For
this RFI report, Section 1 provides the site-specific background and target
closure standard. Section 2 describes field actions and the closure evaluation.
Section 3 summarizes the findings, evaluates 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).
Investigations
have been on-going at SWMU B-20 since 1994.
The results of the first phase of investigation at the site are
documented in the Remedial Investigation Report for B-20 Former Open
Burn/Open Detonation Area (Parsons ES, 1995d) and results of the second
phase are documented in the Addendum to the Remedial Investigation Report
(Parsons ES, 1996b). To meet TNRCC
closure requirements (described in Section 1.4), the addendum report recommended
additional UXO removal activities and remediation of a large volume of
contaminated soil. The additional
UXO removal activities were the primary task of the current phase of
investigation. Since the UXO items
were removed when identified, this phase of the investigation is also considered
remediation. Based on the current
status of SWMU B-20/21, the objectives of this phase of
investigation/remediation are to meet requirements of the Consent Order for RFIs,
and to continue work towards meeting TNRCC RRS1 closure requirements.
In
addition to the Consent Order requirement to conduct an RFI, interim measures
are also required to address SWMU B-20/21 soil that has been sifted to remove
UXO. Remediation or removal of this
contaminated soil is also necessary to meet TNRCC closure requirements.
The UXO removal activities are described in this report, but activities
related to interim measures and the sifted soil are addressed in the Soil Pile
Disposition Assessment Report currently 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 that
report, data regarding the geology, hydrology, and physiography are also
available for reference.
1.1.2 SWMU B-20/21
1.1.2.1 Site Description
SWMU
B-20 is a former OB/OD area used periodically between 1946 and 1987 to treat and
dispose of waste ordnance. During
that period, ordnance and other waste was detonated, buried, and disposed of on
the ground surface at the site. SWMU
B-20 consists of approximately 33.5 acres surrounded by wooded areas in the
northeastern portion of CSSA (Figure B20/21-1).
The area is sparsely vegetated with grasses and cedar shrubs.
Gravel roads form the south, west, and north boundaries of the site.
Figure B20/21-1 shows an aerial photograph taken of CSSA in 1998.
At
the time that investigations began at SWMU B-20 in 1994, site features included
an inactive bunker west of the western gravel road; a standpipe, reportedly used
on one occasion for the static firing of a rocket motor; and an electrical
junction box in the central portion of the site. Broken aboveground conduit was visible in the
central-southeast area of the site. Fifteen
craters were identified in the northern and central portions of the site.
Six of these craters located in the northern portion of the site were
presumably used during the early history of the site.
Five mounds of soil from the site that were stockpiled for use in
covering explosives prior to detonation were present in the eastern portion of
the unit. At the time that
investigations began, inert metal scrap and UXO was scattered across the entire
site. In addition, waste was buried
and on the ground surface in the northern portion of the site.
Due
to its proximity to the B-20 site, SWMU B-21 was incorporated into the B-20
investigation. SWMU B-21 was a
disposal area for small arms ammunition containing shells, shot, and sand
originating from the Building 90 Test Fire Room. The B-21 area measures
approximately 50 feet by 15 feet, and is located at the southeast tip of SWMU
B-20. Two similar small arms
ammunition disposal areas were observed within the B-20 site.
These areas measured approximately 60 feet by 10 feet and 20 feet by 8
feet.
Background
information regarding the location, size, and known historical use of SWMU
B-20/21 is also included in Volume 1-2, behind the
SWMU B-20/21
tab. This volume also includes a
Chronology
of Actions and a Site-Specific Work Plan Addendum for SWMU B-20/21.
1.1.2.2 Potential Sources of Contamination
The
potential sources of contamination at SWMU B-20/21 are burned or buried waste
consisting primarily of ammunition and debris from ammunition detonation.
CSSA records indicate the B-20 site was used for detonation of
conventional explosive ordnance and other ordnance items, static downward firing
of one rocket motor, disposal of scrap metal from detonation activities, and
disposal of small arms ammunition. SWMU
B-21 was a disposal area for small arms ammunition, containing shells, shot, and
sand originating from building 90 and the rifle range.
Additional information regarding types of ordnance items disposed at the
site is included in
Section 2.2.2
of the Remedial Investigation Report
(Parsons
ES, 1995d).
Contaminants of potential concern include metals, explosives, and perchlorates.
Previous investigations at the site included VOC and SVOC analyses;
however, these compounds were not detected in any of the soil samples collected
at the site. The last phase of
investigation at the site identified 2,4-TNT, arsenic, barium, cadmium, lead,
and mercury in soil or rock at concentrations above RRS1 levels.
1.1.2.3 Site Location
SWMU
B-20/21 is located within the North Pasture area of the outer cantonment (Figure
B20/21-1). The SWMU is approximately 1,500 feet west of the eastern
facility boundary and 2,000 feet south of the northern boundary.
Well CS-I, the nearest well to the site, is located about 800 feet to the
east. SWMU B-24 is located
approximately 2,100 feet southwest of the site and RMU 5 is located
approximately 400 feet to the west. Gravel roads form the west, south, and north perimeters of
the SWMU.
1.2 - Environmental Setting
1.2.1 Site Soils and Topography
There
are three soil types at SWMU B-20/21. The
majority of the site is covered with Crawford and Bexar soils (Figure
B20/21-2). A small area in the eastern portion of the site is covered by
Krum Complex soils and in the northern and western portions of the site,
Brackett-Tarrant Association soils are present. The Krum Complex soils receive sediments and runoff from
higher elevation soils and permeability is very slow.
Crawford and Bexar soils occur in broad, nearly level to gently
undulating areas with slopes of 0 to 5 percent. The soils are stony, very dark gray to dark reddish brown,
noncalcareous clay, about 8 inches thick. Brackett-Tarrant Association soils are
formed on
hills with 8 to 30 percent slopes and consist primarily of soils that developed
over limestone. Most CSSA soils are typically calcareous clay, ranging in depth
from 4 to 60 inches and are underlain by limestone. SWMU B-20/21 appears to be fairly typical, with silty clay
observed to depths ranging from 0.5 to 11 feet bgs and underlain by limestone.
Detailed descriptions of the CSSA soil types are provided in the
Environmental Encyclopedia (Volume 1-1, Background Information Report, Soils
and Geology).
The
elevation of the site ranges from approximately 1,370 feet above sea level on
the western side of the site, to approximately 1,310 feet above sea level on the
eastern side of the site (Figure B20/21-2).
Except on the far east side of the site, the ground slopes gently to the
east, dropping approximately 10 feet in elevation every 100 feet.
On the east side of the site, the ground surface slopes to the northwest. The site is vegetated with native grasses, isolated clusters
of live oak stands, and juniper.
1.2.2 Geology
The
Upper Glen Rose is the uppermost geologic stratum in the SWMU B-20/21 area (Figure
B20/21-3). 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. The
Upper Glen Rose is estimated to be up to 150 feet thick 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 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 known to be two major fault
(shatter) zones at CSSA: the North Fault Zone and the South Fault Zone. The SWMU
B-20/21 area is located north of both of these zones (Figure B20/21-3).
Additional information on structural geology at CSSA can be found in the
Environmental Encyclopedia (Soils and Geology, Background Information Report,
Volume 1-1).
In
soil borings drilled at SWMU B-20 during previous investigations, the Upper Glen
Rose Limestone was encountered at depths ranging from 0.5 feet to 11 feet bgs.
The white to very light gray limestone contained fossils of pelecypods
and gastropods, solution cavities, and calcite veins.
Soil boring logs are provided in Appendix E of the Remedial
Investigation Report for B-20 (Parsons ES, 1995d).
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. During
drilling at SWMU B-20 in 1994, perched groundwater was encountered at a depth of
10.5 feet in a soil boring drilled adjacent to the bed of the unnamed creek that
crosses the east side of the site. No
water was encountered in any of the other site borings.
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 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. Regionally, 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. 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, with some seasonal
fluctuations. However, local flow
gradient may vary depending on rainfall, recharge, and possibly well pumping.
The
nearest water well is Well CS-I, located approximately 800 feet northeast of
SWMU B-20/21. Well CS-I is used for watering livestock and is operated by a
windmill. The nearest off-site
water well, RFR-2, is located over one mile northwest of the site. Groundwater levels within Well CS-I typically range from 102 to 200 feet
bgs, but have exceeded 260 feet bgs during periods of drought. COPCs detected above AFCEE RLs in Well CS-I include barium, copper, lead,
and zinc. Additional information
regarding the water wells at CSSA is presented in the Environmental Encyclopedia
(Volume 5).
Drainage at the B-20 site is generally to the northeast in two runoff channels
within the Cibolo Creek watershed. The
larger channel begins just north of the gravel road at the southern site
boundary, drains into a small pond, and continues northeast to the livestock
pond (Tank I). Groundwater from
Well CS-I feeds into the tank/pond northeast of B-20/21. The surface area of the pond is less than one acre. An earthen dam exceeding six feet in height causes the collection of
surface water in the livestock pond. The
smaller channel runs northeast along the eastern site boundary until it branches
into the larger channel. Both
channels are ephemeral, and the small on-site pond is dry during periods of
little to no precipitation. Water
remains at the livestock pond (Tank I) during dry periods due to the pumping of
Well CS-I. Due to higher elevations north, west, and south of the site,
these two channels receive all site runoff.
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 site to SWMU B-20/21 is a burnt rock
midden located north of SWMU B-24.
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 Evaluation (Volume 1-6).
Land
within 0.25-mile of SWMU B-20/21 is classified as "Evergreen Forest
Land" in
Figure 1.1 of the Technical
Approach Document for Risk Evaluation. There are no
buildings within 0.25-mile of the site, but Well CS-I, which is used for
watering livestock, is located approximately 800 feet to the northeast.
Well CS-MW3-LGR, a groundwater monitoring well, is located approximately
3,500 feet south and downgradient of SWMU B-20/21.
The nearest residential area is approximately one mile west of SWMU
B-20/21. In addition, Fair Oaks
Elementary School is over one mile northwest of the site.
A
small herd of cattle, maintained on CSSA by the USDA-ARC, roam freely throughout
selected areas of the Inner Cantonment and the North Pasture. Additionally, wild
game species, including white-tailed deer, axis deer, and wild turkey, roam
freely throughout CSSA. A map of
the deer hunting stands which 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
B-20/21 is located within an area where hunting is allowed.
Deer blinds 28, 29, 30 and 33 are all within 1,000 feet, and blind 32 is
within 1,500 feet of the site.
Four water reservoirs are maintained at CSSA for the purpose of sport fishing.
Two of the reservoirs are located in the northwestern and northeastern
portions of the North Pasture while the other two are located near the western
boundary of the Inner Cantonment. One
reservoir, known as Tank I, is located approximately 500 feet east of SWMU B-20/21
and is fed by the small stream that bisects the eastern portion of the B-20/21
site.
The
nearest potential habitats for local endangered species (Figure 11, Volume 1-1,
Background Information Report) are 2,000 feet to the southwest (Black-Capped
Vireo) and 600 feet to the northwest (Golden-Cheeked Warbler).
1.3 - Previous Investigations
Investigation
of SWMU B-20/21 began in February 1994, after EPA issued a Compliance Order in
June 1993 requiring preparation and implementation of a closure plan for the
site. A chronology of actions at
SWMU B-20/21 is located in Volume 1-2 and Volume 3-1, behind the SWMU
B-20/21 tab of the Environmental Encyclopedia.
Investigations at the site prior to the current RFI activities included a
geophysical survey, UXO removal, advancement of soil borings, collection of
environmental samples from surface soil, subsurface soils, sediments, surface
water and groundwater samples.
1.3.1 Preliminary Screening, 1994
In
January and February 1994, the Red River Army Depot (RRAD) responded to the
Compliance Order by collecting preliminary samples to provide an estimation of
the nature and extent of contamination for environmental investigation planning
purposes. Samples were collected
from areas of possible contamination, including from within four craters, near
one soil mound, from the small on-site pond, and from the livestock pond to the
northeast.
No
explosives were detected in any of the samples.
Arsenic in three surface soil samples exceeded RRS2 criteria.
Barium, cadmium, and lead in the surface water sample collected from the
small on-site pond exceeded freshwater criteria (30 TAC 307). Additional information regarding this preliminary sampling is
included in
Section 2.4 of the
Remedial Investigation Report (Parsons ES,
1995d).
1.3.2 Phase I Remedial Investigation, 1994-1995
In
March 1994, the Partial Facility Closure Plan, B-20 Detonation Area
(Parsons ES 1994) was submitted to USEPA Region VI.
The first phase of the investigation was conducted in November and
December 1994. The purposes of the
first phase of the investigation were to determine if any UXO items remained at
the site and to determine if chemicals had been released.
The scope of the investigation included sampling of surface soil,
subsurface soil and rock, sediment, surface water, and groundwater, and removal
of UXO on the ground surface. Results
of the investigation are summarized below.
Detailed descriptions of results can be found in the Remedial
Investigation Report for B-20 (Parsons ES, 1995d).
The
explosives analyses conducted during this investigation were performed by ITS
Laboratories in Richmond, Texas. In
1999, due to unacceptable practices by ITS, the EPA determined that the
analytical results were questionable and therefore, could not be used to
document site conditions.
1.3.2.1 UXO Removal
A total of 193 UXO items were found during the first phase of the investigation. Most items were fragments of ordnance containing explosive residue. Some of the items were chunks of raw explosive. The majority (162 of 193) of the items were found within the original
site boundary, but a substantial portion (31 of 193) was found outside the
original boundary. All UXO
identified at the site was found on the ground surface. The UXO Specialists indicated that this UXO probably blasted out of the
craters during detonation. Ordnance
detonated in a crater can be blasted several hundred feet, explaining why some
UXO items were found up to 55 feet from the site.
To
address the possibility of buried UXO in the craters, magnetic surveys were
conducted at each crater. The
magnetometer was used in areas most likely to contain buried UXO (craters)
rather than across the entire site due to interference caused by the large
amount of scrap metal at the site. Magnetic
anomalies were identified in 10 of the 15 craters.
Although
the entire B-20 site and much of the surrounding area was methodically swept for
UXO items, vegetation obstructed visual identification of UXO items on the
surface. The RI report concluded that additional UXO items likely
remained on the ground surface, and potentially existed in the subsurface at the
craters.
1.3.2.2 Surface Soil Sampling
A
total of 43 surface soil samples were collected at the site during the RI. Metals levels in eighteen of the 43 samples exceeded background (RRS1)
criteria. Analytes exceeding
background levels included arsenic, barium, cadmium, lead, and mercury. In addition, 2,4-TNT was detected above the PQL in one
sample. These exceedances were
detected in the following areas:
All
of these areas, except the large area in the west-central portion of the site,
also exceeded RRS2 criteria.
1.3.2.3 Subsurface Soil Sampling
Metals
levels in several borings exceeded RRS1 and RRS2 criteria. Since
most of these samples were collected within rock and since groundwater was not
encountered during drilling of these borings, the RI report concluded that it is
unlikely that these metals levels would have an adverse affect on human health
or the environment. At the time
that the RI report was prepared, arsenic and mercury were identified as metals
exceeding RRS1 criteria. However,
background levels have since been revised, and lead levels detected in three
soil borings also now exceed RRS1 criteria.
1.3.2.4 Sediment, Surface Water, and Groundwater Sampling
No
contaminants were detected in the natural surface water features at the site
(the ephemeral stream and the small pond). However, during the investigation, water was present in several craters;
and contaminants in this water exceeded RRS2 criteria. Sediments at one crater exceeded RRS1 metals concentrations. Sediment samples were also collected from two other craters, the
ephemeral stream crossing the site, the small on-site pond, and the livestock
pond northeast of the site.
A
groundwater sample was collected at one boring where groundwater was
encountered. All analyte
concentrations were below MCLs.
1.3.3 Phase II Remedial Investigation, 1995-1996
Phase
II of the remedial investigation was initiated in September 1995 and included
additional surface soil sampling, drilling and sampling of three soil borings,
and additional UXO clearance activities. Amendments
to the project plans were prepared in September (Parsons ES, 1995f) and December
1995 (Parsons ES, 1995g). Results
of the investigation are summarized below.
Detailed descriptions of results can be found in the
Addendum to the
Remedial Investigation Report for B-20 (Parsons ES, 1996b).
1.3.3.1 UXO Removal
UXO
removal activities during the second phase of the investigation included
vegetation reduction and removal activities within and around the site,
additional surface sweeps within the site after vegetation reduction, surface
sweeps in areas outside the boundary, and subsurface UXO removal in the northern
six-acre area of the site.
UXO
specialists from UXB International used a Schodstedt GA-52B Locator, a
magnetometer which identifies ferrous items up to a depth of 10 feet, to aid in
UXO identification. The boundaries of the area outside the site were defined by
conflagration patterns identified during the first phase of the RI, review of
historical aerial photographs, and field identification of UXO.
In
December 1995, subsurface magnetic anomalies in the northern portion of the site
(which was divided into eight grids) and also in the 15 craters were excavated
and removed. While the craters in
the southern portion of the site contained very little buried debris, the
northern portion of the site was found to contain a significant amount of buried
debris, including some UXO. These
items were identified with a Foerster Ferek (Mk-26) Ordnance Locator, flagged
for later excavation, and removed during a field effort that lasted until March
1996. Over 37,000 magnetic contacts were identified in the portion
of the area that was surveyed. These
contacts were caused by clay lenses, metal-containing debris such as cans and
wire, and, to a small extent, UXO. A
total of 300 subsurface UXO items were identified in the area investigated. In addition, 19,000 pounds of scrap metal were excavated and removed. UXO found during the phase II investigation was destroyed
during detonations on January 31, 1996 and May 6, 1996.
Because
so many magnetic contacts were encountered during the subsurface UXO removal
activities in the northern portion of the site, only six of the eight grids
could be cleared due to budget constraints. Therefore, the addendum report recommended additional subsurface UXO
removal activities at the site. Because
the area had apparently been used for solid waste disposal, the report concluded
that RRS1 closure would be possible if the waste was left in place.
1.3.3.2 Surface Soil Sampling
Additional
surface soil samples were collected in the south-central portion of the site to
aid in the delineation of the extent of metals exceeding background
concentrations in that area. In
areas where raw TNT was observed, surface soil samples were collected and
analyzed for explosives using immunoassay testing procedures to assess the
extent of contamination associated with such items.
Results
of the surface soil metals analyses identified areas where background metals
concentrations were exceeded. These
results indicated that estimated 17,900 yd3 of soil exceed background
concentrations in the south-central portion of the site.
A map from the Phase II RI which shows the areas with above-background
levels of metals contamination (using 1997 background levels, which have since
changed) is included in Appendix G.
The
results also revealed that the extent of metal contamination had not been
completely defined to the south of the site.
Results for the immunoassay testing of the soils for explosives indicated
that the extent of contamination in the vicinity of the raw TNT was very limited
and, therefore, the presence of these items at the site has not resulted in
widespread contamination by explosive constituents.
The
addendum report made three recommendations for addressing contaminated surface
soils at the site: