Abstract: A combined chemical injection and mixing system including an injection stream pipe, a target pipe disposed within the injection stream pipe, and a plurality of injection quills is described. The injection stream pipe encloses the plurality of injection quills, and the plurality of injection quills each independently includes a quill check valve and a quill flange. A method for mixing at least one chemical in a pipeline is also described. The method includes providing a chemical injection and mixing system configured to a pipeline, forming a pipeline treatment system, providing a fluid flow in the pipeline treatment system, injecting at least one chemical via the plurality of injection quills, and mixing the at least one injected chemical in a mixing zone of the chemical injection and mixing system, thereby mixing the at least one injected chemical in the fluid flow.