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Sampling Plan- 152 East 11th Street, Tracy, CA Page 5 <br /> area of the Tracy Auto Parts frontage and westerly in the direction of the 152 East 11th <br /> Street property However, no records were found to indicate that any investigation of the - -- cn I tS2 <br /> extent of contamination emanating from the unauthorized release on the 208 East Street � ' Q <br /> property has been conducted It is expected that results from analysis of soil and fi <br /> groundwater samples from the proposed well NAV 5 will aid understanding of this issue �., " <br /> The Polk Indices for the City of Tracy shows that the property at 205 East 11th Street, LU <br /> which is now the site of Center Appliance (Refer to Figure 3 for location), was occupied <br /> from at least 1956 until sometime after 1970 by a service station doing business as Douglas us <br /> Service Station Experience shows that the probability is very high that, at some tame over <br /> the life of a facility of that age, significant losses of fuel hydrocarbons occurred into the <br /> subsurface and may be affecting soil and groundwater not only in the downgradient <br /> direction (including in the direction of the Beacon Station) but also under the sidewalk <br /> along the Eleventh Street frontage of Center Appliance The searches completed to date <br /> have found no record of any tank removal, subsurface investigation or regulatory oversight <br /> of this property <br /> The Polls Indices also indicate that, although very few operating service stations remain, <br /> from the 1940s until relatively recently a very large number of the lots along East 11th <br /> Street were the sites of gas stations Many were in close proximity to and some, in addition <br /> to those described above, were co-gradient or possibly up-gradient of the to the subject <br /> properties One such facility is known to have been situated immediately to the west of the <br /> vacant lot that, as shown on Figure 2, is situated adjacent to the Beacon Station <br /> Interpretation of Area Affected by Hydrocarbons <br /> To aid in selecting sites for the additional monitoring wells requested by the SJCPHS, the <br /> available geotechnical and geochemical data from the investigations previously conducted <br /> on the 152 and 1.53 East 11th Street properties were synthesized and used as the basis for a <br /> conservative interpretation of the hkely lateral extent to which the subsurface has been <br /> affected by hydrocarbons This interpretation is presented on Figures 2 <br /> The interpretation on the figure was developed from evaluation of available data from <br /> analyses of samples of soil and groundwater, visual and olfactory indicators noted in the <br /> boring logs, groundwater level data, principles of hydrogeology and contaminant transport, <br /> and experience with similar investigations at sites of generally similar hydrogeology In <br /> making the interpretations, consideration was given to specific factors related to the site and <br /> its environs that might influence the distribution of hydrocarbons in the subsurface This <br /> included consideration of the probability that backfill in utility trenches (particularly the <br /> storm and sanitary sewer trenches that run north from the Navarra property to the north <br /> side of East 11th Street) provide high permeability channels for groundwater flow <br /> The interpretation shown on Figure 2 shows how fuel components may have moved down <br /> the groundwater gradient from the 152 Eleventh Street property It does not attempt to <br /> show areas of the subsurface beneath the 153 East Street site that are affected by <br /> hydrocarbons or postulate the effects of the known leakage from the underground tanks <br />