COMPLIANCE INFO - Laserfiche WebLink

Home Browse Search

Pilot Study Workplan May 25, 2018 Diamond Foods Inc. Page 8 concentrations, the total calcium and total chloride results did exceed their respective background concentrations. In November 2001 and January 2002, ATC advanced borings SB1 through SB9. The borings were placed in locations upgradient and downgradient from the closed vaults to evaluate the lateral extent of impacted soil. Hexavalent chromium was detected at relatively low concentrations in soil samples from borehole locations SB1 through SB9 from the 20 and 40-foot depths with the exception of SB8 at 40 feet. The highest concentrations of hexavalent chromium were detected in the samples from off-site boring SB9 at 1.5 and 2.6 milligrams per kilogram (mg/kg). Concentrations of hexavalent chromium in the samples from borings SB1, SB2 and SB3 ranged from 0.09 mg/kg to 0.61 mg/kg. Concentrations of hexavalent chromium were lowest in borings SB4 through SB8, ranging from 0.0010 mg/kg to 0.0074 mg/kg. Hexavalent chromium was not detected in the soil sample from SB8 at 40 feet bgs above method detection limits. The Total Threshold Limit Concentration (TTLC) for hexavalent chromium compounds is 500mg/kg. Hexavalent chromium was not detected in any soil samples collected from borehole locations MW-4 through MW-8 from the 40 and 50-foot depths. The three samples collected from SB10 were analyzed for alkalinity by EPA Method 310.1, ammonia by Standard Method 4500, nitrate by EPA Method 300, total organic carbon (TOC) by ASTM D2974, Hexavalent chromium by EPA Method 7199, volatile organic compounds by EPA Method 8260B, and arsenic, total chromium, copper, total iron, total manganese, and zinc by EPA Method 6020. The three soil samples collected from SB11 were analyzed for hexavalent chromium and total chromium. Results of previous site assessments show that the extent of impacted soil is limited to the immediate vicinities of the closed vaults. 3.2 POLLUTANTS IN GROUNDWATER The monitoring well network at the site consists of nine wells screened in the shallow aquifer (MW-1 through MW-8 and MW-10) and one well screened in the deeper aquifer (MW-9). Quarterly or semiannual monitoring has been performed since the wells were installed. Historically, the most impacted well at the site was MW-3, located adjacent to Vault 8. Following pilot study activities hexavalent chromium detected in the well has decreased to concentrations less than laboratory reporting limits and have not rebounded after a period of over two years. The reported concentrations of hexavalent chromium in the remaining monitoring wells sampled exceeded the California Department of Public Health public health goal (PHG) 0.00002 mg/L. In March 2018, the highest concentrations of hexavalent chromium in monitoring wells were reported in MW-5 (0.094 mg/L), MW-7 (0.025 mg/L) and MW-10 (0.021 mg/L). Additionally, the reported hexavalent chromium concentrations detected in the pilot study wells OBSW-S and OBSW-D were 1.300 mg/L and 0.11 mg/L, respectively. While these are currently the most impacted wells at the site, the concentrations in the observation wells are exhibiting an overall downward trend since the injection of calcium polysulfide into the groundwater formation. Historical depth to water data is summarized in Table 1. Historical groundwater analytical data is summarized in Tables 2, 3, 4 and 5. Figure 4 shows the lateral distribution of hexavalent chromium in groundwater at the site.