Ground-Water Levels in the Ozark Aquifer along the Viburnum Trend, Southeastern Missouri, 2001-05

During 2001, eight monitoring wells were installed along the Viburnum Trend to determine if dewatering of lead-zinc mines in the St. Francois aquifer affected water levels in the surficial Ozark aquifer. The well locations were chosen specifically to investigate the effects of different mining scenarios. Before data collection, much of southern Missouri, including the Viburnum Trend area, experienced a drought that began in late 1999. Dry conditions existed in the area until early 2002, about the time data recorders were installed in the monitoring wells.

The water-level data indicate no long-term, continuous water-level declines occurred from 2002 to 2005 at five monitoring wells (VT-2, VT-3, VT-5, VT-6, and VT-7), four of which are over active mining areas. Conversely, these five wells had increasing water levels with time. Another well (VT-4) placed over an active mining area, did have a long-term water-level decline (about 30 foot) that developed during the study. On a local scale, the water-level data from this well reinforces conclusions of previous investigations that report small areas of drawdown in the Ozark aquifer may be present along the Viburnum Trend as the result of mine dewatering.

A monitoring well (VT-1) installed over an abandoned mine where flooding is occurring showed an increasing water-level trend. Another well (VT-8) installed in an area where mining was expected to occur after well installation showed a lowering ground-water trough in 2004 and 2005. Comparing monthly precipitation and daily mean water-levels differences at these two wells indicates that for most of the period from 2002 to 2005, the converging water-level difference that occurred can be explained by local precipitation differences rather than being mining induced. Local precipitation differences, however, do not explain the 15-foot decrease in water-level difference that was observed during the period January through June 2004.