Effects of acidic recharge on groundwater at the St. Kevin Gulch site, Leadville, Colorado
Effects of acidic recharge on groundwater at the St. Kevin Gulch site, Leadville, Colorado (in Evolution and remediation of acid-sulfate groundwater systems at reclaimed mine-sites, Joseph J. Donovan (editor) and Arthur W. Rose (editor))
Geochemistry - Exploration, Environment, Analysis (February 2001) 1, Part 1: 3-14
- acid rock drainage
- adsorption
- aquifers
- Arkansas River valley
- attenuation
- cadmium
- Colorado
- copper
- dissolved oxygen
- Eh
- environmental effects
- geochemistry
- ground water
- hydrochemistry
- hydroxides
- iron
- iron hydroxides
- Lake County Colorado
- Leadville Colorado
- metals
- North America
- oxides
- oxygen
- pH
- pollution
- recharge
- Rocky Mountains
- Saint Kevin Gulch
- Sawatch Range
- soils
- solutes
- sulfate ion
- sulfur
- surface water
- surveys
- U. S. Rocky Mountains
- unconfined aquifers
- United States
- wetlands
- zinc
- Tennessee Park Basin
The acid rock drainage-affected stream of St. Kevin Gulch recharges the Quaternary sand and gravel aquifer of Tennessee Park, near Leadville, Colorado, lowering pH and contributing iron, cadmium, copper, zinc and sulfate to the groundwater system. Dissolved metal mobility is controlled by the seasonal spring runoff as well as oxidation/reduction (redox) reactions in the aquifer. Oxidizing conditions occur in the unconfined portions of the aquifer whilst sulfate-reducing conditions are found down gradient where semi-confined groundwater flow occurs beneath a natural wetland. Iron-reducing conditions occur in the transition from unconfined to semi-confined groundwater flow. Dissolved iron concentrations are low to not detectable in the alluvial fan recharge zone and increase in a down gradient direction. The effects of low-pH, metal-rich recharge are pronounced during low-flow in the fall when there is a defined area of low pH groundwater with elevated concentrations of dissolved zinc, cadmium, copper and sulfate adjacent to St. Kevin Gulch. Dissolved metal and sulfate concentrations in the recharge zone are diluted during spring runoff, although the maximum concentrations of dissolved zinc, cadmium, copper and sulfate occur at selected down gradient locations during high flow. Dissolved zinc, cadmium and copper concentrations are low to not detectable, whereas dissolved iron concentrations are greatest, in groundwater samples from the sulfate-reducing zone. Attenuation of zinc, cadmium and copper beneath the wetland suggests sulfide mineral precipitation is occurring in the semi-confined aquifer, in agreement with previous site investigations and saturation index calculations. Adsorption of dissolved zinc, cadmium and copper onto iron hydroxides is a minor attenuation process due to the low pH of the groundwater system.