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Wixom WWTP Biosolids Fields Area of Interest (Wixom, Livingston County)

EGLE Site Lead: Sydney Ruhala, RuhalaS@Michigan.gov or 517-599-5356. Content last updated August 24, 2022.

Background

As part of the Industrial Pretreatment Program (IPP) PFAS Initiative, the Michigan Department of Environment, Great Lakes, and Energy (EGLE), sampled the effluent (i.e. the treated wastewater discharged from the treatment plant) and biosolids for PFAS at the city of Wixom Wastewater Treatment Plant (WWTP). Results indicated that high levels of PFAS, specifically PFOS, were being passed through the treatment process at the plant. PFOS levels were 269 parts per trillion (ppt) in the effluent and 2,150 parts per billion (ppb) in the biosolids.

Biosolids are the nutrient-rich organic materials resulting from the treatment of domestic sewage in a WWTP. Biosolids can be a beneficial resource, contain essential plant nutrient and organic matter, and are recycled as a fertilizer and soil amendment.

The city of Wixom has an EGLE approved Residuals Management Plan, which has allowed the WWTP to land apply biosolids produced at the plant since 2000. The city of Wixom WWTP stopped land application of biosolids in the Spring of 2018 and has since sent accumulated sludge to a landfill. The city has worked with the sources of the PFOS--two industrial facilities that discharge wastewater to the WWTP--to install treatment to remove PFAS at the source and have since seen significant reductions in PFOS concentrations in both the effluent and biosolids generated at the WWTP.

Due to the high levels of PFOS found in the biosolids, EGLE evaluated land application sites that historically received biosolids from the city of Wixom WWTP. Following a field selection process which considered  PFAS levels in biosolids, application amounts and rates, acreage used, soil types and other factors, five fields located in Livingston County were selected for sampling. The objective was to determine if there was any impact from the land application of PFAS contaminated biosolids to the soil, groundwater, or adjacent surface water bodies.  Crop and eventual beef sampling was also conducted.

Estimated groundwater flow direction varies across the site, including southwest, northwest, and northeast across the biosolids fields, depending on location.

Four residential wells and one livestock well adjacent to the biosolids fields were tested for PFAS in November 2019 as part of the investigation. All five wells were non-detect for PFAS. Out of abundance of caution, EGLE tested an additional 20 residential wells near the biosolids fields for PFAS in October 2021. PFAS was not detected in 18 of the 20 wells. Two wells had PFAS detections below the drinking water criteria.  One of the two wells where PFAS was detected was also resampled in December 2021 and PFAS detections were below the drinking water criteria.

Wixom WWTP Biosolids Fields Area of Interest Residential Well Sampling Results

Recent Accomplishments

  • On April 7 and 8, 2022, EGLE contractors collected samples of water from an additional 30 residential drinking water wells out of an abundance of caution. PFAS was non-detect in all 30 wells.
  • On April 27, 2022, EGLE collected samples of water from an additional two residential drinking water wells out of an abundance of caution. One well was non-detect for PFAS, while PFAS was detected in the second well below criteria. EGLE also collected a surface water sample along one of the biosolids fields where a spring was present. PFOS was detected in the surface water sample above criteria at 22.7 ppt.
  • On May 11, 2022, EGLE collected a sample of water from one additional residential drinking water well out of an abundance of caution. The well was non-detect for PFAS.
  • On June 6, 2022, EGLE held a virtual meeting for local residents who had their drinking water wells tested for PFAS to share the results and answer questions.

Next Steps

  • EGLE will continue to work to determine the extent of PFAS contamination in the area of the biosolids fields.

Residential Well/Alternate Water

  • 57 residential wells have been sampled.  EGLE will expand residential drinking water well testing in the area if determined to be necessary.
 

Sampling Results Summary

Type of Sample

Date Sampled (or Range)

Number of Sample Results Received

Number of Samples above Criteria*

Groundwater Monitoring Wells

September 2019 - March 2021 6 1
Residential Wells November 2019 -May 2022 57 0
Surface Water April - May 2022 13 12
* Residential well and groundwater monitoring well results are compared to EGLE Part 201 criteria for 7 PFAS compounds effective 12/21/2020:  PFOS (16 ppt), PFOA (8 ppt), PFNA (6 ppt), PFHxS (51 ppt), PFHxA (400,000 ppt), PFBS (420 ppt), and HFPO-DA (370 ppt).
* Surface water samples are compared to Rule 57 non-drinking water values of 12 ppt for PFOS, 170 ppt for PFOA, and 670,000 ppt for PFBS.

Sampling Notes

  • The 2019 surface water samples were collected from four surface water ponds located adjacent to the biosolids fields as well as 8 locations with standing water on the fields.

Historical Timeline

    • In April 2019, EGLE contractors sampled soil, surface water, perched (i.e., standing) water and a tile drain for PFAS at two biosolids fields. Locations of soil samples were selected based on previous studies, soil types, surface water flow and were generally biased towards areas with the highest potential to be impacted.
    • In August 2019, EGLE contractors installed three pairs of nested groundwater monitoring wells (one deep and one shallow at each location) at two biosolids fields.
    • In September 2019, EGLE contractors sampled the groundwater monitoring wells installed in August 2019 for PFAS. PFAS was not detected in the three deep wells. PFAS was detected in two of the shallow wells, at concentrations below criteria.
    • In November 2019, EGLE contractors sampled soil, surface water, and perched water on an additional two biosolids fields. EGLE contractors also tested water from four residential drinking water wells and one livestock well adjacent to the biosolids fields. All five wells were non-detect for PFAS.
    • In November 2019 - 2021, EGLE collected grasses (sorghum), corn silage, and haulage to determine if the crops were uptaking PFAS from the biosolids fields. Samples were processed by Eurofins for Michigan Department of Health and Human Services (MDHHS) lab analysis.  There are no standards for sampling, processing, or analysis of crops.  In the spring of 2021, the analytical results were received.