Em4885 irrigation management practices to protect ground water

These steps will now be briefly discussed.
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CHAPTER 5
Determination of current or future water quality problems
The question is whether current assessments of surface and ground water quality indicate
that contamination has occurred. Indications from casual observations of surface waters
include algal blooms, floating dead fish, heavy sedimentation, and odors. Water wells
should be periodically tested for contamination, especially if it is likely that the aquifer
would serve as a drinking water supply. The Washington State Water Quality Guide
contains sections on assessing potential contamination of surface and ground water from
leaching and runoff of nutrients and chemicals.
There are three main areas of interest when assessing the potential for problems:
1. Chemical/Nutrient Properties - determine the potential for adsorptivity, that is, will
the chemical attach itself to soil particles readily? How fast will the chemical
degrade? Is the chemical/nutrient highly soluble? Are the forms used volatile?
2. Soil Characteristics - The main factors are:
a. texture - governs area available for adsorption as well as water holding
capacity and permeability.
b. organic matter - more organic matter means more area for adsorption.
c. structure - governs permeability and may indicate erosiveness.
3. Site conditions - climate (particularly wind and rain patterns),
depth to ground water
A combination of a coarse-textured soil, overlaying a shallow aquifer, used for intensive
irrigated agriculture would likely indicate that extraordinary precautions are required.
On the other hand, a flatly sloped, heavier-textured soil, with good structure, overlaying
no aquifer, might not require anything more than normal management.
Identification of problem contaminants
If soils are erosive this might indicate that phosphorus moving with sediments, and the
sediments themselves, could be a problem. If the soil is coarse-textured and overlays a
shallow aquifer, leaching of nitrates or other chemicals may be a concern. Certain
chemicals with high persistence, adsorption, or solubility are candidate contaminants.
Water quality tests should indicate which chemicals or nutrients are a current problem.
Note that tests do not have to indicate a chemical or nutrient to be over the limit before
a water quality program is initiated. Tests that show chemical levels approaching legal
limits should be taken as early warnings. Note that WAC 173-200 provides for the
establishment of “early warning values” for ground water quality. If the results of a
water quality test exceed the value it must be reported to the Department of Ecology.