Seasonal Changes in the Characteristics of Suspended Sediment Metal Transport in a Mining-Impacted Stream

Over the past three years, a decision tree has been developed to rank mine waste sites for potential environmental impacts. This approach relies on simple leach tests to determine the chemical composition and toxicity of water in contact with mining wastes. When the pH of the leachate solutions is less than 5, the toxicity of the water is certain. However, when the pH of the leachate solutions is greater than 5, lower concentrations of toxic metals make toxicity assessment uncertain and a simple "in-vitro" test is necessary. These methods were used to evaluate a mine site that is marginally impacted. The Tip Top Mine in Gamble Gulch, Colorado is a high mountain site where the stream upstream of the mine is pristine and downstream of the influx of acid rock drainage, the aquatic ecosystem is marginally impacted. Aquatic toxicity assessments, made using a microbial enzyme bioassay, were conducted to determine the impact of contaminants on the stream. All tests show that the stream water upstream of the adit inflow is unimpacted. However, the stream downstream of the inflow shows concentrations of Al, Cu and Zn that are only slightly higher than acute aquatic toxicity limits. Leaching tests on stream sediment samples taken at the adit entrance show concentrations of contaminants that are also higher than toxicity limits. Simple enzyme bioassay tests, using metals sensitive bacteria, were conducted to establish the toxic response of the sediment leachate. The preliminary results show that leachate water upstream of the adit is not toxic and downstream, the leachate solution is marginally toxic. Duplicate leach tests and enzyme bioassay tests were conducted to determine the reproducibility of these approaches.

Section: Comparison Of the Waters At The Tip Top Sitementioning

confidence: 99%

Leachate and Enzyme Bioassay Toxicity Assessment Tests at the Tip Top Mine, a Marginally Impacted Site

Moehle¹,

Ranville²,

Choate³

et al. 2006

“…The sampling visit was in mid-July, and by this time, spring runoff was over and the stream was at base flow conditions. In an analysis of nearby North Clear Creek, Harvey et al (2003) found that dissolved metals concentrations are significantly lowered during high flow conditions. Assuming the concentrations of the metals in the adit water remain constant, the concentrations of dissolved Al, Cu, and Zn, which were above aquatic toxicity levels in July 2004, could be reduced to below those toxicity levels during high flows.…”

Section: Comparison Of the Waters At The Tip Top Sitementioning

confidence: 99%

Characterization and Leach Test Assessment at the Tip Top Mine, a Marginally Impacted Site

Moehle¹,

Fox²,

Ranville³

et al. 2005

The Tip Top Mine in Gamble Gulch, Colorado is a high mountain site where the stream above the mine is pristine and below the influx of acid rock drainage, the aquatic ecosystem appears to be impacted. An aquatic toxicity assessment study was carried out to determine the impact of contaminants on the stream and to test the leaching methods and simple toxicity tests that have been developed at the Colorado School of Mines. All tests show that the stream water above the adit inflow is pristine. However, the stream below shows concentrations of Al, Cu and Zn that are slightly above acute aquatic toxicity limits. Leaching tests on stream sediment samples taken below the adit entrance show concentrations of contaminants that are on the borderline of being toxic. Physical and chemical assessments of the mine waste piles on the site show that they are not impairing the immediate vicinity or the stream. It appears that the cause of any aquatic toxicity is the adit water entering the gulch or the heavy oxyhydroxide precipitates lining the streambed below the mine site.

“…During some times of the year, a black coating is present on the rocks; it was found that this coating is predominantly comprised of manganese (Harvey et al, 2003). Since the HFO is the dominant sorbent for metal sorption in the stream, the purpose for this research was to compare observed concentrations of particulate copper and zinc, over a twoyear period, with Visual-MINTEQ model predictions, based on the use of HFO as the sole sorbent.…”

Section: Introductionmentioning

confidence: 99%

Comparison Between Observed and Model Predicted Particulate Metal Transport in a Mining-Impacted Stream (North Fork Clear Creek, Colorado)

Butler

Ranville

Ross

2005

Self Cite

Abstract. Acid-mine drainage (AMD) is an important source of metals to aquatic ecosystems. Once these metals are input to oxygenated stream water of neutral pH, there may be oxidation of metal ions, precipitation of metal oxyhydroxides, and co-precipitation and/or sorption of metals. Understanding the fate and transport of these metals requires knowledge of the distribution of metals between the suspended solid and dissolved phases. Models exist for the prediction of sorption of metals to oxyhydroxides phases, primarily for hydrous iron oxide (HFO). Visual-MINTEQ now includes a database for a second hydrous oxide phase: hydrous manganese oxide (HMO), which may prove to be an important sorbent for some metals in mining-impacted systems. This paper discusses the comparison between model predicted and observed percentage particulate copper and zinc in stream water collected over a two-year study of the North Fork of Clear Creek, Colorado. It was found that the model over-estimated the percentage of particulate copper actually observed, using HFO as the sole sorbent phase, but that the comparison was within a factor of two. Inclusion of HMO for modeling of the zinc improved the prediction of percentage particulate zinc; however, results indicate that there may be another process controlling particulate zinc in the stream. Additional