SITE INFORMATION AND CORRESPONDENCE_FILE 2

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Mr. Ken Gillies • • Page 2 of 3 Gillies Trucking 22 July 2009 3931 Newton Road, Stockton The benefit to the proposed logging of the monitoring wells, beyond possibly tightening the correlations between sand units, is not clear to the EHD. The EHD has reviewed the site data to reevaluate the potential for the deeper sand units to be significant conduits for contaminant migration, and therefore justify obtaining a high degree of confidence with the unit correlations. It appears to the EHD that the deeper units do not function in such a manner and that the main effort at this time should be to mitigate impacted soil in the vadose zone and shallow saturated zone. The basis for this interpretation is as follows: • Figures 5, 6 and 7 of the QMR show that only groundwater in the First Riverbank (FRB) sand unit, nominally 50 to 75 feet below surface grade (bsg) contains groundwater impacted to a degree sufficient for mapping the plume of impacted groundwater, whereas the Second (75 to 100 feet bsg) and Third (100 to 125 feet bsg) Riverbank (SRB and TRB, respectively) sand units do not. • Whereas a majority of FRB well hydrographs in the QMR, and all of the SRB and TRB well hydrographs do not show a correlation between groundwater elevation and contaminant concentration, FRB wells GT-16A, GT-17A, GT-20 and GT-21 do appear to show such a relationship. When groundwater is elevated enough to occur in the Modesto sand unit (nominally shallower than 60 feet bsg), groundwater is intensely impacted in monitoring well GT-10. • Judging average concentrations by eye from the hydrographs, the average dissolved total petroleum hydrocarbons quantified as diesel (TPHd) concentration in the Modesto exceeds 5,000 micrograms per liter (pg/L), and is approximately 200 Ng/L in the FRB, 75 pg/L in the SRB, and is close to the analytical method detection limit of 50 pg/L in the TRB. These observations indicate to the EHD that the SRB and TRB are not likely to be significant contaminant migration pathways if impacted soil in the vadose zone and in the shallow saturated zone is mitigated, thereby reducing the source of contaminants fluxing into groundwater. If the soil is successfully mitigated, the importance of having a high degree of confidence in the correlations of the sand units diminishes; therefore, until a technical justification for the natural gamma-ray and induction logging is provided, the EHD cannot approve the recommendation. The EHD believes that the observations noted above sufficiently demonstrate what the significant problems on your site are; therefore the EHD does not believe that an updated PAR is required at this time. The EHD will certainly reconsider this if presented with additional information and technical argument. As noted above, the work plans to pilot test SVE and to complete the lateral delineation of impacted groundwater have not been submitted to the EHD; the work plans were due on 01 April 2009. Also to comply with Resolution 2009-0042, the EHD will not direct the immediate submission of the work plans until our site reviews are complete, but it may be to your advantage to submit the plans and conduct the SVE test, and possibly initiate the remediation, while groundwater elevation appears to be dropping, thereby increasing the vadose zone and the volume of soil that can be remediated by SVE if the method can be used successfully. If submitted, the work plan(s) will receive the prompt attention of the EHD. Other criteria for site closure were noted in the EHD letter of 23 January Monitoring Reduction and Comment Letter 0709