Why the Best People Leave First After an Acquisition, and What to Do About It
The Integration Playbook | Article 4 of 9 | This series examines the seven decisions that determine whether an environmental firm acquisition delivers value. Start with Article 1 here.
The most valuable thing in any environmental consulting acquisition is not the contracts, the equipment, or the brand. It is the people who built the client relationships, hold the technical knowledge, and embody the firm's reputation in the market. And in most acquisitions, those are also the people most likely to leave.
Retaining them is not an HR problem. It is a leadership problem, and one that has to be solved before the deal closes, not after.
Why the Best People Leave First
Uncertainty in an acquisition is not experienced equally. The people who negotiated the deal have information. They were in the room, or close enough to know what happened. The project managers, senior scientists, and technical leads who hold the client relationships were not. They find out the same day as everyone else, sometimes from a company-wide email that arrives before anyone has answered their questions, sometimes from a colleague down the hall, sometimes from a client who read the press release and has called to find out what is going on.
From that moment, the question every one of them is quietly working through is: what does this mean for me?
The employees with the deepest institutional knowledge, the strongest client relationships, and the most critical technical skills are typically the hardest to retain after an acquisition. They are also the ones most likely to be approached by competitors. Competitors notice when an acquisition closes. Recruiters begin making calls within days. The senior hydrogeologist with fifteen years of agency relationships, the remediation PM who has run the same client's portfolio for a decade, the technical lead whose name appears on the firm's most significant reports: they all know people.
And it's a slippery slope. If employees see colleagues leaving after an acquisition, it negatively affects morale and increases the likelihood of further departures. The first departure is rarely the last. It signals something to the people who remain. It confirms the story they had already told themselves about the uncertainty ahead.
This is the retention problem that acquiring firms consistently underestimate. The people who negotiated the deal are accounted for. The project managers, technical leads, and senior staff who hold the client relationships often are not.
The Cost Is Higher Than the Calculation Suggests
When a senior technical professional leaves an environmental consulting firm in the normal course of business, replacing them is expensive. SHRM research suggests that replacement costs can be as high as 50% to 60% of a person's salary, with overall costs ranging from 90% to 200% when you account for the full impact on the business. For a senior environmental engineer earning in the $110,000 to $130,000 range, the direct and indirect cost of a single departure runs well into six figures. That calculation accounts for recruiting, onboarding, and productivity drag while the position is empty.
It does not account for what happens to the client.
In environmental consulting, a senior professional is rarely just an employee. They are a seller-doer with relationships that took years to build. When a client's trusted contact at a firm they just learned was acquired stops returning their calls, the client does not wait to see who shows up next. In a market where most sophisticated buyers have two or three capable firms on their shortlist, a disrupted relationship is an invitation to test the next option.
The AEC industry's staff turnover rate reached 14.1% in 2024, already elevated before accounting for the additional disruption of post-acquisition uncertainty. A firm running at elevated turnover under normal conditions can see that number climb sharply in the months following a close, particularly in the 60 to 90-day window when people decide whether to stay.
What Drives People Out
The mechanics are straightforward and mostly about information.
When a deal closes, acquired employees face an overwhelming set of questions. Will my role change? Will my compensation change? Do the people now running this firm understand what we do and why it matters? Is the culture that made this place worth being at going to survive the transition?
Most acquiring firms intend to answer these questions, but they are usually not prepared to answer them on Day One, with specificity, for every person who matters. Even when the communication plan is finalized before close, the sequencing of who hears what and when is often improvised rather than designed. And word travels fast, making it even more challenging to deliver a message that has already been muddied by a game of corporate telephone.
Differences in compensation packages, including salary, benefits, retirement plans, and bonus structures, can incentivize employees to seek better opportunities elsewhere. These are the visible triggers. But the less visible trigger is something that precedes all of them: the absence of a credible picture of what life looks like inside the combined firm. When that picture is not provided, people build their own. The version they build is almost always more uncertain than the truth.
The professionals who leave in the first 90 days are not usually leaving because they received bad news; they are leaving because they received no news, or news that was too vague to act on, and they had a better offer in hand by the time clarity arrived.
The Plan Needs to Exist Before Day One
The communication plan for acquired employees is an integration deliverable that should be ready before close, and should address three things, for every person who matters, in the first days after close.
What is your role. Not in general terms, and not with a promise to work through the details. The specific answer: what you will be doing, who you will report to, and what that reporting relationship actually means for your day-to-day work.
What is your compensation. This includes salary, bonus structure, benefits, and anything that was tied to the acquired firm's ownership or profit participation model. If the answer to any part of this is still being worked out, that needs to be said plainly, with a specific date by which it will be resolved. Vague commitments to 'keep things whole' or 'honor existing arrangements' do not hold up against a competitor's concrete offer.
What does the culture of the combined firm look like. This is the hardest part to communicate because it cannot be summarized in a memo. It has to show up in how the integration is conducted. The people who stay long enough to see whether the culture claim is real are the ones who were given enough of the first two things to give the third one a chance.
The firms that handle this well identify which people, if they departed, would significantly hurt the current or future business, treat them as key, and proactively engage them before uncertainty drives the conversation. That triage has to happen before close, because after close, the recruiting calls have already started.
The People Who Are Hardest to Replace
There is a category of person in every environmental consulting firm who is disproportionately hard to replace, and who rarely appears on the formal org chart in a way that reflects their actual value.
These are not always the highest-compensated people. They are often the senior project manager who has run every major account in a specific sector for a decade. The technical specialist whose knowledge of a particular regulatory framework or contaminant type is the reason certain clients call. The long-tenured office leader whose relationships with state agency staff smooth things that would otherwise take twice as long.
And then there is another category entirely: the people who hold the place together without appearing on any revenue report. The proposal coordinator who knows every subconsultant relationship. The office manager who knows where every project file lives and how every system actually works. Lose them, and the operational fabric of the acquired firm starts to unravel in ways nobody anticipated when they were running the numbers on the deal.
Article Two in this series noted that due diligence rarely identifies these people because their value does not show up in titles or compensation. It shows up only when they are gone. In the context of talent retention, this observation has a specific consequence: if the acquiring firm did not identify these people during due diligence, they arrive at Day One without a retention plan for the people who most need one.
Earnouts Create a Retention Illusion
Earnouts are common in environmental consulting acquisitions, particularly in founder-led deals and PE-backed roll-ups, and it is worth explaining how they work before examining what they miss.
In a typical earnout, the selling firm does not receive its full purchase price at close. A portion of the total consideration is paid out over a future period, usually two to five years, contingent on the firm hitting agreed-upon financial targets. The structure benefits both sides in theory: the buyer reduces the risk of overpaying for performance that does not materialize, and the seller has a direct financial incentive to stay engaged and drive results during the integration period. For selling principals, the earnout is often a meaningful number. Walking away early means leaving real money on the table.
Earnouts serve a genuine purpose. They align the seller's incentives with the acquirer's goals during the period when integration risk is highest, and they keep the people who built the firm motivated to protect what they built. But they solve a narrower retention problem than they are often credited with solving.
An earnout holds principals. It does not necessarily hold the layer beneath them.
The earnout also creates a dynamic that surfaces later, usually in the third or fourth year, that most of the workforce never sees coming because they were never told the clock was running. What they do notice is when a principal's engagement starts to shift. The founder who championed the acquisition internally becomes harder to read. The advocate who smoothed the early friction is less present. People do not need to know the financial details to sense that something has changed. And when that shift is visible enough, the uncertainty that unsettled people at close tends to return.
What Good Looks Like
The firms that retain talent through acquisitions do a handful of things differently.
They start earlier. Key people are identified, and their situations are mapped before close: what they are currently earning, what they value about the firm's culture, what their specific concerns are likely to be, and what it will take to give them a credible picture of their future.
Then they communicate with specificity. The communication is not about the vision for the combined firm. It is about the specific individual. What their role will be. What their compensation will be. Who they will work with, and why that is a good thing for them. Generalities are not enough when a competitor is offering specifics.
They do not mistake principal retention for firm retention. Retaining the project-level professionals who hold the client work requires a separate plan, and the firms that handle this well know the difference.
The first 90 days set the tone for the next several years. The people who stay do so because they were given enough clarity to trust what comes next. The people who leave do so because they weren't. What happens in that window is not just a retention story. It is the foundation for every client relationship and every growth decision that follows.
The Connection to What Comes Next
Article One in this series introduced the seven decisions in sequence for a reason. Brand shapes how clients receive the news. Talent retention determines whether the people who deliver on the brand promise are still there to do it.
Client communication works best when the right people are still there to have it. A retention gap does not stay contained to the talent decision; it shows up in every client conversation that follows.
The next article in this series examines Decision Three: client communication. Who tells the clients, what they say, and how the timing of that communication affects the revenue the acquisition was meant to protect.
References
Stambaugh Ness. (2025). Building a Strong Foundation: Employee Retention Strategies for AEC Acquisitions. stambaughness.com
Zweig Group. (2025). Financial Performance Report of AEC Firms. zweiggroup.com
Society for Human Resource Management (SHRM). (2025). The Myth of Replaceability: Preparing for the Loss of Key Employees. shrm.org
Stambaugh Ness. (2026). Why AEC Post-Acquisition Integration Determines M&A Success. stambaughness.com
