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EPA announced the availability of the revised
recommended ambient freshwater water quality
criteria for copper on February 22, 2007. Both the
new and the old criteria are formulaic. The previous
criteria formula was hardness based. The new
criteria formula uses hardness, pH and Dissolved
Organic Carbon (DOC). Generally speaking, the new
criteria acute concentration will be more stringent
for surface waters with a pH of 7.0 and below, when
the hardness is less than 300 mg/l CaCO3
and the DOC is less than 16 mg/l.
The implications could be
significant to POTWs and Industrial dischargers.
NPDES dischargers to surface waters, municipal and
industrial alike, will need to determine the extent
to which the new criteria may tighten up existing
discharge limits. For example, if the receiving
water’s water quality numbers are:
|
pH |
6.5 SU |
|
Hardness |
40 mg/l as CaCO3 |
|
DOC |
2 mg/l |
The new criteria concentration
will be 1.9 µg/l, or 1/4 of what it had been
previously (Figure 1.) That is quite a dramatic
decrease.
We will now be delving in waters
where corrosion byproducts become critical.
Industrial dischargers may have to consider changing
existing pipe materials or modifying their water
chemical balance to improve corrosion control. POTWs
may have to begin practicing pollution abatement on
the water treatment side of their utility services.
The impact of this new criteria
on Pretreatment Programs will likely be greater.
Metal concentration pretreatment limits are
typically derived considering inhibition of the
treatment process, the land limiting constituent for
biosolids disposal and pass-through. A 1.0 mg/l
headworks inhibition concentration limit is not out
of the ordinary. About 99% of the copper will
partition to the biosolids leaving upwards of 10
µg/l in the water column. If this example were used
with the receiving water conditions previously
cited, the headworks concentration would have to be
reduced to less than 0.2 mg/l for the criteria not
to be exceeded.. Thus pass-through would be the
controlling factor in setting the pretreatment limit
fo copper.
Reissuance of NPDES permit limits will trigger
tighter effluent concentrations for copper which, in
turn, will likely cause tightened pretreatment
limits. Major operating expenditures for chemicals
and maintenance/capital expenses for copper source
elimination and or treatment can be expected as
well.
A copy of
the new document is available on the
EPA website.
For more information, contact
Lee Beetschen. |
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