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In contrast to the pretreatment program, most aspects of the water-quality regula-
tory system are largely controlled at the state and federal levels. The NPDES system is
administered through the EPA; however, similar to many environmental statutes, most
states have assumed active management responsibilities, with the ERA maintaining an
oversight role. National effluent and pretreatment standards have been promulgated for
55 industry types (Table 6-2). However, facilities not associated with a specific category
must meet general discharge requirements intended to protect water quality.

Ambient-Water-Quality Control

In addition to a nationally based system of discharge controls based on industry types, a
second regulatory strategy is based on ambient water quality. Subject to federal review,
states are required to establish water-quality standards for intrastate waters. If discharge
standards are not sufficient to meet these ambient regulations, additional discharge stan-
dards must be imposed.

This system of water-quality control has resulted in substantial improvements in
water quality. Point sources of pollution have been controlled to such an extent that
much of the remaining pollution comes from nonpoint (or diffuse) sources. Nonpoint
pollution originates from a variety of small sources that in combination may result in
significant pollution; examples are agricultural storm water runoff carrying fertilizers
and pesticides and oil dripping from cars and trucks. The EPA estimates have indicated

191

Source: U.S. Environmental Protection Agency, Subchapter N, Effluent Guidelines and Standards, 2001.
http://www. epa. gov/docs/epacfr40/chapt-I. info/subch-N. him.

that between 50 and 70 percent of impaired or threatened surface waters are affected by
nonpoint source runoff from agriculture, with urban runoff responsible for another 5 to
15 percent.