Off-Lake PM10 Reductions in Areas Adjacent to Lakebed Dust Controls

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GREAT BASIN UNIFIED AIR POLLUTION CONTROL DISTRICT

157 Short Street, Bishop, California 93514-3537

760-872-8211 Fax: 760-872-6109

October 9, 2015

MEMORANDUM

Subject: Off-lake PM10 Reductions in Areas Adjacent to Lakebed Dust Controls

From: Duane Ono and Chris Howard

To: Phill Kiddoo, Grace Holder, Nik Barbieri, Ken Richmond and Julia Lester

ABSTRACT

Windblown dust in the Owens Lake area can be generated from the exposed lakebed as well as 

from off-lake areas. Most of the off-lake dust source areas are located near the lakebed. These are 

primarily areas where windblown sand and dust originating from the lakebed were deposited. An 

investigation of the history and morphology of the Keeler Dunes found that the natural dune area 

expanded following the drying of Owens Lake, which exposed the barren lakebed to wind erosion. 

Observations of the Keeler Dunes found that following the implementation of shallow flood dust control 

measures in 2001 in the area west of the dunes, the dunes not only stopped expanding, but began to 

erode along the upwind edge after the sand source was cut off. Similar to the Keeler Dunes, other offlake dust source areas are closely tied to erosion activity in adjacent lakebed areas. With the limited 

supply of sand and dust in these off-lake areas, PM10 that is present in the deposited soil is expected to 

be winnowed out over time, resulting in lower PM10 emissions and ambient impacts. Such a decrease 

in PM10 emissions and impacts were observed at Owens Lake near the Dirty Socks PM10 monitor site.

A comparison of off-lake and lakebed PM10 impacts measured at the Dirty Socks monitor site in this 

study found that dust from off-lake areas was closely linked to dust activity in adjacent lakebed areas. 

The results showed that the downward trends in on-lake PM10 exceedance numbers and concentration 

levels closely matched the trends in off-lake areas. A projection of this relationship found that if 

lakebed source areas cause no new federal exceedances, as expected for the required dust controls on the 

Owens Lake bed, then the off-lake areas would also show compliance with the federal standard.

INTRODUCTION

Windblown dust in the Owens Lake area can be generated from the exposed lakebed as well as 

from off-lake areas. Most of the off-lake dust source areas are located adjacent to and or near the 

lakebed. These are primarily areas where windblown sand and dust originating from the lakebed were 

Phillip L. Kiddoo

Air Pollution Control Officer
Off-Lake PM10 Reductions in Areas Adjacent to Lakebed Dust Controls

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deposited. An investigation of the history and morphology of the Keeler Dunes found that the natural 

dune area expanded following the drying of Owens Lake, which exposed the barren lakebed to wind 

erosion. Similar to the Keeler Dunes, many of the off-lake dust source areas adjacent to the lakebed 

were created as a result of transported windblown lakebed soils. (GBUAPCD, 2012)

If off-lake deposits were created as a result of material transported from the exposed lakebed, it 

would make sense that cutting off the source of transported soil would stop the growth of the off-lake 

dust areas. Indeed, observations of the Keeler Dunes found that following the implementation of 

shallow flood dust control measure in 2001 in the area west of the dunes, the dunes not only stopped 

expanding, but began to erode along the upwind edge. This was especially observed on the northern 

margin of the dunes where some dunes disappeared, exposing the underlying rocky alluvial fan. 

(GBUAPCD, 2012)

With the limited supply of sand and dust in these off-lake areas, much of the PM10 in the dunes 

should be winnowed out over time, and we would expect to see lower PM10 emissions and ambient 

impacts as the dunes shrink. In this study, a comparison of off-lake and lakebed PM10 impacts 

measured at the Dirty Socks monitor site was performed to evaluate how off-lake PM10 impacts 

changed after dust controls were implemented on the lakebed. The Dirty Socks site is one of seven 

PM10 monitor sites currently operating near the Owens Lake shoreline. This site is unique because of 

its long history of data collection before and after implementation of nearby dust controls, and the high 

number of exceedances caused by both lakebed and off-lake dust source areas. Its location and history 

made it especially useful for this study.

METHODOLOGY

PM10 monitoring data collected at the Dirty Socks monitor site from July 1999 through 

December 2012 was separated into exceedance days (PM10 > 150 μg m-3

) that were caused by 

windblown dust generated from lakebed source areas and those that were caused by dust from off-lake 

areas. Continuous PM10 data was collected using a federally-approved TEOM (Tapered Element 

Oscillating Microbalance) PM10 monitor. Hourly PM10 and wind direction data were paired to 

determine which hours had PM10 generated from lakebed source areas, which were assumed to be when 

the wind direction was greater than 234 degrees, or less than 50 degrees. Hours when dust was assumed 

to be generated from off-lake areas were the remaining hours. A 24-hour average PM10 concentration 

for each exceedance day was calculated for lakebed sources and off-lake sources by assuming that the

PM10 concentration was 20 μg m-3 for the off-lake wind direction hours for lakebed exceedance days, 

and conversely, 20 μg m-3 for the lakebed wind direction hours for off-lake exceedance days. The 

resulting off-lake and lakebed exceedance days were then evaluated to determine how the exceedance 

frequency and concentration values changed over time, especially before and after the implementation of 

dust control measures on the southern portion of the lakebed starting in 2003. The map in Figure 1 

shows the location of the Dirty Socks monitor at Owens Lake and the adjacent dust control areas and 

when they were completed. Dust controls near the Dirty Socks monitor were primarily shallow flooding

and managed vegetation. The area marked as the Olancha Dunes is the approximate location of a 

natural dune formation. The primary off-lake dust source areas that impact the Dirty Socks site are not 

distinctly mapped, but are scattered along a band approximately 2-km in width adjacent to the southeast 

shoreline.
Off-Lake PM10 Reductions in Areas Adjacent to Lakebed Dust Controls

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Figure 1. Location of the Dirty Socks PM10 monitor and dust control areas with their completion date in 

the southern portion of Owens Lake.

RESULTS AND DISCUSSION

The concentrations for off-lake and lakebed-caused exceedances at the Dirty Socks monitor 

site are plotted in Figure 2. The solid markers indicate data collected before dust control measures were 

implemented, and the hollow markers are for data collected after dust control measures were 

implemented. PM10 concentrations on the Y-axis are plotted on a log scale in order to show the 

concentration trend more clearly over the large range of PM10 values. It can clearly be seen that the 

frequency of PM10 exceedances for both off-lake and lakebed exceedances decreased significantly after 

2003 when the managed vegetation and shallow flood dust control measures were completed in the area 

north of the Dirty Socks monitor. The frequency of exceedances also declined after dust control 

measures were completed in 2006. Figure 1 shows the locations of dust control areas near Dirty Socks 

and their dates of completion.
Off-Lake PM10 Reductions in Areas Adjacent to Lakebed Dust Controls

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Figure 2. The frequency and magnitude of PM10 exceedances at the Dirty Socks monitor site decreased

after the completion of dust control measures on the lakebed in 2003.

It should be noted that the Dirty Socks monitor site was shut down from January 2013 through 

December 2014, and that there were no monitored exceedances at Dirty Socks when the site resumed 

operation during the first six months in 2015 which included the more active spring dust period. 

Although the lack of exceedances in early 2015 may indicate that dust controls might have succeeded in 

mitigating both the on-lake and off-lake exceedances, six months of data is insufficient to evaluate longterm trends, especially following a two-year data gap. Therefore, the 2015 data is not included in this 

report, and the analysis period concludes at the end of 2012.

The annual number of exceedances for off-lake and lakebed areas is plotted in Figure 3. It 

shows that the frequency of exceedances has decreased over time, especially following the completion 

of dust control measures using managed vegetation and shallow flooding in 2003 and 2006. The 

downward trend in the number of exceedances is more clearly seen in Figure 4 with the 3-year average 

number of exceedances. The 3-year average is comparable to the method used to determine attainment 

with the federal PM10 standard, which must average one PM10 exceedance-day or less over the last 

three years.
Off-Lake PM10 Reductions in Areas Adjacent to Lakebed Dust Controls

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Figure 3. The annual number of exceedances at Dirty Socks caused by lakebed source areas dropped 

after the completion of dust control measures in 2003 and in 2006.

Figure 4. The long-term trend for the number of exceedances is seen by calculating a 3-year rolling 

average.
Off-Lake PM10 Reductions in Areas Adjacent to Lakebed Dust Controls

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Figure 5. A comparison of the 3-year rolling average number of exceedances shows that the frequency 

of off-lake exceedances tracks closely with the frequency of lakebed-caused exceedances.

A variation on Figure 4 is seen by plotting the average number of exceedances for off-lake and 

lakebed source areas against each other as shown in Figure 5. By assuming a linear relationship and 

extrapolating this trend to less frequent lakebed exceedances, it projects that if the average number of 

lakebed-caused exceedances is less than one, then the number of off-lake exceedances would be less 

than one as well. Dust control requirements for lakebed areas at Owens Lake are intended to cause zero 

exceedances at the shoreline, therefore the average number of exceedances caused by off-lake sources 

would be expected to be less than zero following the extrapolation of the trend, or zero for the practical 

purpose of projecting compliance with the federal standard.

The PM10 concentration trend as seen in Figure 2 indicates that the magnitude of exceedances 

from lakebed sources is going down, but it also appears to indicate that, that downward trend also 

applies to impacts from off-lake sources. Similar to the 3-year average for the number of exceedances, a 

3-year rolling average for the exceedance values was plotted for off-lake and lakebed areas in Figure 6. 

Since the magnitude of exceedances caused by off-lake source areas appears to follow the 

concentrations from lakebed areas, this comparison provides additional support for the idea that off-lake 

and lakebed dust source areas are connected, and that controlling lakebed source areas will have 

corresponding benefits for controlling dust from off-lake areas.
Off-Lake PM10 Reductions in Areas Adjacent to Lakebed Dust Controls

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Figure 6. A comparison of the 3-year rolling average of PM10 exceedance concentrations for off-lake 

areas shows that it follows the exceedance concentrations caused by lakebed areas.

CONCLUSION

This analysis provides evidence that off-lake and lakebed dust source areas at Owens Lake are 

connected, and that controlling lakebed source areas will have corresponding benefits for controlling 

dust from off-lake areas. A comparison of off-lake and lakebed PM10 impacts measured at the Dirty 

Socks monitor site showed a linear relationship between the on-lake and off-lake impacts. This analysis 

indicates that if lakebed source areas are no longer causing exceedances of the federal PM10 standard, 

as expected for the required dust controls at Owens Lake, then the adjacent off-lake areas would also be 

in compliance with the federal standard. 

REFERENCES

GBUAPCD, 2012. Great Basin Unified Air Pollution Control District, “Final Staff Report On the Origin 

and Development of the Keeler Dunes,” Bishop, CA, November 16, 2012.

http://www.gbuapcd.org/keelerdunes/originanddevelopment/finalstaffreport/Final%20Staff%20Report_

Final20121116%20complete.pdf