Dear Mr. Alcamo:

Tetra Tech EM Inc. (Tetra Tech) is submitting analytical results for two surface water samples collected by Tetra Tech's subcontractor, Earth Tech, Inc., at the Illinois Central Spring (ICS) treatment facility near the above-referenced site on April 4, 2003, during nonstorm (low-flow) conditions. Paradigm Analytical Laboratories, Inc. (Paradigm), of Wilmington, North Carolina, analyzed the samples for polychlorinated biphenyl (PCB) congeners using U.S. Environmental Protection Agency (EPA) Method 1668.

Tetra Tech reviewed Paradigm's analytical data to evaluate whether the data met the data quality objectives specified in the quality assurance project planan for the above-referenced work assignment. Tetra Tech's review was conducted in general accordance with procedures discussed in EPA's "Contract Laboratory Program National Functional Guidelines for Organic Data Review" dated October 1999, with modifications as necessary to meet the explicit requirements of EPA Method 1668.

The table in Enclosure 1 summarizes Paradigm's analytical results. Enclosure 2 provides the complete sample analytical results as reported by Paradigm in its data package deliverable for the two surface water samples. No quality control problems arose during these analyses, so no qualifications were applied by Tetra Tech. Of the requested 209 PCB congeners analyzed for using EPA Method 1668, about 168 distinct peaks are resolved in the sample chromatotgram; therefore, the laboratory reports a combined concentration for various congeners that co-elute around the same retention time (and therefore are very difficult to quantitate separately). Based on the table in Enclosure 1, this situation is evident for PCB congeners 44, 47, and 65 as reported by Paradigm for both samples.

Because the samples were collected from the ICS treatment facility effluent only 10 minutes apart, they are essentially field duplicates and yielded practically identical results. (The laboratory deems an uncertainty of 30 percent to be routine, but the highest relative percent difference between these two samples was only 3.2 percent.) The presence of trichlorobiphenyls (TriCB) and tetrachlorobiphenyls (TetraCB) is expected because the ICS treatment facility influent is usually identified as containing PCB

Aroclor 1248, and a typical congener analysis of that PCB mixture contains about 20 percent TriCB, 60 percent TetraCB, and 20 percent pentachlorobiphenyls.

The Paradigm analytical results are usable for all purposes as reported. If you have any questions regarding the nonstorm event surface water sample analytical results, please call me at (312) 946-6491.

Sincerely,

Jeffrey Lifka
Site Manager