DEVENS -- The Devens Restoration Advisory Board met June 20 to discuss a pair of projects in the pipeline: sediment remediation at Plow Shop Pond, identified in the Army's overall clean-up plan as Area of Concern 72, and site remediation at the Shepley's Hill Landfill, a former Fort Devens dumping ground.
Closed now for many years, Shepley's Hill has been identified as the source of higher than normal arsenic levels in nearby Plow Shop Pond and an "arsenic plume" proceeding from the site to the water table below the lower half of Ayer's Main Street.
The Army's Base Realignment and Closure Division (BRAC) has been working with the RAB on plans to clean it up.
State and federal agencies such as EPA and DEP raised some sticking points, however, such as whether the extent of the proposed cleanup was sufficient; that is, could the affected groundwater be restored to its original, drinkable state? EPA's Ginny Lombardo said it was doable but the Army considered it unnecessary.
According to the RAB's BRAC representative, Robert Simeone, the Army's goal was to remove contaminated soil and stop the arsenic flow, preventing further contamination.
Late last year, with the final plan still in the works, the Town of Ayer declared a moratorium on any well-digging in the targeted area of Main Street, where most if not all residences and businesses are hooked up to town water.
Property owners were notified: No new wells would be permitted, nor could existing wells be used, whether tainted with arsenic or not. To ensure public safety, town water would be the only option from now on.
Ongoing remediation includes an operating facility at the old landfill site that the Army believes has outlived its useful purpose and has said it wants to close by a certain date. But PACE, an Ayer environmental watchdog group, has strongly argued to keep it open.
At the recent meeting, RAB facilitator Robert Simeone, BRAC's civilian environmental coordinator, said that the latest version of the draft clean-up plan, with questions answered, has been sent to all parties, with a July 8 deadline date for added commentary.
But that was pretty much the only mention of Shepley's Hill. Most of the discussion centered on the Plow Shop Pond sediment remediation project, set to start in July.
Rachel Leary, of Sovereign Consulting, Inc., the firm hired to plan and execute the project, updated the board on the process, with revisions since the last RAB meeting.
Besides Simeone and Leary, the group at the table included representatives of state agencies such as Fish & Wildlife and MassDevelopment; EPA and DEP; members of PACE and the group's consultant.
A Rhode Island contractor experienced in environmental clean-up of wetlands areas has been hired to do the work at Plow Shop Pond, which will consist of lowering the water level of the pond by four feet and removing contaminated sediment from the bottom.
Leary explained the how and why of the project and itemized the work, step by step, from measures to ensure that invasive plant species don't spread while areas of the 30-acre pond are exposed to sample analyses of contaminants during the process to public safety measures such as fencing, warning signs and odor control while the work is ongoing.
Environmental concerns raised since the project was first proposed have been addressed, Leary said, and her company has been working with the Ayer Conservation Commission and Devens Enterprise Commission, the one-stop permitting authority for Devens.
From site preparation and pumping to excavation to habitat restoration, the work should take two to three months, Leary said, wrapping up in September or October.
Questions and Answers
Q: There's a plan to monitor the soil samples while work is in progress, but is there a monitoring process for later and a mitigation plan for the future, if needed?
A: Yes. Follow-up should be fairly simple, Leary said, and chances of left-over soil contamination posing a risk are slim, since the area has a "very woody pond edge and not a very large wetland."
Q: Sediment from borings contained peat four or five-feet down. Do you pull that up, too?
A: "We should be above that level in Red Cove," Leary said, which is one of two areas of Plow Shop Pond the project will tackle. The other is the Railroad Roundhouse section.
Acknowledging that it's tough to remove the contamination, the standard method is to "harvest arsenic" only from the top two inches, she said, while this operation will take away more than a foot of muck. Well within parameters but "no need to disturb the peat." She added that in the railroad roundhouse area, most contamination came from byproducts, which is "different" from Red Cove, with deposits above the peat.
Q: How do you know when you reach the four-foot drawdown mark?
A: GIS coordinates, measured via GPS.
Q: How accurate are such measurements?
A: Plus or minus two-inches on the equipment, with "local survey control" at the shoreline. "We may put in a few stakes, too," Leary said.
Q: Were any other methodologies considered?
A: Feasibility studies were done. Hydraulic dredging and capping were also explored.
Q: Why not hydraulic, then?
A: It's a very small area for that; a lot of land surface is required. With "zero shoreline" in Red Cove, it would be necessary to pump sediments up the hill, which would be "super challenging" and costly. Besides, "it's not a very green solution," Leary said, noting that hydro-dredging "uses a lot of energy."
Q: If the new idea to support the road (for workers to get into the downsized pond) doesn't work, is there an alternative besides drawing the water level down more?
A: "We think it will work," Leary said. But there's a back-up plan with amphibious vehicles."
Further explaining the clean-up process, Leary said scooped-up sediments would be deposited at the shoreline to "decant" or de-liquefy, aided by a solidification agent such as cement, kiln dust or Pearlite. Then, it will be shipped off-site.
Q: Where to?
A: Railroad Roundhouse sediment can go to landfills, since it's not hazardous by state environmental standards, maybe some of the Red Cove sediment, too.
Q: If it's not hazardous, why remove it?
A: It's not hazardous in a landfill, mixed with binding agents, but it poses "unacceptable risks" to creatures and their habitat in the pond.
RAB and PACE member Laurie Nehring asked Simeone to reach out to Ayer businessman Calvin Moore, who owns a deteriorating dam that he's been fixing and which might be affected by the project. Although he is on the RAB mailing list, he should be specifically notified that major work is about to begin, Nehring said. Simeone agreed.
Q: How expedited is this process?
A: "Our goal is to get in and out," Leary said, the biggest concerns being safety and weather.
Q: How did this solution come about when "we were so far apart" not long ago? Nehring asked.
A: Two conference calls resolved the differences, Leary said. DEP and EPA concerns, for example. "When we expressed all of those to the Army, they felt it was all manageable," EPA's Ginny Lombardo said. "We went for a compromise."