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Statistical methods used for comparing vegetation sample data. For veve[a[ion cover. total cover, and production, HGCC compared acreage-weighted means from the reclaimed area to acreage-weighted means From the reference areas. Shrub density was compared to the 300-.uem/acre standard using aone-tailed t-test evaluated at [he 90 percent confidence level. HGCC's presentation of its comparison of revegetation and reference area sample data. Co~:er and production values for 1996 :ue compared in Table 7a of Exhibit ! of [he bond release application: 1997 values are compared in Table 7c. Species diversity was determined from species relative percentages shown on pages B-?d and B-42 of Exhibit L Those data, and Tables 7a and 7c, reflect data from proportional sampling in 1996 and simple random sampling in 1997. As requested by the Division, additional cover and production samples were collected from several small non-contiguous parcels which comprised less than 490 of the reclaimed acreage. No transects or quadrats fell within the non-contiguous parcels under the statistically valid sampling scheme employed. The data from those p;ucels were collected to provide additional documentation; these data are summarized in Tables 2c and 3e of Exhibit 1 of the bond release application. Comparison of cover sample data to cover success. The Division's review verified that the cover data are statistically valid at the 9090 level, and consistent with Phase II and III bond release requirements, were collected in each of the last two consecutive years of the liability period. Table 1, below, shows that in both 1996 and 1997, cover on the bond release block exceeded the 9090 cover values on the reference areas. Table 1 Comparison of vegetation cover Reference area values (90% of sample mean) 1996 cover 66% 1997 cover 71% Bond release parcel sample mean 78% 78% Division's Ending that percent cover is sufficient for bond release. Based on the comparison shown in Table 1, the Division finds that vegetative cover on the bond release block has met the requirements for Phase II and Phase lII bond release. Comparison of production sample data to production success criteria. The Division's review verified that [he production data are statistically valid at the 909o confidence level, and consistent with Phase II and TII bond release requirements, were collected in each of the last two consecutive years of the liability period. The following table, Table 2, shows that in both 1996 and 1997, production on the bond release block exceeded the 9090 production values on the reference areas. Hayden Gulch Mine Page 7 May 25, 1999 Phase II/III Bond Ralaasa