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sY.hllf4V ��,Eb J _ .yffi�c�/.7fcSI -�i+� ANDERSON GEOTECHNICAL CONSULTANTS, INC. File No. 2070-2 6 July 1990 a San Joaquin County Local Health District Environmental Health Division 1601 E. Hazelton Avenue Stockton, CA. 95201 RECEIVED J U L 12 1990 Attention: Diane Hinson, R.S. ENVIRONMENTAL HEALTH Subject: Rainbo Baking Company PERMIT/SERVICES 2651 S. Airport Way Stockton, California ADDITIONAL MONITORING WELL INSTALLATION WORKMAN Dear Ms. Hinson: T1:;-. letter is to address the issue of additional investigative work which we recommend be performed at the Rainbo Bakery site in Stockton, California, In accordance with our workplan dated 4 April 1989, we have completed two soil borings and + installed two additional monitoring wells at the subject property. Soil borings 99-1 and 90-2 were completed on 14 February 1990, one at each end of the tank excavation. MW-6 was drilled up- gradient from the tank excavation on 'S February 1990 while MW-7 was drilled down-gradient from the tank excavation on 21 February 1990. Figure 1 shows the locations of the wells and borings along with the calculated directions for the groundwater gradients. During our soil borings,we performed continuous sampling in order that we may better understand the stratigraphy of the underlying soil profile in the vicinity of the tank excavation. Figure 2 illustrates what we believe to be the underlying stratigraphy at the location of the tank excavatior:. Logs of the borings and wells ran be found at the end of this correspondence. Table I summarizes the analytical results for soil samples obtained from borings 90-1 and 90-2 and monitoring wells MW-6 and MW-7. Laboratorl analyses for the soil samples retrieved during borings 90-1, 90-2 and th:, installation of MW-6 indicate the presence of detectable amounts of contamination. Soil obtained from boring 90-1 at a depth of 33 feet exhibited detectable levels of toluene, ethyl benzene and xylenes. Laboratory analyses suggest the soil in boring 90-2 as well as the soil obtained from the installation of MW-6 to contain detectable levels of toluene. Because no other contaminants were detect,-d in the samples, we believe the values of toluene found to occur in boring 90-2 and MW-6 may be anomalous; perhaps a quality assurance/quality control problem. Analytical results of the groundwater samp[cs'.eirieved from monitoring wells MW-6 and MW-7 are summarized in Table II. Groundwater samples obtained from MW-7 exhibited detectable levels of:TPH and BTEX. To confirm this result, we resampled this well. The second sample also exhibited detectable levels of TPH incl I3T!✓X- Bused on these data, it appears thai the 631 Commerce Drive, Roseville,CA 95578 • (816)786.6883 (916)969.8883 •An Employ#a0wned Company