Cumulative Impact Analysis

Contents

What is in this report

1. 1Summary
2. 2The Specific Geographical Area
3. 3Burdened Areas intersecting the SGA
4. 4Elevated Indicators
5. 5Construction phase: project impacts on the Elevated Indicators
6. 6Operations phase: project impacts on the Elevated Indicators
7. 7Avoidance, minimization and mitigation
8. 8Project benefits and the Community Benefits Plan
9. 9Conclusion, and what would change it
10. 10Community input, and how to take part
11. 11Sources, methods and terms

Figures

1. 1The facility boundary for the state suitability tool
2. 2Parcel, leased work area and equipment area
3. 3Project location and landmarks within one mile
4. 4The Specific Geographical Area and the Burdened Area it intersects
5. 5The site's block group, its MassEnviroScreen score and what drives it
6. 6US grid battery fires since 2019 with a public record: cells, enclosure, public orders, and what sampling found
7. 7Shelter and evacuation orders at US battery fires: how often, and how long, by battery type
8. 8What reached the environment at real battery fires, by comparability
9. 9Where the pad drains, where Gillespie Road drains, and the ridge between them
10. 10Elevation from Gillespie Road through the pad to McIntyre Pond
11. 11Which way the wind blows: ten years at Worcester Regional Airport
12. 12What the land does to anything that leaves the pad, stage by stage
13. 13Modeled sound sources on the current layout
14. 14Receptors within one mile and the night-time contours
15. 15Night typical case: preliminary screening before any fixes
16. 16Mitigated equipment plus a 20 ft wall, a test case in the preliminary screening
17. 17Terrain profiles to the four nearest houses
18. 18What the 34 open decisions are about
19. 19What is not known yet, and when it will be

A Cumulative Impact Analysis asks one question in five steps: does this project add to burdens a community already carries? The site sits in a census block group the state has designated a Burdened Area, so every step applies. This working draft records the steps taken, the preliminary answer to each, and what still has to happen before the answer is final.

The 2024 Climate Act requires an applicant for an energy facility to assess the existing environmental burdens and public health consequences in the area around a proposed site, and, where that area is subject to an unfair or inequitable burden, to identify any impact of the project that would likely result in a disproportionate adverse effect, any impact that would increase or reduce the effects of climate change, and the remedial actions proposed for either. 980 CMR 15.00 sets the method. The Office of Environmental Justice and Equity's Standards and Guidelines for Cumulative Impact Analysis, April 2026, sets the standard. This report follows the Board's CIA Report Template, part by part, so that the filed version can be checked against this one.

The Specific Geographical Area, or SGA, is the ground the analysis examines. It is drawn as a fixed distance from the Facility Boundary, and the distance depends on the kind of facility. For a clean energy storage facility it is one mile.

Explanatory comments. The one-mile ring measured from the Facility Boundary encloses about 2,770 acres, and it lies entirely within the Town of Charlton; no other municipality's boundary is inside it. Measured from the parcel boundary instead, the ring encloses about 2,840 acres and adds no block group. The block-group analysis in Section 3 was run both ways and reaches the same result.

A Burdened Area is a census block group with a MassEnviroScreen score of 75 or more, or a median household income of 65 percent or less of the state median. Three block groups lie inside the one-mile SGA. One of them qualifies, and it is the one the whole project sits in.

Explanatory comments. Block group 250277561023, scoring 19.7, lies about 1.04 miles from the Facility Boundary and does not intersect the SGA. The host block group is the only Burdened Area in Charlton. It qualifies under 980 CMR 15.04(1)(a) on its score; its median household income of about 82 percent of the state median does not trip the 65 percent test in 15.04(1)(b). It is not an environmental justice population under the state's separate definition, and this analysis is not an environmental justice screening: 980 CMR 15.00 uses MassEnviroScreen and the Burdened Area test, and nothing else. Because about 1,142 feet of the gen-tie easement runs outside parcel 43-A-1, the check was run on every parcel that hosts a project component; every one falls in the same block group. Under 980 CMR 15.04(5) the analysis relies on the indicator data current when the pre-filing period began on April 9, 2026, which the project understands to be the February 27, 2026 build and will confirm with the Division of Public Participation. Because the SGA intersects a Burdened Area, the analysis continues under 15.05(3) rather than concluding.

MassEnviroScreen scores every block group on 30 indicators, each as a percentile against every other block group in the state. For a clean energy facility, an indicator above the 50th percentile is an Elevated Indicator, and the project has to assess its effect on each one. The host block group has 16.

What drives the score

The host block group's score of 80.9 is the statewide percentile of the product of two group scores, pollution and climate burden at 45.0 and population characteristics at 57.0. Inside the first, the environmental effects component at 86.0 ranks 99.7th of the 5,109 Massachusetts block groups, while the pollution exposure component at 23.3 ranks about 15th. Moving the effects component alone to the statewide median would drop the score from 80.9 to about 40. The effects component is where the burden is: cleanup sites at the 90.8th percentile, groundwater threats 88.4, solid waste sites 85.6, impaired water bodies 83.7, hazardous waste generators 81.4. The second driver is chronic disease prevalence in the sensitive populations component: adult cancer at the 83.3rd percentile, high blood pressure 80.4, premature mortality 74.0, coronary heart disease 73.0, COPD 62.8. These health figures come from CDC PLACES model estimates and MassDEP rates, and they are identical for the two block groups because the estimates are made at a coarser geography.

Explanatory comments. The state's technical documentation says a high percentile does not by itself mean a regulatory threshold is exceeded or that a health risk exists; the percentiles compare one block group with the others. Three of the four health indicators and the two air quality indicators nearest the threshold, PM2.5 at 54.2 and ozone at 49.9, are regional values shared across central Massachusetts rather than anything local to Carpenter Hill Road. The low birth weight indicator returns no value for either block group, so 29 of the 30 indicators are scored. The neighbouring block group, analysed voluntarily, also carries 16 indicators above the 50th percentile, with a different set: it adds drinking water non-compliance and unemployment and drops solid waste sites and pediatric asthma. Elevated Indicators there have no legal status under 980 CMR 15.02, because the definition applies only where the SGA intersects a Burdened Area, but the project impacts assessed in Sections 5 and 6 reach it in the same ways and the same conclusions apply.

For each Elevated Indicator, the question is whether construction of the project would materially exacerbate the condition it measures: worsen it, leave it alone, or improve it. The test in the template's Appendix B looks at standards, perceptibility, measurability, duration, geographic extent, resilience, social and health effects, and the potential for contamination to migrate. Construction runs 12 to 18 months.

The determinations below take account of the measures the project has made a firm commitment to undertake, as 980 CMR 15.07 allows. Those are the commitments on the public Commitment Tracker and the permit requirements the project cannot avoid; the tracker links each to what closes it. Where a determination depends on a study that is not finished, the row says so.

Explanatory comments. Two Elevated Indicators would have carried a different answer without firm commitments: impaired water bodies, because sediment from 10 acres of disturbance above a wetland chain is the kind of impact the indicator measures, and groundwater threats, because of the soil the pad sits on. In both cases the commitment that bounds the impact is required by a permit the project cannot avoid, which is the strongest kind of commitment for the purposes of 980 CMR 15.07. The MEPA Office and MassDEP raised the wetland delineation, stormwater and run-on at the September 4, 2026 consultation, and the rows above are consistent with what the project told them.

In operation the facility charges and discharges batteries, burns nothing, has no stack, uses no process water and discharges no wastewater. The impacts that remain are the ones that come from the equipment itself: a credible fire event, the liquids on site, cooling fan and inverter noise, new impervious surface, and cleared forest. This section assesses each against the 16 Elevated Indicators, then asks the Climate Act's separate question about the effects of climate change.

The fire event: what the US record shows

The wildfire risk row above waits on the fire protection engineering report. What can be set down now is the record of what has happened at grid battery fires in the United States, because residents have asked whether shelter and evacuation orders are the exception or the rule, and because the record is what the Emergency Action Plan is written against. For scale, EPRI's global incident database shows the failure rate falling from about 4 events per gigawatt-hour of installed storage in 2018 to about 0.04 in 2025, a drop of about 99 percent, while installed storage worldwide grew to nearly 700 gigawatt-hours; those totals are floors, because most US fires are reported only voluntarily. Nineteen US grid battery fires since 2019 have a public record of the response. Twelve led to a shelter-in-place or evacuation order, four to road closures only, and three to no order, so an order is the rule once smoke is visible near people. Every order at an outdoor unit or container was lifted within a day, except Escondido's two days and La Verne's three. The orders that ran a week or more were at batteries inside a building. At the three outdoor fires in lithium iron phosphate units, the chemistry this project uses, no one was asked to leave home. Where air, soil or water were sampled afterwards, the two outcomes that reached the environment, metal deposition in a marsh and a later lawsuit alleging PFAS chemicals in public wells from the firefighting runoff, were both at batteries inside buildings. At the outdoor fires with published sampling, hydrogen fluoride was not detected at the perimeter, hydrogen cyanide was measured close to the units at three fires, in every case below the occupational exposure ceiling, and the wells tested afterwards were clean. This is the record, not a prediction for this site. It is sorted by what is comparable: outdoor lithium iron phosphate units first, outdoor units of other chemistry next, batteries inside buildings last.

Where anything leaving the pad would go

Two questions from public comment are about reach: whether smoke from a fire would settle on the homes along Gillespie Road, which the comment describes as a valley, and how far anything carried in runoff or firefighting water would travel. Terrain answers the first in part. Gillespie Road lies about a mile north of the pad, and an 820-foot ridge stands between them: the pad sits at about 719 feet, the road between about 707 and 762 feet, and no downhill route from the pad reaches the road. Ten years of wind records at Worcester Regional Airport show the wind from the west about 40 percent of the time and from the site toward Gillespie Road about 10 percent of hours. This is terrain and wind climatology, not a plume model. The site-specific gas plume analysis is a published commitment, filed with the Application and posted here, and has not started. This report commits to the analysis, not to its result.

For the second question, the land south of the pad does two things to anything that leaves it: it dilutes it by area and it holds it in wetlands. The pad is about 7.5 percent of the land draining through its own outlet, 2 percent of the land draining past T Hall Road half a mile away, about 1 percent at Burlingame Road, and 0.2 percent of the 1,651 acres that drain through McIntyre Pond. Fifteen mapped wetlands, 63 acres in all, lie on the path before the pond, and more than half of its length runs through mapped wetland. Those shares describe area, not concentration, timing or containment. That is why firewater capture and the stormwater design are commitments whatever the shares say, and why a baseline of soil and water conditions before construction is proposed for the scope of the Emergency Action Plan and the monitoring program.

Sound: a preliminary screening model, not yet confirmed by a sound engineer

The adult high blood pressure row rests on the sound study. What exists today is a screening-level model built in September 2026 by the project team. It is preliminary and has not been reviewed or confirmed by a sound engineer; its figures are posted in the Slide Library marked that way and are reproduced here so the row can be checked, not as a result. The model stands in the manufacturer's published data for the earlier Megapack unit for the Megapack 3, which has none yet; spreads 136 units over the 40 rows on the current drawing; uses the standard outdoor propagation method with terrain screening; and has no measured background, so it cannot say whether the policy is met, only what background would be needed. On that basis the night typical case puts about 59 dBA at the closest property line, 54 at the landowner's house and 48 at the nearest neighbour. The mitigation package the model tested, a night fan cap, low-noise transformers and a 20-foot wall, brings those to about 51, 47 and 43. The model's own reading is that the two closest property lines do not meet the policy with the rows where they are, so the layout is expected to change, and that the professional study should test setting the pad lower into the slope and berms on the north and southwest sides. Trees are given no credit, because the state requires the leaf-off case. Every number here is a screening figure with a stand-in source and no measured background, from a model no sound engineer has confirmed. The professional study against the MassDEP noise policy, with the Megapack 3 data, replaces it, and the final levels are whatever that study finds.

The effects of climate change

The Climate Act asks separately whether the project would increase or reduce the effects of climate change on the area. Both directions apply. The facility stores electricity and returns it to the grid when demand is highest, which supports the region's reliability as more of its supply comes from wind and solar and less from fossil generation; that reduction in the effects of climate change is regional, not confined to the block group, and the Board weighs it in the Application. Locally, the project clears up to 10 acres of forest, which is a loss of carbon storage and shade, and adds about 5 acres of gravel and equipment that will run warmer than the woods around it on a hot day. Both local effects are small in extent, and the block group's extreme heat indicator sits at the 18th percentile and is not elevated. The site's own climate exposure, high for extreme precipitation and extreme heat by 2070, is an input to the stormwater design and the equipment thermal specification rather than an impact on the community.

Explanatory comments. Every operating determination above is preliminary because three studies it rests on are not finished: the fire protection engineering report with the hazard mitigation analysis, the sound study against the MassDEP noise policy, and the final stormwater and containment design after the borings. Each is a published commitment with a place on the Commitment Tracker, and each is filed with the Application. If any of them shows that an Elevated Indicator would be materially exacerbated, Section 7 becomes a table of Remedial Actions under 980 CMR 15.08 rather than a list of commitments, and this report is reissued to say so.

980 CMR 15.08 requires Remedial Actions only where a Disproportionate Adverse Effect is found. None is found in this draft. The measures below are listed anyway, in the mitigation hierarchy the guidance sets out, because they are the reason the answers in Sections 5 and 6 are no, and because the Board can make any of them an enforceable condition.

The regulation counts a benefit for CIA purposes only if it has a geographic, economic, public health or scientific connection to where the Burdened Area and the SGA overlap. The benefits below meet that test. Anything drawn from the draft Community Benefits Plan is a proposal, still being shaped with the Citizen Advisory Committee and open for public comment through November 30, 2026, and is labelled that way.

The Community Benefits Plan

The project has been writing a Community Benefits Plan with a Citizen Advisory Committee since June 3, 2026, following the Office of Environmental Justice and Equity's Standards and Guidelines for Community Benefit Plans and Agreements. The working draft, version 0.1, went to the committee on September 10, 2026. Version 0.2 was published as the public comment draft at the September 30 public forum, and comment runs through November 30, 2026. It groups what residents have raised into the state's four categories, writes each proposed commitment as an outcome with a measure, a duration, a decision-maker, a funding source and a remedy, and lists the mitigation the permits already require separately so that none of it is counted as a benefit. The priorities most connected to the Elevated Indicators are fire readiness, well protection and the town's finances. Whether any of the plan becomes a signed Community Benefits Agreement is a decision for the Town of Charlton and the project together; the statute requires the project to pursue a plan, and the Board gives a plan or an agreement due weight under 980 CMR 15.11(3). The plan is linked at the end of this report.

On the record so far, the project is not expected to materially exacerbate any of the 16 Elevated Indicators in block group 250277561012 in construction or in operation, so no Disproportionate Adverse Effect is identified and no Remedial Action is required under 980 CMR 15.08. That conclusion is preliminary, and this section says exactly what it rests on.

Under 980 CMR 15.11 the Board assesses the adequacy of this analysis, makes its own finding on whether the project has given due consideration to cumulative impact and has adequately avoided, minimized or mitigated any Disproportionate Adverse Effect, considers the Community Benefits Plan, and may add enforceable conditions. The project's part is to bring the Board a record it can rely on. This working draft is the first version of that record; it is updated when the studies above finish, shared again with Key Stakeholders, and filed in final form with the Application in early 2027.

The rule requires the project to gather community input during pre-filing and address it in this report. The guidance says lived experience is data. This section records what residents and officials have raised that bears on the analysis, where the record of it lives, and the two ways a reader can change what this report says.

Two ways to change this report

• Tell us what it is missing. The state's guidance says extraordinary local conditions, a source not in the data, or an error in the underlying data are all reasons to look again. Send it to the contact below, raise it at a meeting, or use the comment form on this site. We check it, answer on the Engagement Log, and revise this report if it changes an answer.

• Petition for a full analysis of a neighbouring block group. Under 980 CMR 15.04(6), ten or more residents or businesses of a block group that intersects the SGA but is not a Burdened Area, at least one of them a Key Stakeholder, may ask the project during pre-filing to analyse that block group as if it were one, with a copy to the Director of the Division of Public Participation and the Director of the Siting Board. If the project declines, the group may petition the Director within 14 days after the Application is filed, stating the extraordinary circumstances. Block group 250277561013 is the one this applies to, and this draft already analyses it voluntarily.

Translation, interpretation or another accommodation for any meeting about this analysis is available on request. The Language Demographic Analysis of September 4, 2026 found no language spoken by five percent or more of the population within a mile who also speak English less than very well, and the project provides Spanish and Portuguese on this site voluntarily.

The indicator definitions and sources are the state's, from Appendix A of the CIA Report Template and the MassEnviroScreen technical documentation. The method for deciding whether an impact is material is the template's Appendix B, applied row by row in Sections 5 and 6.

How materiality was judged

For each Elevated Indicator and each phase, the analysis asked the template's Appendix B questions in order: whether construction or operation would likely exceed a public health, environmental or climate standard; whether a casual observer would notice the impact; whether it can be measured; how long and how often it occurs; whether it would extend the burden beyond its present geographic extent; how it affects the ability of the indicator to absorb and recover from disturbance; whether it affects social, economic or cultural conditions or public health; and whether contamination could migrate on or off site by air, ground or water. An impact was called material only if the answers pointed to a lasting, measurable worsening of the condition the indicator measures. Where the answer depends on a study that is not finished, the row says so and the conclusion is conditional.

Terms used in this report

Cumulative Impact Analysis (CIA)

The process by which an applicant identifies, considers and addresses the combined effect of past and present activities plus the proposed project on the environment, public health and climate resilience in a Burdened Area (980 CMR 15.02).

Specific Geographical Area (SGA)

The area within a fixed distance of the Facility Boundary, set by facility type in 980 CMR 15.05(1). One mile for a clean energy storage facility.

Facility Boundary

The outermost boundary of the project site, such as the outermost area of construction or disturbance or the fence line, and for a linear component the edge of the right of way (980 CMR 15.02).

Burdened Area

A census block group with a MassEnviroScreen score of 75 or more, or a median household income of 65 percent or less of the state median (980 CMR 15.04(1)).

MassEnviroScreen

The state's screening tool, maintained by the Office of Environmental Justice and Equity, that scores every census block group on 30 indicators and produces a cumulative burden percentile.

Indicator

One statistical measure of environmental exposure, environmental effect, climate risk, sensitive population or socioeconomic condition in a block group, expressed as a statewide percentile.

Elevated Indicator

For a clean energy facility, an indicator above the 50th percentile statewide, identified only where the SGA intersects a Burdened Area (980 CMR 15.02).

Project Impact

An effect, positive or negative, on the environment, socioeconomic or public health conditions, or climate resilience, from construction or operation of the project.

Disproportionate Adverse Effect

A Project Impact likely to materially exacerbate an Elevated Indicator in a Burdened Area intersecting the SGA, after positive and negative impacts are weighed, with a net negative result (980 CMR 15.02).

Remedial Action

An action that avoids, minimizes or mitigates a Disproportionate Adverse Effect (980 CMR 15.08).

Benefit

A positive effect on public health, the environment or climate resilience with a geographic, economic, public health or scientific nexus to the overlap of the Burdened Area and the SGA (980 CMR 15.02).

Key Stakeholder

Abutters, community organizations, municipal and regional officials, labor and apprenticeship representatives, and Tribes, as 980 CMR 16.02 lists them.

Category 5 water

A water body on the state's Integrated List that is impaired and needs a pollutant budget (a TMDL).

UL 9540A

The test method for evaluating thermal runaway fire propagation in battery energy storage systems.

NFPA 855

The National Fire Protection Association standard for the installation of stationary energy storage systems, applied through the state fire code.

SPCC plan

A Spill Prevention, Control and Countermeasure plan under federal oil pollution rules, for a site that stores oil above the threshold.

Questions about this report

Jonathan Santiago, Project Development Associate, ESA Solar. jsantiago@esa-solar.com or 407-232-7440 ext. 251.

Translation, interpretation, or another accommodation for any meeting about this report is available on request.

The live version of this report, the slides, every map in it at full size, the Commitment Tracker, the Engagement Log, and every document it rests on are at carpenterhillpower.com/reports/cumulative-impact. When a version of this report is replaced, the old one stays readable, with the date it changed and the reason.

Related

• Site Suitability Analysis: carpenterhillpower.com/reports/site-suitability
• Slide Library: every figure in this report at full size: carpenterhillpower.com/slide-library
• Draft Community Benefits Plan: carpenterhillpower.com/benefits/plan
• Engagement Log: what people asked and what we said: carpenterhillpower.com/engagement-log
• Commitment Tracker: carpenterhillpower.com/commitments
• State Standards and Guidelines for Cumulative Impact Analysis (April 2026): carpenterhillpower.com/documents
• How We Follow the Siting Rules: carpenterhillpower.com/siting-rules

Carpenter Hill Power, LLC · 131 Carpenter Hill Road, Charlton, Massachusetts · Preliminary draft v0.4 · October 11, 2026