Several types of data are needed to assess the flux of Cr(VI) from the excavation into the groundwater. As described in this plan, these data include 1) temporal Cr(VI) data in the shallow groundwater beneath the pit; 2) hydrologic data to interpret groundwater flow and contaminant transport; 3) hydraulic gradient data; and 4) as a contingency action if necessary, vertical profiling of Cr(VI) concentrations in the shallow aquifer beyond the depth possible with aquifer tubes.