A voluntary investigation by GAC Chemical Corp. into contamination associated with a historic sulfuric acid plant on its property found buried sulfur and acidic groundwater at the former plant site and acidic conditions on the adjacent shore.

The company plans to remediate the contaminated area by removing the sulfur, stabilizing an eroding bank, and adding an alkaline buffer to treat groundwater.

Activist group Friends of Penobscot Bay and Dr. Mark Green, environmental science professor at St. Joseph's College, conducted a study of shoreline sediment early this year which yielded similar results, though the organization could not persuade any official channels to investigate further.

DEP had done a visual inspection of the Kidder Point site in October 2013 at the request of the activist group and determined that no investigation, erosion control or remediation was necessary. Environmental Specialist Karen Knuuti, who wrote the memo on the inspection, said in a Dec. 10 interview at the Bangor DEP office that, although she had noted water flowing over an area with sulfur visible on the ground would run off toward an area of discoloration on the shore, it was not clear if the discoloration was caused by the runoff. She said her supervisors determined that further investigation was not necessary.

However, GAC opted to initiate its own investigation and entered into an agreement with DEP through its Voluntary Response Action Program to investigate and clean up any contamination found in exchange for liability protection. The company has recently submitted to DEP an investigation summary, public involvement plan, and remediation and shoreline stabilization plan.

The environmental services company CES Inc., based in Brewer, conducted the comprehensive investigation. According to the investigation summary report, CES reviewed reports of 24 sulfuric acid spills that occurred between 1981 and 1997 and found spills that "occurred prior to GAC acquiring the site [in 1994] [have] the potential to impact the tidal zone.”

CES measured pH of the sediment at 45 locations along the entire shoreline of GAC's property in August. Six locations measured between pH of 2.2 and 3.0. CES identified that area as well as the vicinity of the historic sulfur acid plant as an area of interest for further study.

The low numbers indicate high acidity. A pH of 7 is neutral, and the average pH of seawater is slightly basic at 8.1. Green said in his April 9 report on his study of samples collected by FOPB that sediments with pH measurements in the 6's and below should be considered incapable of supporting any marine life.

CES also sampled soil and groundwater in the area of the historic sulfuric acid plant and found them to be acidic as well. Boring samples were taken to determine soil types and groundwater depths. Sulfur was found in five borings, and groundwater pH was measured as low as 1.73 in one boring.

In October, test pits were excavated up to seven feet deep to determine the extent of the buried sulfur. Sulfur was found under a layer of clean fill at varying depths in the 12 pits on GAC property from 2 to 54 inches, in a layer measuring between 2 and 16 inches thick. CES indicated the presence of this subsurface sulfur layer was previously unknown to GAC.

When asked if he thought previous owners had buried the sulfur prior to selling the property, GAC President President David Colter said in a phone call Dec. 16, "Delta Chemical ran a sulfuric acid plant and had a pile of sulfur behind it. It would appear they brought in fill to cover it, but that would be speculation."

The investigation summary concluded that the sulfur is the source of the low pH measured and that no other possible acid sources were encountered. It stated the long-term storage of sulfur at the site and its presence in the soil creates conditions for soil bacteria to produce sulfuric acid. The sulfuric acid infiltrates into the soil and groundwater, which flows from northeast to southwest in that area.

The study also concluded that low pH conditions are limited to where sulfur is present or to areas immediately downhill of the sulfur because an underlying impermeable clay layer is blocking groundwater from spreading to other areas.

CES recommended "removal of visible sulfur to the extent practical … and in-situ treatment (i.e., lime application or other soil amendment to increase pH)."

According to the remediation plan, sulfur on GAC property will be excavated and stored in a covered, leak-proof container. The proposed clean-up goal is to leave no more than 4-percent sulfur in the soil and to neutralize the remainder with alkaline product and limestone applied to the soil surface, in accordance with the 2011 “Guidelines for Landfill Disposal of Sulfur Waste and Remediation of Sulfur Containing Soils” publication by the government of Alberta, Canada. Erosion and sediment control will be done before the excavation work begins.

GAC has also proposed shoreline stabilization at an eroding bank near the former sulfur plant and treatment of the low pH groundwater flowing into the intertidal area. The plan outlines excavating from the high-water line to the elevated area, adding limestone-based rip-rap and alkaline material, leveling slopes, adding geotextile and planting vegetation.

Because the plan is still under review by DEP, Colter said they have not yet developed cost estimates for the remediation plan.

"We're pleased with the progress we have made to date working with CES and DEP," said Colter.

Friends of Penobscot Bay President Ron Huber is calling for greater public involvement in the GAC's VRAP proceedings, and for the removal of the acidic mud in the intertidal area.

"The idea that the company and its consultants are sufficient stakeholders to arrive at the level of cleanup of a public resource in this harbor is outlandish and a slap in the face to those stakeholders, Friends of Penobscot Bay, to the Town of Searsport Shellfish Committee, and all who care about bay fish and wildlife that will benefit by a reduced acid burden," Huber said in a press release.

GAC did seek input on the remediation plan from environmental science professor Green, who also serves on the state Ocean Acidification Commission. Green did not recommend dredging in the intertidal area. In a Nov. 13 email to GAC, which CES included in the public communication plan, he wrote:

“I think removing the source material, applying the alkalinity buffer to treat the groundwater, and stabilizing the slope of the problem area represents the perfect remediation approach. I don't think dredging the intertidal area where low pH pore waters were originally found is appropriate and, at least in my opinion, would add nothing to the remediation plan. In fact, dredging this region would be detrimental, could easily create a whole range of other issues, and will not do anything to rectify the problem…. In my opinion, once [the sulfur is] gone, the acidity problems of the intertidal will quickly correct themselves.”

The public communication plan states that GAC will provide VRAP documents to the Augusta and Bangor DEP offices and to the town of Searsport, where they are available for public viewing, and that the company will notify the town manager when remediation activities are to begin and when they are complete.

The Searsport Selectmen will discuss the plans at their Dec. 16 meeting.

The story has been updated to include comments by GAC President David Colter.

Related articles:

Study finds acidic mud at Kidder Point

Activists continue to push for official investigation of Kidder Point erosion

GAC to voluntarily test samples of shoreline sediment