**7. The assessment on groundwater organic pollution**

#### **7.1. The methods of groundwater organic pollution assessment**

#### *7.1.1. The four steps of NAS*

The four steps of NAS was proposed by National Academy of Sciences, United States(NAS), was an assessment method on human health risk that led by the accident, air, water, soil and other medium. The method mainly in the following aspects: the hazard identification (quali‐ tative evaluation the degree of hazards of the chemical substances on the human health and ecological); dose-response assessment (quantitative assessment the toxicity of chemical sub‐ stances, established a relationship between the dose of chemical substances and the human health hazard); exposure assessment (quantitative or qualitative estimate or calculate the ex‐ posure, exposure frequency, exposure duration and exposure mode); exposure attribute (us‐ ing the data to estimate the strength of the health hazards in the different conditions or the probability of the certain health effects). This method can qualitative analysis or quantitative analysis of groundwater contamination, or combine them, the results could be quantify and analysis, and provide more detailed information to the decision-makers.

#### *7.1.2. The four steps of EPA*

In 1989, U.S. Environmental Protection Agency (EPA) promulgated the "risk assessment guidance for superfund: Human health evaluation manual", there was a similar assessment method to NAS method [22]. The steps following as data collection, exposure assessment, toxicity assessment, risk characterization. Contrast the two methods, NAS is more common methods, the use range wider, suitable for a variety of health risk assessment; the EPA meth‐ od is more specific, it emphasis on the various parameters of the collection of contaminated sites, for the evaluation of contaminated sites, it more operational.

dermal absorption. Ingestion includes drinking of fluids as well as using water for rinsing

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Determination of average exposure levels for a particular population is quite difficult. This is due to difficulties in acquiring sufficient water-quality data, in identifying the exposed in‐ dividuals, and in quantifying the concentrations in the different exposure pathways. For a given groundwater contamination problem, the U.S. Environmental Protection Agency stresses the importance of identifying both the currently affected population as well as pos‐ sible changes in future land use. Subpopulations that may be especially sensitive to expo‐

When attempting to estimate exposure to larger population entire countries, for example other concerns arise. Cothern [25] computed the average population exposure to volatile or‐ ganic compounds in the United States, based on data from several thousand ground- and surface-water supplies. National exposure was estimated as a straight extrapolation of the concentration intervals from the original data. Best- and worst-case assumptions were ap‐ plied for handling the "below detectable" category. Crouch *et al.* [26] applied an alternative approach to estimate population exposure levels. Rather than estimating a distribution for exposure, they made the worst-case assumption that individuals are exposed to water at the

According to the Risk Assessment Guidance for Superfund Volume I: Human Health Evalu‐ ation Manual (Part E, Supplemental Guidance for Dermal Risk Assessment) (U.S. EPA) [27], we calculation the dermal absorbed dose (DAD) and ingestion absorbed dose (IAD) [28].

´ ´ ´´ <sup>=</sup> ´ (5)

DAD *DA EV ED EF SA event BW AT*


),

and cooking of foods. Dermal absorption includes swimming and bathing.

sure should also be identified [24].

*7.2.2. Health risk calculations*

Where:

maximum measured concentration for their water supply.

DAD=Dermally Absorbed Dose (mg/kg-day),

SA=Skin surface area available for contact (cm2

DAevent=Absorbed dose per event (mg/cm2

EV=Event frequency (events/day),

ED=Exposure duration (years),

BW=Body weight (kg),

AT=Averaging time (days).

EF=Exposure frequency (days/year),

#### *7.1.3. The MMSOILS model*

The MMSOILS model is multi-media model which describe the groundwater, surface water, soil and air in the migration of chemicals, exposure and food chain accumulation [23]. Con‐ taminate sites is multi-phase, multi-media complex. The model including the migration and transformation of pollutants module and human exposure module. Migration and transfor‐ mation module include: (1)atmospheric transport pathway; (2)soil erosion; (3)groundwater migration pathway; (4)surface water pathway; (5)food chain bioaccumulation. Human expo‐ sure are: (1)adopt from drinking water, animals and plants and soil; (2)atmospheric volatiles and particulate inhalation; (3)soil, surface water and groundwater contact with skin. The model could be simulate a comprehensive migration pathway and widely used in foreign countries, and the parameters could be analysis the uncertainty.

#### *7.1.4. The DRASTIC method*

The DRASTIC method is a national standards system that developed by US EPA to evalua‐ tion aquifer vulnerability. It including: Depth to Water(D); Net Recharge(R); Aquifer me‐ dia(A); Soil Media(S); Topography(T); Impact of the Unsaturated Zone Media(I); Conductivity of Aquifer Hydraulic(C). Assignment of each element from 1 to 10, and them proportional to the degree of vulnerability of groundwater. At the same time, each element is assigned a weight, the weight should be reflect the sensitivity of groundwater. The model can objectively assess the groundwater vulnerability of different areas, and its assumption that all regions of the aquifer has a uniform trend. But all the geological, hydrogeological and other conditions are different, and the model calculations defect, the DRASTIC method has some limitations.

#### **7.2. Health–based risk assessment**

#### *7.2.1. Estimating population exposure levels*

An important step in health risk assessment is the quantification of actual human exposure. Exposure can be expressed as either the total quantity of a substance that comes in contact with the human system or the rate at which a quantity of material comes in contact with the human system (mass per time or mass per time per unit body weight. The exposure assess‐ ment evaluates the type and magnitude of exposures to chemicals of potential concern at a site. The exposure assessment considers the source from which a chemical is released to the environment, the pathways by which chemicals are transported through the environmental medium, and the routes by which individuals are exposed. Parameters necessary to quanti‐ tatively evaluate dermal exposures, such as permeability coefficients, soil absorption factors, body surface area exposed, and soil adherence factors are developed in the exposure assess‐ ment. Exposure to chemicals in water can occur via direct ingestion, inhalation of vapors, or dermal absorption. Ingestion includes drinking of fluids as well as using water for rinsing and cooking of foods. Dermal absorption includes swimming and bathing.

Determination of average exposure levels for a particular population is quite difficult. This is due to difficulties in acquiring sufficient water-quality data, in identifying the exposed in‐ dividuals, and in quantifying the concentrations in the different exposure pathways. For a given groundwater contamination problem, the U.S. Environmental Protection Agency stresses the importance of identifying both the currently affected population as well as pos‐ sible changes in future land use. Subpopulations that may be especially sensitive to expo‐ sure should also be identified [24].

When attempting to estimate exposure to larger population entire countries, for example other concerns arise. Cothern [25] computed the average population exposure to volatile or‐ ganic compounds in the United States, based on data from several thousand ground- and surface-water supplies. National exposure was estimated as a straight extrapolation of the concentration intervals from the original data. Best- and worst-case assumptions were ap‐ plied for handling the "below detectable" category. Crouch *et al.* [26] applied an alternative approach to estimate population exposure levels. Rather than estimating a distribution for exposure, they made the worst-case assumption that individuals are exposed to water at the maximum measured concentration for their water supply.

#### *7.2.2. Health risk calculations*

According to the Risk Assessment Guidance for Superfund Volume I: Human Health Evalu‐ ation Manual (Part E, Supplemental Guidance for Dermal Risk Assessment) (U.S. EPA) [27], we calculation the dermal absorbed dose (DAD) and ingestion absorbed dose (IAD) [28].

$$\text{DAD} = \frac{DA\_{event} \times EV \times ED \times EF \times SA}{BW \times AT} \tag{5}$$

Where:

od is more specific, it emphasis on the various parameters of the collection of contaminated

The MMSOILS model is multi-media model which describe the groundwater, surface water, soil and air in the migration of chemicals, exposure and food chain accumulation [23]. Con‐ taminate sites is multi-phase, multi-media complex. The model including the migration and transformation of pollutants module and human exposure module. Migration and transfor‐ mation module include: (1)atmospheric transport pathway; (2)soil erosion; (3)groundwater migration pathway; (4)surface water pathway; (5)food chain bioaccumulation. Human expo‐ sure are: (1)adopt from drinking water, animals and plants and soil; (2)atmospheric volatiles and particulate inhalation; (3)soil, surface water and groundwater contact with skin. The model could be simulate a comprehensive migration pathway and widely used in foreign

The DRASTIC method is a national standards system that developed by US EPA to evalua‐ tion aquifer vulnerability. It including: Depth to Water(D); Net Recharge(R); Aquifer me‐ dia(A); Soil Media(S); Topography(T); Impact of the Unsaturated Zone Media(I); Conductivity of Aquifer Hydraulic(C). Assignment of each element from 1 to 10, and them proportional to the degree of vulnerability of groundwater. At the same time, each element is assigned a weight, the weight should be reflect the sensitivity of groundwater. The model can objectively assess the groundwater vulnerability of different areas, and its assumption that all regions of the aquifer has a uniform trend. But all the geological, hydrogeological and other conditions are different, and the model calculations defect, the DRASTIC method

An important step in health risk assessment is the quantification of actual human exposure. Exposure can be expressed as either the total quantity of a substance that comes in contact with the human system or the rate at which a quantity of material comes in contact with the human system (mass per time or mass per time per unit body weight. The exposure assess‐ ment evaluates the type and magnitude of exposures to chemicals of potential concern at a site. The exposure assessment considers the source from which a chemical is released to the environment, the pathways by which chemicals are transported through the environmental medium, and the routes by which individuals are exposed. Parameters necessary to quanti‐ tatively evaluate dermal exposures, such as permeability coefficients, soil absorption factors, body surface area exposed, and soil adherence factors are developed in the exposure assess‐ ment. Exposure to chemicals in water can occur via direct ingestion, inhalation of vapors, or

sites, for the evaluation of contaminated sites, it more operational.

countries, and the parameters could be analysis the uncertainty.

*7.1.3. The MMSOILS model*

100 Organic Pollutants - Monitoring, Risk and Treatment

*7.1.4. The DRASTIC method*

has some limitations.

**7.2. Health–based risk assessment**

*7.2.1. Estimating population exposure levels*

DAD=Dermally Absorbed Dose (mg/kg-day),

DAevent=Absorbed dose per event (mg/cm2 -event),

SA=Skin surface area available for contact (cm2 ),

EV=Event frequency (events/day),

EF=Exposure frequency (days/year),

ED=Exposure duration (years),

BW=Body weight (kg),

AT=Averaging time (days).

$$\text{IAD} = \frac{\rho \times \text{UI} \times \text{EF} \times \text{ED}}{\text{BW} \times AT} \tag{6}$$

When calculating the risk of a variety of substances in a variety of ways, figure out all noncancer risk and cancer risk respectively, then add all risks together. Regardless of synergistic

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Groundwater treatment technologies are mainly as follows: pump and treat, air sparging,

Pump and treat is the most common form of groundwater remediation. It is often associated with treatment technologies such as Air Stripping and Liquid-phase Granular Activated

Pump and treat involves pumping out contaminated groundwater with the use of a submersi‐ ble or vacuum pump, and allowing the extracted groundwater to be purified by slowly pro‐ ceeding through a series of vessels that contain materials designed to adsorb the contaminants from the groundwater. For petroleum-contaminated sites this material is usually activated car‐ bon in granular form. Chemical reagents such as flocculants followed by sand filters may also be used to decrease the contamination of groundwater. Air stripping is a method that can be ef‐

For most biodegradable materials like BTEX, MTBE and most hydrocarbons, bioreactors can be used to clean the contaminated water to non-detectable levels. With fluidized bed bio‐ reactors it is possible to achieve very low discharge concentrations which will meet or ex‐

Depending on geology and soil type, pump and treat may be a good method to quickly re‐ duce high concentrations of pollutants. It is more difficult to reach sufficiently low concen‐ trations to satisfy remediation standards, due to the equilibrium of absorption (chemistry)/

At the figure 2, we can know how does pump and treat technology work. This system usual‐ ly consists of one or more wells equipped with pumps. When the pumps are turned on, they pull the polluted groundwater into the wells and up to the surface. At the surface, the water

Air sparging is an in situ groundwater remediation technology that involves the injection of a gas (usually air/oxygen) under pressure into a well installed into the saturated zone. Air sparg‐ ing technology extends the applicability of soil vapor extraction to saturated soils and ground‐ water through physical removal of volatilized groundwater contaminants and enhanced

goes into a holding tank and then on to a treatment system, where it is cleaned [29].

effect and antagonistic effect.

*8.1.1. Pump and treat technology*

Charcoal.

**8. The countermeasures and suggestions**

**8.1. The countermeasures for groundwater pollutions**

in-situ groundwater bioremediation and in-situ reactive walls.

fective for volatile pollutants such as BTEX compounds found in gasoline.

ceed discharge standards for most pollutants.

desorption processes in the soil.

*8.1.2. Air sparging [30]*

Where:

IAD= Ingestion absorbed dose (mg/kg-day),

ρ= Pollutant concentration in groundwater (mg/L),

U=Drinking amount per days (L/d),

EF=Exposure frequency (days/year),

ED=Exposure duration (years),

BW=Body weight (kg),

AT=Averaging time (days).

The DAD and IAD can be represent with continuous ingestion dose (CDI).

Based on the carcinogenesis of contamination, the risk could be classified into cancer risk and noncancer hazard.

**1.** Noncancer hazard: Generally, the reaction of the body to non-carcinogenic substance has a dose threshold.

Lower than the threshold, they could not affect our health adversely. The non-carcinogenic risk to represent with hazard index (HI). It is defined as a ratio that continuous ingestion dose with reference dose [28].

$$\text{RH} = \text{CDI} / \text{RfD} \tag{7}$$

Where: CDI= continuous ingestion dose (mg/kg-days), RfD= reference dose (mg/kg-days).

**2.** Cancer risk: There does not have dose threshold for the carcinogenic. Once it exist in environments, it will affect human health adversely. Cancer risk will be represent with risk. It is defined as a product of continuous ingestion dose with carcinogenesis slope factor.

$$\text{CDI} \times \text{SF} \tag{8}$$

$$1\text{--exp}(\text{-CDI}\times\text{SF})\tag{9}$$

(If the low dose exposure risk>0.01)

Where: SF= carcinogenesis slope factor (mg-1•kg•d)

When calculating the risk of a variety of substances in a variety of ways, figure out all noncancer risk and cancer risk respectively, then add all risks together. Regardless of synergistic effect and antagonistic effect.
