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Wm. T. Hunter & Associates 2220 Loma Vista Dr. Registered Geologists Sacramento, CA 95825 Petroleum &Mineral Appraisers (916) 972-7941 • FAX (916) 972-1683 June 25, 1998 Wendy Wiles, Engineering Geologist CRWQCB, Central Valley Region 3443 Routier Road, Suite A Sacramento, CA 95827-3098 RE: FIRST HALF 1998 GROUNDWATER MONITORING REPORT FOR 1145 W. CHARTER WAY, STOCKTON, CA - INDEPENDENT TRUCKING FACILITY We have enclosed a copy of the field report, results of water analyses, a groundwater gradient map, and maps showing inferred lines of equal concentrations of benzene, toluene, ethylbenzene, xylene, TPHg, and TEPH for the above property. The field work was performed on March 31, 1998 by Del-Tech Geotechnical. There are eight (8) wells on the Independent Trucking facility, and one on the adjacent property to the west, JM Equipment. Seven wells were placed by the owner of the property, W.W. Miles; and one, MW-5, was placed by Nomellini Construction Co. to monitor existing soil & groundwater contamination which is present on the site adjacent to the east. We are no longer collecting data from this well. MW-9 was placed on JM Equipment property immediately to the west in an attempt to identify the source or sources of gasoline compounds detected in monitoring wells at the west side of the subject property. Field observations and laboratory analyses of soil & water samples revealed extremely high levels of gasoline compounds - refer to the our quarterly report dated April 9, 1997, for more information., Further monitoring is the responsibility of the owners of that site, and we are no longer sampling it. Del-Tech reported that all of the wells on the property are in poor condition. The well box for MW-1 has been dislodged and the top of the casing possibly damaged. The top of MW-2 is broken off, and water depth measurement is not accurate. Once it is repaired, it will have to be resurveyed. The top of the casing in MW-3 has had an extension glued on it after pouring a cement pad around the well. The well box of MW-4 is in very bad shape, and the monument on MW-6 has been broken off. We have obtained a cost estimate for restoring the integrity of those wells, and will seek approval from the Cleanup Fund staff before we begin work. PLATE I shows the inferred potentiometric surface based upon the latest sampling. The gradient is to the northeast; it varies from .007'/ft. at the west end of the property to .00291/ft at the east end- The average depth to water during this sampling was 13.64' bgl, or -7.37' msl datum, a rise of 5.42' since October. The is the highest level recorded since monitoring began. The top of the well screen is at 20' below grade in MW-4; at 18' in MW-1, 2, & 3; and at 15' in MW-6, 7, 8, & 9. Although the water table is now slightly above the tops of the screens, it does not invalidate the results of the sampling. • 1