DNAPL MANAGEMENT AT CREOSOTE-IMPACTED SITE

摘要

Up to one million gallons of dense nonaqueous-phase liquid (DNAPL) creosote are present in the saturated zone at a former wood treating facility in northern California. DNAPL management at the site has consisted of a combination of strategies, including: in situ bioremediation enhancement; passive recovery; and, a technical impracticability (TI) waiver. Implementation of the in situ bioremediation program, designed to enhance the biodegradation of polynuclear aromatic hydrocarbon (PAH) impacts in groundwater resulting from the presence of the creosote DNAPL, had marginal effects on the removal of the dissolved-phase PAHs. The enhanced biological activities appeared to increase the production of biosurfactants, resulting in the increased mobility of PAHs in and downgradient from the source area. Therefore, the bioremediation program was discontinued. The passive recovery system consists of one well located in the area of mobile creosote. The well has two separate screened intervals; each 10-foot screen is located immediately above a clay lens, where free creosote is perched. Mobile creosote enters the well through the two screened intervals and collects in a sump at the bottom of the well. Approximately 650 gallons of creosote have been recovered from the source area during eight years of passive recovery. An evaluation of the technical impracticability of groundwater restoration in creosote DNAPL-impacted areas of the site resulted in EPA Region 9 issuing a TI waiver in 1999. The TI waiver and passive creosote recovery are being implemented at the site. This strategy has saved millions of dollars in potential remediation costs that would have been ineffective in restoring groundwater quality.