GREAT BASIN UNIFIED AIR POLLUTION CONTROL DISTRICT

MEMORANDUM

Date: June 2, 2010

To: Data Processing Staff

From: Chris Lanane

Subject: Coso Junction PM10 Monitoring Station Siting Review

During the first quarter of 2010 the TEOM at the Coso Junction station has monitored 

two (2) violations of the Federal PM10 standard, one on March 9, 2010, and the other on 

March 18, 2010. During the March 9 violation, winds during the hours of highest 

concentration were out or the north; during the March 18 violation, winds were out of the 

west. Staff began investigating these violations to determine whether they were a result 

of windblown dust from Owens Lake or from more localized sources. Bill Cox, the 

District Director of Technical Services, noted in the beginning of the investigation that 

the recent photographs taken for the District 2010 Annual Network Monitoring Plan 

showed that the vegetation that had been in place for several years in the area 

immediately around the station had died off, exposing friable soils that could be lofted by 

the wind. It was determined that a site visit was necessary in order to determine whether 

local sources were now exposed that could unduly influence the PM10 data collected 

from the Coso Junction station.

On May 27, 2010, District staff, including Dan Johnson, District Air Monitoring 

Technician Specialist and the Coso PM10 monitor operator, Chris Lanane, District Air 

Monitoring Specialist, and Colleen Brock, Coso Operating Company Compliance 

Officer, met at the Coso Junction station to assess the potential sources in the area around 

the station. It was determined that, over the past few years, after Coso Operating 

Company staff had moved out of the office at the Junction site, the watering of vegetation 

in the area around the Junction station had stopped. The vegetation has gradually died off 

to the extent that it no longer provides sufficient cover for the dust source area. Further, 

an access road to the station had been covered with gravel, which had provided sufficient 

cover to prevent local source material from being lofted by the winds. Since January 

2010 a contractor has been onsite who has installed an equipment trailer near the 

monitoring station. The contractor staff has been driving along the site access road 

several times each day in order to collect equipment from the trailer. The increase in 

vehicle trips over the access road has driven the gravel deeper into the ground and caused 

exposure of the source material. This exposure of material from the dying vegetation and 

from the increased trips on the access road has heavily influenced the PM10 

concentrations monitored at the station since January 2010, and, as such, the station no 

longer meets the EPA siting criteria for a PM10 monitor.
The Coso Operating Company staff will be putting together a letter describing their 

mitigation plan that will be sent to Duane Ono, District Deputy Air Pollution Control 

Officer, within the next two weeks. Their plan is to revegetate the areas where die-off 

has occurred and to add a layer of gravel to the access road and all areas over which there 

will be vehicular traffic. The traffic itself will be limited to the station operators for the 

monitoring station and other monitoring station support personnel as needed. By the time 

of the meeting, Ms. Brock had already had the contractors move their trailer to the gravel 

parking lot approximately 100 meters east of the station. In the short term, Ms. Brock 

indicated that water would be applied to the vegetated areas and to the driveway areas in 

order to both mitigate the local dust problem and to facilitate the development of a 

competent crust that would protect the emissive surface.

Because of the undue influence of the local sources on the Coso Junction PM10 

concentrations, District staff has determined that PM10 concentrations monitored at the 

site since January 2010 are suspect and should not be used for any compliance 

determination. The station should be reassessed at the end of June and at least monthly 

thereafter to determine whether local influences have been sufficiently mitigated to allow 

for the PM10 concentrations to be used to characterize the broader, regional-size (tens to 

hundreds of kilometers) area for which the site was originally designed.