Exhibit 21.1
List of Subsidiaries
| Name | Jurisdiction of Formation or Incorporation | |
| Alta Vista Solutions, Inc. | Delaware | |
| Atlantic Engineering Laboratories, LLC | Delaware | |
| Atlas TC Holdings LLC | Delaware | |
| Atlas Intermediate Holdings LLC | Delaware | |
| Atlas Technical Consultants Sole Member LLC | Delaware | |
| Atlas Technical Consultants LLC | Delaware | |
| ATC Sole Member LLC | Delaware | |
| Arrow Environmental Holdings GP LLC | Delaware | |
| Arrow Environmental Holdings LP | Delaware | |
| Arrow ATC Holdings LLC | Delaware | |
| ATC Group Partners LLC | Delaware | |
| ATC Group Holdings LLC | Delaware | |
| ATC Group Services LLC | Delaware | |
| ATC Group Services (CA) Inc. | Delaware | |
| ATC Group Services (CT) Inc. | Delaware | |
| ATC Group Services (MA) Inc. | Delaware | |
| ATC Group Services (MI) LLC | Delaware | |
| ATC Associates of North Carolina, P.C. | North Carolina | |
| Atlas ATC Engineering Inc. | New York | |
|
ATC Engineering, LLP |
New York | |
| Long Engineering, LLC | Delaware | |
| O’Neill Service Group LLC | Delaware | |
| WesTest, LLC | Colorado | |
| Quality Assurance Engineering, Inc. | California | |
| Caitcon, LLC | California | |
| Atlas Engineering West Inc. | California |