Download - National Environmental Services Center - West Virginia ...

J U R I E D A R T I C L E
FIGURE 1
Implementation of phosphorus effluent limits by year, 1970 to 1997(Source: Litke, 1999).
Small Flows Quarterly, Fall 2004, Volume 5, Number 4
Great Lakes and Lake Champlain
initiatives. Since that time, the
number of new permits with phosphorus
concentration limits has
declined, but has remained steady
at about 40 permits a year during
the 1990s. The numbers indicated
in Figure 1 do not include restrictions
on loads, per se, but only
phosphorus concentrations. With
the shift in focus toward allocation
of loads, as prescribed in TMDL
rules, there is an increasing emphasis
on restricting phosphorus
loads from dischargers rather than
phosphorus concentrations.
The National Water Quality Inventory
(EPA, 2002) summarizes
the extent and sources of impairments
for the nation’s water bodies.
Nutrients were reported as the
leading pollutant/stressor for lakes
and reservoirs, affecting 50 percent
of impaired lake acres, while
nutrients were the fifth leading
pollutant/stressor for rivers, affecting
20 percent of stream miles
(EPA, 2002). The report also indicates
that 12 percent of impaired
lake acres were a result of municipal
point sources, while 10 percent
of impaired river and stream miles
listed municipal point sources as a
leading source of impairment
(EPA, 2002). While the focus of
water pollution control has, in
many respects, shifted from point
sources to nonpoint sources, discharges
of phosphorus from
WWTPs continue to be a major
source of impairment for many of
the nation’s waters.
Current Status of
Phosphorus Control
As of August 1997, there were
approximately 16,000 WWTPs
listed in EPA’s Permit Compliance
System, serving almost 190 million
people or roughly 75 percent
of the U.S. population (Litke,
1999). About 7.3 percent of these
plants (representing 17 percent of
total WWTP discharge) had phosphorus
limits in their permits,
while 15.3 percent of listed plants
(representing 40 percent of total
WWTP discharge) were required
to monitor phosphorus (Litke,
1999) [1]. Phosphorus limits at
most plants ranged from 0.5 to
1.5 mg/L (Litke, 1999).
Figure 2 indicates the distribution
of these plants. Most plants
were clustered around the Great
Lakes or on the Eastern seaboard,
with a significant concentration
around the Chesapeake Bay, a
distribution that reflects the phosphorus
control programs instituted
in these regions.
Unlike the diffuse phosphorus
emissions from agricultural nonpoint
sources, WWTP emissions
can be directly controlled through
the NPDES permitting system.
Thus, if several phosphorus
sources are identified, phosphorus
control at WWTPs may be
deemed the source that can be
controlled with the greatest degree
of certainty, from both legal and
biophysical perspectives. Thus,
the number of nutrient 303d list-
ings attributed to nutrients, a revitalized
TMDL program, and the
premise that emissions from point
sources are more controllable than
for nonpoint sources has given
new impetus to additional phosphorus
controls at WWTPs.
While phosphorus effluent limits
have been instituted at WWTPs
in several regions of the U.S., including
the Great Lakes, Chesapeake
Bay, and Lake Champlain
watersheds, small WWTPs (usually
defined by design flow) have generally
been exempted from phosphorus
limits. These exemptions
have been based on the premise
that it is too costly for small communities
to fund phosphorus removal.
In addition, other things
being equal, the environmental
impact of small WWTPs is much
less than larger plants, because
the amounts of phosphorus emitted
are much smaller. Finally,
from an efficiency standpoint, the
cost per pound phosphorus removed
is often much higher for
smaller plants than for large
plants because small plants cannot
achieve the economies of scale
typically needed to achieve lowcost
removal.
Despite these factors, phosphorus
removal for even very small
WWTPs is sometimes considered.
The following section of this paper
presents a case study where phosphorus
controls were considered
for WWTPs in six small communities
in a phosphorus impaired wa-
38