The following chart is a compilation of CL-Out bioremediation results from eleven different sites where ground water was contaminated by trichloroethylene (TCE). The sites represent all kinds of geological conditions with the full range of TCE concentrations in ground water.
CL-Out bioremediation was used in a keyhole treatment to reduce the mass of contamination near the source and down gradient concentrations in the plume. At a former manufacturing facility in Ohio the concentration of PCE near the source was over 100,000 ug/L. Down gradient of the source the PCE concentrations were less than 10% of the source concentration. Aggressive treatment in the source area reduced the source concentration and in the down gradient plume.
After one treatment with CL-Out bioremediation, the concentrations decreased as follows:
PCE was reduced from 120,000 to 12 ug/L.
TCE was reduced from 2,000 to 12 ug/L
Cis 1,2-DCE was reduced from 9,500 to 8,100 ug/L.
Vinyl chloride, however, increased from 1,200 to 22,000 ug/L.
The vinyl chloride increased as the aggressive cometabolic treatment stimulated some incomplete reductive dechlorination.
Down gradient from the source, the concentrations decreased with slight to no increase in daughter products. The following results were measured in the down gradient plume:
PCE reduced from 5,000 to 1,600 ug/L.
TCE reduced from 43 ug/L to BDL.
Cis 1,2-DCE was reduced from 140 to 23 ug/L.
Vinyl chloride was not detected before or after treatment.
Keyhole treatment was a cost effective approach to reducing the mass of contamination in a ground water plume by focusing aggressive treatment on the source area. Concentrations in the rest of the plume decreased as the microbes and treated water dispersed through the plume.
A pilot study of the applicability of CL-Out aerobic cometabolism of PCE and other chlorinated solvents was completed at Vandenberg Air Force Base. The pilot study consisted of injection in a single well and groundwater sampling at four surrounding wells to monitor the progress of bioremediation. During the pilot study, samples were analyzed for the contaminants and breakdown products, microbial population, and dissolved oxygen.
After three months, sampling showed the following contaminant removal near the injection well:
PCE reduced from 44 to 2.6 ug/L.
TCE reduced from 330 to 57.3 ug/L.
Cis 1,2-DCE reduced from 30.7 to 6.2 ug/L.
Vinyl chloride was not detected before or after treatment.
The ground water stayed aerobic during the 90 day pilot study. The CL-Out population reached a maximum of 9 million cells per milliliters 14 days after injection. The CL-Out population was maintained above background populations for at least 60 days and reached as far as 50 feet down gradient.
For more information about the pilot study results, contact CL Solutions.
A history of spills and/or releases at two adjacent dry cleaning facilities near Houston, TX, resulted in significant soil and shallow groundwater contamination with PCE and daughter products. Soil was relatively permeable, with rapid groundwater flow beneath the site. A long, narrow, off-site plume extended beneath a residential neighborhood. Chemical oxidation was employed initially with only limited success in the areas of highest contamination. To take advantage of the soil permeability and other site conditions, the response action was amended to include enhanced aerobic bioremediation by cometabolism. Specialty microbes were introduced into the plume in several injections over a 15-month period. This approach achieved total contaminant level reductions in the source area from 1,600 to less than 40 µg/L, and at the front edge of the plume, levels decreased from 500 to 5 µg/L.
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Dry cleaning solvent spills in a storage area lead to the contamination of soil and ground water on the property of a 50-year-old dry cleaners in the middle of a hot brownfield redevelopment. After the contaminated soil was excavated for off site disposal to the most practical extent, residual perched ground water contamination impacted the redevelopment of the property.
The soil excavation was used as an infiltration gallery as part of a recirculating ground water recovery and treatment system. The flushing reduced contaminant concentrations, but the levels were still far above the levels required to achieve no further action status. CL-Out was added to the recirculating ground water and the cleanup goals were achieved in less than two years and were maintained through two years of post treatment monitoring.
Geology and Hydrogeology
The site is on a fluvial terrace adjacent to the Ohio River. The shallow soils are clayey silts to sit to eight feet deep. An interbedded sandy zone that formed the first water-bearing zone was encountered from 8 to 12 feet deep. Perched ground water occurred in the sandy zone at 12 feet below grade.
Ground Water Contamination
The size of ground water plume that resulted from the spills was estimated to be 3,500 square feet. The ground water contamination was mainly PCE with a maximum concentration of 11,000 ug/l prior to soil removal or ground water treatment. The daughter compounds TCE and DCE were detected up to 17 and 12 ug/l respectively. After three years of recirculation and flushing, the maximum PCE concentration was reduced to 2.3 ug/l and the daughter compounds were below detection limits.
CL-Out bioaugmentation was implemented to supplement the flushing system. By adding CL-Out on two occasions over two years, the contaminant concentrations were reduced to below drinking water standards. During two years of post treatment monitoring the DCE concentrations rebounded to above the MCLs. CL-Out bioaugmentation was implemented again and within three months the contaminant levels were below drinking water standards and remained below drinking water standards for nine months. After post closure monitoring verified the cleanup goals would be maintained, the KDEP issued a “No Further Action” letter for the site.
The following chart shows the PCE contaminant trend in one of the key monitoring wells during the remediation and post closure monitoring.
The CL-Out cost during this remediation project was less than $10,000.