SITE INFORMATION AND CORRESPONDENCE 1988 - 2001

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PUBLIC, HEALTH SERVICES ,. .ro SAN JOAQUIN COUNTY m ?� ENVIRONMENTAL HEALTH DIVISION Karen Furst, M.D., M.P.H., Health Officer ill 304 East Weber Avenue,Third Floor • Stockton, CA 95202 clFo�i 2091468-3420 OCT 0 9 2001 HENRY CECCHINI CECCHINI CECCHINI & GIOVANNONI FILE � 3000 E EIGHTEENTH ST ANTIOCH CA 94509 RE: DELTA TRUCK (former) SITE CODE: 1800 3535 E. Cherokee Road RO#000118 Stockton, CA 95205 San Joaquin County Public Services, Environmental Health Division (PHS-EHD) has reviewed the 16 August 2001 "Problem Assessment Report" (PAR) submitted by Advanced GeoEnviron mental Inc on August 28, 2001 and has the following comments. PHS-EHD and a representative from the Central Valley Regional Water Quality Control Board (CVRWQB) evaluated the comments and conclusions included in the PAR and have concluded that the "No Further Action" requested cannot be granted at this time. Due to the large mass of residual petroleum contaminated soil and elevated levels of Methyl tertiary butyl ether (MtBE) and 1,2,-dichloroethane (DCE) still present in the groundwater at the site, further Investigation in areas described below must be completed. The groundwater"grab' sample collected at 70' below ground surface ('bgs) from soil boring "B- 17" adjacent to the former unleaded gasoline underground storage tank (UST)#6 detected MtBE at 9,700 µg11 during June 1999. The lateral extent of this contaminant must be delineated. Additionally, the 950 µg11 of DCE detected in monitoring well "UST-5"when last sampled during June 2001 must be delineated. Contamination was detected in soil samples collected from monitoring well "UST-1" during it's construction in September 1990 at 50' to 70' bgs. UST-1 was constructed with the screened interval passing from a sand lens interval at 83'-87' bgs through a clay layer from 87'-97' bgs and ending in another sand layer at 97'-103' bgs. It appears that the construction of this monitoring well is allowing contaminants (DCE) in the upper sand zone to migrate downward to the lower sand zone and contribute to it's degradation. It is the conclusion of PHS-EHD and the CVRWCB that this monitoring well be destroyed by over-boring it to it's total depth with a minimal 10" hollow stem auger. In order to address the unresolved concerns with both MtBE and DCE at this site, PHS-EHD will require a multi-zoned investigation north-northwest of"B-17" and "B-12" and south of"B-8". The permeable sand zone at 65' bgs is to have a monitoring well installed so that it's screened interval is constructed to overlap this zone. No more than five feet of screened casing should be placed at this depth. The other zone of concern in this same area is the sand zone from 80' to 90' bgs. No more than ten feet of screened interval of casing should be installed in this well. If separate monitoring well borings are to be installed, ensure that the wells are no closer than five feet horizontally from each other. A nested monitoring well is acceptable and so is the new 1.7" OD extruded polyethylene/Teflon multi-level pre-constructed casing. Your cost-effective analysis and Cleanup Fund pre-approval will determine the most acceptable type of well. A Division of San Joaquin County Health Carc Scrvices