Blast Observation and Quarry Tour at Birdsboro

 

On September 29. 2021 H & K conducted a tour of the Birdsboro Quarry  several residents and Township personal attended. 

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Blast Event Map showing all collected Blast Event details 

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Blast Event Table showing “cooked down” scientific/technical information as collected at all required Blast Monitoring locations and our Blast Observation Tent location on 9-29-21.

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Actual “Shot Report” as generated by Maine Drilling & Blasting. Very detailed report,  

 

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The Bureau of Mines set the criteria for blasting back in the 1970s and 1980s. At that time, they determined that ground movement at 4" per second was enough to crack (minimal damage) horse hair plaster (what is considered the most fragile material) within a home. They then essentially cut that benchmark in half and stated that blasting could not exceed 2" per second in ground movement. 

HK agreement with Township states that blasting can not exceed 1" per second of ground movement. 

Across the board, HK has established a history of being below 0.5" per second of ground movement per blast (less than half that required by the township, and a quarter that required by the Bureau of Mines)

 

HK uses seismographs to measure each blast, typically located at the two closest dwellings to the blast location. All blasts are recorded. 

 

That blast was at 

0.1"/ second (ground movement), 120 dbs (airblast) at the site

0.07"/second (ground movement), 103 dbs (airblast) at 408 Hopewell St (closest dwelling).

Blast reading at 253 Hopewell Street was not even on the scale. 

 

This particular blast required 27 blasting holes and produced approximately 30,000 tons of material.

 

HK blasts 2-3x per week. 

Variability impacts each blast and how people in different locations feel it. 

 

GROUND VIBRATION (a seismic wave that moves through the ground following a blast)

Earthquakes are low frequency ground movement. Vibration travels very slowly, creates a lot of movement.  Structures do not respond well to low frequency movement. 

Blasting events are high frequency ground movement. Vibration travels very quickly. Structures hold up well with high frequency movement. 

Vibration tends to travel backwards from the blast as the energy is released forward into the blast zone. 

 

AIRBLAST & SOUND  (a concussion or pressure wave that moves through air following a blast)

Airblast and Sound travel forward with the energy and direction of the blast. Houses tend to act as sails - where the air movement and sound will tend to rattle and shake a home. 

 

BAROMETRIC PRESSURE

High Barometric Pressure (low ceilings and clouds) can bounce airblasts back down to earth in surprising ways and locations miles away from a blast site.

 

All blasts are designed with the nearest structures in mind and to control the path of least resistance and how the rock falls. 

Methodology of a Blast

1) Design and engineer the Blast

2) Paint it on the ground

3) Copied to a hole Log (depth, spacing, size of holes, hole angles, etc)

4) Driller uses Hole Log to drill the blast holes

5) Field Engineers arrive on site and send probes down the holes to measure depth, straightness, size, etc to confirm holes match design criteria

6) Blast commences

 

Blasting and Quarry Operations are monitored by 

• Mine Safety and Health Administration

• Game Commission

• Fish and Boat Commission

• Army Corps of Engineers

• PA Department of Environmental Protection

 

In summary, blast characteristics (direction of initiation, face, quarry level, etc.), intervening variables (wind speed, wind direction, temperature, barometric pressure, cloud cover, etc.) will all impact how adjacent properties "feel" the blast itself. People's sensitivities to air/sound vs vibration and frequency will also impact how they react to a blast. The path of vibration backwards from the blast, the airblast forwards in the direction of the blast, and the pressure systems in the sky above will all impact how different properties, structures, and people will react to the blast itself.  Studies have also shown whether one is inside a structure at the time of a blast or outside will also impact their perception of the severity of a blast. Shane Legray, the subcontractor conducting the blasting at the quarry, noted that in his personal experience, when inside a home "a blast feels different" than when outside and structural vibrations will vary from home to home based on a variety of factors including the construction of the home (height, layout, materials used, etc).  Interestingly, a study conducted by TJ Schultz on noise annoyance and blasting reported in the Journal of Acoustical Studies of America in 1978 concluded that " ... anyone who has simultaneously measured the noise just outside and inside a house knows that the exterior and interior exposure bear very little relation to one another."  

 

A study conducted by Stanley Jacobs, PhD out of Villanova in 1995 entitled An Assessment of the Perceived Effects of Quarry Blasting on a Suburban Residential Area provides research concluding that the acoustic signals generated by blasting generate more annoyance than vibrations, and the " ... human response and annoyance problem from air-blast is probably caused primarily by wall rattling and the resulting secondary noises" inside a home vs the vibration of the blast itself. In that same study, Jacobs cites a source pointing out that perception of quarries in general also impacts how people respond to actual blasts themselves-  blasting noises, for example, can be genuinely annoying if only because "they remind people of other dislikes, such as early-morning machinery noise, truck traffic, dust, perceived adverse impact on property values or environmental concerns." This study, which surveyed residents living adjacent to quarries in PA  and compared their perceptions of the quarry and  blasts vs the actual blasting data itself, found that the highest contributing factor to complaints to people adjacent quarries was the "startle effect," where residents react to the noise and vibration who were unaware a blast was coming. See conclusions from this study below:

 

 It is obvious from the results obtained that the noise and vibration associated with quarry blasting are a significant and continuing source of annoyance to Swedesburg and Swedeland residents. These factors are viewed as more annoying than any other quarry activity (such as alarms and truck traffic) or any other source of annoyance in the communities (such as aircraft and street traffic). It appears that these factors (especially vibration) derive their annoyance value from the startling effects of blast events -- the fact that they occur on an irregular and unexpected basis. Public reactions to blast noise are probably often reactions to secondary noise generated by vibrations of structural components (e.g. windows, ceiling, walls and floor) or furnishings, rather than actual blast noise. In a sense, it may be  similar to fearing thunder more than the lightning which created the noise. 

 

The "startle" aspect of the experience of a blast event is a major source of annoyance. Disseminating a schedule of blast events and/or initiating a warning system may reduce the effects associated with this factor.  

 

There appears to be an extremely strong tendency to over-report or to exaggerate the frequency of blast events actually experienced.  This may reflect a strong negative perception of the quarry's blasting activities, rather than an accurate reporting of actual experiences.

The intercorrelations of the ratings of the experience of a blast event, and the consistent results from the regression analyses, suggests that weather (specifically temperature) is significantly related to the experience of a blast event.

 

Data from the (Blast) Diary clearly indicate that residents are able to accurately perceive the occurrence of blasts and that such blasts are intrusive and annoying. However, the effects of quarry operations seem to extend beyond that which is clearly and unequivocally attributable to operations, per se. Some of the public annoyance and antagonism that is directed at Glasgow Quarry appears to be either inherited from earlier operations, prior to contemporary regulation and oversight by the Commonwealth, or due to a generalized dislike of quarry operations stemming from real sources of annoyance, such as dust and dirt, possible property damage and the periodic startling experience of blast noise and/or vibration. A persistent problem and source of tension between quarry and community may be the widespread public impression that the quarry is disinterested, at best, concerning its effects on surrounding communities (see especially Tables 34, 35 and 36). A more concerted attempt at building a positive relationship by both residents and quarry personnel could reduce some of that tension. There seems to be a very limited level of knowledge and familiarity with quarry operations on the part of most residents, and certainly very little by way of positive identification with the operation. These, it is felt, are factors which can and should be addressed through community relations and educational programs. 

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