Earlier this month, environmentalists celebrated the U.S. Environmental Protection Agency's announcement of a final plan to clean up a long-festering pit of toxic sludge along the San Jacinto River east of Houston. The strategy is one they’ve long demanded: a near-total excavation of the San Jacinto River Waste Pits, where dioxins and other carcinogenic pollutants have festered since a paper mill company began disposing of its waste near the river in 1965. The plan also requires the companies found responsible for the dump to foot the $115 million cleanup bill. But at least one of those companies, along with some state and local industry groups, continue to oppose the approach. That has environmental and advocacy groups worried they may try to wiggle out of cleanup obligations amid negotiations with the EPA — even though Administrator Scott Pruitt, who has moved to dismantle many other Obama-era environmental rules, has expressed support for the plan. The EPA proposed the cleanup strategy for the infamous Superfund site in 2016 when Obama was still in office and took public comment on it toward the end of the year. The final version, unveiled on Oct. 11, calls for the construction of temporary berms around the submerged pits before some 212,000 cubic yards — around 15,000 truckloads — of the toxic paper mill sludge is excavated and carted away to a yet-to-be-determined waste disposal facility. In 2011, McGinnes Industrial Maintenance Corp. and International Paper Co. paid $9 million to install a temporary cap on the pits and have since argued that containing the pollution is the environmentally safer option. But environmental and advocacy groups and local environmental prosecutors have said such infrastructure is vulnerable to weather-related and other disturbances, pointing out that the temporary cap was damaged during Hurricane Harvey and has occasionally needed repairs. (In 2015, divers found a 20-foot hole in it.) Some of them say the companies’ opposition to the plan is less about protecting the environment than their profits — it's widely acknowledged a permanent cap would be much cheaper than excavation. "The bottom line is the cap is a riskier option because we know it's a matter of time before a cap fails, and if it fails, it's an uncontrolled release [of toxins]," said Scott Jones, the director of advocacy at the Galveston Bay Foundation. He said the foundation has asked the EPA to pay for the cleanup and seek restitution through the court system if the companies refuse to cooperate. “We’re worried that the fight will continue,” he said. In a statement following the EPA’s announcement of the cleanup plan, McGinnes issued a statement that said the company “cannot support a plan for the site that provides less protection to all affected communities than the existing cap already has provided.” The industry groups that have come out in opposition to the plan also focus on environmental concerns. Excavation could leave the site exposed and inadvertently allow chemicals to escape the site and leach into the river, said J.T. Edwards, a spokesperson for the Galveston Maritime Business Association, a coalition of about 25 area individuals and businesses. “To do a dredge of this type, of this magnitude, you really have no safeguards against accidental contamination of both the Galveston and Trinity bays,” he said. The San Jacinto River flows into both of those bays, home to seafood that is the lifeblood for many local restaurants and fishermen. If anything unexpected happens during cleanup and chemicals escape into the river, Edwards said it could devastate the area environmentally and economically. The Texas Association of Manufacturers was more guarded in a statement issued in late September, but said a "full cleanup" could cause "potential environmental harm." Opponents to excavation have long cited a 2016 Army Corps of Engineers study, which suggests that reinforcing the site’s temporary cap with a more fortified version may be a less risky move than site removal. However, Jones said the study also highlights a cap’s vulnerability to erode during weather events like floods and hurricanes. The EPA announced the cleanup plan less than two weeks after confirming that the temporary cap was severely damaged by rains from Hurricane Harvey, exposing “underlying waste material.” A nearby sediment sample collected by a dive team showed dioxin levels 2,000 times higher than the level for which EPA would consider the site to be clean. During a trip to the Houston area last week, Pruitt said he recognized the "urgency" to clean up the site as quickly as possible given the damage that occurred during Harvey. (Pruitt, who repeatedly sued the Obama-led EPA as Oklahoma attorney general, has deemed the cleanup of Superfund sites a priority.) "We're going to use every bit of jurisdiction, every tool under the statute, to ensure that we get this area remediated," he told a Houston television station.    After discovering the breach, the agency ordered McGinnes and International Paper to conduct follow-up testing to determine if the contamination had migrated further. According to a statement from the companies on Wednesday, six additional samples indicated that “no migration from the originally sampled area occurred post-storm.” The companies said the samples showed toxin levels in sediment samples comparable to those found prior to Harvey. "No release of dioxins ... has occurred from the San Jacinto waste pits site as a result of Hurricane Harvey, according to results from new sampling of sediments," the joint statement said. Rock Owens, who oversees environmental cases for the Harris County District Attorney’s Office and has sued the companies over the pits, called the statement misleading and said more testing is necessary to determine the full extent of Harvey’s impact on the waste pits. Jim Blackburn, an environmental lawyer and environmental science professor at Rice University, said that excavation was the right call but will have to be done very carefully. He said the waste pits' location in a waterway vulnerable to hurricane storm surge and other weather-related events and the dangerous nature of dioxins — even in small concentrations — make excavation of the site complicated. “The details matter tremendously on something like this,” he said. "They have to get the engineering done correctly.” The EPA estimates it will take two years before the cleanup begins. The agency is now entering into a 60-day negotiation period with McGinnes and International Paper where they will seek to secure the companies' cooperation. Owens said he's concerned that the cleanup process could take even longer if the companies resist. But he said there is still a job to be done. “It’s a big pile of poison that needs to be taken away,” he said. Disclosure: Rice University has been a financial supporter of The Texas Tribune. A complete list of Tribune donors and sponsors is available here.