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MM =--ZA7 z M, a !,4 '-P hydrocarbon (TPP) contrimi notion dot,, not generallN, require immediate additional notion. board onginvarg emphnnire that this dors not mean that some action might riot be required in the future. Still, the afte in ansigned a low priority nleno it In situnted in an arra of hl$:h hydrogeolng1c concern. The detection of more than 100 ppn, 71,11 in the native nail beneath it tank Is generally considered grounds for requiring ort additional Investigation in the form of roll borings and inotalIntion of at least one groundwater monitoring well followed by periodic monitoring. Tha detection of 1000 ppm TPH is usually viewed by the Board no an unacceptable level of fuel saturation which will mandate excavation of the effected ground down to the furthest practicable reach of conventional excavating machinery followed by soil borings and installation of groundwater monitorir;:: wella. Other regions use different standards for dotermining when a groundwater investigation will be required. For example benzone its often aced In l"eu of TPH. Even very low levels of benzene are often seen as grnundt for requiring 4M a aubaurface investigation. This criteria may be relaxed or stiffened depending on the location of the site in relation to different groundwater systems. the depth to water, type of soil, and the concentrations of benzene involved. The above standards apply only to fuels. When samples taken In connection with a waste oil tank or a solvent tank are found to contain even small amounts of any of the EPA priority pollutants (ouch as TCE, PCE, DCE etc. which are detected by EPA methods 8010, 8020. and 9240) more stringent 7 standards are often applied. in these cases, soil boringa and monitoring well installation may be required if there 13 any detectable amount of any of the EPA priority pollutant compounds. When contaminants are found to hnvo reached the water underlying a site, the Board customarily requires that additional work be undertaken in order to define the extent of the contamination. Sampling Report 88055-C-2 CHEVRON 1918 page 12