AWWQRP Background
The Pima County Regional Wastewater Reclamation Department
(PCRWRD), in Tucson, Arizona has been funded by the U.S. Environmental
Protection Agency (EPA) to conduct the Arid West Water Quality
Research Project (AWWQRP).
The objective of the project is to improve the scientific base
for regulation of water quality, protection of species, habitats,
and uses of watercourses, and designation of appropriate treated
wastewater effluent controls in ephemeral and effluent-dependent
watercourses of the arid and semi-arid western states.
   
The arid and semi-arid portions of the western U.S. extend from
south-central Texas west to southeastern California and north through
Oregon on the east side of the Sierra Nevada and the Cascade ranges
to the Canadian border in eastern Washington. The region
includes a small part of southern Idaho, and then extends eastward
through Montana to central North Dakota, and south through central
South Dakota and Nebraska; small portions of western Kansas and
Oklahoma are included, and essentially all of Arizona, New Mexico,
Colorado, Wyoming, Utah, and Nevada are in the region. Five
EPA regional offices are involved in regulating water quality in
these seventeen states.
Arid and semi-arid region
Ephemeral and effluent-dependent streams characterize many waterways
of the arid West. Ephemeral river and stream channels are dry for
most of the year, carrying water only in response to rainfall events
or spring snow melt. See, for example, the hydrograph for the Santa Cruz River a few miles downstream
from Tucson, Arizona. Stream segments that derive essentially all
their flow from wastewater treatment facilities are termed effluent-dependent.
Aside from considerations of the aquatic habitat that must be protected
in these streams, the effluent contribution to a riparian habitat
supporting amphibian and terrestrial communities must be considered.
Thus there are not only multiple uses but sometimes competing uses
associated with the quality and quantity of the water. The project
was created to address concerns that the water quality criteria
developed under the Clean Water Act - on which state water quality
standards are based - may not be appropriate for arid and semi-arid
ecosystems.
Hydrograph
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