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Work Plan for Expedited Additional Site Assessment Tracy Corners Shopping Center 3225 North Tracy Boulevard Tracy,California 95376 Partner Proposal Number P14-129814.4 May 5,2015 Page 12 operated as a dry cleaning facility since 1992. Although the current closed-loop dry cleaning machine (installed in 2007)uses a hydrocarbon-based solvent(DF-2000 Aliphatic Hydrocarbon Fluid)for dry cleaning purposes, the prior closed-loop dry cleaning machine (operational from 1992 to 2007), used chlorinated solvents, particularly tetrachloroethene (PCE), during the dry cleaning process. Chlorinated solvents are highly mobile chemicals that can accumulate in soil and groundwater. These solvents,even when properly stored and handled, can migrate into the subsurface as a result of small releases associated with onsite operations. Partner observed two 55-gallon steel drums(one containing new DF-2000 Aliphatic Hydrocarbon Fluid and one containing dry cleaning process waste sludge) adjacent to the dry cleaning machine. Steel secondary containment was noted around the dry cleaning machine. In addition, no significant staining or cracking was observed in the area around the dry cleaning unit or around the hazardous waste storage area. According to the most recent waste manifest on site,Technichem,a licensed transporter of hazardous waste, collects the waste sludge. According to the property manager, a prior subsurface investigation performed in 1999 indicated that soil beneath the dry cleaning tenant space had not been impacted by chlorinated solvents. However, based on the length of time between the prior subsurface investigation and the change from the PCE-based dry cleaning machine to the hydrocarbon-based dry cleaning machine(approximately eight years),the former use of chlorinated solvents represented a recognized environmental condition. Partner completed a Phase II investigation for the Quality Cleaners unit in the Tracy Corners Shopping Center to investigate the potential impact of PCE and related chlorinated volatile organic compounds in sub-slab soil gas as a consequence a potential release or releases from the dry cleaning facility. The work was summarized in Partner's on December 19, 2014 report.The scope of the Phase II Investigation included the installation of four sub-slab soil gas probe samples and analysis of four samples and one duplicate sample for PCE,trichloroethene(TCE),cis-1,2-dichloroethene(cis-1,2-DCE),trans-1,2-dichloroethene(trans- 1,2-DCE), and vinyl chloride. PCE was detected in the four sub-slab soil gas sample and one duplicate sample. The maximum concentration of PCE was 3,300 micrograms per cubic meter(pg/m3);one sample(and the duplicate sample) contained TCE at 350 pg/m3.Soil gas data was used to calculate theoretical indoor air concentrations using the DTSC recommended attenuation factor.Applying the applicable DTSC foundation attenuation factor of 0.05 resulted in a calculated theoretical indoor air concentration of 165 pg/m3 of PCE and 17.5 pg/m3 of TCE. The calculated indoor air concentrations indicate PCE and TCE could be greater than the DTSC recommended value for PCE of 2.08 pg/m3 in the four samples and above the EPA Regional Screening Level (RSL)for TCE of 3.0 pg/main one sample. Due to the presence of PCE and TCE in sub-slab soil gas samples, Partner recommended soil and groundwater be sampled to further assess the PCE and TCE at the subject property. As summarized in Partner's January 27, 2015 report, the sampling detected PCE in groundwater proximate to the Quality Cleaners unit in excess of regulatory screening levels. Specifically, on January 13, 2015, four soil borings were advanced to the south and upgradient of the location of the dry cleaning machine. Three of the groundwater samples contained PCE, the greatest concentration at 30 micrograms per liter (pg/L) from a boring located approximately 100 feet southwest of the dry cleaner machine location. Partner's field personnel discerned that it was possible that the sewer lateral associated with the dry cleaner was to the southern exterior of the dry cleaners suite.