ARTICLE INDEX
Volume 3, Number 4
August 1993
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IDAHO'S WATER
RESOURCE
Water is a finite resource essential to life. Water sustains Idaho's
fish and wildlife, agriculture, industry, mining, forestry, hydropower
generation, recreation, and growing population. Idaho's rivers and
lakes are renowned for their water sports and provide some of the most
spectacular natural scenery in the world. Water is precious, and its
management determines the quality of Idaho's environment.
Idaho's population uses the second largest amount of water in the United States, consuming 22.3 billion gallons per day. Only California uses more. On a per captia basis, Idaho is the nation's top water user -- 22,000 gallons per person daily. Idaho is also the country's fourth largest user of groundwater. Groundwater comprises only 22 percent of Idaho's total water use, but it accounts for nearly 95 percent of our drinking water.
Initially, water provided an abundant fishery and a means of travel for Idaho's Indians. In 1805, Lewis and Clark navigated Idaho's rivers on their journey to the West.
Irrigated agriculture in Idaho began in 1843. By 1899 more than half a million acres were under irrigation. By 1905 irrigation drew so much water from the Snake River that a 10-mile stretch near Blackfoot went dry. People then first realized the limits of Idaho's water resources. They responded in 1906 by building Milner Dam, Idaho's first large irrigation storage project. In 1945, surface water in southern Idaho became limited so irrigators turned to groundwater to help irrigate what is today more than 4.1 million acres.
Agriculture is Idaho's largest industry and its largest water user. Agricultural water use in Idaho averages 21.6 billion gallons per day. Agriculture accounts for 97 percent of Idaho's total water use and about 15 percent of the nation's total agricultural withdrawals. Only California uses more agricultural water.
Due in large part to irrigation, Idaho ranks first in the nation in the production of potatoes, barley, and commercial trout; second in spearmint; third in sugarbeets, hops, peppermint, and onions; fourth in prunes and plums; fifth in dry beans and sweet corn; and sixth in alfalfa hay and sweet cherries. Between 1987 and 1990, Idaho's average annual agricultural commodity sales exceeded $2.2 billion.
Industry and mining account for two percent of Idaho's water use. Mining uses about half of this water; food processing operations and pulp and paper mills use the rest.
Domestic and commercial water use (for homes, restaurants, and office buildings) comprise only one percent of Idaho's water use. Although the percentage of total use is small, per capita use is high. Idahoans use nearly 311 gallons per person per day in their homes and businesses -- more than the residents of any other state.
Recreation and toursim are also water dependent. Idaho's world-class fishing, backpacking, and river running attract outdoor enthusiasts from all over the world. Tourist revenues contribute over $1 billion annually to the state, at least half of it natural resource related.
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HOW VALUABLE IS
GROUNDWATER?
(This is the first in a series of articles on the costs of
groundwater contamination)
Determining the true cost of a groundwater contamination incident
requires assessment of the value of the groundwater resource in
question. A clear understanding of these value sources and resulting
contamination cost estimates suggest important implications for
researchers and policy makers.
A review of the uses for groundwater is important because it is the actual or expected use of the resource that primarily gives it value. In some cases, there may be no acceptable way to restore the lost services of groundwater. In these cases, the cost of the incident is equal to the net benefits of the aquifer when it was clean. There are a number of use values that may be lost due to contamination. In most cases, however, cost-effective remedies are available, and the added cost of these remedies represents the cost of the incident rather than the use value itself.
Municipal Use Value. Although municipalities account for only 10 percent of water withdrawn in the United States, such uses are generally thought to be the most important and highly valued. Municipal supplies provide for residential use as well as for fire-fighting and other outdoor uses. In most systems, water rates are not set in competitive markets, and often rates are not designed to cover the costs of development, treatment, and delivery. As a result, it has been difficult to conduct statistical studies of the willingness to pay for potable supplies of municipal water.
A survey of literature on water demand reveals that the value of water, at the margin, varies widely across different regions. In a survey of how much consumers would be willing to pay to avoid a 10 percent reduction in water use, the answers (in 1988 dollars) ranged to as high as the equivalent of about $5 per year per household. (90 percent of households in the United States pay less than $110 per year for water service.)
Industrial Use Value. Industrial use accounts for about 10 percent of water withdrawn in the United States, with the dominant use being for cooling. Because many industrial processes are not sensitive to the quality of the water, contamination may not preclude such uses. But, in the event that water use must be curtailed, recycling and reuse costs range from about $10 to $100 per acre-foot. In special uses, recycling and extra quality treatments may push the cost up to $400 per acre-foot.
Irrigation Use Value. Some of the most productive farmland in the country is irrigated land in the West. Many researchers have assessed the value of extra crop yield attributable to irrigation. These "marginal value products" for water vary widely in value from near zero to more than $100 per acre-foot, depending on the crop and the geography of the area. The wide range of values clearly shows that water is not marketed and transported easily to the point of its highest valued use. Rather it is used in activities of very different productivity and these "inefficient" uses are protected by legal and institutional barriers.
As water markets mature, however, we can expect to see only higher-valued water uses. Also we can expect the price to reflect a more uniform marginal value. As water rights become more "transferable," municipal users will bid up the price, and less water will be used in irrigation.
Option Value. Besides actual use value, water supplies also may be valued for potential future use. There is much public interest in protecting groundwater for the future. A study that assessed residential willingness in Cape Cod to pay to protect potable groundwater from possible nitrate contamination focused on several scenarios representing different levels of risk of future contamination. The present value of protecting the aquifer ranged from $5 million to $25 million per 1,000 households. This represents a willingness to pay from $500 to $2,500 per year per household for groundwater protection.
In summary, use and option values can be viewed as an approximation of the cost of contamination. Most contamination incidents can be managed at a low enough cost that uses will not be foreclosed.
Existence Value. Finally, society may desire to protect
groundwater as a resource with intrinsic value separate from any desire
to avoid the direct costs associated with contamination. Because this
existence value also is lost when groundwater is contaminated, it may
motivate even greater protection efforts.
(Adapted from Groundwater and Public Policy, Series No. 4 by W. B.
O'Neil and R. S. Raucher)
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HOW DOES STORAGE AND HANDLING OF
MATERIALS AND WASTE IMPACT GROUNDWATER?
(This is the second in a series of articles on the causes of
groundwater contamination)
Contaminants can enter groundwater from more than 30 different generic
sources related to human activities. These sources commonly are
referred to as either point or non-point sources. Point sources are
localized in areas of an acre or less, whereas non-point sources are
dispersed over broad areas.
The most common sources of human-induced groundwater contamination can be grouped into four categories: waste disposal practices; storage and handling of materials and wastes; agricultural activities; and saline water intrusion.
Groundwater contamination as the result of storage and handling of materials includes leaks from both above-ground and underground storage tanks, as well as unintentional spills or poor housekeeping practices in the handling and transferring of materials on industrial and commercial sites.
Leaking Underground Storage Tanks. Possibly as many as 7 million steel tanks are used to store petroleum products, acids, chemicals, industrial solvents, and other types of waste underground. The potential of these tanks to leak increases with age. About 20 percent of existing steel tanks are more than 16 years old, and estimates of the total number that presently leak petroleum products range from 25 to 30 percent. Underground storage tanks appear to be a leading source of benzene, toluene, and xylene contaminants, all of which are organic compounds in diesel and gasoline fuels.
Transporting and Stockpiling. Many materials and wastes are transported and then temporarily stored in stockpiles before being used or shipped elsewhere. Precipitation can leach potential contaminants from such stockpiles; storage containers can corrode and leak; and accidental spills can occur -- as many as 10,000 to 16,000 per year, according to EPA estimates.
Mining practices. Mining of coal, uranium, and other substances and the related mine spoil can lead to groundwater contamination in several ways:
Oil-Well Brines. Since the 1800s, hundreds of thousands
of exploratory and production wells have been drilled for oil and gas
in the United States. During production, oil wells produce brines that
are separated from the oil and stored in surface impoundments. EPA
estimates that 125,100 brine disposal impoundments exist that might
affect local groundwater supplies.
(Adapted from Groundwater and Public Policy, Series No. 3 by D. W.
Moody, USGS)
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PESTICIDE USE PATTERNS IN
SOUTHWESTERN IDAHO
Tim Stieber, University of Idaho Water Quality agent, conducted a
survey of current grower pesticide use and management practices in the
Idaho Snake-Payette Hydrologic Unit Water Quality Project (HUA). The
Snake-Payette HUA comprises over 840,000 acres in Canyon, Gem, Payette,
and Washington counties in southwestern Idaho.
Breakdown products of the herbicide Dacthal have been detected at low concentrations in many areas of the Snake-Payette Rivers HUA. The herbicides 2,4-D and metribuzin, and the insecticide Diazinon have also been found in rural well water samples.
The specific objectives of this survey were:
Eleven of the more than 50 crops grown in the HUA were selected for this survey because they collectively represent about 80 percent of the planted land within the HUA. The selected crops included: alfalfa, beans, corn (field and sweet), hops, mint, onions, orchards, potatoes, small grains, and sugarbeets.
Thirty-five local fieldmen and representatives of 19 private companies actively participated in this survey. Data were collected by using both grower interviews and field records. The data collected in 1992 covered 13,000 acres of cropland, which represented 3.6 percent of the irrigated acres in the HUA.
Pesticide Use. Growers in the HUA rely on multiple applications of the same and different pesticides for chemical control. Depending on the crop, between two and 12 pesticide applications are made each year. With 12 pesticide applications, onions are the most intensively managed crop. Conversely, field corn receives an average of two pesticide applications per season.
Between one and six separate herbicide applications are applied each season to crops in the HUA. Sugarbeets receive the greatest number of applications, while sweet corn, hops, and small grains generally receive only one application.
One to five insecticide applications are common on crops in the HUA. Onions and orchard crops receive the greatest number of insecticide applications due to onion thrip and codling moth pressures. Field corn and small grains average only one insecticide application each season.
The ranges in average number of pesticide applications for the 11 crops in the HUA survey were 1 to 6.5 for herbicides, 1 to 4.7 for insecticides, 0 to 3.6 for fungicides, and 0 to 2.9 for miticides.
The results of this survey will allow the targeted development of education and implementation programs to best meet the goals of the Snake-Payette Rivers HUA. A brochure on the results of this survey is available at no charge. You can request a copy of brochure WQ-19 by writing to the editor of WATER QUALITY UPDATE.
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IMPROVING DRINKING WATER WELLS: WELL
CONSTRUCTION
Poor well design can allow groundwater contamination by allowing rain
or smowmelt to reach the water table without filtering through soil.
Wells located in pits, or without grout or a cap, can allow surface
water to carry bacteria, pesticides, fertilizer, or oil products into
your drinking water supply. Proper well design reduces the risk of
pollution by sealing the well from anything that might enter it from
the surface.
The way in which a well was constructed, even if the design is sound, affects its ability to keep out contaminants. Several things that should be checked are described in the following sections. Well construction information may be available from the person who drilled your well, from the previous owner, or from the well construction report.
Casing and Well Cap. The well driller installs a steel or plastic pipe called casing during construction to prevent collapse of the borehole. The space between the casing and the sides of the hole provides a direct channel for surface water (and pollutants) to reach the water table. To seal off that channel, the driller fills the space with grout (cement, concrete, or a special type of clay called bentonite, depending on the geologic materials encountered). Both grout and casing prevent pollutants from seeping into the well.
You can visually inspect the condition of your well casing for holes or cracks at the surface, or down the inside of the casing with a light. If you can move the casing around by pushing against it, you may have a problem with your well casing's ability to keep out contaminants, In areas of shallow (less than 20 feet from surface) fractured bedrock, check on the condition of your well casing by listening for water running down into the well. (Pump should not be running.) If you do hear water, there could be a crack or hole in the casing, or you are not cased down to the water level in the well. Either situation is risky.
To prevent contaminants from flowing down inside of the well casing, the driller installs a tight-fitting, vermin-proof well cap to prevent easy removal by children, and entry by insects or surface water. The cap should be firmly installed, with a screened vent incorporated into it so that air can enter the well. Check the well cap to see that it's in place and tightly secured. Wiring should be in the conduit. If your well has a vent, be sure that it faces the ground, is tightly connected to the wellcap or seal, and is properly screened to keep insects out. The well code requires a vermin-proof cap or seal for all private wells. (Not all wells have caps. Some may have pumping equipment attached at the surface.)
Casing Depth and Height. Casing depth is important and depends on subsurface geologic materials. Wells cased below the water level afford greater protection from contamination.
Casing should extend one to two feet above the surrounding land. This prevents surface water from running down the casing or on top of the cap and into the well.
Well Age. Well age is an important factor in predicting the likelihood of high nitrate concentration. A well constructed more than 50 years ago is likely to be at the center of the farmstead; it may be a shallower well and is probably surrounded by many potential contamination sources. Older well pumps are more likely to leak lubricating oils, which can get into the well. Older wells are also more likely to have thinner casing that is corroded through. Even wells with modern casing that are 25 to 40 years old are subject to corrosion and perforation. If you have an older well, you may want to have it inspected by a qualified well driller.
Well Type. There are three major types of wells: dug wells, sand point or driven wells, and drilled wells. Dug wells pose the highest risk of allowing drinking water supply contamination because they are shallow and often poorly protected from surface water. A dug well is a large-diameter hole (usually more than 2 feet wide), which is often constructed by hand. Driven-point (sand point) wells, which pose a moderate to high risk, are constructed by driving assembled lengths of pipe into the ground. These wells are normally smaller in diameter (2 inches or less) and less than 50 feet deep. They can only be installed in areas of relatively loose soils, such as sand. All other types of wells, including those constructed by a combination of jetting and driving, are drilled wells. Drilled wells for farm use are commonly four to eight inches in diameter.
Well Depth. Shallow wells draw from the groundwater nearest the land surface, which may be directly affected by farmstead activities. Depending on how deeply the well casing extends below the water table, rain and surface water soak into the soil and may carry pollutants with it.
In general, the deeper the well, the more likely that the water is safe
for human consumption. Conversely, shallow wells are more likely to
contain pollutants if they are situated near heavy human activity.
(Adapted from Farm-A-Syst, Fact Sheet G3536, University of
Wisconsin)
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Comments to webmistress: karenl@uidaho.edu
All contents copyright © 1997-2003. College of Agricultural and Life Sciences, University of Idaho. All rights reserved. Revised: January 3, 2003