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Jim McArdle -2- November 30, 1982 I believe it important that the stabilization of the existing excess fill be resolved expeditiously. The potential consequences of failure for the surface drainage system during a high-flow event would be serious. In keeping with the applicant's indication, contained in Section G.2.1 of the amended interim plan, that "Exxon expects.to have definitive plans for the regrading of the material below the falls by mid-1983", I recommend that we require submission of completed plans for regrading and channelization of the affected area by April .31,1983. Further, in order to avoid exposure to an additional potentially damaging spring discharge season, I recommend that we require completion of the proposed regrading and channelization project by December 31, 1983. The applicant discusses channelization of Davis Gulch below tfie Davis Gulch falls, within Areas 5a and 19b in several separate sections of the amended interim plan application document. It is important that this design element be resolved. Upon final reclamation of the site, a permanent channel.,. capable of accommodating the project maximum flood, should be in place. Any hydraulic structure designed for a lesser flow is temporary by design intention. The consequences of failure during the project life must be evaluated in relation to potential health and safety,and environmental hazards. Any proposed facility will be evaluated in this regard. Hydraulic facilities which propose capacity less than project maximum flood may be acceptable as temporary facilities, but could require redesign and reconstruction in order to satisfy the requirements for amended or resumed activity, or final reclamation. Area 6: "Mine Bench" As a permitted area, the entire site is under the control of the applicant. Control should preclude the exposure of the public to a health and safety hazard represented by the open crusher foundation excavation. Area 7: "Upper Middle Fork" The amended interim plan document describes the surface hydrology and sediment control implications of the proposed amendment of the Middle Fork dam. Following State Engineer's review and approval of the revised plans for the Middle Fork dam, the permit for the Colony Project will require appropriate amendment. Area 9: "Davis Gulch Dam" In response to earlier Division adequacy comments, the applicant has amended its surface hydrology and sediment control analyses to reflect the existing Coffer dam and the deletion of the originally approved Davis Gulch dam. The applicant observes that the final resolution of whether or not the Davis Gulch dam will be constructed cannot be projected at this time. However, it is important that down- stream channelization problems be resolved expeditiously, as discussed under Area 5a, above.