Development of failure scenarios for biosolids land application risk assessment

Although deviations from standard guidance for land application of biosolids occur in practice, their importance is largely unknown. A list of such deviations (plausible failure scenarios) were identified at a workshop of industry, regulators, and academic professionals. Next, a survey of similar professionals was conducted to rank the plausible failure scenarios according to their severity, frequency, incentive to ignore control measures, gaps in existing control processes, public concern, and overall concern. Survey participants rated intentional dumping (unpermitted disposal) as the most severe of the failure scenarios, lack of worker protection as the most frequent scenario, and application of Class A biosolids that have failed to meet treatment standards as the scenario for which incentives to ignore control measures are highest. Failure of public access restrictions to application sites was the scenario for which existing controls were judged the weakest; application of biosolids too close to wells was ranked highest for public concern and for overall concern. Two scenarios for which existing controls were considered weaker, site restriction violations and animal contact leading to human exposure, were also rated as frequently occurring. Both scenarios are related in that they (1) involve inappropriate access to a site before the required time has elapsed, and (2) could be addressed through similar biosolids management measures.