Milltown Reservoir

Milltown reservoir impounds about 180 acres of water at the confluence of the Blackfoot and Clark Fork rivers (Figure 3). The Clark Fork River at that... 

Figure 3. Map of Milltown Reservoir showing main tributaries and the location of some of the wells used for hydrogeologic and geochemical monitoring. (Data are taken from references 9 and 12.)...

Preliminary work (10) on the transition from oxidized surface sediment to reduced subsurface sediment in Milltown Reservoir showed that the redox transition occurs in the upper few tens of centimeters. Strong chemical gradients occur across this boundary. Ferrous iron in sediment pore water (groundwater and vadose water) is commonly below detection in the oxidizing surface zone and increases with depth. Arsenic is also low in pore water of the oxidized zone, but increases across the redox boundary, with As(III) as the dominant oxidation state in the reduced zone. Copper and zinc show the opposite trend, with relatively high concentrations in pore water of the oxidized surface sediment decreasing across the redox boundary. 

Figure 4. Cross section of Milltown Reservoir site showing the migration of the arsenic plume from contaminated...

Figure 5. Generalized model of groundwater flow when Milltown Reservoir is at full stage (A) and at low stage (B). (Modified from reference 12.)...

Figure 6. Hydrograph of Milltown Reservoir stage during the temporal geochemistry and hydrogeology study (12). (Data are from Montana Power Company records.)...

Mobilization of contaminants in Milltown Reservoir can be explained by a model in which groundwater composition is controlled by successive diage-netic reactions during the transition to and from oxic and anoxic environments as the reservoir stage changes (12). Several important reactions govern the mobility of contaminants in this system ... 

In Milltown Reservoir sediments and other metal sulfide contaminated systems (18), FeS2 (pyrite) in this reaction can be replaced by any number of other metal sulfides (for example, arsenopyrite, chalcocite, galena, and... 

Milford Lake (Reservoir), Kansas, USA 20 sediment core samples Milltown Reservoir Montana, USA Milwaukee Harbor, Lake Michigan,... 

Nichols, E.M. (2003) Monthly variations in metal and arsenic concentrations before and after the draw-down of the Milltown reservoir. Abstracts with Programs. The Geological Society of America, 35(5), 37. 

Mickey, J.W. and Moore, J.N. (1997) The effects of discharge variation on the dissolved concentrations of trace metals and arsenic through Milltown Reservoir, Montana. Abstracts with Programs-Geological Society of America, 29(6), 149. 

About 200 km upstream from Milltown Reservoir, large-scale mining and processing of copper ores over the last ca. 100 years at Butte and Anaconda... 

Figure 9 Aerial photograph mosaic showing Milltown reservoir at low flow in 1989. Main features are labeled in Fig. 2. The photograph covers approximately 3600 m in the horizontal (E-W) direction.

EMC2, 2000, Milltown Reservoir Draft Focused Feasibility Study Report Anaconda, ARCO. 

ENSR, 1991, Preliminary phase 1 remedial investigation report- Milltown reservoir sediments superfund site Executive summary for exhibits 1, II and III. Fort CoUins, Colorado,... 

Milltown reservoir sediments superfund site, remedial investigation Fort CoUins, Colorado, ENSR Consulting and Engineering. 

HLA, 1986, Milltown reservoir feasibility study Denver, Colorado, Harding Lawson Associates. 

Titan, 1994, Milltown reservoir sediments operable unit, working draft, final remedial investigation report Volume 1, Prepared for Atlantic Richfield Company, Prepared by Bozeman, Montana, Titan Environmental Corporation. 

Milltown Reservoir Sediments Operable Unit Final Draft Remedial Investigation Report Anaconda, ARCO. 

Milltown Reservoir Sediments Site Draft Feasibility Study Report, ARCO. 

---