INSPEC09399

• Permit No: C1981012
• IBM Index Class Name: Inspection
• Doc Date: 7/8/1997
• Doc Name: OSM INSPECTION REPORT
• Inspection Date: 6/10/1997
• Media Type: D
• Archive: No

(s 50%, or 26° 34'); lifts constructed in layers 2 feet thick or less compacted to 90%;
and maximum lift thickness of 50 feet. Surtace runoff is routed to pond 008 at the
RDA's southern toe by ditches constructed along its eastern and western sides. Side
ditches were designed with trapezoidal cross-sections, maximum depth of 1.38 feet and
a top width of 15 feet. The permittee determined that the steep slopes and high flow
velocities characteristic of the channels in the side ditches would require an average
riprap size greater than 3 feet in diameter. Finding that impractical, the permittee
designed each side ditch to be armored with Reno mattress in lieu of unconfined riprap
armoring. Reno mattress is a series of rectangular, gabion baskets filled with 2-inch to
10-inch diameter roG<. The permit provides for mattresses to average about 9 inches
thicc and the roGc to average between 4 and 6 inches in diameter. According to the
permit, the design depth of the V-shaped side ditches vanes for the segments of side
ditch extending from the top of the fourth lift to the bottom of the first lift. It provides for
a maximum depth of 1.39 feet, inside slopes of 3h:1 v, and unspecified top widths.
The upstream diversion is designed to convey drainage from a 100-year, 24-hour event,
Based on the permit, it is to have a minimum depth of 2.95 feet (inGuding 1 foot of
freeboard) and a top width of 17.7 feet. DMG approved a minor permit revision to
relocate the upstream diversion about 50 feet higher than its present location.
Presently, the diversion conveys commingled drainage from the refuse pile and the
undisturbed area up-gradient of it to pond 008. When constructed, the new diversion
will carry only undisturbed area drainage and will discharge it at points east and west of
the refuse area. Pond 008 was designed to handle runoff from an 85.1-acre watershed,
inGuding 61.4 acres of refuse, for a total of 15.14 acre-feet of water.
The RDA will cover an area of about 66 acres when it is completed. It will occupy
essentially all of the watershed in which is located. Height of the underdrain is designed
to be at least 8 feet and no more than 16 feet. The pile has a design capaGty of 12.7
million cubic yards and 10 lifts. Each terrace is designed to be about 20 feet wide, to
slope inward at 3 to 5 percent, and to slope at 3 to 5 percent from the center to the east
and west side ditches. A minimum of four feet of non-toxic material must be placed on
top of the coal waste following final grading prior to final revegetation as required by
section 4.10.4(5).
Field measurements were taken to spot heck the RDA's construction and were
approximate. Measurements of terrace inslopes and terrace slopes to the east and
west side ditches were difficult to take due to the very slight grades. Slope steepness
and terrace width measurements were as follows: first lift outslope, 28°; first terrace
width, 31 feet; first terrace side slopes to east and west, almost 0%; first terrace inslope,
average of 2.8%; second lift outslope, 23°; second terrace width (at center) 21 feet;
second terrace side slope to the west, 2%; second terrace inslope, average of about
2.9%; third lift outslope, 26.5 degrees; third terrace width, average of 18 feet; third
terrace side slope to the west, almost 0°~; third terrace inslope, average of 3%.
Piezometers on the three ten-aces were checked. No water was found in TH-201 on the
first terrace. Depth to the static water level in TH-202 on the second terrace was 71.4
5 1997 New Elk Special Focus