Long Term Changes in the Limnology and Geochemistry of the Berkeley Pit Lake, Butte, Montana

Abstract

The Berkeley pit lake in Butte, Montana is one of the largest accumulations of acid mine drainage in the world. The pit lake began filling in 1983, and continues to fill at a rate of roughly 10 million liters d -1. This paper details how changes in mining activities have led to changes in the rate of filling of the pit lake, as well as changes in its limnology and geochemistry. As of 2005, the Berkeley pit lake is meromictic, with lower conductivity water resting on top of higher conductivity water. This permanent stratification was set up by diversion of surface water -the so-called Horseshoe Bend Spring -into the pit during the period 2000 to 2003. However, the lake may have been holomictic prior to 2000, with seasonal top-to-bottom turnover events. The present mining company is pumping water from below the chemocline to a copper precipitation plant, after which time the Cu-depleted and Fe-enriched water is returned to the pit. Continued operation of this facility may eventually change the density gradient of the lake, with a return to holomictic conditions. A conceptual model illustrating some of the various physical, chemical, and microbial processes responsible for the unusually poor water quality of the Berkeley pit lake is presented.

Physico-chemical gradients and meromictic stratification in Cueva de la Mora and other acidic pit lakes of the Iberian Pyrite Belt

“…Because this pit lake is connected to an extensive system of underground galleries and shafts, it is possible that warm, high salinity water from the underground mines is migrating into the deep pit lake. A similar idea was proposed to help explain the elevated temperature and poor water quality of the monimolimnion of the Berkeley pit lake in Montana, USA (Davis and Ashenberg 1989;Gammons and Duaime 2006;). Regarding point 3 (above), progessive filling of pit lakes by waters of very different chemistry, density and/or temperature can be a key factor to develop meromictic conditions (Castendyk and Webster-Brown 2007).…”

“…Davis and Ashenberg 1989;Gammons and Duaime 2006;Pellicori et al 2005). Salinity gradients with depth have been described in the monimolimnia of some other German open cast mining lakes, such as those of Soldbald Stassfurt or Rassnitzer See in the Merseburg-Ost area (Boehrer and Schultze 2008).…”

“…The precipitation of this mineral through reaction (1) (Bigham et al 1996;Bigham and Nordstrom 2000) has been observed to constitute the principal Fe-buffering mechanism in other pit lake regions, such as those of Lusatia, Germany (Regenspurg et al 2004, Totsche et al 2003, or Butte, Montana, USA (Gammons and Duaime 2006;Pellicori et al 2005): However, in the anoxic and reducing environment of the monimolimnion, the water becomes undersaturated with respect to all Fe(III) minerals (Fig. 8a).…”

An Overview of the Mining History and Geology of Butte, Montana

“…Recent journal articles include an examination of the mineralogical controls on mine water chemistry in the Berkeley and Continental Pits (Newbrough and Gammons 2002), an investigation of the geochemistry of uranium and rare earth elements in the Berkeley pit lake (Gammons et al 2003a), and a geochemical and stable isotope investigation of the pit lake and surrounding mine waters (Pellicori et al 2005). In this issue of Mine Water and The Environment, papers are presented on long-term changes in the limnology and geochemistry of the pit lake (Gammons and Duaime 2006), characterization of the pit lake sediment and its pore waters (Twidwell et al 2006), and the distribution of dissolved organic carbon in the lake and its bottom sediment (Cameron et al 2006). Other scientists at Montana Tech are actively engaged in characterizing the microbiology of the Berkeley pit lake (Mitman 1999), and exploring for bioactive metabolites isolated from extremophile organisms that could have pharmaceutical benefits (Stierle and Stierle 2005).…”

Evaluation of the Potential for Beneficial Use of Contaminated Water in a Flooded Mine Shaft in Butte, Montana

“…The US Environmental Protection Agency (EPA) has determined that there are no feasible methods for remediating this ground water (EPA 1994). At the current time, the majority of the mine water is draining to the nearby Berkeley pit lake (Davis and Ashenberg 1989;Gammons and Duaime 2006), and therefore does not pose a threat to down-gradient watersheds or water supplies. Meanwhile, the city of Butte (pop.…”