Submitted to: Water Environment Federation
Publication Type: Proceedings
Publication Acceptance Date: 10/16/2001
Publication Date: 10/16/2001
Technical Abstract: Oocysts of the protozoan Cryptosporidium parvum can contaminate public drinking water supplies and cause outbreaks of Cryptosporidiosis. Subsurface movement through soil has received very little attention to date as a pathway for oocysts. To evaluate the significance of this pathway, three laboratory experiments were performed to investigate subsurface transport of oocysts. Experiment I was carried out in a vertical 18 cm-long column filled either with glass beads or silica sand, under conditions conducive to fingered flow. Experiment II involved an undisturbed, macroporous soil column subjected to macroporous flow. Experiment III aimed to study the lateral flow on an undisturbed soil block. The columns and soil samples were subjected to artificial rainfall and were allowed to reach steady-state, after which contaminated calf feces were applied at the surface, along with a known amount of KCl to serve as tracer, and rainfall was continued at the same rate. The breakthrough of oocysts and Cl demonstrated the importance of preferential flow on the transport of oocysts. Peak oocyst concentrations of oocysts were not retarded compared to Cl, but occurred before the Cl peak. Recovery rates for oocysts were low, ranging from 0.1 to 10.4 percent of the oocysts originally applied. The numbers of oocysts present per liter of effluent were still orders of magnitude higher than the ID50 for healthy adults. These results suggest that the transport of oocysts in the subsurface via preferential flow may create a significant risk of groundwater contamination.