Appendix A Equations Former ChlorAlkali Plant, Human Health and Environmental Risk Assessment - 2013
A1 Introduction This appendix presents the methodology and equations used to quantify exposures via inhalation, ingestion and dermal absorption. The approach adopted is in accordance with guidelines/protocols provided by NEPC and enhealth (enhealth 2012; NEPC 1999 amended 2013), with many of the equations derived from the USEPA (USEPA 1989, 1991, 1996, 2002, 2004a, 2009). A-1 P age
A2 Calculation of Chemical Intakes A2.1 Intakes via Ingestion The assessment of ingestion exposures requires evaluation of a number of pathways that can be grouped into the ingestion of water and ingestion of soil. Ingestion of Water This includes evaluation of the following pathways: Ingestion of groundwater during incidental contact during intrusive works, where groundwater is sufficiently shallow; and Ingestion of groundwater extracted from an irrigation bore. 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 (dependent 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 (dependent on age) (kg) = Averaging time for threshold (=ED x 365) and non-threshold exposures (=70 years x 365) (days) Ingestion of Soil Assessment of intake via the ingestion of soil is evaluated using the following equation: Daily Chemical Intake IS IRS FI B CF EF ED CS (mg/kg/day) BW AT Cs IRs FI B CF EF ED BW AT = Concentration of chemical in soil (mg/kg) = Ingestion rate of soil (dependent on age and activity) (mg/day) = Fraction of daily ingestion that is derived from contamination source assumed to be 1 or 100% unless noted otherwise (unitless) = Bioavailability or absorption of chemical via ingestion assumed to be 1 or 100% unless noted otherwise (unitless) = Conversion factor of 1x10-6 to convert mg to kg = Exposure frequency (days/year) = Exposure duration (years) = Body weight (kg) = Averaging time for threshold (=ED x 365) and non-threshold exposures (=70 years x 365) (days) A-2 P age
A2.2 Intakes via Dermal Exposures The assessment of dermal exposures involved quantification of intakes from water (extracted groundwater and groundwater exposures during excavations) and soil. 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 300-400 µm). The epidermis consists of four layers, the outermost layer being the stratum corneum (SC) (approximately 10-40 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-3 P age
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. The value for all forms of mercury in soil of 0.001 cm/hr has been obtained from the Risk Assessment Information System (RAIS) database available on the website (http://risk.lsd.ornl.gov/index.shtml) which is maintained by the Oak Ridge Operations of the US Department of Energy, current to 2013. Dermal Contact with Soil Dermal absorption of chemicals from soil depends on the area of contact, duration of contact, bond between the chemical and the soil and the ability of the chemical to penetrate the skin. With respect to inorganic mercury there is some evidence to suggest adverse health effects have occurred following dermal application of some products containing mercury. While not considered in the derivation of the current HIL, dermal intakes of inorganic mercury were identified as of potential concern, although noted to be difficult to quantify. Hence the assessment here has considered dermal intakes of inorganic mercury to provide a conservative assessment of total exposure. As the assessment presented has focused on potential dermal absorption of inorganic mercury, the assessment has been generally undertaken using the approach presented by the USEPA 1. The USEPA (1989 and 2004a) define a simple approach to the evaluation of dermal absorption associated with soil contact. This is presented in the following equation: 1 The assessment of dermal absorption has been presented within the CHHRA (URS 2005) using the Hawley (Hawley, JK 1985) approach. This approach is relevant for organic chemicals, however its relevance for inorganic chemicals is not clear. Hence the approach adopted by the USEPA where both organic and inorganic chemicals are considered has been adopted for the assessment of mercury. A-4 P age
Daily Chemical Intake SAs AF ABSd CF EF ED Cs (mg/kg/day) BW AT Cs SAs AF ABSd CF EF ED BW AT = Concentration in soil (mg/kg) = Surface area of body exposed to soil per day (cm 2 /day) = Adherence factor, amount of soil that adheres to the skin per unit area which depends on soil properties and area of body (mg/cm 2 per event) = Dermal absorption fraction (unitless refer to discussion below) = Conversion factor of 1x10-6 to convert mg to kg = Exposure frequency (days/year) = Exposure duration (years) = Body weight (dependent on age) (kg) = Averaging time for threshold and non-threshold exposures (days) Dermal Absorption Fraction (ABSd): The approach undertaken by the USEPA utilises a dermal absorption fraction typically derived from experimental studies on different chemicals. On the basis of the studies undertaken and a number of simplifications, ABSd values have been recommended for a range of 10 chemicals and default values for other semi-volatile chemicals. No default is defined (in USEPA, 2004a) for volatile organic chemicals or inorganic chemicals. It is considered that, with regards to soil exposures, volatile organic chemicals would volatilise from soil on skin and should be accounted for in the assessment of inhalation exposures. For inorganics, the speciation is very important to dermal absorption and hence no generic default values have been determined. More commonly used values for the assessment of dermal exposure to organics and inorganics utilise defaults for ABSd for organics of 0.01 and inorganics of 0.001 as presented on RAIS (Risk Assessment Information System), along with the few chemical-specific values available. The value of ABSd has no consideration of exposure time. Experimental studies used to define ABSd values are associated with dermal application over 24 hours (i.e. the event is considered to be a 24 hour day by default). Due to the lack of information about the rate and relationship of absorption of chemicals through the skin over shorter exposure periods, the USEPA methodology does not recommend adjusting the ABSd to account for exposures over times less than 24 hours, rather it recommended adjusting exposure frequency and exposure duration to reflect site conditions. The approach adopted by Fitzgerald D.J. (SAHC 1991) in the setting of a response level for benzo(a)pyrene where intake via skin absorption for a 2 ½ and 6 year old child utilised the general approach presented by the USEPA with the dermal absorption value over 24 hours. However, for an adult the intake via skin absorption considers exposure to soils over 12 hours and adjusted the intake using a linear relationship for absorption. While many other response levels (in various papers in SAHC) have been established following this approach, they are typically set for a 2 ½ year old child where dermal absorption associated with soils over 24 hours is considered to be relevant. Other references where dermal absorption over shorter exposure periods than 24 hours (using the linear approach) are presented in the following: Di Marco P.N. and Buckett K.J. (SAHC 1996) in Derivation of Health Investigation Levels for Beryllium and Beryllium Compounds Di Marco P.N. (SAHC 1993) in The Assessment and Management of Organochlorine Termiticides where exposures over 24 hours (children), 8 and 10 hours (adults). A-5 P age
Di Marco P.N. and Buckett K.J. (SAHC 1993) in Derivation of A Health Investigation Level for PCBs Hence for the assessment of potential exposures by workers on the FCAP, dermal exposures have been assessed based on a 12 hour exposure, assuming workers wash at the end of each work day. A2.3 Intakes via Inhalation The assessment of inhalation exposures has been undertaken 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 dependent 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 (dependent 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) This equation has been adopted for the assessment of vapour and particulate/dust exposures. Dust has been assumed to be present as respirable size particulates that can enter and reach deep into the lungs. A-6 P age
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 (MfE 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 k g l k k g,h2o l,co2 18 MW 44 MW 0.5 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 age
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 100 10 1301 y 998.33 8.1855 (T 20) 0.00585 (T 20) 2 3.30233 Concentration in Soil Water Volatilisation is assumed to be a first-order process: C s C o e K ' L6t /(3600d) 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 age
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 / 600d 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. A-9 P age
A4 Calculation of Air Concentrations A4.1 Introduction The assessment of vapour migration and vapour intrusion into buildings can be undertaken using a number of different models depending of the building type considered. While the model and approach adopted for the different building types differs, the initial processes associated with partitioning from a source concentration in soil or groundwater to vapour phase (directly above the source) is the same. In addition, all the models currently used consider diffusion as a key mechanism for vapour phase transport through the subsurface. The methodology for estimating vapour diffusion is the same in each model. The vapour phase concentration at the source can be estimated using the following relationships: Where soil gas data are available and relevant to the quantification of vapour intrusion, the measured soil gas concentration is considered to be the concentration at the source, with diffusion modelled through overlying soils (from point of measurement to the surface of building); and Where no soil gas data are available, the concentration at the source is based on theoretical partitioning from the groundwater or soil source, see below, with subsequent diffusion modelled through the overlying soils. The following presents the equations (Johnson & Ettinger 1991; Johnson, Hertx & Beyers 1990) used to estimate the vapour phase concentration directly above the source and diffusion through overlying soils. A4.2 Vapour Phase-Partitioning Groundwater Source For a groundwater source, it is assumed that the vapour phase concentration directly above the groundwater is in equilibrium with the groundwater and the concentration is related to the groundwater concentration by Henry s Law: C source C HL (g/cm 3 ) Equation VS1 water Where: C water = concentration in water (at top of groundwater, g/cm 3 ) HL = Henry s Law constant (unitless) The concentration within the vapour phase will increase proportionally with the concentration in groundwater (at the top of the groundwater table), until it reaches saturation. At some point the saturated vapour phase concentration will be reached, which is an upper limit of the vapour phase concentration. The saturated vapour phase concentration is estimated using the following relationship: VP MW SVPC (g/cm 3 ) Equation VS2 T 62361 A-10 P age
Where: VP = vapour pressure of the contaminant (mmhg) MW = molecular weight (g/mol) T = soil temperature (K) 62361 = conversion (mmhg/k* cm 3 /mol) Soil Source For a soil source, it is assumed that the vapour phase concentration directly above the soil is in equilibrium with the source and the concentration is related to the soil concentration by the following: C C H' soil S source (g/cm 3 ) Equation VS3 ws k d S H' as Csoil = Concentration in soil source zone (g/g) H = Henry s Law constant (unitless) S ws as = Soil bulk density (g soil/cm 3 soil) = Volumetric water content in soil source zone (cm 3 water/cm 3 soil) = Volumetric air content in soil source zone (cm 3 air/cm 3 soil) K d Koc f oc = Soil-water partition coefficient (cm 3 air/g soil) = K oc x f oc = Soil organic carbon partition coefficient, chemical specific (cm 3 /g) = Soil organic carbon fraction (unitless) The equilibrium vapour phase concentration is proportional to the soil concentration up to the soil saturation limit (C sat ), which is calculated using the following (with the saturated vapour phase calculated using Equation VS2): C sat S [H' as s ws Kd ] (mg/kg) Equation VS4 s S = Pure component solubility in water (mg/l) When residual phase is present the vapour concentration is independent of the soil concentration but proportional to the mole fraction of the individual component of the residual phase mixture as below. A-11 P age
Effective Diffusion The total overall effective diffusion coefficient can be calculated for n different soil layers between the source and the enclosed floor (including the capillary fringe where relevant). This is estimated using Equation D1. L T L i eff D i L eff T D T n Equation D1 Li 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) refer to Equation D2 3.33 3.33 eff ai Dw wi D i Da 2 Equation D2 2 ni H' ni 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 ) A4.3 Vapour Intrusion Indoors A4.3.1 Farmer Model The potential concentration of volatile chemicals inside a range of building types can be estimated using a box model as detailed by Farmer (Farmer et al. 1980) as modified by SD DEH (SD-DEH 2000). The model is simple and is relevant to a range of building types that are constructed on or above the ground. The model is not relevant for the estimation of concentrations in a building with a subsurface basement. The model is used to assess vapour intrusion indoors only and assumed that the source is nondepleting. A-12 P age
The steady-state vapour-phase concentration of a contaminant inside a building (C building ) is calculated by using Equation F1. C indoors Esurface FS FC g/m 3 Equation F1 ER V E surface = Emission rate measured from the surface of the ground beneath the building (g/s), calculated using Equation F2 (or directly measured) FS = fraction of floor above source, unitless FC = fraction of emission entering through floor, unitless. ER = air exchange rate, (per s) V = volume of the building (m 3 ) Csource Deff Aarea ER (g/s).equation F2 D C source D eff A area D = estimated vapour phase concentration at source (g/cm 3 ) refer to Equations VS1 to VS5 as relevant for the source assessed = effective diffusion coefficient through the vadose zone (cm 2 /s), refer to Equations D1 and D2 = area of the emission (cm 2 ) - (width x length of area) = depth to source (cm) The fraction of emissions entering through the floor (FC) is also referred to as an attenuation factor that relates the concentration directly beneath the slab to that above the slab. A range of attenuation factors are relevant to buildings and include the following (SD-DEH 2000): Dirt floor (no slab) attenuation factor = 1.0 Old slab attenuation factor = 0.1 New/improved slab attenuation factor = 0.01 Coated slab attenuation factor = 0.001 (note the use of the factor requires data to demonstrate this is achieved) Crawl-space attenuation factor = 0.3 (see details below) An attenuation factor can also be used that is representative of a building constructed on piers with a crawl-space. A4.3.2 Johnson & Ettinger Model The potential concentration of volatile chemicals inside a building constructed on a concrete slab with or without a sub-surface basement has been estimated using the Johnson & Ettinger Model (USEPA 2004b). This model is consistent with the equations outlined by Johnson & Ettinger (1991) as recommended in the Soil Screening Guidelines (USEPA 1996) and the Risk Based Corrective Action at Petroleum Release Sites (ASTM 2002). The model is used to assess vapour intrusion indoors only and assumed that the source is nondepleting. A-13 P age
Conceptual Model (from Johnson and Ettinger 1991) Equations The steady-state vapour-phase concentration of a contaminant inside a building (C building ) is calculated by applying the Johnson and Ettinger model assuming a steady-state mass transfer (i.e., infinite). This is calculated using Equation JE1. C C Equation JE1 indoor source Where C indoor = the steady-state vapor-phase concentration of a contaminant inside a building (g/m 3 ) = attenuation coefficient [unitless], refer to Equation JE2 = vapour concentration at the source (g/m 3 ), refer to equations VS1 to VS5 (as relevant). C source The attenuation factor is calculated using the following: Q exp D soil L A D Q eff T building D Q AB L eff T building T AB L Q exp D T D Q soil eff T soil L A A L B T Q exp D soil L A 1 Equation JE2 A-14 P age
Where: D eff T. = total overall effective diffusion coefficient. Refer to Equations D1 and D2. A B = area of the enclosed space below the ground level which will vary depending on whether the building has a basement below the ground or not (cm 2 ). Q building. = building ventilation rate which is calculated using building parameters and air exchange rate (cm 3 /s). Refer to Equation JE3. L T = separation distance between the source or soil gas measurement and the building (cm). Q soil. = volumetric flowrate of soil gas into the enclosed space. This represents the convective flow of vapours into a building though s in the floor and walls. It incorporates pressure driven flows and a default value of 5 L/min is recommended (2003), however it can be calculated using Equation JE5. L = enclosed space foundation or slab thickness (cm). D = effective diffusion coefficient through the s (cm 2 /s). A = area of total s which varies depending on whether there is a basement or not (cm 2 ), refer to Equation JE4. The building ventilation rate is calculated using Equation JE3 for the building dimensions representing the living space of the building. It assumes that the total air volume entering the structure is mixed and that the vapour entering the structure is instantaneously and homogeneously distributed. Q building (LB WB HB ER) Equation JE3 3600 Where: L B = length of building, (cm) W B = width of building, (cm) H B = height of building, (cm) ER = air exchange rate, (per hour) 3600 = conversion from hours to seconds A AB L n AB B W B (2 L B L h 2 W B L h ) Equation JE4 Where: AB = area of enclosed space below ground, (cm 2 ) n = ratio of area to total area (unitless) A = total area, (cm 2 ) L h = depth below ground, (cm) The volumetric flow rate of soil gas into the building is calculated using Equation JE5. This represents the advective/convective flow rate of contaminant vapours in soil surrounding the building via the s in the building floor and walls. It incorporates pressure driven flows into the building that may be associated with wind effects on the structure, stack effects due to heating or an unbalanced mechanical ventilation. This is of particular importance where a basement is present and where heating /ventilation effects are of significance. Tracer testing of buildings where advection is the primary mechanism for intrusion into the building suggested a typical range for Qsoil from 1 to 10 L/min, with 5 L/min selected as a default by the USEPA (2004b). The equation represents potential openings for soil vapour entry into a building. These openings include floor/wall joints associated with floating concrete slabs or a perimeter drain /sump system. The soil vapour permeability used is that for the type of material immediately under the slab. A-15 P age
2 P k v X Q soil Equation JE5 Z ln 2 r Where: P = pressure differential between the soil surface and the enclose space, (g/cm.s 2 ) which may range from negligible (0.001-20Pa, or 0.0001 to 2 g/cm.s 2 ) k v = soil vapour permeability, (cm 2 ), calculated based on soil type beneath slab as per USEPA 2003 X = floor-wall seam perimeter, (cm) = viscosity of air, (g/cm.s) Z = depth below ground level, (cm) r = equivalent radius, (cm), refer to USEPA 2003 for approach. However, for buildings constructed as slab-on-grade in climates where the potential for pressure differences to be driven by long term heating or unbalanced ventilation systems, the potential for pressure driven flows (advection) is considered negligible, consistent with the approach adopted in the ASTM guidance (2002). This results in Qsoil to be essentially negligible and hence the attenuation factor is simplified and can be calculated using the following (as per ASTM 2002): eff DT / L 1 ER L T B eff D T / LT ER LB eff DT / L (D / L T ) Equation JE6 Where: D eff T. = total overall effective diffusion coefficient. Refer to Equations D1 and D2. L B = enclosed-space volume: infiltration area ratio (cm). ER = enclosed-space air exchange rate (1/sec). L T = separation distance between the source or soil gas measurement and the building (cm). L = enclosed space foundation or slab thickness (cm). = effective diffusion coefficient through the s (cm 2 /s). D A4.3.3 Model Assumptions The following represent the major assumptions/limitations of the Farmer and J&E Model. 1. Contaminant vapours enter the structure primarily through s and openings in the walls and foundation. 2. Convective transport occurs primarily within the building zone of influence and vapour velocities decrease rapidly with increasing distance from the structure. 3. Diffusion dominates vapour transport between the source of contamination and the building zone of influence. A-16 P age
4. All vapours originating from below the building will enter the building unless the floors and walls are perfect vapour barriers. 5. All soil properties in any horizontal plane are homogeneous. 6. The contaminant is homogeneously distributed within the zone of contamination. 7. The aerial extent of contamination is greater than that of the building floor in contact with the soil. 8. Vapour transport occurs in the absence of convective water movement within the soil column (i.e., evaporation or infiltration), and in the absence of mechanical dispersion. 9. The model does not account for transformation processes (e.g., biodegradation, hydrolysis, etc.). 10. The soil layer in contact with the structure floor and walls is isotropic with respect to permeability. 11. Both the building ventilation rate and the difference in dynamic pressure between the interior of the structure and the soil surface are constant values. Use of the J&E Model as a first-tier screening tool to identify sites needing further assessment requires careful evaluation of the assumptions listed above to determine whether any conditions exist that would render the J&E Model inappropriate for the site. If the model is deemed applicable at the site, care must be taken to ensure reasonably conservative and self-consistent model parameters are used as input to the model. Considering the limited site data typically available in preliminary site assessments, the J&E Model can be expected to predict only whether or not a risk-based exposure level will be exceeded at the site. Precise prediction of concentration levels is not possible with this approach. A4.4 Vapour Migration to Outdoor Air and into Excavations There are a number of models available for estimating potential concentrations of chemicals within the outdoor air environment associated with the migration from a subsurface source. Limited guidance is available for the estimation of concentrations in an excavation, hence the outdoor model adopted has also been utilised for calculations of concentrations within an excavation. The estimation of concentrations in outdoor air can be undertaken using two different methodologies outlined in the Soil Screening Guidelines (USEPA 1996) and the Risk Based Corrective Action at Petroleum Release Sites (ASTM 2002). The model is used to assess vapour intrusion indoors only and assumed that the source is nondepleting. The relevant equations associated with the estimation of outdoor air concentrations based on the approach outlined in the USEPA document Soil Screening Guidance (USEPA 1996, 2002). This model uses air dispersion models to provide an estimate of potential dispersion of emissions above the ground as presented below. C J S o Equation O1 9 Q / C 10 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 A-17 P age
Q / C 2 (ln(acres) 18.4385) ) 11.91 exp( ) Equation O2 209.7845 Where: Q/C = Dispersion term calculated for area (g/s/m 2 per kg/m 3 ) based on climates similar to Los Angeles which is considered relevant for much of Australia, however for other areas, relevant parameters are selected. Acres = Area of the source outside (acres) A simpler approach more commonly used for small subsurface sources is the outdoor model presented in the ASTM (2002) guidance. Outdoor air concentrations have been estimated using a simple box model, which accounts for some atmospheric mixing. The concentration of volatile contaminants within the breathing zone of outdoor air has been estimated using Equation O3. C outdoor C VF (mg/m 3 ) Equation O3 S Where: C s = concentration at the source (mg/m 3 ) VF = volatilisation factor calculated for emissions from the source to air, refer to Equation O4. As noted with the indoor air model, the vapour phase concentration at the source can be estimated using the following relationships: Where soil gas data are available and relevant to the quantification of vapour migration, the measured soil gas concentration is considered to be the concentration at the source, with migration modelled through overlying soils (from point of measurement to the surface); and Where no soil gas data are available, the concentration at the source is based on theoretical partitioning from the groundwater or soil source, as presented in Equations VS1 to VS5 (as required). The volatilisation factor is calculated using the following: VF air eff s D W...Equation O4 U L GW = Wind speed above the ground surface in the ambient mixing zone (cm/s) = Ambient air mixing zone height (cm) = Depth to groundwater (= height of capillary zone, h cap, + height of unsaturated zone, h v ) (cm) W = Width of source area parallel to wind or groundwater flow direction (cm) (i.e. width and breadth of breathing zone) eff D ws = Effective diffusion coefficient between the groundwater and soil surface (cm 2 /s), refer to Equations D1 and D2. U air air L GW ASTM (2002) also provides equations for estimating emissions to outdoor air from sources that are close to or at the surface of the ground. A-18 P age
Emissions into Excavation or Trench Volatile COPC have the potential to accumulate within trenches or excavations in areas where excavations intersect or are located directly above contaminated soil or groundwater. Workers have the potential to be exposed to these COPC when working in or near the trench or excavation. It is unlikely that workers would spend an entire workday within any excavation or trench, and any exposure near the trench or excavation would result in exposure to significantly lower concentrations due to dilution. Concentrations within an excavation have been estimated using the ASTM (2002) outdoor air model presented above, however the depth to the source is adjusted to reflect to depth from the base of the excavation to the source, the dimensions of the excavation are used and the wind speed is adjusted to reflect a more confined space scenario. A typical excavation is estimated as 1m x 10m x 1 to 1.5m depth (ANZECC (ANZECC 1992) notes the depth of most services is between 1 to 2m below ground surface). A wind speed considered representative of a more confined space within an excavation is 0.5 m/s. Where groundwater seeps into an excavation, concentrations of volatile chemicals in groundwater that could be inhaled during excavation work can be estimated using an upper-bound volatilization factor (VF). The VF is based on workers in trenches flooded with groundwater off-gassing volatile organic compounds (VOCs). A methodology developed by the USEPA has been used to estimate a VF from water (VF w ) (USEPA 1999). The EPA method examines the mass of a chemical that could be transferred from water to air and assumes: L VF w m 3 k lg X k H 1000L 3 m (mg/m 3 air)/(mg/l water) k lg = a conservative estimate of the overall mass transfer coefficient from the liquid phase to the gas phase of 3.0 x 10 6 m/s (USEPA 1999) X = an average trench length of up to 30 meters (USEPA 1999) H = an average trench depth of 3 meters (USEPA 1999) µ = average wind speed in excavation of 1 mph (0.45 m/sec) over a year s time (USEPA 1999) k = an air mixing rate between trench air and ambient air of 50%; uniform mixing of air occurs in the trench (USEPA 1999) Using these assumptions, the USEPA s default, upper-bound volatilization factor (VF w ) of 0.133 litres per cubic metre (L/m 3 ) has been adopted (USEPA 1999). The VF w is applied directly to the relevant groundwater concentrations assumed to seep into an excavation to estimate an air concentration in the flooded trench. If this VF were considered in relation to phase partition equations for dissolved phase and LNAPL sources, the air concentration in an excavation would be approximately 2000 times lower (based on dispersion and dilution in excavation) than the vapour phase concentration estimated at an LNAPL source, assuming the product floods into an excavation. A-19 P age
References ANZECC 1992, Australian and New Zealand Guidelines for the Assessment and Management of Contaminated Sites, Australian and New Zealand Environment and Conservation Council and National Health and Medical Research Council, ASTM 2002, Emergency Standard Guide for Risk-Based Corrective Action Applied at Petroleum release Sites, American Society for Testing and Materials, enhealth 2012, Environmental Health Risk Assessment, Guidelines for assessing human health risks from environmental hazards, Commonwealth of Australia, Canberra. Farmer, WJ, Yang, MS, Letey, J & Spencer, AW 1980, Land Disposal of Hexachlorobenzene Wastes Controlling Vapour Movement of Soil, United States Environment Protection Agency. Hawley, JK 1985, 'Assessment of health risk from exposure to contaminated soil', Risk Anal, vol. 5, no. 4, Dec, pp. 289-302. Johnson, PC, Hertx, MB & Beyers, DL 1990, 'Estimates for Hydrocarbon vapour emissions resulting from service station remediation and buried gasoline-contaminated soils', Petroleum Contaminated Soils, vol. 3. Johnson, PC & Ettinger, RA 1991, 'Heuristic Model for Predicting the Intrusion Rate of Contaminant Vapours Into Buildings', Environmental Science and Technology, vol. 25, no. 8, pp. 1445-1452. MfE 1999, Guidelines for Assessing and Managing Petroleum Hydrocarbon Contaminated Sites in New Zealand, Appendix 5A Irrigation Water Criteria. NEPC 1999 amended 2013, Schedule B(4), Guideline on Health Risk Assessment Methodology, National Environment Protection Council, SAHC 1991, The Health Risk Assessment and Management of Contaminated Sites, Proceedings of the First National Workshop on the Assessment of Site Contamination, Adelaide. SAHC 1993, The Health Risk Assessment and Management of Contaminated Sites, Proceedings of the Second National Workshop on the Assessment of Site Contamination, Adelaide. SAHC 1996, The Health Risk Assessment and Management of Contaminated Sites, Proceedings of the Third National Workshop on the Assessment of Site Contamination, Adelaide. SD-DEH 2000, Users Guide to the Vapor Risk 2000, San Diego County Department of Environmental Health, Land And Water Quality Division Site Assessment and Mitigation Program. USEPA 1989, Risk Assessment Guidance for Superfund, Volume I, Human Health Evaluation Manual (Part A), Office of Emergency and Remedial Response, United States Environmental Protection Agency, Washington. USEPA 1991, Risk Assessment Guidance for Superfund: Volume 1 - Human Health Evaluation Manual (Part D, Development of Risk-based Preliminary Remediation Goals), Office of Emergency and Remedial Response, United States Environmental Protection Agency. USEPA 1996, Soil Screening Guidance: Technical Background Document, Office of Emergency and Remedial Response, United States Environmental Protection Agency. USEPA 1999, Derivation of a volatilisation factor to estimate upper bound exposure point concentration for workers in trenches flooded with ground water off-gassing volatile organic chemicals, Denver, CO. A-20 P age
USEPA 2002, Supplemental Guidance for Developing Soil Screning Levels for Superfund Sites, Office of Emergency and Remedial Response, United States Environmental Protection Agency. USEPA 2004a, Risk Assessment Guidance for Superfund, Volume I: Human Health Evaluation Manual, (Part E, Supplemental Guidance for Dermal Risk Assessment), United States Environmental Protection Agency, Washington, D.C. USEPA 2004b, User's Guide for Evaluating Subsurface Vapor Intrusion into Buildings, United States Environmental Protection Agency, Washington. USEPA 2009, Risk Assessment Guidance for Superfund, Volume I: Human Health Evaluation Manual, (Part F, Supplemental Guidance for Inhalation Risk Assessment), United States Environmental Protection Agency, Washington, D.C. A-21 P age