In 1956, Dr. Ludwig resigned from the USPHS and started Engineering-Science, Inc. (ES). His modus operandi was to hire mostly M.S. and Ph.D. students recruited from his network of academic colleagues who would adapt their research knowledge into practice. At that time, hiring engineers with graduate degrees was more unusual than common. ES expanded rapidly with offices in key cities in the United States, including a research laboratory and office in Oakland (1956), later in Washington, D.C. (c. 1966), headed by his longtime USPHS associate Gordon MacCallum, and then in Austin, Texas, started by Dr. Davis Ford (1968). The firm grew rapidly with important projects throughout the country, and it started to develop an international clientele. Dr. Ludwig was by this time (1969) a legend in environmental engineering. In the same time, the field was experiencing a golden age—research was advancing knowledge, graduate programs were spreading, the practice was flourishing, and the public had adopted a widespread environmental ethos that was being translated by politicians into laws and policy. At that time, ES was, arguably, at the crest of this movement. It was one of the most visible firms in the field and at the forefront of innovation. This was due not only to Dr. Ludwig individually but also to the way he had structured the firm with both depth and breadth of expertise and leadership. In addition, Dr. Ludwig had extensive involvement with professors from throughout the country.
ES was actually, though, part of a larger corporate structure. One entity was a construction company that had financial difficulty. The “way out” was a buyout offer in 1968 by Zurn Industries of Erie, Pennsylvania. The new corporate structure did not work out, and Dr. Ludwig left the firm in 1972 to set up his own consulting practice in Washington, D.C. ES was later purchased by its employees and remained prominent in the field through 2004, when its identity was assimilated fully by Parsons, an international construction company.
In 1973, Dr. Ludwig’s private practice led him to Bangkok where he started a new firm, Seatec International, which has influenced environmental engineering throughout Southeast