Warm Springs Pond #2 



Climatic setting. The net annual precipitation balance for the 

 Warm Springs ponds (from the MAPS database) is -20 inches, placing 

 these sites mid-range in evaporative intensity when compared to 

 other sites of the intermontane basins. Mean monthly precipitation 

 for the Anaconda climatic station shows a broad summertime maximum. 

 The 3-year running average of annual precipitation was below the 

 long-term average from 1986 through 1992. In 1993 (the year prior 

 to sampling) , precipitation exceeded the long-term average by about 

 8 inches. Regionally, precipitation totals in 1994 were below 

 average . 



Geologic setting. The Warm Springs Ponds are underlain by mill 

 tailings, heavily contaminated historic stream sediments and 

 chemical precipitates deposited by Silver Bow Creek. The ponds are 

 constructed over earlier alluvial deposits of Silver Bow (and Warm 

 Springs?) Creek in the neighborhood of 20 feet in thickness, which 

 in turn overlie Tertiary-aged sediments up to several hundred feet 

 thick. 



Hydrologic type. The Warm Springs Ponds are a complex of 

 artificial impoundments constructed and managed for the purpose of 

 capturing tailings and treating contaminated streams (Silver Bow 

 Creek, Mill Creek and Willow Creek) draining the Butte and Anaconda 

 areas. Water inflows, outflows, routing and chemistry are 

 manipulated in order to meet water treatment objectives. The 

 design and operation of the ponds have been altered significantly 

 in the past 5 years (see below). 



Basin characteristics. Silver Bow Creek and most of the flow of 

 Mill and Willow Creeks carried by the Mill-Willow Bypass enters 

 Pond #3 near the WET78 sample site, where continuous pH adjustment 

 by lime injection occurs. Up to 300 cfs is discharged from Pond 

 #3 by two outflow structures into Pond #2; Pond #3 inflow in excess 

 of 300 cfs is routed back into the Mill-Willow Bypass and out of 

 the pond system. Outflow from Pond #2 discharges to the lowermost 

 channel of the Mill-Willow Bypass and on to the Clark Fork River. 

 No water is intentionally routed to Pond #1, the oldest cell in the 

 pond complex. Seepage from Pond #2 to the downgradient Pond #1 

 occurs, joining precipitation falling on the Pond #1 surface. 

 Ground-water outflow from Pond #1 to the alluvium downgradient also 

 occurs . 



The operation of Pond #2 changed during the 5 years prior to the 

 DHES sampling in order to improve effluent water quality. The 

 stage of Pond #2 has been raised in order to permanently flood 

 areas of tailings which in the past were subject to fluctuating 

 water levels and variable redox conditions. Increased head in Pond 

 #2 appears to have increased ground-water outflow to Pond #1. 

 Prior to raising water levels in Pond #2, the surface was treated 

 with lime to immobilize metals. 



