Norwich – Norwich Public Utilities will hold an informational meeting Wednesday on a draft plan to address the 14 remaining areas of Combined Sewer Overflow, where storm water overflows into the sewer system and causes raw sewage to dump into rivers during heavy rainfall.

NPU is under a state Department of Energy and Environmental Protection consent order to correct the sewage overflow problem, and officials will give an overview of the problem and the proposed plan during a public meeting at 6 p.m. at NPU headquarters, 16 S. Golden St. The draft plan is posted on the NPU website, www.norwichpublicutilities.com, and hard copies are available for viewing at NPU.

NPU and the city have worked on reducing the number of CSO locations and the number of incidents when raw sewage flows into the Thames and Shetucket rivers over the past several decades. Prior to the efforts, the city had more than 70 such locations. The number was listed at 43 in 1972 and by 2005 was reduced to 14 sites.

Larry Sullivan, NPU wastewater integrity manager, said Norwich has about 60 incidents per year when raw sewage flows into the rivers. Once all the work is done to separate the storm and sewer systems, Sullivan said that number will be cut to about four incidents per year. Water quality improvements also will be monitored.

The amount and severity of sewage overflows depend on weather conditions. More storm water ends up in the sewer system during heavy downpours, when the ground is frozen or saturated. Sometimes, incidents of a half to 1 inch of rain can cause sewage overflows into the rivers, Sullivan said. “Hard hitting quick rain” causes more overflow, he said.

Sullivan said the draft plan, although nearly 150 pages, is the shortened version of the more than 500-page document that will be submitted to the DEEP for approval. The plan, which is the result of engineering studies and flow calculations, took 18 months to compile and cost about $1 million. The plan was funded with a loan through the Connecticut Clean Water Fund.

Sullivan said no cost estimates will be available for the work to eliminate CSOs until the plan is approved by the DEEP.

At Wednesday’s meeting, engineers will give a 30-minute overview of the problem – including a definition and explanation of Combined Sewer Overflows – and will outline the plan. Members of the public will have a chance to offer comments and ask questions about the work.

Pending DEEP approval, NPU officials hope to start construction on the project in fall of 2019, starting with the CSO in the area of the Eighth Street Bridge. All construction work would be done in the roadways, with no disruption to sewer service to homes and no construction on private property, NPU spokesman Chris Riley said.

c.bessette@theday.com