A Sound and Dust Decision - A Hanson Aggregates operation in California addresses community concerns with equipment solutions.
(Previously published in Pit & Quarry)
By Rodney E. GarrettA California quarry finds that installing sound and dust barriers helps eliminate community barriers at the same time.
 | | Challenge Reduce quarry operations-sourced noise and dust. Solution Metso Minerals Trellex dust-encapsulating systems installed over one primary and four secondary screens. Tip An independent sound-levels study prompted the company to increase the number of acoustic sound walls installed in the crushing/ screening areas. |
At Hanson Aggregates’ San Marcos quarry operations in San Marcos, California, the company erected sound and dust barriers at the quarry to eliminate potential barriers between it and the local residents. The results have been positive to say the least.
Hanson has a good reputation for being a good neighbor. The company works hard at achieving and maintaining the good neighbor image. Establishing a good rapport with local residents, however, requires time and a concerted effort on Hanson’s part. So a new quarry-operations management team was put into place at the San Marcos facility.
Four years ago the company assigned Jud Harvey as its new plant manager. Harvey already had 11 years experience in the quarry industry both as an equipment operator and in management positions. About the same time, Ken Kindler was appointed the area manager in charge of the San Marcos quarry, a sand production facility, a land reclamation project and two hot-mix asphalt (HMA) plants. His previous experience has been operating HMA plants for 20 years.
Harvey reports to Kindler and both say they are a good match. Kindler has good overall business management skills, while Harvey’s forte is in hands-on quarry operations managing. Rounding out the technical skills is Ron Thompson who oversees the electrical and sophisticated computerized automation systems at this and other plants.
How does this play into the company being a good neighbor? There are three key elements in the Hanson equation that lead to success with the local people. One key was put into action early on and with good reason. At their start at San Marcos, Kindler and Harvey realized that a relational improvement with their neighbors was highly desirable. One reason was that builders/developers were in the process of building new homes near the quarry. In fact, some homes are within 400 ft. of the quarry’s crushing/screening operations.
The homes there are priced at about $450,000. Needless to say, this home price-bracket carries a demographic that reflects middle to high-income professionals who are aesthetically discriminating in standards of living. Simply put, their tolerance for chaos is nil.
The reason people of such means choose to live near the quarry is related to the high demand for high quality homes in an area where building lots are becoming scarce to find. The other reason for building here is that the quarry’s years are numbered. In the not-too-distant future, this quarry will be permanently shutdown and the area suit-ably restored for building more beautiful homes.
Taking all these conditions into consideration, Kindler and Harvey realized the importance in establishing a good rapport with the neighbors. Harvey says that establishing a good rapport is much more than acting on the aphorism that says, "a good defense is a good offense." He explains,"[Hanson] could have a quarry operation in the middle of the desert and still we would practice that which is environmentally sound."
Early, Kindler and Harvey held a meeting with the local residents, a planning com-mission and some of Hanson’s top management people. At the meeting, Hanson management assured everyone they would reduce quarry operations-sourced noise and dust, plus halt crushing/screening operations at nights and over the weekends.
Hanson’s assurances were followed by Kindler and Harvey carrying them out straightaway. "Our management did more than just make promises," says Kindler. "They gave us the wherewithal to start a meaningful program that was acceptable to
the neighbors."
The program included:
- The planting of 250 trees to beautify the quarry area.
- An irrigation system was installed for watering the trees.
- A gate was installed at the quarry entrance to prevent people from driving cars into the quarry during closed hours. These late-night activities understandably had many neighbors feeling ill at ease.
- A mechanical tire cleaner was installed on the quarry’s exit roadway that leads to the public streets.
- To further ensure clean streets, the company bought and operates a street-cleaner.
- The facility’s night lights have been repositioned so the lighting is less intrusive to the surrounding homes.
- Strobe lights are used instead of alarms during the night.
An independent sound-levels study prompted the company to increase the number of acoustic sound walls installed in the crushing/screening areas. The results were very good. Prior to adding more walls, the sound levels recorded in the surrounding neighborhoods were 75 dB(A).
Now, periodic independent monitoring indicates levels ranging from 62 to 65 dB(A), which are within the maximum 65 dB(A) noise-level allowed. A sound level is reduced by half if the measured level is reduced by 10 dB(A). One other significant action taken was that a 1,500-ft.-long berm was built for deflecting some sound patterns.
Dust and noise control
Hanson’s actions mentioned above have been a good start towards being a good neighbor. Nevertheless, fugitive dust sailing in and around the neighborhood is not acceptable either. Unlike sound, which falls off as it travels away from its source, airborne dust can be carried by wind for thousands of feet before it settles.
To control airborne dust at the quarry, the haul roads are constantly sprayed with water. All conveyor transfer points and crushers have low-pressure water spraying systems, some automatically controlled by Allen-Bradley PLC systems. Each crusher has its own bag-house. Completing the dust-control system are Metso Minerals' Trellex dust encapsulated units installed over one primary and four secondary screens.
The Trellex system serves a two-fold purpose. For one, it reduces - 5 to 6 decibels - noise levels that are created from the operating screen and the rock dancing in the screens as it is being separated by size. Screen noise levels can be further reduced by installing Trellex SQ Modular (1 ft. x 1-ft.) chute linings - which typically reduce noise levels by 10 dB(A) - and Trellex screening media such as the rubber panel systems. While no screen noise levels were recorded here, they were recorded at another quarry, according to Metso Minerals. With all three type Trellex systems installed on the screen, the noise level was reduced from 95 dB to 76 dB.
Nevertheless, the main function of the Trellex encapsulated system is to confine the airborne dust to the interior of the screen housing. Not only does it confine the dust, it is instrumental in the dust being forced to re-settlement on the rock by negative pressure. This encapsulated system is used here in conjunction with the low-pressure water spray system.
Low-pressure water spray systems are effective in reducing fugitive dust but often at the cost of screens blinding with rock fines. This trade-off is costly, according Harvey. It requires the daily cleaning of wire screens. It can be argued that installing a high-pressure water spraying system or chemical foam applications system will greatly reduce the fugitive dust without blinding the screens because of the significant reduction in water requirements. This is true, however, these systems cannot reduce the rapid wearing of steel screens associated with screening abrasive crushed rock. The answer to this quandary, says Harvey, is to install rubber panel screens.
Harvey uses two Metso Minerals screening media for the secondary screening systems. For the larger size rock screened at two triple-deck 8-ft. x 24-ft. screens, a Trellex T-Flex- US rubber panel system was installed. This panel demonstrates outstanding longevity compared to steel screening. It also has a unique attachment system enabling screening apertures to be located at the perimeter, thus eliminating fines collection here. The top decks are fitted with the 35-mm thick, 4-ft. square panels featuring a 1.5- in. aperture. Fitted to the middle decks are 25-mm thick, same size panels with 1.0-in. apertures.
For the finer screening, the Trellex Superflex tension panel is used. This rubber screening panel has outstanding useable life and self-cleaning (anti-blinding) characteristics. It is designed for screening relatively small-sized aggregates where blinding can be a serious problem. Here, it is installed at the middle deck of two 8-ft. x 24-ft. triple-deck screens. The size is a 4-ft. x 4-ft. tension panel, 5.5 mm thick with an 0.437-in. (7/16-in.) aperture.
So there are two elements included in the good-neighbor equation. Hanson making operations concessions to the neighbors and giving the quarry management team the re-sources required for bringing promises to fruition.
As for the third element, it is the person-al relationships being created between Han-son employees and the residents.
To that end, the company has built walking trails throughout the unscathed areas of the premises for the enjoyment of the neighbors. Kindler is on the board of directors and executive board of the Boys & Girls Club, which organizes activities of interest to boys and girls.
The company also supports a youth baseball league, a Navy league and once each year the company sponsors a picnic for company employees and residents. There are also formally conducted school tours for showing the children how aggregates are made and what they are used for. Both Kindler and Harvey enjoy this contact with their neighbors as much as the neighbors do. Barriers have been torn down and friendships have been created as a result.
| | Trellex: an economical approach | |
| It is very economical to use Trellex panels, according to Jud Harvey, plant manager. His records show that changing steel screens and cleaning blinded ones required three men, three to four hours daily. The total number of annual man-hours exceeded 3,000. Harvey prefers not to say what the cost per hour is. Each quarry has different labor costs but, based on $35 (including benefits), the labor costs exceed $100,000 per year. By comparison, the Metso Trellex screen media have a useable life expectancy of 18 months with maintenance carried out once every six months by four men at 16 hours each. As for the life expectancy of steel screens, they last here about six weeks because of the abrasive blue granite being processed. At $900 per deck, the steel screens will cost $11,610 every 18 months compared to $8,000 per deck for a Trellex product. Wire screens still have a place at some quarries where so many different size aggregates are made that it necessitates the constant changing of different aperture screens. The capital investment for rubber screens at $8,000 per deck would be too great if many different screens must constantly be changed. Cooley Equipment is the local Metso products supplier. Metso and its dealers have a close business relationship for help bringing both service and products to their customers in a timely fashion. |
For more info on the products, please contact Claes Larsson.
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