## To: Rochelle Bo yd , U.S. Environmental Protection Agency, OAQPS

From: Mark Bahner , RTI International Date: August 2 3 , 201 2 Subject: Clean Charge C ycles Statistical Analysis

**1.0 BACKGROUND**  **/EXECUTIVE SUMMARY** The proposed Secondary

Aluminum NESHAP revisions published in the Federal Register on February 14, 2012 required that furnaces melting other than clean charge use “one or more” cycles of clean charge before being able to switch the furnace designation. The Aluminum Association and Alcoa commented that using one or more cycles of clean charge was not necessary because test data indicated that the first cycle of clean charge has emissions comparable to the second and third cy cle o f clean charge. This memorandum reports on the results of a statistical analysis of the data. Based on a statistical analysis of the data, the Aluminum Association and Alcoa comment that there is no need to wait one or more cy cles before switching furnace designations appears valid. There was not a statistically significant difference between mean or median emission s of the first cycle, second cycle, and third cycle. All tables are presented at the end of this memorandum. **2.0 TEST DATA**  Test data were provided by the Aluminum Association and Alcoa in their comments in April 2012, which were place d in the Secondary Aluminum NESHAP docket (EPA Docket ID No. EPA

- HQ

- OAR

- 2010

- 0544). These data included the first cy cle emissions results and the average emissions for the first three runs. The data are shown in Table 1. More detailed data were obtained fom Alcoa in July 2012. These data included not just the first cycle emissions and the average emissions for the first three runs, but also the emissions for the second cycle (run) and third cycle (run). The data are summarized in Table 2.

## Page **2** of **5**

**3.0 STATISTICAL ANALYSIS**  Statistical tests were performed comparing mean and median values for the cycles, as shown in Table 3

. Means were compared using a paired t

- test. The null hy pothesis is that there is no difference in the mean difference. The paired t

- test first takes the difference of , for example, the first and second cycle, and calculates the mean of the differences , and tests if the mean of the differences is zero. The interpretation of the results is that a p

- value <= 0.05 provides statistical evidence that the average of one cycle is different from the average of the other cycle. A p

- value >= 0.05 does not provide evidence against the null hy pothesis that the average of both cycles is the same. Based on the results in Table 2, there is no evidence that the averages of the cycles are different. The paired t

- test is based on a normality assumption: For PM (lb/ton): The Shapiro

- Wilk test was used to evaluate normality ; p - v alues were 0.9388 (first cycle), 0.2385 (second cycle), and 0.321 2 (third cycle). All values suggest that the first, second, and third cycle has a normal distribution. For HCl (lb/ton): The Shapiro

- Wilk test was used to evaluate normality; p - values were 0

. 022 (first cycle), 0. 1572 (second cycle), and 1.061E

- 07 (third cycle). Results sugg e st that first cycle and third cycle data are not normal. For conclusions about the difference between these cycles the Wicoxon test should be used. Caution should be used given the small sample size. The Wilcoxon signed rank test was used to ev aluate the difference in the medians. This test is preferred if the assumption of normality doesn’t hold. The same interpretation as described previously

holds for p

- values. Based on the results described above, there is no evidence that the means or medians of the cycles are different.

## Page **3** of **5**

**Table 1. Data Provided by the Aluminum Association and Alcoa in April 2012**  **(Docket ID No. EPA -**  **H Q**  **- OAR** **- 2010**  **- 0544)** 

## Table 2. Additional Data Provided by Alcoa

Furnace Te st Date Pol lutant Em issi ons - Fir st Cycl e Aft erDi rty Charge Emi ssi ons -

Se co nd Cy cl e Aft er Di rty Charge Emi ssions

-

Th ir d Cycl e AfterDi rty Charge Em issi ons - Aver age o f 3 Te st Runs Group 1

Furnace Em issi on Li mi t Emi ssions

- 1st Cycl e AfterDi rty Charge Emi ssions

-

2n d Cyc le Aft erD irty Charge Emi ssi ons -

3rd Cycl e Aft erDi rty Charge Aver age Note Me lt er#7 2001 PM ( lb /ton) 0. 006 0. 006 0. 040 0. 017 0. 4 0. 005770 0. 006280 0. 040160 0. 01740 Me lt er#7 2001 HCl ( lb/ton) 0. 001 0. 001 0. 001 0. 001 0. 4 0. 000484 0. 000595 0. 000506 0. 00053 Ye llo w highl ig ht i ndi ca tes roundi ng e rror Me lt er#7 2001 D/F ( ug/M g) 0. 004 0. 003 0. 096 0. 034 15 0. 0038 0. 0034 0. 0956 0. 03427 Me lt er#7 2006 PM ( lb /ton) 0. 042 0. 043 0. 012 0. 032 0. 4 0. 0416 0. 0433 0. 0122 0. 0324 Me lt er#7 2006 HCl ( lb/ton) 0. 002 0. 002 0. 001 0. 002 0. 4 0. 00162 0. 00151 0. 00126 0. 00146 Ye llo w highl ig ht i ndi ca tes roundi ng e rror Me lt er#7 2006 D/F ( ug/M g) 0. 017 0. 006 0. 001 0. 008 15 0. 0170 0. 0055 0. 0014 0. 0079 Me lt er#7 2011 PM ( lb /ton) 0. 023 0. 011 0. 017 0. 017 0. 4 0. 0228 0. 0110 0. 0174 0. 0171 Me lt er#7 2011 HCl ( lb/ton) 0. 083 0. 012 0. 009 0. 010 0. 4 0. 0832 0. 01175 0. 00886 0. 00964 Me lt er#7 2011 D/F ( ug/M g) 0. 062 0. 094 0. 086 0. 081 15 0. 0620 0. 0942 0. 0862 0. 0808 Un it#3 2007 PM ( lb /ton) 0. 263 0. 258 0. 200 0. 240 0. 4 0. 2629 0. 2581 0. 2001 0. 2404 Un it#3 2007 HCl ( lb/ton) 0. 208 0. 197 0. 234 0. 213 0. 4 0. 2081 0. 1968 0. 2343 0. 2131 Un it#3 2007 D/F ( ug/M g) 3. 14 19. 060 8. 600 10. 3 15 3. 14 19. 06 8. 60 10. 27 Ro unded to 3s igf ig s Un rounde d Te st Re port Data

## Table 3. Additional Data Provided by the Aluminum Association and Alcoa

**Pollutant Comparing the Mean (p**  **- values)**  **Comparing the Median (p -** **values)**

**First Cycle vs**  **Second Cycle**  **First Cycle**

**vs Third Cycle**  **Second**

**Cycle vs Third Cycle**  **First Cycle**

**vs Second Cycle**  **First**

**Cycle vs Third**  **Cycle Second** 

**Cycle vs Third Cycle**  PM (lb/ton) 0.473 0.975 0.888 1 1 0.75 HCl (lb/ton) 0.43 0.422 0.27 1 0.5 0.371 D/F (lb/ton) 0.659 0.401 0.506 1 0.5 1