Late Wisconsinan ice-deposited clayey till comprises the surficial geology. Glacial deposits are lake-planed, very flat, and are smoothed waves in glacial lakes. Glacial sediment includes sand, silt, and clay patches on the surface and lies over Silurian-aged Lockport Dolomite formation bedrock which can be encountered at 3 to 6 feet below ground surface. Topographically, the area has very low relief (not a lot of change in elevation over the area). The fractured dolomite and limestone contains the main regional unconfined aquifer. Groundwater is encountered between 5 and 11 feet below ground surface and flows toward the north-northwest with some flow to the northeast.
Targeted Environmental Media:
 Fractured Bedrock - Light Non-aqueous Phase Liquids (LNAPLs)
The dissolved-phase hydrocarbon plume was present approximately 150 feet north of the point of release.
Major Contaminants and Maximum Concentrations:
- Benzene-toluene-ethylbenzene-xylene (BTEX) (35,200 µg/L)
- 1,2,4-Trimethylbenzene (pseudocumene) (0 µg/L)
- 1,3,5-Trimethylbenzene (0 µg/L)
- Naphthalene (0 µg/L)
No technologies selected.
- Bioremediation (In Situ)
Comments:
In January 2005, the release of 8,500 gallons of gasohol (gasoline containing 10% ethanol) was addressed by neutralizing or recovering product on the ground surface and later removing impacted soil. Vacuum recovery, pumping, and bailing of free-phase product took place through November 2006. A granular activated carbon treatment system was installed after sampling results showed the presence of benzene in the residential well.
The pilot test consisted of aerobic bioremediation facilitated through biosparging. Four injection wells were installed near the center of the plume to inject air and nutrients and support monitoring. Injection pressures ranged from 4 to 10 pounds per square inch (psi) in shallow injection points and 3 to 14 psi in deeper injection points. Flow rates in the shallow points ranged from 0.2 to 1.6 cubic feet per minute (cfm) and 0.2 to 1.3 cfm in deep points.
Full-scale operation included the addition of the nutrients nitrous oxide and tri-ethyl phosphate.
State cleanup levels (drinking water standards)
After the pilot test began, no contaminants of concern were detected in the site supply well and increased dissolved oxygen and oxidation reduction potential levels in the wells around the perimeter reflect significant rates of biodegradation in downgradient monitoring wells. The system went into full-scale operation in December 2007 and after 21 months, monitoring shows hydrocarbon concentrations decreasing with increased respiration rates. Plume contaminant concentrations decreased considerably, some to below cleanup standards. The plume mass has been reduced by 90 percent since full-scale implementation and the plume footprint has been reduced by 70 percent since biosparging operations began.
When pilot testing scaled-up to full field implementation, a more intensive monitoring was included to (1) add appropriate additional injection points; (2) minimize the spread of the plume; and (3) add nitrous oxide and tri-ethyl phosphate nutrient injection. One injection well showed little response; that well probably is located outside the area of influence; additional efforts will be required to address contamination concentrations in that well. During optimization of the system, four injection wells were shut down and rebound was observed; therefore continued operations were deemed necessary.
References:
Heaston, Mark S., Hartig, Leslie L., Robinson, Melissa, and Woodward, David S. 2010. Enhanced Aerobic Bioremediation of a Gasohol Release in a Fractured Bedrock Aquifer. Remediation Journal, Volume 20, Issue 2, pages 45ý59, Spring 2010.
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