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Discussion of Figure 7

An autosampler was used to obtain hourly samples before and during a storm that occurred on June 21 and 22, 2001. Six hourly samples, which serve as an indication of background baseflow conditions preceding the storm, were collected before rainfall began. The rainstorm lasted about 14 hours and produced slightly more than 3 cm of precipitation. An additional 21 hourly samples were collected during the period of the storm hydrograph.

Concentrations of arsenic, cadmium, copper, and nickel were substantially higher during the period of pre-storm baseflow than they were during the period of storm discharge. This suggests that some dilution of solute concentrations at the outlet is still occurring during storms. On the other hand, the concentrations of nickel and copper were higher during the storm than the average values of those same elements determined from quarterly samples. In addition, arsenic and lead were detected in several of the storm samples, but they tended to be absent (or below the detection limit) in most of the quarterly samples. On a more positive note, chromium and molybdenum were consistently observed in quarterly samples but remained below the detection limit throughout the period of storm sampling. Taken as a whole, these findings emphasize the uncertainty associated with the chemical composition of the waters discharging at the outlet. This is, in part, because waters originating in the reclaimed area are probably not in equilibrium, and also because the water that discharges at the outlet also receives some flow from seeps that are discharging onto the site from a previously reclaimed area to the northeast.

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