Application of Harvey-Garabedian model for describing bacterial removal in Sand Abstraction Systems associated with ephemeral rivers

There have been concerted efforts to find alternative sources of water for small rural communities in the Southern Africa region, and one such initiative is Sand Abstraction Systems (SAS) or infiltration galleries. The sand formation of the riverbed of an ephemeral river is utilised as a natural filter giving potable water of high quality, but is prone to pathogenic contamination. The main objective of our study was to test the suitability of Harvey and Garabedian model for describing bacterial removal in SAS. The Harvey and Garabedian model with some modifications was adopted due to the few parameters required in applying the model. The coefficients and media properties were established from laboratory experiments and field studies. The implicit finite difference method was applied to solve the numerical model equation and to simulate the aquifer response to Escherichia coli for Nkayi SAS. The results of the bacterial simulation from the model fitted well with measured field data and with a small margin of error between the field results and the model (+/-5 coliform count/100 ml).