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RESPONSE TO COMMENTS (December 2010) <br /> DRAFT WORK PLAN FOR GROUNDWATER MONITORING WELL INSTALLATION, SOIL GAS AND GROUNDWATER INVESTIGATION,AND <br /> GROUNDWATER MONITORING, October 2010 <br /> Army Aviation Support Facility, 2000 Stimson Road, Stockton,CA <br /> OTIE Contract Number:W91238-09-D-0017, DO 0004,Amendment 01 <br /> tt Doc. Source Section/Page Comment Response(Contractor) <br /> 2 WP CVRWQCB Page 6, Section This section discusses the results for Boring B-28, but this Figure 3 and Figure 4 were updated with the <br /> 2.3 boring is not shown on the referenced figure. Add this approximate location of existing boring B-28. <br /> boring to Figure 3. <br /> 3 WP CVRWQCB Page 8, Section Revise this description of the groundwater monitoring well Revised as requested. <br /> 3.3 installations to indicate water-tight lockable well caps or <br /> plugs will be used. <br /> Also, this section should indicate the proposed well <br /> screen interval from 30 to 60 feet bgs may be modified <br /> based on the data collected from the investigation <br /> borings. If solvents rather than petroleum hydrocarbons <br /> are the primary contaminants of concern in the <br /> groundwater,then the proposed screen interval may not <br /> be optimal. <br /> 4 WP CVRWQCB Page 11, Section Extensive soil vapor sampling is proposed in the Draft Revised as requested. <br /> 3.7.2 Work Plan, but the discussion of soil vapor sampling <br /> procedures is lacking in details. It is not sufficient to state <br /> CANG will follow Cal EPAs Draft Advisory—Active Soil <br /> Gas Investigation(March 2010). Revise this section to <br /> discuss shut-in testing(vacuum test), purge volumes, <br /> purge volume testing, leak testing,the frequency that <br /> duplicate samples and blank samples will be collected, ... <br /> etc. <br /> Based on problems recently observed at other sites, <br /> Central Valley Water Board staff recommends use of a <br /> shroud and portable instrument that can quantify the <br /> tracer compound selected for leak testing, so any loose <br /> fittings can be tightened or replaced prior to sample <br /> collection. Without these additional measures, CANG <br /> may incur significant remobilization costs. Per the Draft <br /> Advisory, if the tracer compound is detected in Summa <br /> samples at concentrations that exceed the target VOC <br /> reporting limits by a factor of 10 or greater,the results <br /> may not be defensible and resampling is recommended. <br /> 4 <br />