Temporal and Spatial Monitoring of Escherichia coli and Pathogen Indicators in the Shallow Groundwater and Vadose Zone, Abbotsford, British Columbia, Canada

Long-term monitoring studies have shown the Abbotsford-Sumas Aquifer has elevated nitrate concentrations as a result of widespread agricultural land use on the aquifer, and some of those same studies have implicated poultry manure as a major source of the nitrate. However, few studies have examined the potential for pathogen loading to this shallow, vulnerable aquifer despite the continued application of manure. The main goal of this field study was to investigate temporal and spatial patterns of bacterial loading to the aquifer. The field program included sampling of regional groundwater monitoring wells from across the study area including a local creek, along with installing lysimeters for monitoring soil water in the vadose zone at a test site in the central portion of the study area. The monitoring program targeted the fall and winter months, when rainfall is greatest and leaching of contaminants through the soil is considered to be most likely.;Twenty-seven shallow monitoring wells were selected for sampling from October 5, 2009 to April 27, 2010, and analyzed for fecal indicators ( E. coli and total coliforms) as well as selected chemical parameters. Results indicate 4 of the 432 of groundwater samples collected contained E. coli, whereas 276 contained total coliform, and 54% had nitrate concentrations exceeding the Canadian drinking water guidelines (10 mg-N/L). All of the surface water samples from Fishtrap Creek contained E. coli and total coliform, but nitrate never exceeded the drinking water guideline. Pockets of high nitrate concentrations were not found to be consistent with trends in bacteria detections, which may suggest transport between bacterial colloids and dissolved chemical species of the same manure source differs.;The vadose zone test site was established with pan lysimeters below four 1 m by 1 m plots that were treated on October 5, 2009 with poultry manure, potassium bromide, and fluorescent microspheres. Over a six-month period a 4-log reduction in E. coli in the top 30 cm from initial seeded concentrations was observed, and up to a 3-log reduction in microsphere concentrations in the top 50 cm. Bromide peaked in concentration early on, suggesting rapid soil flushing occurs for conservatively transported parameters. Prior to soil sampling, blue dye was applied to the soil plots to stain water flow paths. Microsphere concentrations at dyed locations were greater than in non-dyed soil samples suggesting colloids and solutes follow similar flow paths. Manure was sampled at two additional test plots following the lysimeter experiments to quantify E. coli survival in the source material on the ground surface. A die off rate of 0.1 log/day was calculated for a six-month period, indicating long-term survival occurs. Overall, E. coli mobility appears restricted to the shallow soil profile and, due to different transport processes for bacteria and solutes, does not correlate with other agriculturally derived parameters, such as nitrate.