Memorandum

TO: Portland Cement NESHAP Docket

From Keith Barnett, US EPA

Subject: Intra

- quarry Variability Estimate for Mercury

DATE: July 21, 2010

A kiln is tied to it s quarry. In assessing kilns’ performance for mercury, w e have 30 days of limestone data

- that means data from the parts of the quarry which were mined and utilized during this 30 day period. Variability of inputs beyond this 30

- day period can be and

was estimated by EPA using statistical extrapolations. EPA also received inf ormation from commenters concerning intra

- quarry mercury variability, and EPA has studied other means (beyond statistical extrapolations), of assessing intra

- quarry mercury variability based on the data presented by the commenters. Specifically, EPA evalua ted whether mercury variability in the limestone quarries of two of the best performing kilns could be further informed by the mercury variability of nearby limestone quarries which are part of the same geologic limestone

formation.

Kilns # s 1248 and 1259 are among the best performing kilns for mercury. They share a common quarry. Kilns #123 9 , 1376, 1688 and 1690 also quarry limestone from the same limestone geologic formation as kilns #s 1248 and 1259

. All six of these kilns are located i n or near Midlothian, Texas. M idlothian sits atop the Austin Escarpment, a thick limestone (calcium carbonate, CaCO 3 ) formation inclined to form a ridge that runs N ortheast to

S outhwest across Northern Texas. T he Austin Escarpment was formed during the Cretaceous

Period d uring which the ocean rose and fell in multiple episodes

. This resulted in the deposit of multiple layers of limestone deposits interspersed with sand and clay la y ers having compositions following the environment in which they formed: sh allow marine, deltaic, and

coastal . The limestone layers of the Austin escarpment is thought to have formed in clear, warm, shallow marine waters, from the accumulation of shell and coral debris

. The Austin

escarpment , also called the Austin chalk formatio n, is an unaltered and unmetamorphosed limestone deposit 1 , so the mercury present is likely a relic of the mercury content of the environment during which it formed

. That is to say that mercury content of the ocean during the

Cretaceous Period was influence d by volcanic activity, seafloor spreading, and other geological

processes

. The marine organisms living in that environment accumulated mercury in proportion to the level in the environment and their lifespan

. As these marine organisms died and added to

th e sediment deposition of what is now the Austin chalk (limestone) formation, the mercury from those organisms is incorporated in to that deposit

. Not surprisingly, the level of mercury in this unaltered sedimentary formation is very low

.

1 Dallas Paleontological Society. Surface Geology of Dallas and Tarrant Counties, Texas. Phil Scoggins,. 2010. 10 pages. http://www.dallaspaleo.org/details/surface_geology.htm.The variation s in mercury concentrations within an unaltered sedimentary limestone deposit such as the Austin chalk are thought to be primarily from variations in the duration of the shallow marine environment and the mercury levels of the oceans during the Cretaceous period in which these deposits were formed. So although different samples of limestone from this formation may vary in mercury content from one sample to another, they should all be within a low range. In addition, o ne would not expect a geogenic (that is, original to the rock) high mercury level to occur within this particular limestone deposit.

Based on th is information we believe that the mercury variability

– the variability, not

the level

-- of all thr ee quarries is identical . Therefore , mercury data from the three quarries can be used to estimate the quarry mercury variability in any one of these quarries (specifically the quarry serving the two MACT floor pool kilns

- 1248 and 1589 ) over time. The limestone is influenced by the time when it is formed. Since the amount of mercury being deposited in any point in time will vary, you would expect that the mercury level in these quarries varies depending on the level of the strata they are currently mining. Therefore, one way to estimate this variance is to look at these three quarries and determine if their mercury levels vary , and if so, the extent of that variability

.

For each facility we have the following information:

Table 1. Quarry Mercury Information for Midlothian

As noted, k ilns 1248 and 1589 are floor kilns (due to controls). Kilns 1248 and 1589 are the same facility ; kilns 1376, 1688, and 1690 are the same facility . The distance between these

facilities ran ges from 2 to 9 miles. (See attached Google Earth map ; the placemarks denote kiln locations.)

The three averages range from 0.059 to 0.021. The low ends of the ranges are similar, but the high end of the ranges varies, with 1239 being the highest and 1 248 being the lowest. In order to estimate the variability based in th is information, we calculated an average of the three quarries, and the average relative standard deviation. This resulted in a n estimated variance of

0.38. This variance would be added to the calculated variance based in daily emissions to incorporate this variance over time.

We have additional information for a second location where there are two facilities (three kilns). There facilities are next to each other.Table 2. Quarry Mercury Data for Mason City

Kilns 1246 and 1316 mercury levels were almost all below the detection limit

. A pparently the detection limit for kiln 1356 was lower, so it is more difficult to discern the

differences here. For this reason, data from this location was not used in this analysis. A Google Ear th map of this location is attached. The untitled placemarks denote kiln locations.

In order to incorporate this information into the floor calculation we calculate the relative standard deviation of the three qua rries as shown in Table 3.

Table 3. Cal culation of the Relative Standard Deviation for the Three Midlothian Quarries.

Quarry Limestone Concentration

(ppm)

1 0.059397

2 0.020893

3 0.027433

Average Hg Content of three Quarries 0.035908

Std Deviation of Averages 0.020603

Relative Standard Deviation 0.573779

.Attachment 1 Geologic Map of Texas

Attachment 2 Google Earth Map of MidlothianAttachment 3 Google Earth Map of Mason CityMidlothian is located close to the highest elevation in Ellis County atop the Austin Escarpment, a thick chalk ridge that runs in a northeast to southwest direction. The Austin Escarpment through Midlothian represents a 600

- year potential limestone reserve that has att racted three cement plant operations

.