KELLOGG — Silver Valley residents may have noticed heavy equipment operating recently between Kellogg and Smelterville. The work is part of ongoing maintenance and remediation at the A-4 property, a 13.5-acre former gypsum repository within the Bunker Hill Superfund site. 

The property, located along Silver Valley Road near the entrance to the Galena Ridge subdivision, is owned by Stauffer Chemical. According to the Idaho Department of Environmental Quality, Stauffer is responsible for maintaining the repository's protective cover system under an approved operations and maintenance plan. 

Historical records indicate the repository contains gypsum waste generated by the former phosphoric acid and fertilizer plant that operated as part of the larger Bunker Hill industrial complex. The site was capped with mine waste rock in the mid-1990s. A few years later, an additional 6 inches of clean soil was placed over the impoundment. 

The current work follows observations made during routine inspections that identified deficiencies in the site's cover system. Portions of the cap had settled in recent years, allowing water to collect in low-lying areas rather than drain away from the repository. 

"The A-4 property between Smelterville and Kellogg is a pre-existing gypsum repository owned by Stauffer Chemical," said Andy Helkey, Kellogg remediation program director for DEQ. "Stauffer is responsible for maintaining the property under the conditions of their approved operations and maintenance manual." 

Helkey said one requirement of the maintenance plan is maintaining positive drainage across the capped repository. 

"Over the past few years, it had been documented that portions of the cap had settled, allowing water to pond in areas over the repository surface," he said. "Stauffer Chemical is funding the necessary repairs as the responsible property owner to bring the cap into required specifications set forth in the operations and maintenance manual to allow for stormwater to drain off the surface." 

According to DEQ, crews are regrading the site to restore positive drainage and reconnect existing drainage channels, helping prevent surface water from pooling over the capped impoundment area. Settlement monuments are also being installed to monitor future changes in site grading. 

Jason Guardipee, a remediation analyst with DEQ, said the visible construction activity does not involve removing contaminated materials from the property. 

"Currently they are stripping the top 6 inches of clean topsoil to reuse for growth media," Guardipee said. "Additional gravel is being imported to establish the subgrade. The area will be hydro-seeded at the end. No material will leave the site." 

Once grading is complete, crews will place a new 12-inch clean soil cap across the repaired areas and establish a vegetated cover designed to protect the repository and promote long-term stability. 

"Visually it looks like a lot of work being done, but it's basically just a regrade/recap to establish positive drainage," Guardipee said. 

While the project is considered routine maintenance rather than a new cleanup effort, it is part of the long-term management strategy for containment areas established during remediation of the Bunker Hill Superfund site. Maintaining the integrity of caps and drainage systems helps prevent erosion, limit water infiltration and ensure contaminated materials remain safely contained.