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United States Department of the Interior OFFICE OF SURFACE M[NING Reclamation and Enforcement BROOKSTOWERS RECEIVED 1020 I STH STREET DENVER, COLORADO 80202 hnaR o9 i~'~~ MINED LAND RFCLAMATION ~ COAL COLO. DL'1. OF NATURAL ktSO~RCES Mr. Peter H. Evans MAR ~' IORI Reclamation SDecialist Mined Land Reclamation Division 423 Centennial Building 1313 Sherman Street Denver, Colorado 80203 RE: Rev~~i(/e[[~w~~_of GEC Minerals, Inc., Blasting Plan Dear Mr.~~vans: This is a follow-up on your request for assistance in reviewing the blasting plan submitted by GEC Minerals, Inc. TAAR Staff ITas reviewed the plan and finds that tlTere is•insufficient data to support the use of a modified scaled distance equation at this time. This is particularly tlTe case since CEC has proposed to blast within 110 feet of a fuel tank and 160 feet of a liquid propane tank. The modified scaled distance equation submitted by t1te applicant was based on a regression analysis of only 14 data points. It is not statistically valid to base predictions from regression lines on less titan 30 data points. When less than 30 points are used, ttte regression equation derived can only be used as an indicator, not as an accurate predictor of peak particle velocity. Another problem wit1T the regression analysis is tlTat the area of greatest concern from a compliance standpoint is to tlTe left of the 14 data points. Of particular Snterest is at what scaled distance the peak particle velocity equals one inch per second. The applicant shotLld he instntcted to collect data within the 5 to 20 scaled distance range along with the same range they are presently using. The applicant should explain in detail the exact statistical method that will be used to analyze the new data, particularly with respect to tlTe 95% confidence level equation that in the current sllhmittal recommends a scaling factor of 38.8. The enclosed regression analysis confirms [hat as far as it goes, the data have been interpreted properly by the applicant. However, because of the small quantity of data, the 95% confidence interval belts indicate a wide range of variability around the critical one inch per second peak particle velocity area, again indicat.tng that more data must be collected.