Methods for the Estimation of Mine Infiltration. Bruce Leavitt PE PG, Consulting Hydrogeologist Washington, Pennsylvania. Mine Infiltration h as been used to: Estimate inflow during mining; Calculate the rate of mine flooding; Estimate post closure mine discharge; and
Bruce Leavitt PE PG, Consulting Hydrogeologist
Project mine discharge from underground mines for mine water utilization under varying amounts of annual precipitation.
Project groundwater discharge from surface mine backfills in support of stream mitigation.
mines gaining water from barriers
"average" inflow rates
mines losing water to barriers
Large quantities of water are discharged annually from flooded mines in the Pittsburgh Basin.
The bulk of this water is untreated.
Water quality has improved over time.
The flooded mines of the Pittsburgh Basin represent the second largest aquifer in the region.
Utilization of this water could benefit industrial water users, and reduce the environmental mining legacy.
Recharge inches =
( Precipitation (October – May) – 6.68 inches) * 0.27
Average Killing Frost – October 1
End of Recharge – May 31
Surface mining operations are being required to provide mitigation for stream values that are lost due to the mining operation.
One mitigation option is to create a constructed stream segment to replace the lost stream.
Discharge from mine spoils, either back stack or valley fill, can be used as a water source for the mitigation.
An estimate of discharge from mine spoils is needed to project the flow and duration of flow from these designs.
The Rule of Thumb method is not appropriate in this application.
Precipitation data obtained from Messinger and Paybins, 2003
Daily stream flow data downloaded from USGS Web site.
Minimum 0.5 inches of rain in a 2 day period.
Base flow proportionally increased from pre rain level to the post rain level either 3, 4, or 6 days following the rain event.
Three Outliers: two were months of normal precipitation preceded by a month of abnormally high precipitation.
The outliers skew the regression to a higher flow rate.
Equation with outliers removed:
Q = 0.405e0.130P
Where: Q is gpm per acre and P is monthly precipitation.
The Rule of Thumb is quick and easy, but is only appropriate for surface mines and even then may be significantly in error.
The Leavitt 1996 method is based on Pittsburgh seam unflooded underground mines and is not appropriate at less than 200 feet of overburden.
The McCoy method is appropriate to flooded Pittsburgh seam mines, but places a lower limit on the infiltration rate despite overburden thickness.
Surface mine hydrographs show significant response to precipitation, while the hydrographs from underground mines do not.
Surface mine recharge can occur any time there is sufficient precipitation.
Recharge to underground mines is negligible during the growing season and can be delayed until the soil has been resaturated.
Estimation of the amount of groundwater available from surface and underground mines based on precipitation is possible.