Eastern Bernalillo County is a historically rural, mountainous
area east of Albuquerque, New Mexico. Historically, the primary
economic activity consisted of subsistence farming and ranching
and support of these activities from small communities. During
the last 40 to 50 years, however, the area increasingly has become
the site of residential developments. Homes in these developments
typically are on 1- to 2-acre lots and are serviced by individual
wells and septic systems. Between 1970 and 1990, the population of
the area increased from about 4,000 to more than 12,000, and housing
units increased from about 1,500 to more than 5,000.
Results of analysis of water samples collected from 121 wells
throughout eastern Bernalillo County in 1990 indicated that (1)
total-nitrate concentrations in 10 samples exceeded the U.S.
Environmental Protection Agency national primary drinking-water
regulation maximum contaminant level of 10 milligrams per liter
as nitrogen; (2) total-nitrate concentrations may be related to
the length of time an area has been undergoing development; and
(3) large dissolved-chloride concentrations may result from geologic
origins, such as interbedded salt deposits or upward movement
of saline ground water along faults and fractures, as well as
from domestic wastewater disposal.
Ground water throughout eastern Bernalillo County was assessed to
be highly susceptible to contamination by overlying domestic
wastewater disposal because (1) soils in more than 95 percent
of eastern Bernalillo County were determined by the U.S. Department
of Agriculture Natural Resources Conservation Service to
have severe limitations for use as septic-system absorption
fields and (2) a fractured carbonate geologic terrane, which
typically has large secondary permeability and limited sorption
capacity, is at the surface or underlying unconsolidated material
in 73 percent of the area. Ground-water-level rises following an
episodal precipitation event during July 22-27, 1991, were large
and rapid, particularly in the fractured carbonate terrane. This
response indicates a significant hydraulic connection between the
land surface and the water table.
