The environmentalist group that helped block a proposed landfill for Clarksburg in upper Montgomery County has issued an 11th hour appeal to state authorities to change their plans for a sewage sludge trenching project on the same site.

[WORD ILLEGIBLE] that a geological fault lies below the land surface, the Ten-mile Creek Conservation Committee has charged that sludge trenching over the fault could pollute new reservoir of drinking water in the western part of the country.

Burial of sludge, the toothpaste-like solid residue of sewage treatment, is scheduled to begin Monday for 45 days on the Clarksburg site.

The Clarksburg project is one of several temporary sites selected by the county for deposit of residue from the regional Blue Plains sewage treatment plant in the District of Columbia until permanent sludge dumping grounds are approved next year in Montgomery, Prince George's and the District.

The three localities are operating under a federal court order to find permanent sludge sites by mid-1979 within their own boundaries to avoid what U.S. District Judge John L. Smith Jr. has called a potential sludge "emergency" in the area.

The conservation committee is "not against the (Clarksburg) site," said Gerald Loeb, one of its members. But it wants the county to refrain from trenching sludge in the six to eight acres over the so-called "Segovia fault." The county's present plans include sludge burial over 25 acres.

The committee is particularly concerned that pollutants permeating the soil could contaminate water that will be collected downstream in the Little Seneca Reservoir to be built by the county and the Washington Suburban Sanitary Commission at Boyds.

However, the environmentalist group was unable to convince the state health department, which granted the permit for sludge burial, that the fault, long studied by Dr. A. Segovia of the University of Maryland, actually exists.

"There is no fault that we can determine," said Ronald Nelson, administrator of community health programs for the state health department. "We drilled right through the ground where they think it is."

Nelson said that his agency "put all the benefits on the side of the evironmentalists and the people" and even stopped issuance of the permit to do more soil tests before approving sludge trenching on the land.

The conservation committee is further hampered by the administrative appeals process that, even if set into motion, would not begin for 30 days - which would be several weeks into the short-term project.

Although the committee asked the governor's office to intervene, a spokesman for the governor said that the written appeals procedure would preclude that option.