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RE: E-M:/ Plan would let sewage flow into Michigan lakes
- Subject: RE: E-M:/ Plan would let sewage flow into Michigan lakes
- From: fred cowles <email@example.com>
- Date: Sat, 1 Jan 2005 14:43:02 -0800 (PST)
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- List-name: Enviro-Mich
- Reply-to: fred cowles <firstname.lastname@example.org>
Enviro-Mich message from fred cowles <email@example.com>
This is a response to two comments by Curl and Harris
The draft policy would allow mixing of sewage that has
received partial treatment with sewage that has
received full treatment during wet weather periods.
Typically ?full treatment? means both physical
treatment like screening and sedimentation, and
secondary treatment like activated sludge or fixed
film bioreactors. ?Partial treatment? would imply
just physical treatment. ?Filtered? is not usually
used in this context as filtration is normally a
tertiary treatment process that is employed to produce
a very high quality effluent. The question of
disinfection is one that varies from state to state.
Michigan requires that all sewage discharges be
disinfected, but many states do not.
The draft EPA blending policy would not authorize any
water quality standards violations. Therefore, in
Michigan, all blended discharges would need to be
disinfected. Secondly, the policy would not authorize
any effluent limit violations.
Effluent limits are determined on the basis of the
more stringent of two criteria. The first is the
national standard of ?secondary treatment?. This is
often thought of as ?biological treatment? but in fact
is determined by chemical analysis of a few
parameters, not by the kind of treatment provided.
The secondary treatment standard is met if the
discharge contains less than 30 mg/l Biochemical
Oxygen Demand (BOD), contains less than 30 mg/l
Suspended Solids, and has a pH in the neutral range (6
to 9). The standard is more complicated than that and
the details can get very confusing. The most
important additional requirement for this discussion
is the requirement for 85% removal of influent BOD and
The second criterion upon which the effluent limits
are determined is compliance with the state water
quality standards. In Michigan, this results in the
need for all facilities to remove phosphorus and to
provide disinfection. In many locations around the
state other effluent limits are needed such as lower
BOD and Suspended Solids limits, limits on Ammonia,
limits on various heavy metals and other toxicants.
COD or Chemical Oxygen Demand is seldom used to
describe the quality of domestic sewage. It is more
appropriate for industrial wastes.
Since the draft blending policy requires that both
criteria must be met, environmental protection is
properly assured. If it is not, then the issue is
adequacy of the water quality standards or the
effluent limits. So the debate over the policy should
be on the proper interpretation of the secondary
treatment regulation promulgated in the 1970s. This
gets into the details of how the 85% removal
requirement is calculated and when variances to the
requirement should be approved.
In environmental terms one would think that the
quality of a blended effluent would not be as good as
the quality of full treatment. This would be a hasty
conclusion. Treatment efficiency declines in wet
weather. So this remains an open question.
I am not taking a position on blending one way or the
other. I would just like the discussion on the topic
to relate to the real issue and not on emotion. The
News article was pure emotion. ?Do you want to drink
raw sewage?? on one side, and ?We can?t afford to
control pollution.? on the other.
The policy will allow the discharge of filtered and
diluted raw sewage (with no secondary treatment). The
question come down to comparing the discharge of
sewage that has been filtered and given secondary
(biological) treatment and disinfection, and a mixture
of that and sewage that has only been filtered, and
asking whether this is "acceptable" in terms of public
health and environmental concerns. In particular, the
BOD and COD of the blended discharge will be higher
than fully treated sewage, while the blended sewage
may or may not (as far as I can tell) be disinfected,
as is the fully treated discharge. Reading
www.epa.gov/npdes/blending does not answer these
questions as it does not give specific information on
BOD, COD and bacterial standards for fully treated vs
blended discharges. It would be appreciated if
someone here could address these issues more
explicitly. --Rane L Curl
could you provide some basis for your claims "will not
significantly improve environmental protection" and
"does not weaken environmental protections" . . .
craig k harris
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