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Practitioner's Tool / Seasonally High Groundwater

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===Groundwater for Site Evaluation===

[[File:Groundwater 01.png|right|200px]]

The depth of groundwater is very important when considering sites for on-site effluent leaching. If groundwater is too high, it may result in a direct conduit between the leaching trenches and drinking water supplies. Additionally, high groundwater conditions require special construction techniques when installing tanks and pipelines.

The depth to groundwater can be established by monitoring wells in the area by probing and measuring to the static water depth. Drinking water wells, however, are often excavated more deeply to obtain water of higher quality. For these wells, water-bearing soils (aquifers) in the upper reaches of the soils (perched aquifers) are sealed off to protect the quality of deeper supplies; therefore, evaluation of drinking water wells may not give the entire picture of groundwater at the site you are evaluating.

~~[[File:Groundwater 01.png|right|200px]]~~

Evaluating the soils can also give clues as to the depth of groundwater. The primary clue is the presence of mottles, or areas of soils discoloration, as shown in the image to the right. This condition is primarily caused by the deposits of metal ions left on the soil while in saturated conditions. Technically, these mottles are known as redoximorphic (redox) features—features caused by the reduction and oxidation of chemical compounds while saturated. While the chemistry may be complex, the signs are easy to see. Look for the highest elevation of redox features in the soil profile to determine the limit of seasonally high groundwater.

Winona

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