Fig. 1.

Acidity (mg L^{−1}) for the Upper Freeport sites, best-fit first-order decay function (*k* = 0.0273), upper and lower confidence intervals, and, when adjusted so that mean cumulative difference = 0 (*k* = 0.0395), extrapolated to the year 2050. Horizontal dashed line represents the cutoff acidity to begin passive treatment (100 mg L^{−1}). CAD, cumulative average difference; LCL, lower confidence limit; UCL, upper confidence limit.