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4 2 3 6 Piping Given the past problems with inorganic precipitates collecting at the injection wellhead valves, suggest that the head loss through the full length of the infection pipelines be compared with either initial head loss or that loss predicted in design Although adequate velocities probably exist in the piping to prevent collection of soft scale at low points in the piping, encrustation may have occluded some of the piping 4 2 4 Regulatory Changes The Installation is in the process of re-evaluating the clean up goals and may seek a modification to the permit to less stringent risk-based objectives The Installation has initiated a scope of work with an independent contractor to look at optimizing the treatment system and to explore alternatives to enhance the current technology The study also includes a new look at risks posed by the ground water and addresses alternative action levels for the COCs The RSE team supports these actions 4 2 5 Recommended Studies outside the Scope of the RSE 4 2 5 1 Recommended Studies As stated above, the Installation and District are currently re-evaluating the risk posed by the site in order to reconsider the cleanup goals The ME team concurs with this action which was outside the scope of the RSE More detailed computer modeling optimization studies of the pumping system should be considered using the existing MODFLOW model and an algorithm such as MODMAN In addition, the team recommends the spinner logging of wells with both shallow and deep screened intervals, re-evaluation of the SHMP dosage by an independent authority, the determination of the required dosage of CO2 to control pH of the influent/effluent, and the studies necessary to support the conversion to the use of the diffusion samplers 4 2 5 2 Estimated Costs for the Recommended Studies Spinner logging of extraction wells with both shallow and deep well screens would cost approximately$7,000, based on costs obtained from Welenco, Inc of Bakersfield, CA The re-evaluation of the SHMP dosage could be done strictly through a review of the previous M&E/Calgon study or through a new study at cost comparable to the earlier study The treatability study for the conversion to the use of CO2 may be done at no cost by a CO2 vendor (based on contacts made by RSE team members) The diffusion sampler studies would potentially require duplicate analysis for at least one round at a possible analytical cost of$7,500-10,000 and approximately 90 person hours 5 Summary In general, the RSE team found the system to be well maintained, and operating as intended The system design appears to have been appropriate given what was known about the site at the time of construction The system performance appears to be protective of the public and the environment Reductions of contaminant concentrations in ground water have been observed, but the drop in concentrations has slowed, consistent with the normal behavior of ground water extraction systems A number of changes in the remedial approach or the operation of the system are suggested to possibly reduce future operations and maintenance costs These changes are listed below Rough estimates of potential savings are shown in parentheses, where available 1) changing either the dosage of SHMP or using CO2 to control inorganic precipitate formation ($50,000-143,000 annually), 2) defining source areas and removal of residual mass from the vadose zone undertaken if determined to be a continued threat to ground water, 06/07/99 Page 13 of 14