REP06591

• Permit No: C1980003
• IBM Index Class Name: Report
• Doc Date: 2/12/1999
• Doc Name: 1998 ARR TABLE OF CONTENTS, EXHIBIT 1 THRU 3
• Permit Index Doc Type: ANNUAL RECLAMATION REPORT
• Media Type: D
• Archive: No

• MONTGOMERY WATSON
Mining Group
Date: Febtvary 5, 1999
To: Project File
From: Toby Leeson
Subject: H-G Coal Slump Mitigation - As-built Report
Between June 22 and 27, 1998, Montgomery Watson completed slump mitigation construction
activities at H-G Coal Company's (HGCC) Hayden Gulch Coal Mine. The slump mitigation was
conducted to stabilize an earthen slump near the former headwall in the southeastern portion of
the fotmer mine area. The work was approved by the Colorado Division of Minerals and
Geology as Minor Revision No. 13 (MR-13) in a letter dated May 13, 1998.
The following drainage features were installed as part of the slump mitigation work:
• • Two French drains were installed laterally across the body of the earthen slump;
• Two toe drains were installed at the toe of the slump; and
• One surface ditch which was constructed immediately upslope of the slump area.
Figure No. 1, which is included in the 1998 Annual Reclamation Report shows the locations of
the slump mitigation drainage features.
The two French drains were constructed laterally across the slump body. The upper French drain
was installed across the head scarp and the lower drain was installed about half-way between the
head scarp and the toe. As shown on Figure No. 1, there is a third French drain that was installed
upslope of the slump. This French drain was installed by HGCC in 1994 as part of MR-07.
Drawing 1 shows a plan-view of the French drain construction. The two drains installed in 1998
were excavated to a maximum depth of 12 to 14 feet at their eastern ends to zero depth (day-
lighted) at their western ends. Both drains are approximately 40 inches wide. Six inches oft f-
inch screened gravel were placed along the bottom of each trench and 6-inch PVC drain-pipe
with'/a-inch holes was laid on top of the bedding gravel. The PVC drain-pipe was glued at each
20-foot joint. The trench and drain-pipe were surveyed to assure a minimum 2 percent grade.
Following placement of the drain-pipe, the trench was backfilled to within 2 to 4 feet below
ground surface (bgs) with ± 1-inch screened gravel. The final 2 to 4 feet of open trench above
the gravel were backfilled with excavated spoils and topsoil. Topsoil was stripped from the
disturbance area and stockpiled prior to trench excavation. The top 18 inches of the open
• trenches were backfilled with the stockpiled topsoil