As requested by the U.S. Environmental Protection Agency (EPA), Tetra Tech EM Inc. (Tetra Tech) is submitting a data evaluation summary for split sample analytical data for all split samples collected from April to September 2001 under the above-referenced work assignment. Tetra Tech has compared its sample analytical data to data submitted by Viacom, Inc. (Viacom), and its contractor, PSARA Technologies, Inc. (PSARA). Tetra Tech's findings are summarized below.

From April 4 through September 27, 2001, PSARA collected a total of 13 groundwater samples for polychlorinated biphenyl (PCB) analysis and split the samples with Tetra Tech. Tetra Tech shipped its split Groundwater samples to TriMatrix Laboratories, Inc., of Grand Rapids, Michigan, for analysis; PSARA shipped its split Groundwater samples to Heritage Environmental Services, LLC, of Indianapolis, Indiana, for analysis.

The split samples were collected from either Groundwater monitoring wells or piezometers at the Lemon Lane Landfill, Bennett's Dump, and Winston-Thomas Wastewater Treatment Plant (WWTP) sites in Bloomington, Indiana. All split sample analytical data results are summarized in the table on the next page.

Viacom's PCB results are mostly similar to Tetra Tech's PCB results. A few PSARA samples yielded higher PCB concentrations than the corresponding Tetra Tech samples (for example the samples collected on August 9, August 16, and September 27, 2001). The PCB chromatogram patterns for the samples often are not good matches to the chromatogram patterns in the Aroclor standards used for calibrating the analyses. These differences reflect mixtures of Aroclors in the samples and environmental degradation of the PCBs. The quantitative results for any sample depend on (1) the peaks selected by the laboratory for quantifying each Aroclor, (2) the identification of the Aroclor(s) in each sample, and (3) the actual PCB mixture in the portion of each sample used for analysis. Laboratories and analysts vary with regard to the first two factors and therefore routinely yield different PCB results. Outside of limitations inherent in the nature of the PCB analyses, Tetra Tech has a high level of confidence that the Tetra Tech and PSARA Groundwater PCB concentration results are accurate.