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the outcome, MSHA and OSM may need to revise guidelines that establish
minimum expectations and levels of investigation for site characterization,
design, construction, operation, and closure of coal refuse impoundments.
If underground mine workings are near the basin area of an existing or
proposed impoundment, it is important to assess the status of coal barriers that
separate the mined-out area from the surface. Currently, no federal regulations
address the amount of outcrop coal barrier to be left or the depth and nature of
the overburden that is required. OSM has studied the problem of outcrop
barriers but has not published conclusions to date. The committee
recommends that MSHA and OSM jointly pursue the issue of outcrop coal
barrier width and overburden thickness and its competence and develop
minimum standards for them.
Procedures in place for monitoring embankment structures, which include
visual inspections and instrumentation, appear to be performing as envisioned
in the regulations MSHA implemented. For monitoring to be successful, it
should be applied to all potential failure modes. The committee believes,
however, that there are opportunities for additional, continuous monitoring that
may offer timely warning of potential failure of an embankment or basin. The
committee recommends that MSHA and OSM consider requiring
additional continuous monitoring in specific instances and evaluate
automation of monitoring instruments.
SITE CHARACTERIZATION
The committee examined two parts of the question of site characterization,
the accuracy of mine maps and the use of geophysical techniques to delineate
the extent of underground mine workings in situations where maps do not exist
or may not be sufficiently accurate.
The committee notes that the accuracy of mine maps has improved with
the use of modern surveying equipment and practices, but also concludes that
additional improvements in surveying practices, recording information on maps,
and storage of maps and related information are necessary and possible.
Therefore, the committee recommends that MSHA work with OSM and
state agencies to establish standards for mine surveying and mapping.
These should include the following:
Determining surface coal outcrop locations by aerial topographic
measurements, where adjacent to existing or proposed refuse
impoundments,
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