ARCHIVED REPORTS_2018 REV SITE INV WK PLAN+

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Brusca File No. 1370 Page 8 March 1, 2018 Murphy Parkway Property Excavation and Materials Management Plan Arsenic: It is widely considered impractical to evaluate arsenic by comparison to the referenced screening levels since background concentrations of arsenic in native soils often exceed the screening levels by two to three orders of magnitude. More commonly, arsenic concentrations are compared to background/naturally-occurring soil arsenic concentrations for screening purposes. AGE summarized soils metals data from the site area as a part of the site investigation and characterization work (see referenced Site Assessment Summary Report). Based on data presented in the Site Assessment Summary Report, background arsenic soil concentrations occur within a range of non -detect to 8.6 milligrams per kilogram (mg/kg); such a range is not uncommon for alluvial deposits within the Central Valley. Per California Department of Toxic Substances Control guidance for the development of arsenic cleanup goals, the upper limit of the data set (8.6 mg/kg) is selected as the arsenic screening level for evaluation of the stockpiled wastes for reuse at the site.5 It is noted that the soil sample containing 8.6 mg/kg arsenic at the site was collected from Test Pit T129, situated on the subject parcel over 800 feet southeasterly of the areas historically subject to waste handling, and, as such, is appropriate for background arsenic determination. Petroleum Hydrocarbons: The listed USEPA-RSL values for total petroleum hydrocarbons are defined by carbon ranges (fractions) that are not typically reported via the EPA Method 8015B test method. As such, for reuse purposes any detected petroleum hydrocarbon concentrations will be compared to San Francisco Bay Regional Water Quality Control Board (SFBRWQCB) Environmental Screening Levels (ESLs) for commercial/industrial shallow soil exposure.6 In the event that soil sample data from any of the stockpiled waste materials exhibit laboratory data exceeding hazardous waste criteria or the screening levels cited above, additional sampling of the relevant 250 cubic yard section(s) of stockpiled waste materials may ensue to further define the portion(s) of the stockpile exhibiting these characteristics. Any stockpiled waste materials that are identified to contain the tested analytes at concentrations exceeding the described hazardous waste criteria or the referenced screening levels will be subject to the offsite disposal procedures described below in Section 6.7. All other removed/stockpiled waste materials will be deemed acceptable for onsite reuse in engineered fills. In addition to the environmental protocol established herein, the stockpiled waste materials will be subject to review by the project Geotechnical Engineer to determine whether these materials are suitable for onsite reuse from a geotechnical standpoint. 6.7 Removal/Offsite Disposal of Any Unacceptable Materials Identified at the Property In the event that the laboratory testing and evaluation (as described in Section 6.6) demonstrate that removed/stockpiled waste materials contain chemicals of concern at levels that warrant removal from the property for offsite disposal, written approval/acceptance of the materials from ' Department of Toxic Substances Control; "Arsenic Strategies, Determination of Arsenic Remediation, Development of Arsenic Cleanup Goals"; January 16, 2009. 6 San Francisco Bay Regional Water Quality Control Board; "Environmental Screening Levels"; February 2016. BruscaAssociates.com • P.O. Box 332, Roseville, CA 95661 • Phone (916) 677-1470