ARCHIVED REPORTS_2018 VERIFICATION RPT (DEC)

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Brusca File No. 137-002 Page 7 December 14, 2018 Murphy Parkway Property Waste Materials Management Verification Report 5.0 WU1 MATERIALS REUSE EVALUATION AND WORKPLAN Per the provisions of the approved EMMP, the laboratory data from the samples of stockpiled materials removed from WU1 were evaluated to determine whether these materials are acceptable for onsite reuse in engineered fills during site development. As shown on Tables IV, VI, and VII, none of the 49 samples of the stockpiled materials from WU1 contained total metals, petroleum hydrocarbons, PCBs, SVOCs or dioxins/furans at concentrations above the commercial/industrial screening levels established in the EMMP (or in the case of arsenic, above the site-specific background concentration of 8.6 milligrams per kilogram established in the EMMP). Additionally, none of the results exceeds hazardous waste criteria established in the California Code of Regulations (CCR) Title 22, Division 4.5. As such, these results indicate that the stockpiled materials from WU1 are acceptable for onsite reuse. Additionally, the project geotechnical engineering firm (Raney Geotechnical, Inc.) observed the stockpiled materials and determined that the materials were acceptable for onsite reuse from a geotechnical standpoint. Reuse evaluation for the materials removed from WU1 included consideration of the potential for future impact to groundwater as a result of possible leaching of metals from the materials. As shown on Table V, the DI WET concentrations from the tested samples for the majority of the Title 22 metals do not exceed California Maximum Contaminant Level (MCL) drinking water concentrations. However, the concentrations of DI WET arsenic, chromium and lead concentrations detected in most of the samples exceed the MCL values. We noted that several groundwater samples have been collected and tested beneath the WU1 area as a part of past site assessment work, and none of the groundwater samples from this area have contained lead or chromium at concentrations above their respective MCL values, despite the fact that waste materials were handled and stored in this area for several decades starting in the 1960s (and during operation of the PNA facility, much greater volumes of wastes were stored in this area than were removed during the recent waste management work). As such, it does not appear likely that the chromium and lead in the removed/stockpiled waste materials represent a significant threat to groundwater quality. It is noted that elevated concentrations of arsenic (above the MCL value) have been detected in groundwater at various locations beneath the subject property, including beneath the WU1 area. However, in general, the distribution of elevated concentrations of arsenic in groundwater beneath the site is somewhat erratic, and some of the groundwater samples collected beneath WU1 in the past have not contained elevated concentrations of arsenic. It is known that naturally-occurring elevated concentrations of arsenic exist in groundwater in other areas of San Joaquin County, and the arsenic detected in groundwater beneath the subject property may also be naturally occurring. To further evaluate the leaching potential of arsenic in the stockpiled materials removed from WU1, we compared the estimated mass of the DI soluble arsenic contained in the stockpiled materials to a potential volume of receptor groundwater beneath the site. Based on an average DI WET arsenic concentration of 0.02 milligrams per Liter (mg/L), and recognizing that the DI WET test utilizes 50 grams of materials and 500 milliliters of water as an extractant, we calculated the total mass of DI soluble arsenic in the stockpiled materials to be approximately 4,120 grams. Assuming, that the entirety of this mass is leached to groundwater, a saturated zone void ratio of 0.5, and a twenty-foot depth of dispersion and diffusion within the saturated zone, the soluble arsenic mass in the stockpiled materials would represent 0.007 mg/L beneath the 48-acre property; this value is below the drinking water standard for arsenic (0.01 mg/L). This mass calculation likely substantially overestimates potential arsenic impact to groundwater because the DI WET data utilized is from the samples with