SITE INFORMATION AND CORRESPONDENCE_FILE 2

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Gene Conti 29 June 2015 Regarding Pending Case Closure for Gillies Trucking Page 2 of 3 3931 Newton Road Groundwater monitored by the wells cited above generally have contaminant concentrations that are below the laboratory analytical method quantification limits, the exception being monitoring well GT-32, which recently (January 2015) yielded groundwater sample containing 100 micrograms per liter (Ng/1) total petroleum hydrocarbons quantified as diesel (TPHd), which in this case is considered to be near the margin of the plume; other chemicals of concern (CDCs) such as benzene, ethylbenzene, or methyl tert-butyl ether (MTBE) were not detected in the sample from this well when last analyzed for those constituents (January 2011). While it is possible that some dissolved diesel has migrated past the eastern margin of the subject site at an approximate depth of 65 feet below surface grade or greater, the data indicate that it is at low concentrations and does not contain significant concentrations of the compounds with quantified health risk and hazard. The former domestic wells on the Gillies site (now destroyed) were sampled and analyzed for COCs; the initial onsite domestic well was impacted by dissolved diesel in June 1999 (3,300 pg/1) and in March 2001 (64 pg/1), but was otherwise not impacted again until it was destroyed. The other onsite domestic water well, designated GT-WSW1, was impacted by TPHd at 120 pg/I and total petroleum hydrocarbons quantified as motor oil (TPHmo) at 250 pg/I in March 2008 and by total petroleum hydrocarbons quantified as gasoline (TPHg) at 170 pg/I in January 2009, but was then not impacted during the ensuing nine monitoring events until its destruction in 2014. A water supply well on one of your parcels, designated GT-WSW2 in the recent Gillies reports, has been sampled twice, the most recent in 2010, and the groundwater it produced was not impacted either time by detectable concentrations of dissolved hydrocarbons. The data, as a whole, has lead the Gillies Trucking consultant to conclude: 1) that while there is still contamination on the Gillies site, it is unlikely to pose a significant threat to human health or the environment; and 2) that the case should be considered for closure. In this the EHD and the Central Valley Regional Water Quality Control Board (CVRWQCB) have concurred. Removal of the estimated 14,060 pounds of contaminants from the site does not mean that all significantly impacted soil and groundwater were removed; it is estimated that on the order of 42,500 pounds of contaminants remain on the site. Most of this is inferred to be stuck to grains of soil and naturally occurring organic matter in the soil and is not very mobile at this time, as evidenced by the trend of declining contaminant concentrations in groundwater monitored on the site. The subsurface of the Gillies property has been impacted by the unauthorized release from the former UST system since at least 1989, or at least 26 years. As the contaminant mass is not known to have impacted your well during that time and the contaminant mass is declining under the effects of natural attenuation, it seems increasingly less likely that the plume will impact your well in the future. The EHD cannot issue a letter certifying that this site has no remaining contaminants as it is actually known to have contaminants as described above, but even if it was thought that no contaminants remained the EHD would not issue such a letter. The EHD does point out that the SWRCB issued a draft Review Summary Report, signed 29 December 2014 (but not issued in final form), in which the SWRCB recommended case closure for the site; and that the responsible party's consultant recommended case closure, to which the CVRWQCB and the EHD concurred.