(BCN) — The Bay Area Air Quality Management District has extended its air quality advisory for wildfire smoke in eastern Contra Costa County through Wednesday. The Marsh Fire has burned more than 500 acres near the shoreline of Bay Point and Pittsburg since May.

The smoldering fire is now mostly consuming peat, a spongy material formed by the partial decomposition of organic matter, usually plant material found in wetlands. Millions of gallons of water have been pumped into the area from the Delta and Contra Costa Water District diverting water at Mallard Slough since last week.

Smoke has been impacting the areas of Pittsburg, Antioch, Oakley and Brentwood. Contra Costa County Fire Protection District officials said peat fires are very difficult to extinguish, though this one is nearly out of fuel. Peat can be found down to 6 feet below the surface.

The fire started May 28 near a Bay Point homeless encampment. It flared up more than a week ago and threatened PG&E lines and homes near Pittsburg before firefighters got it back under control. The air quality advisory is not a Spare the Air alert, but people with sensitivities to smoke and other pollutants are advised to take precautions such staying indoors with the windows and doors closed and using re-circulated air in vehicles when driving.

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Although efforts to flood the fire have begun to make progress, air officials expect smoke from the fire to affect the area through Wednesday, at least. Onshore winds during the day are expected to disperse smoke, but as winds die down overnight localized pollution levels may rise during the overnight and early morning hours. Pollutant levels are not expected to exceed the national 24-hour health standard.

Check for air quality readings at http://baaqmd.gov/highs.

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