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MODELS AND METHODS FOR PETROLEUM HYDROCARBON RISK ASSESSMENT: ONSITE, LUSTRISK, AND HSSM
Citation:
Weaver*, J W. AND M. Small. MODELS AND METHODS FOR PETROLEUM HYDROCARBON RISK ASSESSMENT: ONSITE, LUSTRISK, AND HSSM. Presented at 12th National Underground Storage Tank Conference, Portland, OR, March 21-23, 2000.
Impact/Purpose:
The objective of this research is to develop a multicomponent, mass-balance-based model for simulating transport of spilled oils with and without dispersant treatments.
Description:
U.S. EPA has developed three tiers of models for analysis of fuel releases from underground storage tank (UST) systems: 1) OnSite; 2) LUSTRisk, and 3) the Hydrocarbon Spill Screening Model (HSSM). The tiered approach to modeling allows users to select a model based upon the amount of data available at the site and the complexity of analysis required for the simulation. All of these models incorporate improved description of the source area by considering the presence of light non-aqueous phase liquids (LNAPL). The first tier, OnSite, is analogous to a "back of the envelope calculation," and runs interactively from a web site. OnSite consists of a collection of on-line calculators for solving basic contaminant fate and transport equations, simple models and unit conversion factors. Calculations include groundwater gradients, retardation factors, effective solubilities from fuels, plume diving and simple transport models where the source is defined by a fuel-contaminated zone. This collection of calculators is intended to be used by state regulators to evaluate modeling reports, by consultants for analysis of site data, and as a site assessment tool in its own right. Only Internet access and a JavaScript-enabled browser (current or recent versions of Netscape Navigator or Internet Explorer, for example) are required. The web site includes a tutorial and case study to give concrete examples of OnSite usage. (http://www.epa.gov/athens/software/training/WebCourse/part-two/onsite/index.html).
The second tier, LUSTRisk, provides a more sophisticated model and a more highly integrated user interface. The LUSTRisk model allows computation of risks associated with petroleum hydrocarbon lenses in contact with ground water. LUSTRisk performs iterative dissolution and transport simulations for multiple chemicals (e.g. BTEX and MTBE) migrating from a single petroleum release. Two-dimensional fate and transport is computed, comparisons are made to site data, and risks associated with ingestion of ground water are calculated. LUSTRisk is implemented as a set of Microsoft Excel spreadsheets, which provide a convenient interface for data input, calculation, and graphically analyzing results. LUSTRisk is currently undergoing peer review and is available in beta version only. The third tier, HSSM is the most sophisticated model of the group. HSSM is a stand-alone modeling system that includes extensive input guidance for unfamiliar input parameters, online databases of parameter values, automatic report generation, comparison against field data and more. HSSM simulates the emplacement of the petroleum during a defined release scenario, formation of the lens of fuel in the subsurface, dissolution in groundwater, as well as fate and transport in a shallow aquifer. HSSM allows simulation of long duration releases where petroleum continually is added to the source. Estimation of source volume from field data and various release scenarios are provided to assist with difficult inputs. Graphical and textual output from the model is written to HTML files which are viewed with a standard Internet browser. This material is formatted as a pre-written report that contains a narrative description of the problem simulated, description of the sources of input parameters, and model results. These are provided for partially for convenience, but more importantly to encourage proper documentation of modeling studies. All of the above software will be available on a CD at the meeting.