itation in a calcareous soil irrigated with high fluoride water. Soil

Lysimeters filled with Freedom silt loam soil (fine-silty, mixed, mesic, Xerollic Calciorthids) were irrigated with geothermal well water from south central Idaho. The water contained 7 mg F/L. Alfalfa (Medicago swim L.) was grown in the lysimeters and the water was applied at a rate to give either a 0.30 or 0.15 leaching fraction. After irrigating the 1.0 m deep soil samples for 600 d, over 98 % of the added F remained in the soil. Soil extract and lysimeter leachate analysis showed that fluorite precipitation was occurring in the upper profile, but only after another fluoride adsorption mech-anism was saturated and the fluoride and calcium ion activities ex-ceeded the CaF2 ion activity product. The F concentration in the upper profile extracts exceeded 20 mg F/L and with the additional high F water irrigation, the soluble F would be expected to leach deeper in the soil. Under field conditions the F would be expected to eventually move into the groundwater with continued irrigation with high F water. Additional Index Words: ground water contamination, water pol-lution, fluoride adsorption, leaching, water soluble fluoride