NCS000202_USG Letter to DENR_20130411

April 11, 2013
Mr. Ken Pickle, Stormwater Staff Engineer
North Carolina Department of Environment and Natural Resources
Division of Water Quality
1617 Mail Service Center
Raleigh, NC 27699-1.617
Re: USG Stormwater Permit No. NCS000202 — TSS and Aluminum Benchmarks
Dear Mr. Pickle:
Please accept this letter as a recap of our discussion via teleconference on Thursday, April 4th
United States Gypsum Company (USG) operates a mica processing facility in Spruce Pine, NC
under individual stormwater permit NCS000202. The Plant has four stormwater outfalls which
discharge to property owned by the Feldspar Corporation before eventually discharging to the
North Toe River. Semiannual analytical sampling has been completed for TSS, Aluminum,
Magnesium, Lead and pH. Results are regularly submitted on Discharge Monitoring Reports to
the North Carolina Department of Environment and Natural Resources (NCDENR). Over the
permit term, the benchmarks for TSS and Aluminum have been exceeded more than four times at
multiple outfalls. Concrete sumps were installed in 1999 to trap suspended solids before reaching
the Plant's stormwater outfalls. The project has reduced solids in stormwater effluent
considerably since initial installation. Per the Tiered Program in the stormwater permit, monthly
analytical sampling was implemented starting in 2010.
The initial 2013 storm water sample was below the 100 mg/L TSS benchmark at all outfalls. The
USG Spruce Pine Plant believes that this positive result is due to the elimination of a satellite
mica storage pile towards the end of 2012. The Plant's Stormwater Pollution Prevention Plan
will be updated to reflect this new BMP and mica will not be stored in this location going
forward. We will continue to collect monthly samples to ensure that TSS stays below the permit
benchmark. If additional benchmark excursions are noted, USG will investigate additional
engineering controls or increased housekeeping.
The Spruce Pine Plant cannot meet the 0.75 mg/L aluminum benchmark. EPA Method 200.7
performed by Pace Analytical Services, hie., digests the entire sample in a mixture of
hydrochloric and nitric acids and then determines the amount of aluminum present. However,
this method does not relate the actual contribution of mica present in storm water to the dissolved
aluminum content of the North Toe River. Mechanical and/or chemical weathering processes do
not easily liberate aluminum from muscovite mica, the Plant's main raw material. When

Mr. Ken Pickle
NCDENR, Division of Water Quality
Pae 12
aluminum is liberated it forms either aluminum oxide or aluminum hydroxide, which are both
insoluble in water. USG is unaware of any other onsite sources of aluminum that may contribute
to the stormwater results.
Please see the attached technical memo written by Mr. Roger Sharpe, Director of Geotechnical
and Mining Services at USG, for more details on aluminum in mica. USG is unaware of a
different sample method which does not dissolve mica that may be present in trace amounts.
Filtering the sample will not remove all of the mica, even if the TSS benchmark- is maintained.
For the reasons presented within, USG requests that the aluminum benchmark be removed so
that future sample results are not counted as permit excursions. We are willing to work with
NCDENR to reach practical administrative solution to this issue.
Should you have any questions regarding this letter or the attached technical memo, please
contact me at 770-454.1533.
Sincerely,
Randy Ruddell
Plant Manager
United States Gypsum Company
722 Altapass Highway
Spruce Pine, NC 28777
Enclosure
Cc: Chuck Cranford, NCDENR - Asheville Regional Office
Tim Fox, NCDENR — Asheville Regional Office
Randy Kenyon, USG
Roger Sharpe, USG
John Bolden, USG

TO: Randy Kenyon — Spruce Pine April 1, 2013
Randy Ruddle — Chamblee
John Bolden — Chicago
CC: Greg Kinser — Chicago
Tony Suveg - Chicago
FROM: Roger D. Sharpe — Director, Geotechnical and Mining Services
SUBJECT: Spruce Pine — Aluminum Content of Stormwater Runoff Samples
Samples of surface water runoff from the Spruce Pine Plant often have a dissolved
aluminum content exceeding the limit of 750,ug/L set by the Division of Water Quality
of the North Carolina Department of Environment and Natural Resources. During the
period August 2009 through January 2013 composite samples of the four permitted
outfalls varied from 917µg/L to 38,600 �tg/L. The analyses represent the total aluminum
content after the samples are digested in a mixture of nitric and hydrochloric acid. This
data does not accurately represent the actual dissolver) aluminum content of the runoff
into the North Toe River. The predominant mineral in the runoff is muscovite, which is
very resistant to mechanical and chemical breakdown by natural processes. Muscovite
discharged as runoff does not significantly contribute to the total dissolver) aluminum
content of the Nortli Toe River. Background levels of dissolved aluminum in the North
Toe River Watershed (>I50 square miles of mica -bearing rocks) varied from about 100
to 1,600,ug/L.
Muscovite (K 2Al4[Si6Al2020I(0H)4) is one of the most chemically and mechanically
resistant minerals that occurs in the types of rocks underlying the North Toe River
Watershed (NTRW.) It is very robust and remains relatively unaffected during chemical
and physical weathering/erosion of the muscovite -bearing parent rocks. The general
chemical weathering processes for rocks such as granite, pegmatite and mica
schist/gneiss are shown below:
® Feldspars (orthoclase and plagioclase) undergo hydrolysis to form kaolinite clay,
releasing Na and K ions, which are removed by leaching by groundwater.
9 Biotite and/or amphibole undergo hydrolysis to form clay and/or vermiculite
and oxidation to form iron oxides.
® Quartz and muscovite are very resistant to weathering and remain as residual
minerals.
The Spruce Pine Plant is located very close to the downstream end of the drainage basin
of the NTRW, which covers more than 1.50 square miles. The drainage basin is underlain
predominantly by metamorphic rock of the Ashe Metamorphic Suite (AMS) which
includes mica schist and gneiss, quartz -feldspar gneiss, amphibolites gneiss and schist,
minor ultramafic rocks and marble. The AMS has been intruded by plutons and thick-
veins
hickveins of igneous rock including white granitic rock, known as "alaskite" and pegmatites.
Muscovite is abundant in the mica schist/gneiss, alaskite and pegmatites. A limited
number of samples taken from the Toe River taken upstream of the USG and Feldspar
Corporation plants have total dissolved aluminum values of about 100 to 1,600 µg/L.
This is significant because it represents the total amount of aluminum contributed to the
surface water from a drainage basin over 150 square miles in area.

When muscovite is removed by erosional processes the crystals abrade into smaller and
smaller particles, remaining suspended in stream and river flow and transported over
great distances. Muscovite has one perfect cleavage plane and is easily split into thinner
and thinner sheets. Muscovite derived from the erosion of the Appalachian Mountains is
found in beach deposits all along the Atlantic and Gulf Coasts. Larger muscovite particles
and/or "books" of crystals may settle into the stream/river sediments or be carried in the
bed load. The (total) aluminum content of stream sediments in the Spruce Pine area is in
the range of 32,000 to 64,000 [.g/L.
Muscovite does not naturally contribute a significant amount of aluminum into fresh
water runoff and stream flow due to its relative insolubility in the common forms,
aluminum oxide and aluminum hydroxide.
* Aluininurn mainly occurs as A13+ (aq) under acidic conditions, and as Al(OH)4- (aq)
under neutral to alkaline conditions. Other forms include AIOII2+ (aq) and AI(OH)3
(aq)
* The most abundant aluminum compounds are aluminum oxide and aluminum
hydroxide, and these are water insoluble.
0 Aluminum forms during mineral weathering of feldspars, such as and orthoclase,
plagioclase, micas and bauxite subsequently ending up in clay minerals, such as
kaolinite or halloysite.
* The information below is from a 1929 technical document of the U. S. Department of
Agriculture titled "Alteration of Museovite and Biotite in the Soil", 1929, USDA
Technical Bulletin 128:
* Muscovite, under ordinary conditions, is one of the least alterable of minerals.
* The feldspar of a granite may be completely kaolinized, while the embedded
plates of mica retain their brilliancy almost unchanged.
o One of the most frequent alterations [of muscovite] is that of hydration, a part of
the potassium being replaced by hydrogen; or at the same time it may take up
other bases and thus the mineral may pass into vermiculite, a somewhat indefinite
compound to which no formula can lie assigned.
o Muscovite as well as biotite releases potash (potassium) to plants, and both are as
will adapted for supplying potash as potash feldspar. (2) The release of potash to
plants by muscovite is in opposition to the prevailing opinion a<< to the capacity of
this mineral to weather, pointing, as it does, to an actual weathering. This appears
to consist in removal of potash but with preservation of the external physical
properties of the mineral.
• Studies on the laterites of Guinea finds that the weathering of muscovite under
lateritic. conditions results in loss of alkalies, particularly of potash, with a
corresponding gain in water, the end product of weathering having essentially the
composition of kaolinite.
Roger D. Sharpe P.G.
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Director, Geotechnical and Mining Services
United States Gypsum Company