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TO: Tina Ndoh, U.S. EPA/OAQPS/SPPD - Minerals and Manufacturing Group

FROM: Eastern Research Group, Inc.

DATE: March 24, 2015

SUBJECT: Site Visits to Mosaic Plant City and Mosaic New Wales

SUMMARY

The EPA and ERG visited two Mosaic facilities located in Florida (i.e., Plant City, FL

and New Wales, FL) on March 4, 2015. These site visits primarily focused on gypsum 

dewatering stack and cooling pond operations, and control technique options that were (or could 

be) included in the management plan proposed in subpart AA. This memorandum documents the 

topics that were discussed at these site visits.

PARTICIPANTS

Mosaic Plant City

Tina Ndoh – EPA

Brandon Long – ERG

David Jellerson – Mosaic

Phong Vo – Mosaic

Jeff Stewart – Mosaic

Ron Brunk – Mosaic

Richard Karppe – Mosaic

Bob Gray – Mosaic

George Sharrock – FDEP

Syed Arif – FDEP

Jeff Koerner – FDEP

Jason Waters – EPC HC

Quaid Noor – FDEP

Mosaic New Wales

Tina Ndoh – EPA

Brandon Long – ERG

David Jellerson – Mosaic

Phong Vo – Mosaic

Jeff Stewart – Mosaic

Ghani Baig – Mosaic

Michael Haldavnekar – Mosaic

George Sharrock – FDEP

Syed Arif – FDEP

Jeff Koerner – FDEP

Jason Waters – EPC HC

Quaid Noor - FDEP

TOPICS OF DISCUSSION

The EPA and Mosaic discussed Mosaic’s current operating practices and described how the 

proposed work practices in subpart AA related to their facilities. Specifically, the following 

items applicable to subpart AA were examined:
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 Rim ditch building: Mosaic uses a rim ditch on all of the gypsum dewatering stacks. They 

explained this involves an inner and outer dike, and rim ditches are mainly used due to 

stability and safety concerns. They did observe the rim ditch does minimize surface area 

of the gypsum dewatering stack pond, to the extent the slurry is deposited in the width of 

the rim ditch which allows for a more controlled gypsum slurry buildup. The gypsum 

dewatering stack top is segregated into cells via the rim ditch, and each cell’s surface area 

decreases as the gypsum slurry fills it in. The alternative to the rim ditch technique is 

where no inner dike is used. Mosaic also stated that when new gypsum dewatering stacks 

are built, there is about a two year period where the rim ditch technique is not possible. A 

base layer of gypsum needs to be developed first, and the rim ditch technique can be 

employed after this.

 Discharge pipes: Mosaic does not submerge discharge pipes at any of their plants. Solids 

buildup, potentially resulting in blockage of the pipe, and back pressure were concerns 

with submerging discharge pipes. They stated there is a high solids content in the process 

water and gypsum slurry. Certain ponds were also above grade, which adds issues for 

submerging discharge pipes. Mosaic commented that submerging gypsum slurry 

discharge pipes was particular problematic; these pipes are moved around the gypsum 

dewatering stack and purposely elevated. The largest source of emissions from discharge 

pipes is where hot process water is discharged into the cooling ponds; we observed a 

strong odor at this location resulting from the fluorides.

 Side slope closure: Mosaic stated that when they close side slopes of gypsum dewatering 

stacks a soil cover is not necessarily added. They typically “grass” their side slopes for 

closure. Mosaic implements side slope grassing to help with gypsum dewatering stack 

stability, and it is an engineering decision on when and where to grass. Mosaic typically 

steps-in at 75-120 feet increments. The reference to ‘50 feet from the top’ in the work 

practice language was concerning; they did not understand how it would practically be 

implemented nor why it was necessary to include this restriction. Mosaic also explained 

that the side slope closure process include drain installation and grading and can take up 

to two years to complete each step-in.

 Mosaic noted that cooling ponds must have a certain volume and surface area of water to 

support rainfall and plant process water needs. Mosaic also stated they do evaluate 

cooling pond surface area at facilities and recently conducted an analysis of their Bartow 

plant. They also evaluated their Plant City cooling ponds and did not change their cooling 

pond area as a result, the area was appropriate for the plant. 

 Mosaic’s primary focuses when managing their gypsum dewatering stacks and cooling 

ponds are stability and water management.
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 Mosaic did not offer any additional control technique options that could be included in 

the proposed management plan.

 Mosaic explained concerns with adding clarifiers to the rule, which would cost them 

millions of dollars to add control devices. They remarked that not all clarifiers at the New 

Wales plant are controlled. Certain wet scrubbers for their clarifiers may only be installed 

to improve odor control and worker safety and may not necessarily have the level of 

control efficiency typically observed on wet scrubbers.

 Mosaic remarked that for most, if not all, of their wet scrubbers, pressure drop is 

monitored. Adding the 5 inch pressure drop requirement would affect their monitoring 

procedures. Mosaic also noted that it is common for fluoride control scrubbing systems to 

have pressure drops less than 5 inches.