When ground water is tapped by wells, microbial and chemical deposits often develop. Sloughing and clogging may occur in the distribution system adding considerable expense to the operation of the water systems as well as imparting taste and odor to the water itself. The physical and microbial basis of these deposits was studied using microbial flocs found in Southern Illinois as a model system. These flocs proliferate at the air-water interface of a domestic flush tank producing copious amounts of flocculent material. Observation of the flocs by phase microscopy revealed a dense population of bacteria with several distinct morphological types. Analysis was done by scanning and transmission electron microscopy. Results of chemical analysis of the well water indicated low levels of organic material, wheras results of gas chromatographic analysis indicated high amounts of methane were present in the water. (Author)