WSP02347

• File Number: 8102
• Description: Arkansas River Basin Basic Hydrology
• State: CO
• Basin: Arkansas
• Water Division: 2
• Date: 5/7/1999
• Author: Inter-Fluve Inc
• Title: Fluvial Geomorphic Assessment of Upper Arkansas River - Final Report
• Water Supply Pro - Doc Type: Report/Study

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3. Historic Impacts: Mining, Flow Augmentations, and Project
Reach Land Use

3.1. Mining Impacts

The Leadville mining district has produced in excess of $800 million in silver, lead, zinc,
gold, and copper since the mid 1800's (Collins and Collins, 1986). Smelting operations
have also utilized significant quantities of manganese, bismuth, and iron. Mining in the
area commenced around 1860 on California Gulch when placer gold was discovered. By
1875, the gold mining had essentially ceased, in part due to the difficulty of processing a
heavy gray mineral that was present in high concentrations in the placer deposits. This
material was identified as cerussite (lead carbonate) in 1876, which is a common lead ore
that forms upon the interaction of carbonated waters with galena (lead sulfide; Hurlbut
and Klein, 1977). The cerussite ore also contained large amounts of silver. The lead-
silver ore was mined extensively until about 1902. From about 1903 to after WWI, large
quantities of zinc carbonate ore were mined in the Leadville district. Since about 1923,
base metal complex sulfide ores have constituted the primary mining activity in the
region. Between 1859 and 1966, approximately 24 million tons of ore were produced in
the Leadville district (Studzinski, 1996). Some local mines have actively produced gold
ore in recent years (Collins and Collins, 1986).

Mining waste generated in the Leadville region over the past 150 years has been directly
disposed of on the Arkansas River floodplain, and has been transported down the
Arkansas River project reach via upstream tributaries including California Gulch (BOR,
1999), These tailings are located along the channel margin and floodplain within the
project reach, and consequently constitute a potential source of contaminants for the
active channel (URS, 1977). As the channel course has shifted laterally through time,
many tailing deposits are located away from the main channel in relict channel features
and on the adjacent floodplain or low terrace surfaces. Additional concern has been
expressed that mine tailings have been transported though irrigation ditches and
deposited in broad fields in the valley bottom. Within the project reach, some of the
tailings have been identified as phytotoxic, such that vegetative reinforcement of channel
banks and floodplain surface is locally limited (URS, 1997).

The delineation and geochemical analyses of tailings within the project reach is ongoing.
To date, approximately 90,000 cubic yards of tailings have been mapped and
geochemically evaluated along the project reach CURS 1997; 1998). Treatment strategies
for the tailings were undergoing feasibility evaluations at the time of this investigation,

Sediment control measures have been implemented on California Gulch to reduce the
quantity of tailings delivered to the project reach. Whereas historic sediment loading out
of California Gulch likely consisted of substantial quantities of sand and finer grained
material, sediment control measures will reduce both the size and volume of sediment
introduced in the future.

May 7, 1999

Fluvial Geomorphological Assessment
Upper Arkansas River

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