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Section 319
NUNPUINT SUURCE PROGRAM SUCCESS STPRY
London Extension Mine Drainage Treatment Project Removes Heavy Metals
WatPrbndv Imnrnvpd South Mosquito Creek, in central Colorado, has been plagued
'} * -*..» foryears by toxjc metals from an abandoned gold mine. A
drainage treatment system was constructed to increase the pH of the water and reduce
heavy metal concentrations. The treatment system has reduced zinc levels in the creek to
below the chronic toxicity level, on average meeting water quality standards and achieving
part of the total maximum daily load (TMDL).
Problem
The London Extension Tunnel, a historic
gold mining site, is the largest single source
of metals contamination to the Mosquito
Creek watershed (located 3 miles east of the
Continental Divide). Although the streams in the
watershed are classified as cold water aquatic
class 1, widespread metals contamination has
severely depleted aquatic life in Mosquito Creek
and essentially eliminated it in South Mosquito
Creek. Further compounding the metals
problem are the elevation (approximately
1 1 ,600 feet) and severe winter weather, which
limit accessibility to the site. In 1998 Mosquito
Creek was placed on the state's 303(d) list
as impaired by zinc, lead, and cadmium, and
South Mosquito Creek was listed as impaired
by zinc, cadmium, iron, and manganese. A
TMDL was established for both segments with
zinc as the controlling parameter.
End ot corrugated
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Sludge
Delta
Project Highlights
The mine drainage treatment system mixes kiln dust with acidic
runoff to increase the pH of the drainage water. Once a pH of
between 9.5 and 10 is achieved, metals are precipitated out in a
settling pond and the clean water is returned to the creek.
In 1997 the London Extension Tunnel mine
drainage treatment system was constructed
to address heavy metal contamination in
surrounding watersheds. Acidic drainage is
collected in the mine and conveyed to a tank,
where cement kiln dust is added. After the
acidic drainage mixes with the kiln dust, the
water flows to a settling pond outside the
mine. The low-cost, low-maintenance system
successfully uses cement kiln dust as a cost-
effective neutralizing agent in place of other
commercially available neutralizing agents.
When the effluent pH is maintained at between
9.5 and 10.0, the system removes more than
99.8 percent of the heavy metals.
Few best management practices (BMPs) were
available that could be applied to this site.
Aside from the use of neutralizing agents, the
only other BMP that could have been effec-
tive is hydrologic controls within the mine
workings. However, rotting timbers at several
locations near the mine entrance made the
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entrances unstable and prevented the safe
installation of hydrologic controls within the
mine workings.
Results
Since the construction of the mine drainage
treatment system, monitoring samples show
significant decreases in zinc concentrations.
Zinc levels in South Mosquito Creek are below
the chronic toxicity level and on average meet
water quality standards. Additional verification
will be required to confirm that the creek is in
full compliance with water quality standards.
The treatment system removes approximately
50 percent of the zinc in the drainage, about
26 pounds of zinc per day, and averages a total
metal removal of almost 47 pounds per day. On
a yearly basis, approximately 8.5 tons of metals
that formerly entered South Mosquito Creek are
now captured by the treatment system.
Additional investigation and remediation will be
required for the main stem Mosquito Creek to
attain water quality standards. Since the TMDL
includes both segments, goals for Mosquito
Creek will need to be attained to meet the
overall TMDL. However, the project dem-
onstrates achievement of part of the overall
TMDL goal, and South Mosquito Creek should
now be able to support a brook trout fishery.
Partners and Funding
The following partners were involved in this
project and provided funding, in-kind services,
and technical assistance:
• Colorado Department of Natural Resources,
Division of Minerals and Geology ($21,376)
• Colorado Department of Public Health and
Environment, Water Quality Control Division
($53,118 in section 319 funds)
• London Mine Limited Liability Company
(landowner) ($16,661)
• Colorado School of Mines ($9,240)
Construction costs for the treatment system
were around $100,000, and the cost of system
operation and maintenance is estimated to be
$10,000 annually, plus labor costs. To date EPA
section 319 funding has provided $53,118 for
the London Extension Tunnel mine drainage
treatment project. With matching funds, the
total amount spent was $100,395.
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'. U.S. Environmental Protection Agency
\ Office of Water
a Washington, DC
EPA841-F-05-004X
October 2005
For additional information contact:
Laurie B. Fisher
Colorado Department of Public Health
and Environment, Water Quality Control Division
303-692-3570 • laurie.fisher@state.co.us
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