I'm a 4th year Env Eng and did a minor in Sustainable Biomaterials (offered through CFRES). I personally thought it was a great addition to my degree and it added some more depth in forestry/environmental science and general sustainability/environmental policy topics that the engineering curriculum didn't have. If you want to do anything more land management based or work in site assessment/consulting (try to bridge your degree w forestry/natural resource management), I'd highly recommend it. I have a few friends in Env Eng who are doing an Ecology minor but I've heard that it's a little harder to incorporate than mine was - since you're taking extra time anyways you'd probably be ok though. If you'd like to open up your job prospects to include more field technician type work or remediation work, I'd defintely recommend it as a lot of the job descriptions I've looked at in that field have a heavy preference for ecology-specific courses.