FRESNO DESK - A new government study of San Joaquin Valley water quality has been released this week. The findings confirm that Fresno drinking water, while still safe to drink, contains increasing amounts of contamination from both urban and rural land use.
The study area in Central California has been closely monitored since 1992. It includes the towns, ranches, and farming areas on the West Side of the San Joaquin Valley and the cities and farms all the way to the western slope of the Sierra Nevada.
The purpose of the ground water Land-Use Studies was to assess the concentration and distribution of water-quality constituents in recently recharged ground water, and then to examine the natural and human factors affecting the quality of shallow ground water underlying various land uses.
The Study focused on the effects of rural development and agricultural land use in vineyards, almond orchards and in areas which there was crop rotatation for corn, alfalfa, and vegetables.
Wells provide the sole source of drinking water for many rural communities and for the cities in the Fresno area.
A variety of chemicals, including nitrate, can pass through the
soil and potentially contaminate well water. Nitrate comes from
nitrogen, a plant nutrient supplied by inorganic fertilizer and animal
manure. Additionally, airborne nitrogen compounds given off by
industry and automobiles are deposited on the land in precipitation
and dry particles.
Other urban nonagricultural sources of nitrate include lawn fertilizers, septic systems, and domestic animals in residential areas.
Beneath agricultural lands, nitrate is the primary form of
nitrogen. It is soluble in water and can easily pass through soil to
the ground-water table. Nitrate can persist in well water for
decades and accumulate to high levels as more nitrogen is applied to
the land surface every year.
Well over 500 million pounds (active ingredient) of pesticides with different levels of toxicity, solubility, and persistence, are annually applied to agricultural crops to control pests, fungus, and disease.
Some pesticides can travel far from where they are applied, and may harm freshwater and marine organisms, damaging recreational and commercial fisheries. Pesticides in drinking water supplies can pose a risk to human health.
The EPA has established enforceable drinking water standards for 13 currently used pesticides, and more are pending. The presence of regulated pesticides above specified levels in water supplies requires additional treatment, placing added costs on water utilities and their customers.
In a recent EPA survey of drinking water wells reported that 10 percent of the community water system wells and 4 percent of rural domestic wells contained at least one pesticide. It is a widespread problem.
Pesticides or their transformation products have been detected in the groundwaters of 43 States.
However, the EPA estimates that less than 1 percent of the community water systems and rural domestic wells had concentrations high enough to pose a health danger.
The Sierra Nevada is predominantly forested land, and the Coast Ranges and the foothills of the Sierra Nevada are rangeland. Most of the Valley floor is used for agriculture.
The government report cites changes to drinking water quality is still at safe levels in spite of the increasing levels of contaminants in Fresno drinking water due to large amount of irrigated agriculture, which affects the quality of both surface and ground water in the entire San Joaquin Vallley reagion.
An unwanted indirect by-product of Fresno's premiere agricultural economy is that some contamination of Fresno's drinking water is taking place. It is unavoidable that sediment from eroding land affects surface water, and nutrients from fertilizers and manure, pesticides, and salts from irrigation can affect both surface water and well water.
Tilling the soil and/or leaving it without vegetative cover for some period of time results in accelerated soil erosion. Varying proportions of sediment from eroding fields may be delivered to surface ponding basins depending on topography, distance, and land cover.
Sediment harms ponded water when excessive amounts collect clouding the water and coating the leaves of plants. That deprives them of sunlight needed for growth. The deposition of sediment reduces the useful life of reservoirs, clogs ditches and irrigation canals, blocks navigation channels, resulting in increased dredging costs.
The most dramatic effect of sediment buildup is the raising of stream beds and burying streamside wetlands.
Sediment can also increase the likelihood and severity of floods. In addition, suspended sediment can increase the cost of water treatment for municipal and industrial water users.
According to EPA, siltation is one of the leading pollution problems in U.S. rivers and streams, and among the of four problems in lakes and estuaries.
The USGS Report concludes that San Joaquinw Valley well water is the exclusive source of drinking water for nearly 3 million Valley residents and is safe to drink.
For readers who would like to take a closer look at the Report, review it at USGS Circular 1159: Water Quality in the San Joaquin-Tulare Basins .
