Where are you based? Country wise?
You can do a few things, the following would likely be the most effective:
1. Advertise online (linkedin is free to post on discussions telling people about the job with an email address). Otherwise well known jobsites like totaljobs.com or cvlibrary.com would charge you to advertise and the candidates would likely be no better. Specialist sites like justengineers.com would be better for that.
2. Head hunt it yourself, i.e. if you know an ex colleague or a competitor call them up and ask them straight if they're looking for work.
3. Speak to a recruitment consultant / agency. Building Careers is a well known construction industry recruiter in the UK. I work for them... send me over an email to Matthewkirk@buildingcareersuk.com and I wil pass you onto my colleague who deals with engineers! This is certainly the quickest and easiest way; and can often also be the most cost effective.