City of Prince George - Snow Disposal at the Lansdowne Road ...

also contained in the collected snow at low concentrations, and that the snow additions
increased the effluent concentrations of them as well. Therefore, the metals toxicity of the
effluent may have been increased to some degree by the snow additions. However, it should
be noted that the snow additions significantly lowered the temperature of the WWTC effluent,
and the toxicity of metals is theoretically reduced at lower temperatures, due to lower rates of
metabolism in the fish. Since the permit at the WWTC does not include any limits for metals,
snow additions to the chlorine chamber are unlikely to be limited by metals concentrations,
unless those concentrations are high enough to cause a failure to pass the 96 hour LC50 toxicity
bioassay. As described in Section 5.2, the 96 hour LC50 bioassay tests showed the WWTC
effluent to be non-acutely toxic in all cases.
The data in Table 2 show that the water hardness (due to calcium and magnesium) and the
phosphorus concentration were marginally reduced by the snow additions, likely due to
dilution by the softer snow melt water. A reduction in water hardness tends to increase the
toxicity of metals; however, the decrease in hardness due to snow additions was marginal
(138.6 mg/L as calcium carbonate in the influent versus 135.1 mg/L as calcium carbonate in
the effluent), and is unlikely to have a significant effect on effluent metals toxicity.
5.2 Effect of Snow Disposal on WWTC Effluent Toxicity
The purpose of the bioassay tests was to evaluate the effects of snow additions on the toxicity
of the WWTC effluent. According to the 96 hour LC50 bioassay, the WWTC effluent was non-
acutely toxic with and without snow additions, at both the standard bioassay testing
temperature of 15 o C and at the actual temperatures recorded in the WWTC effluent during the
snow melting test (Appendix 6).
As described earlier, the toxicity of ammonia and metals is theoretically reduced at lower
temperatures. However, note that the sample of undiluted WWTC effluent tested at 15 o C
resulted in no mortalities, while the sample of undiluted effluent tested at 11 o C resulted in 10%
mortality (one of ten fish). Similarly, the sample of WWTC effluent mixed with snowmelt
water tested at 15 o C resulted in no mortalities, and the sample of the mixture tested at 5 o C
resulted in 30% mortality (three out of 10 fish). This apparent anomaly might be explained by
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