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Final AOC-50 RCRA Facility Investigation Report
Section 2 - Field Investigation
As outlined in the Environmental Encyclopedia site-specific work plan (Volume 1-3, AOC-50), the field investigation for AOC-50 included performing geophysical surveys to locate metallic waste situated at or near the ground surface and to identify disturbed areas, excavate up to 175 cubic yards of Wheelabrator blast cleaning operations waste and underlying soils, and to collect ten surface soil samples. All field activities followed those protocols established in the Sampling and Analysis Plan (Volume 1-4, Field Sampling Plan, Quality Assurance Project Plan, and DO5068 Addendum).
Electromagnetic (EM) and ground penetrating radar (GPR) geophysical surveys were conducted at AOC-50 in December 2001. Prior to collecting EM or GPR data, a grid system was established at the site that encompassed the areas of suspected ground disturbance. These grids consisted of staked locations separated by intervals ranging from 10 to 50 feet, depending on the size of the area and the amount of obstructions, if any. The perimeter of the AOC-50 geophysical survey grid is illustrated in Figure AOC50-4.
2.1.1.1 Electromagnetic Induction
EM data were collected at 2-foot intervals along transects separated by 10 feet using the established geophysical survey grid (Figure AOC50-4). 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.
The 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 feetalong 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 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 the AOC 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 each site.
GPR is a surface geophysical technique that uses high-frequency electromagnetic energy. Pulses of short-duration electromagnetic energy are transmitted into the subsurface from the radar antenna that is moved across the ground surface at a slow and uniform pace. The radiated energy encounters heterogeneities or anomalies in electrical properties of the subsurface, which causes some energy to be reflected back to the receiving antenna and some to be transmitted downward to deeper material. The amplitude or strength of the electromagnetic energy reflected from subsurface materials depends on contrasts in the electrical properties (conductivity and dielectric constants) of those materials. The reflected signal is amplified, transformed to the audio-frequency ranges, recorded, processed, and displayed. Recorded data displays the two-way travel time for a signal to pass through the subsurface, reflect, and return to the surface.
The observed time for the reflected signal to return to the antenna from a subsurface feature is an indication of the depth to the reflector. The two-way reflection time can be converted to depth if the electromagnetic wave velocity of the subsurface material is known. In the absence of such information, an approximate time to depth conversion can be estimated by using published values of material velocity for different soil types.
GPR surveys were conducted with a GSSI SIR-2 instrument to further investigate the information obtained by the EM survey. Five GPR profiles were created in the north-south direction and three were created in the east-west direction (Figure AOC50-4). A 400 mega-hertz (MHz) antenna with a range setting of 100 nanoseconds (ns) was used for all profiles. The survey was conducted in accordance with procedures outlined iin Volume 1-4, Sampling and Analysis Plan, DO5068 Addendum. The individual GPR survey profiles were conducted over anomalies that were detected during the EM-31 survey. If no anomalies were identified during the EM-31 survey, the GPR was used to gather background information for the site.
GPR profiles are sequentially numbered as they are created throughout the day. Multiple sites are generally surveyed in any one-day and test profiles are created for each site during the investigation. The GPR profile number is not related to the number of profiles created at the site. GPR profile numbers 11 and 14 are included in this report.
The field crew was mobilized to the site on March 12, 2001. Prior to the initiation of excavation activities, the site was swept by a Parsons UXO avoidance team using handheld magnetometers. The only items found were two spent rifle grenades. All visible Wheelabrator blast cleaning operations waste was also marked for removal during the comprehensive sweep of the area. Eagle Construction and Environmental Services (Eagle) mobilized to the site on March 13, 2001. The subcontractor over-excavated approximately 200 cubic yards of soil and Wheelabrator blast cleaning operations waste. During the activities, a backfilled trench was discovered at the southeast corner of the excavation area. The visible contents included banding material, horseshoes, glass, and soil. Excavation was halted and CSSA, AFCEE, and AETC were notified. A conference call was held on March 16, 2001 to discuss a modification to the delivery order that would allow for the characterization and removal of the contents of the trench.
Eagle re-mobilized to the site on April 9, 2001 to excavate and stockpile the contents of the trench. During that excavation, additional buried Wheelabrator waste was discovered. AFCEE, CSSA, and AETC were notified that additional material had been discovered. On April 10, 2001 AETC requested that work be suspended until the SOW modification was completed. Eagle was de-mobilized from the site until further notice. Samples of the excavated trench material and the additional Wheelabrator waste were collected and submitted to O’Brien & Gere Laboratories for profiling on April 12, 2001.
Using a backhoe, CSSA and Parsons personnel excavated test pits to determine the lateral extent of the additional Wheelabrator blast cleaning operations waste. The reconnaissance trenching indicated that the extent of the additional buried Wheelabrator waste was limited to less than 50 cubic yards. The soil piles of the excavated trench material were estimated as an additional 200 cubic yards onsite.
Waste profile documentation was signed by CSSA on June 20, 2001, for the non-hazardous waste material and submitted to Waste Management, Inc. on June 26, 2001 for the acceptance of an additional 250 cubic yards of AOC-50 excavated material. The profile was approved by Waste Management on July 5, 2001.
The remainder of the site interim measures (IM) work was completed between the dates of August 13, 2001 and August 20, 2001. The additional 200 cubic yards of stockpiled material from the excavated trench plus the 50 cubic yards of additional Wheelabrator waste was loaded and transported to the Covel Gardens landfill (Waste Management, Inc.). The site was re-graded, and the contractor and equipment was demobilized. Thirteen confirmation samples were collected from AOC-50 and the source area of the waste near Building 90. Samples were submitted to O’Brien & Gere Laboratories for VOC, explosives, and metals analyses. The sampling points were located and recorded using the CSSA Trimble Global Positioning System (GPS) on August 22, 2001.
According to 30 TAC 335.559(G) near-surface soils are those situated within two feet of the land surface. Surface soil samples were first collected at AOC-50 in December 1999. The Wheelabrator (Sample AOC50 NP-1) and the soil six inches directly below it (Sample AOC50-1) were sampled.
In August 2001, 10 subsurface soil samples were collected to determine the extent of contamination at AOC-50 after the trench was backfilled (Figure AOC50-5). These samples were analyzed for VOCs, metals and explosives.
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 1-4, Sampling and Analysis Plan, DO5068 Addendum. Environmental sampling also included the collection and submittal of quality assurance (QA) and quality control (QC) at those frequencies outlined in the AFCEE QAPP (Volume 1-4, Quality Assurance Project Plan).
Subsurface soil samples were first collected in April 2001 at three
locations in the bottom of the excavated trench that contained household
waste. The three samples, AOC50-T1,
AOC50-T2 and AOC50-T3, were collected at three separate depth intervals. AOC50-T1 was collected at 4.5 to 5.0 feet,
AOC50-T2 was collected at 3.0-3.5 feet and AOC50-T3 was collected at
2.5-3.0 feet.
These samples were
analyzed for metals and VOCs.
In accordance with the approved work plan, groundwater samples were not collected in association with the current AOC-50 investigation.
2.1.6 Waste Characterization Samples
In September 2000, one waste characterization sample (AOC50 NP-1) was then taken to determine the recyclability of the Wheelabrator waste. This sample was analyzed for total metals.
In April 2001, two waste characterization samples were also collected from the stockpiles soils after the excavation activities to confirm that the soil was non-hazardous for disposal in a landfill. One more waste characterization sample was taken of a deeper Wheelabrator waste horizon. The three waste characterization samples (AOC50‑COMP1, AOC50-COMP2 and AOC50-NP01) were analyzed for VOCs and metals.
The EM surveys revealed evidence of one subsurface anomaly related to past waste disposal activities. This anomaly was found to be a household trash trench. 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 AOC (Figure AOC50-6 and Figure AOC50-7). The GPR surveys were conducted to further investigate the information obtained by the EM survey. The GPR also revealed no evidence of subsurface anomalies. The GPR profiles included in this report (Figure AOC50-8 and Figure AOC50-9) represent the typical 400 MHz antenna survey profiles that were produced at AOC-50. Resolution of the profiles was poor due to the homogeneous nature of the soil and underlying bedrock. The vertical scale on the profile, Time in ns, can be converted into feet using the following formula:
Range = Depth x Time (ns) x 1.5
Where
Range = 100 ns for profiles with a 400 MHz antenna.
Depth = depth below ground surface in feet.
Time = 4.5 ns per foot, this is the value given for dry limestone in the GSSI SIR-2 instruction manual.
According to this equation, the depth that represents 100 ns is 14.8 feet. The 2 way travel time is only an estimate and can vary somewhat from site to site and also within the profile itself.
The interpretation of subsurface conditions is based on analysis of the recorded sections. Buried objects such as pipes and tanks are usually evident as prominent hyperbolic reflections on the GPR records. Subsurface soil changes can be difficult to interpret, but often can be discerned as a lateral change in the texture or reflection character of the GPR signal. Optimal subsurface conditions for use of GPR are dry sandy soils. The presence of even minor amounts of clay may effectively limit depth of investigation to less than a few feet due to absorption and reflection of the electromagnetic energy. Stratigraphic changes are often very prominent and may affect the GPR readings. The use of GPR to determine landfill boundaries and buried waste disposal trenches can be at times very successful due to contrasts in reflection character between the natural stratigraphy outside the trench boundaries and the disturbed soils within the disposal areas.
In accordance with the approved work plan, soil gas samples were not collected in association with the current AOC-50 investigation.
As described in Section 2.1.3, two surface soil samples collected in 1999 from AOC-50 were analyzed for metals. Results are summarized in Table AOC50-1. None of the metal concentrations exceeded background levels. A complete list of analytical results for all AOC-50 samples is provided in Appendix A.
In August 2001, ten surface soil samples were collected in various locations in AOC-50. The detected analytes found in these samples are summarized in Table AOC50-2. These ten subsurface soil samples were analyzed for VOCs, explosives, and metals. No VOCs or explosives were detected above their respective RLs. All of the background level exceedances for metals occurred in four samples: AOC50-SS02, AOC50-SS03, AOC50-SS05, and AOC50-SS06. Samples AOC50-SS02, AOC50-SS03, AOC50-SS05, and AOC50-SS06 exceeded the background level for cadmium of 3.0 mg/kg with concentrations of 10.3 mg/kg, 4.84 mg/kg, 5.34 mg/kg, and 4.22 mg/kg, respectively. Samples AOC50-SS02, AOC50-SS03, AOC50-SS05, and AOC50-SS06 exceeded the background level for lead of 84.5 mg/kg with concentrations of 1,227 mg/kg, 76,200 mg/kg, 124.7 mg/kg, and 592.2 mg/kg, respectively.
The chromium background level of 40.2 mg/kg was exceeded in sample AOC50-SS05, which had a chromium concentration of 56.10 mg/kg. Samples AOC50-SS02, AOC50-SS03, and AOC50-SS05 exceeded the background level for copper of 23.2 mg/kg with concentrations of 28.88 mg/kg, 1,041.4 mg/kg, and 27.71 mg/kg, respectively. Samples AOC50-SS03 and AOC50-SS05 exceeded the background level for zinc of 73.2 mg/kg with concentrations of 361.5 mg/kg and 142.8 mg/kg, respectively.
As described in Section 2.1.4, three subsurface samples (AOC50-T1, AOC50-T2, AOC50-T3) collected from the bottom of the excavated waste trench in April 2001. These samples were analyzed for metals and VOCs. None of the samples had metals concentrations and all of these detections were well below their respective RLs. The analytical results for these samples are summarized in Table AOC50-3.
In accordance with the approved work plan, ground water samples were not collected in association with the current AOC-50 investigation.
2.2.6 Waste Characterization Samples
As described in Section 2.1.6, one waste characterization sample (AOC50 NP-1) was taken in September 2000 to determine the recyclability of the Wheelabrator waste. The detected constituents from sample AOC50 NP-1 are presented in Table AOC50-4. This sample’s iron concentration was high enough of a metal concentration for recycling. Newell Recycling does not accept military wastes, therefore, the waste was disposed of at Covel Gardens Landfill instead.
In April 2001, two waste characterization samples (AOC50-COMP1 and AOC50‑COMP2) were collected from the stockpiled soil from the excavation activities and one sample (AOC50-NP01) was collected from a newly found, deeper Wheelabrator waste horizon. The detected constituents from these samples are provided in Table AOC50-5. All three samples were determined to be non-hazardous by both state and federal criteria.