Two well-groomed, grassy hills in north Baton Rouge seem ordinary enough, but beneath the surface are the remains of their history as disposal pits for hazardous material.

In the 1960s and 1970s, before environmental laws were largely in place, petrochemical facilities handed over waste material to Petro-Processors of Louisiana for disposal at two sites, one along Brooklawn Road and the other along Scenic Highway.

The area is now going through its third five-year review from the U.S. Environmental Protection Agency, a process that checks up on how corrective actions are progressing.

“We go back at least every five years to make sure the remedy implemented is still appropriate,” said Bart Cañellas, remedial program manager with EPA.

EPA staff reviews activities over the past five years, visits the site and looks over records, and conducts interviews with people familiar with the site — regulators, university researchers or site workers.

EPA also sends out a fact sheet to those who have expressed an interest in the site and to let the surrounding community know that a five-year review is being done and it is accepting public comments. The five-year review is underway with a target to be done with the report by the end of the year, Cañellas said.

Cañellas said the agency hasn’t received many concerns or problems in past reviews.

“EPA will have to continue doing these reviews for every five years,” Cañellas said. “I’m not sure how many more we’ll have to do. It can be a long time.”

The U.S. Justice Department sued Petro-Processors and the petrochemical companies that contributed waste material deposited at the site. By 1984, a consent decree was issued by the U.S. District Court in Baton Rouge ordering the cleanup.

In the 1990s, the sites were a beehive of activity above ground with waste being pumped into incinerators and the resulting ash being hauled away for disposal. Almost 200 wells were used at the Brooklawn site alone, pumping material into the on-site incinerators.

That operation was completed in about 2000, and the pumps and associated equipment were removed in 2007 and 2008, said Bill Dawson, president of NPC Services Inc. — the company formed by the petrochemical facilities to handle the cleanup.

After that large-scale cleanup was done, a multidecade program began to monitor and handle waste products that got into the ground at both sites — known collectively as the Petro-Processors of Louisiana Superfund site.

At the Brooklawn site, the natural organic soils are enough to provide food for a host of organisms that help break down the remaining hazardous compounds and keep the plume of material confined within property.

At the Scenic Road site, the plume of hazardous material is traveling down a corridor of underground sand — left over from an old waterway of some kind — so there isn’t enough natural organic matter to feed the microbes. As a result, molasses is injected into the sand layer to feed the microbes to break down the material.

There are two areas where molasses is injected to help bacteria break down the material. Another set of monitoring wells is being drilled closer to the river so the company can determine whether the material is free of contamination. If they find contaminants, enough space remains to take corrective action before reaching the Mississippi River.

After being tested in the early 2000s for effectiveness, the microbes have been doing a good job of keeping the material from traveling off-site by breaking it down into various nonharmful components.

“We build up so many bacteria around the well screen (sometimes) that we have problems pumping more molasses into the system,” said Keith Horn, staff environmental scientist at the state Department of Environmental Quality. “It will take a very long time for the process to work themselves out.”

The company formed to handle the monitoring and treatment at the site — NPC Services Inc. — owns all of the property that includes the plumes of material.

The company does computer modeling to predict where the plume is headed and then does well testing to either confirm that projection or make adjustments, Dawson said.

In addition to the contaminants that seeped into the ground around the immediate site, the company also had to address contamination in nearby swamp areas.

The open pits at the Brooklawn location were at such a low level that when the Mississippi River floods, it would sweep over the ponds and drag out contamination. That contamination was heavier than water, so it ended up settling at the bottom of the bayou channel near the pits. A protective layer of material was laid over the bayou channel and gets inspected regularly to make sure it stays in place.

Testing in the area has shown that it’s working.

Follow Amy Wold on Twitter @awold10 .