How to have a 2 column text block reduce to 1 column BEFORE the next break point

I have a 2 column text block that I’d like to have reduce to 1 column once the viewport width reduces to a certain size. The layout breaks just before the tablet breakpoint (991px wide) and causes the 2nd of the two columns to venture off-screen. I would like for the two columns to stack vertically into a neat 1 column list.

read-only link

the offending text block is about halfway down the page, next to the “what I do best” heading.