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August 4, 1992 Page 2 • As you will note, toluene at a concentration of 11 .8 micrograms/kilogram (µg/kg) was reportedly detected in the two soil samples from the 1 ,000-gallon tank excavation using one analytical method (EPA Method 8020). The soil samples were analyzed by a second method, U.S. EPA Method 8260, to confirm the results of the first method. The concen- tration of toluene was ',slow the detection limit of 5 µg/kg using the second analytical method. This detection limit is consistent with the detection limit for toluene recommended in the Tri-Regional Guidelines. Discussions with staff at Columbia Analytical Services, Inc., a state- certified analytical laboratory, indicate that discrepancies of this magnitude in analytical results between the two methods at these low concentrations should not be unexpected. This is particularly true for soil, given the het- erogeneous nature of soil. One point that was brought up, however, is the fact that identical analytical results to one decimal place were reported for toluene in two different soil samples. Given the heterogeneous nature of soil, identical analytical results are highly unusual and therefore suspect. Additionally, it has been EMCON Associates' experience that when there are detectable concentrations of toluene present due to a release of petroleum hydrocarbons, there are also detectable concentrations of ben- 0 zene, ethylbenzene, and xylenes. Additionally, there would also likely be detectable concentrations of gasoline. The lack of any of these com- pounds being detected in the two samples causes us to consider the ana- lytical results for the toluene to be suspect. For these reasons, it is EMCON Associates' opinion that greater faith should be placed on EPA Method 8260 (gas chromatography/mass spec- troscopy) analytical results than the results of EPA Method 8020 (gas chromatography/flame ionization detection). In addition, it is EMCON Associates' opinion that the toluene reported to be present in the soil sam- ples is not present above the 5 µg/kg detection limit. A third factor to consider is the low concentration of toluene reportedly detected. It has been EMCON Associates' experience that in tank excava- tions where ground water has not nor has risen into the excavation, the base of an excavation is the location where the highest concentration of detected compounds will be present. The depth to ground water at the 103 North E Street site has been reported to be as shallow as approxi- mately 30 feet below the ground surface and currently is reported to be approximately 60 feet below the ground surface. Therefore, even if toluene • p#V90V900202