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Wm. J. Hunter & Associates 2220 Loma Vista Dr. Registered Geologists Sacramento, CA 95825 -Qetroleum &Mineral Appraisers �- fi (916) 972-7941 FAX (916) 972-1683 2 7 PM 17 RESULTS OF SAMPLING OF MW-4 PERFORMED ON 12/2/1997 Marci's Diesel Service 2969 Loomis Road, Stockton, CA Site Code 2015 PURPOSE OF WORK: On September 4, 1997, MW-4 was placed at the above site in an attempt to more accurately define soil & groundwater contamination encountered during prior work. The County EHD requested that the well be purged and sampled the next day (Friday) rather than wait until Monday. The results of the that work is described in the WJH report titled "REPORT COVERING RESULTS OF PLACEMENT OF MONITORING WELL #4. " On November 25, 1997, the San Joaquin Co. EHD responded to that report and requested that MW-4 be sampled again. Refer to EXHIBIT A for a copy of that correspondence. That work was performed on December 2, 1997; the results are discussed below. DISCUSSION OF RESULTS OF LATEST WORK: On December 5, 1997, Del-Tech Geotechnical determined depth to water on the four monitoring wells on the property. MW-4 was purged & sampled under the direction of Margaret Lagorio of the San Joaquin Co, EHD. A diesel sheen was noted on the purge water from that well. A copy of the field log prepared by Del-Tech, along with the chain of custody and laboratory reports are included as EXHIBIT B. The lab results of the work performed in September& December are included as TABLE III& TABLE IV respectively. It is interesting to note that benzene and xylene, (measured at very low concentrations from the September event) were ND in December. However, TEPH as diesel increased about 750% from 3030 ug/L to 22,900 ug/L. MW-4 is located less than 10 feet from the removed UST's, which prior work had shown the presence of diesel components beneath the tanks. PLATE I shows the potentiometric surface based upon the December sampling. The gradient has shifted about 140° from southwest to northeast. PLATE H shows gradient directions since initiation of the project. The latest data supports prior information which indicates a very limited aquifer with no discernable regional (or local) gradient. The water table had risen an average of 0.62' since the September sampling. Ground- water elevations have fluctuated a maximum of slightly over 6 feet since monitoring began, indicating a very limited aquifer. r t