the site-specific background and closure standard. Section 2 describes field action and the closure evaluation. Section 3 summarizes the findings, evaluates attainment of the data quality objectives, provides recommendations, and certifies the site closure, if applicable. References cited in this report can be found in the Bibliography (Volume 1-1 of the Environmental Encyclopedia).

In addition to the Consent Order requirement to conduct an RFI, interim measures are also required to address SWMU DD soil that has been inspected to remove UXO. The UXO removal activities are described in this report, but activities related to the interim measures are addressed in the Soil Pile Disposition Report, being prepared under a separate delivery order.

1.1 - Background and Site Description

1.1.1   CSSA

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

1.1.2   SWMU DD Area   Site Description

The DD Area consists of approximately 1.71 undeveloped acres in the southern inner cantonment area of CSSA (Figure DD-1). 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 estimated to be about 2 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. There are no utilities at the site. As shown in Figure DD-1, the southern portion of the site contains numerous live oak and juniper cedar trees.

Background information regarding the location, size, and known historical use of the 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 DD Area.   Potential Sources of Contamination

The potential source of contamination at the SWMU DD Area is buried wastes consisting primarily of fuses, Stokes mortars, and scrap metal. Excavation activities performed at the site have 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.   Site Location

The SWMU DD Area is located in the south-central portion of the inner cantonment (Figure DD-1). 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, 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 the unit. A gravel road forms the southwestern boundary of the site and a paved road is the northern boundary.

1.2 - Site Environmental Setting

1.2.1   Site Soils and Topography

The elevation of the site is approximately 1,280 to 1,290 feet above sea level (Figure DD-2). The site is located on a topographic saddle, with 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 way drain to the east to Salado Creek, which is about 2,000 feet to the east of SWMU DD.

The DD Area lies in the Brackett soils with 12-30 percent slopes. (Figure DD-2). 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 DD Area appears to be fairly typical, with silty clay observed down to 4.5 feet bgs, underlain by limestone and packstone.

1.2.2   Geology

The Upper Glen Rose is the uppermost geologic stratum in the area of DD Area (Figure DD-3). The Upper Glen Rose consists of beds of blue shale, limestone, and marly limestone, with occasional gypsum beds. Generally, it outcrops in stream valleys and at the ground surface where soils are poorly developed or eroded. Where present at CSSA, the Upper Glen Rose may be up to 150 feet thick. It is underlain by the Lower Glen Rose, which is estimated to be 300 feet thick beneath CSSA. The Lower Glen Rose is a massive, fossiliferous, vuggy limestone that grades upwards into thin beds of limestone, marl, and shale. The Lower Glen Rose is underlain by the Bexar Shale facies of the Hensell Sand, which is estimated to be from 60 to 150 feet thick under the CSSA area. The Bexar Shale consists of silty dolomite, marl, calcareous shale, and shaley limestone. The geologic strata dip approximately 10 to 12 degrees to the south-southeast at CSSA.

Based on current published information, there are two known major fault (shatter) zones at CSSA: the North Fault Zone and the South Fault Zone. The DD Area is located almost entirely within the South Fault Zone that trends to the northeast, and transects the southern portion of CSSA (Figure DD-3). Additional information on structural geology at CSSA can be found in the Environmental Encyclopedia (Volume 1-1, Background Information Report, Soils and Geology).

1.2.3   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 are discordant in adjacent wells completed at approximately the same elevation. Principle 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. Regional groundwater flow appears to be to the southeast.

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. Principle 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. 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 DD Area. Well CS-9 is currently part of CSSA’s water supply system, along with well CS-10. The nearest off-site water well is Well CS-1, located approximately 2,700 feet southeast of the 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 tributary of Salado Creek located approximately 500 feet southeast of SWMU DD. This tributary merges with Salado Creek approximately 2,100 feet southeast of the DD Area, immediately upstream of the point where Salado Creek exits CSSA. Another small tributary is located approximately 1,150 feet west of the DD Area. This stream exits CSSA at the southwest corner of the site.

1.2.4   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 3500 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 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.

1.2.5   Potential Receptors

A land use survey discussing local 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. The 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).

The majority of land within 0.25 mile of SWMU DD 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 the Inner Cantonment and in 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 Evaluation (Volume 1-6). SWMU DD is located within an area where hunting is allowed. The closest deer blind (#8) is located approximately 750 feet northeast of SWMU DD.

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).

1.3 - Previous Investigations

No investigations had been conducted at SWMU DD prior to the current investigation.

1.4 - Closure Standard

As described in Section 4.3 of the Technical Approach Document for Risk Assessment (Volume 1-6), CSSA has opted to pursue closure of the SWMU DD Area under the Risk Reduction Rule (30 TAC §335). If the site concentrations do not exceed background, then the site will be closed using RRS1. If the site exceeds background, then a determination will be made regarding the feasibility of cleaning the site to meet background concentrations. If the decision is made to clean the site to background, closure under RRS1 will be sought. However, if it is determined that the site cannot be closed to meet background concentrations, then the site will be closed under TRRP. Notification of intent to close sites identified to date (including the DD Area) in accordance with the former RRR was sent to the TNRCC on July 12, 1999. TNRCC acceptance of this notification was received on October 5, 1999.

RRS1 requires that the site be closed following removal or decontamination of waste, waste residues, and contaminated operation system components; and demonstration of attainment of cleanup levels (30 TAC §335.554). If closure requirements under RRS1 are attained and approved by the TNRCC Executive Director, then the owner is released from the deed recordation requirement.

Since the COCs for SWMU DD are VOCs, explosives, and metals, the cleanup levels should be the RLs for VOCs and explosives, and the background levels for metals. Chlorinated VOCs and explosives are man-made chemicals, and rarely occur naturally. Background metals levels were statistically calculated for CSSA soils and the Glen Rose Limestone, and are reported in the Second Revision to the Evaluation of Background Metals Concentrations in Soils and Bedrock (Parsons, February 2002).

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