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Work Plan for UGT Investigations -3- 7 November 1991 DDRW, Sharpe Site these samples, these concentrations may indicate that ground water could potentially have been impacted. Furthermore, these concentrations are not significantly different than the concentrations of diesel, gasoline and BTX in samples from D-19, D-39 and D-43. These latter three tank samples were listed on Table 2-5, indicating that additional investigative work would be required at these sites. Therefore, based on the Tables, it is unclear what criteria were used to determine whether a tank site needed further investigation. Sharpe needs to define the criteria by which a site was determined to need additional investigation. Page 2-7. The Plan lists the maximum allowable soil total petroleum hydrocarbon (TPH) levels or cleanup levels for soils contaminated with diesel, gasoline BTX's as 100 mg/kg, 10 mg/kg and 0.005 mg/kg, respectively. I do not concur with the proposed cleanup levels for diesel and gasoline because the rationale for selecting these concentrations was not presented and because the depth at which these contaminant concentrations were found is unknown. Ground water at Sharpe may be as little as about five to ten feet below the depth of the tanks. Therefore, it may not be acceptable to leave, for example, 100 mg/kg of diesel in the soils as this concentration may continue to degrade ground water if left in-place. Sharpe needs to provide the rationale for uniformly selecting these concentrations cleanup levels for every tank site. Further information is needed, such as the depth of the existing soils sample data, depth to ground water and types of soils to determine the appropriate cleanup level for each UGT. However, the proposed cleanup level for BTX of 0.005 mg/kg in the Plan is acceptable. In the Tri -Regional Board Staff Recommendations, the Practical Quantitation Limit (PQL) is 0.005 mg/kg. If Sharpe cleans up the soils at the tank sites to the PQL, then this would be acceptable because it would be considered a "clean closure" for soils at the tank site and would be acceptable. Page 2-7. Table 2-3 lists the tanks which meet the LUFT Manual Guidelines and thus, would not need further investigation. The Plan also establishes 0.005 mg/kg as the cleanup level for BTX's. However, several of the tanks (D-8, D-10, D-17, D-21, D-29, D-32, D-33, D-41 and D-45) listed in this Table have concentrations above the 0.005 mg/kg cleanup level established for BTX's in the Plan. Therefore, these tanks would not be considered as having had an adequate investigation and cleanup, per the criteria established in the Plan. Page 2-10. Table 2-5 summarizes those tanks which need additional investigation. It is apparent that the tanks targeted for additional soils boring were based on the investigative approach to complete an investigation for a particular tank site rather than to perform additional investigations to fill data gaps. This proposed investigative approach is acceptable. However, the remaining tank sites will require investigation at a later date to determine whether there were leaks from the removed tank, whether ground water has been impacted and whether the tank site needs remediation. Page 2-10. Table 2-5 indicates that a soil boring was to be installed at tank site D-6 due to the elevated concentrations of pesticides in the soils sample.