| The North China Plain has been suffering from the water shortage for many years. In this area, groundwater is the main source for water supply. With the development of society and economy, impacts of human activities on the evolution of groundwater are becoming more and more significant. Releasing of hazardous substances into environment, to a great extent, endangers the groundwater quality. This problem is more pronounced in the place where groundwater is used as the only drinking water source in the North China Plain. Since the late 1970s, many studies have been carried out on the inorganic hydrogeochemical aspects of groundwater in this region and great achievements have been made. However, to date, there is no investigation on groundwater organic contamination that has been systematically done in a regional scale. Little information is available on organic contamination of groundwater using as water supply source. Since most of the organic compounds detected in the groundwater are toxic and carcinogenic, there is a need to systematically assess the groundwater quality and its suitability for drinking in the North China Plain. Therefore, it is of great significance to acquire knowledge on the current condition of groundwater quality and contamination, to access the groundwater quality and its suitability by proper methods, and to predict the leachability of target organic compounds detected in groundwater.The objectives of this work are (1) to select simple and feasible methods or modify the existing methods for groundwater quality and drinking suitability evaluation; (2) to investigate the organic contamination of groundwater, based on the available data to classify the main classes of organic contaminants and briefly discuss the contamination source and their possible relationship with typical inorganic components (e.g., total hardness) in groundwater; and (3) according to the physical and chemical properties of organic compounds, to predict their leachability from soil s and sediments by suitable model, in order to provide scientific evidence for further risk assessment.As a part the project Investigation of Groundwater Organic Contamination in the North China Plain, the author has availability of data for the huge region from collaborating institutions. In the field, the water samples were collected according to the standard sampling procedure issued by China Geological Survey and the relating information about the sampling sites were careful investigated. Based on the analytical data from the nationally qualified laboratories and available hydrogeological data, GIS mapping, multivariate statistics and modeling approaches were applied for data processing. The main works carried out are described as follows:1. Groundwater quality assessmentAccording to the analyzed results of the water samples, the groundwater quality was assessed by single index method and comprehensive assessing method (i.e., Nemerow index). In order to make the assessment results to be easily interpreted in a practical sense and closely relate to the drinking water standards, in this work, the criteria of Nemerow index classification were adjusted. The assessed results indicated that the groundwater quality in the North China Plain is controlled by the inorganic items, such as total hardness, total dissolved solids (TDS), fluoride, and nitrate. The organic compounds including benzo[a]pyrene, volatile phenols, and carbon tetrachloride determine the quality assessment results of 4% water samples due to their high concentrations.2. Assessment of suitability of water for drinkingAccording to the actual hydrogeological and economic condition, and the toxicity (e.g., carcinogenicity) of investigated compounds, a more feasible method to assess the suitability of water (including groundwater and surface water) for drinking purpose was put forward. By using this method, the suitability of waters for drinking were evaluated. The results showed that 60.8% of waters are suitable for drinking purpose. Among these, 18.4% waters have certain compound concentrations classified as Class IV, which does not meet the national standard for drinking water. However, these compounds are not quite harmful to human health at this concentration range. A few waters (4.9% of the total samples) need to be simply treated to meet the quality requirement for drinking due to the high concentration of some compounds, even they do not have high risk to human health.Analyzed results of 84 samples indicated that necessary treatments are necessary if they are used for drink. Most of these waters have relative high fluoride concentrations. The available hydrogeological data implies that the high fluoride content is mainly caused by the natural geological conditions. This is also the reason for the high content of iron and manganese in some groundwater. Among the samples of this class, there are 22 samples with high content of arsenic, lead, benzo[a]pyrene, and carbon tetrachloride. Because these compounds are considered carcinogenic, further sampling and monitoring work should be carefully conducted for the waters with high concentration of these compounds. Based on the detail information on the origin of these hazardous substances, necessary measures should be taken.3. Assessment of groundwater organic contaminationThirty-eight organic compounds were chosen as target items for testing in the lab for totally 245 samples, in which there are three surface water samples. The analyzed data indicated that there were organic contaminants detected in 93 samples. Among the target compounds, chloroethylene, 1,1-dichloroethylene, dichloromethane, 1,2-dichloroethylene, 1,1,1 -Trichloroethane, and hexachlorobenzene were not detected in all the water samples. The maximum number of compounds detected in one site is 11. The organic compounds with a detection frequency (ratio of number of samples with organic compound(s) detected to the total number of samples) higher than 4.5% include trichloromethane, toluene, tetrachloroethlyene, benzo[a]pyrene, chlorobenzene, benzene, and 1,2-dichlorobenzene. According to the standards of groundwater quality (China Geological Survey, 2007), the concentrations of carbon tetrachloride, benzo[a]pyrene, and volatile phenols were higher that that for class III, which corresponds to the drinking water standards. It should be noted that there were organic contaminants detected in some deep groundwater samples. This suggests that further monitoring work should be carried out for these sites.From the statistic results in the large region, it can be easily found that the groundwater organic contamination is relatively more pronounced in the urban areas. There is a close relationship between the extent of groundwater organic contamination and the increase of total hardness in groundwater.4. Classification of leachability of target organic compounds and the relationship between their leachability and detection frequencyIn order to prevent organic contamination of groundwater, to predict the environmental fate of organic contaminants from their quantitative structure is a useful method. This is especially helpful under the condition that there is not enough data or it is difficult to take measurement. In this study, the leachability of 91 target organic contaminants (among them, 58 compounds are China Priority Organic Pollutants) was studied by groundwater ubiquity score (GUS). The half life (DT50) and organic carbon sorption coefficient (Koc) of the chemicals were calculated by the US EPA software EPI Suite (V3.20). The results showed that there is a close relationship between GUS and Koc of the investigated chemicals and their leachability is mainly controlled by Koc. There was no direct relationship of GUS with octanol -water distribution coefficient (Kow) and solubility (S) of the chemicals. The statistic results showed that there is a relatively close relationship between the leachability of organic compounds and their detection frequency in groundwater in the North China Plain.
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