Months after the Machado Wastewater Treatment Facility received approval for a $54 million expansion, the San Miguel Community Services District (CSD) is preparing to clean up more than 20 years of accumulated sludge to prepare for the upgrades.
For nearly two decades, two of the facility’s four treatment ponds have collected sludge without any full-scale removal.
“As the solids accumulate in the ponds, it reduces efficiency, reducing the plant’s ability to break down additional solids,” San Miguel CSD General Manager Kelly Dodds explained in an email to New Times. “If the solids levels are allowed to build too much, the solids start carrying over in the plant effluent, affecting the effluent quality.”
The Machado facility, located on Bonita Place, has been treating San Miguel’s wastewater since 1944, but has not seen major upgrades since 1999. In July, the San Luis Obispo County Planning Commission approved a long-anticipated expansion that will more than double the plant’s treatment capacity, from 200,000 gallons per day to at least 500,000, meeting state requirements for 30-year growth projections.
The facility must complete dredging before it can build new infrastructure. The district is moving forward with a request for proposals (RFP) for a contractor to dredge and press an estimated 125 dry tons of sludge from two of its ponds.
According to a Nov. 20 staff report, San Miguel has struggled to stay on top of its sludge since the district was formed nearly 25 years ago. The last contracted dredging occurred in 2007-08, but only two ponds were cleaned before budget constraints forced the district to halt the project. Since then, sludge has been removed only incrementally—about 20 percent per year—using pumps that can’t handle dense material and a drying basin with limited storage.
“With the plant creeping closer to capacity over the last 25 years, and the inadequate ability to remove sludge independently, it is recommended that the district contract for the dredging and pressing of sludge from treatment ponds 3 and 4,” staff wrote in the report.
Getting rid of the dense material will increase the facility’s efficiency and protect the ponds that receive the treated water, which percolates back into the groundwater basin.
The treatment plant is permitted through the State Water Resources Control Board, and that permit includes on-site sludge management, Dodds said.
New Times reached out to the State Water Resources Control Board but did not receive comment before publication.
“When removing sludge from the treatment plant, the district works with other regulatory agencies to ensure that the environment and public are protected during transportation and disposal,” he said. “The district generally disposes of the sludge at a landfill, which is under tight regulation. Any sludge we deliver undergoes extensive testing for regulated contaminants before it can even be loaded onto trucks.”
Cost estimates for the project have not yet been released, but funding is expected to come from wastewater revenues and, pending approval, state grant funding tied to plant construction.
Residents near the facility may notice temporary odors and increased truck traffic during the project.
“Neighboring homes may experience some odors, but they dissipate quickly once work stops each day,” Dodds said. “Trucks will be routed away from neighborhoods whenever possible.”
The RFP is scheduled for release soon, with proposals due Dec. 19, and a potential contract award in early 2026. ∆
This article appears in Dec 4-14, 2025.