Covering up the air quality problem at Mono Lake: Just add water

“The principal values plaintiffs seek to protect, however, are recreational and ecological—the scenic views of the lake and its shore, the purity of the air, and the use of the lake for nesting and feeding by birds … it is clear that protection of these values is among the purposes of the public trust.”

Supreme Court of California, February 17, 1983

Almost forty years have passed since the California Supreme Court’s landmark Public Trust ruling, and Mono Lake hovers at an artificially low level, generating the worst particulate air pollution in the nation.

Decades of past excessive water diversions by the Los Angeles Department of Water & Power (DWP) dramatically lowered Mono Lake, reduced its volume by half, and exposed 18,000 acres of lakebed. The diversions resulted in devastating ecological, scenic, and recreational impacts, and created an air quality hazard that persists to this day. Today, Mono Lake is 12 feet below its target management level, and on windy days the exposed alkali lakebed emits large plumes of dust, producing air quality violations that exceed the public health standards of the federal Clean Air Act.

The number and degree of exceedances are not trivial. Mono Lake has, unfortunately, achieved notoriety for being the source of the most concentrated particulate air pollution measured in the United States for the past nine years. According to the Great Basin Unified Air Pollution Control District, “the magnitude of the PM-10 concentrations at Mono Lake are the highest in the nation and the frequency of the violations of the National Ambient Air Quality Standard is unsurpassed.” PM-10 is defined as particulate matter of ten microns or less, or one tenth the diameter of a human hair. Particles of this size are small enough to become lodged in the lower respiratory tract and can cause short-term and chronic respiratory problems.

First Owens, now Mono

For many years the dry Owens Lake, 120 miles south of Mono Lake, was the largest source of PM-10 pollutants in the country. Unlike Mono, Owens dried up after DWP fully diverted the Owens River over a century ago. After a lengthy and contentious legal process that began in the late 1990s, DWP was required to fix the air quality problem at Owens Lake. To achieve this, DWP engineered an extensive mitigation project to control dust-emitting soils over large portions of the dry lakebed. The project is so large that it is easily identified on satellite imagery. The effort achieved a high level of air quality attainment for PM-10 emissions at a cost that has surpassed $1.5 billion, and the total cost continues to grow.

The landscape engineering solutions that worked on the surface of dry Owens Lake—spreading gravel, planting salt grass, and constructing berms, pipelines, and sprinkler systems—would not be appropriate at Mono Lake. These methods would shatter the scenic integrity of the lake and the basin, which is recognized and protected by a State Natural Reserve and the Mono Basin National Forest Scenic Area, the first federally designated Scenic Area in the United States. Such methods would also cause adverse impacts to the lake’s ecology, and ultimately, would be submerged by the rising lake.

“The only feasible method”

When the California State Water Resources Control Board issued Decision 1631 in 1994, setting a management level for Mono Lake, they understood that the air quality problem at Mono Lake would be effectively remedied by allowing more water to flow into Mono Lake. The State Water Board concluded, “The only feasible method of reducing the PM-10 emissions sufficiently to come into compliance with the National Ambient Air Quality Standards is to increase the water elevation of Mono Lake and submerge much of the exposed emission source area… Improving air quality at Mono Lake by reducing the severity of periodic dust storms in the Mono Basin would also protect the views and scenic resources for which the Mono Basin is widely known.”

DWP’s Mono Basin stream diversions continue annually based on lake level thresholds established in Decision 1631. While the annual total diversions are much less than those of the last century, the continued water diversions have delayed the lake’s rise and Clean Air Act violations continue.

The path to compliance

The Clean Air Act establishes national emission standards for hazardous air pollutants, including PM-10. The Environmental Protection Agency (EPA) regulates under the Clean Air Act and works with states to ensure compliance. The Great Basin District works in partnership with the California Air Resources Board and EPA and it, along with the 34 other local air districts in California, is the lead agency for regional air quality monitoring and enforcement. Great Basin’s district covers Alpine, Inyo, and Mono counties, a territory larger than the state of Maryland.

Earlier this year, Great Basin sent a letter to the DWP Board of Commissioners asking that “immediate action” be taken to remedy significant air quality violations at Mono Lake. Citing the need to raise the lake to stop the emissions, the letter requests that DWP staff “enter into discussions with [Great Basin] staff on minimizing, even to the point of fully curtailing, the taking of water from the Mono Basin.”

Unless significant precipitation arrives this winter, the low lake level could automatically reduce the allowed DWP diversions from 16,000 to 4,500 acre-feet. This has happened before, and the increasingly water-efficient City of Los Angeles was able to conduct business as usual.

DWP spent $1.5 billion to fix the air quality problem at Owens Lake. Great Basin poses a more affordable, feasible, and ecologically beneficial solution for Mono Lake—allow more water to flow into Mono Lake to attain air quality compliance sooner rather than later. Great Basin will hold a workshop this fall in Lee Vining, and it may help clear the air regarding future air quality actions at Mono Lake.

This post was also published as an article in the Fall 2021 Mono Lake Newsletter. Top photo by Elin Ljung.