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FORMER REFINERY TREATABILITY STUDY
A treatability study was conducted by EcoVac Services for a Major Oil Company to assess the efficacy of various remedial alternatives at a former Refinery and Bulk fuel distribution terminal in the greater St. Louis area. Eleven distinct remedial approaches were evaluated during this treatability study, consisting of various combinations of traditional surfactant and biosolvent flushing, surfactants in combination with dual-phase/multi-phase extraction, in-situ chemical oxidation (ISCO), ISCO in combination with traditional surfactant flushing, and pump and treat.
The use of solubilizing and mobilizing surfactants was compared as well as ones formulated to have specific gravities less than water to facilitated liberating contaminants and causing them to become buoyant in the saturated zone by injection and capture in EcoVac designed nested well configurations.
The subject site is located adjacent to the Mississippi River and was the site of refining operations from 1908 until operations were suspended in 1980. The site is nearly 800 acres in size. Various remediation systems are in operation at the site.
The site is located within the Mississippi River floodplain valley, consisting of valley fill comprised of recent alluvium and glacial sediments. Four stratigraphic units exist within the valley fill, exhibiting a coarsening downward sequencing. From the surface down, the valley fill consists of fine-grained floodplain deposits underlain by an (often silty) fine sand unit, beneath which is a coarse sand/gravel unit underlain by a basal clay on top of the bedrock (at >100 feet).
The static groundwater depth in the area of interest is 23 to 25 feet within the fine grain and coarse sand/gravel units. The chemicals of concern are a mixture of gasoline, diesel, kerosene, as well as crude oil in isolated areas. The vertical interval of concern extends below the floating NAPL, to an approximate depth of 60 to 80 feet bgs (i.e. approximately 35 feet to 55 feet below the static water table surface), which is the depth to which prior source water wells depressed the water table. The particular challenge of the site is to address those impacted soils that exist well below the static water table.
TREATABILITY STUDY RESULTS SUMMARY
TPH reduction in the column tests ranged from 3.2% to 95.4%, as graphically represented below. The greatest recovery result (95.4%) was attained utilizing SURFAC® (surfactant injection/capture combined with dual-phase/multi-phase extraction), employing a specially formulated surfactant. Four variations of traditional surfactant flushing achieved removals ranging from 7.2% to 75.6%. Traditional surfactant flushing combined with biosolvents (two permutations) realized removals ranging from 56.5% to 73.6%. Traditional surfactant flushing followed by ISCO resulted in a removal efficiency of 66.6%. The ISCO (only) process attained a removal efficiency of 8.3%. Pump and treat and the ISCO/surfactant flushing (with no groundwater withdrawal) simulations achieved removal efficiencies of less than 4%.
Several unique remediation/surfactant delivery techniques were also provided as part of the treatability study.