Just finished the 'murkey' water in the gully. The results look promising. I used a combination of Ulco's and Oshyan's suggestions. I think we're there. With Oshyan's idea I only set the Volume 1 density to 0.8. With Ulco's idea, I used the same color as Oshyan's except I darkened it a bit. Full render time is getting close.
Also, see the truck's orange lights are back!