Groundwater in the Great Lakes Basin

converted to nitrite in the human stomach, the overall
IARC evaluation is that ingested nitrate or nitrite
under conditions that result in endogenous nitrosation
is probably carcinogenic to humans (IARC, 2007).
The guidelines and regulations for nitrate and nitrite in
drinking water are set based on the risk of methemoglobinemia
for infants (blue baby syndrome). Blue baby
syndrome can occur when nitrate measured as nitrogen
concentration in drinking water is above 10 mg/L.
Nitrate is converted to nitrite in the acid environment
of the stomach. Nitrite interferes with the ability of
infants’ red blood cells to carry oxygen to the tissues.
This risk exists for infants under six months of age
(Centers for Disease Control and Prevention, 2003).
The risk is eliminated by breast-feeding or by using
water supplies without nitrate to reconstitute infant
formula rather than contaminated well water.
U.S. EPA has established a MCL of 10 mg/L for nitrate
measured as nitrogen in drinking water. The MCL
for nitrite is set at 1 mg/L measured as nitrogen (U.S.
EPA, 2007a). Canada’s MAC is 45 mg/L nitrate which
is roughly equivalent to 10 mg/L measured solely
as nitrogen (45 mg of nitrate contains 10.2 mg of
nitrogen). If nitrite is measured separately, the MAC is
3.2 mg/L nitrite (GCDWQ, 06/1987).
In a 1994 study the Wisconsin GNHS and the
Department of Health and Family Services (DHFS)
found that in an estimated 9% to 14% of private water
wells the concentration of nitrate exceeded 10 mg/L. In
2005 the Wisconsin DNR integrated three extensive
databases to map nitrate concentrations throughout
the state in private wells. 11.6% of the most recent
private water samples from 48,818 wells equaled or
exceeded 10 mg/L nitrate in the groundwater. The
highest exceedences were in Calumet, Columbia, Dane,
LaCrosse and Rock counties where exceedences of
the nitrate standard were in the 20% to 30% range
(Wisconsin DNR, 2006).
Radionuclides
Radionuclides, in particular radium-226/228, are
present in groundwater largely due to the decay of
uranium and thorium. Both human and animal studies
indicate that radiation exposure at low to moderate
doses can increase the long-term incidence of cancer.
Animal studies in particular suggest that the rate of
genetic malformations may be increased by radiation
exposure (World Health Organization, 2006).
The guidelines for radionuclides in drinking water in
Canada are found in Annex B and for the United States
in Annex D. As a routine measure drinking water is
screened for gross alpha and gross beta radiation. The
MAC for gross alpha radiation is 0.1 Bq/L. The MCL is
15 pCi/L. The Canadian and United States MAC and
MCL are roughly equivalent (0.1 Bq = 17 pCi). The MAC
for gross beta radiation is 1.0 Bq/L (GCDWQ, 02/1995).
The MCL is 4 millirems/year (U.S. EPA, 2007a). If
these guidelines are not exceeded, the likelihood that
the MAC or MCL for specific radionuclides will be
exceeded is very low. U.S. EPA has a MCL of 5 pCi/L
specifically for the total of radium isotopes 226 and 228.
No measurable radiological health effects are expected
from consumption of drinking water if the concentrations
of radionuclides are below the guideline and
regulation levels.
Radionuclides exceed the drinking water standard for
gross alpha and radium in many public drinking water
systems in eastern Wisconsin. The radionuclides are
found in the Cambro-Ordovician rock in a band that
is roughly coincident with the Maquoketa subcrop
pattern. This aquifer has radium concentrations as high
as 30 pCi/L. Nearly 60 public drinking water systems
exceed the gross alpha standard. Radium and its
progeny are the primary alpha emitters causing these
exceedences (Wisconsin DNR, 2006).
Radon
Underground rock containing natural uranium
continuously releases radon into groundwater. Radon
is released from water as it is used. Highest exposures
from this source often occur with showering. Aeration
with release of the radon into an unconfined environment
will rapidly reduce the concentration of radon
in the air. The use of radon-containing groundwater
supplies not treated for radon removal for general
domestic purposes will increase the levels of radon in
the indoor air, thus increasing the dose from inhalation.
Radon-222 and its short-lived decay products caused
about 19,000 deaths due to lung cancer in the United
States in 1998 (NRC, 1999). The United States National
Academy of Sciences (NRC, 1999) reports an approximate
100-fold smaller burden of lung cancer from
exposure to radon in drinking water in the home, about
160 cases. The report also assessed that the risk of
stomach cancer caused by drinking water that contains
dissolved radon is extremely small, at about 20 deaths.
U.S. EPA was directed by the 1996 Safe Drinking
Water Act to establish an MCL for radon. In 1999 the
U.S. EPA issued a proposed rule with two options, an
MCL of 300 pCi/L and an Alternative MCL of 4000
pCi/L. The AMCL would apply to communal water
supplies serving 10,000 persons or fewer that were
associated with a state or operator multimedia mitigation
program. Removal of radon from water requires
a costly aeration system. 99% of the population risk
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