PART I Evaluation of groundwater screening values for volatile contaminants among different countries

Transcription

1 PART I Evaluation of groundwater screening values for volatile contaminants among different countries Part of: THE USE OF VAPOUR INTRUSION MODELS TO EVALUATE GROUNDWATER SCREENING VALUES FOR VOLATILE CONTAMINANTS Upendo Syikilili Msc Thesis In Environmental Sciences March 2012 Supervised by: André van Amstel Frank Swartjes Environmental Systems Analysis

2 THE USE OF VAPOUR INTRUSION MODELS TO EVALUATE GROUNDWATER SCREENING VALUES FOR VOLATILE CONTAMINANTS Upendo Syikilili Msc Thesis In Environmental Sciences March 2012 No part of this thesis may be reproduced without contacting the Environmental Sysytem Analysis Group Supervisors: Examiners: 1. Drs. Andre van Amstel 1. Andrѐ van Amstel Wageningen University 2. Prof. Rik Leemans Environmental System Analysis Group (ESA) P.O. BOX AA Wageningen 2. Dr. Frank A. Swartjes National Institute for Public Health and the Environment (RIVM) Laboratory for Ecological Risk Assessment A. Van Leeuwenhoeklaan MA Bilthoven 2

3 CONTENTS PART ONE... 5 Evaluation of groundwater screening values for volatile contaminants among different countries INTRODUCTION TO THE PROBLEM Scope Statement of the problem Research questions METHODOLOGY Data collection Data analysis Limitations RESULTS AND DISCUSSION Overview of groundwater screening values Application scale for the groundwater screening values Differences in groundwater screening values based on purpose of applications Differences in groundwater screening values applied for negligible risks (target values) Differences in groundwater screening values applied for further investigation Differences in groundwater screening values applied for remedial actions Differences in groundwater screening values based on protection targets Groundwater screening values based on human health and ecosystem target (for remedial values) Groundwater screening values based on human health and ecosystem target (for further investigation) Derivation methods Level of protection Exposure pathway considered in deriving groundwater screening values Toxic data used for derivation of groundwater screening values Models and equations used for derivation of groundwater screening values Discussion CONCLUSION AND RECOMMENDATIONS Conclusion Recommendations APPENDIX

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5 PART ONE Evaluation of groundwater screening values for volatile contaminants among different countries 5

6 2. INTRODUCTION TO THE PROBLEM 2.1. Scope Groundwater screening values are also known by different terms such as trigger values, target values, intervention values, clean up values guideline values, and threshold values (Carlon, 2007). These values are established or adopted by many industrialized countries so as to regulate and manage land and groundwater contamination (Fishwick, 2004; European Commission, 2007). Groundwater screening values provide guidance upon which the quality of groundwater is judged safe, when risks are negligible to human and environment; or judged seriously contaminated, when the risks are unacceptable, and hence remediation actions are required; or judged slightly contaminated, thus further investigation is necessary. Most of groundwater screening values are on the one hand, developed on the basis of the guidelines that protect human health and environments provided by international organizations, for example, the World Health Organization and Water Framework Directive. On the other hand, are developed on the basis of local conditions such as geographical, cultural and political conditions. The differences in local conditions make the variability in groundwater screening inevitable. Therefore, some countries establish more stringent values than others (Wcisło & Krzyżak, 2011). The differences in groundwater screening values have a significant impact on the economy, as it has been explained in section Many various studies have been made on assessment of soil screening values. From the literature review it is indicated that derivation methods (in terms of algorithm and input parameters values), geographical aspects (soil properties, building), political aspects (purpose of application, toxicological reference), and cultural differences cause disparities in numerical values of soil screening values among different countries (Carlon et al., 2007; Provoost et al., 2008a; Cavanagh, 2006). The study of Provoost et al., (2008a) points out that derivation methods and political aspects are the most important cause of the disparity. However, it is not known if this could be also the case for the groundwater screening values. 6

7 2.2. Statement of the problem Groundwater screening values have not been studied as much as soil screening values. As a result, little is known about the differences in groundwater screening values and the reasons for the differences among countries. Therefore, it is imperative to gain an understanding on the extent of variability in groundwater screening values among countries and the technical reasons responsible for the disparity. This understanding is very important for the experts of risk assessments as well as decision makers on human health and environmental matters Research questions Research questions were formulated on the basis of the objectives of the study. As it is presented section 1.2, the specific objectives for this part of the study were to identify the differences in groundwater screening for the volatile contaminants and figure out the technical reasons responsible for the disparities among countries. Based on these objectives the following research questions were formulated: 1. To what extent do groundwater screening values differ among countries? 2. What are the technical reasons for the variation in groundwater values? 7

8 3. METHODOLOGY 3.1. Data collection The data was collected through a questionnaire (appendix 1). Copies of questionnaire were sent via to the experts of sixteen involved countries. This method was used because, it is timely and cost efficient means of data collection (Kumar, 2005). The questionnaire involved several questions about the purpose for developing groundwater screening values, protected targets, protection levels, exposure pathways and derivation methods (particularly, models, assumptions, scenarios) that are used to derive the groundwater screening values. Literature review was also used to collect necessary data for this study. A thorough review of scientific articles, books, published and unpublished reports about soil and groundwater screening values, vapour intrusion models, and groundwater contamination from the library of Wageningen University and RIVM was conducted. Unstructured interviews with experts from RIVM were also used to collect information about groundwater screening values, exposure models like CSOIL and VOLASOIL. Interview was important as it provided not only firsthand information but also supplemented and verified the collected data from secondary sources like reports and articles (Kumar, 2005). This part of the study involves sixteen countries namely, Australia, Austria, Belgium Flanders, Belgium Walloon, Czech Republic, Denmark, Finland, Germany, Ireland, Italy, Lithuania, the Netherlands, New Zealand, Poland, Spain, and the United States of America. Ten volatile contaminants that are commonly detected in groundwater in most of the participating countries are selected, so as to be used to identify the difference in groundwater screening values. These contaminants include: benzene, ethylbenzene, toluene, naphthalene, vinyl chloride, trichloroethene, tetrachloroethene, trichlorobenzene, tetrachlorobenzene, and Methyl tert-butyl Ether (MTBE) Data analysis With reference to the importance of purpose and derivation methods in the differences in soil screening values as Provoost et al., (2008a) pointed out in previous paragraphs (2.1). The 8

9 purpose and derivation methods for the groundwater screening values were used as the main criteria upon which differences and the reasons for disparity in groundwater screening values were examined. Analysis of differences in groundwater screening values for ten volatile contaminants among sixteen countries was done in analogue with the analysis in the study of Carlon (2007) where soil screening values were evaluated based on derivation methods. Analysis was firstly done by comparing the numerical values based on application purposes. Application of screening values depends on levels of risk on a contaminated site. Basically, there are three categories of levels of risk, namely negligible, intermediate (warning), and potentially unacceptable risk. According to Carlon and Swartjes (2007), screening values are used for targeting long term environmental objectives or short term objectives for remedial actions when risks are negligible. An intermediate or warning risks level means that the risks are slight, thus screening values are applied for further investigation. Potential level of risks implies serious risks; hence, screening values are used to determine actions such as remediation and restrictions in land use on contaminated site. Figure 2 below shows categories of application based on risk levels. Risk levels Negligible risk Warning risk Potentially unacceptable risk Application Long term objectives Further investigation Remediation Screening values Target values Trigger values Clean up values Figure 1. Screening values based on risk levels and different applications. Adopted from (Carlon and Swartjes, 2007) 9

10 Since most screening values are risks based, models, equations and exposure pathways are typically involved in derivation (ITRC 2005). Therefore, analysis of derivation methods was done in order to obtain the reasons for the variability in groundwater screening values. The analysis was specifically done by assessing protection targets (human health, ecosystem and groundwater resource), protection levels, exposure pathways, models, human exposure equations and toxicological data used to determine the numerical values for the groundwater among countries that are involved in this study Limitations Since not all participating countries use English as the official language, it was not possible to comprehend the information especially on the derivation methods that was available in the language other than English from some countries. Additionally some countries provided the groundwater screening values without the details on derivation methods. As a result analysis of derivation methods was done only for few countries. 10

11 4. RESULTS AND DISCUSSION 4.1. Overview of groundwater screening values Most countries involved in this study have developed the groundwater screening values by themselves. Some countries like Finland and New Zealand have no groundwater screening values. Instead they use drinking water standards and soil values for groundwater protection respectively, to regulate and manage contamination in groundwater. Spain also has no national groundwater screening values. However, under the QUASAR project some groundwater screening values have been developed for Catalonia community in Spain. Thus the values that are presented in this study are for Catalonia and not for the Spain as a whole. In USA each state develops her own groundwater screening values based on the Maximum Contaminant Level for drinking water (MCL), (USEPA, 2002). Thus, difference in screening values among states is common. In order to get values that represent the whole USA and be able to compare with other countries, the MCL values were regarded as remedial values in this study because they are used to develop clean-up values by different states. A general overview of the numerical values for the groundwater screening values without considering any criteria such as the purposes, protection targets, and derivation methods is presented in table 1 and 2. Since some values are given for a group of contaminants while other values are for a single contaminant, an overview of these groundwater screening values in microgram per litre is presented separately. Table 1 shows groundwater screening values for groups of contaminants and table 2 is for numerical values given for a specific single contaminant. Table 1. General overview of groundwater screening values in µg/l for groups of contaminants. Contaminants NL GER ASTRI IRE FIN Σ PAHs Σ Volatile hydrocarbons 18 ΣThrichloeth &tetchloroethene Σ Chlorinated benzene 1 Σ Chlorinated hydrocarbons 18 Σ Trichlorobenzene 0.01* 10 1 Σ tetrachlorobenzene 0.01* ΣNaphth& methylnaphthalene 2 * target values 11

12 NL: Netherlands, GER; Germany, ASTRI: Austria, IRE: Ireland and FIN: Finland Table 2. General overview of groundwater screening values in µg/l for ten contaminants among sixteen countries Benz Ethyb Tol Nap Vichl Triet Tetret Triben Tetben MTBE Australia Austria (TV) Belgium Flanders (TR) (IV) (TV) Belgium Walloon (TR) (IV) Czech Denmark Finland Germany Ireland Italy Lithuania Netherlands (TV) (IV) * New Zealand Poland Spain USA * Indicative level for serious contamination + At close distance to receptor (TV) Target values; (TR) Trigger values; (IV) Intervention values Benz (Benzene); Ethyb (Ethylbenzene); Tol (Toluene); Naph (Naphthalene); Vichl (Vinyl chloride); Triet (Trichloroethene); Tetret (Tetrechloroethene); Triben (Trichlorobenzene); Tetben (Tetrachlorobenzene); MTBE (Methy tert-butyl Ether) 12

13 4.2. Application scale for the groundwater screening values Groundwater screening values can be generic or land use specific. The results show that most of the countries including Australia, Austria, Belgium Flanders, Belgium Walloon, Czech Republic, Denmark, Finland, Italy, the Netherlands, Poland, and Spain (Catalonia) have generic groundwater screening values. The groundwater screening values that are meant for specific land use was reported by Lithuania only. The scale of application for groundwater screening values differs. Eleven countries out of sixteen reported to use their values at national scale. Austria and Spain use their values at local scale. Belgium Flanders and Walloon use groundwater screening values at a regional level. Other countries like Ireland did not report the application scale for their groundwater screening values. On this basis it can be concluded that most values are generic and are used at the national level Differences in groundwater screening values based on purpose of applications In order to identify the differences in groundwater screening values among countries, a comparison of these values was done. However, comparing the numerical values without distinguishing them into purpose of application was not useful. The reason for this is that, groundwater screening values among countries are used for different purposes as it is described in section 3.2. This comparison of numerical values is mainly important for decision makers. Comparison was done only for countries that indicated the application of their values in the questionnaires. In this respect, Finland, New Zealand and Poland were not included. Other countries like Australia reported to use the groundwater screening values for all three mentioned categories of application. However, no distinctive values for each application were provided. In this case, the provided values were used in this study as values for remedial actions because; these values are practically the most relevant as far as this study is concerned. The USA did not explicitly indicate the application of the MCL. However, these 13

14 values are used as a basis for development of clean-up values (USEPA, 2002). In regard to this, MCL values were regarded as remedial values. Different applications of groundwater screening values among sixteen countries are presented in table 3. From this table, it is shown that six countries out of sixteen use the groundwater screening values for negligible risk and sustainable groundwater quality. Six countries use the screening values for further investigation when there is an indication of exceedance. Seven countries explicitly indicated that their values are used for taking remedial actions. Four countries; Germany, Italy, Ireland, and Poland, reported to use groundwater screening for other purposes (as indicated in table 3) than the ones pre-indicated in questionnaire. Table 3. Application purposes for groundwater screening values among sixteen countries Country negligible risk further investigation remedial actions Other Australia Austria Belgium Flanders Belgium Walloon Czech Denmark Finland Germany Defines insignificant changes in chemical properties of groundwater & concentration of groundwater pollution Ireland Assess chemical status of groundwater Italy Target values at point of compliance generally fixed at the property boundaries Lithuania Netherlands New Zealand Poland Assess chemical status of groundwater 14

15 Spain USA Differences in groundwater screening values applied for negligible risks (target values) The differences in groundwater screening numerical values that are used for setting up long term environmental objectives (negligible risks) are shown in figure 3. It is apparent that the difference in groundwater screening values is between 1 and 1.5 orders of the magnitude. However, the difference is less proportional per contaminant and among countries. The big extent of difference is for trichloroethene, which has a difference factor of 240 between the lowest and the highest values. The small extent of difference is for benzene, trichlorobenzene and MTBE. These contaminants have a difference factor of 1 to 5 between the lowest and highest values. Naphthalene, vinyl chloride and tetrachloroethene have a difference factor of 100 between the lowest and the highest values. Figure 2. Graphical representation of groundwater screening values for negligible risk purposes 15

16 Differences in groundwater screening values applied for further investigation The differences in groundwater screening values that are applied for further investigation are illustrated on figure 4. Based on this figure, there is a difference of 2 orders of magnitude. Difference in factors indicates that Naphthalene has the highest difference factor of 600 between the lowest and the highest values compared to other contaminants. The lowest difference factor of 13 is indicated for benzene, ethylbenzene, vinyl chloride, tetrabenzene and MTBE. Further, it is shown that Belgium Walloon has the highest values for almost all contaminants compared to other countries. Ireland and Italy seem to have the lowest numerical values for many contaminants except for trichlorobenzene. Figure 3. Graphical representation of groundwater screening values for further investigation purposes Differences in groundwater screening values applied for remedial actions The differences in groundwater screening values that are used for remediation purposes are shown in figure 5. Generally there is a difference of 2 orders of magnitude for this category of application. The huge difference among the contaminants is noticed for ethylbenzene, which has a difference factor of 304. The low difference factor of 4.2 is for trichlorobenzene and MTBE. Trichloroethene and benzene have a difference factor of 100 for and 90 16

17 respectively between the lowest and the highest values. Naphthalene, vinyl chloride, and tetrachloroethene have a difference factor of 50, 66 and 34 respectively between the lowest and highest values. Belgium Walloon has extremely high values compared to other countries except for benzene, naphthalene and trichloroethene. The Netherlands has the highest values for tetrachloroethene, while Spain (Catalonia) has the highest values for benzene and naphthalene contaminants. Australia has lowest numerical values for benzene and vinyl chloride compared to other countries. Likewise Lithuania seems to have low numerical values for many contaminants including ethylbenzene, toluene, naphthalene, vinyl chloride and trichlorobenzene. Figure 4. Graphical representation of groundwater screening values for remedial action purposes 4.4. Differences in groundwater screening values based on protection targets Protected target or receptor refers to any person and or/ medium that may be affected by the release of toxic chemicals. In regard to groundwater contamination, protected targets include human health, ecosystem, surface water, and groundwater as a resource. Generally speaking, 17

18 all targets need to be protected. However, this is not the case as each country decides to protect a target which seems to be of great importance to them. These results are primarily relevant for the scientific community. Human health is a fundamental target for all sixteen countries. As it is shown in table 4, many countries do protect groundwater in connection with drinking water function. Seven countries have indicated to protect ecosystems as well. None of the sixteen countries indicated to protect groundwater resource regardless of its functions. Protection of surface water was reported by Lithuania and Germany only. Due to the strong link between surface and groundwater, in many countries like the Netherlands, protection of groundwater implies protection of surface water as well. Table 4. Protection targets considered in groundwater screening values among countries Countries Human health & groundwater for drinking Australia Austria Belgium Flanders Ecosystem Groundwater as a resource Surface water Belgium Walloon Czech Rep. Denmark Finland Germany Ireland Italy Lithuania Netherlands New Zealand Poland Spain USA Groundwater screening values based on human health and ecosystem target (for remedial values) Since the main protection target for all countries is human health, a comparison of numerical values in previously section 4.2.1; and is satisfactory for showing difference in groundwater screening values meant to protect human health target. Differences in groundwater screening values based on the protection target human health and ecosystem 18

19 was done by using remedial action numerical values due to is practicability relevance. In figure 6, it is illustrated that, groundwater screening values differ for orders of magnitude that range from 1.5 to 3. High extent of difference between the lowest and highest values is for ethylbenzene and toluene, whereas, low extent of difference between the lowest and highest values is seen for the vinyl chloride and benzene. Figure 5. Graphical representation of groundwater screening values (remedial values) for human and ecosystem protection target Groundwater screening values based on human health and ecosystem target (for further investigation) Identification of differences in groundwater screening values meant for the protection of human health and ecosystem based on values applied for further investigation values is shown in table 5. Based on this table, it is quite obvious that no meaningful trend of differences is shown because; there are no values for most contaminants., The absence of numerical values for some contaminant is either because the country has not developed numerical values for the contaminant at all, or there is a numerical value for the contaminant but, it is for a group of contaminants (as it is shown in section 4.1, table 1), and hence is not useful to compare it with non-group contaminant values. 19

20 Table 5. Groundwater screening values in µg/l based on human health and ecosystem protection target (further investigation values) Benz Ethyb Tol Naph Vichlo Triet Tetret Triben Tetben MTBE Czech Republic Germany Ireland Benz (Benzene); Ethyb (Ethylbenzene); Tol (Toluene); Naph (Naphthalene); Vichlo (Vinyl chloride); Triet (Trichloroethene); Tetret (Tetrechloroethene); Triben (Trichlorobenzene); Tetben (Tetrachlorobenzene); MTBE (Methy tert-butyl Ether) 4.5. Derivation methods Most of health-based groundwater screening values are derived by using risk assessment approaches which involve equations, exposure assumptions and toxic potency estimates (ITRC 2005). In this respect, level of protection, toxicological data, exposure pathways, and models were mainly focused in this study as criteria for examining the reasons for the differences in groundwater screening values Level of protection The level of protection is a very important factor in derivation of screening values. Screening values that are meant for protection of human health, are derived based on target excess risk level for carcinogens and/or hazard quotient (HQ) for non-carcinogens under generic exposure assumptions. Level for carcinogens, is an acceptable level for cancer risk, which implies the likelihood that a person might develop cancer from exposure to contaminants (ITRC, 2005). The Hazard Quotient is a calculated exposure from a single contaminant in a single medium divided by its safe exposure doze (Bozkurt, 2009). The levels of protection are presented in table 6. From this table, it is clear that levels of protection vary significantly among countries. Consequently, groundwater screening numerical values differ accordingly. Nine countries out of sixteen reported their level of 20

21 protection, while, seven countries out of sixteen (Czech, Denmark, Finland, Lithuania, Ireland, New Zealand, and Poland) did not provide their level of protection. Two countries out of nine (that indicated the level of protection) protect human health at the level of 1/10,000. One country out of nine considers 1/100,000 level to protect human health. The protection level of 1/ 1,000,000 is used by six countries out of nine (inclusive USA which has multiple levels). The USA protect receptors at level which ranges from 10-4 to As a result levels of protection differ among the states within USA. Table 6. Human health based - protection level Country Protection level Acceptable risk of cancer Hazardous Quotient (HQ) Australia 1* Austria 1*10-6 Belgium Flanders 1*10-5 Belgium Walloon 1*10-4 Germany 1*10-6 Italy 1*10-6 Netherlands 1* Spain 1*10-6 USA 1* * Exposure pathway considered in deriving groundwater screening values Human beings can be exposed to contaminations through different pathways. Ingestion, air inhalation and dermal are among the common exposure pathways. Thirteen countries out of sixteen consider water consumption as the main exposure pathway in derivation of generic groundwater. Nevertheless, the developed groundwater screening values are used to assess the risk of contaminated groundwater for humans not only through water consumption but also via other pathways. The Netherlands and Spain consider more pathways including water consumption, dermal, crop ingestion, and inhalation of air during derivation process Toxic data used for derivation of groundwater screening values As far as human health is concerned, the toxicity data are very important to determine the level of negligible intake of toxicity. Basically two main types of data, namely human and eco-toxicological data are considered in derivation of groundwater screening values. The use of this data depends on the political and scientific aspects of a particular country. 21

22 Since most countries use drinking water function to develop groundwater screening values, human toxicity data are widely used. However some countries use both human and ecotoxicological data. Among other countries, Germany, and the Netherlands have clearly stipulated that, both human toxicological and eco-toxicological data are considered in deriving groundwater screening values. Germany chooses a low value between human toxicity data and eco-toxicological data as groundwater screening value (which are known as insignificance threshold for groundwater in Germany). The national toxicological data are mostly used, but in case the national toxicological data are not available, data from other sources like WHO, EPA and IRIS are used (LAWA, 2004). The Netherlands use human and eco-toxicological data for development of groundwater screening values for the purpose of remediation (intervention values) and they use eco-toxicological data only to develop screening values for negligible risks known as target values (Swartjes, 1999) Models and equations used for derivation of groundwater screening values Exposure models are commonly used in risk assessments. As a result, various models and human exposure equations are involved in derivation of the groundwater screening values. The information about models, equations and procedures that were used to developed groundwater screening values for Belgium Walloon, Czech republic, Denmark, Finland, Austria, Spain, Lithuania, Italy, Germany, and Poland, was either not publicly available or was available in the local language, hence comprehension of the information was limited. A few countries including Belgium Flanders, the Netherlands and the USA, described the derivation methods. Belgium Flanders Belgium Flanders uses the available values in the Flemish regulation on drinking water for threshold substances. If the values are not available or in case of non- threshold substances, the following WHO equation is used: RW = TDI BW P C Where, RW is the guideline value; TDI is the tolerable daily intake; BW is the body weight (default values are 60 kg for adults, 10 kg for children and 5 kg for infants; P, is the fraction 22

23 of the TDI allocated to drinking water (this value is chemical specific, if data is lacking the default value is 0.1); and C is the daily drinking water consumption (default values are 2 litre for adult, 1 litre for children and 0.75 litres for infants). In case of non-threshold carcinogenic, the TDI is replaced by the dose corresponding to an excess lifetime cancer risk of 1/ exposed individual and the P values equals to 1. The Netherlands In the Netherlands the groundwater screening values provided in Soil Remediation Circular (2009), have been derived on the basis of three risk limits namely human toxic limit, ecotoxicological and soil equilibrium risk limits. Human risks limit refers to concentration in groundwater for which the sum of the oral inclusive dermal and exhalative risk indexes equal 1. In addition, the lifelong average for oral exposure is also calculated by summing up exposure of children and adults with a relative weight of 6/70 for a child during 6 years and 64/70 for an adult during 64 years (Swartjes, 1999). 2liter Cgw + 1 liter Cgw = RfD BWa BWch Where, Cgw is concentration in groundwater (mg/dm 3 ); BWa is body weight of an adult (70 kg); BWch is the body weight of a child (15 kg); RfD: Reference doses (mg/kg/day); and TDI is tolerable daily intake. Eco-toxicological risk limit implies concentration at which 50% of the ecosystem could be affected (Hazardous Concentration 50). The risk limit for soil equilibrium means, partitioning of the solid phase and the pore water. The general intervention value is obtained by taking the lowest value of the three risk limits. Essentially, the CSOIL model under a standard situation (residential with garden scenario) is used to develop groundwater screening values in the Netherlands. Input parameters and default values are available in Waitz et al., (1996); Otte et al., (2001). The VOLASOIL model is used for assessment of risks of vapour intrusion (Bakker et al., 2008). The United States of America (USA) The information on the procedure of the USA s screening values is provided by United States Environmental Protection Agency (USEPA). The Johnson-Ettinger (JEM) model is mostly used to derive the clean-up for groundwater and soil screening values for volatile contaminants (USEPA, 2002). JEM, like CSOIL and VOLASOIL, is a steady state model that 23

24 assumes infinite source and equilibrium partitioning. They do not consider biodegradation protection. From literature, it is indicated that most of the vapour intrusion models that are used to derive soil screening values are also used to derive groundwater screening values (Carlon, 2007). For example, CSOIL and JEM, have been used for development of clean-up or intervention values for both groundwater and the soil. Many studies have been done on soil screening values. Therefore, the information from those studies is applicable for this study as well. The study of Provoost et al., (2008a); Provoost et al., (2008a); Turcynowicz and Robinson (2007); and Carlon (2007), report that models mainly differ in terms of algorithms and input parameters and the values of input parameters (default). These differences lead to discrepancies in results of the models (calculated concentrations), which eventually result in differences screening values. Provoost et al., (2008a) argue that, when algorithms and other scientific and political parameters were harmonized, the variation decreases to 1 order of magnitude from 2 to 4 orders of magnitude for soil screening values for the residential land-use. This reflects a significant role of scientific and political factors in screening numerical values. Ireland and Finland Ireland and Finland, just like many other European countries considered the guidelines from Annex 2 (part A) of the Water Framework Directive (groundwater quality) (WFD, 2009), in determining the groundwater screening values. However, the reliance on these guidelines differs from one country to another. For example, Ireland used 75% of the relevant drinking water standard provided by EU water framework to derive groundwater screening values because insufficient data was available. Finland used 50% of the drinking water standards (EC, 2010). The difference in percentage of the use of drinking water standards between these countries results in differences in groundwater screening values Discussion Unavailability of data in English language reduced the intended scope of the analysis, especially analysis of derivation methods for groundwater screening values upon which the reasons for differences in groundwater screening values were expected to be gained from. However, this study was able to provide an insight on the reasons for the differences in groundwater screening values based on the information provided by few countries. In 24

25 addition, the reviewed literatures on soil screening values played an important role in finding the reasons for the differences in groundwater screening values. This was quite ideal approach to deal with unavailability of data because, most models used to derive soil screening values are used also for groundwater screening values in most countries. Moreover, comparison of groundwater screening numerical values without categorizing them into purpose of application was not useful. Therefore, comparison of numerical values for groundwater screening was made based on application categories as described in section3.2. Some countries had to be excluded in the analysis because, they did not indicate the applications of their values. As a result, the number of countries that was previously intended to be covered in analysis was reduced. Although the scope of the analysis was limited to few countries, the analysis of differences in numerical values based on application categories was useful approach that logically identified the differences among countries. Generally speaking, the differences in groundwater screening values between the lowest and highest numerical values based on purpose of applications range from 1 to 2 orders of magnitude. This magnitude of difference is not far from 1 order of magnitude of difference in soil screening values as reported by Swartjes et al (2011). The results show evidently that some countries have more stringent values than others. For instance, Belgium Walloon has extremely high values (less stringent) especially for remedial action (clean-up) values (figure 5) for almost all contaminants except for trichloroethene. The high values have a connection to the historical background of extensive industrial activities. In general, Austria, Italy, Ireland, the Czech Republic, and Denmark have low/stringent values for negligible and for further investigation purposes. This could be due to less industrial activities compared to Belgium Walloon, the Netherlands and Germany. It is also shown that the differences among contaminants vary quite considerably. For example, a remarkable disparity for remedial values is indicated for ethylbenzene, trichloroethene, naphthalene, and tetrachloroethene contaminants. Small extent of disparity is shown for trichlorobenzene and MTBE (4.3.3). As a matter of fact, few countries have values for trichlorobenzene and MTBE. This could be the reason for the low disparity that has been observed. 25

26 The results show that there is variation in terms of protection levels, targets and toxicological data that are considered in derivation of groundwater screening values. This variation is basically due to the choice that each country makes depending on political and scientific reasons. The choice of toxicological data is also influenced by availability of data and the source of data. Some data are nationally based while others are internationally based, from World Health Organization (WHO). Therefore, using the same type of data does not necessary mean that the data are the same. Consequently, the differences in groundwater screening values are inescapable. In-depth analysis of the toxicological data used for derivation of the groundwater screening values was impossible because of the lack of data. Due to this, it was not possible to exactly identify and compare different toxicological data. It was also hard to know which exact data was taken as groundwater screening values for countries that consider both human and ecotoxicological data. This is relevant for Germany and the Netherlands in Section Models and equations used to derive groundwater screening values differ in terms of algorithms, input parameters and parameters values (Provoost et al., 2008a). Section for example, clearly shows the difference in default values for the equations for the tolerable daily intake via water consumption. For instance, the weight for a child is 10 kg and for an adult is 60 kg for the Belgium Flanders; while for the Netherlands it is 15 kg for a child and 70 kg for an adult. Likewise, default values of the input parameters and processes that are involved in various models, have some disparities (Otte et al., 2001). For example, biodegradation process is not considered in CSOIL, VOLASOIL and JEM models. While Turcynowicz and Robinson (2007) point out that the Australian vapour intrusion model (CSIRO) includes biodegradation process. Such disparities lead into differences in developed screening values. The different purposes of application for the groundwater screening values, different levels of protection, different toxic data considered in derivation, the differences in equations default values and different values of input parameters as well as algorithms of the models have been observed in this study as responsible factors for the variability in groundwater screening values. This observation is analogue with the study of Carlon and Swartjes (2011) and Provoost et al, (2008a) which point out the same factors to be responsible for the difference in soil screening values among different countries. However, unlike soil screening values which 26

27 are primarily derived by vapour intrusion models, some groundwater screening values are also derived on the basis of drinking water standards only. 27

28 5. CONCLUSION AND RECOMMENDATIONS 5.1 Conclusion Groundwater screening values are established to regulate and manage groundwater contamination. The difference in groundwater numerical values among countries lead to inconsistent decisions on management of contamination. This study answers two research questions concerning the extent of the difference in groundwater screening values and the reasons for the variability in those values. With reference to the question about the extent of the differences in groundwater screening values, this study concludes that, 2 orders of magnitude of differences in groundwater screening values for volatile contaminants exist among countries. However, the difference magnitude per contaminant is not proportional. Ethylbenzene has shown a high extent of difference in groundwater screening values whereas, low level of difference has been shown for the trichlorobenzene and MTBE. As a response to the second question, this study indicates that the difference in groundwater screening numerical values is caused by political and technical factors. Political factors include: purpose of developing groundwater screening values in terms of protection target (human health, ecosystem and groundwater as a resource); application of values (such as negligible risk, further investigation and remedial actions); toxicological data (such as human and eco- toxicological data); and level of protection (which range from 10-4 to 10-6 ). Technical factors include: derivation methods (such as models and equations, in which different default values for equations and /or input parameters, algorithms, and different input parameters are used). In nutshell, the differences in above mentioned factors lead considerably to the differences in groundwater screening numerical values. 28

29 5.2 Recommendations Differences in groundwater screening values lead to different decisions on contaminated sites. These decisions have a great economic impact. In order to minimize the differences and its consequences, this study recommends that, there should be some efforts to increase consistency of risk assessment tools (models, equations, toxicological database and protocols) for groundwater quality assessments based on the same contaminated site scenario by using similar approach. This is possible by involving experts from different countries to develop a flexible risk assessment tools concentrating on the technical part and not the geographical, cultural and political factors (Swartjes et al., 2009). In addition, guidance for use (including a manual which allows the flexible use of the risk assessment tools by choosing different input parameters), a series of optional risk assessment tools, and boundary conditions of their applicability should be provided (Swartjes et al., 2009). 29

30 APPENDIX Appendix 1 QUESTIONNAIRE FOR THE FOREIGN EXPERTS Introduction: We are conducting research on groundwater screening values. The main intention is to identify the differences in groundwater screening values and figure out the reasons for the variation among countries. We greatly appreciate the information that you previously sent us. However, we are still missing some information. Therefore we kindly ask you to fill in this questionnaire so that we can fill the information gap. 1. Do you have groundwater screening values for the following contaminants? Contaminant Benzene Ethylbenzene Toluene Napthalene Viny chloride Value (ug/l) Contaminant Trichloroethene Tetrachloroethene Trichlorobenzene Tetrachlorobenzene MTBE Value (ug/l) 2. Have the groundwater screening values developed by your country or instead developed by others? Yes [ ] or No [ ] If adopted what is the source? What is the purpose for developing or adopting the groundwater screening values? a. Target values for negligible risk/ remediation objective b. Values for further investigation c. Values for actions or remediation 4. What is the scale for the application of these groundwater screening values? a. National b. regional c. local d. Other, specify. 5. Are these groundwater screening values a. generic [ ] b. land use specific [ ]? 6. Do these groundwater screening values consider the following exposure pathways? a. water consumption b. air inhalation c. both a & b d. others. 30

31 6. What is protection target and level of protection? Protection target Yes No Protection level (eg acceptable risk of cancer, HC etc Concentration Human health Ecosystem Groundwater as a resource Surface water Others specify. 7. For every protection target you consider give documentation about the procedure or describe the procedure By procedure we mean the algorithms, models, input parameters, exposure scenarios, etc Thanks for your cooperation! 31