Publication Summary

Ecology′s Surface Water Investigations Section conducted a limited Class II survey and receiving water study of the Tekoa Wastewater Treatment Plant (WTP) and Hangman Creek on August 30-31, 1988. Streamflow during the study was estimated to be about 63 percent of the 7-day, 10-year (7Q10) low flow. Biological oxygen demand (BOD) and total suspended solids (TSS) removal were within permit limits. Disturbance of the solids accumulated in the chlorine contact chamber during recent cleaning resulted in poor disinfection and violations of fecal coliform discharge limits.

Ecology′s Surface Water Investigations Section conducted a limited Class II survey and receiving water study of the Tekoa Wastewater Treatment Plant (WTP) and Hangman Creek on August 30-31, 1988. Streamflow during the study was estimated to be about 63 percent of the 7-day, 10-year (7Q10) low flow. Biological oxygen demand (BOD) and total suspended solids (TSS) removal were within permit limits. Disturbance of the solids accumulated in the chlorine contact chamber during recent cleaning resulted in poor disinfection and violations of fecal coliform discharge limits. Degraded conditions in Hangman Creek resulted from lack of effluent dilution (1.6:1, receiving water: effluent) as well as agricultural nonpoint sources. Conditions showing deterioration below the WTP included: dissolved oxygen and macroinvertebrate viability, as well as nutrient and fecal coliform loading. A total maximum daily load analysis indicated extreme chlorine toxicity at dilution ratios less than 45:1. Temperature, dissolved oxygen, nutrient and bacteria loading calculations also indicate water quality violations at 7Q10 flows. Recommendations include installation of a chlorine removal system and effluent removal from the creek when dilution is less than 10:1.