en Environmental Health, Sciences, and Engineering Environmental Health, Sciences, and Engineering پژوهشي Original Article <p style="text-align: justify;"><span style="font-size:14px;"><span style="font-family: times new roman;"><strong>Background:</strong> This research aims to measure and study spatial changes, and the reason behind the increasing nitrate content in water wells in the Central District of Khodabandeh County in the Zanjan Province.<br> <strong>Methods: </strong>The nitrate and nitrite content, electrical conductivity, dissolved oxygen, temperature, total hardness and pH were measured at 40 sampling stations in the study area. The obtained features were categorized into four classes by principal component analysis. The kriging and cokriging methods along with electrical conductivity and total hardness covariates were used to study the spatial changes. By using the cross-validation method, the linear model for cokriging method with electrical conductivity covariate was selected as the best model for nitrate zoning in ArcGIS 10.2 software.<br> <strong>Results:</strong> The principal component analysis indicated that nitrate feature was in the same classification as that of electrical conductivity and total hardness. The comparison of surface digital elevation model, geology and land use maps with nitrate zoning indicated that nitrate pollution in the south and south-west regions was due to geological content, agricultural activities, and the discharge of human sewage into absorbing wells.<br> <strong>Conclusion: </strong>The findings of the present research revealed that lowlands with agricultural use had more nitrate content than other uses, and the most important reason could be attributed to the excessive use of nitrate containing chemical fertilizers.</span></span><br> &nbsp;</p> Nitrate, Geostatistics, Kriging, Cokriging, Khodabandeh 13 20 http://jhehp.zums.ac.ir/browse.php?a_code=A-10-140-1&slc_lang=en&sid=1 Younes Khosravi khosravi@znu.ac.ir 10031947532846009507 10031947532846009507 Yes Department of Environmental Science, Faculty of Science, University of Zanjan, Zanjan, Iran. Abbas Ali Zamani zamani@znu.ac.ir 10031947532846009508 10031947532846009508 No Department of Environmental Science, Faculty of Science, University of Zanjan, Zanjan, Iran. Abdol Hossein Parizanganeh h_zanganeh@znu.ac.ir 10031947532846009509 10031947532846009509 No Department of Environmental Science, Faculty of Science, University of Zanjan, Zanjan, Iran. Mir Ali Asghar Mokhtari amokhtari@znu.ac.ir 10031947532846009510 10031947532846009510 No Department of Geology, Faculty of Science, University of Zanjan, Zanjan, Iran. Akbar Nadi Ak_nadi@znu.ac.ir 10031947532846009511 10031947532846009511 No Department of Environmental Science, Faculty of Science, University of Zanjan, Zanjan, Iran.