1

TO: Tina Ndoh , U

. S

. EPA/OAQPS/SPPD

- Minerals and Manufacturing Group

FROM: Eastern Research Group, Inc.

DATE: March 24 , 2015

SUBJECT: Site Visit s 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. Th ese site visit s primarily focused on gypsum dewatering stack and cooling pond operations

, and control technique option s 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

– EP C HC Quaid Noor

– FDEP Mosaic New Wale s

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, t he following
items applicable to subpart AA were examined :2

 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 st ack 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 stack s 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 pip es at any of their plants . Solids buildup

, potentially resulting in blockage of the pipe, and back pressure were concerns with submerging discharge pipe s

. 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, an d 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 imple mented 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 Pla nt 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.3

 Mosaic did no t 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 scrubber s.

 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 system s to have pressure drops less than 5 inches.