MARINETTE — Some 94% of the drinking water wells on fields where biosolids from the Marinette and Peshtigo Wastewater Treatment facilities have been spread recorded PFAS levels below the federal health advisory limit of 70 parts per trillion (ppt) for PFAS, and 87% had detections below Wisconsin’s proposed 20 ppt groundwater standard. Moreover, 77% of the wells were non-detect or below the reporting limit, according to a report Tyco submitted to the Wisconsin Department of Natural Resources this week.

In coordination with the WDNR, Tyco voluntarily performed the testing on 61 fields covering 30 square miles of ground where biosolids were deposited. Biosolids application on farm fields is a common technique used to fertilize fields, is practiced across the country, and is an activity permitted by the WDNR in Wisconsin. The biosolids in question were spread between 1996 and 2018.

According to the report, these results add to the data that Tyco has collected and submitted to the WDNR that is providing the community with a clearer indication of where PFAS is and isn’t in the area. The Marinette and Peshtigo communities contain numerous industrial facilities that are likely contributing sources of PFAS to the wastewater treatment plants in the City of Marinette and the City of Peshtigo.

As the test results came in, Tyco reported the findings to the WDNR and the company voluntarily offered bottled water to residents whose wells tested above 20 ppt.

The testing was conducted by Arcadis, Inc., Tyco’s environmental consultant, with the assistance of the WDNR. The test “has not identified a consistent PFOA or PFOS distribution across the study area in drinking water” above Wisconsin’s proposed groundwater standard of 20 ppt.

Here are the key findings from the study:

■ The reporting limit, approximately 1.8 parts per trillion (ppt), refers to limitation inherent in the tests. A finding below the reporting limit means the actual result is somewhere between 0 and 1.8 ppt.

■ 20ppt is not a drinking water standard but the groundwater quality enforcement standards proposed by the Wisconsin Department of (Natural Resources/Health Services).

In the report, Arcadis cited a variety of factors that make it likely there are multiple sources of PFAS beyond Tyco’s Fire Technology Center.

For example, the City of Marinette tested lines from the five wastewater zones that send water into the treatment facility and identified levels of PFAS in all five lines. But since Tyco only sent wastewater into three of the lines — a practice that was stopped in March 2019 — other sources almost certainly contributed to the presence of PFAS in the biosolids.

In addition, the report noted, because the biosolids also came from the Peshtigo wastewater facility, and Tyco historically contributed very little wastewater to that plant, other industries must be responsible for PFAS in the Peshtigo-derived biosolids.

The study identified only “isolated areas” where several drinking water wells exceeded the groundwater standard. “Based on infrequent detections of PFAS results above the proposed (groundwater standard), the land applied biosolids do not appear to be causing widespread contamination of drinking water,” the report concluded.

The combination of these factors point to some localized and other sources of PFAS unrelated to Tyco that have not been identified as part of this program.