A state administrative magistrate has set aside most of the fines assessed by the state Department of Environmental Protection against Joseph N. and Evelyn R. Alosso for alleged septic violations at their home in Oak Bluffs.

In October 2004, the DEP had sought a $28,310 civil penalty against the Alossos for the alleged violations at the house they built on Carol Lane.

But in a partial summary decision issued Oct. 3, Administrative Magistrate Mark L. Silverstein vacated $19,685 of the penalty “because the undisputed material facts do not support the alleged violation or show that the violation was willful on the petitioners’ part.”

Mr. Silverstein denied a summary decision on the remaining $8,625 penalty, which was assessed for discharging to a new septic system before a certificate of compliance was issued. The magistrate wrote that several factors pertaining to the penalty remain genuinely disputed, as well as the willfulness of the alleged violation.

For the most part, however, the magistrate ruled that the state agency incorrectly assessed what had happened at the Carol Lane property and threw out most of the related penalties.

“It was supposed to have been a modest dream home for a middle-class family; a single-family, two-story modular house to replace an older one-story home that Joesph N. Alosso and Evelyn R. Alosso had first rented and then purchased,” Mr. Silverstein wrote. “But the dream home soon became a house of enforcement horrors.”

The DEP said the new house had too many bedrooms, that the capacity of its new sewage disposal system exceeded what was authorized, and that other state septic rules had been violated.

“The evidence shows it to be beyond dispute, however, that the original house had four bedrooms rather than three as [the DEP] alleged,” Mr. Silverstein wrote.

“Consequently, the design capacity of the new on-site sewage disposal system was not increased over the volume that the original house was authorized to receive, the new house is not ‘new construction’ as the Title 5 regulations define it, and the nitrogen-loading limitations that the regulations impose upon new construction in nitrogen-sensitive areas do not apply here.”

State Title 5 rules cover on-site septic disposal.

Similar to summary judgment in superior court, summary decision means that the facts are undisputed and the case must be decided solely on the issue of law.

Mr. Alosso supervises both the Edgartown and Oak Bluffs municipal sewage plants. He was a member of the Oak Bluffs board of health when the new septic system was installed.

“I’m pleased with what the magistrate ruled,” Mr. Alosso said yesterday. “I think the magistrate looked at the evidence. He said there was never any doubt that it was a four-bedroom house.

“Somebody convinced somebody at the DEP that this should be looked at,” he said. “I think politics can be really nasty. That’s why people don’t go into politics.”

Mr. Alosso estimated his legal costs at between $18,000 and $20,000. He said the money could have gone toward the college educations of his son and daughter.

“It’s a travesty of justice,” he said. “It looks like somebody should be held accountable . . . the only one who ended up spending money was the one who didn’t do wrong.”

Last April, the Massachusetts Ethics Commission terminated its inquiry into whether Mr. Alosso violated the state conflict of interest law by unlawfully wielding his influence as a town official and board of health member during construction of the septic system.

In the 47-page partial summary decision, Mr. Silverstein writes that the original ranch house on the Alosso property, a .17-acre parcel at intersection of Carol Lane and County Road, was built in 1971. The owner of the home from 1972 to 1992, Daniel C. Dion, said that the house had four bedrooms: two on the first floor and two in the finished basement.

In 1995, the Alossos, who had been leasing the house from subsequent owners, bought the house. The bank mortgage appraisal said the house had four bedrooms.

In 2003, the Alossos decided to renovate the house, but later opted to tear it down and put up a two-story modular house with four bedrooms on the second floor. They also decided to install a new septic system to replace an existing cesspool.

The DEP said based on assessing records the house had only three bedrooms; this was the foundation for most of its case against the Alossos.

But Mr. Silverstein found that unchallenged witness reports from Mr. Dion and Mr. Alosso, along with unchallenged appraisal reports, “shows it to be beyond genuine dispute that the original house had four bedrooms — two in the finished basement and two on the first floor.”

By placing the number of bedrooms at four, Mr. Silverstein began to knock down parts of the DEP’s case.

The design flow capacity of the new system, he found, could handle the flow from a four-bedroom house. Because the new flow didn’t exceed state requirements, the new house did not qualify as new construction and hence did not violate septic rules in an area designated as sensitive to nitrogen loading. The magistrate vacated the corresponding $8,625 of the overall penalty.

The magistrate also set aside penalties stemming from the DEP’s contention that subsurface components of the new disposal system had been backfilled prior to final inspection ($1,000); that a certificate of occupancy had been issued before a certificate of compliance had been issued for the new septic system; that the system had been built closer to the property line than Title 5 rules allow ($8,625); and that two percolation tests had not been performed at the site of the new system ($1,000.)

Ed Coletta, a spokesman for the DEP, said yesterday that once Mr. Silverstein completes his summary decision, the commissioner of the department will review the decision and accept or reject it.

The commissioner’s decision then may or may not be appealed in the superior court, Mr. Coletta said.