In addition, separate intervention boundaries must be established for each
of the above mentioned
facilities to comply with NR 182.075. The intervention boundary would be
set at the perimeter of
each facility. If a measured or interpolated exceedance of a groundwater
standard occurs at the
intervention boundary, a formal evaluation of facility performance would
be conducted. This would
include assessment of data from lysimeters, leak detection devices, wells
and well nests, and
construction and operational records. If the evaluation indicates the groundwater
standard would be
exceeded at the compliance boundary, an appropriate remedial action plan
would be developed and
implemented.

MWDF - Groundwater monitoring of the MWDF during the construction, operation
and
closure/reclamation phases is collectively referred to as operations monitoring.
The monitoring wells
are uniformly distributed around the MWDF, either near the compliance boundary
or near the edge of
the facility with most of the locations consisting of multi-level piezometers.
These piezometers
would provide access to the hydrologically significant deposits.

    Baseline - Baseline groundwater quality would be established at the MWDF
by monitoring on a
    monthly basis for at least twelve consecutive months prior to disposal
of tailings. The well
    system would consist of 22 existing wells and 9 wells to be installed
during the early stages of
    construction (Figure 1-23).

    Operation - Monitoring well locations, schedule of operation, and water
quality parameters for
    assessing groundwater quality changes near the MWDF during operations
are shown on Figure
    1-24. Monitoring to assess MWDF performance also would be conducted as
part of the
    operations monitoring program. To determine the quality/quantity of leachate
seeping through
    the soil liner, two collection lysimeters would be constructed immediately
beneath the bottom
    liner of pond Ti. Pairs of water level observation wells also would be
installed within the
    underdrain and in the tailings above the filter layer. This system would
provide data on the
    operating characteristics of the drainage system and the liner. In addition,
the water quality of
    the leachate collected in the leachate collection system for treatment
in the reclaim ponds
    would be sampled. Liquids collected in the monitoring wells and lysimeters
would be analyzed on
    the schedule and for the parameters listed in Table 1-15.

    To monitor the effectiveness of the MWDF reclamation cover, a moisture
content measuring
    system would be installed to monitor performance. The specific type of
moisture content
    measuring system installed would be specified in the MWDF plan of operation
and possibly
    revised at the time of reclamation to assure the use of the latest technology.

    The locations for the moisture content measuring devices would be selected
during pond or
    reclamation cap construction. The results of the monitoring program for
pond Ti would be used
    to evaluate the effectiveness of pond design and adequacy of the monitoring
systems.

    Closure - Exxon would be responsible for long-term care of the MWDF for
a period of 30 years
    following issuance of a certificate of completion of reclamation for
the last pond. The
    long-term care period starts for the entire MWDF at the completion of
closure work on pond T4.
    Consequently, pond T1, at the end of the 30 year long-term care period,
would have been
    monitored for a minmum period of 56 years. The anticipated sampling schedule
and wells are
    shown in Figure 1-24 and Table 1-15.

    MWDF features to be preserved and maintained during the long-term care
period include
    selected monitoring wells, lysimeters, leachate collection system access
pipes, a perimeter
    access road, and the encircling fence. An electricity supply may be needed
at the site during
    closure and the long-term care period for monitoring well sampling and,
if necessary, leachate
    pumping.

    Monitoring activities would be conducted throughout the long-term care
period. The monitoring
    program would include groundwater monitoring, lysimeter sampling below
the base liner,
    settlement indicators, vegetational analysis, reclamation cover moisture
content monitoring, and
    leachate collection system volume and quality analysis. The monitoring
requirements, however,



may change as data reflecting site performance are generated.



- 42 -