Appendix A Equations and Methodology

Transcription

1 Appendix A Equations and Methodology

2 Table of Contents A1 Introduction... A-1 A2 Calculation of Chemical Intakes... A-2 A2.1 Intakes via Ingestion... A-2 A2.2 Intakes via Dermal Exposures... A-4 A2.3 Intakes via Inhalation... A-5 A2.4 Age-Specific Adjustments to the Calculation of Chemical Intake... A-6 A3 Calculation of Exposure Concentrations Irrigation... A-7 A3.1 Chemical Concentrations in Air During Irrigation... A-7 A3.2 Concentrations in Home-grown Fruit and Vegetable Produce... A-9 A4 Calculation of Air Concentrations... A-14 A4.1 Air Concentrations in Residential Areas Derived from Groundwater... A-14 A4.2 Air Concentrations in Recreational Areas Derived from Groundwater... A-17 A4.3 Air Concentrations in Commercial/Industrial Areas Derived from Groundwater... A-18 A5 Modelling Emissions from the CPWE... A-21 A6 References... A-24

3 A1 Introduction This appendix presents the methodology and equations used to quantify exposures vial inhalation, ingestion and dermal absorption. The approach adopted is in accordance with guidelines/protocols provided by enhealth ( Environmental Health Risk Assessment, Guidelines for Assessing Human Health Risks from Environmental Hazards, June 2002 [reprinted 2004]), with many of the equations derived from the USEPA (1989, 1991, 1996, 1997, 2002, 2004 and 2009). A-1 P a g e

4 A2 Calculation of Chemical Intakes A2.1 Intakes via Ingestion The assessment of ingestion exposures requires evaluation of a number of pathways that can loosely be grouped into the ingestion of water, ingestion of produce and the ingestion of soil and sediments. The assessment of risk presented in the 2010 CHHRA has not indentified any complete or significant exposure pathways for soil or sediments; hence intake equations have not been presented for these pathways. Ingestion of Water This includes evaluation of the following pathways: Ingestion of groundwater during incidental contact during intrusive works, where groundwater is sufficiently shallow; Ingestion of groundwater extracted from a backyard or irrigation bore; and Ingestion of surface water while playing, wading or swimming (it is proposed that unfiltered analytical data be used in this assessment to ensure ingestion of chemicals in water as well as suspended sediment are accounted for in the calculations). The following equation is used to calculate intake of chemicals via the ingestion of water pathways: Daily Chemical Intake IW IRw B EF ED Cw (mg/kg/day) BW AT Cw IRw B EF ED BW AT = Concentration of chemical in water (as relevant for each pathway assessed) (mg/l) = Ingestion rate of water (dependant on age and activity and may be derived using ingestion rate per hour and number of hours undertaking activity or simply an intake per day) (L/day) = Bioavailability or absorption of chemical via ingestion assumed to be 1 or 100% unless noted otherwise (unitless) = Exposure frequency (days/year) = Exposure duration (years) = Body weight (dependant on age) (kg) = Averaging time for threshold (=ED x 365) and non-threshold exposures (=70 years x 365) (days) A-2 P a g e

5 Ingestion of Produce This includes evaluation of the following pathways: Ingestion of home-grown fruit and vegetable crops; and Ingestion of recreationally caught fish. Home Grown Fruit and Vegetables Assessment of intake via the ingestion of home-grown fruit and vegetable crops is evaluated using the following equation: Daily Chemical Intake FV IRp FH B EF ED Cp (mg/kg/day) BW AT Cp IRp FH B EF ED BW AT = Concentration of chemical in produce (as calculated) (mg/kg wet weight) = Ingestion rate of fruit and vegetable produce (dependant on age) (kg/day wet weight) = Fraction ingested which is home grown (unitless) = Bioavailability or absorption of chemical via ingestion of product assumed to be 1 or 100% unless noted otherwise (unitless) = Exposure frequency (days/year) = Exposure duration (years) = Body weight (dependant on age) (kg) = Averaging time for threshold (=ED x 365) and non-threshold exposures (=70 years x 365) (days) Recreationally Caught Fish While there is no longer access to the estuary for any purpose, including fishing, fish that spend time in the estuary that then swim outside into the bay may be caught and consumed by recreational anglers. Assessment of intake via the ingestion of recreationally caught fish is evaluated using the following equation: Daily Chemical Intake IRf FI B EF ED Cf BW AT F (mg/kg/day) Cf = Concentration of chemical in fish (measured) (mg/kg wet weight) IRf = Ingestion rate of recreationally caught fish (dependant on age) (kg/day wet weight) FI = Fraction of fish caught and ingested that is derived from Penrhyn Estuary (unitless) B = Bioavailability or absorption of chemical via ingestion assumed to be 1 or 100% unless noted otherwise (unitless) EF = Exposure frequency (days/year) ED = Exposure duration (years) BW = Body weight (dependant on age) (kg) AT = Averaging time for threshold (=ED x 365) and non-threshold exposures (=70 years x 365) (days) A-3 P a g e

6 A2.2 Intakes via Dermal Exposures The assessment of dermal exposures involved quantification of intakes from water (extracted groundwater and groundwater exposures during excavations). Mechanisms of Dermal Absorption Passive diffusion, as governed by Fick's First Law, is considered to be the main process whereby chemicals enter and permeate through the skin. The human skin is the largest organ of the body and it consists of a thin (approximately 100 µm) epidermal layer superimposed on a thick dermal layer (approximately µm). The epidermis consists of four layers, the outermost layer being the stratum corneum (SC) (approximately µm), which overlays the strata lucidum, granulosum, and germinativum (Figure 1). The SC layer is composed of flat highly keratinised squamous cells that are nonviable and are thought to maintain the barrier properties of the skin. If the SC layer is removed by tape stripping, for example, the permeability of the skin to chemicals increases dramatically. Factors that have an effect on the dermal absorption of chemicals through the skin include: Skin hydration with several studies indicating that skin hydration may increase skin permeability; Thickness of the SC and anatomic regions with higher absorption expected in areas unprotected by thick SC layers; Lipophilicity of chemical. The SC layer tends to be a lipid-rich milieu and hence provides a barrier to hydrophilic compounds but permits the entry of lipophilic compounds; Degree of sediment binding; The presence of surface slicks typically comprised of fatty substances (e.g., lipids from decomposed organisms and oil from petroleum contamination) which typically cover the surface of all natural bodies of water. Environmental factors that include water temperature, ph, turbidity, flow rate (current), and degree of solar illumination. Physiologic factors include genetic-related sensitivity (e.g., tendency to sunburn) and individual differences (e.g., age, the presence of skin disease, skin abrasions). A-4 P a g e

7 Dermal Contact with Water The following equation (as detailed in USEPA 1989 and 2004) is used to calculate intake of chemicals via dermal exposure to chemicals in water: Daily Chemical Intake DW SAw ET Kp CF EF ED CW (mg/kg/day) BW AT Cw = Concentration in water (mg/l) SAw = Surface area of body in contact with water (cm 2 ) ET = Exposure time in contact with water (hr/day) Kp = Dermal permeability/absorption via skin for each chemical in water (cm/hr) CF = Conversion factor of 1x10-3 to convert cm 3 to L EF = Exposure frequency (days/year) ED = Exposure duration (years) BW = Body weight (dependant on age) (kg) AT = Averaging time for threshold (=ED x 365) and non-threshold exposures (=70 years x 365) (days) Kp is a chemical-specific factor that has been derived for a wide range of chemicals. Values for chemicals evaluated have been obtained from the Risk Assessment Information System (RAIS) database available on the website ( which is maintained by the Oak Ridge Operations of the US Department of Energy, current to A2.3 Intakes via Inhalation The assessment of inhalation exposures assumes that exposures associated with the groundwater contamination, emission to air from the CPWE, GTP, HCB Repackaging Plant and former CAP. Intakes via inhalation have been assessed on the basis of the revised inhalation guidance available from the USEPA (2009). This guidance requires the calculation of an exposure concentration rather than an intake. The exposure concentration is based on the concentration in air and the time/duration spent in the area of impact. It is not dependant on age or body weight. Exposure Concentration V ET EF ED Ca (mg/m 3 ) AT Ca = Concentration of chemical in air (as relevant for each pathway assessed) (mg/m 3 ) ET = Exposure time (dependant on activity) (hr/day) EF = Exposure frequency (days/year) ED = Exposure duration (years) AT = Averaging time for threshold (=ED x 365 x 24) and non-threshold exposures (=70 years x 365 x 24) (hours) A-5 P a g e

8 A2.4 Age-Specific Adjustments to the Calculation of Chemical Intake Where identified in the evaluation of toxicity as having a potential mutagenic mode of action in relation to carcinogenicity, the assessment of risk has been conducted to address early-lifetime susceptibility of exposures to these compounds. This has been conducted in accordance with USEPA (2005) Supplemental Guidance for Assessing Susceptibility from Early-Life Exposures to Carcinogens. The assessment of exposure to vinyl chloride has incorporated early-lifetime susceptibility issues in the toxicity reference values adopted. Different values are available that address exposures over a lifetime (including as a child) and those as only an adult. This is an appropriate approach to the assessment of early-lifetime exposures to vinyl chloride. Where no further review and modification of the toxicity reference value has been undertaken, USEPA (2005) guidance recommends adjusting exposure intakes to address early-lifetime susceptibility. On the basis of the USEPA guidance, the following age dependant adjustment factors (ADAFs) adjustment factors have been included in the calculation of chemical intake for potentially mutagenic carcinogens where early-life exposures are of potential concern (refer to Appendix B): For exposures before 2 years of age (i.e., spanning a 2-year time interval from the first day of birth up until a child s second birthday), a 10-fold adjustment. For exposures between 2 and <16 years of age (i.e., spanning a 14-year time interval from a child s second birthday up until their sixteenth birthday), a 3-fold adjustment. For exposures after turning 16 years of age, no adjustment. The above adjustments have been applied to the calculation of chemical intake for each chemical where early-lifetime exposures need to be considered in the calculation of non-threshold risk. Where this has been undertaken in the risk calculations it has been noted in the relevant spreadsheets. These adjustments reflect the potential for early-life exposures to make a greater contribution to cancers appearing later in life. The USEPA also recognises that exposures occurring near the end of life may have little effect on lifetime cancer risk, but lacks adequate data at present to provide an adjustment for this "wasted dose" effect. A-6 P a g e

9 A3 Calculation of Exposure Concentrations Irrigation A3.1 Chemical Concentrations in Air During Irrigation The concentration of organic chemicals in air during irrigation or use of a sprinkler has been estimated using equations presented in Guidelines for the Assessment and Management of Petroleum Hydrocarbon Contaminated Sites in New Zealand Appendix 5A (August 1999). The model is based on a shower model originally developed for estimating concentrations of volatiles in air during showering. The model has been modified to reflect volatilisation from irrigation or sprinkler systems. Given that the shower model does not account for atmospheric dispersion well, the use of the model is limited to potential concentrations in air within and immediately surrounding the spray. Mass Transfer Rates Volatilisation is limited by mass transfer rates. The overall mass transfer coefficient is calculated as: K L 1 k l R T H kg 1 K L = overall mass transfer coefficient (cm/hr) H = Henry s Law constant for contaminant (atm.m 3 /mol) R = gas constant (assumed to be 8.2x10-5 (atm.m 3 /mol.k)) T = absolute temperature of water (assumed to be 293 K) k g = gas phase mass transfer coefficient (cm/hr), see below k l = liquid phase mass transfer coefficient (cm/hr), see below k g k g,h2o 18 MW 0.5 k l k l,co2 44 MW 0.5 k g = gas phase mass transfer coefficient (cm/hr) k l = liquid phase mass transfer coefficient (cm/hr) k g,h2o = gas phase mass transfer coefficient for water (= 3000 cm/hr) k l,co2 = liquid phase mass transfer coefficient for carbon dioxide(=20 cm/hr) 18 = molecular weight of water 44 = molecular weight of carbon dioxide MW = molecular weight of contaminant. A-7 P a g e

10 The overall mass transfer coefficient needs to be adjusted for the shower (sprinkler) temperature and the viscosity of the water at the lower temperature: K ` L K L Tl s Ts l 0.5 K L = adjusted overall mass transfer coefficient (cm/hr) K L = overall mass transfer coefficient (cm/hr) T l = calibration water temperature of K L (K) T s = sprinkler water temperature (K) l = water viscosity at T l (g/m/s) s = water viscosity at T s (g/m/s) For water temperatures less than or equal to 20 o C the water viscosity can be estimated using the following (where T is in o C): y y (T 20) (T 20) Concentration in Soil Water Volatilisation is assumed to be a first-order process: C s C o e K ' L6t /(3600 d) C s = concentration of contaminant in droplet after time t (mg/l) C o = concentration of contaminant in groundwater (mg/l) K L = adjusted overall mass transfer coefficient (cm/hr) t = droplet drop time (= 10s) 6/d = specific interfacial area per unit volume for a hypothetical shower droplet of diameter d cm 2 -area/cm 3 - volume) d = droplet diameter (= 0.2 cm) 3600 = unit conversion used to convert K L from cm/hr to cm/s C s is the concentration in the water droplet which enters the soil and this is the concentration used in the assessment of potential uptake of contaminants by plants (refer to methodology below). A-8 P a g e

11 Mass Volatilised The total amount which volatilises is given by: M s f v Q time s C o M s = mass of contaminant volatilised (mg) = fraction of contaminant volatilised in (mg/mg) f v Q time s C o Concentration in Air K`L t / 600 d 1 e (refer to equation above for detail on parameters in this equation) = volumetric flow rate of water (=30 L/min) = duration of the event (=60 minutes) = concentration of contaminant in groundwater (mg/l) The concentration in the sprinkler air can be estimated from: M Csa V s s C sa = air concentration in shower/sprinkler (mg/m 3 ) M s = mass of contaminant volatilised (mg) V s = volume of air in sprinkler area which is the area for dispersion (m 3 ) - estimated to be the same for adults (assuming adults are gardening low to the ground) and children. A3.2 Concentrations in Home-grown Fruit and Vegetable Produce Methodology The concentration of organic chemicals in edible fruit and vegetables has been estimated using published equations derived from experimental studies. General guidance has been provided by the documents RISC (Version 4, Users Guide, 2001) and Higher Plant Accumulation of Organic Pollutants from Soils (USEPA, 1992) which draws on models provided by Briggs et al (1982) and Travis and Arms (1988). Organic chemicals can enter and accumulate in plants through three main pathways: 1. Root uptake into conduction channels or oil cells (e.g. carrots, parsnips and cress) and subsequent translocation 1 throughout the plant via the transpiration stream. 2. Uptake of organic vapours in the surrounding air into leaves and shoots. 3. Deposition of dust or soil onto leaves and shoots not considered relevant in this assessment. In nearly all cases, a combination of all of these pathways or events influences the total chemical concentration in the plant. The relative importance of each of the pathways will vary from chemical to chemical. While the empirical equations used in this assessment were derived for herbicides in barley (Briggs et al, 1982) and a limited number of lipophilic compounds in leafy aboveground plants (Travis and Arms, 1988) a number of more recent evaluations and models have been developed (Trapp et al and 2004) 1 Translocation is the transport or conduction of liquids within the plant. A-9 P a g e

12 evaluating more polar chemicals such as MTBE, TCE, benzene, toluene and naphthalene as well as lipophilic compounds such as PAHs and dioxins in fruit trees. The comparison of the Briggs and Travis and Arms models with the Trapp models and measured data indicated the following: For polar compounds, there is good agreement between the Travis and Arms model and the Trapp model for the evaluation of concentration in aboveground produce. For polar compounds, there is good agreement between the Briggs model and the Trapp model for the evaluation of concentration in root crops. Unfortunately there are no data available for polar chemicals in studies on plant uptake below or above ground for further comparison. For more lipophilic compounds (such as PAHs and dioxins with log Kow > 5) the Travis and Arms model tends to overestimate potential uptake into aboveground products based on comparison with the Trapp model and data from plant uptake studies. These studies and the Trapp model indicate that for these chemicals uptake into below ground produce is more important and the translocation into aboveground produce can be neglected. This finding is consistent with the assessment approach presented below for the determination of the importance of translocation within the plant. While there are limited data available for the uptake of chlorinated hydrocarbons into produce, the available models provide consistent results which indicate that uptake into root crops as wells as translocation into aboveground crops is important for these chemicals. Similar observations have been noted by Schnabel et al (1997), Anderson and Walton (1995) and Scroll et al. (1994). On this basis, the models selected for use in this assessment are considered appropriate (not expected to under or overestimate uptake) for CHCs. It is noted that the UK Environment Agency (2009) has recommended the use of more complex models for estimating plant uptake of organic compounds. Review of the UK approach does not change the assessment conducted using the more simplified approach outlined below. Hence there is no value in utilising more complex models in this assessment. Root Uptake The concentration of organic chemicals in below ground vegetation is only required for vegetables such as carrots and potatoes which have edible roots, tubers etc. The basis for the equation used to calculate the concentration of contaminants in below ground vegetables is the experiments of Briggs, et al (1982) on the uptake of chemicals into barley roots from growth solution, and the elaboration of a Root Concentration Factor (RCF). The concentration in below ground vegetables is given by: C bgv C w RCF VG bg C bgv C w RCF * VG bg = fresh weight chemical concentration in below ground vegetables (mg/kg); = chemical concentration in soil solution (mg/l); = Root Concentration Factor: the ratio of the chemical concentration in roots (fresh weight basis) and the concentration in solution or water ((mg/kg)/(mg/l)); = empirical correction factor for below ground vegetation which accounts for difference in the barley roots (for which the RCF was derived) and bulky below ground vegetables (unitless). A-10 P a g e

13 Briggs et al (1982) conducted experiments measuring the uptake of several compounds into barley roots from growth solution, and developed the following relationship for the lipophilic 2 compounds tested: RCF logkow RCF K ow = Root Concentration Factor: the ratio of the contaminant concentration in roots (fresh weight basis) and the concentration in water or solution ((mg/kg)/(mg/l)); = contaminant octanol-water partition coefficient (unitless). The above equation was based on experimental results and is generally only valid for lipophilic chemicals with molecular weights of less than 400. The uptake of chemicals with higher molecular weights tends to be dominated by different forces and no longer fit the above relationship. The equation is therefore relevant to the assessment for the key chemicals evaluated at Orica. The equation for RCF provides a wet weight concentration in the plant root, however the equation was established for barley roots which have a different architecture to typical root vegetables, such that spatial distribution of the chemical may be important. A correction factor VG bg which relates the barley crops to the proportions of root vegetables of 0.01 for lipophilic compounds has been derived and used in the evaluation of dioxins (USEPA 1993 and USEPA 2000). While the value is universally applied to all chemicals in the model RISC (2001), the greater potential for translocation of polar compounds (such as chlorinated hydrocarbons) within a plant compared to highly lipophilic compounds (dioxins and PAHs) suggests that the correction factor may not be relevant for the polar compounds. To provide a conservative evaluation of CHCs, VG bg has been set to a value of 1. Uptake by Above-Ground Crops The uptake of organic chemicals into aboveground crops can arise through translocation through the plant from roots to shoots and absorption of vapours. Review of the potential uptake processes indicates that uptake from vapours is relatively insignificant in comparison to models for the uptake of organics into aboveground crops, particularly for chemicals which have a potential for translocation throughout the plant. A number of studies on the plant uptake of herbicides indicate that translocation with plants is very difficult to predict and measure. Some studies have indicated (USEPA, 1992) that although there may be a potential for translocation within a plant, most of the chemical concentration (i.e. 80% to 98% of the total concentration in the plant) was found to be in the root surface which can be removed by peeling rather than in the internal bulky portion of the roots and root cells. There have been even fewer studies undertaken on the effects of translocation of volatile chemicals within plants. It should be noted that the concentration in below ground vegetables which contain oil cells such as carrots, parsnips and cress have been observed to differ from the relationships indicated in this section (USEPA, 1992). The few studies that have been undertaken indicate that these plants will uptake 2 Lipophilic compounds are identified as those tested that have log K ow of 2.0 or higher. A-11 P a g e

14 chemicals from solution more readily, however most of the chemical (50% to 80%) tends to be located in the outer part of the root and hence easily removed when the vegetable is peeled prior to consumption. The relative potential for the translocation of a chemical within a plant is described by the Transpiration Stream Concentration Factor (TSCF) which is related to the log K ow (the octanol-water partition coefficient) of the chemical (Briggs, 1982). The TSCF for a chemical can be estimated as follows: TSCF (logk 2 ow 1.78) exp( ) 2.44 TSCF = K ow = Transpiration Stream Concentration Factor. This is the ratio of the concentration of chemical in the transpiration stream of the plant (mg/l) to the concentration of the chemical in the external solution (mg/l). octanol water partition coefficient (unitless) The TSCF relates the potential concentration of a contaminant in the transpiration stream water of a plant (i.e. the water within a plant which transports nutrients and other chemicals throughout the different part of the plant from the roots) to the concentration of the contaminant in the soil water. Translocation within the plant is considered to be of significance if the calculated TSCF is greater than 0.1. Application of this methodology correlates well with the model and plant uptake model presented by Trapp (2003) which confirms that translocation of CHCs is important. Calculation of Uptake The equation is used for calculating the concentration of chemicals in above ground vegetables (shown below) is based on empirical models developed by Travis and Arms (1988). The outcome of their work was a plant uptake factor B v which can be calculated using the following equation associated with potential uptake from soils: B v logkow (1 MC ) Where: B v = Uptake factor for above-ground crops (mg/kg fresh produce per mg/kg soil) MC = moisture content of fruit and vegetables, taken to be 0.85 or 85% log K ow = chemical-specific log octanol/water partitioning coefficient (l/kg) A-12 P a g e

15 Concentration in Above-Ground Crops The concentration in above-ground crops associated with irrigation water can be calculated using the following equation: C ag C w B v K d C ag C w * B v K d F oc K oc = fresh weight chemical concentration in above ground vegetables (mg/kg); = chemical concentration in soil solution (mg/l); = Uptake factor for above-ground crops (mg/kg produce per mg/kg soil, see equation above) = equilibrium partitioning coefficient (ml/g) = F oc x K oc = organic carbon content of soils (g/g) = organic carbon partition coefficient (ml/g) Key Parameters and Calculations The calculation of concentrations in below ground and above ground fruit and vegetable crops depends on the chemical specific parameters, log Kow, Koc as well as the soil water concentration. Calculations are undertaken for chemicals where concentrations in groundwater are reported above the limit of detection in residential areas. In general, it is assumed that 19% of intake (from home-grown crops) is from belowground crops and 81% is from aboveground crops. Appendix C presents key assumptions and calculations undertaken for estimating concentrations in home-grown fruit and vegetable produce. A-13 P a g e

16 A4 Calculation of Air Concentrations A4.1 Air Concentrations in Residential Areas Derived from Groundwater Indoor Air The model considered relevant for residential areas, which are typically older homes constructed on piers with a crawl space, is the model derived from Turczynowicz (2002). The model presented is relevant to the assessment of finite sources (in this case shallow soil sources) and is based on subsurface migration as described by the model presented by Jury et al (1983) with additional equations applied to concentrations within the crawl-space and indoor air. At Botany the model has been used in the assessment of exposures in residential areas using measured emission rates for these areas. The equations presented by Turczynowicz (2002) are a summary of the equations presented by Robinson (2000) and Turczynowicz and Robinson (2001). The soil transport and soil flux equations presented are based on Jury and are relevant to the assessment of finite sources. While an infinite source solution to the Jury equations is available, they have not been used in this assessment. In a number of residential areas that overly the shallow groundwater plume (assumed to be infinite sources), direct measurement of emission fluxes has been undertaken. The directly measured emission fluxes are used as surface emission rate that may enter into a crawl-space. Turczynowicz (2002) presents the following equations for crawl-space transportation and dwelling transportation: V cs Ccs a C t cs V cs X cs C cs A J cs V D CD a C t D V D X D C D s C D Q CD C cs V x = volume of crawl-space (cs) and dwelling (D) (m 3 ); C x = concentration in crawl-space (cs) and dwelling (D) (g/m 3 ) a = volatile degradation rate in air (per day), refer to discussion below X x = air exchange rate for crawl-space (cs) and dwelling (D) (per day) s = total sinks assumed to be inhalation by occupants only (2 adults and 1 child) (m 3 /day) J cs = emission flux entering crawl-space (g/m 2 /day), based on measured flux emission data Q CD = volumetric flow rate of air from crawl-space to indoor air via floor, walls and ceiling space (m 3 /day) A = plan area of building (m 2 ) Assuming an infinite source and steady-state emissions, then the above equations can be simplified to the following that can be used to calculate concentrations within the crawl-space and indoor air: C cs V cs A Jcs ( a X CS ) C D V D QCD C ( a X cs D ) s A-14 P a g e

17 Volatile Degradation Rates in Air The model requires the use of volatile degradation rates in air. The degradation rate can be derived from published half-life values in air for each of the COPC evaluated. Review of a range of literature sources indicate that published atmospheric half-life values vary significantly. Table A1 presents a summary of half-life values that are available from key data sources, namely Howard (1991), HSDB (Hazardous Substances Database - online database 2005), ATSDR (toxicological profiles for COPC) and WHO (Environmental Health Criteria for COPC). COPC Table A1 Range of Atmospheric Half-Life Values for COPC Atmospheric Half-Life Howard 1991 HSDB ATSDR WHO dichloromethane 19.1 to 191 days 119 days 130 days NA carbon tetrachloride 18.3 to 657 days 366 years = days years with 50 years reasonable >3.9 to 137 years and >330 years 1,2-dichloroethane (EDC) 12.2 to 122 days 63 days 73 days 10 to 53 days trichloroethene (TCE) 1.1 to 11.3 days 7 hours = 0.3 days 7 days 2 to 5 days tetrachloroethene (PCE) 16 to 160 days 96 days 70 to 96 days NA The data presented in Table A1 indicates that for most COPC the published atmospheric half-life values are within a similar range with the exception of carbon tetrachloride and TCE. Half-life values reported for carbon tetrachloride vary from 18.3 days to 366 years and TCE varies between 7 hours to 11 days. There is no specific guidance that enables sources of data such as half-lives to be ranked. Hence the selection of data from the above table is based on professional judgement with the understanding that a range of values for each COPC is considered valid. The data available from HSDB has been adopted for most of the COPC identified (except TCE) as the values presented are generally similar to those presented in the other sources in particular ATSDR and WHO. The half-life value adopted for TCE is 5 days on the basis that it is a conservative value (remains in air longer) and falls within the range presented by Howard, ATSDR and WHO. The value reported in HSDB is low and may not be considered to be conservative. The calculation of degradation rate in air (day -1 ) has been undertaken using the model and formula available from the USEPA 3 for converting half-life to a degradation rate. This conversion uses the following equation: t1/ 2 where t 1/2 atmospheric half-life (days) = degradation rate (days) -1 Using this conversion and the adopted atmospheric half-life values discussed above the following degradation rates have been used in the calculations: 3 Conversion tool available from A-15 P a g e

18 Table A2 Volatile Degradation Rates in Air for COPC COPC Half-Life (days) Degradation Rate (per day) dichloromethane 119 days carbon tetrachloride 366 years = days ,2-dichloroethane (EDC) 63 days trichloroethene (TCE) 5 days tetrachloroethene (PCE) 96 days Outdoor Air The potential concentration of volatile chemicals in the outdoor air has also been estimated using a model. The outdoor air model is presented by the USEPA in the document Soil Screening Guidance (1996 and Supplement 2001 Exhibit D-3). This model uses air dispersion models to provide an estimate of potential dispersion of emissions above the ground. The relevant equations associated with the estimation of outdoor air concentrations are presented below. C o Q / C J S 10 9 Where: C o = Outdoor air concentration (g/m 3 ) J S = Contaminant flux from the surface of the ground (measured) (g/s/m 2 ) Q/C = Dispersion term calculated for area (g/s/m 2 per kg/m 3 ) 10-9 = Units conversion to from kg/m 3 to g/m 3 Q / C (ln(acres) ) exp( ) ) Where: Q/C Acres = Dispersion term calculated for area (g/s/m 2 per kg/m 3 ) based on climates similar to Los Angeles = Area of the source outside (acres) Key Model Parameters and Calculations The equations presented in this section are relevant to the estimation of exposure concentrations indoors and outdoors from measured flux emission rates. The model parameters, assumptions (and relevant references) and all calculations conducted using the above model for residential areas are presented in Appendix C. A-16 P a g e

19 A4.2 Air Concentrations in Recreational Areas Derived from Groundwater The most significant recreational area located above the contaminated groundwater plumes is Botany Golf Course. Exposure at the golf course (and other areas used for recreational purposes) above the groundwater plumes have been modelled on the basis of either measured emission rates or measured soil gas concentrations. The model used in the quantification of air concentrations on the golf course is the outdoor air model presented in Section A4.1. This model has been presented to estimate an outdoor air concentration from measured flux emission rates. To utilise the soil gas data, an emission rate from the surface of the ground has been estimated based on the measured soil gas concentration, depth and diffusion through overlying soil. The following equations have been used to model an emission rate at the surface f the ground from soil gas measurements: Emission Rate C D D A source eff area (g/s) C source = measured soil gas concentration (g/cm 3 ) D eff = effective diffusion coefficient through the vadose zone (cm 2 /s), refer to equations below A area = area of the emission (cm 2 ) - (width x length of area) D = depth to soil gas measurement (cm) The total overall effective diffusion coefficient can be calculated for n different soil layers between the soil gas source and the surface of the ground as follows: L T L i eff D i eff LT D T (cm 2 /s) n L i eff D i1 i = separation distance between the source and the building (cm) = thickness of the soil layer i (cm) = effective diffusion coefficient across soil layer i (cm 2 /s), as calculated below D eff i D a ai ni D w wi H' ni (cm 2 /s) D a = diffusivity in air, chemical specific (cm 2 /s) ai = soil air-filled volume of layer i (cm 3 /cm 3 ) n i = soil total porosity of layer i (cm 3 /cm 3 ) = 1- b/ s b = soil dry bulk density, (g/cm 3 ) s = soil particle density, (g/cm 3 ) - typically 2.65 D w = diffusivity in water, chemical specific (cm 2 /s) wi = soil water-filled volume of layer i, (cm 3 /cm 3 ) All model parameters and calculations conducted in recreational areas are presented in Appendix D. A-17 P a g e

20 A4.3 Air Concentrations in Commercial/Industrial Areas Derived from Groundwater Concentrations Indoors No Basements Commercial buildings in the area are of differing construction to the residential houses. These buildings are expected to be constructed predominantly on concrete slabs, typically with no subsurface basement (not common in Australia). An exception to this would be hotels that commonly have cellars. The situation of public hotels in the investigation area has been addressed separate to this study. The potential for new buildings to be constructed in the area that have basement car park areas is addressed in Section D The potential concentration within a commercial/industrial building has been estimated using maximum measured flux emission rates from representative areas and a box model (Farmer 1980 as modified by SD DEH 2000). The concentration indoors can be estimated using the following equation: C indoors E FS FC ER V surface g/m 3 E surface = Emission rate measured from the surface of the ground beneath the building (g/s) FS = fraction of floor above source, unitless FC = fraction of emission entering through floor or basement, unitless. ER = air exchange rate, (per s) V = volume of the building (m 3 ) The fraction of emissions entering through the floor varies for the different types of buildings considered in the commercial/industrial area. The values considered include: 0.3 for varied building types that may include demountable buildings that may be present on the rail area; and 0.1 for existing commercial areas constructed on a slab. This is a conservative factor that accounts for older slabs that may have some cracks or gaps around services that penetrate the slab. Concentrations Indoors With Basements Existing commercial/industrial buildings in the area are generally constructed on concrete slabs with no subsurface basement. However there is the potential that new buildings constructed in the area may include basement-level car parks or storage areas. The construction of these types of newer buildings is becoming more common in urban areas due to increased pressure on density. The groundwater is shallow in the areas assessed and hence the construction of a building with a basement in this area is expected to be undertaken so as to manage groundwater ingress into the basement. Hence the inhalation of volatile chemicals will be the only complete pathway for exposure (i.e. direct contact except during construction purposes is not a complete exposure pathway). If a basement were constructed where seepage occurred, then risks calculated in this assessment are expected to be an underestimation of actual exposures and a site-specific assessment should be conducted. A-18 P a g e

21 Limited data is available to enable estimation of concentrations in air within basements and ground floor work spaces overlying the basement. Typically estimation of the potential concentration within a basement area would be evaluated using soil gas concentrations measured in the zone of the basement depth. The available soil gas data from depth in the commercial areas has shown few detections of CHCs. Hence the methodology adopted in the 2005 CHHRA has been utilised in the 2010 CHHRA for estimating exposures in buildings with a basement. The review conducted in the 2005 CHHRA considered the estimation of concentrations indoors from older soil gas data or from estimated indoor air concentrations for a building on a slab and a modifying factor. The 2005 CHHRA review identified that estimating basement concentrations using indoor air concentrations and a modifying factor was more conservative that considering vapour intrusion from detected soil gas concentrations. Review of soil gas data collected since the 2005 CHHRA continues to support this outcome. On this basis, the approach adopted for the estimation of concentrations in a building constructed with a basement (and no groundwater seepage) is as follows: Basement Concentrations Estimated from Indoor Air Concentrations The problem of vapour migration in multi-storey buildings is complex due to the partition wall between units as well as the size of the building air envelope. Other key influences include adjacent units, stairwell doors, garbage chutes, elevator shafts, electrical and plumbing ducts, ventilation shafts (air conditioning) and windows. All of these factors vary between buildings and constructions (including the age of the construction) and modelling vapour migration in a multi-storey building is very complex and difficult. It is even more difficult when the proposed building is not defined. An attenuation factor has been adopted to estimate a potential concentration in air within the basement of a building based on estimated concentration within the ground floor as described above. An attenuation factor of 10 has been used, i.e. the concentration in the basement is estimated to be 10 times higher than the concentration in the ground floor. The attenuation factor of 10 used in this assessment is derived from a number of sources as follows: Air data associated with a number of CHCs has been collected for the Pier Hotel in Botany (as part of a separate investigation) (DEC 2004) within the cellar as well as the ground floor areas of the hotel. Observation of this data indicates that basement concentrations were approximately 10 to 15 times higher than concentrations reported on the ground floor. The hotel evaluated has an internal access (stairway) which provides for better air exchange between floors. Larger buildings with car park basements are expected to have a poorer interconnection between the basement and ground floor and hence the lower value (10) is considered relevant for this assessment. Data collected by Olson and Corsi (2001) based on tracer experiments within a multi-storey home (with internal stairway access) indicates that the concentration within the first-floor is approximately 10 times lower than the concentration within the basement. Review of the transfer of tobacco smoke between apartments within multi-storey buildings (between levels and across floors) indicated (CEE, 2004) that the transfer of air between floors of a multi-floor building was 2% for the lower floors, 7% for the middle floors and 19% for the upper floors. The trend was associated with the thermal stack effect during the heating season. During this period, warmer air inside the building is less dense than the outside air resulting in cold air A-19 P a g e

22 from outside entering the lower portion of the building, rising and exiting through the upper floors. Hence the lower floors tend to get most of the air exchange from outside and upper floors get a more significant air exchange from floors beneath. When evaluating vapour migration from a subsurface source, the migration into the ground floor is considered more significant than outside air. Hence concentrations within the first-floor above the ground floor are expected to be diluted with outdoor air resulting in lower concentrations between 2% and 7% of the lower floor concentration. Review of radon simulation results for a range of multistorey buildings (Fang J.B and Persily A.K., 1995) indicates that under a range of temperature and wind conditions the concentration difference between the basement and first floors was between a factor of 0 and 100. A 10-fold factor between concentrations within the basement and the first-floor would provide a conservative estimation of first floor concentrations (derived from ground floor or basement concentrations) under most conditions. Concentrations Outdoors Outdoor exposures have been estimated using measured flux emission rates and the outdoor air model presented for the assessment of outdoor air in residential areas (refer to Section A4.1). Key Model Parameters and Calculations The equations presented in this section are relevant to the estimation of exposure concentrations indoors and outdoors from measured flux emission rates. The model parameters, assumptions (and relevant references) and all calculations conducted using the above model for commercial/industrial areas are presented in Appendix D. A-20 P a g e

23 A5 Modelling Emissions from the CPWE The quantification of exposure associated with emissions from the Car Park Waste Encapsulation required the use of a dispersion model that can model emissions from the encapsulation area to provide an estimate of the potential concentrations of COPC at specific receptor locations. Contaminants discharged into the air are transported over long distances by large-scale airflows and dispersed by small-scale airflows or turbulence, which mix contaminants with clean air. An atmospheric dispersion model is: a mathematical simulation of the physics and chemistry governing the transport, dispersion and transformation of pollutants in the atmosphere; and a means of estimating downwind air pollution concentrations given information about the pollutant emissions and nature of the atmosphere. Most modern air dispersion models are computer programs that calculate the pollutant concentration downwind of a source using information on the: contaminant emission rate; characteristics of the emission source; local topography; meteorology of the area; and ambient or background concentrations of the pollutant. Models can be set up to estimate downwind concentrations of contaminants over varying averaging periods, either short term (e.g. three minutes) or long term (e.g. annual). The AUSPLUME dispersion model is the regulatory model approved for use in NSW by EPA in the Approved Methods and Guidance for the Assessment of Air Pollutants in NSW. AUSPLUME (Version 5.1) has been used in this assessment. Later versions of AUSPLUME (Versions 5.4 and 6.1) are available however the later versions have not updated the algorithms or processes for the modeling of area sources. Hence the version used in the 2005 CHHRA has been used in the revised modeling presented in the 2010 CHHRA and is considered suitable for modeling emissions to air from the Car Park Waste Encapsulation. Meteorological Data Meteorological data used in the Car Park Waste Risk Assessment (URS 2002) was a 1984 file based largely on data from La Perouse, with data from the Botany plant and Mascot Airport used to supplement shortcomings in the data. Meteorological data for both Botany (1995) and Mascot (1995) were provided by the NSW EPA (now DEC) for use in air quality impact assessment for the proposed HCB Waste Destruction Facility (URS, 2002b) on the BIP. Both meteorological data files provided by the NSW EPA were considered in the 2005 CHHRA, with maximum results derived from the Botany data set. The Botany meteorological data set has therefore been used in this revision. A-21 P a g e

24 Emission Source The source of emissions is the Car Park Waste Encapsulation. AUSPLUME can model area sources that are regular shapes (square or rectangle) as well as irregular shapes (based on the co-ordinates of corners or circular sources). Modelling the encapsulation emissions in the Car Park Encapsulation Risk Assessment was undertaken by considering a number of emission areas that correspond with key areas where emission have been measured. These are consistent with those considered in the 2005 CHHRA. These areas sources are (with emission rate noted for HCBD, other emission are calculated for the same areas): A1 (451.9 m 2 ) and A2 (539.1 m 2 ), which represent the cracked portion of the asphalt where cars regularly drive over the car park as access to other areas of the BIP. While the whole area is not cracked, it has been assumed that this is the case for this assessment. The emission rate used for these areas is equal to the average of the maximum considered in the 2005 CHHRA, and the maximum reported from 2005 to 2009 for data collected from location AS02, calculated to be 42.6 µg/min/m 2 for HCBD; A3 (557.8 m 2 ), which is located to the west of A1, and represents some asphalt and some embankment area. The emission rate used in the 2005 CHHRA is the maximum reported from samples collected in this area (AS-8 and EB3). No additional data have been collected from this area; hence, the emission rate considered in the 2005 CHHRA has been adopted, 43.8 µg/min/m 2 for HCBD; A4 (1052 m 2 ) which is located to the west of A2, and represents some asphalt and some embankment area. The emission rate used for these areas is equal to the average of the maximum considered in the 2005 CHHRA and the maximum reported from AS47 and EB5 from 2005 to 2009, calculated to be 33.1 µg/min/m 2 for HCBD; A5 (817.7 m 2 ) and A6 ( m 2 ), which comprise large areas of asphalt car park surface and include the northern and eastern embankments. The asphalt areas included are not cracked, and emission rates collected from these areas are lower than from the cracked sections. In addition, emission rates measured from the northern and eastern embankments are lower (with the exception of HCBD reported from EB1 in 2004, as this is now remediated) than those measured along the western embankments. The emission rate used to model these areas in the 2005 CHHRA was the average of emission rates from the October 2004 sampling round from sampling for locations AS11, AS12, EB6, EB7, EB1 and EB2. Samples have been collected from EB1 following remediation of this area. This reported lower emissions rates than those used in the 2005 CHHRA. These data are from one location only, and are not expected to significantly affect (lower) the emission rate for the whole area. Hence, the emission rates adopted in the 2005 CHHRA have been considered in this assessment, with 8.4 (µg/min/m 2 ) for HCBD; and A7 (154 m 2 ) is a hot spot addressed in the 2005 CHHRA based on data reported from sampling location EB1 in August 2004, where air sampling during intrusive works resulted in a significantly higher emission rate of HCBD reported from this location. The measured data are expected to be associated with the intrusive works being undertaken, and this area has been subsequently remediated, with flux emission data from the area following remediation not detecting HCBD emissions. Hence, this hot-spot, and area A7, is not considered representative of long-term emissions from the CPWE, and has not been included in the 2010 CHHRA. All area sources are 2m above the ground level as the whole soil encapsulation is raised 2 m from surrounding areas. A-22 P a g e

25 Receptor Locations Receptors refer to locations (at ground level) where the concentration of the target chemical is required to be estimated. The location of receptors surrounding the Car Park Waste Encapsulation have been chosen based on the surrounding land use, particularly where there is the potential for sensitive (residential) land use. AUSPLUME accepts receptors in a grid format or as discrete points. To represent recreational, residential and industrial receptors, discrete receptor points have been chosen in the following locations (refer to Figure 7.3 in the main report): Residential area Receptors 1 to 5 located on the eastern side of Denison Street and bounded by Smith Street, Boonah Street, Fraser Street and Wentworth Avenue; Recreational area (Hensley Athletics Field) Receptors 6 (middle of the field), 7 (athletics straight) and 8 (grandstand area); Off-site industrial areas Receptors 9 and 10 located north of the encapsulation; and On-site industrial areas Receptors 12 and 13 located to the southwest and south of the encapsulation. Averaging Period The averaging period is the time frame by which AUSPLUME averages the estimated hourly calculations. The averaging period considered in this assessment, that focuses on chronic, lifetime, exposures is an annual average. Other Parameters Other parameters utilised in AUSPLUME relevant to the assessment of the Car Park Waste Encapsulation are as follows: Selection of urban (industrial) dispersion parameters based on the nature of the surrounding environment; Acceptance of AUSPLUME default model options for the treatment of buoyant emissions (not relevant here), building wake effects (not relevant here), wind speed profiles and temperature profiles; and Assumption that the area surrounding the Car Park Waste Encapsulation is essentially flat. Hence terrain effects have not been considered. A-23 P a g e