ERM is the world's largest specialist sustainability consultancy and the primary "pure-play" benchmark for the sector. Under KKR majority ownership (acquired in 2021 at a ~$2.7B valuation), ERM has transitioned from a traditional EHS firm into a strategic advisor integrating C-suite ESG transformation with boots-on-the-ground technical delivery across 40+ countries and 8,000+ professionals.

Its competitive advantage is the "Boots-to-Boardroom" model — ensuring boardroom-level sustainability commitments are technically feasible and verifiable at the asset level. This bifurcated model captures both high-margin strategy mandates from CSOs and CFOs, and high-volume technical remediation, forensics, and engineering work from EHS and Operations directors.

FY25 gross revenue reached $1.413B, up from $1.323B in 2023. Revenue quality is shifting positively: long-term MSAs and sticky compliance-driven work now drive a larger share versus project-based boutique exposure. ERM targets firm-wide billable utilization of 75–85%, with higher-margin strategy mandates using senior-heavy staffing and lower-leverage technical remediation teams providing volume.

Total reported turnover for FY25 was approximately 19.9% — a known pressure point, particularly in Asia-Pacific at 30.2%, creating an ongoing talent retention imperative. KKR's ownership alongside 580 ERM partners as minority investors provides a structural alignment mechanism, but managing the "Green Skills Gap" remains a strategic constraint on scaling.

APTIM is a $1.2 billion environmental engineering and infrastructure platform carved out from CB&I by Veritas Capital in 2017 for $755M. The company has since delivered 60% revenue growth (8% CAGR) driven by organic expansion in PFAS remediation, coastal resilience, and federal program management — validating the Veritas thesis of a compliance-driven, counter-cyclical asset with government revenue concentration of an estimated 65–80% of total revenue.

APTIM's #1 ENR ranking in Site Assessment & Compliance for three consecutive years is independently verifiable proof of technical execution quality. The company's proprietary Flask to Field™ PFAS methodology and access to federal contract vehicles including OASIS+, a $1.4B DOE Strategic Petroleum Reserve contract, and a $1.5B USAF IDIQ represent structural competitive barriers that are difficult for new entrants to replicate on a multi-year basis.

For PE sponsors, the durability of APTIM's revenue drivers under the current administration is the primary underwriting question. Gaya Capital's risk-adjusted analysis confirms that the core thesis is structurally protected:

Burns & McDonnell is a $7.4 billion titan in the U.S. infrastructure market — 100% employee-owned via ESOP — built on a vertically integrated "Design-Build" engine that captures the entire project lifecycle from advisory through EPC. Its model is explicitly designed to eliminate the margin leakage that occurs when design and construction are separated, positioning BMcD as a single point of accountability for clients executing large-scale capital programs.

BMcD's "wedge" strategy is its most defensible competitive mechanism: the firm leverages funding-enabled advisory (SRF financing support, capital program management) to embed itself upstream in the client relationship, then secures downstream design and construction scope that would otherwise be competed. This model is particularly effective in the utility sector, where BMcD acts as a structural extension of client staff through long-term overflow MSAs — exploiting the industry-wide internal staffing constraints that are forcing utilities to outsource technical work at scale.

Atwell is one of the most compelling PE-backed infrastructure services platforms in the country — ascending from a regional Midwest surveying firm to ENR Top 70 with $424.7M in confirmed 2024 revenue and management-guided targets exceeding $500M in 2025, representing 30%+ year-over-year growth. Under Quad-C Management since 2021, Atwell has executed 20+ acquisitions and built a 2,100+ person workforce across 50+ offices in virtually every major U.S. growth corridor.

The firm occupies the "mid-market sweet spot" — large enough to hold MSAs with major utilities and secure complex federal and municipal programs, yet agile enough to serve private developers and IPPs that the global giants systematically underprice. Revenue per employee benchmarks at $250K+ (2024), approaching the $250–300K range achieved by top-quartile advisory-heavy AEC firms.

Ulteig is a preeminent utility-centric infrastructure platform with 1,500+ employee-owners managing 3,200+ annual projects across its four "Lifeline Sectors": Power, Renewables, Transportation, and Water. Headquartered in Fargo, North Dakota with 16 offices and a presence in 48 states — plus a recently established Costa Rica presence — Ulteig has climbed 100 ENR positions over five years to reach the Top 100 (#85 Pure Firm ranking, 2025).

The investment thesis is built on four pillars: structural revenue resilience (mandatory utility CapEx and federal grant-funded programs); technical barriers to entry (interconnection engineering, FAA Part 139 compliance, integrated ROW acquisition — each requiring years of institutional expertise); public-sector embeddedness (recurring MSA relationships with municipalities and utilities that are effectively never re-competed); and proprietary technology IP (PathFinder grid decision engine, PinPoint transportation planning tool).

Ulteig's 100% ESOP ownership creates a structural condition for a PE-sponsored liquidity event as: (1) employee-owners approach retirement ages with concentrated equity; (2) external capital requirements for continued M&A (four acquisitions since 2019) exceed ESOP financing capacity; and (3) the management team — led by CEO Doug Jaeger (former Xcel Energy executive) and a professionalized board including technology veteran Bhupinder Singh (former Bentley Systems) — seeks an institutional growth partner.

Westwood Professional Services has climbed ENR's Top 500 from #368 in 2018 to #77 in 2025 — a trajectory driven by disciplined M&A (9+ acquisitions), organic growth exceeding 30% year-over-year in 2024, and exceptional positioning across four structural growth verticals. The firm holds national rankings of #3 Wind Design, #5 Solar Design, #6 Battery Storage, and #21 Power Design — a multi-category technical leadership profile that distinguishes Westwood from scale-aggregators and confirms genuine engineering depth.

In August 2024, Blackstone Energy Transition Partners (BETP IV) acquired a majority stake, positioning Westwood as the front-end engineering design (FEED) layer for an integrated infrastructure ecosystem alongside high-voltage insulator manufacturer Sediver and backup power provider Trystar. Blackstone's $5.6B BETP IV fund provides preferred access to energy transition deal flow that no independent mid-market AEC firm can replicate.

SCS Engineers is one of the most defensively positioned platform assets in U.S. environmental engineering — reporting $493M in 2023 revenue (12% YoY growth) driven by a 55-year history of non-discretionary solid waste compliance. The firm is #1 nationally in ENR Solid Waste and ranked #51 overall on ENR's Top 200 Environmental Firms. Unlike the majority of environmental consultancies, SCS operates integrated lifecycle services spanning permitting, construction (RNG facilities, leachate treatment), and long-term OM&M at 650+ landfills — creating annuity-like cash flow highly attractive to PE sponsors.

Under CEO Doug Doerr (30-year SCS veteran, succeeded long-time leader Jim Walsh in January 2024), the firm is executing its 2022 Strategic Plan across four structural tailwinds: PFAS remediation mandates, RNG buildout, federal infrastructure investment, and digital transformation via its proprietary technology platform. SCS is 100% employee-owned (ESOP since 1986) and structured as an S-Corp ESOP — generating no federal income tax on ESOP-attributable earnings, creating structural financial advantages that have compounded technical moat investment over decades.

The April 2024 EPA CERCLA designation of PFOA/PFOS as hazardous substances is the single most significant regulatory event in SCS's addressable market in decades. The impact is multi-dimensional: