Evaluation of Recovery in a Polluted Creek After Installation of New Sewage Treatment Procedures

Response of Hickman Creek near Lexington, Kentucky to alleviation from serious sewage pollution was studied from January, 1973 through July, 1974. Wastes are now handled from an efficient secondary treatment facility and four sequential polishing lagoons before chlorination and discharge to West Hickman branch.Physico-chemical tests gave no strong indication of residual pollution effects at the start of the study, approximately six months after the treatment facility opened. At low flow a slight oxygen sag, probably associated with algal growth in the lagoons, persists downstream from the outfall. Mean values for turbidity, nitrates and COD are somewhat higher at the outfall than at eleven stations within the basin. Orthophosphates are considerably higher in lagoon discharge than elsewhere in the system, which gains some phosphate from bedrock.While the lagoons place some oxygen demand on West Hickman in the form of unicellular algal growth, they can and do receive surges of input that cannot be accomodated in the treatment plant. They would serve as a buffer to the stream in case of operational malfunction, which could overwhelm the small stream at low flow. The lagoons provide some benefits of tertiary treatment.The diversity of benthic macroinvertebrates increased at most stations formerly affected by pollution but did not achieve the levels of two control stations on East Hickman Creek. Fishes reinvaded West Hickman more rapidly than did invertebrates but they also failed to achieve the diversity maintained at the control stations and observed in collections from 1960. Fecal and total coliforms 2 miles downstream from the lagoon outfall were as low or lower than elsewhere in the basin.Changes within the basin were sometimes more clearly seen when stations were grouped by stream order. Urbanization of West Hickman may be causing physico-chemical and biological changes apart from the effects of or alleviation from sewage pollution.The West Hickman Sewage Treatment Plant affords protection to Hickman Creek and produces a safe effluent that has allowed reestablishment of a variety of fishes, invertebrates and aesthetic qualities formerly associated with the stream. Presence of uncontaminated tributaries is thought to have sped observed recovery.