The estimation of the mean concentration of contaminant by statistical methods can reflect the actual pollution level of site more properly, which is of great significance for risk assessment and management decision of contaminated site. In this study, the typical naphthalene soil contamination from coking works contaminated land was evaluated by the descriptive statistics, data check, determination of data distribution and estimation of true mean contaminant concentration based on the statistical methodologies recommended by United Kingdom Contaminated Land: Application in Real Environments (UK CL:AIRE) and the United States Environmental Protection Agency (EPA). According to the Soil Environmental Quality Risk Control Standard for Soil Contamination of Development Land
(GB 36600-2018), the preliminary risk screening was undertaken using soil screening levels under the Category I Land Use Scenario. The results showed that the soil true mean concentration of naphthalene at depth 0-1 m was lower than the screening value, while that at depths 1-2 and 2-4 m was higher than the screening value. Additionally, the naphthalene concentrations at different depths were similar in the spatial pattern where naphthalene spreads from the center to the edge of the contaminated site, thus warranting a detailed risk assessment. In addition, it become apparent by comparing the UK and US statistical methods that the US guidance is more rigorous in which the quantile-quantile (Q-Q) plot and the goodness-of-fit test were performed to identify the distribution of data sets, and the 95% upper confidence limits (UCL95) were used to estimate the true mean naphthalene concentration on the basis of the data distribution. However, statistical guidance recommended by the UK is relatively simple, in which the mean concentration of a contaminant was estimated by the two-way confidence interval based on the Central Limit Theorem (CLT). Furthermore, the UK statistical guidance provides the contaminant spatial distribution by the spatial plot, which was more conducive to estimate the true mean concentration of the contaminant. Therefore, the application of statistical methods in the risk assessment is essential to minimize the uncertainty of results, which is crucial for realizing the refined risk assessment of contaminated land in China.