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
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.
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.
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.
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
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.
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).
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.
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.
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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