Officials of the North Davis Sewer Improvement District want assurances that Hill Air Force Base won't discharge hazardous waste into the sewer system as part of a base environmental cleanup plan.

Hill wants to use the sewer system to discharge water used in future hazardous waste cleanup efforts. But the sewer district's board has directed its staff to investigate the request more thoroughly before giving permission.In the summer 1992, the base will begin extracting groundwater containing the solvent trichloroethylene, a suspected carcinogen, from a dump site near the northeastern end of the runway, said Capt. Ed Heyse, chief of the base Environmental Restoration Division.

After undergoing a steam-stripping operation to rid it of 99 percent of the contaminants, the water will be sent to the base's wastewater treatment plant.

The base would then discharge the treated water into the North Davis sewer system.

DeLore Thurgood, chairman of the sewer district board, said his group wants to know there will be no hazardous waste residue discharged into the system.

"If we get hazardous waste in there, the EPA will come in and ding us," he said.

District Manager Bob Hohman said the base is permitted to discharge its processing water and household waste into the system, but there's no provision authorizing discharge of any other kind of water.

"They would have to provide the necessary guarantees and safeguards as to what they are really going to do before we would even consider it," he said.

Heyse said the treated water will be the same kind the base has been discharging for years.

He said it was somewhat irregular because it is groundwater rather than industrial water, but there's no real difference in the chemicals.

Heyse said the base would discharge about 30,000 gallons per day, or about 5 percent of the total industrial flow already being sent from the base.

If the sewer district turns down the request, Heyse said, the base would consider cleaning it to an acceptable level and then reinjecting it into the ground.

But using the sewer system is a cheaper alternative because existing facilities are used instead of building a new treatment plant on base, Heyse said.