CURRENT STUDIES  

The USGS currently is conducting a 5- to 6-year (investigation has been extended) integrated hydrologic, geologic, and biologic investigation of the possible effects of mining in the new exploration area. This investigation was initiated in October 2000. The Viburnum Trend, an area of active lead-zinc mining located about 30 miles north of the exploration area, offers an ideal laboratory for assessing potential environmental effects of mining in the new exploration area. Because geologic conditions and mining practices in the Viburnum Trend are similar to geologic conditions and likely mining practices in the exploration area, the results of environmental studies on the effect of mining in the Viburnum Trend are transferable to the exploration area.

The planned investigation includes onsite studies of stream, spring, and aquifer hydrology, field geologic mapping, geochemical research on the mobilization of trace elements during the mining of lead-zinc ore, the effect of tailings piles on stream water and sediment quality, surveys of stream biological quality and lead accumulation by aquatic biota, and research on the toxicity of lead and other heavy metals to aquatic biota. This investigation will be conducted by a USGS multi-discipline scientific team.

Big Spring and Greer Spring currently are being studied to determine the physical and chemical characteristics of the springs. Physical characteristics include the extent of the spring recharge areas, spring discharge rates, storage capacity, water turbidity, and ground-water residence time. The methods of investigation include measurements of discharge, turbidity, temperature, and specific conductance in the spring branches. Water-level mapping and dye-tracing are being used to better define the spring recharge areas and measure ground-water travel time. Automatic and manual samplers are being used to collect water samples for chemical analysis. Chemical characteristics being studied include estimates of the rate of carbonate rock dissolution in the spring conduit systems. The information will be useful for evaluating the potential for spring degradation by lead-zinc mining and other human activities.

The St. Francois confining unit is present in the new exploration area and in the Viburnum Trend. To help assess the degree to which the St. Francois confining unit [Geohydrologic Setting] is a hydrologic barrier to ground-water flow between potential mining horizons and the St. Francios aquifer and the surficial Ozark aquifer, the hydraulic properties of the St. Francois confining unit in the Viburnum Trend also is being measured.

Lead-zinc mining has been occurring in the Viburnum Trend area since the 1960's. Although no substantial regional water level declines have been observed in the surficial Ozark aquifer as a result of mining, there was insufficient evidence to state that mining has not lowered ground-water levels. There is evidence that ground-water levels have locally declined in the vicinity of some improperly sealed vent shafts. An investigation currently is underway to assess the impact of mine dewatering on ground-water levels in the surficial Ozark aquifer in the Viburnum Trend area.