ARCHIVED REPORTS_2018 VERIFICATION RPT (DEC)

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Brusca File No. 137-002 Page 8 December 14, 2018 Murphy Parkway Property Waste Materials Management Verification Report the highest total metals results (the actual average DI WET arsenic concentration in the stockpiled materials likely is less than 0.02 mg/L), and the mass calculation assumes that all soluble arsenic in the stockpiled materials leaches to groundwater. Despite the foregoing that suggests that the soluble arsenic, chromium and lead detected in the stockpiled materials removed from WU1 are not likely to represent a significant leaching threat to shallow groundwater quality, as a highly protective and conservative measure we proposed specific procedures to be implemented during the onsite reuse of these materials to mitigate leaching potential. The proposed measures were presented in a Waste Materials Reuse Workplan (Revised Final) dated May 23, 2018.9 Specifically, we proposed that the stockpiled materials removed from WU1 be placed beneath the concrete floor slab of the planned building on the property (and to a lesser degree, beneath planned concrete pavements) so that these materials are not subject to rainwater infiltration and related leaching potential. Additionally, we specified that the materials removed from WU1 would be placed within the upper one-foot of the subgrades beneath the floor slab and concrete pavement sections mentioned above since these subgrades were planned to be treated with cement as a part of construction activities to enhance the engineering/strength properties of the subgrades. The cement treatment of these materials was considered as an additional protective measure to reduce the leaching potential of metals in the materials. It is well recognized that cement treatment of soils can mitigate leaching potential of heavy metal ions by providing both physical resistance to leaching and by creating an elevated pH environment. The cement treatment process results in an impermeable monolith that substantially reduces surface area available for leaching. Moreover, the increased pH of the treated material (caused by alkali nature of Portland cement) limits the solubility of metals. As such, incorporating the materials from WU1 into floor slab and pavement subgrades treated with cement affords an even greater reduction of the potential for leaching of soluble metals in these materials. Following the placement of the WU1 materials beneath the building floor slab (and to a lesser degree beneath concrete pavements) and the treatment of these materials with cement, the potential for leaching of metals from these materials to groundwater is considered to be negligible. Specific measures for the placement and cement treatment of the WU1 materials were presented in the referenced May 23, 2018 Waste Materials Reuse Workplan. The Waste Materials Reuse Workplan was approved by the SJCEHD CVRWQCB and the prior to implementing the waste reuse activities at the site. 6.0 REUSE OF WU1 MATERIALS 6.1 Notification The SJCEHD, the CVRWQCB, and CalRecycle were notified of the work schedule at least one week prior to the onset of construction activities at the site that involved the relocation of the stockpiled materials from WU1 and the placement of these materials within building pad and pavement subgrades. 9 Brusca Associates, Inc.; “Revised Waste Materials Reuse Workplan, Murphy Parkway Property, APN 198-120-009, 17100 Murphy Parkway, Lathrop, San Joaquin County, California”; May 23, 2018.