Changes of underground water quality in the Forest Wasterwater Treatment Plant in the Ilawa Forest District

in the seventies of the 20th century conception of agricultural utilization of wastewater from organic production was adapted for forest conditions. Positive results of initial examinations determined application of this method in bigger scale and building in 1984 Forest Wastewater Treatment Plant at Potato Processing Plant "ILAWA" in Ilawa. Results of two years (2001 and 2006) investigation on quality of underground water on the forestry area, which is irrigated by sewage waters from the Potato Industry Plant Ilawa, are presented in the paper. Area of irrigated object covers 216 ha of forest and is located in the Ilawa Forest District. A network of observation wells was established for estimation of the underground waters quality in the irrigated area and in its vicinity. A comparison of results from 2001 with 2006 showed that concentration of magnesium, potassium, calcium and nitrate in few wells increased. It has been stated that a concentration of nitrate was particularly height, even over 100 mg dm(-3).