In 1988, when it was discovered that soil at the former Waterville Gas Works site contained toxic coal tar, it wasn't a big surprise.

Across the country, many defunct coal-gasification facilities, which had once made gas for use by industries and in cities, were identified as significant toxic waste sites because of coal tar residue on their properties. In 2001, a report by Business Week magazine said that between 3,500 and 5,000 such sites existed nationwise, with estimated cleanup costs in the billions.

Coal tar needs to be cleaned up because it is a known human carcinogen. The samples found at the Waterville site contained cyanide, volatile organic compounds and other pollutants.

According to the Environmental Protection Agency, the gas works' pollution was found adjacent to Holland Brook -- which flows into the Kennebec River -- and in a segment of soil that was 200 feet by 85 feet and about eight feet thick.

Pollutants also were found in groundwater on the site. The entire property is within the 100-year flood plain of the Kennebec River and the nearest residence is within a quarter-mile.

We're pleased to hear that the responsible former owner of the property, Central Maine Power Co., is nearing completion on a state-supervised cleanup of the site. Unlike many other cleanups, where soil is removed, this one almost entirely consists of stabilizing the soil at the site by mixing it with a cement-like additive. Then the site will be capped with up to two feet of soil.

But something is missing in the cleanup plan.

State environmental officials say there are no provisions for post-cleanup monitoring of Holland Brook next to the site, despite the fact that it flows into the Kennebec River.

That's a bad idea.

Millions of state and federal dollars have been spent over the decades to restore water quality in the Kennebec, which was once home to huge populations of migratory fish. Keeping up progress toward a healthy river includes making sure that potential sources of pollution, such as the Gas Works site, are kept track of. Furthermore, we've written off far too many of our blighted urban streams that flow through industrial areas. If the mighty Kennebec is worthy of care, so is little Holland Brook.

While state environmental officials say they are confident in the technology used to stabilize the soil next to Holland Brook, history unfortunately is rife with that kind of confidence being dashed by the reality of a toxic leak.

Central Maine Power should be required to perform several years or more of post-cleanup monitoring of the stream and any other relevant portions of the site, with monitoring protocols approved by the state.

If the technology to clean up Waterville Gas Works merits such confidence, this kind of monitoring will only verify that the confidence is well-placed.