CONSOL was also seeking approval from the U.S. Mine Safety and Health Administration to restart its coal-cleaning plant. Company officials released a diagram showing a large boom being placed across the impoundment, to isolate active slurry disposal areas from the section where the dozer is located and said the move "will not interfere" with recovery of the missing miner.
The area of the saddle dike that failed has been described as about 200 yards long and about 200 feet wide, and is located on the opposite end of the site from the impoundment's main embankment.
"In my thirty years of experience I haven't seen anything like that -- the size of the failure, the mass of material that moved all at once," Pierce said Wednesday. "Something went awry. There was a loss of stability either in the embankment material or in the underlying foundation."
Construction of the embankment involved placing coal refuse on top of previously placed coal refuse, a process in which experts say it is key to allow enough time for wet material from the preparation plan to dry out, harden, consolidate and gain enough strength.
Pierce said that so far, his review of compaction testing and pressure readings for the embankment that failed have not revealed any problems or any violations of regulatory standards.
DEP spokeswoman Kathy Cosco said earlier that "overall compliance for the site has been satisfactory," and agency inspections in the weeks prior to the incident mentioned no problems related to the embankment that collapsed.
Last year, U.S. Office of Surface Mining inspectors warned of water seepage and stability problems at the impoundment, according to the federal agency's records.
OSM's May 2011 inspection report mistakenly refers to the "saddle dike" on the western side of the impoundment, where the collapse occurred, when federal officials were actually concerned about a similar embankment on the eastern edge of the site, closer to the main-stem dam at Nolan Run, officials said.
In that instance, OSM officials were concerned that the main-stem dam appeared to have been built much steeper than the CONSOL construction plans approved by state and federal officials, records show.
"During the winter and spring, areas of this steeper slope have broken off (sloughed) and exacerbated the apparent unstable appearance," the OSM inspection report said.
CONSOL officials assured OSM that the embankment just appeared to be steeper than the approved design.
"When the pool was down last fall, the portion of the earthen soil facing that is below the slurry level was visible and had the appearance and effect of a bench along the upstream slope," a company engineer told OSM, according to the federal agency's report. "I feel that the embankment remains in an uncompromised state and that the design plan is being followed."
No citations were issued by either OSM or DEP.
Reach Ken Ward Jr. at kw...@wvgazette.com or 304-348-1702.