John Devine and John Tarbell, two of the four principals of DTA, co-founded Devine & Tarbell, Inc. in 1988, which soon became Northrop, Devine & Tarbell, Inc., (ND&T). ND&T focused on providing specialized services for hydropower and water resources projects. ND&T was founded on the belief that clients in the hydropower field wanted specialists, not generalists, to service their hydro projects. ND&T grew quickly from a staff of 2 located in Portland, Maine, to 65, with offices in the Seattle area and Sacramento, the latter headed by Jim Lynch, one of the principals of DTA. ND&T was known for its technical innovation and quality.

ND&T was acquired in 1997 by Duke Engineering & Services, Inc. (DE&S), a subsidiary of Duke Energy, headquartered in Charlotte, North Carolina. This acquisition resulted in the formation of a hydropower group with great specialization and depth. The new DE&S Hydropower and Natural Resources business unit included offices in Portland, Maine; Charlotte, North Carolina; Sacramento, California; Bothell, Washington; and Syracuse, New York. In 1998, Cascades Environmental Services was acquired adding an exceptional group of environmental scientists to the team with an office in Bellingham, Washington.
 
In May 2002, Framatome Advanced Nuclear Power (FANP) of Lynchburg, Virginia, purchased DE&S in order to expand its U.S. nuclear consulting services. A short time after the purchase, the principals of DTA approached FANP to inquire about the possibility of acquiring the entire Hydropower and Natural Resources business unit. Negotiations were successfully completed and the transaction was closed on June 30, 2003. DTA entered into business on July 1, 2003.

In 2006, DTA's Board of Directors began converting the structure of the firm to one of employee ownership through the establishment of an Employee Stock Ownership Plan (ESOP). This move assures the long-term viability of DTA to the benefit of our employees and our clients.