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Elevated levels of petroleum hydrocarbons were discovered near the former dispenser island at a former service station in Sheboygan, WI. In hopes of reducing concentrations, soil excavation activities took place in June 2003. A total of 500 tons of hydrocarbon-impacted soils were removed and transported to a landfill for disposal. However, residual contamination continued to affect the groundwater after the excavation. By March 2004, benzene and ethylbenzene had risen to 2,500 ug/L and 1,300 ug/L, respectively. In situ bioremediation using ORC Advanced was chosen to reduce BTEX, naphthalene, and trimethylbenzenes. In the northwest corner of the site, the location of the former UST basin, a total of 480 pounds of ORC Advanced was injected. In the southeast corner, the area of highest contamination, a total of 2,370 pounds of ORC Advanced was injected.
Groundwater sampling results after excavation activities show an increasing trend of contamination. On average, concentrations continued to increase up until the ORC Advanced application due to residual contamination. Concentrations peaked before ORC Advanced injection followed by a significant reduction across the plume. In well MW-5, benzene spiked to 160 ug/L while naphthalene rose to 170 ug/L and in well MW-4 BTEX, naphthalene and trimethylbenzenes all increased. Significant decreases of all contaminants were seen shortly after ORC Advanced injection. In well MW-8 total BTEX was reduced from 6,720 ug/L to 168.8 ug/L, a 97% reduction. Naphthalene concentrations were above the MCL of 20 ug/L in wells MW-1, MW-4, MW-5. ORC Advanced reduced concentrations to non-detect in wells MW-4 and MW-5, leaving 38 ug/L in well MW-1. Monitoring is on-going as concentrations continue to decrease towards MCLs.