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Given this geologic framework, the hydrogeology of the area is dominated by local geologic
<br /> structure and limited available outcrop areas for recharge. Where saturated,the Paleozoic
<br /> carbonate rock formations form the aquifer of the London Syncline(Misantoni,2001). Fracture and
<br /> solution permeability are predominant within this aquifer, and are generally unimpaired by
<br /> mineralization or vein fillings(WCA, 1974). The network of ancillary faults in the footwall also
<br /> increases the permeability of the aquifer and they are typically wateryielding(Singewald and
<br /> Butler,1941;Misantoni,2001).In fact, the current flow of water from the London Mine Tunnel
<br /> appears to the direct result of mining through the water transmitting "W"Fault,shown on Figure 3.
<br /> Due to uplift along the London and Mosquito Faults, removal of the Paleozoic sedimentary rocks,
<br /> and emplacement of approximately 40 to 100 feet of impermeable faultgouge along the London
<br /> Fault, the aquifer appears to be limited in areal extent locally to approximately 3.8 square miles as
<br /> shown on Figure 5. The Belden Shale confines the Leadville Aquifer due to its very limited
<br /> permeability,and acts as an aquitard or aquiclude depending upon how thick the formation is
<br /> (WCA, 1974).
<br /> The aquifer is recharged by direct precipitation and snowmelt overAmerican Flats and adjacent
<br /> catchments,but the amount of recharge is subject to debate. Within these areas, recharge to the
<br /> aquifer occurs over outcrops of the Paleozoic carbonate rocks, through outcrops of highly fractured
<br /> porphyry intrusive rocks,and to a limited extent,where the Belden Shale cover is thin and
<br /> fractured or faulted.Different amounts of recharge have been proposed as follows:
<br /> 1. WCA(1974)proposed that the recharge area was limited to an area of approximately 3.5
<br /> square miles,and assuming a 25%recharge rate over this area,estimated that annual
<br /> recharge may be 1,830AF based on an average annual precipitation of 40 inches falling over
<br /> 2,200 acres.
<br /> 2.In contrast,Jehn Water Consultants(1999)reported that the decreed average recharge
<br /> amount of 7.4 cfs or 5,357AF/yr under Case No. W-8314-76 was based on a maximum
<br /> recharge area of up to 10 square miles, or almost three times the area identified by WCA
<br /> (1974). This area included seven square miles of land located in the adjoining catchment
<br /> south of Pennsylvania Mountain.
<br /> WCA(1974)suggested that the recharge rate and volume could be high due to local faulting,
<br /> fracturing,exposure of the synclinal axis,and lack of streams in the recharge areas,but did not
<br /> directly measure the recharge rate during their investigation. Instead, WCA selected a 25%rate
<br /> which in their judgment was consistent with estimates obtained in other similar mountain
<br /> catchments.In addition,the volume ofgroundwater storage in the aquifer is considered significant
<br /> due to the good water quality and trace element analytical results(WCA, 1974;Brown and
<br /> Caldwell,2007),and relatively consistent discharge from the London Mine Tunnel that ranged from
<br /> 682 to 781 gpm between 1992 and 1998(Jehn Water Consultants, 1999;Jehn Water Consultants,
<br /> 2002).
<br /> Based on limited available water level data and outcrop patterns for the Leadville Limestone to the
<br /> south,the smaller recharge area presented by WCA appears to be supported. Groundwater
<br /> generally appears to flow east southeastward toward the London Syncline based on water levels
<br /> obtained in August 2006 from the Leach Well,AF-10,and the Salvator Drill hole at locations shown
<br /> on Figure 1 (Brown and Caldwell,2007). Once the water reaches the syncline,it appears to flow
<br /> southeastward through the permeable conduits down the plunge of the synclinal axis,and either
<br /> flows past or discharges from the London Mine Tunnel(WCA,1974). The tunnel effectively acts as
<br /> a partially penetrating line sink in the aquifer,as shown on Figure 3, with a static elevation of
<br /> 11,328 feet,and locally controls groundwaterflow(Brown and Caldwell,2007).
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