Off

- Lake PM10 Reductions in Areas Adjacent to Lake bed Dust Controls 1 

## G REAT 

## B ASIN 

## U NIFIED 

## A IR 

## P OLLUTION 

## C ONTROL 

## D ISTRICT 157 Short Street, Bishop, California 93514

- 3537 760

- 872

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- 872

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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 tha t the natural dune area expanded following the drying o f Owens Lake , which expos ed the barren lakebed to wind erosion. O bservations of the Keeler Dunes found that following the implementation of shallow flood dust control

measure s 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 off

lake dust source areas are closely tied to erosion activity in adjacent lakebed areas. W ith 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 PM1 0 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 trend s in on

- lake PM10 exceedance numbers and concentration levels closely matched the trend s in off

- lake areas . A projection of this relationship found that if lakebed source areas caus e no new federal exceedances

, as expected for the required dust controls on the Owens Lake bed , then the off

- lake areas would also show compl iance 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 OfficerOff

- Lake PM10 Reductions in Areas Adjacent to Lake bed Dust Controls 2 deposited. An investigation of the history an d 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

wer e 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 t he 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 al ong 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

- l ake 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 operat ing near the Owens Lake shoreline. This site is unique because of its long history of data collection before and after implementation of nearby dust control s , and the high number of exceedances caused by both lakebed and off

- lake dust source areas. Its l ocation and history

ma d e 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 win dblown 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 direc tion 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 f or 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 th e 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 s hallow flood ing and managed vegetation

. The area marked as the Olancha Dunes is the approximate location of a natural dune formation. The primary off

- lake dust sou rce 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 Lake bed Dust Controls 3 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 dus t 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 la rge 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 measure s w ere 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 location s of dust control areas near Dirty Socks and their dates of completion

.Off

- Lake PM10 Reductions in Areas Adjacent to Lake bed Dust Controls 4 Figure 2. The fr equency 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 i ndicate that dust controls might have succeeded in mitigating both the on

- lake and off

- lake exceedances, six months of data is insufficient to evaluate long

term 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 comp letion of dust control measures using managed vegetation and shallow flooding in 200 3 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 comparab le 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 Lake bed Dust Controls 5 Figure 3. The annual number of exceedances at Dirty Socks caused by lakebed source areas dro pped 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 Lake bed Dust Controls 6 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 exceedance s for off

- lake and lakebed source areas against each other as shown in Figure 5. By assuming a linear r elationship 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 contro l 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, t hat 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 Lake bed Dust Controls 7 Figure 6. A comparison of the 3

- year rolling average of PM10 exceedan ce 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 l akebed 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%20compl ete.pdf