hard drive – What is ASRNewVolume and why is it taking up so much space on my disk?

When I look at my Storage usage in About my Mac, I see a partition called “ASRNewVolume_1606” which is taking up 32GB of unusable space. I went to Disk Utility and I can’t restore the partition to my main disk (El Capitan). How do I remove it and restore that space back to my main disk?

I think this was created when I installed Windows. Not exactly sure though.

Screenshot of Storage usage