PERMFILE69535

• Permit No: C1981071
• IBM Index Class Name: Permit File
• Doc Date: 12/11/2001
• Section_Exhibit Name: PR2 ADEQUACY RESPONSE
• Media Type: D
• Archive: No

• Swale features. The conclusion drawn from this comparison was that the
hillslope gradients along the upper portions of the Swale are not
inconsistent gradients of natural existing slopes within the general area.
Our impression is that the intent of the comparison is to show that the
Swale feature is stable with respect to erosion and/or slumping. The
statement is made that the materials comprising both the swales and the
colluvial slopes are similar in nature; however, for the purposes of
determining erosivity of the bed materials, sampling would be required to
determine the actual nature of the material. In any case, the study does
not address the rill erosion and settling crack on the steep slopes of Area
31 as described in the NOV C-81-061; Attachment A.
RESPONSE:
In the report prepared by Water Engineering & Technology, Inc., the
slope gradient of the upper portion of the Swale area was compared to
slope gradients on colluvial material at the base of the sandstone
cliffs north of the mine. The Division believes that sampling is
required to determine the relative erosivity of the surficial
materials. The comparison in the report is a comparison of morphology
of geologically similar materials. The morphometric parameter used in
the comparison is slope gradient. The similarity of the underlying
materials is based on the similarity in the process that forms each
deposit. In the case of surface mine spoil, sandstone and shale are
fractured, stockpiled, and regraded by mechanical means. colluvial
• material is defined by American Geological Institute (1976) as follows:
A general term applied to loose and incoherent deposits,
usually at the foot of a slope or cliff and brought there
chiefly by gravity.
The colluvial deposit was formed by a mechanical process and from
sandstone and shale sediments much like those which form spoil. The
nature of the lithologic material underlying a landform influences the
morphology of the landform. Therefore, because colluvium and spoil are
formed by' similar processes and form similar geologic materials, it is
concluded that they will function in a geomorphically similar manner.
No evidence of rilling or excessive erosion was observed on the
colluvial slopes and, therefore, it is unlikely that the upper Swale
slopes will form rills or other evidence of erosion.
At the conclusion of the letter the Division states that the report
does not address problems of rilling or settling on steep slopes in
Area 31. It is our recollection that during our first meeting with the
Division on September 10, 1986 it was determined through agreement of
all parties present that our report need not address the problem of the
settling crack in Area 31. It was pointed out at the time that the
crack was in the process of being repaired by CYCC. Regrading of the
crack was complete at the time of our field trip on September 15th
thrcugh 17th. Also, during the field investigations conducted by Water
• Engineering & Technology, Inc., they did not see evidence of active
rill erosion. They surveyed several slope transects on the steep slope
in Area 31 so that they had ample opportunity to view the character of
the slope.