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r A E <br /> Robert Burick <br /> Page 2 <br /> "Step-in" monitoring wells must be installed to effectively <br /> identify and monitor the groundwater contaminant plume at this <br /> site. The data collected in 1987 on the groundwater contaminant <br /> plume definition is outdated and cannot be reproduced as the <br /> information was gathered from soil borings and not monitoring <br /> wells. <br /> In addition, the proposed remedial alternative of natural passive <br /> biodegradation is not acceptable at this time. Although the <br /> plume has not currently migrated off-site and the concentrations <br /> of contaminants appear to be decreasing over time, the current <br /> concentrations of benzene are still above the State of California <br /> maximum contaminant level (California Code of Regulations, Title <br /> 22, Chapter 16, Section 64444.5) and therefore require a more <br /> aggressive approach to remediation. Another important factor <br /> influencing the need for a more active remediation alternative is <br /> the close proximity of the contaminant plume to a municipal well. <br /> PHS/EHD and the Central Valley Regional Water Quality Control <br /> Board (CVRWQCB) use these factors as considerations in <br /> prioritizing cleanup sites. <br /> Therefore, based on the above considerations, a workplan to <br /> investigate the condition of the shallow soils in and around the <br /> former tank pit area, the presence or absence of an additional <br /> tank on the property, and the current configuration of the <br /> groundwater contaminant plume is requested for submittal to <br /> FHS/EHD and the CVRWQCB by April 12, 1993. <br /> The "Monitoring Well Installation Report and Groundwater <br /> Monitoring" report did not include the laboratory documentation <br /> for the soil sample submitted from monitoring well 14. Please <br /> submit this information to PHS/EHD for incorporation into the <br /> report. <br /> In order to reduce overall monitoring costs, a reduction in the <br /> sampling frequency of some of the wells at this site may be <br /> warranted at this time. However, the request for a yearly <br /> sampling frequency for all wells is not acceptable at this time. <br /> A modified sampling plan can be submitted to PHS/EHD for review <br /> and concurrence and must address the following concerns. All <br /> wells on the site must be sampled on a yearly basis. All wells <br /> on the site must be monitored on a quarterly basis for visual or <br /> olfactory evidence of contamination, for groundwater elevation <br /> and flow direction information, and to ensure that the wells <br /> remain in a usable, sealed condition. The downgradient well and <br /> the well located between the contaminant plume and the municipal <br /> well must be sampled on a regular basis (more frequent than <br /> yearly) . Monitoring well 12 must be monitored on a regular <br /> basis to provide information on the levels and distribution of <br />