Marion County approves $32.96 million ARPA-funded guaranteed maximum price for North Santiam sewer plant

Marion County commissioners on May 14 approved a guaranteed maximum price amendment to the county's construction manager/general contractor contract for the North Santiam Canyon Sewer Project, adding $32,958,791 in American Rescue Plan Act funding. The board voted in favor of the amendment; the motion passed unanimously.

The amendment covers construction of a new treatment plant in Mill City to replace an aging temporary facility and to enable future collection system work that will allow rebuilding in fire-affected areas. Chris Einmo, senior project manager with Marion County Public Works, told commissioners the project is at an aggressive schedule to meet ARPA spending deadlines and to begin construction in June.

The project team described the plant as a full modern treatment facility with primary, secondary and tertiary treatment, including ultraviolet disinfection and biosand filters. "These wastewater treatment plants are the first line of defense for all rivers throughout the United States," Einmo said, noting the plant will protect river water quality and downstream water supplies.

County staff said the GMP package was negotiated using a CMGC (construction manager/general contractor) delivery method that divided work into about 50 bid packages and included both subcontracted work and self-performance by the contractor. An independent cost estimator reviewed labor, equipment and bid packages during negotiations. The GMP package lists $26 million as the construction cost for the new treatment plant line item, plus allowances for design evolution, potential material escalation and a $500,000 scope addition for infiltration and inflow repairs in Mill City sewer mains.

Einmo said contingency for the amendment was set at 4.5 percent given the project's phase and involvement of the CMGC, and that the GMP is a guaranteed maximum price: "That means that since it's a guaranteed maximum price proposal, the cost to build will go no higher. It may be lower as certain allowances are not fully utilized." He also said the county received a 1200-C stormwater permit the morning of the meeting, clearing a key regulatory step to begin construction.

Board members and staff emphasized the project's long timeline and regional importance. Commissioners noted the work supports housing recovery in Mill City and Gates and that the county is acting as contracting and pass-through agency for ARPA funds; county staff said no county general funds are being used for the construction contract. The county expects to reach substantial construction completion late in 2025 and to commission plant systems and perform clean-water testing into 2026; bringing the biological reactor online and full operations would require the final discharge permit, which remains a permitting step to complete.

The motion approved during the meeting authorized the board to amend the CM/GC contract with the contractor to add ARPA funding in a not-to-exceed amount of $32,958,791 for a new contract total of $37,538,603 through Dec. 31, 2026. The board approved the amendment by voice vote.