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r ;r Technical Revision No. 34 West Pit Pond Maintenance 11 Analysis of the areas associated with the slide (cause of the slide) Please see the attached memo dated May 5, 1995 from CTL/Thompson regarding the cause of the slide. The Division will recall that this letter was previously forwarded to the Division on May 9, 1995. In that letter we stressed that CTL/Thompson believes the primary factor which initiated the slide was naturally occurring seepage of water from the south. The occurrence of the slide also could have occurred without the presence of the small topsoil stockpile. 21 Remedial Efforts to stabilize the area The debris slide is a function of naturally occurring perched groundwater entering the side of the West Pit Pond. The objective of the remedial methods will be to provide a free draining zone for the water by 1) removing the debris; 21 if possible exposing the expected sandstone units as the source of the water; 31 placing rip-rap type materials covered by filter rock to drain the water into the pond; and 41 reestablishing the side embankment of the pond including the ramp used to access the pond for future dredging. The CTL/Thompson letter also describes these remedial measures. 31 Program to monitor the area After the remediation is completed, a line of visual monitoring markers will be placed across this reestablished pond side slope. Monitoring will occur concurrently with and noted as part of the quarterly pond inspections. The Division will be notified of any substantial movement of the side slope. In addition, after the remediation is completed, a new certified as-built drawing of the West Pit Pond will be submitted to the Division. 41 Seepage Areas The upper seep zones located above the West Pit Pond were addressed by CTLIThompson in the attached letter dated July 6, 1995. Minor instability is judged to be associated not with a bedrock failure but the movement of topsoil at the face of the seep. To enhance stability, once the seeps have dried sufficiently to allow safe equipment access, gravel drains with gravity outlets will be installed. No specific monitoring of this area is judged to be merited nor proposed. 5) West Pit Fill CTL/Thompson has observed no conditions which they believe would compromise the stability of the fill. Colowyo will implement the monitoring plan as currently approved. 61 West Pit Pond -North Slope This small surficial slip feature is a function of the removal of the toe of the associated slope to facilitate turning by scrapers during West Pit Fill underdrain clay removal. The monitoring of this feature indicates it is not a deep seated failure of the bank. This slope will be regraded and repaired concurrent with the other pond repair activities.