Development of a risk-based index for source water protection planning, which supports the reduction of pathogens from agricultural activity entering water resources

Abstract

Source water protection planning (SWPP) is an approach to prevent contamination of ground and surface water in watersheds where these resources may be abstracted for drinking or used for recreation. For SWPP the hazards within a watershed that could contribute to water contamination are identified together with the pathways that link them to the water resource. In rural areas, farms are significant potential sources of pathogens. A risk-based index can be used to support the assessment of the potential for contamination following guidelines on safety and operational efficacy of processes and practices developed as beneficial approaches to agricultural land management. Evaluation of the health risk for a target population requires knowledge of the strength of the hazard with respect to the pathogen load (mass  concentration). Manure handling and on-site wastewater treatment systems form the most important hazards, and both can comprise confined and unconfined source elements. There is also a need to understand the modification of pathogen numbers (attenuation) together with characteristics of the established pathways (surface or subsurface), which allow the movement of the contaminant species from a source to a receptor (water source). Many practices for manure management have not been fully evaluated for their impact on pathogen survival and transport in the environment. A key component is the identification of potential pathways of contaminant transport. This requires the development of a suitable digital elevation model of the watershed for surface movement and information on local groundwater aquifer systems for subsurface flows. Both require detailed soils and geological information. The pathways to surface and groundwater resources can then be identified. Details of land management, farm management practices (including animal and manure management) and agronomic practices have to be obtained, possibly from questionnaires completed by each producer within the watershed. To confirm that potential pathways are active requires some microbial source tracking. One possibility is to identify the molecular types of Escherichia coli present in each hazard on a farm. An essential part of any such index is the identification of mitigation strategies and practices that can reduce the magnitude of the hazard or block open pathways. r

Assessing risk to groundwater quality using an integrated risk framework

“…In contrast, hazards to groundwater quality are most often mapped at a much smaller scale and are usually confined to a well capture zone as part of source water protection planning initiatives (e. (Carmichael et al 1995, Goss and Richards 2008, Liebscher et al 1992). …”

“…A well is considered to be affected if a pathogen source (e.g. manure spreading agriculture or septic system) is located within the one-year capture zone of the well (Goss and Richards 2008). A subset of the hazard assessment (both land use based and point sources thought to be associated with human or animal waste) is used for assessment of Healthcare Cost.…”

“…Because of its association with pathogens and its high mobility and relatively conservative nature, nitrate can be used as a tracer for animal waste. In general, the persistence of pathogens in groundwater is less than one year (Goss and Richards 2008). Therefore, where nitrate reaches a well in less than one year of travel time, there is also a pathogen-related vulnerability for the well.…”

Soil and Waste Matrix Affects Spatial Heterogeneity of Bacteria Filtration during Unsaturated Flow

“…Transfer of pathogens from a source to sinks in the environment is considered under quantitative microbial risk assessment (QMRA) in a modular approach [2][3][4]. Therefore development of any QMRA requires good understanding of the rates of long-term and repeated transfer events with pathogens crossing the interfaces between various sequences of intermediary sinks.…”

A cross-disciplinary toolkit to assess the risk of faecal indicator loss from grassland farm systems to surface waters

“…In fact, Goss and Richards (2008) argue that development of a risk-based index of the potential for pathogens from agricultural activity to impact on water quality is required as an interim stage in the establishment of a fully quantitative microbial risk assessment approach. This paper outlines an approach to farm scale microbial risk assessment through which it may be possible to apportion and act upon such risks in effective and measured ways.…”