A study commissioned to find the cause of an odor that has plagued the Nansemond Parkway area of the city for months has come to the same conclusion many already had — that the Suffolk landfill is the main source of the stench.

“The results of the analysis of one of the samples obtained at the Landfill indicate that the facility is a source of measurable [hydrogen sulfide] concentrations in the air,” states the study drafted by SCS Engineers.

The study was posted on the Southeastern Public Service Authority’s Web site this week, and will be discussed by the authority’s board of directors on May 26. SPSA executive director Rowland Taylor did not return a message requesting comment Wednesday.

The good news for local residents is the study did not turn up levels of any chemical higher than recommended exposure limits for health reasons, but levels did significantly exceed their Agency for Toxic Substances and Disease Registry odor thresholds. The odor threshold is intended to define the lowest level of a certain odor that can be detected by humans.

The study was conducted by taking about 180 readings on the landfill property and in surrounding neighborhoods in March. Most readings were taken in the early morning and evening hours, when residents have reported the most pungent odors. When readings showed a high level of certain chemicals, an air sample was collected and submitted for laboratory analysis.

An air sample taken at the landfill at 7:52 p.m. on March 17 detected a level of hydrogen sulfide of 0.031 parts per million. According to the National Institute for Occupational Safety and Health, a measure of 10 ppm is the recommended exposure limit in the workplace.

Hydrogen sulfide is one of several chemicals generated by rotting trash. The Material Safety Data Sheet for hydrogen sulfide notes exposure for short periods can cause irritation in the eyes, nose and throat, headaches, dizziness, nausea and nervousness. Chronic exposure can cause nausea, headache, shortness of breath, sleep disturbance, and eye and throat irritation. It smells like rotten eggs, according to the sheet.

A second chemical, carbon disulfide, also was detected in air samples during the study. It also was found in lower levels than recommended health limits, but higher levels than the odor threshold. Carbon disulfide also can cause a rotten egg smell. The study seems to point to marshes as the cause of the carbon disulfide odor.

Other odors were noted by engineers during the study, including those of coffee, chemical glue and burning rubber or plastic. The coffee smell was attributed to the Sara Lee plant west of the landfill, and the glue smell to the BASF plant northwest of the landfill. The source of the burning rubber or plastic odor was not determined, the study states.

“Although other potential sources of non-landfill related odors were investigated during the study, no others were noted,” the study says.

The study recommends the trash authority continue the measures under way to reduce odors coming from Cell VI, where it currently is dumping trash. In addition, the authority should evaluate measures it can take to collect more landfill gas from Cell VI.

The study further recommends that a stand of trees between the landfill and nearby neighborhoods that was taken down within the last couple of years be replanted. That property, however, is not owned by the trash authority.

“The screen would not only aid with diffusion and stripping of potential odorous constituents, but would also provide a visual barrier between the Landfill and the neighborhoods,” the study states. “We understand this would not affect odor control in the short-term, but could provide long-term benefit to mitigate odors.”