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GROUND ZERO ANALYSIS, INC. l.'I 1714 Main Street Escalon, California 95320 J 8 Telephone: (209) 838-9888 Facsimile: (209) 838-9883 ENVIRONMENTAL HEALTH DIVISION June 22, 2000 304 E. Weber Ave. Third Floor P. O. Box 388, Sto kton CA 95201-0383 Mr. Harlin Knoll Approved J San Joaquin County Public Health Services Denied ❑ Environmental Health Division Conditions 304 East Weber Avenue, Third Floor Stockton, CA 95202 Date Ott by Subject: Revised Workplan for Additional Subsurface Investigation North of Well MW5 1140 W. Hammer Lane, Stockton, California Dear Mr. Knoll: This letter report is submitted to present a revised workplan to conduct additional subsurface investigation at the referenced site (Figure 1) in accordance with a written request San Joaquin County Public Health Services, Environmental Health Division (PHS/EHD) dated July 8, 1999. This submittal includes revisions to the October 12, 1999 workplan submitted by Ground Zero Analysis, Inc. The revised scope of work has become necessary due to time and scheduling constraints required as a condition of the encroachment permit issued by the City of Stockton (Attachment A). The general scope of work will consist of drilling and sampling one soil boring north of well MW5 to investigate the vertical and lateral extent of residual soil contamination, collecting a discrete groundwater sample to investigate the northern extent of the dissolved contaminant plume, and preparing a technical report that summarizes the methods and results of the investigation. Scope of Work Groundwater in the vicinity of well MW5 contains total petroleum hydrocarbons as gasoline (TPHG) at elevated levels. The lateral extent soil and groundwater contamination has been essentially defined to the east, south and west, but not to the north. The current depth to groundwater at the site is approximately 35 feet below the ground surface (bgs). The proposed boring well will be drilled to a depth of approximately 45-50 feet below ground surface (bgs) in the Hammer Lane right-of-way, approximately 50 feet north of well MW5 to further investigate the extent of subsurface contamination. The location of the proposed boring is shown on Figure 2. Fisch Environmental (C57 4683865) will advance the boring using a Geoprobe 5400 direct push drilling rig. Soil samples will be collected for logging and identification at 5-foot depth intervals. Samples will be collected using a 1 3/4-inch diameter sampler lined with clear acetate or brass sleeves. The portion of the sample to be analyzed will be immediately capped and preserved in an iced cooler at a temperature of approximately 4° Centigrade. Up to three soil samples will be submitted for analysis of TPHG, and benzene, toluene, ethylbenzene, xylenes (BTEX), and methyl tert butyl ether (MTBE) using EPA methods 8015m and 8020, respectively, to investigate the extent of residual gasoline contamination in soil. G:\Data\GROLJNDZE\KNOWLES.HAM\REPORTS\WPaddO6OO.DOC WLES.HAM\REPORTS\WPadd0600.DOC