For this RFI 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 CSSA
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-5
1.1.2.1 Site Description
SWMU B-5 is a former small arms ammunition brass disposal area.
The exact dates of usage for the site are unknown.
The site is located adjacent to a gravel road (Figure
B5-1) and appears disturbed in aerial photographs dating back to 1966.
SWMU B-5 is mostly level and sparsely vegetated.
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-5).
This
volume includes a
Chronology of Actions
and a
Site-Specific Work Plan for SWMU
B-5.
1.1.2.2 Potential Sources of Contamination
Potential sources of contamination at SWMU B-5 include metallic leachate from
metals debris and ammunitions brass along with explosives residue associated
with spent ammunitions and brass waste placed over the ground surface.
The potential COCs associated with these wastes include metals and
explosives. VOCs are added as COCs
to evaluate the potential for typical contaminants associated with disposal
areas.
1.1.2.3 Site Location
SWMU B-5 is located in the south-central portion of the North Pasture at CSSA,
directly north of Gate 6 and just inside the Outer Cantonment Area. The nearest base boundary lies approximately 5,000 feet east
of the site area. SWMU B-5 is a
relatively small site, covering approximately 1.2 acres in area. The site area is bounded on the west by a gravel road and on
the south by a dirt road. Trees
bound the northern and eastern edges of the site
(Figure
B5-1, Site Location Map).
1.2
- Site Environmental Setting
1.2.1 Site Soils and
Topography
Soils present within the site area are representative of
Krum Complex soils (Figure
B5-2, Soils and Topography Map).
The soils are typically calcareous clay. While no descriptions of subsurface
conditions have been gathered at this site and based on investigations conducted
in neighboring areas, it is reasonable to assume that limestone bedrock occurs
within five feet of the land surface.
Detailed descriptions of the various soil types present at CSSA are located in
the CSSA Environmental Encyclopedia (Volume
2, Description of Soil Types and Bedrock).
The site contains little topographic relief and lies at
approximately 1,260 feet above sea level.
The ground surface within the site area of SWMU B-5 slopes approximately
two degrees downward in a west-southwesterly direction (Figure B5-2).
Vegetation present within the site area consists mostly of native
grasses.
To the north and east of the site area, trees dominate the vista.
1.2.2 Geology
The Upper Glen Rose
is the uppermost geologic strata in the area of SWMU B-5 and the north pasture
(Figure
B5-3). 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.
The thickness of the Upper Glen Rose is estimated to be between 0 and 150
feet at CSSA. 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 (regionally known as
the Hensell Shale), which is estimated to be from 60 to 150 feet thick under the
CSSA area. The Bexar Shale consist
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-5 is located
within what is referred to as the North Fault Zone that trends
northeast-southwest, and transects the central portion of CSSA
(Figure
B5-3). This fault (shatter)
zone has been mapped with a width between 2,000 to 3,000 feet, and consists of
multiple normal faults with small throws of displacement.
Numerous faults with small displacements have been located near the site
using mapping, seismic, and GPR techniques.
Vertical displacement between 5 to 30 feet have been reported
(Volume
1-1, Background Information Report),
where
the downthrown blocks typically occur on the southeast side of the fault.
The fracture system associated with this fault zone has been attributed
as a controlling structural feature for the migration of contaminants in the
vadose zone as identified during investigations conducted for other areas at
CSSA.
1.2.3 Hydrology
In general,
the uppermost hydrologic 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 static well levels
are discordant in adjacent wells completed in different beds. 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, 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.
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, 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.
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.
The closest surface
water feature is a northeast-southwest trending tributary that drains southward
to Salado Creek in the South Pasture. It
is located approximately 1,200 feet west of the site
(Figure
B5-1).
Well CS-16, the closest
monitoring well to SWMU B-5, is located approximately 1,060 feet west of
the site.
1.2.4 Cultural Resources
All of the
structures on the post are considered historical 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 to SWMU B-5, a burned rock midden, is located
approximately 3,300 feet northwest of the site area.
1.2.5
Potential Receptors
All of the land
within ¼-mile radius of SWMU B-5 is evergreen forest land.
None of the wells within ¼ mile of the site are currently used for water
supply; however, Well CS-16, a former water supply well is located approximately
1,060 feet west of the site. The
nearest residential area is approximately one mile to the west of SMWU B-5.
A human and ecological sensitive receptor survey has been conducted at
CSSA, and the results are 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 in the
Technical Approach Document for Risk Evaluation
(Volume 1-6).
SWMU B-5
is located approximately 750 feet northeast of hunting stand number 2.
Four water tanks are maintained at CSSA for the purpose of sport fishing.
Two of the tanks 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 nearest
potential habitat for local endangered species, a possible Black-Capped Vireo
habitat, is located approximately 1,400 feet northwest of the site area.
A potential Golden-Cheeked Warbler habitat, another local endangered
species, is located approximately 2,300 feet northeast of SWMU B-5 (Parsons ES,
1993).
1.3
-
Previous Investigations
A chronology of
actions/investigations performed at SWMU B-5 is located in the “B-5” tab of
Volumes
1-2 and 3-1 of the CSSA Environmental Encyclopedia.
A field investigation was intended to be conducted at SWMU B-5 during
September 1993 under a separate delivery order.
Although vegetation at the site area had recently been cleared prior to
the site survey, the site could not be located during the survey.
Expected surficial evidence of fired brass was not found within the area
indicated on the field map, but the area did contain two waste piles and some
unspecified scattered surface debris. The
SWMU boundaries were placed so that the various debris were encompassed within
the site area.
1.4
-
Closure Standard
As described
in Section 4.3 of the
Technical Approach Document for Risk Evaluation (Volume
1-6), CSSA
has opted to pursue closure of most sites 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 background, then closure under
TRRP will be conducted.
A notification of
intent to close sites identified to date (including SWMU B-5) in accordance with
the Risk Reduction Rule was sent to the TNRCC on July 12, 1999.
Acceptance of this notification was sent by TNRCC 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 deed recordation
requirements.
Since the chemicals of potential concern for SWMU B-5 are VOCs and metals, the
cleanup levels should be the RLs for VOCs and the background levels for metals.
VOCs 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 Soil Types
(Parsons, February 2002).
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