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1140.1 <br /> GEOMATRIX <br /> Mr. Don O. Culbertson <br /> Chevron Pipe Line Company <br /> 8 March 1995 <br /> Page 5 <br /> significant source of positive interference is the possible scattering of IR light <br /> caused by particulates (turbidity) in the sample. This method is non-specific <br /> regarding petroleum constituents (alkanes, alkenes, aromatics) and is typically used <br /> as a coarse screen for heavier hydrocarbons in soil. <br /> How can we tell if the groundwater sample results for EPA Method 8015 include <br /> non-dissolved constituents? <br /> The following is an example of a groundwater sample containing constituents other <br /> than the soluble alkanes and aromatics (Bruya and Friedman, 1992). Figure 4a <br /> presents the GC trace from the TPHd (by EPA Method 8015) analysis on the <br /> sample. This trace looks significantly different than the WSF of fresh diesel shown <br /> by Figure 3b. This GC trace (Figure 4a) shows the presence of n-alkanes (marked <br /> X) with more than 6 carbons, which we know are not part of the WSF of PHCs. <br /> Further, it shows the presence of other peaks eluting after 14 minutes (having more <br /> than 14 carbons) and a "hump" of material eluting between 10 and 20 minutes <br /> (approximately 10 to 20 carbons). Tile "hump" is probably composed primarily of <br /> branched and cyclic alkanes and/or oxidized hydrocarbons that are at fairly low <br /> concentrations and are too numerous to stand out individually. We would need <br /> other types of analyses, such as GC/MS, to confirm the constituents present within <br /> the hump. <br /> The sample was centrifuged to separate out non-dissolved components and <br /> reanalyzed (Figure 4b). The n-alkanes are no longer prominent, which makes the <br /> remaining peaks more accentuated, and the hump is greatly reduced. The peaks <br /> eluting later than 14 minutes (C14) are most likely soluble oxidized hydrocarbons or <br /> biogenic materials. <br /> Figure 5 is a chromatogram from EPA Method 8015 analysis of a water sample <br /> collected at the Dividend property (MW-23); this well is screened across saturated <br /> soil affected by residual separate-phase crude oil. The TPH analysis quantitated the <br /> material that eluted between 2 and 30 minutes. Based on results of EPA Methods <br /> 8020, 8310, and 8270 analyses, we know that BTEX or PNAs were not present in <br /> the MW-23 sample. <br /> The sample chromatogram (Figure 5) shows several critical indicators regarding the <br /> presence of non-dissolved PHCs and non-PHCs in the water sample. First, n- <br /> alkanes (>CO are present (marked X). Second, most of the material present elutes <br /> after C14i the detectable WSF of fresh fuels and crude oil is limited to the alkanes <br /> C4 through C6 and the aromatics with 14 carbons or fewer. Third, there is a large <br /> hump of undistinguishable material at C13 and above that is likely branched and/or <br /> cyclic alkanes and degradation by-products (oxidized hydrocarbons or biogenic <br />