### G REAT 

### B ASIN 

### U NIFIED 

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### P OLLUTION 

### C ONTROL 

### D ISTRICT

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 Juncti on 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 viola tion, 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 beg inning 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, D istrict 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 th e 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

c over 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

sev eral 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 veget ation 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 Comp any 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 tim e 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 dri veway 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, Dist rict 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 determi ne 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.