This paper describes an on-going, full-scale anaerobic dechlorination remedial program in Florida, that includes bioaugmentation and bioenhancement of the site groundwater by an ethene-producing culture obtained from another project site in New Jersey, and acclimated to the Florida project site groundwater.
The initial biogeochemical investigation showed that extensive biodegradation had historically occurred at the site. However, microcosm studies indicated that electron donor deficiencies are currently limiting dechlorination of tetrachloroethene (PCE) to cis-1,2 dichloroethene (cDCE), and, furthermore, that dechlorination of cDCE is not possible due to the lack of etheneogens (D. ethenogenes) at the site. The initial detection of low levels of vinyl chloride (VC) and ethene in the site groundwater was interpreted to mean that these daughter products had been generated upgradient (under the building) and had migrated to the wells that were sampled. The loss of the native ethenogen population was attributed to exhaustion of native electron donor.
The remedial measures involve frequent batch injections of dilute sodium lactate solution and ethenogen culture from an anaerobic 100 gallon tank into a series of 4 trenches and 5 injection wells using an automated delivery system. The batch injections have successfully created groundwater mounds to disperse the added amendments.
The remediation system was started up in February 2003. Monitoring over the past several months has indicated remarkable groundwater quality improvement in just five months of operation. Ethene concentrations have increased in all of the significantly impacted wells, and all of these wells show an increase in the ratio of daughter products to TCE and PCE. All of the significantly impacted wells currently show positive polymerase chain reaction (PCR) test results. In well BMP-4 the PCE concentration was reduced from: 940 ppb to 24 ppb and TCE from 130 ppb to 18 ppb. cDCE concentrations were reduced from 1,100 ppb to 63 ppb and VC concentrations from 1,500 ppb to 13 ppb.