Site Suitability Analysis

The state scores every proposed clean energy site on six criteria before the Siting Board decides on it. This report gives the anticipated scores for the Carpenter Hill site, explains what sits behind each one, adds what the site screening found beyond the six criteria, and records how all of it has shaped the design so far.

The Carpenter Hill Power project is a Large Clean Energy Storage Facility, so the Executive Office of Energy and Environmental Affairs' Site Suitability Guidance applies to it under 980 CMR 15.10(1). The rule asks two things of the project before it files. First, run the state's Site Suitability Mapping Tool on the site to derive anticipated Criteria-specific Suitability Scores (980 CMR 15.10(2)). Second, share those anticipated scores with stakeholders during the pre-filing period. This report does the second. The final Site Suitability Report is filed with the Application for a Consolidated Permit under 980 CMR 15.10(3), and the scores in it are final unless the Director revises them on request or the Board applies a modifier.

The scale runs from 0.0, the most suitable, to 5.0, the least suitable. A high score is a reason for the Board to look harder at avoidance, minimization and mitigation, not a bar to approval. The Board considers the scores in its route and site scoring analysis and in its decision on whether to grant the permit (980 CMR 15.10(6)).

980 CMR 15.10 is short. It tells the project which guidance to follow, when to run the tool, when the scores become final, who can ask for them to be revised, and how the Board uses them. This section walks through it so a reader can check the rest of the report against the rule.

The six criteria and how each is scored

The state's tool scores the site footprint on a grid of cells and reports one number per criterion. Four criteria come from statewide index layers. One is a lookup from MassEnviroScreen. One is a yes-or-no overlap test. The tool's own report states the method for each.

Every score depends on what area the tool is asked to score. The regulation names that area the Facility Boundary. This section measures it from the current site plan, shows the three pieces that make it up, and records the two places the drawing and its title block disagree.

980 CMR 15.02 defines the Facility Boundary as the outermost boundary of the project site, such as a building or other structure or the outermost area of construction activity or disturbance, or the project fence line. For a linear component such as a transmission line, the Facility Boundary is the edge of the right of way. The Site Suitability Mapping Tool scores whatever polygon it is given, so the polygon has to be this one.

Two things the drawing and its title block disagree on

• The easement area. The polygon on the plan's perimeter layer is a clean 30-foot corridor over the 2,694-foot route, which is 80,866 square feet or 1.86 acres. The title block says 68,229 square feet, and that figure divided by the same route length gives a width of 25.3 feet. It reads like a title block carried forward from a narrower easement. The project engineer is confirming which width governs. The geometry here uses the drawn 30 feet, the larger of the two.

• The total. The title block's 16.57 acres is 15.00 plus 1.57 and leaves the driveway out. The driveway is ground disturbance outside both the project area and the easement, so under the definition it belongs inside the boundary.

The 15.26-acre project area is the leased work limit, not the clearing. Tree clearing outside the transmission right-of-way is held at or under 10 acres under a published commitment on the Commitment Tracker, and the fenced equipment area is about 5 acres or less. Nothing in the project record designates any part of the parcel outside the Facility Boundary for a particular use, and this report makes no such claim.

These are the numbers the state tool produced for a 5.7-acre site area on July 17, 2026, with the statistics the tool prints beside each one. They are the anticipated scores 980 CMR 15.10(2) asks the project to share. None is final.

The site is not a brownfield, a landfill or previously developed land, so no development-potential modifier applies. The burdens score cannot be changed by design. Under 980 CMR 15.10(5) it may be modified only by mutual written agreement between the applicant and a Local Government, which is a decision for the Town of Charlton and the project together. This report carries the 4.0 as it stands.

A score is a number. This section says what is on the ground behind each one, using the state's own published layers pulled in September 2026, so a reader can see why the site scores as it does and what the re-run is likely to change.

5.1 Social and environmental burdens: 4.0

The site sits inside census block group 250277561012, Block Group 2 of Census Tract 7561.01, 2,525 acres with a population of about 1,525. Its MassEnviroScreen score of 80.9 places it in the above-70-to-90 band, which the tool scores 4.0. Of the block group's five component scores, environmental effects at 86.0 sits at the 99.7th percentile of the 5,109 Massachusetts block groups, while pollution exposure at 23.3 sits at about the 15th percentile, lower than most of the state. The effects component is a weighted count of cleanup sites, groundwater threats, solid waste sites, impaired waters and hazardous waste generators in and around the block group. What MassDEP maps inside it: six cleanup sites, three major regulated facilities, about 3.1 miles of Category 5 impaired stream, most of it Cady Brook, and the north edge of the Southbridge Landfill. None of these is on the parcel.

Because the score is a property of the block group, the design cannot move it. What the project can do is show that it does not add to the burdens the score measures, which is the job of the Cumulative Impact Analysis, and pursue a Community Benefits Plan, which the Board weighs separately under 980 CMR 15.11.

5.2 Carbon sequestration and storage: 3.7

The Ecosystem Carbon Index is high here because the site is forest. The 2016 MassGIS land cover puts evergreen and deciduous forest on 38.4 of the parcel's 47.1 acres, about 82 percent, and on 15.1 of the leased work area's 15.25 acres, about 99 percent. The equipment area is entirely forest. The corrected Facility Boundary adds the gen-tie easement and the driveway, both mostly wooded, so the re-run is expected to score at least as high.

The published commitment that answers this criterion holds tree clearing outside the transmission right-of-way at or under 10 acres. Corridor clearing outside the parcel stays inside the 1.86-acre right of way. The limit of work is drawn on the plans filed with the Application. Replanting to offset the acres cleared is on the Commitment Tracker, and its scope, funding and partners are set in the Community Benefits Plan. Whether the Board also sets a replanting condition is for the permit.

5.3 Biodiversity: 2.9

The Biodiversity Index across the 5.7-acre area is moderate, with a mean of 2.6 and a top-quarter mean of 2.9. The reason the re-run matters is at the parcel's northwest edge. NHESP Priority Habitat PH 865 and BioMap Rare Species Core 869 cover 2.89 acres of the parcel there. Neither reaches the leased work area or the equipment pad. Measured on the current drawing, the work area clears the habitat boundary by about 6 feet, the pad by about 125 feet, and the tie line by about 16 feet, but the access corridor runs within about a foot of it, with roughly 678 feet of the corridor inside 5 feet of the drawn edge. Those distances are finer than the layer's own mapping tolerance.

• BioMap Local Landscape 1077 covers the whole work area, as it covers most of the surrounding upland. No BioMap Core Habitat or Critical Natural Landscape component touches the work area or the pad.

• No Estimated Habitat of Rare Wildlife lies within a mile; the nearest is 1.16 miles away. The nearest other Priority Habitat, PH 851, is 0.93 mile away.

• Vernal Pool Core 648 is 0.47 mile away, Wetland Core 3288 0.20 mile, and Aquatic Core 415 0.34 mile.

• The current design treats the PH 865 boundary as drawn as a no-disturbance line, staked by survey before any clearing. That reading is subject to NHESP's confirmation in the MESA review, which has not yet been filed. NHESP asked on September 4, 2026 for a formal rare species information request as the first step, and it is being prepared for signature. No rare species information is shared without NHESP's written approval.

5.4 Agricultural resources: 0.0

The Agricultural Resource Index is zero across the 5.7-acre area, and the SSURGO soils explain why. The parcel is Charlton, Chatfield-Hollis-rock outcrop, Ridgebury and Paxton soils, all extremely stony or shallow, and none of it is farmed. The one prime farmland unit, 305B Paxton fine sandy loam, covers 0.56 acre at the parcel's north edge by the road. None of it is in the work area or the pad. The corrected boundary clips about 0.009 acre of it where the gen-tie easement meets the road, which is why the re-run is checked rather than assumed to return zero.

5.5 Climate change resilience: 0.0, scored from the state's design standards tool

The mapping tool does not produce this criterion, so its report for this site carries no climate page. The Site Suitability Guidance scores it another way. It takes the higher of two exposure ratings from the state's Climate Resilience Design Standards Tool, one for riverine flooding and one for coastal flooding from sea level rise and storm surge, and converts it on a four-step scale: Not Exposed scores 0.0, Low Exposure 1.0, Moderate Exposure 2.0 and High Exposure 3.0. The tool was run on this site on September 4, 2026 and returns Not Exposed for both hazards, so the anticipated score is 0.0. That fits the site's position. Charlton sits about 35 miles inland, and FEMA's National Flood Hazard Layer places the entire parcel, work area and pad in Zone X, an area of minimal flood hazard, on FIRM panel 25027C0788F effective June 21, 2023; the nearest special flood hazard area is a Zone A about 0.2 mile away. The same run rates the site High Exposure for two hazards the criterion does not count but the design must: extreme precipitation and extreme heat.

5.6 Protected open space: no overlap

No protected or recreational open space in the MassGIS layer lies on the parcel or abuts it. The nearest is a private Agricultural Preservation Restriction 0.17 mile away, protected in perpetuity with no public access, and the corrected Facility Boundary comes within 373 feet of it without touching it. Eleven open space records lie within a mile, among them Prindle Lake Park at 0.64 mile, the Capin Hill Nature Sanctuary at 0.72 mile and the town recreation fields at 0.73 mile. No Area of Critical Environmental Concern lies within 16 miles. The MassGIS layer carries no explicit Article 97 flag; on the usual proxy, publicly owned land protected in perpetuity, nothing on or next to the parcel qualifies.

The regulation says the six criteria do not limit what the Board looks at. The September 2026 screening on LiDAR terrain, published soils and the state layers turned up six findings that matter more to this site than any single score. Each is a desktop finding on published mapping, not survey, and each is paired with the study that answers it.

6.1 Soils under the pad

The equipment pad as drawn sits 76 percent on soil unit 71B, Ridgebury fine sandy loam: poorly drained, hydrologic group D, with a seasonal high water table within inches of the surface over dense till at about 19 inches. It is the parcel's only poorly drained unit, and it runs from the pad down the swale to the swamp. This was disclosed to the Citizen Advisory Committee on August 4, 2026. Geotechnical borings, test pits and piezometers follow after the pre-filing engagement period, before the Application. Foundation, dewatering, recharge and any containment liner follow their results.

6.2 Where the water goes

Flow routing on the state's bare-earth LiDAR shows runoff leaving the pad at its southwest corner and running south, off the parcel after about 670 feet, into a 0.3-acre MassDEP-mapped shrub swamp about 307 feet from the pad edge, then down an unnamed stream toward McIntyre Pond, about 1.3 miles away in a straight line and about 2.1 miles along the stream. Cady Brook, the Category 5 impaired stream that carries much of the block group's burden score, lies in a different drainage to the north. Above the pad, about 45.6 acres of hillside drain onto it, 13.4 of them on the parcel. The current design routes that clean rainwater around the pad and its containment, and the diversion works, not the fence, are what set the width of the clearing.

Seen over the whole mile, the project area sits inside one drainage. About 59 acres of hillside drain onto it from above, and everything that leaves it runs south by a single path, through the shrub swamp and the marsh below T Hall Road, to McIntyre Pond. The one-mile routing runs on a coarser 5-metre grid than the parcel tracing above, so its acreages are approximate: the pad's own catchment comes out at about 49 acres on it, against the 45.6 acres traced at 1 metre, and the one-mile figures are quoted as about.

6.3 Wetlands and the buffer zone

MassDEP maps no wetland on the parcel; the nearest mapped shrub swamp is about 11 feet outside the parcel line. The National Wetlands Inventory maps 0.46 acre of forested wetland on the parcel, outside the work area and about 37 feet above the pad in elevation, so it is not a receptor. No wetland is filled. The 100-foot buffer zone under the Wetlands Protection Act reaches about 0.05 acre into the leased work area at its southern corner, and the interconnection route clips the buffer about 47 feet north of the substation. The pad itself is 292 feet clear. A wetlands specialist has walked the property. The formal field delineation follows after the pre-filing engagement period, before the Application. It is filed with the Charlton Conservation Commission, with the Notice of Intent to follow.

6.4 Slope against the draft standard

The parcel has about 137 feet of relief, from 688 to 825 feet. The Board's draft Baseline Standards, revised August 21, 2026, set a 27 percent slope limit and leave the term site footprint undefined. Measured on a 1-metre LiDAR grid, about 0.11 acre of the pad, 3.2 percent of it, sits at or above the limit; the work area carries 1.37 acres and the parcel 4.67 acres above it. The pad averages 9.7 percent slope on a 5-metre grid and 11.6 percent on a 1-metre grid, and the grid size changes the answer, so any slope figure should say which grid it came from. Grading design, with the stormwater design, addresses the 0.11 acre. Comments on the revised draft standards were due September 11, 2026, and the standard is still a draft.

6.5 Private wells

The MassDEP well database holds 87 records within about a mile: 61 with coordinates plus 29 addressed to Carpenter Hill Road, three in both sets. Domestic wells on the road run 175 to 665 feet deep, median 500 feet, all but one drilled into bedrock. A surface flow-routing screen on the LiDAR classifies the 71 records that can be placed: two domestic wells on T Hall Road, 0.39 and 0.45 mile away, sit downgradient in the pad's own drainage; the landowner's well is about 459 feet northwest and 44 feet above the pad; the Karl Storz public supply wells are about half a mile north with a ridge between. Sixteen Carpenter Hill Road records carry no street number and cannot be placed. The screen follows land surface, not fracture flow in the bedrock these wells draw from, and it does not say whether any well is or is not affected. This report makes no such statement. A door-to-door well survey within half a mile, to locate the unplaced records, has not yet started.

The same records, measured against the pad's ground level, show how deep these wells go. The pad's median ground level is about 716 feet. Of the 49 located domestic wells with a logged depth, every one bottoms out below that level, the median by about 456 feet, and the landowner's well, the nearest to the pad, reaches rock at 22 feet and a depth of 500 feet. Depth does not change which wells the surface screen places downgradient, because the screen classifies by where the wellhead stands, and groundwater under a hill moves down and outward toward the valleys. What depth does change is the pathway that would matter for the wells above the pad, which is flow through fractures in the bedrock rather than surface runoff. That pathway is a question for the groundwater consultation with MassDEP and the monitoring program, not for this screen. This paragraph states the general behaviour of groundwater under a hill, written from the well logs and the terrain. A hydrogeologist has not yet reviewed it for this site, and it is not a finding about any particular well.

6.6 Historic resources, geology and public water supply

• Historic. The Massachusetts Historical Commission inventory records no property on the parcel or in the work area. The nearest is the Isiah Putney House on Tinker Hall Road, built 1784, 0.27 mile away; the Charlton Center Historic District, listed on the National Register, is 0.79 mile away. The MHC Project Notification Form and tribal consultation have not yet been filed.

• Geology. The whole parcel is mapped as thin till over bedrock, with bedrock outcrops within a few hundred feet. The statewide depth-to-bedrock model reads 1 to 3 feet at the parcel corners, while the well records nearby report bedrock from 2 to 80 feet down, so the model understates the till here and borings govern. Seismic soil class A, hard rock, at every sampled point. Quinebaug River basin.

• Public water supply. No Zone II wellhead protection area lies within a mile. The nearest Zone I is the Karl Storz Endovision non-community supply, 0.49 mile away with a 231-foot radius; its interim wellhead protection area is 0.42 mile, or about 2,244 feet, from the parcel. No surface water supply watershed, sand and gravel aquifer or sole source aquifer touches the parcel. The parcel is in the Southbridge Water Department's mapped service area by 0.03 acre at its edge. The current design draws no public water for operations; the fire water supply is being planned with the Charlton Fire Department (Section 7.4).

• Contamination. No Chapter 21E site, activity and use limitation, landfill or groundwater discharge permit is on the parcel. The nearest tier-classified site is the closed Charlton Landfill on Flint Road, 0.75 mile away, which lies outside the site's block group. Karl Storz Endovision, 0.28 mile away, is a MassDEP major facility as a hazardous waste generator.

The siting rules ask the project to say how the site suitability criteria have been incorporated into choosing the site and shaping the design. The honest answer is in three parts: why this parcel, what the screening changed, and what is still open.

7.1 Why this parcel

The parcel sits beside the Carpenter Hill substation, where the 345 kV line built in 1967 meets the region's 115 kV lines. That adjacency is the reason for the site: the facility interconnects through a gen-tie of about 2,694 feet, most of it in an existing easement, rather than through new long-distance transmission. A storage facility can only be built where a landowner agrees to host it, and this is the parcel next to the substation where the project secured a lease. The Stantec Critical Issues Analysis of November 2023 screened the parcel before the lease was signed. The 2026 desktop screening on the state layers found no Area of Critical Environmental Concern within 16 miles, no Chapter 91 jurisdiction at this inland site, no overlap with protected open space, no land mapped as Article 97 on the usual proxy, no wetland on the parcel in the MassDEP layer, and the whole site in FEMA Zone X.

7.2 What the screening changed

7.3 Alternatives on the parcel

The MEPA Office recommended on September 4, 2026 an environmental alternatives analysis covering siting and design alternatives that reduce footprint and clearing, in addition to the battery technology alternatives already considered. That analysis is scoped for the Application. Ahead of it, a desktop search of the whole parcel was run in September 2026 to ask where a pad could go and how the drawn location compares. It holds the recorded New England Power transmission easement along the north line clear, since its deeds bar structures and any change of grade, and it scores every placement on run-on, slope, poorly drained soil, forest cover, distance to the substation and distance to the nearest dwelling.

7.4 Studies complete, in progress and not started

The provisional scores become anticipated scores on the correct boundary before the Pre-filing Notice, and final scores when the Site Suitability Report is filed with the Application. Between now and then, anyone can question them.

How to question a score

Under 980 CMR 15.10(4), the project, the Town of Charlton or any Key Stakeholder who believes a score was calculated on materially erroneous, incomplete or faulty data may ask the Director of the Siting Board for a score revision, in the form the Director prescribes. The request has to name the specific deficiency. The Director decides within 30 days, and a revised score is final subject to any modifier. If you think a number in this report is wrong, tell us first, at the contact below, and we will check it and say what we found on the Engagement Log. That does not replace your right to go to the Director.

Every number in this report traces to a named source with a date. Where a number is a desktop measurement on published mapping rather than a survey, it says so.

Terms used in this report

Criteria-specific Suitability Score

The score for one criterion, 0.0 most suitable to 5.0 least suitable, produced by the state's Site Suitability Mapping Tool for a site footprint (980 CMR 15.02).

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).

Site Suitability Mapping Tool

The state's web mapping tool, maintained by the Executive Office of Energy and Environmental Affairs, that calculates the scores for a drawn site footprint.

Site Suitability Report

The written report of the scores, any modifiers sought, and supporting documentation, filed with the Application (980 CMR 15.10(3)).

Large Clean Energy Storage Facility

A clean energy storage facility above the size threshold in 980 CMR 1.01, which places it under the Siting Board's consolidated permit.

MassEnviroScreen

The state's screening tool that scores every census block group on 30 indicators of environmental exposure, environmental effects, climate risk, sensitive populations and socioeconomic factors.

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)).

Priority Habitat

Land mapped by the Natural Heritage and Endangered Species Program as habitat of state-listed rare species, where work is reviewed under the Massachusetts Endangered Species Act.

Zone X, Zone A

FEMA flood zones. Zone X is minimal flood hazard; Zone A is a special flood hazard area with a one percent annual chance of flooding.

Run-on

Rainwater that flows onto the pad from the hillside above it, as opposed to rain that falls on the pad.

Downgradient

Lower along the direction water moves. In this report it is judged from the land surface, not from a groundwater model.

Request for Score Revision

A request to the Director of the Siting Board to revise a score calculated on faulty data (980 CMR 15.10(4)).