From No. 74 to No. 9: How GSI Environmental Built a Top-10 Firm Without Abandoning Its Model

By Liisa Andreassen

Two years ago, GSI Environmental made its first appearance in the Hot Firm rankings at No. 74. In 2025 it moved to No. 25. This year, as the Houston-based firm marks its 40th anniversary, it landed at No. 9 on the SNZweig Hot Firm list. 

Rapid climbs like that tend to invite a hunt for a single cause, such as a hot market, an acquisition or a new service line. According to GSI President Travis McGuire, the real answer is less dramatic and more useful to other AEC firms. 

Investments That Paid Off 

McGuire points to timing.  

“Our growth is attributed to the cumulative effect of several strategic investments reaching maturity over the past several years,” he says. 

Those investments were both geographic and technical. GSI added offices in Denver, Montana and Atlanta, and built capabilities in aquatic science, mining, sustainability and climate, PFAS and emerging contaminants and services for fast-growing markets such as data centers. Headcount grew from 200 employees in 2024 to more than 250 in 2025. 

The Operating Model Behind the Numbers 

Growth alone doesn’t explain the ranking. McGuire says GSI held on to the structure that has always supported it: a one-firm model under a single P&L, principals who generate work and stay engaged in doing it, and staff and expertise shared across offices. 

The payoff is flexibility.  

“That formula allows us to assemble the right technical team around a client’s problem rather than letting office boundaries or individual service lines determine the solution,” McGuire says. 

For firms adding offices or service lines, the lesson is that new locations and capabilities only pay off if the model connects them. 

Evolution, Not Reinvention 

GSI began in 1986 as a two-person consulting company applying sound science to difficult environmental questions. Its history since then has been a series of expansions into chlorinated solvents and DNAPL, risk-based corrective action, vapor intrusion, toxicology, water resources and litigation support. 

“It’s been an evolution of the original model rather than a reinvention of it,” McGuire says.  

The top-10 ranking, he adds, validates principles the firm has held for decades – hire curious and capable people, give them room to innovate, stay close to clients and stand behind the work. 

Growth brings its own test. McGuire says the firm has to be more intentional about connecting employees across offices and preserving a sense of “one GSI.”  

“Our challenge is not to protect the company from change, but to ensure that the qualities that have made GSI successful remain recognizable as we enter our next chapter,” he says. 

Breadth by Design, and by Client Demand 

GSI’s service list is wide, running from site remediation and air quality to toxicology, carbon capture and sequestration and food-product safety. McGuire says the breadth began organically, as clients brought increasingly complex questions, and later became deliberate strategy. 

The value, he argues, lies in integration rather than the length of the list.  

“Environmental challenges rarely fit neatly within a single discipline,” he says.  

A single regulatory question can also involve technical feasibility, human-health risk, water availability, community concerns or litigation, and a firm that can address all of them together delivers solutions that are defensible and practical. 

Regulation Opens Doors, Relationships Keep Them Open 

PFAS rules, climate reporting requirements and permitting demands all create work for environmental firms. McGuire acknowledges the tailwind but doesn’t credit it for GSI’s rise. 

“Every environmental firm sees the same broad market signals. Differentiation comes from how effectively a firm helps clients act on them,” he explains.  

He describes GSI’s growth as earning a larger role with clients rather than riding a wave or taking share from competitors. A new rule may start the conversation, but trust, responsiveness and technical credibility sustain it. 

Scaling Across 40-Plus Countries 

GSI completed its first international project in Canada in 1995, and its work has since reached more than 40 countries. McGuire says the hardest part of going global is translating strong science into solutions that fit a specific local context, since regulations, data availability, infrastructure and stakeholder expectations vary widely. 

GSI doesn’t assume a U.S.-based solution can simply be exported. Teams start by listening to the client’s operating environment, then pair GSI’s technical expertise with local knowledge and relationships. 

Takeaways for AEC Leaders 

GSI’s rise offers a few lessons for firms with growth ambitions: 

• Give investments time to compound. New offices and capabilities take years to mature. 

• Protect the operating model as you scale. A single P&L and shared staff let GSI build the right team around each problem. 

• Treat regulation as an opening, not a strategy. Market signals are visible to everyone, and execution and trust set firms apart. 

• Localize before you globalize. Listen first, then apply your expertise. 

source https://zweiglist.com/from-no-74-to-no-9-how-gsi-environmental-built-a-top-10-firm-without-abandoning-its-model/