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i f i Wm. J. Hunter & Associates r .t {:�t � � 2220 Loma Vista Dr Registered Geologists ° ' 7�, Sacramento, CA 95825 `Petroleum &Mineral Appraisers - ` F r 2� (916) 972-7941 FAX (916) 972-1683 August 15, 1998 Jeffrey Wong, REHS Trainee San Joaquin County PHS Environmental Health Division Site Mitigation Unit P O Box 388 Stockton, CA 95201-0388 REF: SECOND QUARTER 1998 GROUNDWATER MONITORING REPORT FOR 2315 NO. ELDORADO STREET, STOCKTON; SITE CODE 2080 We have enclosed copies of the field report, water analyses results, a gradient map, and maps showing inferred lines of equal concentrations of benzene, ethylbenzene, toluene, xylene, and TPHg based upon the latest sampling event The field work was done on June 30, 1998 by DelTech Geotechnical Support Services as directed by your office PLATE I shows the approximate potentiometric surface based upon the latest sampling event The gradient is to the northeast, it varies from 02'/ft at the south end of the property to 003'/ft at the north Groundwater was measured at an average depth of 27 70' bgl, a rise of 3 1 P since December This rise in the water table is seen in other wells in the area, and is due to the heavy rains that have occurred this past year PLATES H thru VI show the inferred iso-concentration lines for benzene, ethylbenzene, toluene, xylene, and TPHg based upon the June 30, 1998 data A comparison with the Apnl sampling shows that benzene& ethylbenzene have gone up slightly in MW-1, MW- 2, & MW-3; but have dropped in MW-4, MW-5, & MW-6. Toluene levels went down in MW-1, MW-4, MW-5 & MW-6, and increased in MW-2 & MW-3. Concentrations of xylene increased in MW-2, 3, & 5, but went down in MW-1, 4, & 6. Levels of TPHg went up in MW-2 & 3, but decreased in the other wells TBA was detected in MW-1, 2, 3, 4, & 5. DIPE was detected in MW-3 & 4. All other oxygenates were below detection levels Refer to TABLES B, C & D for a summary of laborabory results to date The water table is now at about 28' bgl, wluch is above the top of the screened intervals in all of the wells This prevents an accurate analysis of changes in levels of contaminants However, a comparison of the maps of equal concentrations from the last four samplings reveals that the configuration of the plume has remained quite uniform This indicates that there is little if any lateral movement 1