080121-08MN006-Sabina Hackett River Project Proposal ... - NIRB

Description of the Existing Environment2004 to 2006. As indicated by the monthly sampling in 2007, sample timing can significantlyaffect water quality values for these streams.6.1.10.5 Lake Sediment QualityAs opposed to water, sediments are less temporally variable in their characteristics, providinguseful composites of environmental conditions over time. Sediments also play an important rolein benthic invertebrate habitat quality, and collecting samples of present sediment conditionsprovides baseline information for later monitoring studies.In August 2007 sediment samples were collected from a number of lakes and streams within theHackett River study area. All sediment samples collected were compared to guidelines for theprotection of aquatic life provided by CCME, namely; the Interim Sediment Quality Guidelines(ISQG) and the Probable Effects Levels (PEL). The more conservative ISQGs are levels belowwhich adverse biological effects are rarely observed, whereas the higher PELs corresponds to theconcentration above which negative effects frequently occur.Lake sediment samples were collected from 21 lakes in August, 2007. The 2007 sedimentquality program focused on characterizing the natural variation in lake sediments with depth andgeographic location. Lakes sampled lay within a number of different watersheds and includedtwo reference lakes located ~ 10 km away from the location of potential mining activities.GeneralSampled lake sediments were predominantly composed of clay, silt, and sand with low gravelcontent and very little organic debris. As expected in Arctic oligotrophic lakes, sediments tendedto be very low in nutrients, with nitrate + nitrite generally below detection limits and AvailablePhosphorus below 140 µg/g. In contrast, sediments tended to be very high in many metals. Forvariables for which CCME guidelines are available (arsenic, cadmium, chromium, copper, lead,mercury, and zinc), lake sediments frequently exceeded CCME guidelines for all parameters.ISQGs for Cd, Cu and Zn were exceeded in all lakes (with the exception of one of the referencelakes), and often by values many times that of the guideline. CCME PELs were also repeatedlyexceeded, at times by as much as 3 to 40 times the PEL concentration. The high metalconcentrations of the sediments in the Hackett River area are a natural product of the high levelsof mineralization in the surrounding area, but do pose a concern in that any disturbance of thesediments may have significant impacts on water quality.Depth VariationIn general, lakes within the study area are small to medium sized with a maximum lake depth of18 m. Sediment samples were collected from each of the following zones within a lake, lakedepth permitting: shallow depth zone (0 -5 m), mid depth zone (5.1 -10 m), and a deep depthzone (> 10 m). The shallow sediments of most lakes in the study area are primarily composed ofmedium to large boulders, with the exception of the southern Camp Basin lakes (Hood, Triangleand Kathy). Although some variables showed a trend of increasing concentrations of variousmetals and nutrients with depth, such as Total P, Total Organic Carbon, Ag, and Hg, mostvariables showed no consistent relationship to depth. Some Boot Basin lakes surrounding thepossible Crown Pillar Pit (Boot, Thigh, Big Toe and Hungrat lakes) exhibited strong increasesJanuary 2008 Hackett River Project – Project Proposal Sabina Silver CorporationReport Version B.1 6–21 Rescan Environmental Services Ltd. (Proj. #833-2)