Update on Darby S&W Sawmill Superfund site

by Michael Howell

The Montana Department of Environmental Quality (DEQ) released an update on December 11 concerning the ongoing sampling activities at the site of the former S&W Sawmill Facility in Darby. The agency is requiring the International Paper Company (IPC) to perform annual groundwater sampling activities to monitor concentrations of contaminants of concern in groundwater underlying and surrounding the S&W Facility, the primary contaminants being pentachlorophenol (PCP) and dioxins/furans.

Groundwater monitoring and sampling activities occurred in July 2025, coinciding with the high groundwater period during the year. A total of 35 monitoring wells were gauged and sampled. Of these monitoring wells, 30 monitor the shallow groundwater at the facility and five monitor deeper groundwater concentrations. Additionally, six domestic water wells for nearby residences or businesses were sampled.

Concurrent with the groundwater sampling, DEQ required IPC to collect surface water and sediment samples as part of investigating groundwater and surface water interactions around the facility. This additional sampling was primarily focused on the Hatch Waste Ditch and ponds associated with or adjacent to the ditch. Samples were also collected from the Tiedt-Nicholson Ditch in a stretch adjacent to the Hatch Waste Ditch. The results are still preliminary.

Initially, the purpose of additional monitoring wells was to collect information regarding the relationships between groundwater and surface water, which included the pond that collected runoff from the Overturf Seep area. Additional groundwater wells have since been installed to delineate dioxins/furans concentrations north of that pond and Overturf Seep areas driven by the identified groundwater and surface water interaction in this area. These additional wells have demonstrated that as the dioxins/furans plume travels away from the former facility properties toward the east, the plume turns north toward the first pond location and appears to follow US Highway 93 toward a second pond located on the southern edge of the 3169 U.S. Highway 93 property.

According to the summary report, concentrations of PCP in ditch/pond sediment samples did not exceed any ecological or human health direct contact generic screening levels but did exceed the generic leaching to groundwater screening levels at some locations. Results did, however, indicate that dioxins/furans levels exceeded ecological screening levels. 

All but one sample exceeded the residential direct contact screening level, and three samples exceeded the commercial/industrial direct contact screening level.

The preliminary results from the 2025 monitoring activities in July in the Hatch Waste Ditch showed sediment levels below the leaching to groundwater levels for PCP and below the dioxins/furans residential cleanup level for properties. Although the surface water results for waters in the ditch and two connected ponds was below levels for PCP contamination, all the samples exceeded the Montana DEQ-7 Surface Water Standard for dioxins/furans.

The sediment sample from the Tiedt-Nichalson Ditch did not exceed levels for PCP. Nor did it exceed the ecological screening level for dioxins/furans or the direct contact residential screening level. But surface water at this location did exceed the DEQ-7 surface water standard for dioxins/furans. 

Further testing at all these sites was done in November, but those results may not be available until March 2026. 

According to State Superfund Project Officer Robert Roll, DEQ does not currently intend to require IPC to perform additional ditch sampling activities.

“The data collected appears to be adequate to characterize the Hatch Waste Ditch and allow IPC to move forward with evaluating cleanup options in the Feasibility Study,” said Roll. “While sediment in the ditch does not presently appear to exceed direct contact exposure-based cleanup levels, exceedances of surface water standards will likely necessitate steps to be taken to address the groundwater/surface water interaction that is seen in surface water in the ditch.”

Roll said the company’s Feasibility Study will likely contain options for clean-up that may include such activities as soil removal, or capping the contaminated soils at the facility site to prevent or reduce further leaching into the groundwater, or other options. DEQ will then review the options presented by the company and make its own determination of how to proceed with the clean-up. This will be a public process.

Roll said in terms of the cost, the taxpayers will eventually be picking up a portion of the costs under the Controlled Allocation Liability Act. When they apportion liability among present and past responsible parties, the “orphan share” is the part belonging to liable parties that don’t exist anymore, he said. In this case, according to Roll the orphan share is up around 58%. The current property owner IPC was allocated about 39% of the costs. The remaining 19% was allocated to other still existing parties. He said the costs of clean-up work is initially paid for by the liable parties and is then submitted to DEQ for review and determination if it is all justifiable. The parties can then request reimbursement for 58% of those costs.

Randy Maxwell, who has an interest in the ditches involved and was instrumental in getting DEQ to expand the testing in that direction, said,  “I’m not surprised by these results. I pushed them to examine the Ellis property and they finally looked at that. When they did, IPC ended up buying the property. They have been buying up property all along the way as the testing has proceeded. Now we are finally at the river on Mr. Sass’s property, so maybe we can move forward with a plan for clean-up. I may not see the results in my lifetime, but at least we are moving in the right direction. But I feel sorry for all the people being affected by this.”

Mike Sass, who owns the property at the end of the Hatch Ditch, said that he had received the letter from DEQ but hasn’t talked with DEQ yet about the results.

“It’s not good,” said Sass. “I have a home site on that property with an approved septic permit. I’m not sure now how to proceed.” He said he was talking to an attorney about it.