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Section 3 - Conclusions and Recommendations
SWMU B-9 was suspected to be a miscellaneous solid waste (metal debris)
disposal area. EM
and GPR geophysical surveys conducted in November 1999 revealed no geophysical
anomalies that were potentially related to past waste management activities.
A soil boring investigation was completed in
March 2000 to verify the presence or absence of VOCs, SVOCs, metals, and
explosives. Three soil
borings were completed to depths ranging from six to eight feet.
Three soil/rock samples were collected from each boring, resulting in a
total of nine samples submitted for analysis.
Analytical data gathered during this investigation indicated concentrations of
zinc, mercury, dichlorodifluoromethane,
methylene chloride, and toluene present in the
subsurface soils slightly above RRS1 soil/rock background levels.
Background levels for metals were statistically calculated for CSSA
soils and the Glen Rose Limestone and are reported in the Second Revision
to the Evaluation of Background Metals Concentrations in Soils and Bedrock at
CSSA (Parsons, February 2002). The
sample quantitation limit (SQL) was used as the RRS1 levels for VOCs, SVOCs,
and explosives.
Zinc was detected above RRS1 criteria in two samples; however, both
concentrations were below the Texas-specific median background level for zinc
of 30 mg/kg (30 TAC 350.51(m)). Mercury
(0.2 mg/kg) exceeded the RRS1 level (0.1 mg/kg) in one limestone bedrock
sample collected at a depth of 7.5 to 8 feet bgs.
This one slight exceedance at this depth is not considered to be a
threat to human health or the environment.
Furthermore, mercury was not detected above the reporting limit in any
of the other site samples.
The analyte dichlorodifluoromethane, a chemical primarily used in
refrigeration and cooling systems, is not associated with any waste management
activities at CSSA. Low levels of
dichlorodifluoromethane were detected in eight of the nine samples at SWMU
B-9, and it was detected in all of the other soil samples collected at another
site (SWMU B-23) that same day. Dichlorodifluoromethane
was not detected in any of the samples collected at SWMU B-23 the previous
day. It is suspected that the low
level detections of this analyte at SWMUs B-9 and B-23 are a result of
contamination at the analyzing laboratory.
The low level detection of methylene chloride (0.0055 mg/kg) in one
sample is also suspected of being associated with laboratory contamination.
Toluene was detected at a very low concentration (0.0074 mg/kg) in only one
surface soil sample.
All data generated during the SWMU B-9 investigation were reviewed to confirm
conformance with the AFCEE QAPP; and the data verification reports are
included in Appendix C. All data
are considered useable for site characterization purposes.
Although several results are flagged with an “M”, these results are
considered usable because the matrix interference is minimal and does
significantly affect the sample results.
Although several results are flagged with a “J”, these results are
considered usable because the estimation of quantitation does not
significantly affect the sample results.
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 SWMU B-9, along with an evaluation of whether each
DQO has been attained, is provided in Appendix
D. As described in Section 1, the main objectives of the SWMU
B-9 investigation are to determine if the site meets TNRCC requirements for
RRS1 closure and to meet requirements of the 3008(h) Administrative Consent
Order.
Because exceedances of RRS1/background criteria were very slight, and geophysical survey results did not show evidence of buried waste, RRS1 closure is recommended for this site.