PLYMOUTH, Maine — The Maine Department of Environmental Protection has set new odor limits for composting facilities that deal with municipal solid waste — including controversial compost manufacturer Soil Preparation Inc.

The levels are much higher than what residents who live near the Plymouth plant want.

“Clearly, we’re disappointed that the DEP really sided with the company,” said Rep. Kenneth Fredette, R-Newport, who sponsored a 2013 law that directs the DEP to create nuisance odor regulations for human waste composters.

John Barry, Soil Preparation plant manager, said he understands where neighbors are coming from, especially given the nature of his business, and added that the company is making strides to improve the odor situation.

“We want to be good neighbors,” he said Thursday when he stopped by the Bangor Daily News with environmental consultant Ted Johnston, who works for Soil Preparation, to demonstrate the n-butanol odor intensity scale the DEP will be using. “We will continue to investigate any opportunity we can to resolve the issue.”

When Fredette put forth LD 141, the bill ordered the Maine DEP to create solid waste management rules for septage and wastewater treatment sludge processors such as Soil Preparation to measure odors, and the initial odor limit was 25 parts per million.

The new final DEP rules state, however, that an odor can be called a nuisance if it is detected at 300 ppm for more than four hours a month, or 600 ppm for three hours a month.

While residents are upset with the higher odor threshold, Johnston said Friday that the requirements are “going to be a challenge” to meet.

The DEP created an odor intensity referencing scale that ranges from one to five, and is based on humans detecting the intensity of n-butanol in distilled water and comparing it with odors detected at or beyond the boundary of the plant.

“Level 1 consists of 150 parts per million,” the new DEP final rules state. “Subsequent levels (Levels 2 through 5) increase by a factor of 2 based on a volume to volume basis.”

An odor is deemed a nuisance if there is “an intensity greater than or equal to 3 for a duration of 60 minutes or more on at least 3 days in any 30-day period” or if there is “an intensity greater than 2 but less than 3 for a duration of 90 minutes or more on at least 4 days in any 30-day period.”

Johnston said, “It’s a very difficult set of regulations for Soil Prep but we think it’s probably reasonable. … It’s very tough. 150 parts per million — that is where it starts — and if we hit 300 [ppm] we’re in trouble.”

The DEP’s final odor management rules recently were signed by the commissioner and were filed Thursday by the secretary of state’s office, according to Paula M. Clark, division of solid waste management director for the Bureau of Remediation and Waste Management.

The DEP did allow a transitional period that gives Soil Preparation, the only municipal solid waste composting company in the state, until March 1, 2015, to come into compliance.

“We’re not going to wait,” Johnston said. “Soil Prep is looking to do what they can as quickly as they can. We’ve experimented with different things over the years and we’ll continue to do so. We’re meeting with some engineers and odor experts to explore with them what has worked elsewhere in the country.”

Soil Preparation is licensed to accept septic waste and sludge for processing into organic non-food crop fertilizers and has been using advanced alkaline stabilization with subsequent accelerated drying, known as the N-Viro Soil Process, since 2000, according to a DEP memorandum.

The company got a DEP permit this spring to install a biosolids gasification line designed to reduce odors by using new technologies that will “bake the odor right out of it,” Johnston said.

The company, which employs about 20-25 people, is investing more than $10 million into the gasification technology, he said.

The new DEP rules also require companies in violation of the odor levels to create an odor management plan to address the problem and to document everything, including reports of violations, that was happening at the plant during the reported violation, and other factors, such as the weather, on the day of the report.

“That’s because dense, moist air traps it,” Barry said of odors produced at the plant by moving materials. “There are certain things we don’t do on hot and humid days.”

“The goal, in the DEP’s charter, is to ensure the public isn’t exposed to nuisance odors,” Johnston said. “This has some real teeth to it and it’s going to be rough and it’s going to be a challenge.”

Even though the company officials say the new DEP rules are stringent, they are not strong enough for Fredette, the Maine House minority leader.

“We’ve already filed an appeal with the department and we’re meeting with Governor [Paul] LePage in August to fight for more acceptable levels,” Fredette said.