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Management of Excavated Materials Generated During WDS Investigations • Excavated materials generated during the site investigations were disposed of offsite. Typically WDS investigations consisting of excavating temporary exploratory test pits or trenches do not require that the excavated materials be disposed of offsite. Wastes excavated during a site investigation are typically temporarily stockpiled in the adjacent to the area excavated and then after the excavation is documented, photographed, logged and samples are collected, it is backfilled in the reverse order that it was excavated. Disposal of excavated materials offsite results in unnecessary project costs related to transportation and disposal. • Photographs of exploratory trenching indicated numerous stockpiled areas and it appears that some of these stockpiles remained at the site for several months. There is no information to indicate whether Best Management Practices (BMPs) were employed to ensure the excavated stockpiled material remained contained. Analytical Testing—Soil and Waste Samples • Based on available documents reviewed, analytical testing from trenches T1 to T23 appears to have consisted of only soil samples from a depth of approximately 5 feet bgs. Based only on reviewing the tables, it appears that analytical data is minimal for trenches T24 through T110 (not adequately described in the text of documents) reviewed and it is not clear whether the samples analyzed from these trenches consisted of soil, soil mixed with wastes or wastes since a summary table, descriptions of materials encountered and trench logs were not provided. Geophysical Survey • Reportedly, a geophysical survey was conducted; however,the report was not available for review. A geophysical survey is typically conducted prior to, or concurrent with, the waste characterization and delineation site investigation to assist with selecting and locating proposed exploratory trenches to delineate wastes. • The results of the geophysical survey are typically presented in the site investigation report and a copy of the report provided as an appendix. In addition, typically the results of the geophysical survey are plotted onto an aerial photograph along with trench and/or boring locations and results and all this information is used to estimate the lateral and vertical extent of wastes. Based on what was available for review,this does not appear to have been conducted. Waste Type(s)and Extent • It appears that initially the WDS investigation was limited to the northern covered waste disposal area and during the course of the project, additional wastes were discovered and the area of investigation was expanded. Based on information provided, the lateral extent of surface disturbances which could be related to waste disposal areas and areas of suspected waste disposal, based on review of available historical aerial photographs appears to be greater than the areas adequately evaluated during the site investigations. Meaning, that it is possible that wastes could be present at other locations that were not investigated. It is understood that the scope of work was limited to the property and that wastes extend beyond what was subject of investigation/remedial action. • Based on the numerous documents and reports reviewed, it appears that there were no concise descriptions of the types of wastes encountered based on the borings and 110 trench excavations, geophysical survey and other background information. There was an absence of information provided in the report text and on figures or tables about the lateral and vertical extent of wastes. WDS investigation (or Preliminary Site Assessment [PSA] reports) should have a section in the document describing the types and extent of wastes. This report section would describe the types Ninyo&Moore 1 500 E.Louise Avenue,Lathrop,San Joaquin County,California 1 104690095 1 August 11,2017 7