Hg-Contaminated Industrial and Mining Sites in N. America
105
several chloralkali plants where leaks of caustic soda radically altered groundwater chemistry (highly alkaline pH caused extraction of soil organic matter) and
led to unusual partitioning of mercury almost entirely to the dissolved phase.
Bellingham Bay in Washington has received effluent from a chloralkali plant
since 1965. No recent information was available for this site. Earlier, Bothner et al.
(1975) and Bothner (1973) investigated the spatial and temporal distribution of
mercury in bay sediments after releases from the facility were sharply reduced in
1970. Bothner (1973) estimated total releases from the facility to be about 18 Mg
prior to 1970. These investigators attempted to measure and model decreases in
mercury in the estuarine sediments after point source releases were greatly
reduced. Their results suggested that decreases in sediment concentrations (with
a half-time of 1.3 years) were mainly due to particle-associated mercury being
diluted by sediment-mixing processes and by bottom-current transport of
resuspended sediment. They also found that fluxes of dissolved mercury from
anoxic sediments were significantly greater than from oxic sediments.
Howe Sound near Squamish, British Columbia, received effluents from a
chloralkali plant beginning in 1965 and ending in 1994. Approximately 40 Mg of
mercury are estimated (Harbo and Birdwell 1983) to have been discharged into
the sound prior to 1970 when the releases were greatly curtailed. Upper Howe
Sound was closed to all fishing in 1970 but reopened again to sport fishing in
1978. A long record (1970 to present) of annual monitoring of Dungeness crabs
shows rapid decreases from values close to 2 ~lg g -I in 1970 to values around
0.2 ~lg g -] in 1975, followed by no subsequent changes. The site is currently
implementing a number of corrective actions, including containment (slurry wall
technology), capture and treatment of groundwater, and demolition of buildings.
3
Nature and Effectiveness of Remediation Strategies
Few mercury-contaminated sites in North America have actually undergone
deliberate comprehensive remediation, nor have the consequences of specific
corrective actions always been determined, and thus information on the
effectiveness of remediation strategies is rather limited. This is not to imply
that no corrective actions have been undertaken. In addition to the corrective
actions described earlier and summarized in Table 3, many sites have at least
experienced default remediation by virtue of having processes which employed
mercury discontinued or altered to reduce or eliminate losses to the environment. At a few sites (e.g., Saltville, Oak Ridge), process buildings have been razed
or decontaminated, and contaminated soil covered with clean soil or excavated
for disposal/treatment. Excavation or capping of Hg-contaminated soils has been
a common-corrective action. Excavated soils have been commonly treated to
reduce or stabilize mercury by a variety of technologies, but the floodplain soils
(approx. 30 000 m 3 , >400 ~lg g-I) from the Oak Ridge site were disposed of by
reburial in a landfill with a leachate collection and monitoring system. There are
105
several chloralkali plants where leaks of caustic soda radically altered groundwater chemistry (highly alkaline pH caused extraction of soil organic matter) and
led to unusual partitioning of mercury almost entirely to the dissolved phase.
Bellingham Bay in Washington has received effluent from a chloralkali plant
since 1965. No recent information was available for this site. Earlier, Bothner et al.
(1975) and Bothner (1973) investigated the spatial and temporal distribution of
mercury in bay sediments after releases from the facility were sharply reduced in
1970. Bothner (1973) estimated total releases from the facility to be about 18 Mg
prior to 1970. These investigators attempted to measure and model decreases in
mercury in the estuarine sediments after point source releases were greatly
reduced. Their results suggested that decreases in sediment concentrations (with
a half-time of 1.3 years) were mainly due to particle-associated mercury being
diluted by sediment-mixing processes and by bottom-current transport of
resuspended sediment. They also found that fluxes of dissolved mercury from
anoxic sediments were significantly greater than from oxic sediments.
Howe Sound near Squamish, British Columbia, received effluents from a
chloralkali plant beginning in 1965 and ending in 1994. Approximately 40 Mg of
mercury are estimated (Harbo and Birdwell 1983) to have been discharged into
the sound prior to 1970 when the releases were greatly curtailed. Upper Howe
Sound was closed to all fishing in 1970 but reopened again to sport fishing in
1978. A long record (1970 to present) of annual monitoring of Dungeness crabs
shows rapid decreases from values close to 2 ~lg g -I in 1970 to values around
0.2 ~lg g -] in 1975, followed by no subsequent changes. The site is currently
implementing a number of corrective actions, including containment (slurry wall
technology), capture and treatment of groundwater, and demolition of buildings.
3
Nature and Effectiveness of Remediation Strategies
Few mercury-contaminated sites in North America have actually undergone
deliberate comprehensive remediation, nor have the consequences of specific
corrective actions always been determined, and thus information on the
effectiveness of remediation strategies is rather limited. This is not to imply
that no corrective actions have been undertaken. In addition to the corrective
actions described earlier and summarized in Table 3, many sites have at least
experienced default remediation by virtue of having processes which employed
mercury discontinued or altered to reduce or eliminate losses to the environment. At a few sites (e.g., Saltville, Oak Ridge), process buildings have been razed
or decontaminated, and contaminated soil covered with clean soil or excavated
for disposal/treatment. Excavation or capping of Hg-contaminated soils has been
a common-corrective action. Excavated soils have been commonly treated to
reduce or stabilize mercury by a variety of technologies, but the floodplain soils
(approx. 30 000 m 3 , >400 ~lg g-I) from the Oak Ridge site were disposed of by
reburial in a landfill with a leachate collection and monitoring system. There are