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3 i October 13 , 1988 Page 3 Chevron U . S.A. 16400-105-03 Subsurface conditions which comprise the physical character of a site , such as soil matrix homogeneity and heterogeneity and soil moisture , affect the transport of vapors , as well as the contaminant vapor distribution. Such factors must be considered in data interpretation with regard to data quality and utility. W The soil vapor survey consisted of eight soil vapor sample points , with each sampling location situated at the 3 foot below grade depth. The sampling locations are shown on the site plan included as Plate 2 at the end of the text. METHODOLOGY The soil vapor survey was conducted at the subject z property by means of obtaining a subsurface soil sample , preparation of the sample for vapor extraction, and analysis of the extracted headspace vapors by means of a portable " field gas chromatograph . t As a result of overhead obstructions and the activity a associated with the retail facility, subsoil samples were • obtained by means of coring through surface pavements and concrete with an electrically operated coring machine , then hand augering the subsoils to obtain a sample at the selected K depth. A total of eight hand augered soil borings were advanced to an approximate maximum depth of 3 feet below the existing grade . A Dames & Moore geologist was present during augering to assist in obtaining relatively undisturbed samples of the subsurface materials , to field screen samples with a device capable of detecting volatile organic hydrocarbons as a trace gas , and to make observations of the site conditions . Subsoil samples were obtained by means of hammering a stainless-steel sleeve lined split-barrel sampler into the subsoils . Between sampling attempts , the sampler was dissassembled and washed in a trisodium phosphate (TSP ) solution, rinsed twice with purified water, and reassembled with stainless-steel rings to minimize the potential of spreading contaminants among samples , if any were present . After samples were obtained , each sample was prepared by placing approximately 20 grams of soil into a 45 milliliter glass vial Distilled water was then added to the vial to the 30 milliliter mark , leaving approximately a 15 milliliter headspace , and was capped with a flexible teflon-lined septum. The vial s,as agitated , and a headspace vapor sample was extracted from the vial , utilizing a gastight syringe through the septum of the vial .