Study: Nitrate Slowly Moving into Oregon-area Aquifer
Shallow aquifers supplying drinking water to rural residents of
southern Deschutes and northern Klamath counties near La Pine, Ore.,
are vulnerable to contamination by wastewater from on-site, residential
wastewater disposal (septic) systems, according to the findings of a
study by the U.S. Geological Survey (USGS).
At present, relatively few wells in the La Pine area have nitrate
concentrations greater than EPA's drinking water standard of 10 parts
per million. However, the USGS study predicts that unless nitrogen
loading from septic systems can be reduced, future development will
lead to water quality problems in the area.
The USGS investigation focused on a 250-square-mile area that
included rural residential areas between Sunriver and La Pine and was a
part of efforts by Deschutes County and the Oregon Department of
Environmental Quality (DEQ) to evaluate alternatives for protecting
shallow aquifers that supply drinking water for most residents of the
area.
According to David Morgan, the USGS study's chief, "Our
investigation agrees with previous assessments by DEQ and others, which
found that nitrate contamination is a threat to the quality of water in
the primary aquifer underlying the La Pine area."
Nitrate is formed when nitrogen in household wastewater is exposed
to oxygen in soils around and beneath on-site septic systems. The
presence of elevated nitrate levels in drinking water is significant
because of its potential health effects. The most commonly known
effect, methemoglobinemia, or "blue-baby syndrome," occurs in infants
and children, where the oxygen-carrying capacity of the blood is
diminished.
USGS geochemist Stephen Hinkle, a member of the study team, noted
"Groundwater moves very slowly in this area because of the low rainfall
and recharge. We age-dated groundwater in the area and found that most
people are drinking water that recharged at least 30 to 50 years ago --
before most of the area was developed. The most contaminated water is
currently near the water table, but is moving downward."
Although water in most wells is within EPA drinking water standards,
Morgan noted "Our models predict that, at planned residential
development densities, nitrate levels in many parts of the aquifer will
eventually exceed the standards unless nitrogen loading from
residential septic systems can be reduced."
In addition to constructing a model to predict the evolution of
nitrate contamination in the shallow aquifer beneath the La Pine area,
the USGS study developed a simplified tool that can be used by land and
water managers to determine the maximum capacity of the aquifer to
receive nitrate while still meeting water quality goals.