The contractor arrived Monday to begin work on a major expansion of Coupeville’s sewer plant.

Malcolm Bishop, Public Works director, said a second clarifier will be added, thereby increasing the plant’s capacity. The existing plant has been operating near capacity for several years.

The increase will keep pace with the town’s projected growth, Bishop said, but the capacity difference won’t be huge. “It keeps us up with growth,” he said, “but a big reason for expansion is redundancy.”

Two clarifiers will allow the plant to better handle excess inflow caused by stormy weather. A few years ago a storm caused an overflow problem, which resulted in pollution in Penn Cove. “It affected the shellfish harvest,” Bishop said. The larger plant will lessen the chances of a repeat of that incident.

The $880,000 project was made possible by a state grant combined with a zero-interest loan from the state. Coupeville sewer rates were increased about two years in anticipation of the project, Bishop said, so ratepayers won’t face any immediate increases due to the project getting under way. The contractor is Seabord Construction of Seattle, and it has 180 days to complete the job.

A second phase of the expansion project is planned to begin in about 10 years to keep up with the town’s 20-year growth projection.

The sewer plant serves about 750 customers, including all city and county buildings, the hospital, senior housing, schools and the business district.