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The user may choose chemicals of concern from a standard library of 86 chemicals; the user may add or delete chemicals from the library and alter the physical, chemical and toxicological properties of each.

The database includes the following chemical properties: vapor pressure, solubility, Henry's Law coefficient, log octanol/water partition coefficient (log K_ow), organic carbon partition coefficient (K_oc), inorganic partition coefficient (K_d), diffusive coefficients in air and water degradation rates and vegetable uptake factor.

The database also includes the following toxicological properties: USEPA carcinogenic classification, toxicity parameters (cancer potency factor and reference dose),  absorption adjustment factors and skin permeability coefficient.

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RISC 4.0 has a large surface water and sediment criteria database containing data for several different countries, allowing the user to compare modeled surface water and sediment criteria with regulatory standards from around the world.

• The RISC database contains freshwater and marine surface water criteria from the following databases:
• United Stated Environmental Protection Agency Ambient Water Quality Criteria
• United Kingdom Environmental Quality Standards
• Australia and New Zealand Environmental and Conservation Council Guideline for the Protection of Aquatic Ecosystems
• European Commission Water Quality Objective
• Canadian Council of Ministers for the Environment Freshwater Aquatic Life Guideline
• The sediment criteria in the database is from the National Oceanographic and Atmospheric Administration

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RISC can be used to estimate the potential for adverse human health impacts (both carcinogenic and non-carcinogenic) from several exposure pathways including:

• Ingestion of soil

• Dermal contact with soil

•  Ingestion of groundwater

• Dermal contact with groundwater

• Dermal intake in the shower

• Inhalation in the shower

• Inhalation of outdoor air

• Inhalation of indoor air

• Ingestion of surface water

• Dermal contact with surface water

• Ingestion of vegetables grown in contaminated soils

• Ingestion of vegetables irrigated with groundwater

• Ingestion of irrigation water

• Dermal intake of irrigation water

• Inhalation of irrigation water spray

RISC gives the user the ability to calculate additive risk due to multiple pathways, compounds and receptors.

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An Excel spreadsheet based on the Risk-Based Corrective Action (RBCA) algorithms can be used to replicate the tiered RBCA process

• RBCA is a decision-making process for assessment and response to subsurface contamination and is based on protection of human health and environmental resources. 
• The RISC software has an extensive Excel spreadsheet that can be used as a screening tool
• The spreadsheet contains all of the chemicals in the RISC software
• The input values in the spreadsheet are customizable so that multiple Risk-Based Screening Levels (RBSLs) tables can be generated (i.e. different soil types) and saved under different file names.

Basic Steps in a Risk Assessment     

     Tier 1: Excel Spreadsheet Comparison

• Tier 1 involves initial site assessment and classification of the site based on conservative RBSL that are non-site specific. 

• The spreadsheet can be used ‘as is’ for a Tier 1 look-up table

• Default values may be modified to create Tier 1 tables for new receptors or exposure scenarios.

     Tier 2: Fate and Transport Modeling

• Tier 2 involves evaluating the site using more site-specific information and/or evaluating alternative compliance points

• The RISC software package contains fate and transport models that may be used to develop site-specific clean-up levels which are applicable to Tier 2 analysis

• The user can also perform probabilistic exposure evaluations using RISC's Monte Carlo option with site-specific data for a Tier 3 analysis

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Fate and transport models in RISC are designed to be used to estimate receptor point concentrations as part of a risk assessment. 

• Fate and transport models can distinguish between the presence or absence of phase-separated product (NAPL) in the source zone
• Analytical models in the software include: vadose zone leaching model, groundwater model, and a saturated soil model (for NAPL at the watertable)
• Volatilization models for indoor and outdoor air and simple groundwater to surface water interactions
• The groundwater models simulate three-dimensional dispersion.

RISC includes the following embedded chemical fate and transport models:

• Leaching from vadose zone soil source to groundwater
• Saturated soil source at the water table impacting groundwater
• Dispersion, advection, retardation and degradation of groundwater as it moves in an aquifer
• Emissions from soil to outdoor and indoor air (including models considering biodegradation)
• Emissions from groundwater to indoor air
• Sediment partitioning and surface water mixing models 

The models listed above may be linked together.  For example, the saturated soil model can be linked with the groundwater model and then used to estimate volatile emissions to indoor air at at downgradient location.

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RISC allows the user to determine risk-based TPH (total petroleum hydrocarbon) targets using the TPH fractions proposed by the U.S. Air Force led TPH Working Group.

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The RISC software package includes a comprehensive user’s manual with indepth example problems.

Developed By:

Lynn R. Spence, Spence Environmental Engineering, Pleasanton, California

Terry Waldon, BP Oil International, Sunbury, UK