Surface Scan Fail / crash

I have a 2014 iMac running 10.12.6 and TechTool Pro 10.0.1. My internal 3TB hard drive is not working well. I created an eDrive on an external hard drive and booted from it. Last night I started up the Surface Scan and had it running. It was finding many bad blocks. I left it to run over night. This morning it had Quit (crashed?). There was no Report. It said nothing had been run to report on. Hmm… I started up the Surface Scan again this morning. Again, many bad blocks were being found and listed. I left it running checking on it every few minutes. The last time I checked it had run 3+ hours. It had processed about 1,500,000,000,000 blocks out of the 5,000,000,000,000 or so being checked. I came in the last time and the application had again Quite/Crashed. There is no Report logged. It said no test had been run. I am disappointed that the app could not test my hard drive.

I believe my next step to reformat my 3TB hard drive.

Walt