Noise Study at Marine Base Is Generating a Lot of Heat : Environment: Public officials worry that new data could halt development near El Toro air station. At issue is which measurement standard is used.

A study projecting aircraft noise around the U.S. Marine Corps Air Station at El Toro is causing concern among public officials and developers who fear that the findings could upset land-use plans and halt nearby home construction.

Both the city of Irvine and the Irvine Co. have expressed reservations about the Marine Corps draft study, which is the first step in a formal reassessment of the El Toro base’s impact on surrounding communities when the base replaces older aircraft with new fighters.

Under Orange County and Irvine land-use policies, the so-called “noise contours” around airports and military air bases limit the development of homes, and to a lesser extent, offices and stores. The noise lines look much like elevation contours on a topographic map.

Military and city officials have three noise-measurement plans before them: one measuring aircraft decibel levels the current way, the second measuring noise on an “average day,” including holidays and weekends, and a third that measures noise on an “average busy day” basis. The latter would register more noise and the “average day” measurement would gauge the least, officials say.

“We like to be able to rely on (noise) lines that hold up over time,” said Irvine Mayor Larry Agran. “This has been the continuing problem with the Marine Corps. . . . The rules of the game seem to change every five years, based upon new studies. . . . That kind of development renders the whole planning process somewhat of a joke.”

Larry Thomas, an Irvine Co. vice president, said: “What up until now has been a certainty, with respect to the (planning) interests of the city and the company and the Marine Corps, now potentially has been made more uncertain. . . . It’s the prospect of that uncertainty . . . that has gotten our attention.”

City and county officials have said the new noise contours could prevent residential development of property owned by the Irvine Co. west of the “El Toro Y” freeway interchange, where the San Diego and Santa Ana freeways meet.

It also could affect some development in the Aliso Viejo and Foothill Ranch communities, officials said.

But Col. Jack Wagner, community plans and liaison officer for Marine Corps bases in California and Arizona, said the new noise lines will have little impact on nearby neighborhoods.

“They’re planting a lot of bum soup in the community,” Wagner said. “The number of (aircraft) operations is declining. The noise lines are shrinking more than they are increasing. . . . What’s the complaint?”

The noise study is the first step in a formal process to reassess the relationship between the air station and the surrounding residential and commercial areas. Known as the Air Installations Compatible Use Zones (AICUZ) program, the reassessment should be completed by September.

Both Orange County and Irvine will base many planning decisions on the noise study, which will include the new noise contours. Although the Marine Corps provides the data, the planning decisions are the responsibility of the local governments.

The Marines undertook the new study because they are retiring older A-4 and A-6 attack aircraft and replacing them with the modern F/A-18 Hornet fighters, which have different noise characteristics.

The draft noise study projects 65,187 annual jet operations at El Toro beginning in 1992. The figure includes landings, takeoffs and overhead maneuvers. A 1981 study projected up to 72,000 annual flight operations for the foreseeable future, but flight operations dipped significantly in 1986, 1987 and 1988 as the Marines retired older aircraft.

Local officials are uncertain about what the study will mean for land-use planning largely because of a new wrinkle introduced by Navy officials in Washington. The Marine Corps is part of the Department of the Navy.

The complication is a new, alternative noise measurement included in the El Toro draft study that differs from measurements used in previous studies. Current noise contours and the land-use plans based on them were last established in the 1981 study.

The previous studies based noise contours on aircraft landings, takeoffs and training maneuvers conducted during an average day of operation. Because very few flights are scheduled at El Toro on weekends and holidays, the average-day noise level is significantly lower than the level on a normal operating day.

While the new study also includes an average-day measurement, it adds an additional measurement of noise levels on an average busy day, when normal operations are being conducted. Contours for the average busy day are, by definition, larger and include more area than contours for the average day.

The key line on the new noise maps is one that measures the area where the aircraft noise level is 65 decibels or greater. County and city planning policies, based on state noise standards, generally prohibit residential development within the 65-decibel line, and restrict commercial development in the area.

The average-day 65-decibel line in the new study actually encompasses a smaller area than the existing 65-decibel line set in 1981, Wagner said.

But the 65-decibel line for the average busy day in most areas lies well outside the existing boundary, raising the possibility that local governments would restrict development in a larger area than previously planned.

“What is the real noise impact on the ground to the people who are hearing the noise?” asked Alan Zusman, the Navy’s noise-measurement study manager. Zusman said the Navy’s goal is to come up with the best available measurement of the impact of aircraft noise on the people who hear it in surrounding areas.

The average-day measurement may underestimate that actual impact, Zusman said. “So we decided another way to do it was look at the average busy day, when a station is in normal operation.”

But Wagner at El Toro said the Marines will recommend that local governments adopt the more lenient average-day standard because that was the method used in the last noise study.

“The previous AICUZ (noise-measurement) studies have served the city and the county and the Marine Corps well for land-use planning purposes for over 15 years. Let’s not change techniques if they’ve served us well,” Wagner said.

“You have to compare the average day with the average day,” he said. “Do not look at . . . average busy day. The final line will be based on average day, it will not be based on average busy day.”

The head of Orange County’s Environmental Management Agency, Michael M. Ruan, said the county probably will go along with the Marines’ recommendation.

But Irvine officials are not so sure.

“We are looking at it from a health and safety standpoint,” said Peter Hersh, Irvine’s manager of planning services. “We want to see if we are justified in distinguishing one (standard) versus the other. We want to get all our facts together before we decide which one we are going to base our land-use policy on.”

Added Mayor Agran: “What I’m looking for is a legitimate methodology that bears some relationship to the real world, and in the real world, people are frightened, they are annoyed and they are pointing the finger politically when there is an unacceptable level of noise.

“If the Marines are telling us the (noise) footprint should be larger, they may well be right. But what we have to do is get from them reliable figures . . . that will hold up, not just for a year or two, but forever, for our planning process.”

In addition to raising concerns about the different noise standards, public officials have suggested that the Marine Corps noise study, which is based on a computer model, ignores test data indicating that the noise levels actually are much lower than the computer has projected.