Environmental Engineering Reference
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through small tributaries into South San Francisco Bay. Other large mercury
mining districts—Clear Lake, Knoxville, East Mayacmas, and Wilbur Springs—
range up to 100 km north of the estuary and drain eventually to the northern reach
(now via the Yolo Bypass). The New Idria district, North America's second largest
mercury producer, is more than 100 km south of the estuary in the San Joaquin
River watershed. Post-1945 production of mercury at many of these locations was
by reworking surface tailings (Holmes 1965). The legacy of these mining activities
has been presented in studies addressing mercury speciation, chemical weathering,
and erosion (Conaway et al. 2004; Domagalski et al. 2004; Ganguli et al. 2000;
Kim et al. 2004; Lowry et al. 2004; Rytuba 2000, 2003; Slowey et al. 2005a;
Thomas et al. 2002). It is unclear if contamination from any but the largest of these
districts, New Almaden, has a great influence on mercury concentrations in the
estuary itself; and despite the size and proximity of New Almaden to the estuary,
there is little to suggest that New Almaden-derived contamination is a pervasive
and overwhelming mercury source in the estuary compared to industrial activities
and gold mining.
Use of Mercury in the Region
The majority of mercury produced in California in the late 19th and early 20th cen-
turies was used in gold mining (James 2005; Nriagu 1994), principally in hydraulic
mining and dredging activities in the California Sierra Nevada (Nriagu and Wong
1997). Contamination from this mining activity has occurred principally by hydrau-
lic mining debris transported through the watershed to the estuary (Conaway et al.
2003; Hornberger et al. 1999; Hunerlach et al. 1999; Jaffe et al. 1998; Marvin-
DiPasquale and Agee 2003). An estimated 12 million kg mercury was used for gold
recovery in California, and 4.5 million kg was lost to the environment in placer
mining operations throughout California (Alpers et al. 2005; Churchill 2000).
Although the bulk of the hydraulic mining sediment reached the estuary near the
turn of the 20th century (Hornberger et al. 1999), studies on upstream geomorphol-
ogy and geochemistry of hydraulic mining sediment show that this is still a perva-
sive and actively eroding source of contamination (Hunerlach et al. 1999; James
2005; Savage et al. 2000; Slowey et al. 2005b).
By the mid-20th century, the use of mercury in gold recovery fell drastically, and
the major use of mercury became the incorporation into electrical devices and at
chloralkali facilities (Nriagu 1987). Environmental uses, such as antifouling paint,
pesticides, fungicides, and slimicides for wastewater treatment, also represent the
use of tens of thousands of kilograms of mercury per year in the United States:
the authors are unaware of specific data for California. Between 1945 and 1970,
more than 100,000kg/yr of mercury was used in agricultural applications in the
U.S. (Nriagu 1987), mainly in seed treatment and foliar applications (D'Itri 1972);
however, the State of California did not require reporting of pesticide use by type
until 1970 (Federighi 2001), making estimates of mercury use in agriculture difficult
at best. Other industrial uses and sources are presented in Table 2.
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