July 23, 2012

Reply to

Attn Of: OEA-095

MEMORANDUM

SUBJECT: Mendenhall Valley PM10 Limited Maintenance Plan Determination

FROM: Chris Hall

ECU Air Data Analyst, OEA

TO: Keith Rose

STAPU Air Planning Team, OAWT

Claudia Vaupel

STAPU Air Planning Team, OAWT

Introduction

At the request of the Air Planning Team in OAWT, I have conducted a Limited Maintenance 

Plan (LMP) review for the Mendenhall Valley PM10 Non-attainment Area (NAA) for calendar 

years 2007 through 2011. Based on a data quality and statistical analysis I have found that the 

Mendenhall Valley PM10 NAA meets the attainment and design value criteria necessary to

qualify for the Limited Maintenance Plan optioni. 

Background

On September 16, 2010, EPA determined that the Mendenhall Valley PM10 NAA attained the 

PM10 NAAQS as of December 31, 1995. Supporting this decision were data through December 

31, 2009, which showed no exceedances of the standard. In order for EPA to re-designate this 

area to attainment there must be an approved Maintenance Plan in place. For the Mendenhall 

Valley Alaska DEC intends to submit a Limited Maintenance Plan (LMP). To qualify for the 

LMP option the NAA in question must be attaining the PM10 NAAQS, and in the most simplistic 

case, that the average Design Value (ADV) must be below the LMP defined design value (DV)

for both the 24-hr and annual PM10 standardsii.

In February 2009, ADEC submitted to EPA a LMP for the Mendenhall Valley. Utilizing data 

through December 31, 2004, ADEC showed that the NAA had been attaining the PM10 NAAQS

and that the 24-hr and annual ADVs were below the 24-hr and annual LMP defined DVs. 

OAWT recently initiated a review of this submittal and, based on the 2001 LMP memo,
determined that the most recent five years of data needed to be used to calculate the annual and 

24-hr ADVs. Therefore the purpose of this review is to determine if the Mendenhall Valley 

PM10 NAA would qualify for the LMP option based on a review of the most recent five years of 

data. Subsequent to the issuance of the 2001 LMP option memo, EPA revoked the annual PM10

standard. 71 Fed. Reg. 61,114 (Oct. 17, 2006).

Data Requirements

Section IV of the 2001 LMP guidance memo states that to qualify for the LMP option the area 

should be attaining the PM10 NAAQS, the 24-hr ADV must be below the 98 μg/m3, and the 

annual ADV must be below the 40 μg/m3. As mentioned above EPA determined that the 

Mendenhall Valley NAA attained the PM10 NAAQS based on data from the Floyd Dryden site as 

of December 31, 1995.

Data Quality Review

PM10 data through 2009 was previously reviewed for data quality to support the OAWT July 16,

2010, attainment determination for the Mendenhall Valley NAA. A data quality review of the 

most recent two years of data has also been performed and is summarized here to support the 

LMP analysis. 

ADEC certified to EPA that the PM10 data from these monitors in the AQS database is accurate. 

Data completeness was 97% and 100% for calendar years 2010 and 2011 respectively. In 

addition each of the eight quarters had greater than 75% data completeness, thus the data meets 

the completeness criteria specified in §2.3(b) of 40 CFR 50, Appendix K. 

Precision results met quality objectives where variation between the collocated PM10 samplers 

was less than 10% in both 2010 and 2011. Monthly flow rate verification results showed that 

both PM10 samplers operated within the required specifications for these two years. Quarterly 

audits were performed by ADEC QA staff with passing results.

Based on these quality control results the PM10 data is of appropriate quality and is usable for 

determining LMP eligibility for the 2007-11 timeframe.

Data Substitution

In the 2nd quarter of 2008 data completeness was 73% with 4 missing sample days for the Floyd 

Dryden site. In the 3rd quarter of 2009 PM10 data completeness was much lower with 14 missing 

days. For this LMP review, data substitution, following EPA regulationiii and guidanceiv was 

utilized to determine a 24-hr and annual ADV to compare to the respective LMP defined DVs. 

The optimal source for data substitution is from a collocated monitor but as ADEC did not begin 

operation of a collocated PM10 monitor at Floyd Dryden until October 2010, this is not a viable 

substitution option. The second option is to substitute the highest recorded value from the same 

quarter for the missing data points. This high substitution value can be from any of the years 

within the data set of interest (i.e., 3rd quarter 2007, 2008, 2009, 2010, or 2011). 

For the 2nd quarter 2008 the highest substitute value found was 27 μg/m3 which was recorded on 

May 20, 2010. For 3rd quarter 2009 the highest substitute value found was 27 μg/m3 which was 
recorded on September 17, 2010. Substituting this value for the 4 missing days in 2008, and the 

14 missing days in 2009, still yields an ADV of 45 μg/m3for 2007-2011. 

LMP Design Value Computation Results

24 Hour PM10 NAAQS

Four DV determination methods are provided within this section. Each method has value and 

drawbacks individually, but as a group they can provide convincing evidence that an area is 

either meeting or exceeding the 24-hr LMP defined DV. These methods are outlined in the EPA

‘PM10 SIP Development Guideline’, EPA-450/2-86-001, June 1987.

For calendar years 2007 through 2011 there are a total of 299 valid 24-hr average data values. 

The DV estimations provided below are for the totality of these five years rather than an average 

of the three 3-yr DV averaging periods. This approach was used due to the limited amount of 

data points over this 5 year timeframe.

Method 1 – Exponential Distribution

The following equation is used to determine the ADV and is based on a fitted trend line plotted 

on a semi logarithmic graph for the data points of interest:

Equation 1: 

 

Where

a = slope of the line

e = 2.71828

Y = 1/365 = 0.00274

b = y intercept

x = Average Design Value (i data points) = ADVi

By solving Equation 1 for ‘x’ we get the following equation:

Equation 2: ADVi = 

 

 

 

 

 

 

Equation 2 can now be used to determine a design value if the slope and y intercept are known.

The following are two similar ADV determinations for the Mendenhall Valley PM10 data sets. 

The first determination uses all available data from 2007 through 2011 (299 data points). The 

second determination uses only the top 10% of data points (i.e., the 30 highest concentration data 

points).

Chart 1 is the semi log graph of all 299 data points. The equation of the line, as auto determined 

by Excel, provides the needed slope and intercept values (a = 1.2662, b = -0.147). Substituting 

these into equation 2 gives us the following equation and ADV result.

Equation 3: ADV299 = 

 

 

 

 = 41.74 = 42 μg/m3
Chart 1 – 2007-11 Design Value Computation, 299 data points

Similarly using the values provided in Chart 2 we are able to determine the ADV for the upper 

10% of data points (30 data points).

Equation 4: ADV30 = 

 

 

 

 = 41.41 = 41 μg/m3

Chart 2 - 2007-11 Design Value Computation, 30 data points

Method 2 – Graphical Estimation

The second method provided in the 1987 PM10 SIP Development Guideline is the graphical 

estimation method. This is a visual method that estimates the ADV by determining the 

intersection point of the data trend line and the 1/365 line. The intersection points and ADV 

estimates are provided in both charts by the red lines. In both charts the ADV is very close to 42 

μg/m3. Note that the determination of the slope of the trend line is subjective to a certain degree 

and as such leads to slightly varying ADV determinations. For the 2007-11 Mendenhall PM10

data set these variations are inconsequential as the values are less than have the LMP limit.

y = 1.2662e-0.147x

R2 = 0.9884

0.001

0.01

0.1

1

0 10 20 30 40 50

y = 1.0221e-0.143x

R2 = 0.9322

0.001

0.01

0.1

1

0 10 20 30 40 50
Method 3 – Upper 10% Tail Distribution

This method is a straight equation and only uses the high 10% of data values.

Equation 5: ADV = X90 + 3.61828(U90 - X90)

Where

X90 = 90th percentile value

U90 = mean of the upper 10% of values

For our data set X90 = 17 and U90 = 22.67. Solving the equation yields an ADV of 38 μg/m3.

Method 4 – Tabular Estimation Method

Lastly the fourth and the most straight forward ADV determination method is the Tabular 

Estimation method (see table below). The Tabular Estimation method is particularly useful in 

that it is the only method that allows for data substitution without skewing ADV results for the 

Mendenhall Valley. 

No. of Daily Values Rank of Upper 

Bound

Rank of Lower 

Bound

Value Used for ADV

≤ 347 - 1 Highest Value

348 to 695 1 2 Second Highest Value

696 to 1042 2 3 Third Highest Value

1043 to 1390 3 4 Fourth Highest Value

The Mendenhall Valley 2007-2011 PM10 data set contains less than 347 data points therefore the 

ADV value is the highest data value using the Tabular Estimation method. For Mendenhall 

Valley the highest value is 45 μg/m3. 

Annual PM10 NAAQS

The ADV for the annual standard is simply the arithmetic mean of all the daily values within the 

data set. For the 2007-11 timeframe the average concentration is 8 μg/m3, which is well below 

the LMP defined DV of 40 μg/m3. Substituting 27 μg/m3for the 18 missing sample days for 

2008 and 2009 raises this ADV to 9 μg/m3.

Summary

In summary each computational analysis described above shows that the 2007-11 PM10 ADVs

for the Mendenhall Valley are well below the annual and 24-hr LMP defined DVs. Using the 

most conservative approach the 24-hour ADV was found to be 45 ug/m3, and the annual ADV 

was found to be 9 μg/m3. Based on the data quality and statistical results, it has been shown that 

the Mendenhall Valley NAA attains the PM10 NAAQS for 2007-2011, and the design value for 

that period qualifies the Mendenhall Valley NAA for the LMP option.

 

i

‘LMP Option for Moderate PM10 Non-attainment Areas’, August 9, 2001, as approved by Lydia Wegman designee,

ii An area may still qualify for the LMP option if it cannot meet these basic CDV criteria by meeting the site-specific 

CDV. Determination of the site-specific CDVs was not necessary for this LMP analysis.

iii See 40 CFR Part 50, Appendix K, §2.3(b).

iv In this case we follow the EPA ‘Guideline on Exceptions to Data Requirements for Determining Attainment of 

Particulate Matter Standards’ EPA 450/4-87/005, April 1987.