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McBillin Real Estate Investment - 2 - 7 November 2016 2154 S. El Dorado Street Stockton, San Joaquin County Previously, two groundwater zones have been investigated: between 20-40 feet bgs (shallow), and between 80-93 feet bgs (deep). Shallow groundwater has been assessed with shallow monitoring wells, in which depth to groundwater was approximately 22 feet bgs in May 2016. Deep groundwater has been assessed only via borings, and no deep wells have been installed. The proposed scope of work will help to: Assess soil gas concentrations for potential vapor migration to indoor air on the property and to neighboring residences to the east. Delineate the lateral and vertical extent of groundwater pollution to the northeast, east, and southeast to evaluate potential threats to nearby water users. Assess shallow soil concentrations on the property to evaluate potential risks from dermal contact. Assess shallow soil in the vicinity of the former Tank#1 to evaluate if a release from the former waste oil tank occurred. I concur with the proposed scope of work provided the following comments are incorporated: Shallow monitoring wells should be constructed with a 15-foot screened interval, ideally with 5 feet of screen above static water level, and 10 feet below. Please install proposed shallow well MW-13 with 15 feet of screen, and adjust the total installed depth based on field observations, in order to properly target the water table interface. Proposed borings 6-16 and B-17 are approximately 540 feet east and 710 feet southwest, respectively, from previous boring B-7. These distances may be too great to provide useful delineation of groundwater pollution. Please advance B-16 and B-17 approximately 150 feet to the east and southeast of B-7, respectively, and advance two (2) additional borings approximately 150 feet east and southeast of B-16 and B-17, respectively. Grab groundwater samples were proposed to be collected from borings B-14 through B-17 at depths between 55-65 feet bgs, 90-100 feet bgs, and 115-125 feet bgs. These depths do not address possible hydrocarbon impact in shallow groundwater. Shallow groundwater samples should be collected between as close to the water table interface as possible, between 30-40 feet bgs. Additionally, deep groundwater impacts were observed in groundwater collected from borings B-6 through B-8 in four-foot temporary screen intervals ranging between 86-93 feet bgs, with benzene concentrations ranging from 25 micrograms per liter (ug/L) to 760 ug/L. In the Site Assessment Work Plan, AGE indicates that groundwater samples will be collected from proposed borings B-14 through 13-17 between 90-100 feet bgs. These groundwater samples should be collected at similar depth intervals to those collected in 13-6 through B-8, from the most permeable soils between 85-95 feet bgs. The deepest proposed groundwater collection depths in B-14 through B-17 are between 115- 125 feet bgs. As benzene concentrations were reported in B-14 through 6-17 as high as 760 ug/L at 90 feet bgs, deeper groundwater should be assessed. However, the proposed depths appear to be excessive. These deepest samples should be collected from the most permeable soils encountered between 105-115 feet bgs. Please collect grab groundwater samples from borings B-14 through B-17, as well as the two (2) additional borings requested in Comment 2 above, from 30-40 feet, 55-65 feet, 85-95 feet,