Case Study as part of a Web-based
Technical and Regulatory Guidance
Wellington-Oro Water Treatment
Plant
Summit County, Colorado
1. Site Information
1.1 Contacts
Mark Meyer
Town of Breckenridge
Telephone: 970-547-7149
E-mail: [email protected]
1.2 Name, Location, and Description
The Wellington-Oro is located in Breckenridge, Summit County, Colorado. The
mining complex contains over 12 miles of flooded workings along the French
Creek tributary of the Blue River. Gold, lead, and zinc mining occurred from
1860s to the 1970s. Dredge operations also occurred along the Blue River
and upstream through French Gulch. Impacts seen in the Blue River were traced
back to a seep of the Wellington-Oro mine complex, identified as seep FG-6c.
The seep location is at latitude of 39°28'54" N and longitude of 106°1'1" W.
The contaminated media affected are surface water and groundwater.
2. Remedial
Action and Technologies
The Town
of Breckenridge and Summit County decided to purchase 1,800 acres of land
from B&B Mines. The property included the Wellington-Oro mining complex.
As part of the property transaction, the Town of Breckenridge and Summit
County entered into a Consent Decree with the U.S. Environmental Protection
Agency. In the Consent Decree, the Town of Breckenridge and Summit County
agreed to construct and operate a treatment system to treat the discharge
from seep FG-6c and remove the zinc and cadmium.
Discharge flows from the seep range from a winter low of 50 gpm up to a maximum treatment rate of 150 gpm during spring runoff. The contaminated water is characterized by a pH of 6.4 and elevated concentrations of cadmium (0.059 ppm) and zinc (123 ppm). Site cleanup goals are based on the mitigation of human health risk and mitigation of ecological risk.
The Wellington-Oro Water Treatment Plant (WTP) uses a sulfide precipitation process to cause the precipitation of zinc and cadmium sulfides. A small amount of soda ash is added into the process to control the pH to the optimal range for sulfide precipitation. Sulfides, in the form of sodium hydrosulfide, are added in a controlled dose. Dosing is carefully controlled so that zinc and cadmium are removed to discharge limits, but so that an excess hydrogen sulfide gas is not created (nor is too much iron precipitated)
The precipitated solids settle to the bottom of a clarification tank while the treated water flows off the top. The underflow solids from the clarifier are contained in a liquid sludge and are pumped to a plate and frame filter press for dewatering.
3. Performance
The Wellington-Oro WTP began around-the-clock operations in November 2008.
The process removes 99.8% of the zinc and cadmium and has been able to achieve
the discharge limits—225 ppb for zinc and 4 ppb for cadmium. Other metals
not required to be treated, such as iron, remain in solution. The treated
discharge also passes Whole Effluent Toxicity testing for ceriodaphnia and
fathead minnows and is nontoxic.
4. Costs
The Wellington-Oro WTP had a cost of construction of approximately $4.3
million. Since the plant has not been in operation very long, ongoing operation
and maintenance costs are not known and will largely depend on treatment
flow rates and the final disposition of the filter cake.
5. Regulatory Challenges
None encountered.
6. Stakeholder Challenges
No information available.
7. Other Challenges and Lessons
Learned
The main challenge was finding a reliable method to quantify zinc concentrations
in the effluent. The original strategy was to use a colorimetric method on
a spectrophotometer. This method was subject to interference from ferrous
and ferric iron concentrations in the effluent. It was not effective at providing
real-time feedback to control process parameters. An atomic absorption spectrometer
was purchased because it was not subject to iron interference.
8. References
None reported.
