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= ..~_,~-' . III IIIIIIIIIIIIIIII STATE OF COLORADO DIVISION OF MINERALS AND GEOLOGY Depanmenl ul Nalu ral Resources 1313 Sherman SL, Ruom X15 Denver, Colnradu 80201 Phone: (3031 ri6fi-3567 FAh: 13031 R32-H10fi DATE: June 8, 1998 TO: Tom Kaldenbach FROM: Dan Mathews '~ ~`~ RECEIVED JUf~ 11 1998 Division of Minerals & Geology RE: Hayden Gulch Bond Release Application Permit C-80-003 Rny Romer Governor lames ~. Lochhead E~ecwive Dnector Michael B. Long Division Orteclor I have reviewed revegetation success demonstration sections of the February, 1998, Phase II/III bond release application for the Hayden Gulch Mine. Information included in the application including narrative evaluation, data summazies, statistical evaluation, and mapping appeazs to have been provided as required by applicable sections of Rule 4.15 and Rule 3.03. Sampling methodology and statistical comparisons were in accordance with the Division's bond release guideline, and with permit specific bond release sampling plans and statistical methods reviewed and approved by the Division in 1996 and 1997. Information in the application appears adequate to demonstrate that revegetation success standards for herbaceous production, vegetation cover, species diversity, and woody plant density have been achieved for the bond release block (the entire mine azea with the exception of four small shrub establishment enclosures). As noted in various sections of the application, sample adequacy was not achieved for woody plant density in 1996 or 1997, however "reverse null" t-tests as detailed in the application demonstrated that reclaimed densities exceeded the standard in both years, at the 90% level of statistical confidence. This testing approach satisfies the regulatory requirement ,and is statistically valid. Similarly, the application notes that revised 1996 production data did not meet the statistical test for minimum sample size, but states that "given that the reclaimed area productivity is much greater than any of the reference azeas, sample adequacy is of little concern." To confirm this assumption, I ran a one sample t-test, using the reclaimed area data and weighted reference area production standard (90% of reference sample mean). Reclaimed area sample mean was 164.4 g/m2; reference standard was 74.6 g/m2. The t-test continued that reclaimed area mean exceeded the standard, at the 90% confidence -evel. The oily potential problem 1 noted based on review of the data, is the apparent presence of a Canada thistle (Cirsium arvense), infestation in the small "Topsoil Area C" reclamation parcel.