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.~ -2- 3. Identification of locations where riprap will be placed in', channels in both the disturbed and undisturbed areas and documentation of the calculations utilized to estimate that channel velocity would not be erosive after ripraping these locations. 4. Drainage from the coal load-out area, an area included under the meaning of "disturbed area" in 30 CFR 715.17, will be directed into a sedimentation pond(s) in compliance with the final interim regu- lations published in the Federal Register on February 27, 1978. We also understand that water harvesting of Stevens Gulch is not a part of the mine plan under review and, therefore, that mine plan appro- val would not include any approval of water harvesting procedures. The redesigned mining plan, and additional information submitted by CWI through early March of this year, shows that technically-valid methods of predicting the affect on the surface hydrology have been employed in those cases reviewed, though the presentations of analyses and results could be more straight forward. We are pleased that CWa is commited to pass all waters from the disturbed areas through sedi- mentation ponds. We are pleased that CWI has proposed to reduce flows to vegetation buffer strips such that erosion will not be increased. Thus a number of 'our concerns about the impact on the hydrologic system have been lessened and will be further lessened if an adequate hydrolo- gic monitoring system is also stipulated in an approval of a mining; plan. In some instances, the monitoring is required to ensure that the appli- cant's design assumptions are valid. In others, the monitoring is re- quired to warn of unforeseen problems. The monitoring systems we feel should be stipulated must include the following: 1. Flow-activated sampling for suspended solids upstream and at the final discharge point of channels with sedimentation ponds and recorded flow measurements. (The location and type of sampling wil'1 be determined by site-specific conditions. EPA will be pleased to assist with the design of the required network.) 2. Measurements of sediment accumulation in all sedimentation ponds immediately after there has been flow from the channel or cul- vert to the pond. 3. Installation of an erosion/deposition measuring system (e.g. erosion pins) at: a. All vegetation buffer strips. b. Erosion-prone areas of all diversion channels. c. Representative locations along natural drainage channels which receive water from the disturbed area or which i receive abnormal quantities of water from the undisturbed areas. JI ~ ,Iii~~dl,,~L~ilill Uf6