Water Cycle

Although rivers, streams and lakes are very visible sources of water, 95 percent of the U.S. fresh water supply is in groundwater. Half of the U.S. population (in rural areas 95 percent) depends on groundwatcr for drinking. In Kentucky, only 38 percent of those in more urban areas depend on groundwater, but 88 percent of those in rural areas do so (Fig. 1 ). Concern about its quality and potential contamination has made groundwater protection a national issue.

Sources of Drinking Water

Groundwater forms when water moves below the earth's surface and fills empty spaces in and around rocks and porous materials. If enough gathers in one area, groundwater becomes the source of fresh water supplying wells and springs. Under certain conditions, contaminants -including soil nutrients, waste products and chemicals -- can migrate into groundwater sources.
Modern technology can detect extremely low concentrations of chemicals in groundwater. One group of chemical contaminants sometimes found in groundwater is pesticides. These products usually are applied to, or near, the surface of the ground.
Five major factors determine whether they will reach groundwater:
•the practices followed by the chemical applicator;
•the presence (or absence) of surface water from rain or irrigation;
•the characteristics of the product being applied, such as adsorptivity, degradation rate and solubility;
•the type of soil in the area of application, examples being texture and organic matter content; and
•the location of the groundwater - its distance from the surface & the type of geological formations above it.
Only rarely does the combination of conditions occur which allows pesticides to reach groundwater. By being aware of these considerations, you can apply these products in ways which will make the potential for groundwater contamination even less likely.

Good Application Practices
Follow Label Directions
The best way to minimize groundwater contamination is to follow label directions exactly. The label's use instructions, approved by EPA, have been carefully developed after many years of study and testing. If you do not follow them, your treatment may not be effective, you increase the risk of contaminating groundwater and you may be violating the law. Proper timing and placement of pesticide applications are very important.

Mix and Callibrate Accurately
Avoid the temptation to use more product than the label directs. "Overdosing" will not do a better job of controlling the pests -- it will only increase both the cost of pest control and the chance that the material may reach groundwater.
Most growers do not mean to exceed recommended label rates. But field checks have shown that mistakes in preparing tank mix concentrations and in calibrating application equipment often result in the application of too much chemical. Calibrate equipment carefully and recheck it often. Measure chemical concentrates and diluents accurately before adding them to the tank. Rough approximations can lead to serious overdoses.

Prevent Spills and Back-Siphoning
Agricultural chemicals spilled near wells or sinkholes can move into groundwater. Be careful to avoid spills when mixing and loading. To prevent back-siphoning from spray equipment into the well, keep the end of the fill hose above the water level in the spray tank at all times. Use an anti-backflow device when drawing mix water directly from a well or a pond. Inexpensive anti-backflow (back-siphoning prevention) devices for hoses that are used to fill farm sprayers can be purchased from irrigation or sprayer equipment suppliers. Such devices are required by law in some areas. Both private and commercial applicators should observe these precautions.

Prevent Backflow

Dispose of Wastes Properly
Improper disposal of empty containers, equipment rinse water or unused chemicals can cause localized groundwater problems. Dispose of all wastes in accordance with local, state and federal laws.
Triple-rinse or pressure-rinse your containers and pour the rinse water into the spray tank. If you have leftover product in your spray tank, dispose of it in a manner consistent with the product label. Avoid this situation in the first place by mixing only the quantity, you need. Newer application techniques involving chemical injection equipment and bulk handling procedures may further reduce the amounts of waste for disposal.
Do not drain rinse water from equipment near or into ditches, streams, ponds, lakes or other water sources. Rinse waters containing any quantity of certain pesticides are classified as hazardous wastes according to federal and state laws.
Under federal law, farmers may dispose of their own pesticide wastes on their own property in accordance with the product label. But consult the Kentucky Division of Waste Management, Natural Resources and Environmental Cabinet, for specific state requirements.

Use Integrated Pest Management
Integrated pest management ( IPM ) programs combine chemical use with many other production practices to manage pests in ways that are both economically and environmentally sound. These programs include such practices as crop rotation to avoid the build-up of pest populations and to maintain or improve soil conditions; the use of alternate pest control products and pest-resistant crop varieties; and careful pest monitoring to ensure that chemical methods are used only when needed.
You can get information about IPM programs from your local Cooperative Extension Service office.

Consider Surface Water
If there is more water on the soil than the soil can hold, the water (with chemicals in it) is likely to move downward to the groundwater. Prolonged heavy rain or excessive irrigation will produce excess surface water. Use weather forecasts and observations and irrigation scheduling to predict when excess surface water may be a problem.
Long-range weather forecasts predict the weather and probability of rain over a period of several days. Daily forecasts do an even better job of predicting the amount of rain to expect. Common sense observations also can be helpful. If your own knowledge of local weather signs causes you to suspect heavy rain, it would be prudent to delay the application of certain products to prevent wash-off or surface run-off.

Chemical, Soil and Geological Factors
Chemicals
Agricultural chemicals vary in their potential for moving to groundwater. Three major characteristics influence such movement:
•Solubility -- Chemicals vary greatly in water solubility; the greater the water solubility, the more potential for movement of the product to groundwater.
•Soil adsorption -- Some chemicals become tightly attached ("strongly adsorbed") to soil particles and do not move in the soil. Some are not so strongly adsorbed, and are more likely to move.
•Persistence -- Some chemicals break down quickly; "persistent" materials take a long time to break down. The more persistent ones are more likely to reach groundwater over a period of time.
You can get more information on product characteristics from your Cooperative Extension Service office or pesticide dealer.

Soil
Soil characteristics are also important in the movement of chemicals. Your local Soil Conservation Service can help you determine which types of soil are in your area.

Three major soil characteristics affect chemical movement:
•Soil texture is an indication of the relative proportions of sand, silt and clay in the soil. Pest control products tend to be adsorbed mostly on clay and organic matter. Coarse, sandy soils generally allow water to move rapidly downward and offer few opportunities for adsorption. Finer textured soils generally allow water to move at much slower rates, and they contain more silt and organic matter to which pesticides and other chemicals may be adsorbed. Most Kentucky soils are in or near the silt loam class, which has relatively high adsorptive capacities. Exceptions may be found near rivers where sandier soils may predominate.
•Soil permeability is a general measure of how fast water can move downward in a particular soil. The more permeable soils must be carefully managed to prevent any form of chemical from reaching groundwater.
•Soil organic matter influences how much water the soil can hold before movement occurs. Increasing organic matter will increase the water-holding capacity of the soil. Some pesticides may also be adsorbed onto organic matter.

Geology
Geology controls the occurrence and movement of groundwater and therefore has an important effect on groundwater quality. Different types of rocks have different magnitudes of permeability. ( Permeability is a measure of how fast water can move through a rock. )
Six physiographic regions occur in Kentucky (Fig. 2). These regions are based primarily on the type of rock units that underlie each area.

Figure 2

•The Ohio River Valley and Mississippi Embayment (Jackson Purchase) are composed of loose to semiconsolidated sediments ranging in size from gravel to sand, silt and clay. Because groundwater flows between the grains, these units are said to have intergranular permeability (Fig. 3 ). Recharge to these geologic units from rainfall or irrigation can bc rapid, thereby allowing for the easy downward movement of pollutants to the groundwater table.

Figure 3 and 4

•The Eastern and Western Coal Fields of Kentucky arc composed primarily of granular rocks such as sandstones, siltstones and shales. Because these units have been compacted into hard bedrock, permeability (and related groundwater movement) is less than in the semiconsolidated sediments of the Ohio River Valley and the Mississippi Embayment. Therefore, all other factors being equal, the potential for groundwater pollution is reduced.
•The Mississippian Plateaus and the Bluegrass regions arc underlain by limestone and dolomite. Although these rocks are very dense, they have a tendency to dissolve along fractures and other zones of weakness and form solution channels (Fig. 4). Development of sinkholes at the surface, connected by open solution channels beneath the surface of the ground, results in what is called a karst system. In some cases these solution channels have widened during vast amounts of geologic time to form cave and cavern systems such as Mammoth Cave. Because surface water is free to move directly into sinkholes and then rapidly through the underground solution openings, pollutants can easily contaminate the groundwater in karst systems.
Two additional factors are important concerning the potential pollution of groundwater. If groundwater occurs within a few feet of the soil surface, pollutants are more likely to reach it than if it is present at greater depths. Also, fractures such as faults or joints occasionally occur in the rocks and, like sinkholes, provide open pathways for entry of pollutants to the groundwater system, even if the groundwater is tens of feet beneath the land surface.
Kentucky is fortunate because hydrologic atlases, topographic maps and geological maps are available at the Kentucky Geological Survey for every part of the state. These maps point out many of the geologic features that affect our groundwater quality and provide useful information for protecting this valuable resource.

PUTTING IT ALL TOGETHER
 

IF...	THEN ...
you are mixing or applying agricultural chemicals near a well	do not dispose of leftover spray mix near a well; do prevent back-siphoning from sprayer tank; avoid spills or clean them up.
you are applying agricultural chemicals on sandy soil with low organic matter content or to a field where the groundwater is near the soil surface	be aware that a product with higher water solubility, longer persistence and low soil adsorption has a greater probability of reaching groundwater. Use the lowest effective rate recommended for this soil type. Use IPM practices whenever possible.
you are mixing or applying agricultural chemicals near sinkholes or areas draining directly into rivers or streams	remember that surface runoff or spills can wash directly into the sinkhole or the stream. Leave an adequate untreated barrier immediately surrounding the sinkhole or drainage area. Do not dispose of chemical products or waste materials in drainage areas near sinkholes, or near streams.
you need further information on soils, location of groundwater, or agricultural chemical products	consult your Cooperative Extension Service office, the Soil Conservation Service, or your farm service representative or dealer for advice.

Photographs:
National Agricultural Chemicals Association -- pages 4 (upper left), 5, 6, 8 and 11
The Pennsylvania State University -- page 7
University of Kentucky -- pages 3, 4 (lower left) and outside back cover

Illustrations:
National Agricultural Chemicals Association -- front cover, pages 3 ( top ) and 5
University of Kentucky -- pages 3, 9 and 10
Selected for use in Kentucky by M.P. Johnson, Department of Entomology.

Additional Extension educational materials available:
Videotapes:
Preventing Agricultural Groundwater Contamination in Kentucky -- 10-minute videotape (video number V5-AGR-0238 )

Publications:
Understanding the Water System, IP- 1
Nitrogen in Kentucky Soils: Sources-Reactions-Fertilization, AGR-4 3
Soil Testing: What It Is and What It Does, AGR-57
Nitrogen Fertilization of Wheat, AGR-87
Preparation of Surface-Mined Coal Spoils and Establishment of Vegetative Covering, AGR-89 Cropland Rotations for Kentucky, AGR-91
Controlling Soil Erosion With Agronomic Practices, AGR-96
Surface Water Management Systems, AGR-97
Strip Cropping and Contouring, AGR-98
Tillage and Crop Residue Management, AGR-99
No-Till Corn, AGR- 100
No-Till Soybeans, AGR- 101
Erosion -- Its Effect on Soil Properties, Productivity and Profit, AGR-102
Fertilization of Cool Season Grasses, AGR-103
Fertilization and Liming for Corn, AGR- 105
Land Application of Sewage Sludge, AGR- 120
Land Application of Sewage Sludge: A Worksheet, AGR-121
No-Till Small Grain Production, AGR- 113
Herbicide Persistence and Carryover in Kentucky, AGR- 139
Herbicides with Potential to Carry Over the Injure Rotational Crops in Kentucky, AGR-140
Managing Slowly Permeable Soils: For Tobacco and Corn Production in Kentucky, AGR-14 3
The Nature and Value of Residual Soil Fertility, AGR- 144
Water Supply Quality and Testing AEN-55
Certified Water Testing Laboratories, AEU-4
Drinking Water Analysis Costs, AEU-37
What is Your Farm's Potential to Pollute Your Drinking Water Supply, AEU-38
Drinking Water Standards, WQ-1
Health Effects of Drinking Water Contaminants, WQ-2
Water Testing and Interpretation:The Secondary Drinking Water Standards, WQ-3
Home Water Testing WQ-4
Drinking Water:Treatment Guidelines, WQ-5
Understanding Pesticide Labels and Labeling, ID- 100