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MARKETS 
Use of Mercury Speciation to Characterize a Historic Cinnabar Mine and Retort: Maricopa County, Arizona
James N. Clarke, R.G. (MACTEC Engineering and Consulting, Phoenix, Arizona USA)
Deborah Barsotti, Ph.D, DABT, (MACTEC, Hamilton, New Jersey USA)
ABSTRACT:
The United States Forest Service (USFS) performed a Removal Preliminary
Assessment (RPA) of several historic cinnabar mining and processing operations
in 2000 and 2001. The RPA involved collection of sediment, retort tailings, and
surface water samples. The samples that were collected were analyzed for total
metals concentrations, including mercury. The samples were not analyzed for
mercury species. The total mercury concentrations were compared to the Arizona
risk-based residential soil remediation level (RSRL) for elemental mercury of
6.7 milligrams per kilogram (mg/kg). Several retort tailings and soil samples
were detected with total mercury in excess of the RSRL for elemental mercury.
The site is located in a watershed that provides drinking water to the Phoenix
Metropolitan Area; therefore, the USFS ordered an Engineering Evaluation Cost
Analysis (EECA) be conducted as part of a nontime critical removal action for
the site. Utilizing a combination of total metals and mercury speciation data,
MACTEC demonstrated that the mercury species of greatest concern, mercuric
chloride and methyl mercury, were not present above risk-based (recreational
receptor) cleanup levels. Additionally, the analysis indicated that the retort
tailings will not leach mercury to surface water above the Arizona Surface Water
Quality Standards (SWQSs).
INTRODUCTION
The Pine Mountain Mine site (“Site”) is a former cinnabar mine and retort
(mercury ore processing structure) (Figure 1). The Site is located approximately
60 mi (10 km) northeast of the Phoenix, Arizona metropolitan area. The Pine
Mountain Mine is located in the Northwest Quarter (NW1/4) of Section 4, and the
Northeast Quarter (NE1/4) of Section 5, of Township 17 North (T17N), Range 9
East (R9E), Gila and Salt River Base and Meridian, Maricopa County, Arizona. The
Site is further located at approximately 33o 58’ 44” North Latitude and
approximately 111o 26’ 55” West Longitude. The Site is located at an elevation
of approximately 5,200 ft (1,584m) above mean sea level (AMSL). The Site lies
within the boundaries of the Tonto National Forest on land administered by the
Forest Service, and is under the jurisdiction of the Mesa Ranger District.
Cinnabar was discovered in the area in 1911. By 1913, mercury mining, milling,
and retort operations began in the area, which became known as the Mazatzal
Mercury Mining District. The peak periods of mining occurred during World Wars I
and II and during the post-World War II atomic energy program. Several other
cinnabar mines operated in the area.
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