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As outlined in the Environmental Encyclopedia site-specific work plan (Volume 1-3, AOC-42), the field investigation for AOC-42 included a geophysical survey to delineate the southern extent of anomalies C and D, collection of nine surface soil samples and drilling of nine soil borings for subsurface soil sampling. The samples were biased toward anomalies found during geophysical survey activities conducted on the area designated “Salado Creek.” All field activities followed those protocols established in the Field Sampling and Analysis Plan (Volume 1-4, Field Sampling Plan).
A summary of the analytical results of surface and subsurface soil sampling performed is included in Appendix A. The soil boring logs are provided in Appendix B. Parsons personnel, using a Trimble Asset-grade geographic positioning system (GPS) tool, surveyed all sampling points. All sample and corresponding analytical data are being incorporated into the CSSA geographic information system (GIS) database.
A geophysical survey was conducted at AOC-42 in November 1999. The site was measured and divided into 50-foot intervals that were marked with 2-foot wooden stakes forming a surface grid. The grid dimensions were 250 feet at the widest in the east-west direction and 600 feet in the north-south direction (Figure AOC42-6).
The EM-31 survey was completed according to the procedures described in Volume 1-4, Sampling and Analysis Plan, Section 1.1.2. Additional information regarding electromagnetic (EM) induction can be found in Volume 5, Groundwater Investigation and Associated Source Characterization, Section 3.1. Prior to the survey, a site near the AOC that was determined to be free from disturbances and anomalies was selected and marked to perform background checks and calibration. The background checks were also performed after the survey. All calibration before and after background readings was recorded in the field logbook. The data were recorded in a DL720 Polycorder and downloaded into a computer. The data were then processed and evaluated using DAT31 software and later merged using SURFER software.
A ground penetrating radar (GPR) survey was conducted at the site using a Geophysical Survey Systems, Inc. (GSSI) SIR-2 GPR instrument equipped with a 300 megahertz (MHz) antenna. The survey was conducted in accordance with procedures outlined in Volume 1-4, Sampling and Analysis Plan, DO5068 Addendum, Section 2.4. The individual GPR survey profiles were conducted over anomalies that were detected during the EM-31 survey. Additional surveys were also conducted at the site to provide background information. A total of twenty-four survey profiles were created during the field effort. Seven profiles were generated in the east-west direction and seventeen profiles were created in the north-south direction (Figure AOC42-6).
In accordance with the approved work plan, a soil gas survey was not performed in association with the current investigation conducted for AOC-42.
Nine surface soil samples were collected at AOC-42 in March 2001 at locations shown in Figure AOC42-4. The samples were collected at a depth of 6-inches below the surface and were analyzed for VOCs (PCE, trichloroethene [TCE], dichloroethene [DCE] isomers, carbon tetrachloride, and chloroform), explosives, and metals (barium, copper, zinc, nickel, chromium, arsenic, cadmium, lead, and mercury). Samples were analyzed by O’Brien & Gere Laboratory in Syracuse, New York, using methods SW-8260B, SW-6010B, SW-7060A, SW-7421, SW-7131A, and SW-7471A, and SW-7471A. Samples for explosives analysis were analyzed by DataChem Laboratory in Salt Lake City, Utah, using method SW-8330. Samples AOC42-SS01 through AOC42-SS07 were collected to characterize the soil near the linear anomalies located on the eastern side of the AOC. Samples AOC42-SS08 and AOC42-SS09 were collected near two isolated individual geophysical anomalies present in the central portion of the site. At the time of sampling, no visual evidence of contamination was noted.
All samples were collected using a decontaminated stainless steel hand trowel. All decontamination, sample preparation and handling followed those protocols established in the Field Sampling and Analysis Plan (Volume 1-5, Field Sampling Plan, Quality Assurance Project Plan, and RL83 Addendum). Environmental sampling also included the collection and submittal of quality assurance (QA) and quality control (QC) samples at those frequencies outlined in the AFCEE Quality Assurance Project Plan (QAPP) (Volume 1-4, Quality Assurance Project Plan).
Subsurface soil samples were collected from nine borings (AOC42-SB01 through AOC42-SB09) in March 2001 at locations shown in Figure AOC42-4. Two samples were collected from each boring, one sample was typically collected near the soil/bedrock interface and one sample was collected at the borehole terminus. All samples were analyzed for VOCs (PCE, TCE, DCE-isomers, carbon tetrachloride, and chloroform), explosives, and metals (barium, copper, zinc, nickel, chromium, arsenic, cadmium, lead, and mercury) using the same methods and laboratories as the surface soil samples. Samples AOC42-SB01 through AOC42-SB07 were collected to characterize the soil near the linear anomalies located on the eastern side of the AOC. Samples AOC42-SB08 and AOC42-SB09 were collected near two isolated individual geophysical anomalies present in the central portion of the site.
All drilling locations were pre-screened by Parsons unexploded ordnance (UXO) technicians using a Schonstedt® magnetometer. A down-hole magnetometer was also used after every 2 feet of advancement in the soils above the bedrock. No discernable evidence of contamination was noted visually or with a photoionization detector (PID) in recovered soil and rock samples, except at the original location of soil boring AOC42-SB01. This boring had to be relocated because metal and rubber-like material were encountered at a depth of approximately 8 feet in the original location. The original location of AOC42-SB01 where buried waste was found is noted in Figure AOC42-4.
Hydrocarbon odors were noted at SB03 and SB07, but were not volatile enough to register on the PID. Soil boring logs are included as Appendix B. Bedrock was encountered beneath AOC-42 at depths ranging from 9 feet bgs in AOC42-SB01 to AOC42-SB07 and from 11 to 18 feet bgs in AOC42-SB08 and AOC42-SB09.
All samples were collected using either a decontaminated split-spoon sampling device or an NX sized coring barrel with a one-piece removable inner barrel. All decontamination, sample preparation, and handling followed those protocols established in the Field Sampling and Analysis Plan (Volume 1-5, Field Sampling Plan). Environmental sampling also included the collection and submittal of QA and QC samples at those frequencies outlined in the AFCEE QAPP (Volume 1-4, Quality Assurance Project Plan).
Groundwater was only encountered in one soil boring, AOC42-SB06. Approximately 3 feet of water occupied this boring after drilling and the depth to water was 10 feet. However, in accordance with the approved work plan, groundwater samples were not collected.
As described in Section 2.1.1, a geophysical survey was conducted at AOC-42 in November and December 1999. The grid size was 600 feet in the north-south direction and 250 feet in the east-west direction. The site was staked at 50-foot intervals, with temporary stakes at 20-foot intervals to aid in the EM survey. Figure AOC42-6 illustrates the layout of the geophysical survey grid located at AOC-42.
In-phase and quadrature-phase EM data were collected at AOC-42 and completed as one file. Both in-phase and quadrature-phase EM data identified six anomalies or anomalous areas located in the eastern and central portion of the site. Four of the anomalies are amassed in two anomalous areas that are orientated northwest to southeast in a parallel linear pattern. Each linear anomaly is approximately 200 feet in length. Additional anomalies were located in the central portion of the AOC and may be unrelated to the anomalous area on the eastern side of the AOC. Figure AOC42-7 and Figure AOC42-8 show the results and locations of EM data collected at AOC-42.
GPR surveys were conducted to verify the information obtained by the EM survey. Like the EM survey, the GPR also revealed evidence of subsurface anomalies at AOC-42. A total of 24 GPR profiles were created with a 300 MHz antenna at a range setting of 90 nanoseconds (ns). Seven profiles were created in the east-west direction and seventeen were created in the north-south direction. Four GPR profiles, 15, 17, 36, and 37 are included in this report.
The vertical scale on the GPR profiles, time (nanoseconds), can be converted into feet using the following formula:
Range = Depth x Time (ns) x 1.5
Where: Range = 90 ns for profiles with a 300 MHz antenna
Depth = Depth below ground surface in feet.
Time = 4.5 ns per foot (for dry limestone per the GSSI SIR-2 manual)
Using the above formula, all four of the GPR profiles included in this report indicate the presence of anomalies at depths ranging from 1 to 3 feet bgs. The GPR profiles are included as Figure AOC42-9, Figure AOC42-10, Figure AOC42-11 and Figure AOC42-12.
The nature of the anomalies detected during the EM and GPR surveys is not known.
In accordance with the approved work plan, a soil gas survey was not performed in association with the current investigation conducted for AOC-42.
As described in Section 2.1.3, nine surface soil samples collected from AOC-42 were analyzed for VOCs, explosives, and metals. No VOCs or explosives were detected at concentrations exceeding the RLs; therefore, all samples meet RRS1 criteria for VOCs and explosives. Detected metals analytes are summarized in Table AOC42-1, and a complete list of results is provided in Appendix A. Although CSSA plans to pursue closure of the site under RRS1 criteria, Risk Reduction Standard 2 (RRS2) criteria are listed in the table to provide a frame of reference for the RRS1 exceedances.
Copper and mercury were detected above their established background levels. Mercury has an established background level of 0.77 milligrams per kilogram (mg/kg) for soils. Four out of nine samples exceeded background levels for mercury, at concentrations ranging from 0.84 mg/kg to 2.659 mg/kg. The maximum concentration (2.659 mg/kg) was detected at AOC42-SS06, located along the eastern portion of AOC-42. Copper was detected above its established background level of 23.2 mg/kg in only one sample. AOC42-SS09, located on the western side of the AOC and away from the linear trending geophysical anomalies, had a reported concentration of 25.4 mg/kg.
Eighteen subsurface soil samples were collected from nine borings drilled throughout the eastern and central portions of AOC-42 and analyzed for VOCs, explosives, and metals. As noted earlier, buried waste consisting of metal and rubber-like material was encountered at a depth of approximately 8 feet in the original location of soil boring AOC42-SB01. No VOCs or explosives were detected above the laboratory reporting limits. Of the metals analyzed, barium, nickel, zinc, and cadmium were detected slightly above background levels in six samples. The analytical results are summarized in Table AOC42-2 and a complete list of results is presented in Appendix A.
Of the eight samples collected
from Glen Rose Limestone material, five slightly exceeded the applicable
background concentration for zinc of 11.3 mg/kg.
These samples and their concentrations were AOC42-SB01 (14.5-15 ft)
with 15.0 mg/kg; AOC42-SB02 (14-15 ft) with 11.8 mg/kg; AOC42-SB03
(11.0-12.5 ft) with 26.1 mg/kg; AOC42-SB08 (16.5-17.5 ft) with 14.6 mg/kg;
and AOC42-SB09 (13.5-14.5 ft) with
12.0 mg/kg. Additional analytes detected above their applicable background
levels were barium, detected at 14.0 mg/kg in AOC42-SB08 (16.5-17.5
ft), cadmium detected at 0.326 mg/kg in AOC42-SB03 (11-12.5 ft), and
nickel detected at 12.01 mg/kg in AOC42-SB09 (13.5-14.5 ft).
The background levels in Glen Rose Limestone material for barium,
cadmium, and nickel are 10.0 mg/kg, 0.10 mg/kg, and 6.8 mg/kg,
respectively. The reported barium
concentration is well below the Texas-specific median background concentration
for barium of 300 mg/kg. The
reported nickel concentration of 12.01 mg/kg is slightly above the
Texas-specific median background concentration for nickel, 10 mg/kg.
At this time there is no existing Texas-specific median background
concentration for cadmium.
In accordance with the approved work plan, groundwater samples were not collected in association with the current investigation conducted for AOC-42.