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OElizabeth Thayer <br /> August 21, 1995 <br /> Page 3 <br /> C12-C19 range in MW-3, the well located side-gradient of the former USTs. This result is <br /> slightly greater than the detection limit of 50 ,cg/L. <br /> According to the July 1995 ERM-West report, the second sampling event (June 1995) did <br /> not identify any detectable concentrations of TPH as diesel or gasoline or BTEX in MW-1 <br /> and MW-3. However, 56 µg/L of TPH as an unidentified hydrocarbon in the C9-C24 range <br /> was detected in MW-2, the well located down gradient of the former USTs. This result is <br /> very near the detection limit of 50 µg/L <br /> FINDINGS <br /> These results are consistent with previous sporadic findings of unidentified hydrocarbons <br /> (C9-C24 range) present at very low concentrations in the areas of MW-2 and MW-3. <br /> Additionally, the groundwater elevation levels have increased approximately 7 - 7 I/2 feet <br /> in the last two years, yet the range of unidentified hydrocarbons, when present, remains <br /> similar, indicating that the vadose zone soils are not the source, and indicating that there <br /> has been no groundwater impact associated with the site due to rainfall in the last rainy <br /> season Sequoia Analytical (the company that performed the sampling analyses) reported <br /> the chromatographic peaks as petroleum hydrocarbons only because they eluted during the <br /> time range used for the quantification of diesel' ChemRisk decided to evaluate whether the <br /> peaks were in fact representative of petroleum hydrocarbons, or whether they could have <br /> come from some other source(s) <br /> ChemRisk obtained chromatograms of both the diesel standard and the MW-2 sample from <br /> the July 1995 sampling event (Attachment D) from Sequoia Analytical through ERM-West. <br /> The chromatogram for the MW-2 sample had the highest peak at 216 minutes with several <br /> smaller peaks observed at 2 4, 12 3, 15.8, and 17.0 minutes. The chromatogram for the <br /> diesel standard contained numerous peaks (resembling a bell-shaped curve) in the 3.2 <br /> minute to 17 0 minute range. The chromatograms were reviewed by a senior environmental <br /> scientist, Ms. Arlene Putnam, with MBT Environmental, a state certified laboratory <br /> associated with McLaren/Hart According to Ms. Putnam, the chromatogram for the MW-2 <br /> sample is not indicative of diesel or bunker C fuels Ms Putnam indicated that the single <br /> peak described as an "unidentified hydrocarbon in the C9-C24 range" could be related to a <br /> variety of sources, such as degraded organic material (e g. rotting leaves) or laboratory <br /> cleaning agents <br /> f����U 2f�3 e��, �oaol�a oo�+�y�t�wm <br /> A D+vision of McLaren/Hart <br /> Environmental Engineenng <br /> Q,c�-ccroo eew <br />