MIL-HDBK-1005/16
2.3.3
Wastewater Effluent Toxicity. Effluent limits to
minimize the toxic effects of discharges on aquatic life are
increasingly being added to NPDES permits. These limits can
apply to specific aquatic life or can contain general criteria to
limit toxicity.
2.3.3.1
Aquatic Life Criteria. For aquatic life criteria,
acute or chronic values apply. The application of acute versus
chronic criteria depends on a number of items, including the use
classification and the available dilution in the receiving
stream. Generally, if the available dilution is greater than
100 to 1, the acute criteria apply.
2.3.3.2
General Narrative Criteria.
An example of a general
narrative criteria follows:
Toxic substances shall not be present in receiving waters,
after mixing, in such quantities as to be toxic to human,
animal, plant or aquatic life or to interfere with the
normal propagation, growth and survival of the indigenous
aquatic biota.
To address this narrative criteria, most states apply a
whole-effluent toxicity requirement in the permit. The whole-
effluent approach to toxics control for the protection of aquatic
life involves the use of acute and/or chronic toxicity tests to
measure the toxicity of wastewaters. The acute test assesses the
lethality of the wastewater to the test organisms and is
typically conducted for 96 hours or less. The chronic test
assesses growth and reproduction in addition to lethality and is
typically conducted over a 7-day period. Whole-effluent toxicity
tests use standardized surrogate freshwater or marine plants,
invertebrates, and vertebrates. The test is run at the same
dilution as is allowed for the wastewater in the receiving
stream. If the criteria cannot be met, a toxicity reduction
evaluation of the discharge must be conducted.
2.3.4
Negotiation of Effluent Limits. Careful review by the
discharger of the specific basis used for the water quality-based
effluent limits is advisable. In many cases, the basis used to
develop the effluent limits is open to negotiation. Potential
changes to the effluent limitations should also be discussed with
the regulatory agency. In many cases, future limitations may
affect the initial selection and design of treatment processes.
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