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Y <br />�s <br /> 4.1 TPH Concentrations <br /> For Tank T3 and its associated piping, a single soil sample <br /> exhibited a TPH concentration as diesel of 24 mg/Kg. Mr. Lyons has <br /> suggested that this detectable concentration mandates further <br /> investigation. WESTON strongly disagrees with Mr. Lyons <br /> suggestion. <br /> In any situation regarding the presence of petroleum hydrocarbons, <br /> of paramount importance is the protection of groundwater. For this <br /> reason, both the Luft Manual and the Tri.-Regional Guidelines <br /> recommendations recommend that the TPH concentration be evaluated <br /> on an individual basis, taking into consideration site specific <br /> information. <br /> In order to evaluate the potential threat to groundwater, several <br /> factors such as soil attenuation, depth to groundwater and compound <br /> specific leaching potential must be addressed. Mr. Lyons had <br /> informed WESTON that San Joaquin County does not utilize leaching <br /> potential due to the shallow depth to groundwater in the County. <br /> However, in this case, WESTON believes that utilization of leaching <br /> potential is the only scientifically feasible means of assessing <br /> the potential impact of the compound presence on the groundwater <br /> underlying the site. Since the depth to the uppermost water <br /> bearing zone at this site is greater than 501 , evaluation of the <br /> leaching potential at the sate is critical-to determining if the <br /> low TPH concentrations found present a concern. <br /> � ,-- In addition, it is WESTON's understanding that San Joaquin County <br /> is one of the 14 agencies currently participating in the pilot <br /> program for the utilization of the March 1989 Luft procedures. Of <br /> specific importance within the Luft procedures is the utilization <br /> of leaching potential for the determination of the allowable levels <br /> of TPH which may remain in place. Without utilizing leaching <br /> potential, only an arbitrary value can be established for the TPH. <br /> As a final note, in must be emphasized that the TPH concentration <br /> detected was for diesel and not gasoline. It is well documented <br /> that diesel fraction TPH concentrations are less , soluble and <br /> consequently less mobile than their gasoline counterparts. <br /> While WESTON is unsure of the environmental or site specific <br /> information utilized by Mr. Lyons in formulating his <br /> recommendation, WESTON does not feel, based on the existing data <br /> and scientifically based rational, that the compound concentration <br /> detected warrants further expenditures of our clients funds. There <br /> exists an extremely low probability that these compounds will <br /> affect the groundwater. We hereby request that the California <br /> Regional Water Quality Control Board be consulted to provide <br /> u clarification of this issue. <br /> 4.2 Toluene Concentration <br /> ---- ------- ..-.._In._.-reference <br /> a--concern--was--raised-in-regards-to---the - - -- -- -- ----- -- <br /> 1 <br />