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2441 W,Charter Way Page 2 Work Plan—Soil Boring Installation ' GPE Project No.667.2 June 21,2013 ' 1.1 SITE BACKGROUND The subject site is an approximately 28-acre industrial parcel, although it currently is vacant. The southern and western portions of the parcel were formerly operated as a landfill by the City of Stockton. This use occurred beginning about 1959, and was closed at least 20 years ago. In 1999, the California Integrated Waste Management Board (CIWMB), which regulated landfills, conducted a limited assessment of the landfill. The following points summarize some key findings of the assessment. • The agency searched for State, County, and City documents regarding the landfill, but found little documentation available to review. ' • The exact footprint of the landfill is not known, especially regarding the northern extent but the total area appears to be 5 to 8 acres. The depth of the landfill is believed to be about 12 feet, but this may be incorrect. The earthen cap is about 2 feet thick and appears to be in good condition. ' • The nature of the fill material is not definitively known, but is reported to be non- hazardous no evidence has been found to indicate otherwise. It appears that for much but not all of the time, fill material was burned on the site before burial although no incinerator was ever present on the site. The relative amounts of burned and unburned material remain unknown. • In 1999, the State agency CIWMB conducted a preliminary soil gas survey to determine if methane gas was being emitted at significant rates. Elevated methane in soil gas was not detected to a depth of 3 feet. It appears that indoor air sampling from buildings on the site is the only air sampling from beyond the immediate limits of the landfill that has ever been undertaken. The indoor samples did not contain elevated concentrations of explosive gas. According to recent groundwater monitoring information from a nearby site at 2941 Navy Drive, the groundwater surface lies about 6 to 10 feet below the natural surface and flows in an easterly direction. The landfill grade is several feet above the natural grade so the depth to groundwater is expected to be about 10 to 14 feet below the existing surface. 1.2 REGULATORY STATUS In California, the CalRecycle agency (formerly California Integrated Waste Management Board) is charged with enforcing laws and regulations pertaining to landfills including closed landfills. The subject site is classified as one of uncertain but relatively low risk regarding migration of hazardous gasses and leaching potential to affect offsite facilities. 2937 Veneman Ave.,#13240 Geo-Phase Environmental Inc. Phone(209)569-0293 Modesto,CA 95356 Fax(209)569-0295