The DNR is reccommending to the EPC to weaken ammonnia
emmission standards by Waste Water Treatment Plants as
long as they rarely affect aquatic life. Here is there
response to our objections.
The new procedure will result in higher permit limits
compared to existing permits and allow wastewater
treatment plants to discharge higher pollutant loads.
In general, the new permit derivation procedure, as
well as the TSD approach, will result in more relaxed
(less stringent) limits for most wastewater treatment
plants, although this is not universally true for all
plants or for all months. In theory, more relaxed
limits will allow the discharge of more pollutants
such as ammonia, but treatment plants cannot be
operated so as to “push” the limits at all times. When
determining a treatment plant process, the process
selected must be able to meet permit limits
consistently - at all times. Well run treatment plants
typically discharge effluent with pollutant
concentrations well below permit limits and it is
unlikely a doubling or tripling of the average permit
limits will result in a doubling or tripling of the
total mass of pollutants in actual operation. The
higher limits may, however, allow for occasional
“burps” in the biological treatment process without
exceeding permit limits. Despite the temporary
increase in discharge above the normal operational
level (yet below the revised permit limit), water
quality and aquatic life will be protected. Currently,
many municipalities are concerned that occasional
treatment plant upsets could result in permit
violations and potential enforcement actions, even
though aquatic life would not be adversely impacted.Ę
The resulting higher permit limits (especially for
ammonia) will not be protective of aquatic life,
especially during times of low flow. Both the new
ammonia limits and the proposed new permit derivation
procedure are, in fact, protective of all aquatic life
for the vast majority of time. The new permit limits
will not allow short-term exceedances more than once
every three years. Although the frequency of
exceedances theoretically may exceed once in three
years where a protected flow has been adopted in lieu
of a statistically-derived low flow value, the TSD
allows that more frequent exceedances could be
tolerated on smaller streams where the aquatic
population is acclimated to rapid changes and can
quickly recover. Furthermore, the Department uses
steady-state modeling techniques and applies
conservative assumptions in the calculations of the
acute and chronic wasteload allocations by considering
the "worst-case scenario" discharges. As noted in the
EPA's TSD:Ę
In general, steady-state analyses tend to be more
conservative than dynamic models because they rely on
worst-case assumptions. Thus, permit limits derived
from these outputs will generally be lower than limits
derived from dynamic models.Ę
Because of the conservatism built into the wasteload
allocation calculations, the new permit procedure will
be protective of the aquatic life in Iowa streams.Ę
At a time when there is an emphasis to decrease
nitrogen and ammonia inputs to streams from nonpoint
sources, the higher permit limits for ammonia are
going in the wrong direction. Higher ammonia limits
will theoretically allow more ammonia to be
discharged, although, as discussed above, significant
increases are unlikely. Even if more ammonia is
discharged, ammonia quickly degrades in the stream to
non-toxic forms of nitrogen such as nitrate. Higher
ammonia limits will not increase the total nitrogen
discharges into the streams; the total nitrogen
passing through a wastewater treatment facility is
unchanged and only the chemical forms of the nitrogen
in the effluent change. Current regulations (state and
federal) do not limit the amount of total nitrogen
passing through a wastewater facility. Further, as
ammonia limits are established independent of total
nitrogen, ammonia limits will remain in place even in
the event nutrient standards are adopted. In the near
future, wastewater treatment plants may have to
address nutrient removal (nitrogen and phosphorus) by
virtue of a combination of one or more of the
following: numeric water quality standards for
nutrients, nutrient TMDLs, or technology-based
effluent standards for nutrients.Ę
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