<human>: Can you condense the text into a few key points?

Long story short, I am a graduate student in a professional field.  I was given the opportunity to have an unpaid internship/volunteer position this summer at a business in my field.  I jumped at the chance, because it's a great resume builder and extra experience is always a good thing.

BUT, I very quickly discovered that this is not the type of business I really want to gain experience from.  For one thing, I am limited to observing the work of others, even though I am capable and qualified enough to help out, and would learn a lot more by being involved.  Much more importantly, this business's practices are WAY outdated, by at least a decade.  Their safety standards are almost non-existent and literally cringe-worthy.  They are putting lives in danger with their shitty work and I am convinced that they would be shut down if the right people came to investigate.

I do not want to be involved with this group any more.  I had originally told them that I was free to volunteer all summer, but given what I've seen and how little I've gained from it, I would much rather end our relationship early.  However, this is a relatively small professional field, and burning bridges could be a career-killer for me.  Additionally, I have met some really good people at this business who I would like to remain in contact with - it's not their fault that their hands are tied by shitty management.

I'm going in tomorrow for what I'm hoping to make my last day at this place.  How can I sever ties as amicably as possible?  What excuse should I give as my reason for leaving?  I would appreciate any advice /r/relationships can give!
<bot>: unpaid internship at a business with shitty unethical practices.  How can I end my relationship with them in a professional and amicable manner?