Human Health Risk Assessment - Raytheon

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4.3.3 On-Site Trespasser 30 Human Health Risk Assessment DRAFT Although the Site is fenced and site security ensures that access is limited, in accordance with USEPA Region 4 guidance, we have considered potential exposures to an adolescent trespasser. The adolescent trespasser scenario assumes that a child between the ages of 7 and 16 spends an average of two hours per day, one day per week on site where potential exposure to constituents in outdoor air could occur via inhalation. The average daily dose from inhalation of outdoor air is calculated according to equation (4-20). EPCs are provided in Table 5 and exposure factors are summarized in Table 6. We have assumed a body weight of 45 kg and an inhalation rate of 1.2 m 3 /hr based on data presented in USEPA’s Child-Specific Exposure Factors Handbook for a child participating in moderate activities (USEPA, 2002a). Dose and risk calculations for potential exposures to COPCs by on-Site trespassers via inhalation of outdoor air are provided in Appendix A; Table A-3. 4.3.4 On-Site Construction Worker In the event that subsurface excavation is required to support potential future construction activities on-Site, a construction worker could be exposed to COPCs via dermal contact with exposed groundwater and saturated soils and inhalation of COPCs volatilized from the groundwater surface. The construction worker scenario also considers potential exposures to COPCs via incidental ingestion of subsurface soil. The construction scenario is modeled as a one-time event in which the excavation could remain open for as long as 20 days. However, we have assumed that incidental ingestion takes place over the entire construction event, which we have assumed could last as long as 6 months, even after the excavation has been covered. Dermal Contact with Groundwater. For the purpose of estimating potential risks to construction workers from dermal exposure to COPCs, it is assumed that a worker may be exposed to saturated soils and groundwater for 2 hours per day, 20 days per year for 1 year. It is assumed that the worker is wearing long pants, shoes and a short-sleeved shirt but the worker’s head, hands, and forearms could be exposed to saturated soil and groundwater. The dermally absorbed dose (DAD) of COPCs received from contact with saturated soils and groundwater was calculated following USEPA dermal risk assessment guidance for groundwater (USEPA, 2004d) where: and DA event DAD = DAevent ⋅ EV ⋅ EF ⋅ ED ⋅ SA = (4-22) BW ⋅ AT 6 ⋅τ event ⋅ tevent π 2 ⋅ FA ⋅ K p ⋅ Cw if tevent ≤ t * (4-23) ( ) ⎥ ⎥ ⎡ 2 t ⎛ ⎞⎤ event 1 + 3B + 3B = FA ⋅ K ⋅ ⎢ + ⎜ ⎟ p Cw 2 ⎜ 2 ⎟ ⎢⎣ 1 + B ⎝ 1 + B ⎠⎦ DAevent τ event if tevent > t * (4-24)
where: DAD = Dermal absorbed dose (mg/kg-day) DAevent = Absorbed dose per event (mg/cm 2 -event) EV = Event frequency (events/day) EF = Exposure frequency (days/year) ED = Exposure duration (years) SA = Exposed skin surface area (cm 2 ) BW = Body weight (kg) AT = Averaging time (days) FA = Fraction absorbed water (dimensionless) Kp = Dermal permeability coefficient (cm/hr) Cw = Concentration of COPC in Irrigation water (mg/cm 3 ) τ event = Lag time per event (hr/event) tevent = Event duration (hr/event) 31 Human Health Risk Assessment DRAFT B = Ratio of permeabilities through stratum corneum and viable epidermis (unitless) t* = Time to reach steady state (hr) The LADD is calculated using equation (4-21) with the exception that the ADD is replaced by the DAD. Exposure point concentrations for on-Site shallow groundwater are reported in Table 5 and exposure factors are summarized in Table 6. Dose and risk calculations for potential exposures to COPCs via dermal contact with saturated soils and exposed groundwater by on- Site construction workers are provided in Appendix A; Table A-4. Incidental Ingestion of Soil. Some incidental ingestion of saturated soil may occur during subsurface excavation activities. The average daily dose (ADD) from ingestion of soil is calculated using equation (4-25). where: EPC x IR x ET x EF x ED s i ADD = (4-25) BW x ATn EPCs = Exposure point concentration in soil (mg/kg) IRs = Soil ingestion rate (kg/day) EF = Exposure frequency (days/year) ED = Exposure duration (years) BW = Body weight (kg)
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Page 5 and 6: Executive Summary 1 Human Health Ri
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DRAFT CSFd RfDd DA event C w DAD LA
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DRAFT Table A-13. Dose and Risk Cal
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Human Health Risk Assessment - Raytheon

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