The Imperial Valley has exceeded federal health standards for airborne particulates hundreds of times since the early 1990s, according to EPA estimates, with pollution levels sometimes reaching more than double the allowed amount. Nonetheless, the EPA allowed Imperial County to avoid stronger Clean Air Act requirements in 2001 due to county arguments that the region's violations were caused by cross-border pollution from Mexico. In a suit brought by Earthjustice on behalf of the Sierra Club, a federal appeals court ruled in October 2003 that the EPA's waiver violated the Clean Air Act because the facts did not show that all the violations were due to Mexican pollution. The decision was appealed, but on June 21, 2004, the US Supreme Court let the federal appeals court's decision stand. As a result of this decision, the EPA will have to reclassify the air pollution status of the Imperial Valley to trigger stronger air pollution requirements for particulate pollution.
The Imperial Valley has one of the highest childhood asthma rates in the state, and its death rate from respiratory diseases has at times been more than double that of the rest of California as a whole, according to the state's Department of Health Services. This court decision is the first step toward fixing these problems.