# Appendix D

Mendenhall Data Replacement
Documentation

### (This page intentionally left blank)Mendenhall Data Replacement Documentation Hickory and Greensboro/Winston-Salem/High Point, NC Annual PM 2.5 Appendix D Redesignation Demonstration and Ma intenance Plan December 18, 2009 ii 

### TABLE OF CONTENTS

OVERVIEW ...................................................................................................................... ............. 1

Mendenhall PM2.5 Data Imputation for 4Q2006 ............................................................................3

Letter: December 12, 2006, Hoke P. Kimball, Mendenhall Monitoring Site in Greensboro, North
Carolina. ..................................................................................................................... ......................7

Letter: June 6, 2007, Hoke P. Kimball, Surro gate Data for Mendenhall-Guilford County, NC PM2.5 FRM Data 4Q 2006 (37-081-0013)....................................................................................17

Letter: August 28, 2007, R. Douglas Neeley, Response to NCDAQ letter sent June 6, 2007 .....21Mendenhall Data Replacement Documentation Hickory and Greensboro/Winston-Salem/High Point, NC Annual PM 2.5 Appendix D Redesignation Demonstration and Ma intenance Plan December 18, 2009 iii 

### (This page intentionally left blank)Mendenhall Data Replacement Documentation Hickory and Greensboro/Winston-Salem/High Point, NC Annual PM 2.5 Appendix D Redesignation Demonstration and Ma intenance Plan December 18, 2009 1 

## OVERVIEW

Data from the fourth quarter of 2006 at Mendenh all is incomplete due to construction at the monitoring site and complications in relocating th e site. The NCDAQ had to move the site since the school where the monitoring site is located constructed a two-story field house immediately adjacent to the monitoring site (letter to USEPA Region 4, A ppendix D). The school had not notified the NCDAQ of its intention to build the field house. During a routine site visit, the NCDAQ discovered that construction had started within four meters of the monitoring site. At that point, the monitor no longer met the ambient monitoring siting criteria and had to be shut
down and moved.

A new site was promptly found a nd appropriate permits were appl ied for. It took the NCDAQ four months (instead of an estimated 3 weeks) to resolve all the necessary permits and complete
the relocation of the monitor. This unfortunate circumstance resulted in most of the fourth quarter to go unmonitored.

The USEPA guidance does not address missing m onitoring data for an entire quarter. The NCDAQ decided the best option was to develop regressive analysis between Mendenhall and surrounding monitors.

Since there were no fourth quarter 2006 data with which to calculate a proper Mendenhall design value, the NCDAQ decided to present to the USEP A Region, IV an estimate of what the missing
Mendenhall PM 2.5 

### sample values would have been if they had been properly observed, along with the resulting design value summary statistics for their consideration. The estimate is based on linear regression using data acquired duri ng the four years, 2002 through 2005 at surrounding
sites. The monitors examined were Le xington (Davidson County, ID 370570002), Hattie Ave (Forsyth County, ID 370670022), Hopedale (A lamance County, ID 370010002), and Cherry Grove (Caswell Co., ID 370330001). Of the 4 monitors, a regression using a combination of the Hopedale and Lexington monitors prove d to be the best predictor for PM 2.5 

### at the Mendenhall
monitor.

An estimated fourth quarter 2006 value for Me ndenhall is then computed via a regressive analysis using the fourth quarter 2006 data fr om the Hopedale and Lexington monitors. The computed fourth quarter aver age at Mendenhall is 12.92 μg/m 3 

### . This value is then used to obtain annual design values. The Mendenha ll monitor has never violated the PM 2.5 

### standards and has consistently had annual aver ages that were 1 – 2 μg/m 3 

### below the annual PM 2.5 

### NAAQS. The NCDAQ is confident that had the monitor been operating during the 200 6 fourth quarter, the ambient air quality levels would have been cons istent with the estimated values the NCDAQ hasMendenhall Data Replacement Documentation Hickory and Greensboro/Winston-Salem/High Point, NC Annual PM 2.5 Appendix D Redesignation Demonstration and Ma intenance Plan December 18, 2009 2 

### developed. The USEPA has also proposed to determine that the Greensboro/WinstonSalem/High Point nonattainment area has attained the 1997 PM 2.5 

### NAAQS (74 FR 51249).

Attached are the correspondence with the USEPA Region IV regarding this issue as well as the regression analysis for developing the estimated 2006 fourth quarter average.- 1 - 

# Memorandum

To: Hoke Kimball

CC: Joelle Burleson, George Bridgers

From: Wayne L. Cornelius

Date: 2007-05-09 (revised 2008-12-16 and 2009-04-14)

Re: Mendenhall PM2.5 Data Imputation for 4Q2006

Contents

Introduc tion ................................................................................................................... .........................................1 Methods........................................................................................................................ ..........................................2 Results ........................................................................................................................ ............................................2 Discussion ..................................................................................................................... .........................................4 Recommendations ................................................................................................................ ..................................4

List of Tables

Table 1 Regression Analysis using the Lexington, Cher ry Grove, Burlington and Ha ttie Avenue PM2.5 data ....3 Table 2 Regression Analysis using the Lexington and Hopedale PM2.5 data .......................................................3 Table 3 Imputed Raw Data....................................................................................................... ..............................3 Table 4 Quarterl y Summaries.................................................................................................... .............................4 Table 5 We ighted Annual Means and Design Value........................................................................................... ...4

List of Figures

Figure 1 Map of Monitor Lo cations .............................................................................................. .........................2



### Introduction The North Carolina Division of Air Quality (DAQ) is in nonattainment for Davidson County for PM2.5 from the monitoring station in the city of Lexington (AQS Site ID: 370570002). DAQ has performed design value calculations with the PM2.5 data for 2005-2008 for Lexington. These calculations indicate that the design value for this monitor will be in attainment for this time period and thus DAQ will be applying for PM2.5 nonattainment redesignation. Redesignation requires assessing the PM2.5 data from PM2.5 monitors at Mendenhall (Guilford Co., ID 370810013), Lexington (D avidson Co., ID 370570002) and Hattie (Forsyth Co., ID 370670022).

The design value calculations for 20 05-2008 for the Mendenhall site are in complete because no valid PM2.5 data were collected during the fourth quarter of 2006. This happened because of major complications in having to move the site. DAQ moved the site about 100 yards because a 2 story field house that was constructedimmediately adjacent to the monitoring site (unpublis hed letter to Artra Cooper, 12 December 2006). The construction was started without DAQ’s knowledge. When DAQ realized what was happening it was too late to stop the project, the new field house was built, and the site no longer met ambient siting criteria.

Figure 1 Map of Monitor Locations

Since there were no 4Q2006 data with which to calcula te a proper Mendenhall Design value, the DAQ Planning and Ambient staff decided to present to EPA Region IV an estimate of what the missing Mendenhall PM2.5 sample values would have been if they had been properly observed, along with the resulting Design value summary statistics. The estimate is based on linear regre ssion using data acquired during the four years, 2002 through 2005 at surrounding sites including those in the MSA and also Hopedale (Alamance County, ID 370010002) and Cherry Grove (Caswell Co., ID 370330001). These monitor locations are shown in Figure 1 (an extraneous PM2.5 monitoring site at Clemmons, southwest Forsyth County, is also shown for reference but was not used in the analysis).

. 

### Methods The estimation procedure is as follows:

1. Fit a linear regression to the 2002-2005 PM2.5 data of the regressors to determine equation coefficients 2. Estimate missing sample values for Mendenhall by substituting the corresponding observed PM2.5 data in 4Q2006 into the regression equation 3. Compute quarterly averages for Mendenhall including the imputed 4Q2006 data using actual data where available and imputed data where provided by the regression procedure 4. Compute weighted averages for each year 5. Compute the completed Design value for Mendenhall derived by averaging the weighted annual means



### Results I applied two regression fits to the data, starting with the most inclusive possible model, using Lexington, Cherry Grove, Hopedale and Hattie Avenue all as predic tors. Estimates from this model are shown in Table 1. In this combination, Lexington, Cherry Grove and Hattie Avenue are not significant predictors for Mendenhall.

- 2 -Table 1 Regression Analysis using the Lexington, Cherry Grove, Burlington and Hattie Avenue PM2.5 data Call: lm(formula = MH ~ LX + UC + HD + HA, data = MH4q.md3, na.action = na.exclude)

Residuals: Min 1Q Median 3Q Max -3.763 -1.161 -0.3787 0.5814 11.34

Coefficients: Regressor Value Std. Error t value Pr(>|t|) (Intercept) 0.6105 0.5347 1.1417 0.2565
LX 0.1615 0.1165 1.3861 0.1690 UC 0.0791 0.0947 0.8346 0.4061
HD 0.4782 0.1495 3.1982 0.0019
HA 0.2466 0.1414 1.7445 0.0844

Residual standard error: 2.111 on 93 degrees of freedom Multiple R-Squared: 0.8798

The second regression removed Cherry Grove and Hattie Avenue from the model. The resulting model had a residual standard error of 2.094 and R 2 = 0.877. Both Lexington and Hopedale were significant in this regression, but the intercept term was not significant, so I fit the model with its intercept forced to zero. This model’s estimates are shown in Table 2. The regression equation is shown as equation (1)


### HD LX MH *6322.0*3464.0 

### + = (Equation 1)
I fit (1) to the Lexington and Mendenhall data values acquired during 4Q2006. Table 3 shows the regressors for the 22 days with valid data for both regressors, and the resulting Mendenhall estimates. The average of the 22 imputed samples is 12.92.

Table 2 Regression Analysis using the Lexington and Hopedale PM2.5 data Call: lm(formula = MH ~ -1 + LX + HD, data = MH4q.md3, na.action = na.exclude)

Residuals: Min 1Q Median 3Q Max -4.258 -0.9024 -0.1271 0.915 11.67

Coefficients: Regressor Value Std. Error t value Pr(>|t|)

LX 0.3464 0 .0891 3 .8873 0.0002
HD 0 .6322 0 .0957 6 .6042 0.0000

Residual standard error: 2.103 on 107 degrees of freedom

Table 4 shows the quarterly averages for 2004, 2005 and 2006, including the imputed value for 4Q2006 and the 11 actual values for the remaining quarters. Finally Ta ble 5 shows the 3 annual m eans and the overall Design value result that obtains from them, 14.01. Table 3 Imputed Raw Data
**Sampling_Date Mendenhall**  **Hopedale Lexington**  10/02/2006 11.485813 11.1 12.9 10/05/2006 23.900103 24.6 24.1

- 3 -PM2.5 Data Imputation

- 4 - **Sampling_Date Mendenhall Hopedale Lexington** 10/08/2006 6.785218 7.5 5.9 10/11/2006 13.710670 14.4 13.3 10/20/2006 11.761229 11.7 12.6 10/26/2006 11.848665 11.4 13.4 11/01/2006 16.130242 16.2 17.0 11/04/2006 12.507779 13.1 12.2 11/07/2006 10.703944 12.0 9.0 11/16/2006 4.536147 4.6 4.7 11/22/2006 3.983631 4.0 4.2 11/25/2006 16.255683 14.7 20.1 11/28/2006 18.157377 15.9 23.4 12/01/2006 4.790717 4.4 5.8 12/04/2006 9.893171 8.8 12.5 12/10/2006 16.526730 14.8 20.7 12/13/2006 25.615500 24.3 29.6 12/19/2006 18.599245 18.9 19.2 12/22/2006 8.990912 9.4 8.8 12/25/2006 6.246493 6.1 6.9 12/28/2006 14.394680 13.4 17.1 12/31/2006 17.455206 17.2 19.0

Table 4 Quarterly Summaries

Period CY2004 CY2005 CY2006 1Q 11.76 11.45 10.55 2Q 14.40 13.12 13.71 3Q 16.54 19.25 19.07 4Q 13.19 12.21 12.92

Table 5 Weighted Annual Means and Design Value

Period CY2004 CY2005 CY2006 2004-2006 D.V. Mean 13.97 14.01 14.06 14.01



### Discussion I maintain that the estimated Design value presented in Table 5 is an accurate prediction of the result that would have been obtained from Mendenhall for 2004-2006, had siting conditions not changed during 4Q2006. The imputed average is also the most accurate and approp riate value to use for th e 2006-2008 Design value calculations at Mendenhall to assist with the redesignation package for the Lexington site.



### Recommendations Design value calculations for the Greensboro-Winston- Salem-High Point MSA (or any subsequently redefined area that includes Greensbo ro) for any group of years that includes 2006 should use the imputed 4Q2006 value as a surrogate for the missing “actual” 4Q2006 at the Mendenhall site.

For future consideration, we can apply (1) to data acquired after 2006 from Lexington, Hopedale and Mendenhall. We can also repeat the regression fitting exercise using data acquired from the regressor sites in 2007 and later instead of 2002-2005 Either of these actions can be used to demonstrate how well the moved site location “represents” the original location.