History of the IncidentIn 2016, a sinkhole formed beneath a cell of the active phosphogypsum stack at Mosaic’s New Wales facility. Understandably, that incident caused significant community concern. Mosaic subsequently committed to heightened transparency for notable events having the potential to affect the community and that commitment remains today. Interest in the Water Loss Incident has resurfaced during the permitting process to extend the New Wales gypstack south in a new area to accommodate continued phosphate production at the facility. Specifics on the permit and extension are available here. Below is an overview of the event, along with highlights of changes implemented and the ongoing monitoring and maintenance we conduct on the gypstack system at New Wales.
In August 2016, monitoring showed a decline in process water stored atop the west cell of the New Wales south gypstack. After validating that information, the decline was reported to the Florida Department of Environmental Protection (FDEP) and U.S. Environmental Protection Agency (EPA), as well as Polk County. The water loss resulted from a sinkhole that formed beneath the gypstacks, which damaged the stack’s base liner.
In response, Mosaic transferred water from the affected area to other storage areas and began operating or upgraded the recovery well system to recover the process water for management. Mosaic offered free, third-party testing of neighbor drinking water wells upon request and provided bottled water until results were confirmed. We provided daily updates on those results and the incident on our website.
Extensive monitoring confirmed the effectiveness of the recovery effort; there were no offsite impacts from the incident. In October 2016, we signed a consent order with the Florida Department of Environmental Protection (FDEP) relating to repairing the sink hole.
LiDAR is a remote sensing technology (shown here) that uses light in the form of a pulsed laser to provide three-dimensional mapping.
Using LiDAR (Light Detection and Ranging) technology and other assessment tools, the sinkhole was evaluated, and a remedial plan was developed, which called for stabilizing and then filling the sinkhole with grout, essentially sealing the cavity. Instrumentation like piezometers, helped measure water levels and directed the grouting work. By May 2018, the repairs were substantially completed recognizing that maintenance of those repairs likely would be required in the future.
April 2017 aerial view of repair work on top of the gypstack.
Over time, any gypstack will experience some settling and consolidation, which will require periodic maintenance. As this occurs at New Wales, the Mosaic team, paired with third-party experts, continue to monitor the gypstack, groundwater and the repaired area, and submit updates to the FDEP and Polk County.
Some examples of such maintenance include:
- Regrading stack features, including the crown on top of the former sinkhole;
- Replacing and upgrading instrumentation, including geophones, piezometers and collapse monitors; and
- Recovery well pump replacements and repairs.
May 2021 image of the New Wales gypstack, including the remediated area in the center.
Since 2016, Mosaic made significant additional investments in our gypstack management and monitoring at New Wales, including adding a network of state-of-the-art geophones installed around and then on the stack, which monitor micro-seismic energy that can alert us to potential subsurface changes.
Pictured: Geophones being installed at the New Wales gypstack .
The multi-faceted monitoring systems we have in, on, below and around the gypstack are working as intended. They provide real-time information to guide our efforts. We evaluate this data against modelling baselines to identify potential issues.
For example, we recently observed slight increases in water quality data at the recovery well, prompting us to evaluate the cause of the increased sodium and sulfate constituents. As part of that evaluation, we are conducting more frequent monitoring and enhanced geotechnical and geophysical studies. While those efforts continue, we may supplement the grout already in place with some additional binder.
It is common for repaired areas to require additional maintenance. In 1994, Mosaic legacy company, IMC-Agrico repaired an erosion sinkhole using a similar grout plug method. In 2015, grout reinforcement was added as part of its long-term management.
Similarly, as verified subsurface energy events are detected by the geophones we will work proactively to gather additional information and insight related to subsurface activity under the gypstack. This may include voluntary above-liner exploratory drilling to confirm subsurface conditions or moving water between impoundments to allow for more detailed inspections. Activities like that began in October 2021, in response to low energy seismic events.
In March 2022, some of our newer piezometers (monitoring wells) indicated unexpected water conditions in a portion of the Phase II stack, which could be indicative of a liner tear. We provided notice of our observations to our regulators and continued our investigation of the conditions with inclined borings and with the installation of more piezometers.
We also shared with stakeholders there could be an anomalous feature such as a cavity in the underlying geologic formations that is related to natural karst activity, which is common in Florida.
On April 22, 2022, with the assistance of our engineer of record, we confirmed what appears to be a cavity approximately 300 feet below the top of the stack which we suspect is associated with a liner tear. We updated our regulators and key stakeholders of the findings.
On May 11, 2022 during drilling activities from the South side of Phase II East, the casing slipped down the bore hole and led to localized ground slumping and the formation of a depression. The piezometer readings do not reflect any unexpected changes relating to these circumstances. Some social media commentary erroneously said this is a sink hole. This is incorrect. We continue to monitor the conditions closely and the cavity originally identified in late April remains stable. No employees or contractors were injured.
The cavity is below the surface of the stack, and we have taken significant and deliberate steps to mitigate potential impacts, including the following:
- We have removed the bulk of the water in Phase II and any remaining water is physically isolated from the area.
- We continue to construct a gypsum divider dike to isolate the area of interest from the operational areas of Phase II east.
- Our investigation will continue to guide us in developing a repair plan, which will include grouting.
The engineer of record has confirmed that the area of interest is within the zone of capture of the existing facility recovery well system and confirms there are no offsite impacts. We continue to operate the system as designed.
This is confirmation that the measures and instrumentation we have installed are effective in detecting these types of anomalous events and conditions.
On October 24, 2023, we provided an update about the New Wales gypstack. In recent years, we deployed a new monitoring technology which measures seismic activity. The technology is quite sensitive and the monitoring points encircle the stack at various distances and depths. It has proven effective in alerting us to the possibility of an issue which could be occurring far below the stack and liner. We also are employing other monitors to observe changes in water levels in and around the stack. That said we still are working to confirm conditions of the subsurface below this area of the stack. We stopped using this area for stacking around a year ago, and since that time, have removed the process water stored on the stack. The stack is within the zone of capture for a nearby recovery well, so in the event there is a liner tear, water released will be recovered.
We immediately notified the state of circumstances we encountered, and following that, have done outreach to the local community and other stakeholders.
On October 27, 2023, Mosaic did a 7-day follow up with the Florida Department of Environmental Protection (FDEP). Click this link to read the letter.
More South Stack Activities
Phase III New Wales Gypstack Extension
Today, there is an enhanced presence at the New Wales gypstack as we prepare the Phase III East footprint, fortifying the foundation using drilling rigs to grout the area and laying liner.
Moving forward, we will provide updates on our website to describe our ongoing stack maintenance and extension activities to give our stakeholders a better understanding of the nature of our care efforts and due diligence— demonstrating that the promise we made five years ago to act responsibly remains.