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MW-8, and the "necking" of the contours (Figure 25) caused by this decline coincides spatially extremely well to the flexure in the groundwater elevation contours in Figure 15 around these wells. The flexure indicates a slight eastward slope to the water table near these wells, which would explain the decrease in concentration. Samples were obtained from the three wells at the Kwikee site in May 1998, and the drop in concentration since the wells were last sampled in 1995 is astonishing. Although the 10-foot rise in the water table that occurred during this period may be partly responsible for this decline, there is little doubt that more than two years of northward or westward groundwater flow away from the Kwikee site is also involved in the decline in these concentrations. The drop in the concentration in KF-1 is partly responsible for the"pinching" of the TPH-g contours in a north-south direction at the Kwikee site, creating a slight east-west trending concentration axis that extends all the way to MW- 4. Even more extraordinary than the changes in the Kwikee wells is the tremendous decline in the concentration in MW-9. In less than 12 months, the concentration declined from 15,000 ppb to less than 50 ppb. Almost certainly, both the reversal in groundwater flow direction and the rise in the static water level had a role in causing this rapid attenuation. 4.5 Onset of Eastward Elongation. 1999 The shape of the groundwater plume evolved further in late 1998, and by the beginning of 1999 the northeast-southwest orientation had smoothed out considerably (Figure 26). Between MW-5 and MW-1, groundwater flow was slightly northeastward (Figure 16) and the plume was slightly elongate in that direction near MW-1, but elsewhere the flow was eastward or southeastward except along the east side of the mapped area, where flow was to the southwest. The confluence of eastward and westward flow in the central portion of the Kwikee site had the effect of transporting gasoline across Franklin Street to KF-3, extending the east-west concentration axis that had begun to develop but was less prominent in mid-1998. As previously discussed in section 2.4.3, southeastward flow in 1999 is also thought to be responsible for the secondary concentration peak that was observed in MW-6, as hydrocarbons dispersed from the Chevron site across Franklin Street to this well. Unfortunately, this peak is not reflected in Figure 26, because the concentration reported in February 1999 was anomalously low (1-5% of previous and subsequent quarters), as noted in section 2.4.3. 4.6 Plume Rotation and Migration: 2000 The plume elongated further in 2000, and the east-west axis replaced the north-south axis as the dominant feature (Figure 27). In addition, it rotated 50 clockwise on this axis, as inferred from the increase in the TPH-g concentration in MW-6 and the decrease in KF-2 and KF-3. Also, gasoline was detected in the southern part of the Kwikee site when KF-5 was installed, and concentrations in this well surpassed those in KF-3. 17