The Weymouth Compressor Station: Exhibit A in the persistence of toxic burden ‘hotspots’

To date, the unrelenting ‘natural’ gas infrastructure buildout of frack pads, gathering lines, interstate pipelines, compressor stations, power plants, cracker plants and LNG ports has occurred largely ‘upstream’¹ of America’s urban centers. Within urban centers, smaller local distribution pipes dominate —invisible, mundane urban infrastructure. Recently, however, an intrusive push for upstream infrastructure within urban centers is taking shape.

Case in point: The Weymouth Enbridge Compression Station, just south of Boston, Massachusetts.

The preponderance of rural gas compressors (black dots) vs those few sited in high urban density (pink boxes), including the Weymouth compressor. Data: HIFLD Open Data, Mapped by author.

Compressor Stations are a notoriously noxious. Designed to ‘compress’ gas over long distances, they periodically ‘blowdown’ — ie, blowout gas in a pipeline section under tremendous pressure, causing massive spikes in local Hazardous Air Pollutants (HAPS), as well as climate-killing Methane. Beyond both ‘planned’ and ‘unplanned’ blowdowns, a compressor’s ongoing, 24–7 operation is the essence of an incompatible land use.

Of the total 1,368 stations across America, 12 (0.9%) are situated in urban centers with populations greater than 50,000 people within 3 miles of the station.

12 Compressor Stations in dense urban centers — 50,000 or greater persons within 3 miles of the station | Data: HIFLD Open Data, charted by author.

In the case of the Weymouth Enbridge Compression Station, both exceptional urban density and demographic composition are at issue. Based on mapping at the 2 mile proximity seen below, multiple US Census tracts are eligible for Environmental Justice (EJ) consideration:

[Environmental Justice] refers more specifically to “disproportionate impacts on minority populations, low-income populations, and/or indigenous peoples that may exist prior to or that may be created by the proposed regulatory action.”²

EJ Eligible Census Tracts near Weymouth Compressor. Immediately north of the project site is tract 250214178022, as known as Germantown.

Enbridge’s project introduces a myriad of new risks to residents. Potential air quality impacts from this 24–7 gas operation are at the top of the list. While the Weymouth Compressor was permitted utilizing EPA AERMOD methods, that does not mean its non-polluting. Rather, modeling didn’t move the needle enough at the regional scale to deem the project a significant impact on regional air quality. Further, the Weymouth Compressor as situated within its metropolitan region — Boston-Cambridge-Newton, MA-NH — is not proximate to the 2018–19 air monitoring stations for the region. As seen below, the closest station is downtown Boston — 7.3 miles northwest of the site.

The Weymouth Compressor and regional air monitoring stations within the Boston-Cambridge-Newton, MA-NH metropolitan region | Data: US Census, charted by Author.

While regional air quality has improved over time, vexing challenges persist. The region struggles to decrease both ozone and carbon monoxide particularly during increasingly severe, hot summer days³ — a pernicious effect of climate change. Down from 68% of days in the early 2000’s, the region still experiences approximately 35% of days when air quality is compromised.

Number of ‘Moderate Quality’ days 2000–2018 in the Boston-Cambridge-Newton, MA-NH metropolitan region | Data: EPA, graphed by author.

Against this regional backdrop, the Federal Energy Regulatory Commission (FERC) certified the original project application — as it does with virtually every gas industry project that comes before the commission. However, the prevalence of existing EJ geographies coupled with intense, years-long activist pressure, forced a reluctant Massachusetts state to do what the EPA advises as a matter of course when EJ issues are present: take a closer look.

This closer look took the form of a multi-agency analysis resulting in a final Health Impact Assessment (HIA)⁴ for the project — ‘the very first HIA for any gas infrastructure in the State of Massachusetts’. The process featured several disaggregated methods, including community health intakes; localized air sampling and a review of the original Applicant AERMOD modeling for the project.

In this effort to access potential impacts at a much larger scale (closer) than the FERC regional analysis, two critical EPA screening panels seem to have been omitted:

  • An EPA EJSCREEN for environmental indicators⁵
  • A Risk-Screening for Environmental Indicators panel (REIS)⁶

Both products offer insightful screen indicators appropriate for both large and relatively small scale, regional analyses. Their omission from both the FERC certification and state HIA leaves two critical questions unanswered:

  • What is the current and relative toxic burden of immediately impacted communities as compared with a larger region?
  • What is the current and relative vulnerability to toxic burdens of the immediately impacted community as compared with a national scale ?

One of the guiding principles of EJ policy addresses proximity to emission sources — vulnerable populations tend to be proximate hazardous conditions (hazardous waste sites, high traffic roadways, or industrial sites). Indeed, persistent legacy industrial uses typify both the Weymouth Compressor Site itself and it proximate census tracts.

The current compressor site is a brownfield with significant coal and oil storage uses with known ground contamination from coal ash, arsenic and asbestos materials (left, southwest view, date unknown; right northeast view, 1987). Image Sources: left — ( right — via (

Within just one mile, there are six EJ eligible census tract blocks groups that intersect with numerous state and federally regulated industrial emission sources.

Six census tract block groups within 1 mile of the Weymouth Compressor Site.

Utilizing the EPA’s EJSCREEN database, all proximate tracts score exceedingly high across at least one environmental variable. However, one tract— 250214178022 (Germantown) — scores consistently above indices guidance thresholds across nearly all environmental variables. As stated in EJSCREEN guidance:

When using EJSCREEN, the 80th percentile is a suggested starting point for the purpose of identifying geographic areas in the United States that may warrant further consideration, analysis, or outreach.

Southern Edge of Census Tract 250214178022 — known as Germantown. EJSCREEN environmental screen with percentile scores shown at right.

The Risk-Screening for Environmental Indicators panel (REIS), tabulated to a 810 x 810 meter grid cell resolution(162 acres), is best used to evaluate relative environmental risk across a continuous surface. In the following analysis, the REIS grid data was cut to the Boston-Cambridge-Newton, MA-NH metropolitan region, resulting in a comparison region for the primary 1-mile proximity radius. The following three maps, left to right, show the regional pattern across three pertinent risk variables in the REIS data:

  • Toxic Concentration — Concentration multiplied by inhalation toxicity weight, summed over all chemicals impacting cell.
  • Total Risk Score , Cancer — Risk-related score (surrogate dose * toxicity weight * population) using only toxicity values for cancer effects
  • Total Risk Score , Non-Cancer — Risk-related score (surrogate dose * toxicity weight * population) using only toxicity values for non-cancer effects
REIS Variables Mapped at Metropolitan Region — Toxic Concentration | Cancer Score | Non-Cancer Score | Increasing score values are represented by increasing saturated reds in each map. Data: EPA REIS, Mapped by author.
REIS scores — metropolitan region compared to 1 mile project proximity.

As seen in both the maps and summary tables above, elevated risk exists at the 1 mile proximity when compared with both the nation (EJSCREEN), and the metropolitan region (EPA REIS). In other words, the immediate area surrounding the Weymouth Compressor Site is a Toxic Hotspot as defined by the EPA⁷.

In the state’s HIA, standard EPA screening techniques were omitted in favor of a highly disaggregated methodology. While disaggregation is generally a recommended tactic, notoriously bungled data handling⁸ coupled with a heavy reliance on the applicant’s modeling assumptions have left residents without a confident environmental baseline, nor a full understanding of how continuous station emissions including inevitable blowdownswill add to their community’s persistent legacy of industrial uses.

Keeping in mind that the EJSCREEN and EPA REIS scores are relative, designed for screening purposes, they are also not inconsistent with the disaggregated health findings of the HIA. Clearly, evidence points to the existence of disproportionate impacts in the past and present, only to be exacerbated by the Weymouth Project. Federal and State actors should be using all means necessary to alleviate disproportionate impacts and break the cycle of Toxic Hotspots, not creating opportunities for their persistence.

Note: At the time of this writing, the state has begun engagement with Weymouth to install new air monitor(s), presumably near the Weymouth Station⁹. If the Weymouth station is built to completion, this may be the first occasion across nearly 1,500 compressors to consistently gauge air quality impacts from a gas compressor during all activities, including blowdowns. On 2/10/20, the Weymouth air monitor is posting results along the pm 2.5 variable available as follows:

[1]: For this article, the term ‘upstream’ stands in for both upstream and midstream infrastructure, while ‘downstream’ refers to gas infrastructure in urban areas typically operated by local distribution companies (LDCs).

[2]: Technical Guidance for Assessing Environmental Justice in Regulatory Analysis — April 2016.

[3]: Original Atlantic Bridge Environmental Assessment.

[4]: The Fore River HIA.

[5]: EJSCREEN is an environmental justice mapping and screening tool that provides EPA with a nationally consistent dataset and approach for combining environmental and demographic indicators.

[6]: RSEI Scores are numbers to use for comparison and ranking. RSEI Scores are calculated by chemical, by facility or industry, or by geographic area.

[7]: Section 6.5.4 Identification and Analysis of Potential Hot Spots.

[8]: Air Permit OK’d After New Evidence of Carcinogens at Enbridge’s Planned Gas Facility in Massachusetts Left out| Itai Vardi for Desmogblog.

[9]: State to install air-monitoring station in Fore River Basin | Jessica Trufant for The Patriot Ledger.

Stephen Metts is a GIS analyst and instructor based in New York State. His research interests covered in this article include shale gas development and infrastructure; air monitoring data & environmental justice.

GIS Analyst & Instructor | Shale Gas Impacts, Environmental Justice & Climate Change Issues

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