Quantification of metal loads and assessment of metal sources in upper Beaver Creek watershed, Shoshone County, Idaho, May and June 2002

Abandoned mine lands contribute to significant
water-quality degradation in the Beaver Creek watershed
in northern Idaho. Streams in this watershed drain
the northern flank of the Coeur d’Alene mining district,
one of the world’s largest producers of silver and one
of the country’s major historical producers of lead and
zinc for more than 100 years. Effective cleanup of
these streams will depend on accurate characterization
of metal concentrations in streams and various sources
of these metals.
Cadmium, lead, and zinc loads entering Beaver
Creek and its major tributary, Carbon Creek, were
quantified, and source areas for these metals were
assessed during May and June 2002. Metal loads were
calculated for main-stem and surface-inflow sites by
combining measured streamflow with dissolved cadmium,
lead, and zinc concentrations analyzed in waterquality
samples collected during three synoptic sampling
events. To assess the effects of surface and shallow
subsurface inflows on the gain or loss of streamflow
and metal loads, Beaver and Carbon Creeks were
divided into subreaches. Four subreaches were defined
on Beaver Creek using five main-stem sampling sites
(UBC3, UBC5, UBC8, BC10, and BC14); two subreaches
were defined on Carbon Creek using three
main-stem sampling sites (CC2, CC6, and CC9).
During each of the synoptic sampling events, concentrations
of cadmium and zinc were highest in samples
collected at the Carlisle Mine adit between sites
CC2 and CC6. During two of the three synoptic sampling
events, the concentration of lead was highest in
samples collected from a left-bank seep downgradient
from the Idora Mill between sites UBC3 and UBC5.
The largest identified cadmium and zinc source to
Beaver Creek is the surface inflow from Carbon Creek
(between sites UBC8 and BC10), which accounted for
45 to 72 percent of the main-stem cadmium load and
49 to 89 percent of the main-stem zinc load in Beaver
Creek. Another large source of cadmium and zinc to
Beaver Creek is subsurface flow through the tiered
flotation tailings pile near Carbon Center (between
sites BC10 and BC14) into Beaver Creek.
Amounts of lead contributed by source areas to
Beaver Creek vary with streamflow conditions. During
high streamflow, the largest source of lead to Beaver
Creek is the remobilization of fine-grained (less than
0.45-micrometer), lead-enriched particulates from the
streambed throughout the study area. During low
streamflow, bank seepage of subsurface water into
Beaver Creek in the subreach downgradient from the
Idora Mill (between sites UBC3 and UBC5) is the
major source of lead to Beaver Creek. During each
synoptic sampling event, Carbon Creek is a major
source of lead to Beaver Creek.
The Carlisle Mine adit (between CC2 and CC6)
is the largest source of cadmium and zinc to Carbon
Creek and, ultimately, to Beaver Creek, and accounted
for 57 to 88 percent of the total main-stem cadmium
load and 56 to 88 percent of the total main-stem zinc
load in Carbon Creek during each of the synoptic sampling
events. Another source of cadmium and zinc to
Carbon Creek is resurfacing cadmium- and zincenriched
hyporheic flow (possibly originating from
the Carlisle adit or the Carlisle Mill) between sites
CC6 and CC9.
As in Beaver Creek, amounts of lead contributed
to Carbon Creek by source areas vary with streamflow
conditions. During high streamflows, increased discharge
from the Carlisle Mine adit appears to be the
largest source of lead to Carbon Creek; during low
streamflows, resurfacing lead-enriched hyporheic flow
appears to be the major source of lead to Carbon Creek.