The Madison (Wis.) Metropolitan Sewerage District has monitored the chemistry of the effluent leaving its Nine Springs Treatment Plant since the early 1940s. In 1983, the staff research biologist began shocking fish and looking at aquatic insects in the receiving streams as another way to monitor the discharge and protect the environment.The district’s effluent quality always met EPA and Wisconsin Department of Natural Resources (DNR) standards. In 1986, the district doubled the size of the plant, increasing retention time to lower BOD and TSS, adding nitrification, and switching from chlorination to UV disinfection. As effluent quality improved, pollution-intolerant aquatic insects
