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the IWL and ditches) are not fully preventing infiltration through the contaminated soil Vadose zone investigations should be considered If source areas near the IWL and ditches are located, then vadose zone removal actions should be considered (e g , SVE or co-metabolic bioventing) The ongoing investigations regarding other sources in the Industrial Area should continue and actions taken as appropriate to remove significant sources Source removal has the potential to shorten the required operational time for the ground water extraction system 4 2 1 2 Re-evaluation of Cleanup Criteria The RSE team supports the current re-evaluation of cleanup goals The consideration given to alternate cleanup goals of 20 µg/L (or higher) of TCE appears to make sense given the exposure potential at the site 4 2 2 Possible Component Changes' 4 2 2 1 Elimination of the Transfer Pumps Currently water is pumped from the extraction wells to the surge tank, and transfer pumps move water from the surge tank to the air stripping towers If there is enough head available from the extraction well pumps, and if an elevated or taller surge tank is installed, then it may be possible to feed the air strippers through gravity flow from the surge tank The savings in electricity from this change are estimated to be $7,000 per year This and the reduced maintenance would probably not offset the capital cost of modifying the piping and modifying or replacing the existing surge tank The volume of a new surge tank of the same diameter is approximately 208,000 gallons Using an order-of-magnitude parametric cost estimate, the estimated installed cost of the new tank would be $147,000 Thus, replacing the existing tank with an elevated or taller gravity--fed tank is probably not justified John Doe, Project Manager for XYZ, the operating contractor at the site, suggested that another alternative would be to totally bypass the surge tank and pump the water directly from the wells to the top of the air stripper This suggestion deserves further consideration if the influent flow rate is expected to remain fairly constant and the well pumps can provide the additional head This would eliminate the need for the transfer pumps, and could result in power and maintenance savings A new section of piping would have to be installed Also valves would have to be installed to allow the operator to either route the water directly to the strippers, or to route the water to the surge tank This may also require that a new system of interlocks be designed and installed The savings would be in reduced maintenance and power savings from reduced head loss The savings in power from reduced head loss would be at least the same as those from using an elevated or taller surge tank ($7,000) 4 2 2 2 Extraction Pump Longevity The rate at which the extraction pumps are failing at the site appears to be excessive and poses a significant maintenance cost The cause of the failures should be further investigated since there currently is inadequate data to determine the cause The motor design may be inappropriate for variable frequency drive controllers The alternating voltage as output by the controller may be too irregular in aaaition, the long Leads from controller to pumps may attow the development of overvoltages Recommend that the manufacturer of the controller be contacted regarding the problem as well as the motor manufacturer Analysts of the motor winding failure mode should be provided Furthermore, suggest that, for the pump motors running at or near full frequency, Technology is the general action or process in place at the site The technology is implemented by combinations of one or more components Several technologies can be used simuttaneously Examples include Ground Water Extraction Soil Vapor Extraction,Landfill Covers,etc Components are pieces of equipment facilities,or actions that serve a particular purpose to extract contain or treat the contaminants as part of an applied technology Examples include wells,piping,air strippers,carbon treatment,thermal treatment units a monitoring program treated water discharge,etc 06/07/99 Page 9 of 14