According to the 1996 National Water Quality Inventory, a biennial summary of
State surveys of water quality, approximately 40 percent of U.S. water bodies are still
impaired by pollution and do not meet water quality standards. A leading source of this
impairment is runoff. In fact, according to the inventory, 13 percent of impaired rivers,
21 percent of impaired lake acres and 45 percent of impaired estuaries are affected by
urban/suburban storm water runoff and 6 percent of impaired rivers, 11 percent of impaired
lake acres and 11 percent of impaired estuaries are affected by construction site discharges.
The Storm Water Phase II Final Rule is the next step in the EPA's effort to preserve,
protect, and improve the Nation's water resources from polluted storm water runoff.
Phase II is intended to further reduce adverse impacts to water quality and aquatic
habitat by instituting the use of controls on the unregulated sources of storm water
discharges that have the greatest likelihood of causing continued environmental degradation.
Common Pollutants to our waterways include:
Litter and other debris
Uncontrolled runoff from construction sites is a water quality concern because
of the devastating effects that sedimentation can have on local water bodies,
particularly small streams. Numerous studies have shown that the amount of sediment
transported by storm water runoff from construction sites with no controls is
significantly greater than from sites with controls.
During storms, construction sites may be the sources of sediment-laden runoff,
which can overwhelm a small stream channel's capacity, resulting in a streambed scour,
stream bank erosion, and destruction of near-stream vegetative cover. Where left
uncontrolled, sediment-laden runoff has been shown to result in the loss of in-stream
habitats for fish and other aquatic species, an increased difficulty in filtering
drinking water, the loss of drinking water reservoir storage capacity, and negative
impacts on the navigational capacity of waterways.
Who Is Covered by the Phase II Final Rule?
The final rule "automatically" covers two classes of storm water dischargers on a
1. Operators of small MS4s located in "urbanized areas" as delineated by the Bureau of the
Census. A "small" MS4 is any MS4 not already covered by Phase I of the NPDES storm water program.
2. Operators of small construction activities that disturb equal to or greater than 1 (one)
and less than 5 (five) acres of land.
Additional Designations by the Permitting Authority
Small MS4s located outside of the urbanized areas, construction activity
disturbing less than 1 acre, and any other storm water discharges can be
designated for coverage if the NPDES permitting authority, or EPA determines
that storm water controls are necessary.
A regulated small MS4 operator must develop, implement, and enforce a storm
water management program designed to reduce the discharge of pollutants from
their MS4 to the "maximum extent practicable," to protect water quality, and to
satisfy the appropriate water quality requirements of the CWA. The rule assumes
the use of narrative, rather than numeric, effluent limitations requiring
implementation of BMPs.
The small MS4 storm water management program must include the following six
minimum control measures: public education and outreach; public
participation/involvement; illicit discharge detection and elimination; construction
site runoff control; post-construction runoff control; and pollution
A regulated small MS4 operator must identify its selection of BMPs and
measurable goals for each minimum measure in the permit application. The
evaluation and assessment of those chosen BMPs and measurable goals must be
included in periodic reports to the NPDES permitting authority.