FIG. 4. Map showing the position of Lines 1 and 2 relative to the approximate free light nonaqueous-phase liquid plume extent (shown in gold) based on monitoring well data. The monitoring well locations are indicated by black dots. The yellow contour indicates the distribution of the maximum plume thickness under low water table conditions and shows heterogeneity in contaminant transport. A "no data" zone was present near the center of Line 1, preventing continuous imaging from the on-plume to off-plume area. The western section of Line 1 discussed in the text is highlighted in red.