Landfill leachate can pull arsenic from rocks, soil

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01/01/2006

Landfill leachate can pull arsenic from rocks, soil

Evan Brandt , ebrandt@...

http://www.pottstownmercury.com/site/news.cfm?newsid=15850068 & BRD=1674 & PAG=461 & d\

ept_id=18041 & rfi=6

The level of arsenic found in landfill leachate may be heightened by the

leachate itself, a study by the federal government suggests.

Arsenic is a natural element that is widely distributed in the earth’s

crust and, at high levels, is poisonous to people.

It has been connected to bladder, skin, lung and prostate cancer and the

concentration of it allowed in drinking water will be reduced this year as

the result of new federal standards.

Arsenic is most commonly used now as a preservative to make wood resistant

to rotting and decay. In the past, it was a component of pesticides and in

alloys for lead-acid batteries for automobiles.

In the late 1990s, the U.S. Environmental Protection Agency became

concerned with the high level of arsenic found in the leachate from many

landfills in New England.

When abnormally high levels of arsenic -- several hundred micrograms per

liter -- were found in a leachate plume from a landfill in Saco, Maine,

the government decided to investigate.

When the U.S. Geological Survey conducted a study of leachate from that

landfill, which is also a federal Superfund clean-up site, it found some

surprising results.

" USGS studies on the geochemistry of the leachate plume at the Saco

Landfill have shown that the source of the arsenic is not the landfill,

but appears to be the sediments the plume is moving through, " according to

a study report issued in October by the USGS Toxic Substances Hydrology

Program.

What a computer model created from samples and tests at the site showed,

was that " dissolved organic carbon in the leachate plume is dissolving

arsenic from arsenic-containing iron oxides in the aquifer and the

bedrock, " the report showed.

When the organic carbon in the leachate degrades, it removes oxygen from

the water and " creates the conditions that favor the dissolution of iron

oxides and the release of arsenic from the sediments, " the study

concluded.

The study also found that an impermeable membrane installed on top of one

of the landfill cells in 1997 to reduce the amount of arsenic in the

leachate would be ineffective for several years until conditions that

consume the oxygen in water are finally used up.

Once oxygen levels in the groundwater and leachate returned to normal,

less arsenic would be leached out of the rock and soil through which the

leachate is moving, the study found.

*

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