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| Confirm
or Refute Suspected Release of Contaminants
|
 The
Problem:
The City of Oroville had four underground storage tanks excavated from their corporation yard by a previous consultant. The contractor failed to properly pump out residual waste oil within the tank prior to pulling the tank out of the ground with the backhoe bucket. The backhoe bucket ruptured the waste oil UST causing an unspecified amount of product to spill into the excavation. Soil sample analytical results collected within the waste oil UST exaction pit were reported to have high levels of petroleum hydrocarbons and heavy metals. The Public Works Department performed minor over excavation within the UST pit to remove leftover spilled product. Based on the excavation report recommendations by the contractor, the City was order by Butte County Environmental Health and the California Central Valley Regional Water Quality Control Board to further define the extent of soil contamination and assess impacts to groundwater. Four groundwater monitoring wells were installed and it was determined that groundwater was not impacted. Without consulting the City, the contractor recommended costly over excavation and disposal from the waste oil UST pit.
The Solution:
The City came to H&A with their suspicion
that the original contactorís soil samples were collected from
areas impacted by the waste oil tank that was ruptured during
removal. H&A was retained to confirm or refute the presence
of the high concentrations of petroleum hydrocarbons and heavy
metals reported by the previous contractor. H&A in coordination
with Public Works personnel conducted vertical soil sample profiling
from the waste oil tank pit. Laboratory results indicated that
very low concentrations were present and migration of the contamination
was not likely. The RWQCB rescinded their requirement for over
excavation and will be granting closure of the site following
the abandonment of the four unnecessary groundwater monitoring
wells installed by the previous contractor.
The work H&A performed obviated the need for costly over excavation
of the waste oil tank pit and for further groundwater monitoring,
and resulted in considerable cost savings to the City of Oroville. |
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