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MEETNG MWUTES <br /> FEBRUARY 11.1998 <br /> Disco PRoPER1Y <br /> greater. He also stated that initially it is important to understand the vertical component of <br /> chemical transport,influences on current and historical pumping in the area (receptor <br /> survey). He felt it was possible that groundwater movement may have drawn petroleum <br /> constituents downward along a(more or less)diagonal path from the source area toward <br /> the Del Monte Wells and now that the Del Monte wells are no longer in use this deeper, <br /> potentially contaminated groundwater may be moving in a new direction. <br /> Liz Dodge indicated that,based on concentrations of petroleum constituents in <br /> groundwater,the area in the vicinity of MW-1,SVE-4 and NP-1 appears to be in the source <br /> area.She also said that the horizontal extent of chemical constituents may need additional <br /> definition due to change in groundwater flow direction.Two additional wells south of the <br /> Disco property in the Caltrans right of way would be useful to evaluate this. <br /> Ron said plume control measures may be desirable to slow down migration. <br /> Potential future steps identified by Ron include: <br /> 1. Receptor Survey of present and past pumping influences.This would include <br /> investigation of where pumping wells were/are located,years/seasons of operation, <br /> pumping rates, and construction details. Ron indicated that pumping influences may be <br /> evaluated using pressure transducers to assess potential affect of pumping from the <br /> Diamond Well cluster. Ron described these wells as being about 1,000 to 2,000 feet from <br /> the Disco property and south of the freeway.Liz indicated that a survey of wells within <br /> a mile of the Disco site had been prepared for the 1992 RI report and that this could be <br /> updated. Ron an Margaret said that a survey of wells within 2,000 feet of a property <br /> was usually considered sufficient. <br /> 2. Determine depth of constituents in source area -sample soil/groundwater until vertical <br /> extent of ND is identified. 150 feet may be the minimum required depth. Ron <br /> recommended continuous coring,plus cone penetrometer testing. He also expressed a <br /> preference for collecting soil samples from zones that contain more clays and silts <br /> because petroleum constituents are more likely to be adsorbed to these types of <br /> materials. Ron said short well screens should be used to avoid cross contamination of <br /> geologic units.Nancy Bice asked about prevention of contamination during drilling and <br /> sampling and Ron indicated that was also important and that use of sampling devices <br /> such as a Waterloo sampler may be appropriate. <br /> 3. To test the hypothesis that groundwater may have been drawn diagonally downward <br /> from the source area toward the Del Monte wells that were formerly used for water <br /> supply, two deep borings could be drilled,one in the probable source area as described <br /> above, and another one closer to the Del Monte wells.If diagonal transport has <br /> occurred,petroleum constituents would be expected to occur at greater depth in the <br /> borings closer to the former supply wells. <br /> Steve Ronzone asked whether, under item 3 above, a finding of no increase in petroleum <br /> constituents with depth would satisfactorily demonstrate that diagonal migration had not <br /> occurred, or whether additional investigation would be required. Ron replied that new data <br /> or changes in site conditions may require additional investigations. Steve indicated that it is <br /> Del Monte's policy to avoid installing wells on property they do not own. <br /> PAGE 2oF3 '( �{i" k��"p��/���'��1(y <br /> l <br />