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~~{ac i~ vr~~f7''r' v~ <br />MEMORANDUM <br />TO: John Link, County Manager <br />FROM: Paul Thames, PE, County Engineer <br />DATE: February 5, 1998 <br />SUBJECT: Effects of blasting operations at the Orange County Regional Landfill <br />As per your request, I have produced the following report on potential effects of blasting activities at the <br />landfill. <br />In general (that is, not specific to the landfill), the use of explosives to reduce or remove rock formations <br />on and below the surface of the ground has been known to cause incidental seismic (ground roll) damage <br />to neazby man-made structures, including water wells. For example, blasting operations have been <br />known to: 1) crack building footings, foundations and walls; 2) cause wells to collapse entirely or <br />otherwise crack well liner pipe; 3) disrupt, either permanently or temporarily, the flow of water to the <br />well from water bearing fractures; and 4) suspend or re-suspend sediments in wells and water bearing <br />fractures. The extent and shape of the area impacted by seismic effects of blasting operations and <br />intensity of those effects at any particulaz location within the impact azea can and do vary greatly. There <br />is evidence that blasting operations using ammonium nitrate based explosives can cause damage to wells <br />and septic tanks as far distant as 2000 to 3000 feet from the blast center. Some of the factors which, <br />singly or in combination, control the magnitude of the seismic effects include: a) the underlying geology <br />of the vicinity -isotropic or homogeneous rock formations aze very efficient at transmitting vibration <br />whereas heavily foliated or fractured rock formations are very efficient at dampening vibration; and b) <br />the operational procedures and protocols of each blasting event, including the diameter, depth; spacing <br />and number ofbore-holes; the positioning of explosive material within bore-holes; the quantity, type <br />and mix of explosive material (fast ignition explosives such as dynamite cause minimal ground roll and <br />slow ignition explosives such as ammonium nitrate cause more extensive ground roll); the time delay <br />intervals between individual detonations in a single blast event; and weather/temperature conditions. <br />As incidental damages are not uncommon during blasting operations, most contractors and engineers <br />involved blasting operations typically use dynamite or other fast ignition explosives to minimize the <br />extent of the area affected by the blast. Some contractors monitor blast effects with seismographs and <br />by conducting pre-blast inventories or inspections of structures located close to the blasting operations <br />{usually a minimum radius of 500 feet). <br />According to Gayle Wilson, during the last nine years in which he has overseen the operation of the <br />landfill, there have been only two grading/excavation projects requiring the blasting of rock. The first <br />eras at the onset of the Phase I and II construction of the lined (south of Eubanks Road) portion of the <br />landfill (late 1994-95). The second blasting project, during preparation for the construction of the Phase <br />III and IV sections of the lined portion of the landfill, began in mid-December and concluded in early <br />January 1998. Both blasting projects were conducted under a blasting plan required by and approved by <br />the state. In both cases, seisomographs were utilized to verify that the seismic effects of the blast were <br />