Ludington Wastewater Treatment Plant (Ludington, Mason County)

Sydney Ruhala, RuhalaS@Michigan.gov.

The Ludington Wastewater Treatment Plant (WWTP) is located at 5160 West Sixth Street, was constructed in 1974 and was brought online in 1975. The city of Ludington (City) is completing construction upgrades to replace its aging wastewater infrastructure. The upgrades to the WWTP include modifying the former west treatment lagoon from an aerated lagoon to an activated sludge treatment process. Prior to the upgrades, the WWTP consisted of two clay lined treatment lagoons located on the eastern portion of the property.

A pond west of the treatment lagoons was used for storage of wastewater treatment residuals and is identified as the sludge pond. The land for the sludge pond (approximately 30 acres) was purchased by the City from Dow Chemical Company (Dow) in the 1970s. It was formerly part of the 6th Street lime pond site used by Dow to dispose of lime waste material. The WWTP has been pumping treatment residuals to the sludge pond for storage since 1975. On December 15, 2017, EGLE advised the City that this method of residuals storage was no longer allowed, and the City must properly close the sludge pond.

EGLE worked together with the City to address closing the lagoons. As part of the plan for closing the sludge pond and the other large lagoon when the new plant was operational, the City developed a hydro-geo study to look for potential contamination and determine groundwater flow direction from these areas. Of 30 monitoring wells installed, seven exceeded the Part 201 criteria of 70 ppt of PFOS+PFOA. An additional three wells will exceed the proposed drinking water MCL for PFOS and 12 will exceed proposed drinking water MCL for PFOA. The highest concentrations detected were 180 ppt PFOS+PFOA, 140 ppt PFOS, 99 ppt PFOA.

EGLE's Industrial Pretreatment Program (IPP) PFAS Initiative identified the Ludington WWTP as a site of concern due to the acceptance of landfill leachate and historic acceptance of wastewater from plating facilities. Since the initiative, the City has been working with current sources to reduce PFAS. The IPP PFAS Initiative determined that wastewater sludges may contain significant concentrations of PFAS. Because the City's sludge pond was used to store wastewater sludges since 1975, PFAS impacts to groundwater are a concern.

The groundwater contour maps from the hydrogeological investigation indicate that groundwater flow direction in the uppermost aquifer at the site is toward the south (in the vicinity of the sludge pond) and southeast. Based on information included in 2009, 2013, and 2015 Dow Groundwater Monitoring Reports, groundwater in the upper aquifer near the former Dow 6th Street lime pond (located adjacent and west of the site) flows from the north to the east, west, and south. In addition, the tributary on the south side of the site appears to flow in an easterly direction, toward Mosquito Creek, and a tributary located northwest of the site appears to flow in a westerly direction towards the Pere Marquette Lake. Additional investigation will need to be completed to determine if the groundwater flow at the site has a west/southwest flow component.

Content posted July 2020.

EGLE is aware of four residential wells nearby and is working with MDHHS and the local health department to determine if there are any other residential wells in the area for possible sampling in the future.

The city of Ludington will be submitting a Remedial Investigation/Feasibility Study to EGLE. EGLE anticipates receipt of the study in August 2020.