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4.0 DISCUSSION AND RECOMMENDATIONS <br /> In sections 3 2 and 3 3 of our April 1998 work plan, we pointed out that Clearwater Group, <br /> the previous consultant for Mrs Conrady, proposed to inject a total of 1,000 pounds of <br /> ORC into ten borings and to track the results with an extensive monitoring program, but <br /> that the State UST Cleanup Fund requested that the amount of ORC be reduced by 50% <br /> (500 pounds) and that the monitoring program be reduced in scope Clearwater's original <br /> estimate of the required mass of ORC was based on mass-balance calculations A the <br /> volume of oxygen necessary to metabolize the known benzene and gasoline concentrations <br /> The State UST Fund's request for a reduction was apparently based on budgetary <br /> considerations Third-quarter dissolved oxygen and hydrocarbon monitoring indicates that <br /> ORC has not been very effective in reducing contaminant concentrations, it is uncertain <br /> whether a greater mass of ORC would have been more effective, but it appears tf at the <br /> increase in oxygen concentrations that was noted during the second quarter was tem])orary <br /> and that the ORC has probably been depleted <br /> One aspect of the monitoring program that was deleted by the UST Fund's reduction in <br /> scope was periodic sampling to determine whether aerobic hydrocarbon-degrading bacteria <br /> are present in the soil and/or groundwater The purpose of ORC infection was to stimulate <br /> such bacteria to metabolize the contaminants, however, if sufficient quantities of suitable <br /> bacteria are not naturally occurring in the soil, then the addition of oxygen would have little <br /> effect In view of the recent sampling results, we recommend that water samp es be <br /> collected during the next dissolved-oxygen monitoring event (late October) and analyzed <br /> for the presence of bacteria However, this would be an addition to the approved scope of <br /> work and would result in an estimated additional charge of$160 per sample. If the analysis <br /> demonstrates that bacteria are present,then additional time and/or field activities, such as air <br /> spargmg into sparge wells SW-1 and SW-2, as originally proposed by Clearwater, may be <br /> beneficial If insufficient bacteria are present, then the mnoculation of one or more wells <br /> with a bacterial solution may be warranted and effective Such additional activities would <br /> require pre-approval by the UST Cleanup Fund as well as endorsement by San Joaquin <br /> County Environmental Health <br /> 4 <br />