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r <br /> PUBLIC HEALTHSERV�' ICES .4r6li <br /> �SAN JOAQUIN COU TY <br /> JOG[KHANNA M.D., .P.H.Health Officer4P.O. Box 2009 (1601 East Hazelton Avenue •stoc ctom Calif xnla 95201 F +`' <br /> (209)468-3400 <br /> GARY BROPHY Dy <br /> 1235 SLAYTON DRIVE l APR 0 61992 <br /> MANTECA CA 95336 (C(a <br /> RE: 941 E. Yosemite SITE CODE: 1461 <br /> Manteca, CA <br /> San Joaquin County Public Health Ser ices, Environmental Health <br /> Division has reviewed the "Letter Report, Ground Water <br /> Monitoring, Fourth Quarter 1991" and has the fallowing comments. <br /> PHS/EHD cannot concur with the recommendation for closure for <br /> this site at this time. San Joaquin County Flood Control Maps i <br /> (Spring 1983 and 1986) record the seasonal high depth to i <br /> groundwater at approximately 15 feet below ground surface (BGS) <br /> for this site. In 1988, when the monitoring wells were drilled, <br /> the depth to groundwater was approximately 22-23 feet BGS. Since <br /> that time the groundwater has dropped approximately two feet, <br /> possibly leaving the hydrocarbons previously noted in the <br /> groundwater adsorbed to the soil. As the water table rises, it <br /> may again become impacted by the hydrocarbons left behind in the <br /> soil. ! <br /> Hydrocarbons evidenced in the last round of groundwater sampling <br /> indicate this phenomena may be occurring at this site. Depth to <br /> water measurements were recorded only twice in 1991 and may not <br /> be representative of the true fluctuations of the water table at <br /> this site. It is recognized that the bulk of the contaminated <br /> soil was removed during the over-excavation of the tank pit area <br /> in 1989, but the hydrocarbons that may be adsorbed to the soil <br /> remain as an additional source that may impact groundwater. <br /> Should the water table rise to 22-23 feet BGS, where significant , <br /> contamination was noted in the groundwater in 1988 and 1989, the 3 <br /> possibility of increased levels of hydrocarbons impacting the <br /> groundwater in the future exists. <br /> Due to the above mentioned area of concern, the decision to <br /> reduce the frequency of the groundwater monitoring events or the <br /> number of wells sampled should be dependent on site conditions, <br /> namely depth to water data in relation to the contaminant <br /> concentrations. Sampling of the wells at least bi-annually <br /> should continue at this time and depth to water measurements (and <br /> sampling if the water levels indicate) should be done on at least <br /> a quarterly basis and should be included in a quarterly status <br /> report. <br /> A Division of San Joaquin Counry Health('.art Services <br />