An optimized sampling model in the survey of groundwater resource nitrate content of rural areas in the Shandong province

Based on the survey result of the nitrate content of the groundwater samples, this paper studies the variability of nitrate content of the groundwater in the Shandong province by using an optimised sampling model. Meanwhile, it also calculates the sample size required by the survey based on precision (relative error) and guarantying degree of probability. The calculation indicates that the coefficient of variation of nitrate content of groundwater in the Shandong province is 1.12, with the set survey relative error of 10%, confidence probability of 95%, and 482 required survey samples. By using pseudo-random numbers, the residential areas are selected from county level units as the survey sites, and the groundwater sources of the residential sites of villages and townships are taken as the survey targets. The first-order spatial distribution test on the residential sites is conducted by using the nearest neighbor index method, to analyse the spatial relation between the nearest neighbor sites. For the sampling sites which accord with the first-order spatial distribution, the multiple order spatial distribution test is conducted by using Ripley's function, so as to meet the requirement of spatial random distribution of sample sites.