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May 23, 1988 <br /> Page 2 <br /> and underground storage tanks.nks. Each boring is drilled to a <br /> minimum depth of 20 feet below existing ground surface with one <br /> test boring extended to a depth of 40 feet below existing grade <br /> down gradient from the area of the underground storage tanks. <br /> If groundwater is encountered within the 40 foot test boring, the <br /> test boring will be developed into a monitoring well . <br /> Clean sites, sites that have not been developed for storage of <br /> petroleum hydrocarbons, are typically explored as describe above. <br /> For sites that may have been developed and/or currently storing <br /> petroleum products are explored as discussed in your guidelines <br /> as "Category A" sites. These sites are coordinated with Mr. <br /> Winsor prior to field explorations. "Category All sites are <br /> generally explored with 3 to 4 extra test borings due to existing <br /> underground storage tanks of gasoline, diesel and waste oil tanks <br /> or due to closed sites. These test borings are developed into <br /> monitoring wells should groundwater be encountered within the <br /> depth of exploration or backfilled with grout if contaminated and <br /> no groundwater was encountered within the depth of exploration. <br /> Test boring depths for Class A sites are explored p ed according the <br /> CRWQCB guidelines. Our office has developed a simplified flow <br /> chart describing the steps used in addressing "Category All sites. <br /> See the attached Plate 1, "Monitoring Well Flow Chart - For Fuel <br /> Leak Investigations". The illustrated flow chart complies with <br /> the guidelines set by ARCO. <br /> Sampling Techniques <br /> All test borings have beenenerall dr' <br /> g y filled with either a CME-45 <br /> E 45 j <br /> or CME-55 truck-mounted drill rigs equipped with 6-inch diameter I! <br /> continuous flight augers and/or with 3 1/4 or 3 3/4 I.D. hollow <br /> stem flight augers. All test borings are logged by our field <br /> engineer, who also obtains representative soil samples for <br /> laboratory testing. Soil samples are taken at 5 foot intervals <br /> or less as instructed by the field engineer when field conditions <br /> warrant it. <br /> Relatively undisturbed soil samples are obtained by driving a 2. 0 <br /> inch Modified California Sampler or a 2 .5 inch Modified Porter <br /> Sampler containing thin brass liners i n 4o the bo 4;:.nn Of borings. <br />