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----'-7M'r ' <br /> The hydrologic data for the site indicates a shallow, possibly <br /> perched, saturated zone is present at a depth of approximately 12 <br /> feet. The dissolved concentration of benzene in the monitoring <br /> well MW-1 is slightly above the 0.70 ppb action level for <br /> drinking water. The low level of benzene within well .. MW-1 <br /> suggests spreading of dissolved hydrocarbons may be occurring, <br /> although ' we recommend resampling of this"well for confirmation. <br /> The 100 foot surface sanitary seal and significant clay strata <br /> above the perforation, in the domestic well greatly reduces the <br /> potential impact of the dissolved hydrocarbon in the shallow <br /> W groundwater. The higher elevation of groundwater within the <br /> domestic well compared to the monitoring well indicates there is <br /> a vertical gradient upward which would further inhibit downward <br /> w vertical migration of dissolved contaminants. We recommend <br /> future monitoring of well MWI and the domestic well to document <br /> any spreading of shallow contaminated water. While it appears <br /> that thereis a relatively small area in which the shallow <br /> groundwater (above 14 feet) is contaminated with low levels of <br /> dissolved hydrocarbons, we believe a monitoring program is the <br /> appropriate responze. Because of the low permeability of theshallow sediments any spreading will be limited and natural <br /> biodegradation will act to mitigate any threat to groundwater" <br /> resources. if future water analyses indicate significant <br /> spreading of contamination toward MWl, an active cleanup approach <br /> can be undertaken. The monitoring program should include <br /> recording water levels in both wells, purging of at least 4 well <br /> volumes and sampling for BTEX and total volatile ' hydrocarbons as <br /> gasoline. Sampling should be undertaken quarterly. <br /> ( . Implementation of this plan is dependent upon approval by the <br /> Local Health District. <br /> If you have any questions regarding our investigation or would <br /> like to discuss this project further, please contact gyne dt our <br /> newof#ice in Escalon, California (209) 838-3507. <br /> Respectfully, # <br /> WaterWork <br /> - Rusrrll W. Jancal <br /> CA R"igistered Geologist Mn. 3864 <br /> RWJ:e.t <br /> Attachment <br /> cc: David Carls San Joaquin He_a',th <br /> --- -- _ -- ----CA-Regional-Water Quality hca=d-- ----- -- - <br /> i <br />