Geologic, Hydrologic, and Urban Hazards for Design in Desert Environments - Design with the Desert: Conservation and Sustainable Development - page 111

5.7.7 Stormwater Pollution
The built environment differs distinctly from the natural setting by the type of surface.
Urban lands are covered with large expanses of impervious materials such as roads, con-
crete building foundations, driveways, parking lots, and rooftops. Water cannot penetrate
these hardened surfaces and will runoff unless it is captured. As rainwater falls on urban
lands, it picks up contaminants such as sediment, oil, and grease; toxic chemicals and pes-
ticides residues; viruses, bacteria, and nutrients from animal waste and failing septic sys-
tems; road salts; and heavy metals from roof shingles, motor vehicles, and other sources.*
This potent mix of contaminants is transported offsite in the stormwater runoff and may
significantly affect the downstream water quality in the watershed.
The EPA has established the National Pollutant Discharge Elimination System (NPDES)
Stormwater Program to regulate stormwater outflow from three areas: municipal sepa-
rate storm sewer systems, construction activities, and industrial activities. Municipal
waste-water treatment plants from all urbanized areas in the United States are required
to operate under an NPDES permit. All construction sites greater than 1 ac in size are
required to have a general construction permit that regulates the clearing and grading
of the land, movement of soil, and stockpiling of materials. Industrial sites must have a
Multi-Sector General Permit for industrial stormwater discharges. These operations rep-
resent the main sources of discharge of contaminants into the water system, and the EPA
delegates the oversight of the permitting of these operations to the states. †
Stormwater discharges are generally considered point sources of pollution, and devel-
opers or operators of discharge sites may be required to receive an NPDES permit before
they can release stormwater runoff. The intent of these regulations is to prevent or min-
imize stormwater runoff carrying harmful pollutants to discharge into streams, rivers,
reservoirs, or coastal waters. The oversight of stormwater runoff by the EPA presents the
developer or operator of a discharge site a real challenge to manage the onsite activities
to avoid violating the conditions of the permit of operation. The EPA has created several
guidance documents to help manage stormwater runoff, such as the National Menu of Best
Management Practices. ‡
5.7.8 Vegetation Hazard
Fire is a natural process in the southwestern United States that cleanses and rejuvenates
the land of dead and dying plant material. Some types of ecosystems in this region
are dependent upon fire to reverse senescence of plants and rejuvenate vegetation
assemblages, while other ecosystems appear to have seldom burned and are potentially
irreversibly harmed by fire. Moreover, this natural process has been suppressed through
the management of wildfires by the U.S. Forest Service and other federal agencies (see
Chapters 11 and 12). This practice has resulted in a buildup of dry plant material on
the forest floor on thousands of acres of Southwestern forests and increases in woody
vegetation in areas that once were grasslands.
The once sparsely populated forested areas of the Southwest are increasingly being
subdivided to allow the construction of retirement or vacation homes for urban dwellers.
Similarly, retirement subdivisions have created a checkerboard of dwellings in formerly
continuous grassland areas in southeastern Arizona, and the once common fires must be
* http://water.epa.gov/polwaste/nps/urban.cfm (accessed June 23, 2011).
† http://cfpub.epa.gov/npdes/stormwater/swbasicinfo.cfm (accessed June 23, 2011).
‡ http://cfpub.epa.gov/npdes/stormwater/menuofbmps/index.cfm (accessed June 23, 2011).