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The static water level is within a few hundredths of a foot of what it was last year at this time With an average depth of 46 feet, the static level is within the most contaminated portion of the Modesto aquifer The calculated water table elevations were used to construct the groundwater gradient map in Figure 3 A slight north or northeastward slope is apparent, but is interrupted by a slight depression around GT-10 The static water level in this well would have to be raised 0 22 feet to remove this depression and create a smoothly sloping piezometnc surface Because the bottom of the screened interval in this well (60 feet) is within the low-permeability zone at the contact between the Modesto and Riverbank formations, it is possible that the static level is depressed in GT-10 because of this semi-corifirung layer That is, the static water level is below the piezometric level because groundwater is unable to rise through the aquitard to reach the piezometric level The aquitard does not affect the water level in the other wells, which are drilled through it and are screened in the Riverbank aquifer Electrical conductivity, temperature, and pH data from the Modesto and Riverbank aquifers exhibit slight differences that appear to support the suggestion that the Modesto Aquitard forms a semi- confining layer for groundwater (Appendix A) The electrical conductivity of water purged from GT-10 was approximately 200 units above that in GT-1, and the water temperature was approximately I degree Centigrade warmer than water purged from GT-I and GT-6 The pH of water purged from GT-10 was slightly acidic (6 83-6 97), whereas the pH of water purged from GT-1 was slightly alkaline (7 49-7 52) and water from GT-6 is approximately neutral (6 82-7 14) Since GT-10 is screened within the Modesto Formation, GT-1 is screened within the Riverbank Formation, and GT-6 is screened within both, the results suggest that water in GT-6 is a mixture of two water masses that have slight differences in chemistry If water in the two formations is indeed separated by the Modesto aquitard, then the water in GT-10 is perched within the Modesto aquifer channel 3.2 Analytical Results Gasoline and BTEX compounds were detected in GT-10 at concentrations that are very close to those that were measured during the first quarter of 1999, when the water depth was the same In contrast, diesel was detected at a much lower concentration, and in the other wells it was either detected at lower concentrations or was not detected at all (Table 2) Why TPH-g concentrations would remain unchanged while TPH-d concentrations would simultaneously decrease is unclear 4.0 CONCLUSIONS AND RECOMMENDATIONS The groundwater gradient and flow direction continue to fluctuate over a large range of compass directions A northward flow direction has been measured during the first quarter in more than one year, whereas a southward or westward flow direction appears to be more common later in the year It now appears likely that groundwater flow within the Riverbank aquifer is different from flow Swithin the Modesto aquifer, which means that the migration of contaminants within the Modesto 3