Geoscience Reference
In-Depth Information
of one resource affects the other, as well as potentially affecting the flow and qual-
ity of surface-water bodies connected to the ground water system. These effects may
extend over many years or decades. Techniques are needed to predict the effects of
saline ground water development in three dimensions and with time. Variable density
numerical models have been used successfully to simulate the subsurface occurrence
and movement of saltwater in coastal environments in many locations. The use of
these models to quantify the movement of inland saline water resources would aid in
understanding the impacts of utilizing saline water resources for desalination.
Disposal of the volumes of brine produced as a residual product of desalination is
a primary environmental issue associated with desalination. Residual products from
desalination of seawater are pumped to the sea. The expense of geologic disposal of
residual products from inland saline ground water is a major factor that affects the
cost-effectiveness of ground water desalination. Disposal of residual products of de-
salination requires careful consideration of their chemical composition. For example,
disposal in deeper (higher temperature) saline aquifers may lead to precipitation of
minerals, including calcite, and gypsum that have lower solubility at higher tempera-
tures (Kharaka at al., 1997). Underground injection of saline water currently is done in
the US to dispose of oil-fi eld brines.
ARE THERE OTHER SOURCES OF TREATABLE GROUND WATER?
Other sources of ground water may be amenable to desalination. These possibilities,
for which research continues, include treating water co-produced with oil and conven-
tional natural gas (Kharaka et al., 1999) and water co-produced with coal-bed methane
(Rice and Nuccio, 2000). Many oil- and gas-producing formations have associated
water that is only slightly saline (less than 10,000 mg/l), notably in the intermoun-
tain basins of the western US. Coal-bed methane water in the Powder River Basin
of Wyoming is generally less than 3,000 mg/l TDS. The likely presence of organic
compounds in this water complicates treatment.
(Left photograph) A desalination plant for the City of Cape May, New Jersey, was
built inside the brick building of the former Cape May Water Works. (Right photo-
graph) The automated desalination plant can produce from 750,000 to 2 million gal-
lons of water per day. (Photos: Jennifer Kopp, courtesy of CapeMay.com) Saltwater con-
tamination has forced the closure of water-supply wells for the City of Cape May, New
Jersey, and caused concerns about the future sustainability of ground water. Long-term
monitoring of the resource and a numerical ground water model of the aquifer system
of the Cape May Peninsula were key elements to help engineers design an approach to
combine desalination of brackish ground water at some wells and reduce pumping at
others to stabilize the saltwater front (Galloway et al., 2003; Lacombe and Carleton,
2002).
CONCLUSIONS
Desalinated ground water potentially represents an increasing component of the Na-
tion's water supply; however, relatively little is known about saline ground water re-
sources. An improved knowledge base is needed to better define their distribution and
