HILLSDALE — The borough’s environmental consultant told the mayor and council Jan. 13 that state-required monitoring at Centennial Field — a former landfill that closed about 40 years ago — is expected to double in 2026 to nearly $115,000 following the recent detection of methane gas during soil sampling.
The borough previously paid $57,120 for quarterly methane sampling at Centennial Field, as required by the New Jersey Department of Environmental Protection (NJDEP), consultant Lois Spagnola of The Environmental Group said.
Following methane detections during 2025 monitoring, Spagnola said NJDEP has now required three components for 2026:
- Quarterly methane sampling ($57,120)
- A compliance evaluation ($14,600)
- Additional subsurface methane sampling and delineation ($43,120)
The proposed 2026 budget total is $114,840, Spagnola said. Officials said they anticipate including the costs in the borough’s 2026–2027 budget, which is now being developed.
Methane detected below ground during “slam bar” testing
Spagnola said her firm has conducted vent air sampling and subsurface methane testing at Centennial since June 2016.
“Methane has been repeatedly detected within the west and northwest buffer zones and around the Field House structure during several quarters of methane gas surveys conducted in 2025,” she said, citing findings from a report she discussed with council.
In 2025, slam bar testing was conducted at 17 sites around the field’s perimeter, she said.
Slam bar testing involves driving a cylindrical metal tube into the ground and removing a soil “core” to test for methane gas below the surface.
Spagnola said an underground perforated piping system installed throughout the former landfill is designed to allow methane gas to be rendered harmless through contact with air and dispersed through vents surrounding the field. She said no methane gas has been detected at any vents, and that the detections have been limited to subsurface soils identified through slam bar testing.
Spagnola also noted two “significant” disturbances of Centennial Field in 2025 — installation of a new drainage system and new natural grass sod — which she said may have affected how methane moves underground.
State also requires compliance review and expanded off-site sampling
In addition to quarterly monitoring, Spagnola said NJDEP is requiring a compliance evaluation, which will include review and updating of borough and NJDEP files, as well as evaluation of methane monitoring equipment at the field house, groundwater monitoring wells, and air vents.
The proposed additional subsurface methane sampling will be conducted at “multiple sampling locations” outside the landfill property, according to the scope of work.
Spagnola said the 2026 plan calls for testing at roughly 30 to 50 new locations to help delineate the extent of methane movement. Ground-penetrating radar will be used to help identify sampling sites, she said.
The proposal also calls for:
- Review of ground-penetrating radar data and as-built plans
- Mapping to indicate methane plume extent
- Methane data assessment and recommended next steps based on regulatory guidance
- Preliminary DEP coordination regarding a mandated groundwater sampling program
Spagnola said the new slam bar testing would involve two geologists or scientists and take about four days to complete.
Under “limitations,” the proposal notes slam bar testing must be conducted under specific weather conditions. If weather changes unexpectedly and testing cannot proceed, additional charges of $330 per hour per geologist or scientist would apply for lost round-trip travel time.
A former landfill turned recreation site
During a 15-minute presentation, Spagnola provided a brief history of Centennial Field and its evolution from a landfill into recreational ballfields.
She said the landfill closed in 1986, a landfill “mining project” was conducted in 1999 to assess contents, and the site was capped and closed with an approved soil cap in 2005. A field house was completed in 2007, and state-required methane sampling began in 2016, she said.
Spagnola said Centennial was previously used primarily for disposal of bulk waste and leaves.
Community Center update
Councilor Melissa Mazza-Chiong said a grand opening for the Hillsdale Patterson Street Community Center will likely be held this spring, with a date to be confirmed soon.
The community center was provided as a “community contribution” by developer Claremont March in return for housing density bonuses granted under the Patterson Street Redevelopment Plan.
It was not clear when The Piermont, a 256-apartment complex on Patterson Street, will be officially opened, though this summer or fall appears likely. Some council members toured the residences, but leasing does not appear to have started.