San Antonio, Texas, maybe best known for the Alamo, the Riverwalk and the Spurs basketball team, is not readily considered one of the country's large cities. However, according to estimates from the U.S. Census Bureau, San Antonio is now the second most populous city in Texas. More people reside within its city limits than in Dallas, not including suburbs.

Public, residential and commercial construction in San Antonio during the last few years has sustained a strong local market for aggregate. Not surprisingly, growth also has brought development to the rim of what were once rural quarries. And the new neighbors often take a dim view of the operations-blasting in particular-that supplied materials to build their roads, sewers, stores, restaurants and expensive homes.

That is the setting for Vulcan Materials Co.'s Huebner Road Quarry on the northwest side of San Antonio. In the last five years, new apartments and houses have cropped up on the low hills surrounding the more than 40-year-old quarry.

To fit better into the changing community, Vulcan landscaped the entrance and built berms and a stone wall along an adjacent road that also borders a city park and school. It also confined extraction to the lower levels of the quarry to minimize air blast. But as stone at the lower levels and prospects of relocating the operation ran out, the company had to move to the upper level about a year ago to open up more reserves.

Air blast and vibration can be more pronounced on the upper level, said Ronald Hendrickson, Vulcan's South Texas operations manager, and the quarry started receiving more complaints. Legally, Vulcan was well under regulatory limits for ground vibration, Hendrickson said. But realistically, that was not enough to stem complaints, so the company sought ways to further decrease its impact from blasting.

Information-based blasting Efforts to more effectively control blast vibration are highly dependent on accurate information. Plant Manager Frank Bluemel helps design each shot in conjunction with Vulcan's explosives supplier, Austin Powder, and the aid of drillers' logs and a laser face profile.

Vulcan contracted with Blast Design International, New Braunfels, Texas, a joint venture with Ensign-Bickford Industries, to profile the quarry face with a Quarryman laser survey instrument prior to every shot. The survey provides burden information for each hole in the front row to allow appropriate explosives loading. The sections with extra burden can be loaded with higher-velocity explosives, such as an ANFO-emulsion blend. Low-burden sections might be loaded with straight ANFO or, in extreme cases, stemmed through.

Local drilling contractor Rock Busters provides detailed drilling logs for each hole. The logs and face profiles are especially important for operations on the upper level because of the greater occurrence of clay seams and the more thinly bedded limestone. These create a more irregular face profile and more variable burden.

Bluemel monitors each shot with three seismographs along the perimeter of the quarry property and with a video camera. Videotapes not only document each blast, but can show hole blowouts and other minor problems that possibly can be corrected on subsequent shots, Bluemel said.

In its continuous effort to lessen the impact of blasting, Vulcan changed the diameter of its blast holes from 5 11/42 to 4 11/42 in. In conjunction with the smaller hole, Vulcan changed drill patterns on the upper bench from 15 Yen 15 ft to 12 Yen 13 ft. Hole depth remained 45 to 50 ft.

"It increases costs," said Hendrickson, "but it is easier to lessen air blast with a smaller-diameter hole."

The top 10 to 12 ft of each hole typically is stemmed for further air-blast control. Consequently, with the bedded limestone, there is a "fair amount of oversize from the top bench," said Bluemel. Vulcan rotates an excavator with a hydraulic hammer among its three quarries in the San Antonio area to break oversize.

Recently, Vulcan changed the size of each shot in order to reduce the total number of shots. "We used to put off smaller shots because we thought the shorter duration of the shot would be less noticeable to neighbors," Hendrickson said. "We didn't notice that much of a decrease in complaints with the smaller shots.

"We can double the size of our shots and only shoot once a week, which has only half the impact on our neighbors."

The larger shots produce only a slight increase in vibration, Hendrickson said. The change was too recent to gauge neighbor reaction, but "less shots per week disturbs our neighbors less," he said.

Handling complaints The change from a rural to a suburban quarry has necessarily altered the plant manager's focus. Bluemel spends more of his time with blast design, setting out seismographs, videotaping and reviewing each shot, printing out seismograph reports and talking to neighbors who call, Hendrickson said.

If a neighbor does complain, the company has an established procedure to ensure timely response. Bluemel talks to them and completes a blasting-complaint form. This form is faxed to Vulcan's Southwest Division office and a copy is given to the division safety/environmental manager. Either that manager or Hendrickson follows up with the complainant to ensure that they understand Vulcan's blasting program and the safeguards used.

If the neighbor is still dissatisfied, arrangements are made to place a seismograph on their property, monitor a blast and show them the results. Complainants are invited to the quarry to observe a shot.

"We are not confrontational and don't deny what complainants say," Hendrickson said. "We just try to explain what we're doing to minimize [problems]. The sooner we respond, the easier it is to defuse complaints."