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San Joaquin County 0 Environmental Health Department DIRECTOR ? — `9 Donna Heran, REHS `i 600 East Main Street Stockton, California 95202-3029 PROGRAM COORDINATORS Robert McClellon,REHS --�: Jeff Carruesco, REHS, RDI Website: www.sjgov.org/ehd Kasey Foley, REHS Phone: (209)468-3420 Linda Turkatte, REHS Fax: (209) 464-0138 January 12, 2011 Ms. Mabel Keir Ms. Nereida P. Lopez 1103 Grantland Court P. O. Box 6569 Modesto, California 95350 Stockton, California 95206 N r�P Pensco Trust Co Cust Et al .2 .44 -// e C/o Joseph L. & Dorothy Nomelini T E--�o4ja �+�-A 13084 East Highway 26 P, p, dsx )4j- Stockton, California 95206 LCrt nal� � Subject: Lopez Properties gs23G 1601 Turnpike Road Stockton, California 95206 Dear Ms. Keir, Ms. Lopez, and the Pensco Trust Company: The San Joaquin County Environmental Health Department (EHD) has received and reviewed Ozone Bench Scale Test Report (OBST report), dated 18 October 2010, prepared and submitted by Advanced GeoEnvironmental, Inc. (AGE) on your behalf for the above- referenced site. By letter dated 15 April 2010, the EHD had conditionally approved the ozone bench-scale test. The OBST report documents the results from the seven-day injection of ozone followed by a 13-day study of the aftereffects; and a separate study of the effects of in-situ oxygen sparging. Results were similar between the soil samples collected at 20, 25, and 30 feet below surface grade (bsg) combined with groundwater from the 10- to 30-foot depth interval; and soil samples collected at 50, 55, and 60 feet bsg combined with groundwater from MW-10, screened within the 50- to 60-foot depth interval. A brief summary of the OBST and in-situ oxygen sparging findings are presented below: • Hexavalant chromium was not detected in the initial groundwater samples collected from MW-1 and MW-10, but was detected in both combined-soil-and-groundwater samples collected on day one with hexavalent chromium concentrations increasing throughout the seven-day OBST; the highest concentration of hexavalent chromium detected was 410 micrograms per liter (Ng/L) in the soil/groundwater samples collected at the water table zone (10 to 30 feet bsg). After ozone injection was terminated, concentrations of hexavalent chromium decreased in both soil/groundwater samples to less than 25 pg/L. Analytical results for hexavalent chromium generated by oxygen sparging were not reported.