|
||||||
|
||||||
|
|
|
|||||
|
Water Quality Using the Guidelines to Set Objectives Water quality guidelines are used to set ambient water quality objectives for specific waterbodies. The objectives are based on present and future uses, waste discharges, hydrology, limnology, oceanography, and on existing background water quality. In most cases, the objectives will be the same as the guidelines. However, when natural background levels exceed the guidelines, the objectives could be less stringent than the guidelines. In rare instances, for example, if the resource is unusually valuable or of special provincial significance, using objectives that are more stringent than the guidelines could increase the safety factor. Another approach in special cases would be to develop site-specific guidelines by conducting toxicity experiments in the field. This approach is costly and time consuming, and is seldom used. Neither the guidelines nor the objectives derived from them have any legal standing. Objectives can be used to calculate waste discharge limits. These limits are outlined in waste management permits that do have legal standing. Objectives are not usually incorporated as conditions of a permit. Objectives are also used in the preparation of waste management orders and approvals. These documents also have legal standing. Since there
are an endless number of substituted phenols possible, all
with somewhat different toxicity thresholds to individual species,
and it is not practical to determine guidelines for each phenol,
we recommend a site-effluent-and-species-specific determination
for any given situation. This means that one should determine
what species are present in the receiving water, choose several
that are most likely to be very sensitive, amphibian tadpoles
and salmonid fry are normally the species of choice, and carry
out bioassays using a typical effluent mixture of phenols.
The water quality objective developed for the local situation
should be 0.05 of the LC50 determined by the assay in order
to account for any more sensitive species and for atypical,
more toxic, effluent mixtures.
|
||||||
|
|
