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i3 October 13 , 1988 Page 2 <br /> 4 <br /> Chevron U. S .A. 16000-105-03 <br /> i <br /> PROJECT SITE DESCRIPTION <br />!` The subject property is located at the southwest corner <br /> of Benjamin Holt Drive and Pacific Avenue in Stockton, <br /> California. The property is developed as a Chevron service <br /> station , and was active as a retail facility at the time of <br /> our filed investigation. The site was developed with <br /> underground storage tanks , dispenser islands , service station <br /> buildings , surface pavements and planter beds . The subject <br />{ property was rectangular in shape and is estimated to <br /> encompass about one-third of an acre . The underground fuel <br /> storage tank cluster was located near the southwest corner of <br /> the property , and dispenser islands were located along the <br /> eastern side of the property <br /> Please refer to the site plan included as Plate 2 at the <br /> end of the text , which illustrates the general configuration <br /> f of the project site <br /> j SOIL VAPOR SURVEY <br /> A soil vapor survey was conducted at the project site by <br /> Dames & Moore personnel on September 28 , 1988 . Assessment of <br />. presence of volatile organic compounds by the soil vapor <br /> assessment technique is relatively recent in terms of <br /> investigative tools . Soil vapor contamination assessment has <br /> been used to detect a wide variety of volatile organic <br /> tfi compounds . The use of the technique has been useful for <br /> developing boring placement schemes at landfills , gasoline <br /> service stations and a variety of manufacturing facilities . <br /> t4 <br /> ._ The approach to soil vapor contamination assessment is <br /> relatively straightforward The field survey is conducted by <br /> the installation of a small diameter sampling probe into a <br /> prepared sample obtained by exploratory subsoils drilling , <br /> application of vacuum to the distal probe end, withdrawal of <br /> a soil vapor sample , sample analysis , and data <br /> interpretation. <br /> { The soil vapor contamination assessment is possible as a <br /> result of the accumulation of volatile organic compounds in <br /> the gaseous atmosphere of the soil interstices . Some <br /> contaminant vapors can be generated in-situ by anaerobic <br /> microbial degradation , while other contaminant vapors <br /> volatilize or evaporate from contaminated water or non- <br /> aqueous phase liquids such as gasoline <br /> Not all organic compounds respond well to the soil vapor <br /> assessment technique The compound must be sufficiently <br /> volatile to enter the vapor phase in detectable levels , and <br /> have low enough aqueous solubility to allow entry into the <br /> vapor phase , rather than the aqueous phase <br />