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AOC 55 RCRA Facility Investigation Report
Section 2 - Field Investigation
An electromagnetic induction geophysical survey was conducted at AOC 55 in October 2002 to define the limits of the disposal areas. Prior to collecting EM data, a grid system was established at each site which encompassed the areas of suspected ground disturbance. These grids consisted of staked locations separated by intervals ranging from 25 to 100 feet, depending on the size of the area and the amount of obstructions, if any. The grid system and spacing used are shown on individual site base maps. Figure AOC55-5 illustrates the layout of the geophysical survey grid located at AOC 55.
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 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 himself along a transect and, with the instrument parallel to the transect, paced between marked or staked stations separated by 20 feet. The variation in transect footage was related to the size of the site and the number of obstructions.
The EM31 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 AOC 55 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. Contour maps for both apparent conductivity and in-phase data were created for this site.
2.1.2 Preliminary Site Excavations
Test trenches and test pits were excavated on October 29 to 31, 2002 to confirm the results of the geophysical survey, characterize the waste thickness, and evaluate the material present. A total of 8 trenches were excavated in the southeast and southwest quadrants, and 15 test pits were excavated in the northeast and northwest quadrants. The trenches and pits were excavated in areas of geophysical anomalies identified in the EM data. The locations of the trenches and pits are depicted on Figure AOC 55-6.
Excavation subcontract services were provided by Eagle Construction and Environmental Services of Cibolo, Texas. Kyle Caskey, Senior Construction Manager for Parsons, provided contractor oversight during the test trenching operations. Additionally, A UXO Site Supervisor and technician were available to perform UXO avoidance and identification efforts.
The test trenches were excavated using a trackhoe. The trenches were oriented east to west across the suspected disposal area identified in the geophysical results. Trenches were excavated to bedrock resulting in trenches that were approximately seven to ten feet deep. Following completion of the trenching activities, samples for soil characterization were collected and the excavated material was placed back into the trenches. The test pits were excavated at locations of isolated anomalies and were advanced until bedrock was encountered, which was typically less than 10 feet in that area.
2.1.3 Initial Soil Characterization Sampling
On October 30, 2002 six samples collected from the material excavated from the test trenches. The samples were submitted to APPL in Fresno, California, and analyzed VOCs, SVOCs, RCRA metals (totals basis), and Toxicity Characteristics Leaching Procedure (TCLP) metals. The sample results were used to determine the appropriate contaminants of concern for the site and to establish a waste profile to determine landfill requirements in preparation for the removal actions. Analytical results for these samples will also be used to establish analytical requirements for the post-excavation confirmation.
Soil samples AOC55-SW1 through AOC55-SW5 were collected from the material excavated from trenches SW1 through SW5 in the southwestern quadrant. Composite samples of the excavated material were collected for the SVOC and metals analysis. The composite sampling procedure consisted of collecting aliquots of soil material at four to five locations from the stockpiled soil, combining and mixing the aliquots, then filing a sample jar with the soil mixture. A grab sample was collected for VOC analysis and was collected at the approximate middle of each trench alignment and at a depth of approximately 1 foot into the stockpiled soil material.
Sample AOC55-SE1 was collected from the three smaller trenches excavated in the southeast quadrant. The SVOC and metals samples were collected by compositing equal amounts of material from the stockpiles at the three trenches. The VOC grab sample was collected from the stockpiled material at Trench SE1a.
The soil samples were initially analyzed for VOCs, SVOCs, and total metals. These soil sample results were compared to the USEPA’s hazardous waste criteria and the TCEQ’s Class 1 waste criteria to assess possible waste classification. To compare the totals-based VOCs, SVOCs and metals results to the TCLP-based waste criteria, a screening value of 20 times the TCLP waste criteria was applied to the total results to identify areas where the TCLP waste criteria may be exceeded.
Samples that exceeded this conservative screening value for a particular analyte were then re-analyzed for that analyte using the TCLP extraction procedure. Following this screening technique, all soil samples except AOC55-SW1 were found to contain total lead concentration above the screening level, and as a result, all soil samples were analyzed for TCLP lead. In addition, sample AOC55-SE1 exhibited an elevated cadmium concentration that was well below the hazardous screening level; however, the sample was analyzed for TCLP cadmium to verify that Class 1 non-hazardous waste criteria were not exceeded for this parameter.
Laboratory results of the sample indicate that lead is present at elevated concentrations in all samples. Cadmium was detected in the sample from Trench SE1 at an elevated concentration. Three VOC constituents and eight SVOC constituents were detected in the samples at concentrations below the laboratory reporting limits. The VOC constituents present were methylene chloride, naphthalene, and toluene. The SVOC constituents detected in the samples includes: benzo (a) anthracene; benzo (a) pyrene; benzo (b) fluoranthene; benzo (g,h,i) perylene; chrysene; fluoranthene; indeno (1,2,3-cd) pyrene; phenanthrene; and, pyrene.
TCLP analysis for lead was conducted on all samples collected and TCLP cadmium analysis was conducted on sample AOC55-SE1. TCLP analyses were not performed for the VOC and SVOC analytes detected in the totals-based results due to the low concentrations present. Results of the TCLP analyses indicates that the material is below the Class 1 non-hazardous waste criteria and therefore meets Class 2 criteria as specified in State of Texas 30 Texas Administrative Code (TAC) Chapter 335, Subchapter R. Analytical results of the soil samples are summarized in Table AOC55-1 attached.
Initial soil gas sampling results for AOC 55 are discussed in Section 1.3 Preliminary Investigations of this report. No additional soil gas samples were collected at AOC 55 as part of this closure activity.
Site Excavations were initiated in February 2003 with the removal actions consisting of the turning over of soil in approximately 3‑inch lifts and having UXO technicians available to review the turned soil and identify items of concern. Once deemed clear, the soil previously turned over was removed to a stockpile area and the process was repeated until two feet of soil were removed. The findings at AOC 55 using the above approach included the discovery of more than 100 O/E scrap items and many items were found at depths greater than two feet. The items include 75 mm projectiles, 155 mm projectiles and Stokes mortars. Approximately 19 of the items (UXO) may still have contained high explosive filler; however, none were found to be fused. Due to these findings, proper identification and removal of UXO or O/E scrap was recommended for the entire contents of AOC-55. The methodology for identifying and removing O/E scrap was deemed inadequate for soil/waste material destined for an off-post landfill. The potential for “missing” an item using the excavation method of visual identification is high due to the unanticipated number of O/E material and potential UXO items identified. Use of a mechanical method of O/E removal was followed to ensure that all items greater than 2 inches in size were removed.
Soil characterization composite samples were collected from the vertical profiles of soil at AOC 55 on two separate dates. The locations of all samples collected at AOC 55 are presented in Figure AOC55-7. On October 30, 2002, six samples (AOC 55-SW-1 through AOC55-SW-5 and AOC55-SE1) were retained from the preliminary trenches that were advanced in (date). These samples were submitted to APPL., Inc., for analysis of metals, VOCs, and SVOCs. Sample AOC55-SE1 was collected east of the creek, in the area that was identified during the preliminary site trenching as containing waste.
The second sampling event occurred after analysis of the first sampling event had been performed. Because only lead and cadmium were encountered in the samples retained from the trenches, the additional characterization samples (AOC55-SW-6 through AOC55-SW-25) were not analyzed for any compounds except for lead and cadmium. These samples were collected on February 27, 2003, and submitted to APPL., Inc., for analysis.
The samples from the second sampling event were collected in the test pit excavations dug at the site. Their locations were scattered randomly throughout the site, as a means of further characterizing the site and are show on Figure AOC 55-7.
Equipment decontamination procedures, as well as sample collection, preparation, handling, and shipping, are described in the Field Sampling and Analysis Plan (Volume 1‑5, Quality Assurance Project Plan. Quality assurance (QA) and quality control (QC) samples were collected as described in the AFCEE QAPP (Volume 1-4, Quality Assurance Project Plan). Sampling locations were marked with a Trimble Asset-grade GPS with 1-meter accuracy by Parsons ES. Sample locations have been incorporated into CSSA-GIS.
No groundwater samples were collected at AOC 55 as part of this closure effort.
2.1.8 Salado Creek Low Water Crossing
As part of this delivery order a new low water crossing of Salado Creek was constructed. As-built drawings of the low water crossing are provided in Appendix D of this report.
The geophysical survey revealed evidence of subsurface anomalies related to past waste disposal activities. Contour maps of apparent conductivity and in-phase data are presented in Figures AOC 55-6 and AOC 55-7.
Results of the EM quadrature data show a large area of relatively lower readings in the eastern portion of the southwest quadrant. The anomalies having lower quadrature phase values in this area are likely due to the presence of metals and other conductive materials disposed at the site. The EM-31 will display relatively higher readings over conductive items only when the instrument is both directly over the conductor and oriented accurately along the conductor axis.
Several anomalies were identified in the in-phase data in the southwest quadrant that correspond to the anomalies in the EM quadrature data. Numerous EM in-phase anomalies were also detected in the southeast and northwest quadrants that correspond to anomalies in the EM quadrature data. One EM in-phase anomaly was detected in the northeast quadrant as well. Anomalies in the EM in-phase data also possessed relatively lower values and are generally the result of metal objects.
2.2.2 Preliminary Site Excavations
The material encountered in the test trenches included ash that appeared to been generated from an incinerator operation then placed in the AOC 55 area. The landfill also contained bottles that appeared to be waste from the on base cafeteria. These bottles included numerous ketchup bottles, Worcestershire sauce bottles, discarded coke bottles and other types of bottles that were unidentifiable. Also found were several metal water pitchers and broken China plates. One of the broken China plates found was dated 1915. The time of the landfill operation is unknown, but is thought to be between 1920 till 1950 based on aerial photos and on dates found on bottles and plates from the disposal area.
One 155mm projectile casing and two 75mm projectile casings were encountered on the surface. All rounds were identified by the on-site EOD personnel and were moved to a safe area and flagged for future destruction. It appears these items were placed in this area after the AOC-55 landfill was no longer in use. No disposal items were found in the test pits conducted in the northeast and northwest quadrants. Photos of the removal actions are provided in Appendix C of this report.
Based on the results of the geophysical surveys and test trenches, the area of the landfill is estimated to be approximately 115,300 square feet. Using an average landfill depth of 8 feet from the trenching activities, the volume of the landfill is estimated at 34,000 cubic yards. The area of the landfill identified from the geophysical and test trenching activities is depicted on Figure AOC 55-6.
No additional soil gas survey samples were collected at AOC 55 as part of this closure effort.
Parsons excavated the soil/waste material and used a mechanical sifting operation in order to effectively remove all O/E scrap items and ensure UXO material is properly identified. A total of 699 O/E scrap item and one additional UXO potentially containing high explosive fillers for a total of twenty potential UXO items were recovered from AOC 55. A total of 34,020 cubic yards were removed and disposed of at WMI’s Covel Garden Landfill facility as State of Texas Non-hazardous class 2 waste under WMI’s profile number CG‑25436.
Because all waste material and soil were removed to the bedrock contact, closure sampling followed the established protocol in the DQOs. Samples for closure of AOC 55 were taken along the perimeter at 100 foot intervals to confirm all waste and contaminated soil media were removed. Fourteen samples, identified as AOC55-CL-01 through AOC 55‑CL14, were collected from AOC 55 as part of the closure sampling efforts. Twelve samples were collected as a composite of soil media from top of the surface to bottom of the soil profile (approximately 2 foot depth) for lateral definition of AOC 55. Additionally, two sample were taken within the Glenrose limestone to represent bottom locations. All samples were analyzed for CSSA nine metals of concern. The results from the confirmation samples taken in November 2003, shown in Table AOC 55-2 were all below established background values with the exception of two samples. Sample AOC55-CL01 which was taken within the fill material next to Tenberg Drive indicated high lead, cadmium and zinc concentrations, and sample AOC55-CL03 showed slightly elevated lead concentrations.
Due to the elevated concentrations within the fill material identified in sample results for AOC55-CL01, addition removal actions were performed in December 2003 to remove the fill material next to Tenberg Drive. Additional samples were taken near the original location of AOC 55-CL01, as sample identified as AOC 55-CL13, and a location near Salado Creek and Tenberg Drive (AOC 55-CL14). Results of analysis show that the fill material was successfully removed as shown in Table AOC 55-1.
No groundwater samples were collected at AOC 55 as part of this investigation.
All chemistry data obtained during the course of this closure were evaluated for usability by those processes discussed in Section 4.1 of Volume 1-6, Risk Assessment Technical Approach Document.