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Surface and Subsurface Contamination Report Irerracon Sandhu Property Mountain House, California August 12, 2021 Terracon Project No. NA217037 3.5 Current Off -Site Sources of Contamination The following above- or below -ground off-site potential or known sources of contamination were identified from current uses of the surrounding properties: The eastern adjoining property is an active cleanup case due to the release of crude oil to the subsurface from a ruptured pipeline. 4.0 EVALUATION OF IDENTIFIED CONTAMINATION SOURCES Historical Agricultural Land Use — Historically, the site was utilized for row crops from at least 1937 through 2006, which may have included the use of pesticides and herbicides. Most currently used agricultural chemicals do not persist for extended periods of time in the environment if applied appropriately; however, some agricultural chemicals persist in the environment, especially if misapplied. In Terracon's experience, the application of herbicides and pesticides to agricultural fields can leave trace amounts of the compounds in the soil and/or groundwater, that may accumulate overtime due to long-term applications. Crude Oil Pipeline — The crude oil pipeline that transects the northeastern portion of the site represents an environmental concern due to the potential of a release to the subsurface. Crude Oil Release — Based on a review of the regulatory report, Vacant Property Mountain House (23577 South Mountain House Parkway), identified as the eastern adjoining property, is listed on the CLEANUP SITES database. Terracon reviewed the SWRCB online database GeoTracker for records relating to the listing. According to the November 2020 Limited Site Investigation, prepared by Terracon, in December 2013, a piece of farming equipment ruptured a former Chevron crude oil pipeline (now owned by Crimson California Pipeline) and released approximately 31,500 gallons of oil approximately 270 feet east of the site. Terracon collected soil samples from 16 soil borings advanced to 10-30 feet below ground surface (bgs), stockpiles at the southern portion of the property, and from the area near the release and excavation to determine the extent of contamination. Groundwater was not encountered during the investigation. A total of 36 soil samples were collected and analyzed for total petroleum hydrocarbons as gasoline (TPH-g), diesel (TPH-d), and motor oil (TPH-o), volatile organic compounds (VOCs), organochlorine pesticides (OCPs), and chlorinated herbicides (CHs). Soil borings SB1, S67, S610, and S131 1, located in a linear fashion approximately 100 feet east of the site, reported maximum TPH-g and TPH-d concentrations in exceedance of the 2019 Department of Toxic Substance Control (DTSC) screening levels for commercial/industrial soil. Based on the analytical results, Terracon recommended the advancement of additional step -out borings to further delineate identified impacts. Terracon prepared a work plan for additional investigation in April 2021, which was approved by the Central Valley Regional Water Quality Control Board (CVRWQCB) in May 2021. At the issuance of this report, the cleanup case is still on-going. Based on the reported TPH concentrations in exceedance of screening levels for Responsive ■ Resourceful ■ Reliable 9