458
T. Meschede and R. Vogelsberger
2
Extent of Contamination
An extensive sampling campaign was conducted in August and September 1992,
involving real-time air monitoring and several hundred samples of wastewater,
sediments, soil, concrete, and interior and exterior building surfaces. The
sampling results indicated that mercury concentrations exceeded acceptable
levels (based on German and USA standards and guidelines) at numerous
locations, with particular hot-spots in and around the two cell houses, related
workshops, and at a mercury distillationlrecovery unit.
Peak mercury vapor concentrations were found above Soo pg/m3 in the
interiors of the two electrolysis cell houses, compared to the maximum allowable
work-place concentration of 50 ~lg/m3 in the USA. Mercury concentrations up to
7.5 mg/l were found in the wastewater trenches, compared to the standard of
0.05 mg/l mercury under the European Community Regulations (EWG-S2a) for
Waste Water Discharges from Chlor Alkali Plants. Contaminated soil and dirt
were found in many areas of the plant, with particularly high concentrations near
the distillation unit, up to over 200 000 mg/kg mercury. Peak levels in concrete
surfaces of 120 000 mg/kg were measured. Core borings indicate that mercury
contamination extends several centimeters into the walls, floors, and ceilings of
the cell houses.
Typically, mercury concentrations in soil or concrete above 10 mg/kg are
considered to be contaminated.
3
Selection of Feasible Remediation Technologies
An extensive feasibility assessment was performed of various remediation
processes and technologies that have been applied in Europe and North America
for mercury-contaminated sites, including mechanical/hydraulic soil washing,
chemical extraction, thermal treatment, landfill deposition, and others. A
comparison was made of the advantages and disadvantages of each technology
with respect to performance, reliability, risks to humans and the environment,
costs, and other factors, with specific consideration of the particular site
conditions at the MCI facility.
The selected decontamination method comprises a combination of techniques
including:
• high-pressure water cleaning of all surfaces,
• in-situ chemical fixation for lightly contaminated surfaces,
• controlled removal/dismantling of highly-contaminated structures (e.g. the
two cell houses)
• deposition of all solid wastes in a secure landfill.
T. Meschede and R. Vogelsberger
2
Extent of Contamination
An extensive sampling campaign was conducted in August and September 1992,
involving real-time air monitoring and several hundred samples of wastewater,
sediments, soil, concrete, and interior and exterior building surfaces. The
sampling results indicated that mercury concentrations exceeded acceptable
levels (based on German and USA standards and guidelines) at numerous
locations, with particular hot-spots in and around the two cell houses, related
workshops, and at a mercury distillationlrecovery unit.
Peak mercury vapor concentrations were found above Soo pg/m3 in the
interiors of the two electrolysis cell houses, compared to the maximum allowable
work-place concentration of 50 ~lg/m3 in the USA. Mercury concentrations up to
7.5 mg/l were found in the wastewater trenches, compared to the standard of
0.05 mg/l mercury under the European Community Regulations (EWG-S2a) for
Waste Water Discharges from Chlor Alkali Plants. Contaminated soil and dirt
were found in many areas of the plant, with particularly high concentrations near
the distillation unit, up to over 200 000 mg/kg mercury. Peak levels in concrete
surfaces of 120 000 mg/kg were measured. Core borings indicate that mercury
contamination extends several centimeters into the walls, floors, and ceilings of
the cell houses.
Typically, mercury concentrations in soil or concrete above 10 mg/kg are
considered to be contaminated.
3
Selection of Feasible Remediation Technologies
An extensive feasibility assessment was performed of various remediation
processes and technologies that have been applied in Europe and North America
for mercury-contaminated sites, including mechanical/hydraulic soil washing,
chemical extraction, thermal treatment, landfill deposition, and others. A
comparison was made of the advantages and disadvantages of each technology
with respect to performance, reliability, risks to humans and the environment,
costs, and other factors, with specific consideration of the particular site
conditions at the MCI facility.
The selected decontamination method comprises a combination of techniques
including:
• high-pressure water cleaning of all surfaces,
• in-situ chemical fixation for lightly contaminated surfaces,
• controlled removal/dismantling of highly-contaminated structures (e.g. the
two cell houses)
• deposition of all solid wastes in a secure landfill.