Current Issues

Environmental Mercury in California
During the period 1850-1950, mercury was mined and refined at several major deposits in California's Coast Ranges and the resulting quicksilver was used extensively in gold processing operations throughout California. A large amount of mercury was used in gold processing (estimated at 26,000,000 pounds), and a large proportion of it (several million pounds) was lost to the environment. Consumption of mercury-contaminated fish is a possible risk to human health and to ecosystems. Ongoing studies are designed to assess the levels of mercury contamination and bioaccumulation associated with historical gold and mercury mines in several watersheds in northern California. Mercury "hot spots" are being identified for possible remediation in the Bear-Yuba watersheds and the Trinity River watershed in cooperation with Federal land management agencies (Bureau of Land Management and USDA Forest Service). Reservoirs downstream of historical mining activities are being characterized with regard to mercury contamination levels in biota, water, and sediment. USGS scientists are working closely with other federal, state, and local agencies to determine whether reductions in mercury loads will be an effective way to reduce mercury concentrations in fish in the Sacramento River watershed and the Bay-Delta.

Aquifer Storage and Recovery
Aquifer storage and recovery (ASR) is a water resources management technique for actively storing water underground for recovery and use when needed. "Conjunctive use" and "artificial recharge" are closely related management practices, and the terms are sometimes used interchangeably. Conjunctive use is a combination of practices to make the best use of surface water during wet periods and ground water during dry periods, but does not necessarily imply active water storage practices used in ASR. Artificial recharge (AR) is actively moving water into ground-water systems. AR can be seen as the storage part of aquifer storage and recovery.

California Ground Water
The Water Resources Division of the U.S. Geological Survey, in cooperation with Federal, State, and local water agencies, obtains a large amount of data pertaining to the ground-water resources of California each water year. These data constitute a valuable database for developing an improved understanding of the water resources of the State. Beginning with the 1985 water year and continuing through 1993, these data were published in a report series titled "Water Resources Data for California, Volume 5. Ground-Water Data." Prior to the introduction of this series, historical ground-water information was published in U.S. Geological Survey Water-Supply Papers.

Salt Water Intrusion
Saltwater intrusion - the invasion of fresh water by saltwater from the sea or from marine deposits due to ground-water withdrawal - threatens ground-water supplies in many areas along the California coast. A variety of hydraulic and geochemical techniques may be applied to determine the sources and mechanical causes of the saltwater intrusion. Once the causes are determined, changes in spatial distribution and quantity of ground-water pumpage, along with surface water deliveries for artificial recharge, are likely to be required to control intrusion. Current studies are applying solute-transport and hydraulic-optimization modeling techniques to evaluate management options for controlling seawater intrusion in multiaquifer systems.

Drinking-Water Disinfection By-products
Drinking-water is disinfected to kill or inactivate microorganisms, bacteria, protozoa, viruses, and other pathogens that cause serious diseases and death, including cholera, typhoid fever, dysentery, and hepatitis A. While the health benefits of disinfecting public drinking water are indisputable, disinfection processes do produce by-products that can have their own long term health effects. For this reason disinfection by-products (DBPs) and their sources are studied by the U.S. Geological Survey and other organizations, and drinking-water concentrations are regulated by the U.S. Environmental Protection Agency.

Methyl Tertiary-Butyl Ether (MTBE)
Methyl tertiary-butyl ether (MTBE) is used as a gasoline additive for several purposes. It has been added in relatively low concentrations to increase octane ratings in premium grade fuels since the late 1970's. Beginning in the early 1990's MTBE has been added in much higher concentrations (up to 15 percent) to enhance gasoline combustion and reduce tailpipe emissions. Gasoline producers are required to add a fuel oxygenate (chemicals that aid combustion by increasing available oxygen) to California Phase 2 Reformulated Gasoline to reduce air pollution, especially carbon monoxide. MTBE is the most common fuel oxygenate, used in more than 80 percent of oxygenated fuels. MTBE is credited with contributing to significant reductions in carbon monoxide and ozone levels in many of these areas.

Surface Water
The U.S. Geological Survey (USGS) stream-gaging program provides streamflow data for a variety of purposes that range from current needs, such as flood forecasting, to future or long-term needs, such as detection of changes in streamflow due to human activities or global warming. The development of data on the flow of the Nation's rivers mirrors the development of the country.

Water Quality (QW) in California
Unlike some of the other topical categories that address specific processes, water quality is a broad term for conditions that render water unfit for some use. Although most commonly applied to contamination of water by dissolved or suspended chemical constituents, the term also includes physical degradation that may be due to changes in temperature and the amount of suspended sediment, for example. Water quality degradation in California is caused by a wide variety of processes, some naturally occurring and some man-induced. The State Water Resources Control Board Water Quality Assessment concludes that agriculture is the largest source of water quality degradation of rivers, streams, and ground water in California. Other major sources are silviculture, leaking underground storage tanks, urban runoff, septic and sewage treatment systems, mining, and industry. The three most predominant pollutants responsible for impairment of rivers and streams are pesticides, sediment, and pathogens, and for ground water are salinity, nutrients, and pesticides.