Hermann Sanitary Sewer System Evaluation (SSES)
On April 19, 2009, MDNR issued a new Missouri State Operating Permit (MSOP) for Hermann's Wastewater Treatment Facility (WWTF). In the fact sheet contained with the MSOP, it was indicated that the WWTF was routinely exceeding design flows. Based on an inspection report issued in December 2008, it was believed that a large contributing factor in the exceedance of the system's design flow was stormwater inflow and infiltration (I&I). A schedule of compliance was mandated within the MSOP which outlined the submittal of annual updates regarding capital improvements to the City's sanitary sewer collection system, which were focused on the elimination of storm water I&I to the system.
The City of Hermann, being aware of the affect of stormwater I&I on the performance of their sanitary sewer collection system, began the process of establishing a formal and comprehensive "Collection System Assessment and Master Plan".
As the first step, CM Archer Group, P.C. was hired by the City to accomplish two concurrent tasks; perform a sanitary sewer evaluation study to identify sources of inflow and infiltration into the collection system that causes drastic increases in flows seen at the treatment facility and investigate alternative wastewater pumping and treatment options.
The existing sanitary sewer collection system was studied to determine the impact of inflow and infiltration on the system's performance. The study that was performed was multifaceted and involved several discrete operations. First a survey of the sanitary sewer system was performed, with the goal of developing an accurate map of the sanitary sewer system. Secondly, sanitary sewer manholes were inspected in an effort to determine the conditions of each structure. While the survey and inspections were performed, flow monitoring of the system was performed so as to determine average daily diurnal flows and the volume of any I&I experienced within the system during rain events. Finally, sanitary sewer lines that were thought to be of significance were smoke tested and inspected with closed loop televising equipment.