340821-001 FINAL United Keno HHERA 4 May 2011

Human Health and Ecological Risk Assessment for the Historic Keno Hill Mine Site
intended to err on the side of caution and therefore likely result in over-estimated intakes. The
level of caution in these assumptions is consistent with the approach typically adopted in risk
assessments (Health Canada 2009a).
Aquatic Assessment
The aquatic assessment was conducted for a total of 12 exposure locations (including
background), which were selected based on water and sediment data availability and to provide a
variety of possible exposure scenarios for evaluation.
The results of the aquatic environment assessment indicated that concentrations of copper, iron,
lead, manganese, silver and zinc result exceed toxicity reference values for fish at a number of
locations. Christal Creek at the Outlet of Christal Lake and the Lower South McQuesten River
are the areas of exceedances for most of the COPC. Zinc concentrations exceed toxicity
reference values at most of the locations. It should be noted that zinc concentrations also exceed
the toxicity reference values at the background locations. However, the results of the aquatic
assessment support that zinc is a key constituent of concern in the aquatic environment. Zinc
levels in fish tissue are elevated in most of the mining affected waters. For example, sculpins
from the Keno Hill area have zinc levels much greater than sculpins captured near the tailings
discharge area at the Faro Mine site. However, fish studies have found that there are no clear
differences in overall fish species diversity between mine-exposed and reference areas since
average relative fish abundance at all mine-exposed creeks and areas downstream of the South
McQuesten River were similar to or higher than the reference area. Thus, the elevated COPC
levels in the water bodies in the Keno Hill area are not adversely affecting fish populations.
Sediment toxicity benchmarks are exceeded for arsenic, cadmium, lead and zinc at all locations
that were evaluated (Lightning Creek, Christal Creek at outlet and downstream of Christal Lake,
Upper and Lower South McQuesten River). Arsenic and cadmium sediment concentrations at
background locations also exceed sediment toxicity benchmarks. Although the sediment toxicity
benchmarks have been exceeded at South McQuesten River and Lightning Creek, benthic
community surveys have reported healthy communities in these two locations. Low numbers and
diversity have however been documented in Flat and Christal Creeks suggesting that the high
concentrations of COPC in sediments in these two creeks may be adversely affecting benthic
communities.
Terrestrial Assessment
An assessment was also carried out for ecological receptors present in the terrestrial
environment. As indicated above, the site was divided up into several different areas. The
receptors that were considered were avian species such as grouse and waterfowl, small
mammalian species such as beaver (aquatic-based diet), fox, hare, marmot and mink(aquatic-
340821-001 – FINAL – May 2011 ES-3 SENES Consultants Limited