Water-quality assessment of the Rio Grande Valley, Colorado, New Mexico, and Texas -- Shallow ground-water quality and land use in the Albuquerque area, central New Mexico, 1993

This report describes the quality of shallow ground water and the
relations between land use and the quality of that shallow ground water
in an urban area in and adjacent to Albuquerque, New Mexico. Water
samples were collected from 24 shallow wells. Samples were analyzed for
selected common constituents, nutrients, trace elements, radionuclides,
volatile organic compounds, and pesticides.

The study area, which is in the Albuquerque Basin in central New Mexico,
was limited to the Rio Grande flood plain; depth to water in this area
generally is less than 25 feet. The amount and composition of recharge to
the shallow ground-water system are important factors that affect shallow
ground-water composition in this area. Important sources of recharge that
affect shallow ground-water quality in the area include infiltration of
surface water, which is used in agricultural land-use areas to irrigate
crops, and infiltration of septic-system effluent in residential areas.
Agricultural land use represents about 28 percent of the area, and residential
land use represents about 35 percent of the total study area. In most of the
study area, agricultural land use is interspersed with residential land use
and neither is the dominant land use in the area. Land use in the study area
historically has been changing from agricultural to urban.

The composition of shallow ground water in the study area varies
considerably. The dissolved solids concentration in shallow ground water in
the study area ranges from 272 to 1,650 milligrams per liter, although the
relative percentages of selected cations and anions do not vary substantially.
Calcium generally is the dominant cation and bicarbonate generally is the
dominant anion. Concentrations of nutrients generally were less than 1
milligram per liter. The concentration of many trace elements in shallow
ground water was below or slightly above 1 microgram per liter and there was
little variation in the concentrations. Barium, iron, manganese, molybdenum,
and uranium were the only trace elements analyzed for that had median
concentrations greater than 5 micrograms per liter. Volatile organic
compounds were detected in 5 of 24 samples. Cis-1,2-dichloroethene and
1,1-dichloroethane were the most commonly detected volatile organic compounds
(detected in two samples each). Pesticides were detected in 8 of 24 samples.
Prometon was the most commonly detected pesticide (detected in 5 of 24
samples). Concentrations of volatile organic compounds and pesticides detected
were much smaller than any U.S. Environmental Protection Agency standards
that have been established.

Infiltration of surface water and the evaporation or transpiration of
this water, which partially is the result of past and present agricultural
land use, seem to affect the concentrations of common constituents in shallow
ground water in the study area. The small excess chloride in shallow ground
water relative to surface water that has been affected by evaporation or
transpiration could be due to mixing of shallow ground water with small
amounts of precipitation/bulk deposition or septic-system effluent.

Infiltration of septic-system effluent (residential land use) has
affected the shallow ground-water composition in parts of the study area on
the basis of the small dissolved oxygen concentrations, large dissolved
organic carbon concentrations, and excess chloride. Despite the loading of
nitrogen to the shallow ground-water system as the result of infiltration of
septic-system effluent, the small nitrogen concentrations in shallow ground
water probably are due to the small dissolved oxygen concentrations and
relatively large dissolved organic carbon concentrations.

The small concentrations and lack of variation of most trace elements
indicate that land use has not substantially affected the concentration