自1984年以来，由于生物膜的存在，康涅狄格州中南部地区水务局（RWA）的分配系统中经常出现阳性大肠菌群样本。根据1989年6月的总大肠菌群规则（TCR），大肠菌群分析方法从细胞密度改变为存在/不存在（PA）方法，大大增加了RWA超过与生物膜相关的环境大肠菌群新的最大污染物水平（MCL）的可能性。由于总大肠菌群规则不允许出现差异，RWA积极支持AWWA的密集努力，让EPA为分配系统中的生物膜导致超过总大肠菌群规则MCL的系统提供差异。 因此，1991年1月，美国环境保护局公布了公用事业公司符合TCR偏差条件的方法和标准。RWA立即开始与康涅狄格州卫生服务部（DHS）合作，尤其是供水和流行病学部门，记录必要的公共卫生信息，并进行符合EPA标准所需的调查，以获得与EPA TCR的差异。1992年6月，RWA正式申请变更，1992年9月，国土安全部批准了变更。本文介绍了RWA实施EPA TCR差异标准要求的分配系统最佳管理实践的经验，以获得并遵守总大肠菌群规则差异。

Since 1984, the South Central Connecticut Regional WaterAuthority (RWA) has routinely experienced positive coliform samples in its distribution system as a result of the presence of a biofilm. The change in coliform analytical methodology from the cell density to the presence/absence (PA) method as required by the June 1989 Total Coliform Rule (TCR) significantly increased the likelihood that the RWA would exceed the new Maximum Contaminant Level (MCL) from environmental coliforms associated with biofilm. Since the Total Coliform Rule did not permit variances, the RWA actively supported intensive AWWA efforts to have EPA provide a variance for systems which exceeded the Total Coliform Rule MCL as a result of biofilms in their distribution systems. Accordingly, in January, 1991, the EPA published the methods and criteria by which utilities could qualify for a variance to the TCR. The RWA immediately began working with the Connecticut Department of Health Services (DHS), in particular the Water Supply and Epidemiology sections, to document the necessary public health information and perform those investigations needed to meet the EPA criteria in order to obtain a variance to the EPA TCR. In June 1992, the RWA officially applied for the variance, and in September 1992, the DHS granted the variance. This paper presents the RWA's experience with implementing the distribution system best management practices required by the EPA TCR variance criteria for obtaining and complying with a Total Coliform Rule variance.