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Final SWMU B-12 RCRA Facility Investigation Report

Section 1 - Introduction

On May 5, 1999 an Administrative Consent Order was issued to CSSA pursuant to 3008(h) of the 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 has been prepared to document the environmental condition and site closure requirements of SWMU B-12 and to recommend further investigation, if necessary, or to provide documentation necessary for site closure.  The main objectives of the SWMU B-12 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-D-0024, Delivery Order RL17.  AFCEE provided technical oversight for the delivery order.  Based upon the project SOW, a set of work plans was established to govern the fieldwork.  These plans include:

Work Plan Overview   (Volume 1-1, RL17 Addendum);

Site-Specific Work Plan   (Volume 1-2, SWMU B-12);

Field Sampling Plan   (Volume 1-4, RL17 Addendum); and

Health and Safety Plan   (Volume 1-5, RL17 Addendum).

For this report, Section 1 provides the site-specific background and closure standard.  Section 2 describes field actions and the closure evaluation.  Section 3 summarizes the findings, evaluates the attainment of 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).

1.1 - Background and Site Description

1.1.1   CSSA

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

1.1.2   SWMU B-12   Site Description

SWMU B-12 is a one acre site reportedly used for disposal of large pieces of scrap metal and various weapons based on historical research and interviews.  In aerial photographs reviewed from 1966, 1973, 1986, and 1991, very sparse to no vegetation was visible.  Today, vegetation at the site remains sparse, consisting of grassy patches.  This area may have been excavated in the past to provide soil for the nearby earthen covered magazines.

An embankment in the southwest portion of the site contains abundant small and large metal debris (including tail fins from dummy practice rounds), clay pipe fragments, ceramic and porcelain shards, and limestone boulders.  Waste material was observed at the surface. This debris was placed along the slope of the embankment at unknown dates.  According to historical records reviewed, large pieces of scrap metal and weapons were embedded into the hillside and the adjacent flat area.  Although historical records review and personal interviews indicated past use of the area as a landfill, the 1995 geophysical survey (described in Section 1.3) did not confirm this.  Visual observation and the geophysical survey results indicated that waste is only present in the area of the embankment.

The flat area of the site contained ponded water in 1995 and 1996.  In 1995, standing water reached a maximum depth of approximately 2 feet in the southeastern portion of the site.  In 2000, during drilling activities, the flat area was dry as a result of the extended drought from 1997 through 1999.  There was no evidence of past waste disposal activities in the flat area.  The site photograph (Volume 3-1, SWMU B-12), taken in January 1999, shows the flat area in the foreground and the embankment in the background.

Background information regarding the location, size, and known historical use of the site is also included in the Environmental Encyclopedia (Volume 1-2, SWMU B-12).  Volume 1-2 also includes a Chronology of Actions and a Site-Specific Work Plan for SWMU B-12.   Potential Sources of Contamination

Historical records review and interviews indicated that SWMU B-12 was used as a landfill area for large pieces of scrap metal.  Visual observation of metal debris (including tail fins from dummy practice rounds) confirmed the presence of metal debris during field investigations.  Large pieces of metal located near the surface are the primary source for contamination of surface and subsurface soils at the site.  VOCs may also be present as records do not fully indicate the nature and extent of waste disposal activities at SWMU B-12.  Other potential COCs include explosive wastes from ordnance-related scrap discovered at the site and SVOCs resulting from waste burning activities that may have occurred at the site.   Site Location

SWMU B-12 is located in the east-central portion of the Inner Cantonment Area and covers approximately one acre in area.  It includes the embankment in the southwestern portion of the site and the flat-lying area to the northeast.  Previous records indicate that scrap metal was observed in both the embankment and the flat area.  This site is located about 1,600 feet from the eastern boundary of the Inner Cantonment (Figure B12-1). Figure B12-1 is based on the 1998 aerial photograph of CSSA.  The general shape of the site is rectangular.  The site is located immediately north of the intersection of Road No.  F-14 and Road No. F-11.  There are no permanent structures at SWMU B-12 with the exception of overhead utilities.  A road made up of an elevated bed of gravel forms the northeastern boundary of the site.

1.2 - Site Environmental Setting

1.2.1   Site Soils and Topography

Two soil types are present at the site, Brackett Soils and Krum Complex Soils (Figure B12-2).  Brackett soils account for approximately 20 percent of the site, and are located on the southwest side of SWMU B-12.  These soils occur on slopes of 12 to 30 percent.  These loamy and clayey soils are very shallow (about 4 inches thick), grayish-brown, and strongly calcareous.  Gravel and cobblestones up to 6 inches in diameter are found at the surface.  The soils develop over soft limestone and are underlain by hard limestone, which gives the slopes a stairstep appearance.  The Brackett soils are nonarable and best suited to native grasses (USDA, 1991).  Krum Complex soils compose the remaining 80% of soils at SWMU B-12.  The surface soil is dark grayish-brown or very dark grayish-brown, calcareous, and approximately 30 inches thick.  The soils developed from slope alluvium of the limestone prairies.  The Krum Complex soils commonly occupy slopes below Tarrant and Brackett soils.  These soils receive sediments and runoff from higher elevation soils and are highly prone to water erosion if unprotected.  Detailed descriptions of the CSSA soil types are provided in the Environmental Encyclopedia (Volume 1-1, Background Information Report, Soils and Geology).

SWMU B-12 is bordered by a 15 to 25 foot tall man-made embankment to the southwest, topographically higher ground to the northwest and southeast and an elevated dirt road to the northeast.  The elevation of the site ground surface in the low-lying area in the center is approximately 1,235 feet above sea level.  The embankment and higher ground along the westernmost boundary are approximately 1,250 feet above sea level.  Due to the surrounding elevated terrain, surface water readily accumulates in the central part of SWMU B-12, especially after a heavy rain event.

1.2.2   Geology

The Upper Glen Rose Formation is the uppermost geologic strata in the area of SWMU B-12 (Figure B12-3). 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.

SWMU B-12 is situated over the geologic contact which divides the Upper and Lower Glen Rose.  The eastern quarter of the site is underlain by the Lower Glen Rose which outcrops at the surface along the eastern edge of the SWMU.  The Upper Glen Rose occupies the remaining portion of the site and outcrops at the surface on the western side of SWMU B-12.

Based on current published information, there are two known major fault (shatter) zones at CSSA: the North Fault Zone and the South Fault Zone.  SWMU B-12 is located approximately 500 feet north of the South Fault Zone (Figure B12-3).  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

In general, the uppermost hydrogeologic layer at CSSA 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. Regionally, 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 water 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.

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, the Cow Creek Limestone, and the Hammett Shale.  The Lower Glen Rose Limestone outcrops north of CSSA along Cibolo Creek and within the central and southwest portions of CSSA.  As such, 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.  Fractures and faults within the Bexar Shale may allow hydraulic communication between the Lower Glen Rose and Cow Creek Limestones.  Groundwater flow within the Middle Trinity aquifer is toward the south and southeast and the average transmissivity coefficient is 1,700 gpd/ft. (Ashworth, 1983).  In general, groundwater at CSSA flows in a north to south direction.  However, local flow gradient may vary depending on rainfall, recharge and possibly well pumping.

No site-specific information regarding groundwater is available.  However, the nearest well is CS-1, an off-post well located approximately 3,500 feet southeast of SWMU B-12.  Between 1992 and 2001, static water levels have ranged between 101 and 268 feet below ground surface in this well (Volume 5).

The closest surface water feature to SWMU B-12 is Salado Creek which is located approximately 1,260 feet east-northeast of the site.  Salado Creek is an intermittent north-south trending creek that exits the CSSA boundary approximately 2,300 feet southeast of SWMU B-12.

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.  The nearest cultural resource is located approximately 1,360 feet to the northeast of SWMU B-12.  The resource consists of World War I era foxholes and trenches that were used for training.

1.2.5   Potential Receptors

A land use survey to identify local and potential future use of groundwater and surface water, a water well survey, and sensitive environmental areas at CSSA was completed on 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 Evaluation (Volume 1-6).

A small herd of cattle is maintained on CSSA by the USDA-ARC.  The cattle roam freely throughout the Inner Cantonment and in selected areas of the North Pasture.  CSSA also manages wild game species for the purpose of hunting.  White-tailed deer, axis deer, and wild turkey all roam freely throughout CSSA.  A map of deer hunting stands which overlook mechanical feeders and planted food plots is located at Figure 5.2 of the Technical Approach Document for Risk Evaluation (Volume 1-6).  SWMU B-12 is located within 1,000 feet of three deer blinds, one turkey feeder and a planted food plot.  Hunting stand #6 and its associated food plot and turkey feeder are located 500 feet northeast of the site, hunting stand #7 is located 800 feet southwest of the site and hunting stand #8 is located approximately 1,000 feet to the southwest.  Four ponds are maintained at CSSA for the purpose of sport fishing.  Two ponds are located in the northwestern and northeastern portions of the North Pasture, while the other two tanks are located near the western boundary of the Inner Cantonment.  The potable water reservoir is located approximately 3,500 feet northwest of the site.

The nearest potential habitats for local endangered species (Volume 1-1, Background Information Report, Figure 11) are approximately 800 feet to the southeast (golden-cheeked warbler) and 2,500 feet to the northeast (black-capped vireo).

1.3 - Previous Investigations

A chronology of actions, including previous investigations, at SWMU B-12 is located under the SWMU B-12 tab of Volumes 1-2 and 3-1 of the CSSA Environmental Encyclopedia.

On May 5, 1995, an EM survey was conducted along north-south and east-west transects using a Geonics EM-31 instrument.  The transects were spaced at 25-foot intervals.  The grid measured 250 feet (north-south) by 100 feet (east-west) and was conducted only in the flat-lying portion of the site.

The EM conductivity and in-phase contour maps are shown in Figure 5.2, Figure 5.3, Figure 5.4, and Figure 5.5 of the Technical Memorandum on Surface Geophysical Surveys (Parsons ES, 1995c).  Results show that no EM anomalies were detected at the site.  Therefore, there is no indication of subsurface debris in the surveyed areas.  The adjacent embankment area contains abundant metal debris and was not surveyed due to surface interference.

1.4 - 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 SWMU B-12 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.  A notification of intent to close sites identified to date (including SWMU B-12) 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 B-12 are VOCs, SVOCs, explosives, and metals, the cleanup levels should be the RLs for VOCs, SVOCs, and explosives, and the soil or rock background levels for metals.  Background levels for metals were statistically calculated for CSSA soils and the Glen Rose Limestone and were reported in the Second Revision to the Evaluation of Background Metals Concentrations in Soil and Bedrock at CSSA (Parsons, February 2002).

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