[Home] [Master Table of Contents]
Final AOC-50 RCRA Facility Investigation Report
Section 3 - Conclusions and Recommendations
AOC-50 is approximately a 1-acre site that is a suspected area that
has been used for disposal of Wheelabrator waste associated with firearm
maintenance. The waste present prior to
excavation was a metallic material that resembles oxidated iron slag. Two initial samples were collected of the Wheelabrator
waste and soil below it. The aerial
extent of the waste was mapped visually and an EM and GPR survey was then
conducted. The Wheelabrator waste was
excavated, removed and disposed of.
During excavation, a household-type trash trench was discovered and also
excavated. Samples were taken of the
bottom of the excavated trench and the area was then back filled and
regraded. Ten confirmation samples were
then collected.
The initial samples taken in 1999, before excavation, and the samples taken from the bottom of the excavated trench were below the background levels for the soil at CSSA. Four of the ten confirmation samples showed cadmium, chromium, lead, copper, and zinc above their respective background levels. No explosives or VOCs exceeded their respective RLs.
The EM and GRP surveys indicated no evidence of subsurface anomalies related to past waste disposal activities.
3.2 - Evaluation
of Data Quality Objectives Attainment
Overall DQOs for the investigations at CSSA are provided in Volume 1-1 behind the RFI Addendum tab (Section 11 of the Work Plan Overview). A detailed list of DQOs for AOC-50, along with an evaluation of whether each DQO has been attained, is provided in Appendix C. As described in Section 1, the main objectives of the AOC-50 investigation are to determine if the site meets TCEQ requirements for RRS1 closure and to meet requirements of the 3008(h) Administrative Consent Order.
All data generated during the AOC-50 investigation were reviewed to
confirm conformance with the AFCEE QAPP; the data verification report is
included in Appendix B. All data are
considered useable for site characterization purposes. Although several results are flagged with an
“M”, these results are considered useable because the matrix interference is
minimal and does not significantly affect the sample results. This compound is not a constituent of concern
at the site. Despite non-compliance of
the percent difference for the continuing calibration, all of the initial
calibration, second source verification and internal standard criteria were
within quality control limits, as described in the data verification report
(Appendix B).
Analytical results for the numerous surface soil samples collected at
the site show localized metals contamination at levels above RRS1
criteria. Also, several of the 3008(h)
RFI requirements, such as identification of waste characteristics and
determination of vertical extent of contamination, have also not yet been
met. Because of the presence of
inorganic constituents in the site soils exceeding RRS1 criteria, analytical
results were not compared to TRRP standards.
Closure of AOC-50 under RRS1 would require excavation and proper disposal of the contaminated soil. Since the vertical and the horizontal extent of the contamination is not completely known, up to 15 additional soil borings with samples taken at multiple depths are recommended. This sampling plan would provide a vertical profile of the metals contamination and allow estimates of the quantity of soil that would require excavation. The contaminated soil would then be excavated. The site would be over-excavated to between one and two feet depth, depending on soil thickness, producing 1,600 to 3,200 cubic yards of material.
Prior to backfilling the excavated areas with clean fill, confirmation
samples should be collected from the trench bottoms and walls to verify that
waste residue has been removed. Due to
concentrations of cadmium, chromium, copper, lead and zinc reported at levels
above RRS1 criteria, these metals should be analyzed for during confirmation
sampling.