Groundwater at the site occurs within a highly fractured unconfined bedrock aquifer. Groundwater flows in a northerly direction.
Targeted Environmental Media:
 Fractured Bedrock
Methyl tertiary butyl ether (MTBE) in site groundwater was detected in concentrations ranging between 100 and 160 parts per billion (ppb). Three residential supply wells northeast of the site have been affected, with concentrations ranging from 1 to 74 ppb. Point-of-entry (POE) treatment was installed on the three supply wells and groundwater continues to be monitored.
Major Contaminants and Maximum Concentrations:
- Methyl-tert-butyl ether (160 µg/L)
No technologies selected.
- Other (Cometabolic Biosparging)
Comments:
Two cometabolic biosparging tests, a 16-week test and a subsequent 24-week test, were completed between November 2002 and May 2005. Gaseous oxygen, nitrous oxide, tri-ethyl phosphate, and a hydrocarbon gas were injected into site wells to stimulate the indigenous bacteria and cometabolically degrade MTBE.
Two primary objectives to achieve site closure include (1) reducing MTBE concentrations to meet the Pennsylvania Statewide Health Standard (SHS) of 20 ppb at the site boundary and (2) achieving a goal of non-detectable concentrations in the off-site supply wells.
Under Pennsylvania law, POE treatment for supply wells must be maintained until nondetectable concentrations of regulated constituents have been achieved. However, Pennsylvania law allows for liability protection when the SHS has been successfully met at the property boundary. Therefore, site closure can be attained without achieving the separately regulated goal of nondetect in residential supply wells.
The results of the two cometabolic biosparging tests indicate an average MTBE reduction of 60 percent for sampled wells and that the SHS has been achieved at the site boundary. Although concentrations of MTBE have been reduced within the residential supply wells, detectable concentrations remain.
The cometabolic biosparging tests have effectively reduced concentrations of MTBE to below the SHS but have fallen short of the meeting the goal of nondetectable concentrations in residential supply wells. Liability protection could be granted for the site without additional on-site remediation; however, continued POE treatment or further off-site remediation will be required.
Reference:
Rodeffer, Timothy L.; David S. Woodward. 2005. Cometabolic biosparging: Meeting the standard, but not the goal. Eighth International In Situ and On-Site Bioremediation Symposium, Baltimore, Maryland. June 6-9.
|
