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Mr Harlin Knoll Environmental <br /> Resources <br /> 27 January 2000 <br /> Management <br /> Page <br /> relatively stable Figure 3 presents the historical chemical concentrations <br /> detected at MW-1 <br /> At MW-4, the chermcal concentrations detected during the most recent <br /> sampling event and a supplemental sampling event (30 November 1999) <br /> were less than those reported prior to ORC injection Concentrations <br /> detected during the 30 June, 2 September, and 28 October 1999 sampling <br /> ' events were highly variable and generally greater than those detected <br /> prior to ORC injection Figure 4 presents the historical chemical <br /> concentrations detected at MW-4 <br /> It is possible that the results of the samples collected during the 30 June, 2 <br /> ' September, and 28 October 1999 sampling events do not accurately <br /> represent the groundwater conditions at this location Based on the <br /> questionable result that was recorded from the groundwater sample <br /> collected on 28 October 1999 at MW-4, a supplemental sampling event <br /> was performed on 30 November 1999 to verify the chemical <br /> concentrations at this location However, due to the previous <br /> inconsistent results in this well, the analytical laboratory (AN/EN of <br /> Marina, California) recommended that the samples be centrifuged prior <br /> ' to analysis By centrifuging the samples, any soil particles in the <br /> groundwater sample are separated from the water so that a true <br /> groundwater sample can be extracted for analysis <br /> As shown in Table 1, the results of samples collected during the <br /> supplemental (30 November 1999) sampling event and the current <br /> sampling event(6 January 2000) are consistent(i e , duplicates result in <br /> reproducible sample results) and contain lower chemical concentrations <br /> ' than samples collected prior to ORC injection Based on these results, we <br /> believe that the inconsistent and higher results obtained during the June, <br /> September, and October results were due to the presence of chemicals <br /> attached to soil particles present in the groundwater samples collected <br /> during these sampling events <br /> ' Overall, chemical concentrations at MW-4 have decreased since ORC <br /> injection was performed The concentration of TPH-g has decreased <br /> from 50 milligrams per kilogram (mg/kg) prior to ORC injection to 43 <br /> mg/kg during the current sampling event All other compounds <br /> detected at MW-4 have shown similar reductions since ORC injection <br /> was completed <br /> a <br />