**3. Types of groundwater organic contamination**

Different types of groundwater contamination sources can pose different threats to human health and different problems in health risk assessment (table 1).

#### **3.1. Volatile organic compounds (VOCs)**

**Figure 1.** Diagram of the Groundwater Pollution [1].

88 Organic Pollutants - Monitoring, Risk and Treatment

Chloroform, tetrachloroethylene and so on [3].

**2. A review of organic compounds in groundwater**

Many studies have been conducted since 1970 to characterize concentrations of organic com‐ pounds in groundwater. In 1977, 16 drinking water wells have been closed in Gray town of Maine state because of there were at least 8 synthetic organics that were detected in drinking water wells. And in 1986, there were at least 33 organics that were detected in drinking wa‐ ter wells in USA [2]. It has been reported trace organic pollutants to be detected in all of 50 states. The U.S. Geological Survey(USGS) collected and assorted the test data the 1926 drink‐ ing water wells in the nation's rural areas from 1986 to 1999. And at least one VOCs were detected from 232 wells and the positive rate was 12%, with the highest positive rate were

Similar conditions are to be found in other countries. In the 80s of last century, based on an inventory of the presence of halogenated substances in raw water of 232 groundwater pumping stations in The Netherlands a compilation of more than 100 organic substances identified in contaminated groundwater, the detection rate of trichloroethylene up to 67% [4]. The organic pollutants could be detected in groundwater in Britain. Flordward studied on 209 water supply wells in Britain shown that the main pollutant in the groundwater are the trichloroethylene and tetrachloroethylene. Beginning in 1974, Environment Agency of Japan conducted a nationwide comprehensive survey of chemical environmental safety. The trichloroethylene in groundwater was reported for the first time. The European Union is the largest pesticide consumer in the world, more than 600 pesticides were applied. Six of the top 10 were European countries in the pesticide application. Atrazine exists in groundwater Volatile organic compounds (VOCs) are organic compounds with chemical and physical properties that allow the compounds to move freely between water and air. VOCs have been used extensively in industry, commerce, and households in the United States since the 1940's. Many products contain VOCs including fuels, solvents, paints, glues, adhesives, deo‐ dorizers, refrigerants, and fumigants. In general, these compounds have low molecular weights, high vapor pressures, and low-to-medium water solubilities [8]. Many of these compounds show evidence of animal or human carcinogenicity, mutagenicity, or teratoge‐ nicity. And these compounds are quite persistent in groundwater, because of their relatively low biological and chemical reactivity. This persistence is assisted by low temperatures, ab‐ sence of light and contact with the atmosphere, and comparatively low microbial concentra‐ tions typical of groundwater environments. By comparison with other organic compounds, VOCs may be transported for relatively long distances in groundwater, as a result of their relatively weak sorption affinity and their resistance to degradation. Because of humanhealth concerns, many VOCs have been the focus of national regulations, monitoring, and research during the past 10 to 20 years.

#### **3.2. The pesticides**

Pesticides consist of a large group of chemicals that are used in agriculture and residential settings to control plant and animal infestation. Pesticides are commonly applied on farms, fruit orchards, golf courses, and residential lawns and gardens. There are several different types of pesticides: Herbicides, Insecticides, Nematocides, Fungicides. Some pesticides do not break down easily in water and can remain in the groundwater for a long period of time. Likewise, the insecticide DDT, though banned for nearly twenty years, can still be found at trace levels in some groundwater. After prolonged exposure to high doses, some pesticides can cause cancer; some can also result in birth defects and damage to the nervous system. The use of pesticides and herbicides is one of the main ways of organic pollution of ground‐ water. Many water wells and irrigation wells have been closed for the byproducts from pes‐ ticides and herbicides be detected in shallow water in Colorado.

22\* Trichlorofluoromethane 75-69-4 VOCs 22 Bentazon 25057-89-0 Pesticides 24 Atrazine 1912-24-9 Pesticides 25 Picloram 1918-2-1 Pesticides 26 Diuron 330-54-1 Pesticides 27\* Benzene 71-43-2 VOCs 27\* Tetrachloromethane 56-23-5 VOCs 29 Chlorobenzene 108-90-7 VOCs 30\* 2-Butanone 78-93-3 VOCs 30 Acetone 67-64-1 VOCs 32\* m- + p-Xylene 106-42-3 VOCs 32\* trans-1,2-Dichloro- ethylen 156-60-5 VOCs 32\* 1,2-Dibromoethane 106-93-4 VOCs 35 Ethylbenzene 100-41-4 VOCs 36 caffeine 58-08-2 Medicine 37 Isopropylbenzene 98-82-8 VOCs 38 o-Xylene 95-47-6 VOCs 38\* 1,1,2-Trichloroethane 79-00-5 VOCs 38\* Bromodichloromethane 75-27-4 VOCs 38\* 1,1,1,2-Tetrachloroethane 630-20-6 VOCs 38\* n-Propylbenzene 103-65-1 VOCs 43 Chloromethane 74-87-3 VOCs 44 1,1,2-Trichloro-1,2,2-trifluoroethane 76-13-1 VOCs 45 Dichlorodifluoromethane 75-71-8 VOCs 46 Metolachlor 51218-45-2 Pesticides 46\* Simazine 122-34-9 Pesticides 48 Bromoform 75-25-2 VOCs 48\* Imidacloprid 138261-41-3 Pesticides 48\* 1,3,5-Trimethylbenzene 108-67-8 VOCs

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\*show the same detection with the front component. CASRN is the register number of chemical substances formulate

by Chemical Abstracts Service, m means meta-position, p means para-position.

**Table 1.** 50 organic pollutants most commonly detected in groundwater [11]


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\*show the same detection with the front component. CASRN is the register number of chemical substances formulate by Chemical Abstracts Service, m means meta-position, p means para-position.

**Table 1.** 50 organic pollutants most commonly detected in groundwater [11]

**3.2. The pesticides**

90 Organic Pollutants - Monitoring, Risk and Treatment

Pesticides consist of a large group of chemicals that are used in agriculture and residential settings to control plant and animal infestation. Pesticides are commonly applied on farms, fruit orchards, golf courses, and residential lawns and gardens. There are several different types of pesticides: Herbicides, Insecticides, Nematocides, Fungicides. Some pesticides do not break down easily in water and can remain in the groundwater for a long period of time. Likewise, the insecticide DDT, though banned for nearly twenty years, can still be found at trace levels in some groundwater. After prolonged exposure to high doses, some pesticides can cause cancer; some can also result in birth defects and damage to the nervous system. The use of pesticides and herbicides is one of the main ways of organic pollution of ground‐ water. Many water wells and irrigation wells have been closed for the byproducts from pes‐

**Ordering Component CASRN Types** Trichloromethane 67-66-3 VOCs Tetrachloroethylene 127-18-4 VOCs 1,1,1-Trichloroethane 71-55-6 VOCs Trichloroethylene 79-01-6 VOCs 1,1-Dichloroethene 75-35-4 VOCs Methyl tert-butyl ether 1634-04-4 VOCs 6\* cis-1,2-Dichloroethylene 156-59-2 VOCs 1, 2, 4-Trimethylbenzene 95-63-6 VOCs Toluene 108-88-3 VOCs Prometon 1610-18-0 Pesticides 1,1-Dichloroethane 75-34-3 VOCs Bromacil 314-40-9 Pesticides Tebuthiuron 34014-18-1 Pesticides 1, 3-Dichlorobenzene 541-73-1 VOCs 1,2-Dichloropropane 78-87-5 VOCs Carbon disulfide 75-15-0 VOCs Deethylatrazine 6190-65-4 Pesticides 17\* 1,4-Dichlorobenzene 106-46-7 VOCs Sulfamethoxazole 723-46-6 Medicine 20\* 1,2-Dichlorobenzene 95-50-1 VOCs 2-Hydroxyatrazine 2163-68-0 Pesticides

ticides and herbicides be detected in shallow water in Colorado.

#### **3.3. The other organic contamination**

Tens of thousands of manmade chemicals are used in today's society with all having the po‐ tential to enter our water resources. There are a variety of pathways by which these organic contaminants can make their way into the aquatic environment [9]. If the groundwater is the drinking water sources, there will be potentially dangerous on human health. Pharmaceuti‐ cals and other organic contaminants are a set of compounds that are receiving an increasing amount of public and scientific attention. Water samples were collected from a network of 47 groundwater sites across 18 states in 2000 [10]. All samples collected were analyzed for 65 organic contaminants representing a wide variety of uses and origins. Thus, sites sampled were not necessarily used as a source of drinking water but provide a variety of geohydro‐ logic environments with potential sources of organic contaminants. organic contaminants were detected in 81% of the sites sampled, with 35 of the 65 organic contaminants being found at least once. The most frequently detected compounds include N,N-diethyltolua‐ mide (35%, insect repellant), bisphenol A (30%, plasticizer), tri(2-chloroethyl) phosphate (30%, fire retardant), sulfamethoxazole (23%, veterinary and human antibiotic), and 4-octyl‐ phenol monoethoxylate (19%, detergent metabolite).

*4.2.1. City and industrial wastewater*

as infiltration ponds.

leaching into groundwater.

must eventually be disposed of, often by land application.

*4.2.2. Land disposal of municipal and industrial waste*

The treatment and disposal of sewage present health risks in both developed and undevel‐ oped countries. In undeveloped countries, sewage may be directly applied to the land sur‐ face. In more developed areas, sewage is generally transported to municipal treatment plants or disposed of in septic tanks and cesspools. Groundwater contamination can result in all these cases. Sewage provides a source of pathogens, nitrates, and a variety of organic chemicals to groundwater. Land application of sewage can provide a direct contaminant source via infiltration. Treatment plants can act as contaminant sources in several ways. Leaks may occur in sewer lines and infiltration may occur from the ponds and lagoons with‐ in the treatment plants. In addition, the sewage sludge that is a product of sewage treatment processes is often disposed on land in conjunction with agricultural activity. Depending on the characteristics of the sludge, the soil characteristics, and the application process, such land application can act as a large non-point source of groundwater contamination. Land disposal of treated waste water can pose comparable risks. Depending on hydrogeologic conditions, septic tanks and cesspools may allow untreated sewage to enter the groundwa‐ ter flow system. In addition, use of solvents to clean out the systems can cause groundwater contamination by synthetic organic compounds. The material cleaned out from septic tanks

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Industrial Wastewaters are applied to land in ponds or lagoons that are either designed to percolate the liquid into the soil or to store and/or evaporate the liquid above ground. In ei‐ ther case, such facilities act as potential groundwater contamination sources. Facilities de‐ signed to intentionally infiltrate into the ground include cooling ponds for power generation and for other industrial processes. The liquids in such facilities may contain potentially haz‐ ardous materials. Storage and evaporation ponds are often lined to prevent infiltration, but are likely to act as groundwater contamination sources under some circumstances, depend‐ ing on surface runoff characteristics, the integrity and permeable of the liner(s), and the groundwater flow system. Poorly designed evaporation ponds may, in many cases, function

In the United States, the big city and small town are commonly found in contaminated groundwater. An test on 39 groundwater supply in small towns conducted by the U.S. EPA,

Land disposal of solid waste is the groundwater contamination source of most current con‐ cern to the general public in many developed countries and of most current regulatory interest.

Solid waste can be disposed in landfills, facilities engineered to safely contain the waste. While landfills may often prevent exposure of solid waste at the land surface, many landfills provide a direct connection with groundwater. In the past, landfill siting was based on the availability of inexpensive, undeveloped land requiring little modification for waste dispos‐ al, rather than on hydrogeologic suitability. Disposed materials often are very susceptible to

it reported that 11 VOCs could be detected in treated or untreated groundwater [12].
