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• EXECUTIVE SUMMARY The depth to groundwater was measured and water samples were collected from five monitor wells and the Gillies domestic well on April 4, 2000 One of the monitor wells had been buned under road aggregate during recent grading activities and could not be located, and the monitor well on the adjacent property could not be accessed because the property owner was not present The depth to groundwater in most wells was almost exactly the same as it was in April of 1999, and ranged between 45 and 47 feet As was true in April 1999, the groundwater flow direction is somewhat difficult to interpret and multiple interpretations are possible, but we favor the interpretation that the flow direction is to the northeast, toward the Gillies domestic well However, the static water level is slightly depressed in the vicinity of GT-10, which is the only well that is not screened within the Riverbank aquifer This suggests that the water level has not risen to the piezometnc surface in GT- 10 because of flow retardation by the Modesto aquitard, which overlies the Riverbank aquifer If this is the case, then the water in GT-10 is perched within the Modesto aquifer above the aquitard and is not in free communication with water in the Riverbank aquifer Electrical conductivity and pH data provide some support to this inference water in GT-10 has a lower pH and higher conductivity than water in the deeper wells (e g GT-1), and water in the wells that are screened within both aquifers (e g GT-6) appears to be intermediate in pH All samples were analyzed for TPH-diesel, and the sample from GT-10 was also analyzed for TPH- gasoline and BTEX Diesel was detected only in two of the five samples, at concentrations that were lower than in April or December of 1999 Gasoline was detected at 1,800 µg11 (parts per billion) in GT-10, and all of the BTEX compounds were also present 1