SITE INFORMATION AND CORRESPONDENCE

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Mr. Stewart Black -4 - 28 February 2017 Multiple lines of evidence suggest that the arsenic release is not related to historical practic- es at the Lesco facility. These include the presence of native arsenic in soil, a documented presence of arsenic in shallow background wells, and the possibility that the site has been built on dredge spoils containing metals. Furthermore, the historical record does not suggest that arsenic or vanadium had been handled at this facility. The fertilizer handling operations have ceased, the structures have been removed, the ma- jority of the soil containing pollutants has been removed, and nitrogen concentrations in shallow groundwater have been removed from on-site well MW-4, and are decreasing in the downgradient well MW-3. Therefore, the declining trends are expected to continue, and wa- ter quality objectives are anticipated to be met in 2021. Extent defined Nitrogen in MW-4, adjacent to the excavation, has decreased to the water quality objective, and the same behavior is expected in MW-3, which is about 200 feet downgradient of the excavation. Nitrogen in this well has been decreasing since the excavation occurred. Estimated Residual Mass About 46 pounds of nitrogen remain in soil. This represents about 1.1% of the mass that was removed. Threat to Groundwater Residual material remaining in soil is a low threat to groundwater, based on its mass. Threat to Human Health ❑ Vapor Intrusion Hazard: The soil excavation removed vapor intrusion hazards to future site workers. ❑ Dermal Contact Hazard: The soil excavation also removed dermal contact hazards to future workers. Public Review On 27 October 2015, a 30-day public notice was circulated to landowners and tenants within a quarter mile radius of the site, and other interested parties. No comments were received by 1 December 2015. Summary Based on the above evaluations, the Central Valley Water Board staff concurs with Deere & Company that the remaining residual concentrations of nitrogen and sulfate at the former Lesco facility do not appear to present either a threat to water quality, human health, or the biota.