ABSTRACT
River Bank Filtration (RBF), artificial recharge (AR) using basins and AR by deep well injection are applied in the Netherlands to cover 19% of the drinking water needs. The recharged aquifers are composed of unconsolidated Quarternary sands or gravels. Field studies (with or without seeding of microorganisms in feed water) and column studies were carried out to quantify the relation between travel time/distance and micro-organism removal (primarily MS2 and PRD1 phages, Clostridium spores and E.coli), and to determine the factors that influence this relation. All studies showed that sandy soils pose a very effective barrier to all micro-organisms. The first 1–6 m of soil passage, in the field, removed all micro-organisms most effectively, probably due to a raised sorption capacity by deep bed filtration of fine particles close to the recharge source. In the case of deep well injection, oxidation of pyrite into ferri-hydroxides, which sorb micro-organisms, offers an additional explanation. Critical situations may arise during flood events where RBF systems draw from gravel aquifers; and where the recollection system is subject to short-circuiting or contamination of the abstraction systems (wells, drains) by animal life or infiltration of contaminated water.
