Discussion of Table 1:

A time-series regression analysis was undertaken to evaluate the relative roles of rainfall recharge and atmospheric pressure changes in determining water-level changes in the saturated coal refuse near Monitoring Well 7. Two sample sets of equal size (N = 125 days) were selected; one set for the pre-reclamation period when the refuse was exposed at the surface and readily received rainfall discharge, and one set for the post-reclamation period when the refuse was buried beneath the FSS layer and soil cap. The statistical model shown in the table above relates the daily change in the water level (WL) at Monitoring Well 7 to the daily change in barometric pressure (B) and the daily total precipitation (P). Because the data were collected as a continuous time series, the model includes an autocorrelated error term (rho) as well as the usual random error term (µt).

As indicated by the statistically significant t-ratios associated with the regression coefficients relating pressure changes and precipitation to water level changes (** indicates significance at the 99 percent confidence level), both of the independent variables were influencing the water-level changes prior to reclamation. A comparison of the regression coefficients themselves indicates that the effect of precipitation was nearly five times stronger than that of pressure change in the pre-reclamation period. In contrast, the results for the post-reclamation period indicate that precipitation events no longer directly influence changes of water level in the buried refuse. Instead, more than 80 percent (R2 = 0.81) of the variability in daily water-level changes is now attributed to changes in atmospheric pressure. The regression coefficient relating pressure changes to water-level changes is known as the "barometric efficiency" of the aquifer. The barometric efficiency of the aquifer in the refuse increased almost five-fold from the pre- to the post-reclamation period. The high barometric efficiency that now prevails is indicative of a confined aquifer that does not have a free connection to the overlying unsaturated zone.