Explosions to excavate material for a water-treatment plant close to Quail Creek Reservoir may have triggered the sudden, massive failure of the reservoir's dike on New Year's Day.

The dike had problems of its own, but the explosions may have further fractured underground formations - at any rate, that's one of the theories being studied by the independent team of experts investigating the $12 million dike failure.The dike leaked almost continuously since the reservoir began filling. Much of the water seemed to be seeping beneath it, following fractures in the underground rock that were perpendicular to the dike.

Construction of the earth-fill dam and dike began in November 1983, and then-Gov. Scott M. Matheson dedicated the reservoir in September 1985.

The team of independent experts investigating the failure has asked for information on explosions used in building the water-treatment plant, which belongs to St. George city.

State Engineer Robert L. Morgan wrote the city, in care of Wayne McArthur, with detailed requests for data. The four specialists want information about "any activity which may have possibly had any influence on the dike," Morgan wrote.

The Jan. 17 letter says that before the next meeting of the panel, the group would like to know about "blasting which took place during the construction of the water-treatment plant downstream of the dike."

It requests information on the number, location and depth of holes drilled for explosive charges; "explosive type used and total pounds of explosives in each hole";and how much of the explosive was detonated per cubic yard of earth excavated.

The team wants any data available about instrument readings during the explosions.

Morgan requested that the reservoir's owner, the Washington County Water Conservancy District, excavate a trench at the bottom of the dike's breach, widening it by 50 feet on both sides to help the team see what the dike's foundation is like where it was not ripped out by the tremendous rush of water during the flood.

This should be done before the team's next meeting, scheduled to start the evening of Feb. 5 in St. George. Before the session ends on Feb. 8, the experts plan to study the dike's foundation.