explosive charges used in rock blasting and energy from bursts or collapses) in an effort to reduce regional amplitudes of seismic signals. The DOE Working Group's recommendations place the burden on the mining industry to reduce the amount of energy going into seismic signals at the source rather than on the monitoring community to identify technical means for discriminating signals. An alternative approach, mentioned more briefly in their report, is to reduce the ambiguity of the nature of mining-related seismic signals.

The recommendations proposed by the working group's report to reduce seismic levels prescribe changes to long-standing mining practices that have been refined to optimize equipment investments and operational costs, efficiency, and safety. The committee believes that the adoption of many of the working group's recommendations could result in a substantial increase in operational mining costs. Unfortunately, the DOE Working Group report makes no attempt to address these cost factors, without which the industry will not be readily receptive to the recommendations. The quantification of these costs is at best a difficult task and is best accomplished on a mine site-specific basis. Some generalized cost calculations associated with adopting some of the blasting recommendations are given in Table 1 and further discussed in Appendix A. In this example, drilling costs associated with changes in blasting practice may increase by a factor of two.

Most of the blasting recommendations made in the DOE Working Group report are based on textbook blasting practices and are dated. Rock breakage is a costly unit operation that is given a high degree of technical attention at most

TABLE 1 Calculation of the cost associated with reducing blasthole diameters and bench heights for two hypothetical cases.

Design Factor

Example 1

Example 2 (modified Example 1)

Bench height

50 ft.

25 ft.

Blasthole diameter (design)

10 in.

8-in.

Hole spacing pattern

24 ft.

17 ft.

Stem length

20 ft.

13 ft.

Yardage of blast

1967 yd3

267 yd3

Explosive loading (1 lb/yd3 per blasthole

1022 lb.

262 lb.

Number of blastholes to meet a weekly production rate of 300,000 yd3

281

1124

Drilled length per week

14,050

28,100

Weekly drilling cost (at $2 per foot)

$28,000

$56,200

Annual drilling costa

$1,461,200

$2,922,400

NOTE: Example 1 summarizes a typical blast design, whereas Example 2 is the modified blast design that limits the charge size used in Example 1 in response to recommendations by the DOE Working Group. This calculation is further discussed in Appendix A.

a Costs depicted are a result of calculations for the hypothetical examples; actual drilling costs could vary by 25% or more.



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