The Virginia State Corporation Commission has retained an engineering consulting firm to investigate leaks at Virginia Power's giant "pumped" storage station in Bath County.

The SCC, the state's powerful utility regulating commission, has hired Shannon and Wilson of Seattle to investigate the engineering, design and construction work on the project and review the measures the utility is taking to prevent further leakage at what will be the largest pumped storage facility in the United States.

The hydroelectric plant has two giant reservoirs, one 1,000 feet above the other.

The water from the upper reservoir flows through vertical tunnels to the lower reservoir, generating electricity as it goes. The water is then pumped back to the upper reservoir. The leaks are in one of the vertical tunnels.

The designer of the project is Harza Engineering Co. of Chicago, according to the SCC. The Daniel Construction Co. of Greenville, S.C., has done the major construction work on the project, SCC officials said.

The action by the SCC was the latest in a series of economic troubles that have beset the $1.65 billion hydroelectric plant since construction began in 1977.

In 1980, Virginia Power (then Vepco) laid off 2,500 workers and moved the completion date of the plant from 1983 to 1985 because of a shortage of money due to a sharp slowdown in the demand for electricity. The delays have added $460 million to the cost of the project.

Leakage at the plant, 160 miles southwest of Washington, began in March in one of three mountainside tunnels used to jet water from one reservoir to another to generate electricity, said James B. Douglas, administrative manager of public utilities at the SCC.

"Tunnel number one was losing water and pressure built up around empty tunnel two and made tunnel two bulge," he said. Virginia Power is "concerned about the leakage and more concerned about the buildup of pressure within the mountain against the tunnels," he said.

If the facility had been in commercial operation at the time of the leakage, it might have caused "a little landslide," said company spokeswoman Nolene Hassett, but the utility "would have been able to control the process." The facility is not near any dwellings, she said.

Hassett said additional work to prevent further leakage problems could add between $28 million and $30 million to the cost of the project, which is 40 percent owned by the New York-based Allegheny Power System. Virginia SCC officials say that if it is determined the problem was caused by company mismanagement, the costs of the project could be assigned to shareholders rather than customers of the utility.

"If it comes out there were major problems and Vepco management botched it, the commission would probably look on that as a reasonable basis to have the shareholders participating in the extra cost," said one official who asked not to be identified.

"Even with the extra work and delay, we still hope to bring the project in ahead of schedule and under budget," said Virginia Power's Hassett. The project was ahead of schedule and about $30 million under budget. "Problems like this are inherent in bringing a plant this size on line."

But the SCC's Douglas said the commission is questioning whether adequate geotechnical exploration was performed, whether the tunnel design properly incorporated the data, whether monitoring procedures were adequate and whether the remedial measures are adequate.