A Spreadsheet-Based Site Specific Risk Assessment Tool for Land-Applied Biosolids

Abstract

Due to the complexity of risk assessments, models tend to be dense and difficult for users to follow and modify in order to meet their needs. A spreadsheet-based tool, named the Spreadsheet Microbial Assessment of Risk: Tool for Biosolids (SMART Biosolids), has been developed for quantitative microbial risk assessment of land-applied biosolids, which is intended to address these challenges. The model combines spreadsheets with add-in visual basic macros in a ra- tional and supportable manner. Spreadsheets serve as a familiar interface for an archive of relevant inputs for parameter values and references.The exposure model is also encoded in the spreadsheet, which allows users to trace back computa- tions through the model and modify parameters if necessary. Add-in macros are used to implement a nested sampling rou- tinethat calls the exposure model encoded in the spreadsheet many times to calculate values for different pathogens and to perform a Monte Carlo uncertainty analysis. An example application finds that adenovirus is the pathogen presenting the highest risk by the groundwater pathway. However, uncertainties are large indicating that additional information on the fate and transport of adenovirus in groundwater would be helpful. The SMART Biosolids model may be useful for in- forming a number of decisions. Regulators and land application program managers may be able to use the model to re- view different sites and determine which sites are most appropriate for land application. Researchers may use the model to integrate information and identify key gaps in knowledge warranting future research.