SITE INFORMATION AND CORRESPONDENCE

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n T & Ti Trucking page 4 11396 Hwy 99 Frontage N, Lodi 1,2-DCA, EDB, and MtBE to delineate the'extent of impacted groundwater. Monitoring wells could then be installed with screened intervals constructed through intervals of concern for repeatable groundwater sampling events. In addition to the topics covered in the meeting, EHD presents the following concerns for your continued investigation.'. Once you have adequately ensured that the 'supply well' is monitored and the drinking water is protected from contaminant infiltration, your next priority should be reducing the MtBE groundwater concentrations below 10,000 pg/l as quickly as possible. This will lower the site's'priority and allow you more time (up to 5 years) to complete the characterization and enter into final remediation. One way to possibly reduce the MtBE concentration now would be by groundwater extraction as an interim remedial action. UST regulations define interim remedial action as any phase of corrective action to abate or correct the actual or potential effects of an unauthorized release. This interim remedial action can occur concurrently with any phase of corrective action'or investigative phase. The potential effect, an impact to the 'supply well', qualifies you to contract for interim remedial action. As listed in the Underground Storage Tank Regulations (CCR, T-23, section 2722b[61) "pumping and treatment of groundwater to remove dissolved contaminants" is one of the approved actions. EHD recommends that prior to installing a groundwater extraction well or j pumping from monitoring wells not intended for production, a qualitative pumping test be conducted utilizing the 'supply well',-as a pumping well and the 'unused well' and selected groundwater monitoring wells as observation wells. An extended groundwater pumping test could-provide valuable information to evaluate the migration potential for dissolved MtBE in shallow groundwater to reach:the deeper groundwater that the 'supply well' is screened in. Quantitative pumping tests of each significant impacted'hydrogeological unit should be designed and performed for site characterization purposes, to evaluate the lateral migration potential of impacted groundwater, and to evaluate groundwater extraction as a final remediation option. The pump test should include a continuous and long pumping action from the `supply well', which could mimic any future;and potential increased demands on the well. The periods of operation and production rate of the pumping well should be recorded. The pumped water should be sampled at the conclusion of the test for analysis for MtBE and petroleum and the produced water should be temporarily stored and characterized just prior to disposal. Level loggers should be installed in the unused well and in the three existing monitoring wells and data should be collected to ascertain if continuous deep pumping is.affecting the shallow groundwater or flow direction.