基于统计方法学的焦化类污染场地风险筛选决策研究
Risk Screening Decision of Coking Works Contaminated Land Based on the Statistical Methodology
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摘要: 利用统计方法学估算场地污染物平均浓度能更客观地反映实际污染程度,这对污染场地风险评估和管理决策具有重要意义. 该研究以某焦化场地中典型污染物——萘为例,分别依据英国CL:AIRE导则和美国ProUCL导则,基于统计方法学对场地土壤萘浓度进行描述性统计分析、数据审查、分布类型判断、真实平均浓度估算,并根据《土壤环境质量 建设用地土壤污染风险管控标准(试行)》(GB 36600—2018)第一类建设用地的筛选值对场地进行了初步风险评估. 结果表明:污染场地0~1 m土壤萘的真实平均浓度小于筛选值,但1~2和2~4 m土壤萘的真实平均浓度大于筛选值;在不同土壤深度上,萘的空间分布特征相似,以场地中心为主要污染源,向四周逐级扩散递减,因此需对场地开展详细风险评估. 此外,通过对比英美两国导则可知,美国ProUCL导则更加严格,利用Q-Q图示法和拟合优度检验法判断场地数据的分布类型,并基于数据分布特征计算相应的95%置信上限值估算污染物的真实平均浓度;而英国CL:AIRE导则相对简单,主要基于中心极限定理通过计算双侧置信区间估算污染物浓度,同时利用空间图判断污染物空间布局,有助于评估场地污染状况. 因此,我国风险评估方法应结合统计方法以降低风险评估结论的不确定性,对实现我国污染场地精细化风险评估具有重要意义.Abstract: 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.
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Key words:
- statistical methodology /
- contaminated land /
- true mean concentration /
- risk assessment
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