SITE INFORMATION AND CORRESPONDENCE

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Mr. Stewart Black - 3 - 28 February 2017 Outside of the influence of the Lesco site, arsenic and vanadium are also present in groundwater to the west. The July 2015 Technical Memorandum - Distribution of Dissolved Arsenic in Groundwater at Rough and Ready Island, West Complex, Rough and Ready Is- land, Port of Stockton (Arsenic Report) showed that 14 shallow monitoring wells on Rough and Ready Island, which lies across the San Joaquin River about 700 feet west of Lesco, contained at least 3 consecutive quarters of dissolved arsenic at an average concentration of 386 ug/L. Furthermore, the Arsenic Report showed that at least 6 monitoring wells had maximum arsenic detections above 600 ug/l. In a 16 March 2016 letter, Central Valley Wa- ter Board staff concurred that the arsenic data in the Arsenic Report appeared to be log- normally distributed and that the higher arsenic concentrations do not appear to be outliers. Because the Lesco site is near Rough and Ready Island and in the same geologic environ- ment, and arsenic was not known to be handled at the fertilizer facilities, Regional Board staff believe that the arsenic found at the Lesco site is naturally occurring. Figure 3 illustrates the distribution of average concentrations of dissolved arsenic at Rough and Ready Island and at the Port of Stockton. Dissolved vanadium was analyzed in 3 shallow monitoring wells at concentrations ranging up to 65 ug/L. Vanadium is also present in subsurface native soil at the Lesco facility at concentrations between 16 and 47 mg/kg. Vanadium also was not known to be handled at the fertilizer facilities, therefore these compounds are also believed to be naturally occurring and not attributed to historical operations. Pesticides Site-wide soil sampling conducted in 2005 and 2006 did not detect chlorinated herbicides or organophosphorus pesticides. However, two of 38 samples contained benzene hexachlo- ride, both of which were removed in the excavation. One sample that was not excavated contained 62 ug/kg dieldrin at two feet bgs, which exceeds the residential soil screening lev- el of 34 ug/kg, but is below the industrial screening level of 140 ug/kg (June 2015 USEPA Regional Screening Levels). DDE and DDT were found in this sample at 103 and 117 ug/kg, respectively, which are below residential screening levels of 2,000 and 1,900 ug/kg. The location of this sample is south of the former truck scale on the boundary be- tween two parcels. The soil samples obtained from 6 feet bgs at this location did not contain pesticide contaminants. Because fewer than 3 percent of the soil samples contain pesti- cides that remain in site soils, herbicides and pesticides do not appear to be constituents of concern at this site. Rationale Deere & Company excavated about 10,800 tons of soil from a footprint of about 29,000 square feet. The excavation removed about 4,200 pounds of nitrogen and about 1,900 pounds of sulfate to depths ranging from 2.5 and 7.5 feet below ground surface. Although sulfate and nitrogen remain in shallow groundwater beneath the site, on-site sources of nitrogen and sulfate in the soil have been removed. Concentrations of sulfate are decreasing in the monitoring well furthest from the adjacent bulk sulfur handling facility, and based on the trend line observed in Figure 2, water quality objectives are expected to be met by 2021. The sulfate concentration in monitoring well MW-4, adjacent to the sulfur handling facility is comparable to sulfate found beneath the sulfur facility and therefore is not believed to be associated with the Lesco facility.