However, new government secrecy is eroding citizens' right to know about toxic pollution and hindering once-productive relationships between the government and citizens.

For example, the Aberdeen Proving Ground Superfund Citizens Coalition, a community group from Aberdeen, Md., relies on information from the Department of Defense to monitor environmental contamination and remediation at the U.S. Army's sprawling Aberdeen Proving Grounds.

The military has used the proving ground for munitions and chemical weapons testing since World War I. As a result, the area is heavily contaminated with chemicals, unexploded ordinance, disposal areas and firing ranges. Out of concern for the surrounding community, the citizens' coalition came together in 1991 to oversee cleanup.

The citizens received a federal grant to retain technical expertise and advocate for the most protective cleanup options. Federal law also compelled the Army to establish an advisory board to work with the Aberdeen community.

However, soon after Sept. 11, 2001, Deputy Defense Secretary Paul Wolfowitz issued a memo instructing Defense Department employees to protect "sensitive but unclassified information" that could be "compiled to reveal sensitive conclusions." These new restrictions are foiling community participation. Security concerns are colliding with citizens' right to know about environmental contamination.

At issue are maps that show plumes of groundwater contaminated with perchlorate, a rocket fuel ingredient used at Aberdeen for decades. Perchlorate contaminates 11 drinking water wells, both on and off Army property. Maps that once documented the extent and location of perchlorate contamination now lacked roads, street names and other orienting information, making it impossible for citizens to track the extent of pollution.

Perchlorate moves rapidly through soil and groundwater, where it can persist for decades. Perchlorate can cause thyroid tumors and can disrupt thyroid hormone levels during pregnancy, leading to mental retardation, loss of hearing and speech, birth defects, and other developmental problems in infants and children.

The citizens do not think shielding public information is the best way to increase security at Aberdeen and note that the information removed from the maps is publicly available through other sources. Street maps and photos of Aberdeen Proving Ground are widely available online. Anyone with a driver's license can still enter the base, which includes a public golf course.

The Homeland Security Act of 2002, a sweeping federal law enacted in response to Sept. 11, includes a parallel provision to shield sensitive but unclassified information. This provision has led federal agencies to remove previously public documents from the Internet, and to deny public access to the location of hazardous materials and facilities.

This new category of "sensitive but unclassified" information could sweep important public information into a black hole.

Ultimately, the Aberdeen citizens sued in district court and won disclosure of adequate maps showing the extent of perchlorate pollution. But lawsuits are expensive and cumbersome and are not as a practical matter always an option.

Public information can help hold government accountable, supplement government regulations with citizen oversight, encourage active citizenry and establish trust. When secrecy appears arbitrary or unfounded, citizens suspect that officials are using national security to avoid public scrutiny and accountability.

A "sensitive but unclassified" designation encourages official passivity, neither fully protecting information nor mandating efforts to fix underlying problems.