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Long-Term Monitoring

Long-term monitoring (LTM) will continue on the Lower Fox River in all operable units for decades to assess progress toward the Remedial Action Objectives (RAOs) (see Cleanup Operations). This is in accordance with Record of Decisions (RODs) and a Long-Term Monitoring Plan (LTMP) required by governing documents for the project and approved by the agencies.


Long-term monitoring (LTM) evaluates fish tissue, surface water and sediment. Surface water and fish will be monitored in all OUs. Sediment quality will be monitored only in Monitored Natural Recovery (MNR) areas (OU2 and OU5).

Engineered cap integrity will be monitored in accordance with approved plans. Refer to the Cap Monitoring and Maintenance Plan (CMMP) for OU1, and the Cap Operations, Maintenance, and Monitoring Plan (COMMP) for OUs2-5 noted below and on the Documents page.

The primary fish species sampled in LTM are walleye (human health index), carp (ecological index) and gizzard shad (young of year forage). The secondary fish species are smallmouth bass (human health index) and drum (ecological index). Fish tissue studies are important in evaluating and updating the human health fish advisories, one of the main goals of the project. Fish advisories are issued by DNR for a variety of contaminants. The PCB Cleanup Project only targeted PCBs. Please see this useful tool for site-specific fish advisory postings in Wisconsin: DNR Fish Advisory Query (

Water sampling includes turbidity, temperature, total PCBs, total organic carbon (TOC) and total suspended solids (TSS).

Chemical isolation layer sampling will be performed on selected caps in OU3 and OU4 to verify that the chemical isolation sand layer has been installed and is functioning as designed.

A schedule of events and a summary of results are discussed below. The LTMP, CMMP and COMMP are available on the Documents page for more detail.


Long-term monitoring takes place in each OU after cleanup operations are complete. Baseline data refers to samples taken in 2006 and 2007 in each OU. It is used to compare sample results in subsequent years to monitor for reductions in PCB concentrations. The cleanup of OU1 was complete in 2009 and the first LTM sampling event took place in 2010. Cleanup of OU2 and OU3 was completed, and the first LTM event took place in 2012. Cleanup of OU4 and OU5 is complete. The first LTM sampling event in OU4 and OU5 took place in 2021. Starting in 2022, all OUs will be sampled in one event and then every five years thereafter to be on the same monitoring schedule throughout the system and to coordinate with EPA's 5-Year Review cycle for this project.

Chemical isolation layer (CIL) sampling of caps takes place after construction is completed and will be performed on the same schedule as LTM.

The schedule is subject to change depending on the completion year for dredging and cap construction in OU4 and OU5. Read the full schedule.

LTM summary for fish

The 2018 LTM Summary Report for OU1-3 fish tissue average PCB concentration results are summarized below.

Fish Species: Carp OU1 OU2A OU2B OU2C OU3
% PCB Decrease Between Baseline and 2018 88% 91% 85% 72% 57%
Associated Statistical Significance Level* p<0.001 p<0.001 p<0.001 p<0.001 p<0.001
Fish Species: Gizzard Shad OU1 OU2A OU2B OU2C OU3
% PCB Decrease Between Baseline and 2018 98% 88% 70% 72% 70%
Associated Statistical Significance Level* p<0.001 p<0.04 p<0.006 p<0.16 p<0.02
Fish Species: Smallmouth Bass OU1 OU2A OU2B OU2C OU3
% PCB Decrease Between Baseline and 2018 65% 58% 59% 51% 68%
Associated Statistical Significance Level* p<0.001 p<0.001 p<0.001 p<0.001 p<0.001
Fish Species: Walleye OU1 OU2A OU2B OU2C OU3
% PCB Decrease Between Baseline and 2018 68% 79% 28% 65% 77%
Associated Statistical Significance Level* p<0.001 p<0.001 p<0.001 p<0.001 p<0.001

* The associated p-level indicates the probability of observing the given concentration decrease under the assumption that no concentration shift has occurred in the fish population between the baseline and Year 2 sampling data. Low p-levels indicate a statistically significant change in concentrations has occurred.

LTM Summary for water

Compared to baseline conditions, 2018 PCB concentration in water has decreased an average of 90% across OUs 1-3.

LTM Summary for MNR sediment

All sediment samples taken in OU2 during 2018 show surficial sediment samples collected during 2018 at the same, or proximal locations collected in 1989/1990, are lower in PCB concentrations. This suggests natural recovery of surface sediments is occurring in this stretch of the river.

LTM Summary for OU3 CIL sediment

Sampling from 2018 in OU3 cap areas shows no measurable levels of PCBs in the sand chemical isolation layer (CIL) above caps. This sampling indicates that a thick layer of clean sand remains in place above the PCB sediments in cap areas.

Cap monitoring and maintenance (CMMP and COMMP)

Engineered caps require long-term monitoring and maintenance by the responsible parties with oversight by the government. Cap monitoring and maintenance are done following approved plans, including the "Cap Monitoring and Maintenance Plan" (CMMP) for OU1 and the "Cap Operations, Maintenance and Monitoring Plan" (COMMP) for OUs2-5. Cap monitoring and maintenance events take place after the installation of caps and continue thereafter regularly in perpetuity. If cap damage is identified at any time, responsible parties must perform maintenance and repair work with approval and oversight by the agencies. The CMMP and COMMP Reports explain the results of each monitoring event. Plan documents and monitoring reports can be found on the Documents page.

Habitat replacement activity along the Fox River.
Habitat replacement activity along the Fox River.

Habitat Replacement

During the process of dredging and capping, material considered fish and wildlife habitat was removed from the river. State and federal guidelines required the responsible parties to replace the removed habitat. Habitat replacement in the river is complete.