Carson River
The Carson River is a northwestern Nevada river that empties into the Carson Sink, an endorheic basin. The main stem of the river is long although the addition of the East Fork makes the total length, traversing five counties: Alpine County in California and Douglas, Storey, Lyon, and Churchill Counties in Nevada, as well as the Consolidated Municipality of Carson City, Nevada. The river is named for Kit Carson, who guided John C. Frémont's expedition westward up the Carson Valley and across Carson Pass in winter, 1844. The river made the National Priorities List on October 30, 1990 as the Carson River Mercury Superfund site due to investigations that showed trace amounts of mercury in the wildlife and watershed sediments.
History
Archaeological findings place the eastern border for the prehistoric Martis people in the Reno/Carson River area, these are thought to be the first humans to enter the area about 12,000 years ago. By the early 1800s, the Northern Paiute lived near the lower Carson River and the present Stillwater National Wildlife Refuge, while the Washoe people inhabited the upper watershed region.The Carson River watershed was a shared territory between these two tribes. The Northern Paiute of western Nevada was grouped into several bands relating to the area that they inhabited. The group that established itself along the Carson River were known in the Shoshone language as "Toituked". The Washoe peoples that had residence in the Carson Valley were also divided into a separate group and called "Pau wa lu". Ancient people and indigenous tribes used the Carson River as a resource for livelihood, depending on the river for fish, waterfowl, plant materials, and especially water in the arid Nevada desert climate. Displacement of these tribes and changes of lifestyle did not take place until the development of European settlements.
The first European settlements in Nevada were the 1851 settlements at Mormon Station and at the mouth of Gold Canyon, both in the Carson River Watershed. In the 1850s and 1860s, the river was used as the route of the Carson Trail, a branch of the California Trail that allowed access to the California gold fields, as well as by the Pony Express. Gold was discovered along the river in the Silver Mountain Mining District in 1860. 1868 Virginia and Truckee Railroad transported ore to the quartz reduction mines along the river. Virginia City, Nevada, along the lower watershed, was home to the world's greatest silver rush, the Comstock Lode in 1859. The Carson Valley provided food and forage for the silver miners and their livestock. The Comstock mining boom critically impacted the watershed and water quality by causing deforested slopes, mine tailings, and steep raw riverbanks above channels cut into the valley floor in many places. These mining operations have also led to high levels of existing mercury concentrations within the watershed.
In the early 20th century, the Newlands Reclamation Act was passed to bring irrigation water into the region for agriculture. The Lahontan Dam, completed in 1914, was constructed as part of the Newlands Irrigation Project. The Truckee–Carson Irrigation District was formed in 1918 as part of the project to divert water from the Truckee River to the Carson Valley for agricultural use.
In 1989, the East Fork Carson River was designated a "Wild and Scenic River" by the State of California from Hangman's Bridge just east of Markleeville, California, to the Nevada border, prohibiting any further consideration of impoundment.
Watershed
The Carson River watershed encompasses and includes two major forks in the Sierra Nevada in its upper watershed region. The East Fork rises on the north slopes of Sonora Peak, much of the water is used for irrigation in the vicinity of Fallon, with limited flows continuing northeast into the Carson Sink.Clear Creek, which begins at about on Snow Valley Peak west of Carson City, is the only perennial tributary of the Carson River mainstem, and is protected by the Nature Conservancy.
Carson River mercury superfund site
The Carson River basin, from New Empire to Stillwater and the Carson Sink, was designated as National Priority Listed due to historic mining activity site under the Comprehensive Environmental Response Compensation and Liability Act in August 1990. This is Nevada's only NPL site and is being jointly managed by NDEP and the U.S. Environmental Protection Agency 9, Region IX, in San Francisco. Millions of pounds of mercury were imported and used in approximately 250 Comstock mills to recover gold and silver. An estimated 14,000,000 pounds of mercury was lost to the environment during that process. Arsenic and lead, which were common constituents of the mined ore, were concentrated by the milling process and were also released into the environment. Therefore, the contaminants of concern at the site are mercury, arsenic, and lead.Mercury, arsenic, and lead are known or suspected carcinogens and/or detrimental to human health in some other way. Mercury is the primary concern regarding the Carson River Mercury Superfund site. Several forms of mercury are prevalent in the open water source, including inorganic mercury and organic methylmercury. MeHg is produced from bacteria in river systems and can be ingested by the wildlife in the area. The methylmercury, due to its specific properties that include it being fat soluble, can lead to bioaccumulation and biomagnification of mercury in Carson River Aquatic wildlife. The contaminants, however, need a route into the human body to have a harmful effect. Direct contact with soils and subsequent ingestion and/or eating fish and waterfowl taken from the CRMS area, which may have already ingested CoCs, provide the most likely route into the body. Small children have the highest risk due to developing bodies and their propensity for ingesting soil while at play. Signs of Mercury poisoning due to oral ingestion are most commonly found to affect kidneys, central nervous system, and development - especially in organic mercury. The EPA and other scientists studied residents of contaminated areas and found no direct evidence of increased metals in blood, hair and urine samples. They did find elevated levels in certain fish and waterfowl. Some of the highest levels in the nation. Human health, if impacted, would be impacted slowly, over years of small amounts of exposure, and could be hard to detect.
The upland contamination source area of the CRMS. OU-1 is undergoing continued management and monitoring to assure public protection from mine wastes. The most significant health risk in OU-1 is direct contact and ingestion of contaminated soils. OU-2 is defined as the water, sediment, and biologic resources of the Carson River, Lahontan Reservoir, Washoe Lakes, Steamboat Creek, associated irrigation ditches, and the Stillwater Wildlife Refuge. EPA Contractor and USGS are continuing studies of OU-2 areas and will produce a. The most significant health risk posed by mercury in OU-2 is the consumption of fish and waterfowl from affected lake and river systems. In the 1990s, the EPA compelled several limited area cleanups to be completed by third parties and completed cleanup on a half dozen areas themselves. The cleanups occurred primarily in residential areas of Dayton. The remainder of the site has not undergone cleanup, and due to the size and scope of the area impacted, most likely never will. Since complete site cleanup is not economically viable. A long-term sampling and response plan was developed to manage site contamination in the future. The LTSRP provides guidance for land development activities to help assure site CoCs do not impact human health and the environment. Typically, soil sampling is required to verify developed area soils do not contain CoCs at levels which may cause harm to human health.
Mercury amalgamation process
The Mercury in the Carson river is primarily introduced into the river through sediment deposition resulting from mine tailings during the Comstock Lode. These tailings were attributed to the mining process that settlers used in the 1850s to recover silver and gold. This process is known as mercury amalgamation. Mercury amalgamation has been mining precious metals since the Middle Ages. Mercury amalgamation is accomplished by pulverizing the ore and covering it with mercury using drums or tables. Once the mercury binds to the gold or silver, it is separated from the barren soil to a retorting vessel where the mercury is vaporized and condensed off of the amalgam. During the Comstock Lode a new, Washoe "hot-pan" amalgamation, the process was created specifically to treat Nevada ore in 1861. Washoe "hot pan" mining used a cast iron pan with the soil mixture, mercury, sulfuric acid, and other materials to remove the precious metals.Losses of mercury that attributed to the contamination of the Carson River and eventually to the CRMS occurred during these processes. Mercury loss in the mining operations ranged from transportation failures, crude equipment, and poor handling. The mercury was transferred using leather bags, pails, and barrels that leaked and spilled. Equipment was not up to standards and not practical for containing tailings. However, most of the mercury loss happened throughout the amalgam process. The recovery amount of the vaporized mercury completely depends on the technology used, and the efficiency of mercury binding depends on the ability of the precious metal. Both of the actions were not completely refined themselves and attributed to as much as 0.7–1 kg of mercury waste/ per tonne of ore processed in Nevada mines.
Hydraulic mining was also used in the Carson River region. Hydraulic mining uses mercury to bond to the gold and silver in the mining slurry. The gold/silver amalgam drops to the bottom of the sluice while gravel and other tailings pass over. As time passes, the mercury is ground into a fine layer that coats the bottom of the sluice and can contaminate the surrounding area through leaks and the effluent of water containing the mercury. It is estimated that this practice in California attributed to mercury losses up to 10-30%.