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' SECOR INTERNATIONAL INCORPORATED www.secor.com S ECOR Hydro. Alkalinity, chloride, hardness, nitrate, phosphorus, and sulfate. GTI provided SECOR with the attached Tables, 1, 1 a and 2, and the laboratory analytical results shown in Attachment Table 1 summarizes the results of the grab groundwater samples taken at three depths: 18 to ' 22 feet, 28 to 30 feet, and 35 to 40 feet and Table 1a summarizes the resampling of groundwater samples from MW-1 (5 to 20 feet) and MW-101 (32.5 to 35 feet). Metals and trace element groundwater samples in Table 1 were unfiltered and acidified prior to submission to the laboratory. Acidification likely resulted in the dissolution of some suspended solids in the samples. Dissolved metals data are Indicative of some contamination from suspended solids. Metals and trace element groundwater samples in Table la were filtered and acidified in the laboratory and did not have concentration artifacts as a result of suspended solids. The results in Table 1 are not representative of dissolved concentrations with the exception of the hexavalent chromium concentration which were observed to be below the limits of detection even though total chromium was observed. Results in Table 1 a are representative of dissolved conditions, and metal and trace element concentrations were below the limits of detection for all constituents except barium, chromium, and molybdenum (MW-1 only). Barium is commonly ' found in groundwater at pg/I levels, and the concentrations are below environmental screening levels (ESLs) proposed by the San Francisco Regional Water Quality Control Board (SFRWQCB). The molybdenum concentration is at the detection limit and.is also below the ' ESL. Total chromium was observed in groundwater samples with and without filtration indicating that total chromium is likely in groundwater at concentrations below the MCL of 50 pg/l, but not hexavalent chromium. At the observed pH in groundwater, chromium (III) is typically not soluble at the observed concentration of 14 and 16 pg/l. It is not clear why total chromium is present in groundwater at this pH, given that the soil concentration is below 50 mg/kg and the dissolved hexavalent chromium concentration is below the limits of detection (see Table 1). ' Table 2 summarizes the results of the soils samples taken from four depth intervals: 10 to 12 feet, 20 to 22 feet, 28 to 30 feet, and 33 to 35 feet. None of the detected metals and trace elements are above regulatory limits. Total chromium concentrations are below the threshold of 50 mg/kg that SECOR uses to evaluate whether a site has the potential to generate hexavalent ' chromium during the application-of potassium permanganate. Potassium permanganate has a much greater ability to generate hexavalent chromium in groundwater because it has a higher solubility and longer half-life allowing it to interact with mineral surfaces and oxidize chromium in ' the mineral phase. The fact that trace levels of total chromium are observed in groundwater indicate that either chromium is found on fine particulate matter that is not removed by filtration, or total chromium is solubilized by a complexing agent at low concentrations. Whether the dissolved total chromium will increase the potential for forming hexavalent chromium during ozone sparging is not clear, therefore SECOR recommends quarterly monitoring for hexavalent chromium for verification purposes. Any hexavalent chromium formed by oxidation will be ' reduced to trivalent chromium and drop out of solution. Concentrations of total chromium are unlikely to exceed the observed levels based on an assessment of soil and water geochemistry. CONCLUSIONS AND RECOMMENDATIONS After an evaluation of the groundwater and soils analyses, SECOR has formed the opinion that ozone sparging should not have an adverse effect on the aquifer. Total chromium observed is ' 2