According to Erwin Utilities Director of Water and Wastewater Matthew Rice, Erwin Utilities is on the EPA’s watch list for violating the Biological Oxygen Demand reduction requirement in its wastewater treatment plant’s permit. BOD is a measure of the amount of organic material contained in the water. A utility may be placed on the EPA watch list when the same violation occurs for three consecutive months, Rice said.
The source of the violations stem from groundwater and stormwater leaking into the sewers, referred to as infiltration and inflow, Rice said.
“The additional clean water leaking into the sewers dilutes the strength of the wastewater coming into the wastewater treatment plant,” Rice said. “Essentially, the wastewater coming into Erwin Utilities’ WWTP is too clean.”
Raw wastewater typically averages 200 milligrams of BOD per liter, Rice said. But, due to the dilution from groundwater and stormwater flowing into the wastewater collection system, Erwin Utilities’ influent BOD averages 120 milligrams per liter.
The Erwin Utilities’ wastewater treatment plant permit requires that no more than 30 milligrams per liter on a monthly average or 45 millgrams per liter for 45 milligrams per liter for a daily maximum for BOD be discharged to the Nolichucky River, Rice said.
Rice said that Erwin Utilities has not exceeded either of these requirements, and that BOD discharged to the Nolichucky River is usually less than 20 milligrams per liter. He said the issue is that raw wastewater coming into the plant is only 120 milligrams per liter. Rice said this adds up to an 83 percent reduction in BOD, less than the required 85 percent. Rice said if Erwin Utilities’ raw wastewater strength was the typical 200 milligrams per liter, producing a 20 milligram per liter effluent would achieve a BOD reduction of 90 percent.
Rice said the infiltration and inflow, also called I/I, at the heart of the problem can be caused by holes or cracks in sanitary sewer piping or by leaking connections and joints in piping.
“Issues on the customer’s side leaking gutters connected to the sewers and sump pumps tied into the sewers all contribute to the problem,” Rice said. “Erwin Utilities works diligently to identify the sources of I/I and corrects them when they are found. Customers are encouraged to disconnect sump pumps in basements from the sanitary sewer line.”
Rice said the American Society of Civil Engineers has estimated that $1.4 billion in wastewater infrastructure improvements are needed in Tennessee over the next 20 years, adding that 75 percent of this cost will be for replacing aging pipes.
“Erwin Utilities is not exempt from this characterization,” Rice said. “Approximately 20 percent of Erwin Utilities’ wastewater system is over 90 years old. Erwin Utilities is doing everything we can to solve this problem as economically efficiently as possible. The goal is to fix the worst problems first.”
To assess the problems, Rice said Erwin Utilities utilizes a robotic camera to inspect sewer lines, and repairs are made to the system when they are discovered.
“Large sewer line rehabilitation projects are then prioritized based on what the inspections find,” Rice said.
Rice said Erwin Utilities has developed and maintains a five-year capital improvement plan and hopes to correct the problem by making improvements at the wastewater treatment plant and in the sanitary sewer collection system.
“In 2014, Erwin Utilities plans to spend $1.2 million on improvements at the wastewater treatment plant and $300,000 on sanitary sewer collection system rehabilitation in the downtown area and along Gay Street in Erwin,” Rice said. “These are some of the oldest parts of the system. Additionally, in successive years, Erwin Utilities plans to spend $200,000 each year rehabilitating parts of the sanitary sewers. Erwin Utilities plans to manage infrastructure improvements by rehabilitating a portion of the collection system each year. This strategy should prove to keep rate increases at modest levels and avoid rate shock to our customers.”
Rice said Erwin Utilities does not have any planned sewer rate increases at this time, but rates are evaluated each year based on planned capital projects, as well as projected operating revenues and expenses.
“I spoke to (Erwin Utilities General Manager) Lee Brown about the rates and he stated that we will evaluate the rates in the spring when we start our budget process and evaluate our financial plan,” Rice said. “A rate increase is not forecasted at this time.”