PRB/pre-drill Application in Difficult Geology (BOS 200®) From Gasoline Released

Summary

Historically, an unknown quantity of gasoline released at an active service station. The released gasoline subsequently impacted soil and groundwater at the service area. The wetland area, downgradient of an embankment, has also been impacted by petroleum. A BOS 200® permeable reactive barrier (PRB) was installed to limit the groundwater mass flux between the source area and the wetlands.

Project Timeline

• June 2015 – BOS 200 PRB Pilot Test
• November 2015 – BOS 200 Full Scale PRB
• February 2017 – PRB Extension

Approach

• 150 ft long PRB – 88 injection points (4 rows of points spaced approximately 7.5 ft apart)
• Due to rubble and blast rock, injection points were pre-drilled using sonic to bedrock interface (ranging from 34 to 57 ft)
• 45,000 lbs of BOS 200 and 28,500 lbs of supplemental food grade gypsum were installed from 26 ft to top of bedrock.
• Injections were completed top down using direct push through the backfilled hydrated bentonite.
• Three new monitoring wells were installed after the pilot test so that the data would not be biased by the activated carbon.

Results

The PRB has been monitored for over 1,000 days post pilot test. The BTEX mass flux continues to be significantly reduced. The terminal electron acceptor (TEA) concentrations are also being monitored. When the contrations decrease to background another round of injections may be needed to recharge the TEAs to maintain biological activity within the PRB.

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