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PUBLIC HEALTH SERVICES <br /> SAN JOAQUIN COUNTY t. <br /> w: X <br /> JOG] KHANNA M.D.,MRH. <br /> Health Officer <br /> CgL�FOR��P <br /> P.O. Box 2009 • (1601 East Hazelton Avenue) 0 Stockton, California 95201 <br /> (209)468-3400 <br /> DAN BARBER 'JAN2 2 1993 <br /> A TEICHERT & SON INC <br /> P O BOX 15002 <br /> SACRAMENTO CA 95851 <br /> RE: 103 North E Street SITE CODE: 1555 <br /> Stockton, Ca <br /> San Joaquin County Public Health Services, Environmental Health Division (PHS/EHD) has completed <br /> the review of the "Problem Assessment Report and Final Remediation Plan", dated December 1992 and <br /> submitted by EMCON Associates. <br /> The remediation alternative of soil vapor extraction,based on the data collected and presented in the <br /> report, appears to be a viable option for the remediation of the soil contaminant plume and possibly the <br /> groundwater contaminant plume also. <br /> The initiation of this type of system should begin as soon as permitting allows in order to promptly begin <br /> treatment of the soil and groundwater plumes at this site. However, as noted in the report, there are <br /> several areas that may need further evaluation and may possibly need to be addressed with modifications <br /> to the existing and/or proposed remediation system to effectively encompass the entire soil and <br /> groundwater contaminant plumes. <br /> As discussed in the report (page 6-2), the areas influenced by the existing piping gallery may not remove <br /> the quantity of hydrocarbons as effectively or efficiently as would wells more selectively designed for that <br /> purpose. The gallery piping is located horizontally at depths of 15 feet below ground surface (BGS) and at <br /> 35 feet BGS. The data suggests, possibly due to differences in the soil lithology, that these gallery 'wells" <br /> have a limited influence on the monitoring wells screened in the deeper zone, from 75 to 90 feet BGS. <br /> These gallery "wells" may not be suitable in addressing those deeper areas of secondary soil contamination <br /> (resulting from the groundwater contaminant plume as it receded with the water table) or the entire <br /> groundwater contaminant plume. <br /> Also, the gallery "wells" may not be able to effectively retrieve contaminants from each different soil layer <br /> identified as being impacted, even in the shallow soils. Wells selectively screened for these layers may <br /> need to be installed to effectively address the entire plume. <br /> The differences in the screen lengths, the amount or degree of influence in each different soil lithology <br /> encompassed by the screen interval and the varying depths of the screen lengths for all existing wells, and <br /> also for any future wells, must be considered when evaluating the effective influence on the documented <br /> and/or inferred soil and groundwater plumes at this site. <br /> A Division of San Joaquin County Health(•are Services �� <br />