supporting water quality standards set forth in this regional water quality
management plan update.
For planning purposes, measures for nonpoint source water pollution control were
grouped into categories.    The first category was defined as basic practices,
which were recommended to be generally applied throughout the Region and included
construction site erosion control, onsite sewage disposal system management, and
streambank erosion controls. The effectiveness of such practices in reducing
nonpoint source pollutant loadings varied by subwatershed and by pollutant. For
conventional pollutants, these practices generally are expected to provide for
a 5 to 30 percent reduction in nonpoint source pollutant loadings. Additional
practices were then considered in incremental steps which would provide 25 and
50 percent reductions in nonpoint source pollutants from urban lands and 25, 50,
and 75 percent reductions in nonpoint source pollutants from rural lands. The
types of practices recommended to be considered for these various levels of
nonpoint source control are summarized in Appendix A.
In the initial plan, water quality simulation modeling was conducted to determine
the level of nonpoint source pollution control needed to meet the water quality
standards associated with recommended water use objectives for each subwatershed
area considered. The resulting recommendations of that analysis are shown on
Map XVIII-9. For nearly all of the Southeastern Wisconsin Region, land manage-
ment practices designed to achieve about a 25 percent reduction in nonpoint
source pollutants, in addition to construction site erosion control, onsite
sewage disposal system management, and streambank erosion controls were recom-
mended to be implemented throughout the entire urban and rural areas. For these
areas, the level of control expected to be achieved when considering the effec-
tiveness of the basic practices, plus the land management practices designed to
achieve the 25 percent reduction, varied, depending upon the specific subwater-
shed considered, ranging for specific subwatersheds from a 30 to 55 percent
reduction overall.
The one exception to this recommendation was that no specific additional nonpoint
source controls were recommended for the 21-square-mile area tributary to the
Milwaukee Metropolitan Sewerage District inline storage deep tunnel system where
stormwater runoff from storms with up to a recurrence interval of about one or
two times per year is to be conveyed to the tunnel system and be stored and then
treated at the District treatment plants, thus providing a high level of nonpoint
source pollution control. In the area tributary to the combined sewer system,
the discharge of stormwater to the surface water system will be reduced from an
average of 50 times per year to 1.4 times per year. Accordingly, a level of
control of nonpoint source pollutants exceeding 90 percent is expected. This is
particularly important in that the area served by the combined sewer system
represents the most highly urbanized area of the Region.      This area contains
concentrations of industrial, commercial, institutional, and transportation land
uses which are expected to generate high nonpoint source loadings and where
controls of nonpoint source pollutants using land management practices would be
difficult and costly.    The control of nonpoint sources in the combined sewer
service area as provided by the inline storage deep tunnel system exceeds that
which could practically be provided by any other practicable means.
Additional urban nonpoint source controls designed to provide about a 50 percent
reduction in pollutant runoff were also recommended to be applied to a total of

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