The Willow Creek Basin: Water, chemistry, and anomalies
- Created on Thursday, 06 September 2012 22:36
- Written by GUINEVERE NELSON
In the heyday of the Creede Mining District, the goal was to extract silver ore in the fastest and least expensive manner. This often entailed dumping material directly into Willow Creek and leaving waste rock and tailings piles exposed to the elements.
In the late 1960’s people were interested in the cause of a fish die off in the Rio Grande that happened after an episodic flood event in Willow Creek. Closer inspection revealed fish did not inhabit the creek. Macro-invertebrates were found but there were a limited number of species most of which are known to be tolerant of high metal concentrations. Riparian habitat was less than optimal. Water samples were taken which indicated high levels of zinc, cadmium, copper, and lead.
The Willow Creek Reclamation Committee (WCRC) was created to find solutions to these problems. To change the effects of historic mining practices, the committee needed to know how these metals interacted with water. To solve these problems, the committee takes water samples twice a year, coinciding with seasonal high and low flows.
Water samples are taken in two methods; the first method involves taking water directly from the stream to the bottle, the second method involves forcing water through a small (0.45 micron) filter. The WCRC is interested what this second, filtered, method indicates. The filtered sample takes larger undissolved molecules out and reveals molecules that are hooked to water and thereby biologically available to whatever may be swimming around in the creek. Through examination the committee has considered pH and heavy metals, fish and zinc, and the creek’s hydrology.
The pH found in Willow Creek water fluctuates from acidic to neutral depending on where a sample is taken from. The pH of water is a distinctive indicator of what heavy metals may be present. The orange sludge outside of the Nelson Tunnel adit looks like algae, but it is Iron III falling out solution, due to the rise in pH as water interacts with air at a pH of 2.
Aluminum is the next to fall out at a pH of 4. As water gets closer to neutral, more metals fall out. Using this information, and the advice of experts, the WCRC uses lime precipitation treatment to raise the pH of Willow Creek and force the heavy metals out of solution at mine sites throughout the basin. However, heavy metals persist in water samples near these sites on an annual basis.
Zinc, an essential element to all life, can be lethal if ingested in excess amounts. The heavy metal zinc is found in high concentrations in the lower reaches of East, West, and Mainstream Willow Creek. Literature and state standards give a concentration amount that is lethal in chronic amounts to fish. Not only are trout ingesting heavy metals through their diet, trout are exposed to heavy metals in the water and are uptaking metals through their gills. Zinc obstructs the biochemical process for fish respiration in waters that are chronically high in these concentrations. However, committee members successfully fish in East Willow Creek. One theory to address this is that fish in East Willow are acclimated to these elevated zinc concentrations.
Many have examined the hydrology of Willow Creek and still no solid answers arise to explain Willow Creek. Of course, the water flows downhill, but after Oxygen 18 isotope data was collected on water flowing out of Nelson Tunnel, scientists explained it to be old water. This means that snowmelt above West Willow takes almost 70 years to percolate through the soil and flow through a network of faults and fractures before reappearing. Creek contents disappear and reappear according to water flow measurements.
As WCRC embarks on the large restoration project in the floodplain, questions still arise. Some data indicates a large loading of heavy metals to the creek as it passes through the floodplain. But, groundwater tests are inconclusive about the movement of water from identifiable hot spots.
The WCRC continues to discuss questions that arise from collecting and analyzing data. Willow Creek still pushes traditional understanding of hydrology and water chemistry. Professional, chemists and resources managers all agree, it is never the same creek twice.
For more information on Water 2012 in the Rio Grande Basin, please visit www.rgwcei.org or www.water2012.org. Also, the Water 2012 traveling display is up this month at the South Fork Carnegie Library. On Sept. 21st, the CDPHE will be hosting a tour of the Summitville water treatment plant. All participants MUST register via www.rgwcei.org, go to the Calendar of Events, on click on the tour date for more details and registration information.