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'~ ~ r III IIIIIIIIIIIIIIII ~ y ::. 999 gun z a i~y9 GLEN A. MILLER 2264 Willow Wood Road Grand Junction, CO 81503 ~o~. N~.t~e: v r C xw~~ . June 24, ] 999 Mr. Dan Jackson U. S. Environmental Protection Agency 999 I8'h Street, Suite 500 Denver, CO 80202-2466 }tE: Draft Statement of Basis, Yankee Gulch Project Class Ill Solution Mining Wells Dear Mr. Jackson: This comment letter was delayed by a mis-mailing of the Draft, I received it yesterday hope my wririen comments will be useful, I'll not be able to attend the July 13'" heazing. My technical and scientific background: I retired from the U.S. Geological Survey after 35 years, 30 of which I worked on groundwater projects, including 10 years as staff hydrologist with the US DOI Oil Shale office, which administered the Prototype Leasing Program of the 1970's-80's. My work there involved detailed hydrologic and water quality effects ofvarious oil shale and sodium extraction plans in the Piceance Basin. From my brief review of the Draft, and past review/comment on the BLM EIS for this Project, there is a maior concern related to the probable movement of brine from the proposed mine cavities into the Parachute Creek Aquifer, caused by caving and subsidence, and then into Piceance Creek. As noted below and in the attached EIS comment letter, this movement is likely to occur during project operations, and almost certain to occur post-project. Neither the EIS nor the EPA Draft Permit address the necessity for adequate monitoring for early detection of brine movement, so that timely prevention remediation measures can be taken. Specific Comments on The Draft 1. P. 2, last Paz. The statement that no "void" will be produced is not likely to be correct. A 600' x 200' cylinder of rich oil shale, when depleted of solid saline minerals by solution mining, will be an extremely weak rock unit. The 200-foot span of the "roof' or sill pillaz will not support itself, Dissolved saline beds, some more than ]0' thick, will certainly leave voids, which will lead to rapid caving, and probably will adversely effect pillars.