Lovelock Review-Miner - Progressive Leadership Alliance of Nevada

Lovelock Review-Miner, June 16 - 22, 2016 - 7
COMMUNITY NEWS
Pit lakes impact river according to study
Water lost to both
evaporation and
contamination
By Debra Reid
Lovelock Review-Miner
Lovelock Valley farmers have
long suspected the river they
depend on has declined due in
part to under-regulated groundwater pumping at open pit mines in
the Humboldt River Basin. In the
legal battle for their surface water,
farmers have an unlikely ally at the
other end of the political spectrum.
The Progressive Leadership
Alliance of Nevada, a social justice
and environmental action group
based in Reno and Las Vegas,
sponsored a two year study of mine
pit lakes in the Humboldt River
Basin. Last week, hydrologic consultant Dr. Tom Myers presented
the results of his study confirming
the link between pit dewatering and
pit lakes, groundwater and surface
flows in the basin’s streams and
rivers.
Nevada gold mines pump millions of acre-feet of groundwater
to keep open pits and underground
mines dry and most of those mines
are in the Humboldt River Basin.
When pits are abandoned, groundwater flows back into the pits and
becomes contaminated by exposed
mine waste and pit walls.
Excluded from state reclamation
requirements, pit lakes are simply
fenced off from the public and
lose millions of acre-feet of water
each year to evaporation. PLAN
and Great Basin Resource Watch
officials claim that pit lakes waste
water and should be reclaimed for
recreation or other public use.
In a written summary of his
study, Myers provided estimates of
the massive amounts of groundwater involved in mine pit dewatering,
abandoned pit lake storage and
evaporation in the HRB. Mine pit
dewatering makes open pit mining
safer but creates an underground
void that can impact the water table
for miles along with surface water
including springs, streams and rivers according to Myers.
He explained how “cones of
depression” below abandoned pits
suck groundwater back to fill the
void.
“Open pit mining that extends
below the groundwater table captures groundwater and can cause a
very large change to groundwater
relations,” Myers wrote. “At mines
in northern Nevada, groundwater
levels near open pit mines have
been lowered as much as 1500
feet and draw down has extended
50 miles from the pit. As pit lakes
fill after mining ends, groundwater
flows into the pit forming a lake.”
Since the early 1990s, Myers
estimates that 3,900,000 acre-feet
or 1.3 billion gallons of groundwater have been pumped during open
pit dewatering in the Humboldt
River Basin. Eventually, the seven
largest pit lakes in the basin will
hold an estimated 1,000,000 acrefeet or 326 million gallons of water.
About 10,000 acre-feet per year of
that pit lake water will be lost to
evaporation according to Myers.
“In 18 years, will have lost
PHOTO COURTESY OF TOM MYERS
Since open pit dewatering at the Lone Tree Mine ended in 2006, the pit lake has pulled an estimated 176,000 acre-feet of groundwater
recharge away from the Humboldt River according to a recent study.
180,000 acre-feet of water to
evaporation- the same amount Las
Vegas wants to pump from Northern Nevada,” according to PLAN.
“The mining industry might say
this is insignificant but we believe
mining companies should (not) be
allowed to waste any water.”
There have been few studies
published on the affects of open
pit dewatering on nearby rivers
but flow gauges on the Humboldt
River above and below Newmont’s
Lone Tree Mine show river flows
have been impacted as groundwater flows back into the aquifer
and pit lake, Myers said in his
summary.
Since open pit dewatering ended
at the Lone Tree Mine in 2006,
Myers estimates the Humboldt
River has lost about 176,000 acrefeet of groundwater recharge due
the pit lake at Lone Tree. With a
capacity of 129,000 acre-feet, the
pit lake has so far collected about
50,000 acre-feet of groundwater but
much of the water flowing into the
lake is lost to evaporation, he said.
“The average additional loss to
the Humboldt River (due to the pit
lake) has been about 22,000 acrefeet per year or about 30 cubic feet
per second for eight years,” Myers
said in the study summary. “This
additional loss rate is about eight
percent of the total average flow in
the Humboldt River.”
Myers said it’s impossible to
predict how much water the Lone
Tree Mine pit lake will ultimately
cost the river but, as of 2015, the
rate of groundwater loss has not
declined. There are many unseen
factors that affect aquifers and
groundwater movement such as
the “hydraulic gradient” around the
abandoned pit and the groundwater
storage capacity of the dewatered
bedrock near the Lone Tree Mine
pit lake.
Without perpetual treatment, the
water in mine pit lakes becomes
increasingly contaminated over
time as salts, acids and minerals
are leached from exposed pit walls.
At Lone Tree, the pit lake water is
treated with lime to reduce acidity
but is not suitable for discharge
into the Humboldt River. In the
1990s, groundwater from open pit
dewatering at Lone Tree was discharged into the river, Myers said.
According to Great Basin
Resource Watch Executive Director John Hadder, some of the
groundwater pumped during pit
dewatering is used for ore processing but most of it is infiltrated
back into shallow aquifers or other
hydrographic basins instead of
back to the deep aquifers where the
water originated.
“Thus, mining operations are
also mining the water; ancient
water that may have not seen daylight for, in some cases, thousands
of years,” Hadder explains in his
GBRW newsletter. “What the
affect of drawing out this deep
water has on the long-term character of aquifers and the region is
unclear.”
According to Hadder, mine pit
lakes are excluded from state reclamation requirements. Instead, pit
lakes are fenced with no beneficial
use, no public access and perpetual
water loss due to evaporation.
Landscape restoration is a routine part of mine reclamation but
back filling pits would be economically unfeasible according to
Rye Patch Gold Senior Exploration
Geologist Ronaldo Silva. Open pits
have yet to reach the water table at
the Florida Canyon Mine but that
could change in the future, he said.
In California, open pits must be
back filled but no recent open pit
mines have been approved in that
state according to Myers. In Montana, cyanide leaching of gold ore
has been outlawed, he added.
PLAN and Great Basin Resource
Watch officials told farmers last
week they plan to lobby for greater
regulation of mine water rights, pit
lake water quality and reclamation
at the 2017 state legislature.
Specifically, the groups recommend that pit lakes “be reclaimed
for post-mining beneficial use”
and that water quality regulations
be enforced to improve pit lake
water. They will push for legislation to require mining companies
to apply for water rights for the pit
lake water lost to evaporation and
reform the “temporary” water permits that allow years of groundwater pumping for mine dewatering.
For the Pershing County Water
Conservation District, the pit lake
study could be useful in court especially if Newmont and Barrick are
allowed to intervene in the district’s litigation against the state
water engineer. The law suit petitions the court for enforcement
of state water laws that prioritize
the district’s senior surface water
rights over junior groundwater
rights including those held by the
mines.
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