20260227 15003500 1.0 TRUE 150000000 5000 FGDC DWEE Nitrate Hot Spot DWEE GIS Department of Water, Energy and Environment DWEE IT Section 245 Fallbrook Boulevard Lincoln Nebraska 68521 US (402) 471-2363 2026-03-03T00:00:00 DWEE GIS Department of Water, Energy and Environment DWEE IT Section 245 Fallbrook Boulevard Lincoln Nebraska 68521 US (402) 471-2363 DWEE GIS DWEE Nitrate This layer contains the results of a Getis Ord hot spot test run on nitrate sample data from the Nebraska groundwater quality clearinghouse. Sample data for 2003-2019 were included in the analysis. For wells where multiple samples were collected between 2003-2019, the median nitrate concentration was used for the test. Gi bin numbers correspond to hot or cold spots and associated confidence interval. Negative numbers are cold spots and positive are hot spots. Zero indicates an insignificant test result. One is significant with a 90% confidence interval, two is 95%, and three is 99%. Z-scores (the Gi Statistic) and P-values are associated with each result. <DIV STYLE="text-align:Left;"><DIV><DIV><P><SPAN>The layer was developed to identify outliers in the data and look for spatially significant hot spots in nitrate concentrations using a Getis-Ord Gi* test (Ord, 1995). This test identifies outliers in the dataset based on the concentration of nitrate and the spatial grouping of sample data. The test critical values and distance band are adjusted based on the results of multi-distance Global Moran’s I test, which helps alleviate the false discovery rate issue common in spatially correlated data. Analysis was performed using ArcGIS Professional (Version 3.1, ESRI, 2023). Figure 13 of the 2023-2024 NE Nitrate in Drinking Water Study shows the relative hot and cold spots for nitrate based on data from 2003-2019. These sample results are accessible from the Nebraska Groundwater Quality Clearinghouse. At wells sampled more than once during the study period, the median concentration was used. Red spots indicate statistically significant hot spots, and blue spots indicate statistically significant cold spots. A hot spot indicates both spatial clustering and high outlier concentrations. Because of the distribution of nitrate concentrations across Nebraska, the relative concentrations of hot and cold spots differ slightly across the state. This analysis shows areas of elevated nitrate concentrations are largely consistent with other studies of nitrate in Nebraska such as those conducted by Spalding (1993), McMahon (2007), and Exner et al. (2014). Land use in these areas is similar to contributing land use patterns identified in modeling efforts such as Wheeler et al. (2015) and Garcia (2017). The average concentration at a hot spot was 14.42 mg/L. The average concentration at a cold spot was 3.71 mg/L. The average for all data was 7.05 mg/L. Grey dots represent sample locations that are not identified as statistically significant hot or cold spots. Figures 14 and 15 in the 2023-2024 NE Nitrate in Drinking Water Study show the distribution of nitrate concentration at points identified as hot spots or cold spots. Table 7 of the same report summarizes the average sample concentration for hot or cold spots. It is important to note that this is not a health measure, and some of the cold spot nitrate concentrations are at wells that exceed the SDWA standard because of their location and concentration relative to the area around them. It is possible to be a statistically significant outlier on the low end, in an area where the overall distribution is higher concentrations, such as in the Bazile Groundwater Management Area.</SPAN></P><P><SPAN>For a complete description see: </SPAN><A href="https://dee.nebraska.gov:443/water/nitrate-drinking-water-study" STYLE="text-decoration:underline;"><SPAN STYLE="font-size:9pt">https://dee.nebraska.gov/water/nitrate-drinking-water-study</SPAN></A></P><P><SPAN /></P></DIV></DIV></DIV> Department of Water, Energy and Environment (DWEE), Nebraska groundwater quality clearinghouse 1 -104.158315 -95.217659 39.911014 43.07036 Bounding area that contains the data. 2026-03-03T00:00:00 20260306 DWEENitrateHotSopot dataset DWEE GIS Department of Water, Energy and Environment DWEE IT Section 245 Fallbrook Boulevard Lincoln Nebraska 68521 US (402) 471-2363 DWEE GIS 13143 Nitrate Hot Cold data developed during the NDEE nitrate study. Nitrate Hot Cold data developed during the NDEE nitrate study. 2026-03-03T00:00:00 DWEE Nitrate Hot Spot Nitrate Hot Cold values DWEE OBJECTID OBJECTID Internal feature number ESRI OID 4 10 0 ESRI object ID field NumberOfNeighbors NumberOfNeighbors Long 10 0 DWEE 0 Number of neighboring features used to calculate the statistic and associated probability. Ranges from 0 to 284. Numbers range from 0-284 HotOrCold HotOrCold Long 10 0 DWEE 0 A categorical variable representing different groups of points. For locations with a positive Gi* value and statistically significant P value, a positive 1, 2, or 3 is assigned to represent a hot spot at a 90, 95, and 99% cutoff point. Negative, statistically significant values are associated with cold spots. Ranges from -3 to 3. Numbers range from -3 to 3 GiStatistic GiStatistic Double 7 3 DWEE 0 The value of the Getis Ord Gi* statistic, which is equivalent to a Z-score. Very high values indicate a high degree of clustering and higher than average concentrations. Values derived from Getis Ord Gi* statistic GiProbability GiProbability Double 7 3 DWEE 0 The probability value for accepting the null hypothesis that the location is not a hot or cold spot. Low P values indicate a low chance that the cluster of wells and nitrate results are random. Values are unique to each point NitrateConcentrationPPM NitrateConcentrationPPM Double 7 2 DWEE 0 Median Nitrate Concentration in mg/L Values are median concentration SourceID SourceID Unique ID field. Long 10 0 DWEE 0 Unique ID field.