SECTION NINE
Observations and Lessons Learned
Table 8-1, the actual costs that have been incurred to this point were just 9% above the
corresponding, adjusted ROD estimate.
Subsequent to original negotiations, the contaminant concentrations in system air emissions were
determined to be significantly below the allowable air emission standards, and RAPCA agreed to
allow USACE to eliminate the need to change the carbon units from the system and to reduce air
compliance monitoring requirements. USACE is planning to reallocate money from any savings
on air compliance monitoring to increase the number of system performance air tests.
Because the system operation is ongoing, the total costs to operate the system are not known at
this time. Actual costs to date are shown in Table B-1, and projected additional cost to complete
is shown in Table B-2.
SYSTEM OPERATION
The emphasis of vapor data collection in the future should shift to the individual extraction wells
rather than the combined extracted flow. In the fifth quarter of the full-scale operation, quarterly
vapor sampling from the individual wells was initiated.
Based on the testing of the untreated and the treated condensate removed by the remediation
system, the potential life of the aqueous-phase carbon units was estimated to be in excess of ten
million gallons.
An SVE system flow rate of less than the design maximum flow rate may be more efficient for
TCE removal than continuous operation at the maximum flow rate. The vendor recommended
that the system be evaluated at moderate SVE system flow rates during the ongoing optimization
of the system.
The data supports the remedial investigation findings that numerous TCE hot spots exist at the
site, and that the presence of TCE (and/or its degradation products) at one location may or may
not be related to its presence at other locations at the site.
Studying the natural degradation of the leachate at the site may provide a more widespread
picture of the fate of contamination at the site than focusing on the natural attenuation of
chlorinated hydrocarbons alone.
Although the impact of the AS system on the degradation of TCE at the site had not been
conclusively determined, it was recommended that the AS system continued to be operated until
an impact/ benefit analysis for the system is completed.
Because one of the contaminant reduction monitoring wells upgradient of the remediation system
had maintained an elevated concentration of TCE, a TCE hot spot may be located upgradient of
this location beyond the influence of the remediation system. An additional AS/SVE well pair
could be added to this area to increase the reach of the remediation system.
9-2
Ft. Griffey Landfill 5 OU Interim RA Report
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