Quantifying Metal Contributions from Multiple Sources to the Clark Fork River, Montana, U.S.A.

Abstract

Identifying and quantifying the contributions of multiple sources of trace elements to stream sediments in a basin containing several possible inputs presents a unique problem related to the investigation of rivers impacted by industrial activity. A multi-source dilution±mixing model was developed and applied to determine the relative contributions to As, Cu and Pb burdens in the Clark Fork River, Montana, a recipient of historical mine wastes as a result of over a century of mining and milling operations. The results identi®ed the Flint Creek drainage as a major source of anthropogenic As (47%) and Pb (35%) to sediments of the Clark Fork River and the Milltown Reservoir, in addition to the major sources associated with mining operations in Butte, MT. The Little Blackfoot River also contributes anthropogenic As (3%) and Pb (4%) to the Clark Fork River, while minor inputs of Cu (1%) and Pb (2%) emanate from the Blackfoot River. The model allows source quanti®cation, and an understanding of the fate and transport of mine wastes in a basin, allowing identi®cation and eventual prioritization of sites destined for remediation.# 2000 AEHS

Modeling framework for sediment deposition, storage, and evacuation in the floodplain of a meandering river: Application to the Clark Fork River, Montana

“…The relatively close agreement between runs 2a and 2b implies that at the reach scale, one of the primary reasons for a decrease in overbank thickness during the mining era was the decrease in suspended sediment concentration experienced as sediment was lost from the channel to the floodplain, not simply dilution of suspended sediment concentration by tributary inflow. (Note that dilution by tributary inflow clearly was important downstream of the study reach [ Helgen and Davis , 2000]).…”

Metal Distribution in Clark Fork River Sediments

“…Early placer mining activity is reflected in the increase of mercury (used to extract gold in placer mining operations) in the <63-μm fraction of the gravel bars from about 0.2 to 2 mg/kg in the CFR downstream from Gold Creek (Figure ). Silver beneficiation in Butte and in CFR tributaries (Figure ) also contributed Pb and Mn, while the copper mining era contributed As (primarily from enargite) and zinc from the center of the Butte copper porphyry deposit ( , ).…”

“…For example, mercury (Hg) was used to amalgamate gold during placer mining from 1864, followed by silver mining that generated Ag-Pb rich tailings from ∼1876, and copper milling and smelting that generated Cu-As tailings from 1879. From 1928 to 1947, Mn was smelted and stored in Butte (12).…”

Mixing and Transport

“…To address metals concentrations in the Clark Fork River in Montana, which experiences multi-source dilution mixing, Helgen and Davis (2000) quantified metal contributions from multiple sources to the river. A representative model was developed and applied to determine the relative contributions of discharges to arsenic, copper, and lead levels in the river, which is a discharge source of historical milling and mine wastes.…”