Sullivan's Island - The town plans major work on its aging sewer system to fix leaky pipes that cause its wastewater processing plant to work harder.

"It can affect your billing eventually if equipment wears out," said Mayor Pro-Tem Jerry Kaynard.

Much of the sewer collection system was built more than 40 years ago. Groundwater and rainwater seep into leaking sewer pipes, which are gravity-fed, he said.

To finance sewer repairs, the town is applying for $1.6 million from the Clean Water State Revolving Fund, said Water and Sewer Department Manager Greg Gress.

The initial phase of the work will cover most of an area from near Breach Inlet to near the lighthouse. Some seven miles of sewer pipe will be cleaned, inspected and stabilized with chemical grouting, which is expected to reduce leakage by 25 to 30 percent.

At the same time, the need for further structural repairs to pipes will be assessed and prioritized. The project will get started this summer and take about five months to complete. The area where the work will happen accounts for about 60 percent of the sewer pipe leakage, Gress said.

Kaynard said water pipes on the island are fine. More than 50,000 feet of water pipe has been replaced or upgraded since 2004. The town buys water from Charleston Water System.

The problem with sewer pipes is exacerbated by the high water table. Dig down three feet on the island and there is water, Kaynard said.

Gress discussed the issue in a 2013 letter to residents.

He said the average wastewater flow treated at the sewer plant in 2012 was 499,000 gallons per day. But on average customers used only 180,000 gallons per day of drinking water. The difference between water consumed and wastewater is caused by leaky sewer pipes.

"In fact, a very heavy rainfall can add almost a million gallons per day of liquids to the volume that reaches the sewerage treatment plant," he said.

In the letter, Gress said that Town Council had OK'd a modest rate hike to pay for water and sewer improvements.

The hike went into effect last summer. It increased by 7.7 percent, or $8.13, the bill for 6,000 gallons per month.

The system has an inflow and infiltration problem common to older sewer collection systems, he said in the letter.

"This means that rain water and ground water find their way into the sewer collection system through cracks and joints and use up pumping and treatment capacity at the wastewater treatment plant," he said.

Much of the island sewer collection system was built more than 40 years ago. The Army constructed some of it 60 years ago.