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iii iiiiiiiiiiiii iii STATE OF COLORADO DIVISION OF MINERALS AND GEOLOGY Department of Natural Resources 1 71 i Sherman 51., Room 215 J+yk~ Denver, Colorado 80203 IIII` Phone:13071 ft66~3567 FAx: 13031 832-8106 DEPARTMENT OF December 1, 1997 NATURAL RESOURCES Ruy Romer To: Larry Oehler, James Stevens governor r lames 5. Loc hhead From: James Dillie ~ t~ec°"veDve°°' Michael B. Long Drvivon Director Re: Review Of Blasting Activities, Portland Quarry, M-77-344 Per your request, 1 reviewed the packet of information that was submitted by the operator in response to a complaint from the Bowie family whose residence is located in Penrose, Colorado; approximately 3000+ feet from the current active quarry area. As noted, the Bowie family nmoved into a newly constructed house in March of 1997. The Bowies allege that the blasting activities at the Portland quarry may have damaged their new honme and may danmage the honme in the future. However, the Bowies did not present any evidence to demonstrate that the blasting activities are, in fact, causing damage to [he stmcture other than providing times and dates of "explosions" for the last three (3) months and stating that "the intensity of these explosions and tremors has escalated over the months, some of which we can actually smell the explosives!" The Bowies add that "this all leads us to believe that we do have a very real problem." The Bowies state that "at this hme we have noticed cracks in our basemen[ walls, Floor and stucco." In order to understand how blasting causes damage to structures one needs to understand the basic principles and paranmeters of the event. 1 will not attempt to explain, or describe in detail, the various aspects of a blast in this report. If interested, the U. S. Department of the Interior's Blasting Guidance Manual (published March, 1987) can provide detailed information about blasting vibrations and its effects. Basically, when a blast is detonated, a great deal of energy is liberated. Some of this energy will be converted into vibrations; either ground motion or air overpressure (airblast). If one, or both, of the vibrations minimally exceed certain threshhold linmi[s, according to the Office of Surface Mining, there is " minimal probability of superficial damage to residential type structures." Both the ground motion and airblast vibrations can be measured with various instruments. Ground vibration is measured as the particle velocity. The maxinmum allowable peak particle velocity for dwellings within 5000 feet (but greater than 300 feet) of the blast site is 1.0 inch per second. This means that if the ground nmotion vibration exceeds 1.0 inch per second there is a minimal probability of superficial damage to residential type structures. Airblast vibrations are measured in decibels (noise) and pounds per square inch (psi). The Bureau of Mines "has said that levels exceeding 120 decibels will produce some annoyance from rattling and fright, with up [0 10% of honmes exhibiting disturbances at 134 dBL." The Bureau of Mines recorrunends [hat "efforts should be nmade to try [o keep airblast levels to 110 dBL in order to reduce annoyance and complaints as much as possible." Threshhold limits are generally set at 129-133 decibels. In order to control ground nmotion vibration, the scaled distance equation (see Blasting Guidance Manuaq