SITE INFORMATION AND CORRESPONDENCE FILE 2

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i 1; . . C I S "! PUBLIC HEALTH SERVICES c SAN JOAQUIN COUNTY = ENVIRONMENTAL HEALTH DIVISION Karen Furst, M.D., M.P.H., Health Officer •`�4 �P 304 East Weber Avenue, Third Floor • Stockton, CA 95202 2091468-3420 STELLA RUI Z APR 13 2001 4491 DURHAM FERRY ROAD TRACY CA 95376 RE: Ruiz Grocery SITE CODE: 1551 4491 Durham Ferry Road Tracy CA 95376 San Joaquin County Public Health Services, Environmental Health Division (PHSIEHD) received on April 9, 2001 two permit applications for the destruction of all monitoring, extraction and air sparge wells used in the investigation and remediation of petroleum hydrocarbon contamination in soil and groundwater at the above referenced site. In correspondence dated December 27, 2000, PHSIEHD requested concurrence from the Regional Water Quality Control Board, Central Valley Region (CVRWQCB) on closure of the site, citing a year of successful remediation efforts that significantly reduced the contaminant impact to both soil and groundwater. The CVRWQCB did not concur with the request for closure, stating concerns that the level of methyl tertiary butyl ether (MtBE) in monitoring well MW-2 was above the Primary Maximum Contaminant Level, a domestic water supply well is located within 80 feet of MW-2, and that the contaminant plume was not defined in the downgradient direction. Review of the nine years of groundwater monitoring data collected from this site indicate that the direction of the groundwater flow appears to reverse itself seasonally, from the predominant direction of north-east in the winter months, to south-west in the summer months. As a result, net migration of contamination at the site appears to be limited to the proximity of the release. While a monitoring point does not exist directly south-west from the source area, the monitoring points located due south and due west give a representative indication of the lateral extent of the plume boundaries. These two points have tested consistently below maximum contaminant levels or non-detect for all petroleum hydrocarbon constituents analyzed. In addition, the on-site domestic supply well has been routinely tested for petroleum hydrocarbon constituents since 1991. With the exception of one detection of benzene at 1.2 micrograms per liter (µg11) in November 1997, the domestic supply well has also been below maximum contaminant levels or non-detect in all analyses. Following notification of the non-concurrence from the CVRWQCB, quarterly groundwater monitoring and sampling was resumed at the site. Two sampling events have occurred since that time. The MtBE level in MW-2 was 1.8 µg11 in February 2001, and 1.3 µg11 in April 2001. The intention was to continue the quarterly sampling for a full A(Division of San Joaquin County Health Care Services