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SWMU B-31 RCRA Facility Investigation/Closure Report
Section 2 - Field Investigation
At SWMU B-31, lead shot-contaminated sand was suspected of having been used as backfill around an active sanitary waste PVC pipe. In an effort to characterize the site and determine its readiness for RRS1 closure, a geophysical investigation was performed in 1996. Also in 1996 and 1997, surface samples were collected, seven excavation pits were dug, and three soil borings were advanced to assess the extent of contamination for metals, explosives, and VOCs. However, the analytical data associated with the surface, subsurface, and excavation test pit samples were rejected by the EPA in 1999 due to questionable practices by the laboratory. Surface and subsurface sampling were repeated in 2000, as described in this section.
An electromagnetic geophysical survey was conducted at SWMU B-31 on March 11, 1996. Prior to collecting EM data, a grid system was established at the site which encompassed the areas of suspected ground disturbance. This grid consisted of a 560 by 40 foot area. The grid system and spacing used are shown on Figure B31-4.
EM data were collected at 2-foot intervals along transects that were separated by 20 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 milliSiemen 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 himself 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-31 that was determined to be free of disturbances and anomalies was selected and marked to perform background checks and calibration. 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 was 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.
In July 1997, seven investigation excavations (test pits) were made to explore for potentially contaminated sand and projectile materials at SWMU B-31 (Volume 1-1, RL33 Work Plan Addendum). The test pits were approximately five feet deep and 6 feet by 6 feet in area. The intent of these excavation activities was to remove contaminated sand and projectile materials and dispose of them. A photo of the excavation process at SWMU B-31 is provided in Figure B31-5 and a photo of an exposed portion of the pipeline is shown in Figure B31-6.
Excavated materials were visually examined for evidence of contamination. Even after conducting exploratory excavations in seven areas, no evidence of shot or other waste material could be found. The pits were backfilled with the same fill material that had been removed. A confirmation sample was collected from the bottom center of each of the seven test pits and analyzed for lead, copper, and zinc. The confirmation samples were submitted to ITS Laboratories for analysis.
However, ITS analytical results were deemed invalid by the EPA in 1999. Since the sewage pipe is an active line, the confirmation samples from pit excavations were not re-collected due to the potential risk of damaging the pipe, and because there was no evidence of waste material.
In accordance with the approved work plan, a soil gas survey was not performed in association with the investigation conducted for SWMU B-31.
On March 12 and 15, 1996, three surface soil samples were collected in the top half-foot of soil to compare constituent concentrations associated with the backfill soils to constituent background levels established for CSSA soils. Sample B31-SS01 was collected from the north end of SWMU B-31, B31-SS02 from the center, and B31-SS03 from the southern portion of the site. Samples were submitted to ITS Laboratories for analysis. The analyses of the subsurface samples that were collected in 1996 were deemed unusable by the EPA in 1999. A Work Plan Amendment was subsequently created to replace the invalid laboratory data (RL17 Work Plan Amendment for Data Quality Rework at SWMU Unit B-31).
On March 13 and 15, 2000, three surface samples were re-collected in the top half-foot of soil at SWMU B-31. These samples were collected adjacent to the location where surface soil samples were collected in 1996 (Figure B31-6). Each sample was analyzed for explosives using EPA method SW-8330 by DataChem Laboratory in Salt Lake City, Utah; and for barium, chromium, copper, nickel, and zinc by method SW-6010A, arsenic by method SW-7060A, cadmium by SW-7131A, lead by SW-7421, and mercury by SW-7471A by O’Brien and Gere Laboratories in Syracuse, New York. Samples were also accidentally analyzed for VOCs (using EPA method SW-8260B by APPL Laboratory in Fresno, California), even though VOCs are not contaminants of concern at this site. Equipment decontamination procedures, as well as sample collection, preparation, handling, and shipping protocols, are described in the Field Sampling and Analysis Plan (Volume 1-4, Quality Assurance Project Plan). QA and QC samples were collected as described in the AFCEE QAPP (Volume 1-4, Quality Assurance Project Plan). All sampling points were surveyed by Parsons ES using a Trimble Asset-grade GPS. Surveying methodology is described in the Amendment to the Field Sampling Plan (Parsons, 2001b). All sample locations and analytical data will be incorporated into the CSSA GIS database.
The surface soil samples collected at SWMU B-31 are representative Krum Complex soils. Generally, the soil associated with the uppermost foot of the soil profile at SWMU B-31 was a dark brown, silty plastic clay, with caliche occurring at approximately one foot below ground surface.
2.1.5 - Subsurface Soil Samples
On August 29 and 30, 1996, three soil borings were advanced at SWMU B-31 in order to assess the potential for contaminant migration from the pipe trench backfill materials (Volume 1-1, RL17 Work Plan Addendum). The soil borings were advanced adjacent to the surface soil samples collected on March 12, 1996. Copies of the Soil Boring Logs are provided in Appendix B. Samples were retained for analysis from B31-SB01 at depths of 6 and 10 feet, from B31-SB02 at depths of 7 and 10 feet, and from B31-SB03 at depths of 5 and 10 feet. These samples were submitted to ITS Laboratories and analyzed for VOCs and metals and explosives. The analyses of the subsurface samples that were collected in 1996 (presented in Section 1.3 of this report) and were performed by ITS Laboratories, Inc., were deemed invalid by the EPA in 1999. A Work Plan Amendment was subsequently created to replace the invalid laboratory data (RL17 Work Plan Amendment for Data Quality Rework at SWMU Unit B-31).
On March 13 and 15, 2000, three soil borings were advanced at SWMU B-31 adjacent to the locations where borings were advanced in 1996 (Figure B31-4).
The Lower Glen Rose Limestone was encountered between 2 and 4.5 feet below ground surface. The Lower Glen Rose was dry, massive, highly weathered, and pale brown. No odor was detected in the mudstone, and no contamination was detected (i.e., visual observations, PID measurements) while the soil borings were advanced. Groundwater was not encountered during the soil boring advancement.
For each boring at SWMU B-31, two samples were collected for analysis. One sample was collected from 4.5 to 5 feet and the second from 9.5 to 10 feet bgs for each boring. Borings RW-B31-SB01 and RW-B31-SB02 were advanced on March 13, 2000, and boring RW-B31-SB03 was advanced on March 15, 2000. Analysis of each sample for metals, explosives and VOCs were conducted by O’Brien and Gere, DataChem, and APPL, Inc., respectively, using methods noted in Section 2.1.3.
In accordance with the approved work plan, groundwater samples were not collected in association with the investigation conducted for SWMU B-31.
Three anomalies were detected at SWMU B-31. However, these three anomalies correspond to non-waste management activities (Parsons ES, 1995). Two are associated with manhole covers, and the third is associated with corrugated metal roofing (Figure B31-4). Both the in-phase component and the quadrature phase components of the EM geophysical survey are provided in Figure B31-7 and Figure B31-8, respectively.
In accordance with the approved rework plan and as described in Section 2.1.2, test pit confirmatory samples were not collected in association with the current investigation conducted for SWMU B-31.
In accordance with the approved work plan, a soil gas survey was not performed in association with the investigation conducted for SWMU B-31.
Because the analytical data for the 1996 samples was rejected by the EPA, only analyses for the samples collected in 2000 are presented. Analytical results for surface samples are presented in Appendix A. The detected constituents are summarized in Table B31-1, with the RRS1 standards applicable to the data. No VOCs or explosives were detected in any of the surface soil samples; therefore, these compounds are not included in the table.
Since no VOCs nor explosives were detected above RLs, the surface soil samples meet RRS1 criteria for these compounds. As shown in Table B31-1, none of detected metals concentrations for surface soil samples exceeded background values for CSSA soils. Therefore, RRS1 criteria for metals have also not been exceeded.
Soil boring logs from the borings advanced in 1996 are presented in Appendix B. As per the Re-Work Plan (RL17 Work Plan Amendment for Data Quality Rework at SWMU B-31), new boring logs were not to be recorded, but the differences between the 1996 and 2000 borings were noted. The borings advanced in 2000 were advanced adjacent to the 1996 borings, and no significant differences in the borings were noted. Because the analytical data for the 1996 samples was rejected by the EPA, only analyses for the samples collected in 2000 are presented. These data are presented in Appendix A and the detected constituents are summarized in Table B31-1, along with the appropriate RRS1 comparison concentrations. RRS1 levels for metals are the background levels in the TNRCC-approved Second Revision to the Evaluation of Background Metals Concentrations in Soil and Rock at CSSA (Parsons, February 2002).
Like the surface soil samples, no VOCs or explosives were detected in any of the samples; therefore, RRS1 criteria have been met for these compounds. As shown in Table B31-1, sample RW-B31-SB01 (9.5 to 10 feet) exceeds CSSA background for the Glen Rose Formation for zinc (11.3 mg/kg) with a reported value of 21.2 mg/kg. RW-B31-SB02 (9.5 to 10 feet) also slightly exceeds the zinc background concentration for CSSA, with a reported concentration of 14.2 mg/kg. These concentrations do not exceed the Texas-specific median concentration for zinc background is 30 mg/kg (30 TAC 350.51[m]).
In accordance with the approved work plan, groundwater samples were not collected in association with the investigation conducted for SWMU B-31.