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SWMU B-10 RCRA Facility Investigation/Closure Report
Section 2 - Field Investigation
As outlined in the Environmental Encyclopedia site-specific
work plan (Volume 1-2, SWMU B-10), planned closure activities
included performing a geophysical survey, a soil gas survey, a UXO survey,
surface soil sampling, and exploratory trench excavation, and waste removal and
offsite disposal. The field activities
were performed according to the
Field
Sampling and
Analysis Plan (Volume 1-4, Field Sampling Plan, Quality Assurance Project Plan).
Electromagnetic and ground penetrating radar geophysical surveys were conducted just south of SWMU B-10 in March 1996. An additional geophysical survey was performed in April 1996. The purpose of the geophysical survey was to determine the extent of the area used for waste disposal.
Prior to collecting EM or GPR data, a grid system was established which encompassed the area of suspected ground disturbance. This grid consisted of staked locations separated by intervals ranging from 25 to 100 feet. Figure B10-5 illustrates the layout of the geophysical survey grid located at SWMU B-10. Because the SWMU B-10 site boundary was adjusted following the extensive excavation that was performed after the geophysical survey, the geophysical survey grid boundary does not match the site boundary.
EM data were collected at 2-foot intervals along transects that were separated by 20 to 50 feet using the established geophysical survey grid. EM measurements were taken using a Geonics EM31-DL ground conductivity meter, and recorded with a Polycorder data logger. The conductivity meter consists of transmitter and receiver coils that are separated by 12 feet. The instrument has a nominal depth of penetration of approximately 16 feet when operated in the vertical-dipole mode. The instrument measures both quadrature- and in-phase components of an induced magnetic field. The quadrature-phase component is a measure of apparent ground conductivity while the in-phase component is more sensitive to the presence of ferromagnetic metal. A lateral variation in apparent ground conductivity indicates a lateral change in subsurface physical properties (i.e., related to degree of disturbance). Apparent ground conductivity is measured with a precision of approximately ±2 percent of the full-scale meter reading which corresponds to approximately 2 milliSiemens per meter (mS/m). The in-phase component of the EM-31 is the response of the secondary to primary magnetic field measured in units of parts per thousand (ppt). The primary magnetic field is due to the current source from the EM-31. The secondary magnetic field is due to induced currents within conductive material in the subsurface.
Data were collected by setting the instrument to record in an automatic vertical dipole mode. Readings were taken at 0.5 second intervals which corresponded to a reading every 2 feet along a given transect. Both apparent ground conductivity (i.e., quadrature phase) and in-phase data were recorded. The operator aligned along a transect and with the instrument parallel to the transect, paced between marked or staked stations separated by 10 feet. The variation in transect footage was related to the size of the site and the number of obstructions.
The EM-31 survey was completed according to the procedures described in Volume 1-4, Sampling and Analysis Plan, Section 1.1.2. Prior to the survey, a site near SWMU B-10 that was determined to be free of disturbances and anomalies was selected and marked to perform background checks and calibration. The background checks were also performed after the survey. All calibration and before and after background readings were recorded in the field logbook.
During each field day, data were transferred from the data logger to computer diskettes. The data were processed using DAT31 software (Geonics, LTD) and contoured using Surfer software. For EM data that were not collected using the data logger, values were recorded on a log sheet, manually entered into a computer file, and contoured using Surfer software. Contour maps for both apparent conductivity and in-phase data were created for each site. Figure B10-5 and Figure B10-6 are the quadrature phase and in-phase geophysical survey maps, respectively.
2.1.2 Soil Gas Survey Sampling
As presented in Section 1.3, a soil gas survey was performed in November 1995 in the area surrounding SWMU B-10. However, only one sampling point was located within the SWMU boundary.
On August 23, 1996, additional soil gas sampling was conducted at the site. A total of seven samples were collected from seven locations within an adjacent area just south of SWMU B-10. Samples were collected at a depth of 3 feet. A duplicate sample was collected at one location (grid point B,1). The samples were analyzed for benzene, toluene, ethylbenzene, total xylenes, cis-1,2-DCE, TCE, 1,1,1-trichloroethane, and PCE.
Samples were collected by manually driving a decontaminated ¾-inch stainless steel hollow sampling rod to the selected depth with a pneumatic hammer. The sampling rod was then backed a few inches out of the ground allowing the detachable point to drop off the sampling probe and exposing a void space of the formation soil vapors were then pulled from the soil through the probe into a Tedlar bag using a portable vacuum pump. The soil formation around the sample rod was purged for at least three probe volumes prior to sample collection.
The samples were then transported to the field GC temporarily located at CSSA for analysis. Samples were analyzed within four hours of collection with an HNu Model 321 GC equipped with an electron-capture detector and a PID with a 10.2 eV light source. A Spectra-Physics model 4400 dual-channel integrator was used to plot the chromatograms, to measure the size of the peaks, and to compute compound concentrations.
In August 1997, a UXO identification effort was performed by UXO specialists from UXB International, Ashburn, Virginia. The UXO specialists traversed the site in a systematic manner to visually identify UXO on the surface, and used Schonstedt magnetometers to assist in identification of metal at or near the surface. In addition, three slit trenches were dug to identify the type of waste disposed at the site, and to determine if any of it was UXO-related.
2.1.4 Waste Characterization Sampling
In December 1999, three exploratory trenches were dug at SWMU B-10 so that samples could be collected for waste characterization. This sampling effort was conducted in anticipation of planned waste excavation and disposal efforts. Two trenches were dug at what was thought to be the northern and southern extents of waste, and the third was dug in the middle of the waste area.
One sample was collected from each trench on December 16, 1999. The samples were designated B10-TM1 (from the middle trench), B10-TN1 (from the north trench), and B10-TS1 (from the south trench), and were collected at the locations shown in Figure B10-7. These samples were sent to APPL Laboratory in Fresno, California for TCLP VOCs (SW-1311/SW-8260B) and TCLP metals analyses. Metals analyses included barium, chromium, copper, nickel, and zinc (SW-1311/SW-6010B); arsenic (SW-1311/SW-7060A); cadmium (SW-1311/SW-7131A); lead (SW-1311/SW-7421); and mercury (SW-1311/SW-7470A).
Because the VOC holding times were missed by the laboratory, three replacement samples were necessary. During the resampling event on January 13, 2000, three samples, identified as B10-T1 (from the southern trench), and B10-T2 (from the middle trench), B10-T3 (from the northern trench), were collected and submitted to APPL Laboratory for TCLP VOCs (SW-131/SW-8260B). Sample locations are shown in Figure B10-7. The December 1999 metals and January 2000 VOCs analytical data were provided to Covel Gardens Landfill in San Antonio, Texas for characterization purposes.
In August 2000, Covel Gardens indicated that TPH, antimony, beryllium, selenium, and silver data were also necessary for characterization. Therefore, on August 22 and 25, 2000, additional trench samples were collected and submitted to APPL for analysis. Samples identified as B10-TS2 (from the southern trench), B10-TM2 (from the middle trench), and B10-TN2 (from the northern trench) were analyzed for TPH (TX 1005). Sample locations are shown in Figure B10-7.
Sample B10-TS2R was analyzed for TCLP antimony, beryllium, selenium, and silver (SW-1311/SW-6010B), and samples B10-TM2R and B10-TN2R were analyzed for total antimony, beryllium, selenium, and silver (SW-6010B).
2.1.5 Waste Excavation and Soil Sampling
On August 7, 2000, excavation was initiated at the southeast
end of SWMU B-10. Eagle Construction and
Environmental Services, Inc. of Cibilo, Texas conducted the excavation, with
oversight from Parsons. Banding material
and ammunition boxes were noted in the excavated area to a depth of
approximately 5 to 6 feet bgs. Other
waste material identified as excavation continued included mufflers, brake
pads, oil filters, miscellaneous 5-gallon containers, an empty 55-gallon drum,
miscellaneous machine gun parts, and an engine block. Field personnel separated out the metal
banding waste material from soils being excavated at SWMU B-10. Approximately 95 percent of the volume of waste
material encountered during excavation was metal banding. Excavation continued north of what was
originally thought to be the northern extent of the SWMU due to the presence of
waste materials. On
On August 22, 2000, soil samples were collected at the top, bottom, and sides of the buried drums, prior to their excavation. These samples were labeled B10-DA-Bottom 1, B10-DA-Top 1, and B10-DA-SE1 and were analyzed by APPL Laboratory for TCLP VOCs (SW-1311/SW-8260B) and TCLP metals. In addition, samples B10-DA-Bottom1 and B10-NE1 were analyzed for total VOCs (SW-8260B). Sample locations are shown in Figure B10-7. Metals analyses included barium, beryllium, chromium, copper, nickel, selenium, silver, and zinc (SW-1311/SW-6010B); arsenic (SW-1311/SW-7060A); cadmium (SW-1311/SW-7131A); lead (SW-1311/SW-7421); and mercury (SW-1311/SW-7470A). Excavation activities were then suspended temporarily to await results of samples collected in the vicinity of the drums.
Excavation resumed on October 4, 2000. Between October 4 and October 31, 2000, fourteen roll-off boxes containing metal banding material excavated from SWMU B-10 were taken to Newell Salvage in San Antonio, Texas for recycling. On October 31, 2000, following final excavation in the northern end of the trench where the drums were located, a sample B10-DE1 was collected from the material excavated and analyzed for total VOCs (SW-8260B) and TCLP VOCs (SW-1311/SW-8260B) by APPL Laboratory.
On November 16, 2000, trench bottom samples were taken at a
depth of three feet bgs from six locations at SWMU B-10 (Figure
B10-8). These samples were labeled B10-TrBott-1,
B10-TrBott-2, B10-TrBott-3, B10-TrBott-4, B10-TrBott-5 and B10-TrBott-6. The final sequential numbers associated with
each sample ID are provided in
Figure
B10-8. Another sample, labeled B10-TrBott-7,
was obtained from
the
sidewall of the excavation. On November
30, 2000, eight additional excavation bottom samples and three additional
sidewall samples were collected. These samples
were labeled B10-TrBott-8, B10-TrBott-9, B10-TrBott-10,
B10-TrBott-12, B10-TrBott-14, B10-TrBott-16, and B10-TrBott-17 along with
B10-Sidewall-13, B10-Sidewall-15, and B10-Sidewall-18.
Approximately 3,640 cubic yards of soil were excavated and disposed at Covel Gardens Landfill between October 12 and November 30, 2000. The ground surface at SWMU B-10 was returned to grade with approximately 2,430 cubic yards of clean backfill clay and excavation was completed November 30, 2000.
In accordance with the approved work plan, no soil borings were drilled in association with the current investigation conducted for SWMU B-10. All soil samples collected during excavation activities are discussed in Sections 2.1.4 and 2.1.5.
In accordance with the approved work plan, groundwater samples were not collected in association with the current investigation conducted for SWMU B-10. Soil borings were not drilled at SWMU B-10 and groundwater was not encountered during site investigations.
The geophysical surveys conducted March 1996 revealed no evidence of subsurface anomalies related to past waste disposal activities. One anomaly, related to the bunker structure located in the center of the area surveyed just south of SWMU B-10 was detected (see Figures B10-5 and B10-8). There was little variation in the data that were recorded during the EM survey, which can be interpreted as homogenous and consistent soil and bedrock profiles throughout the SWMU. Quadrature-phase readings ranged from a low of (-90) milliSiemens per meter (mS/m), to a high of (20) mS/m. In-phase readings during the EM survey ranged from a minimum of (-30) parts per thousand (ppt), to a maximum of (10) ppt.
The geophysical anomaly detected corresponded to the bunker structure that existed in the center of the adjacent area just south of SWMU B-10. Following excavation activities discussed in this report, the bunker structure was no longer present on site. Therefore, no geophysical anomalies indicative of past waste disposal activities were reported for the area just south of B-10.
2.2.2 Soil Gas Survey SamplingThe results of the August 1996 soil gas survey are presented in Table B10-1. Concentrations of PCE detected ranged from 0.43 ug/L to 4.9 ug/L. The maximum concentration was detected at soil gas data point #7 (Figure B10-9). Although PCE was detected in the soil gas, analyses of surface soil samples collected from trenching and excavation performed in 2000 did not indicate detectable levels of PCE in the soils.
The PCE concentration detected at SWMU B-10 is part of a larger soil gas plume in the vicinity of Well CS-16, originating at the most likely source areas SWMU B-3 and SWMU O-1. Investigation does not indicate that a VOC release has occurred at SWMU B-10.
In August 1997, UXO technicians performed a sweep of the SWMU B-10 area delineated in Figure B10-8 and metal debris was detected below ground surface. Three slit trenches were dug to visually observe the buried waste. No UXO was found in the trenches, only buried metal banding material, metal ammunition cans, and a minor amount of small ammunition debris that was removed manually.
2.2.4 Waste Characterization Sampling
Soils were sampled at SWMU B-10 for waste characterization purposes in December 1999, January 2000, and August 2000. Soil samples were analyzed for TCLP metals, TCLP VOCs, and TPH, as described in Section 2.1.4. Constituents reported for TCLP analyses and analyses of totals are summarized in Table B10-2 and Table B10-3, respectively. A complete list of analytical results is included in Appendix A.
None of the sample results exceeded Federal Characteristic Hazardous Criteria or Texas Class 1 Non-hazardous Criteria. The wastes were therefore characterized as non-hazardous by Covel Gardens Landfill.
2.2.5 Waste Excavation and Soil Sampling
Following the metal debris and soils excavation conducted from August to November 2000, trench bottom confirmation samples were collected in November 2000. Table B10-4 presents the detected constituents for two events of confirmation sampling conducted November 16, 2000 and November 30, 2000. In addition, the data from one resampling event is included in Table B10-4. No RRS1 closure criteria exceedances for VOCs were reported for samples collected on November 16, 2000. Metals exceeding RRS1 closure criteria at that time included chromium, copper, and zinc. Elevated chromium concentrations were reported for three samples at concentrations ranging from 44.5 mg/kg to 46.4 mg/kg, which are slightly above the background level of 40.2 mg/kg for chromium. Copper was detected in one sample at a concentration of 53.3 mg/kg, which is above the background concentration of 23.2 mg/kg. Zinc exceeded the background concentration of 73.2 mg/kg in all samples collected November 16, 2000, at concentrations ranging from 75.8 mg/kg to 104 mg/kg.
Additional excavation was conducted from November 16, 2000 through November 30, 2000, when eleven additional confirmation samples were collected along with two field duplicates. Zinc was detected above background in every sample, except B10-TrBott-9, at concentrations ranging from 89.2 mg/kg to 1,100.5 mg/kg. The highest zinc concentration (1,100.5 mg/kg) was detected at B10-TrBott-17. All other metals levels were below CSSA soils background levels, except lead at B10-TrBott-16 where 2,343 mg/kg lead was detected. All VOCs were below RRS1 criteria.
Because all waste material and soil were removed to the bedrock contact, the elevated concentrations at two locations were considered suspect. Therefore, a second sampling event was conducted on April 8, 2003, to resample the two sample locations. The objective for the additional trench bottom samples was to demonstrate that affected soil and debris associated with previous disposal activities at the site had been removed down to the top of the underlying bedrock. The results from the two confirmation samples taken in November 2000 were greater than any previous samples collected for SWMU B-10 including all waste characterization samples and other confirmation samples from SWMU B-10. Additionally, based on field observations all waste and waste residues were removed to the extent practical (i.e.; to bedrock). A sample was collected from a depth of 6.5 feet at B10-16 where an elevated lead concentration of 2343 mg/kg was reported for B10-TrBott-16 (collected in the Fall, 2000). A second sample was collected from a depth of 3 feet at B10-17 where an elevated zinc concentration of 1100.5 mg/kg was reported for B10-TrBott-17 (collected in Fall, 2000).
The results of the April 2003 sampling event were a concentration of 1.27 mg/kg lead was reported for B10-16 and a concentration of 0.63 mg/kg zinc was reported for B10-17. These concentrations are acceptable and do indicate affected soils associated with previous disposal activities at the site were removed prior to placement of clean fill material.
In accordance with the approved work plan, no soil borings were performed in association with the current investigation conducted for SWMU B-10. Results of all soil samples collected during excavation activities are discussed in Sections 2.2.4 and 2.2.5.
In accordance with the approved work plan, groundwater samples were not collected in association with the current investigation conducted for SWMU B-10. Soil borings were not performed at SWMU B-10 and groundwater was not encountered during site investigations.