When you drive by a pit where they have been taking out gravel or other stone, it is aqua blue. Why?

I have never noticed that myself and I have lived most of my life in former glacial terrains where borrow pits of that sort are quite common.

I presume there is not enough water (not deep enough) for the color to be the natural blue of water, so you have to assume there is something in the water causing that coloration. Dissolved salts are not normally elevated in shallow groundwater in that type of sedimentary deposit (not a reactive material and too short a residence time). It could be the result of suspended solids, clays, that give a greenish or bluish tint to the water; many clays can do that.

Just speculating.

I think what you're seeing is a copper mine - the dissolved copper ions (Cu2+) have a vibrant turquoise color.

Here's a pic:

http://www.flickr.com/photos/mars73/473260325/

If that's what you're talking about, it's definitely copper. Some blue-green algae can cause lakes to acquire a vibrant green color.

Here's a pic:

http://aquafornia.com/wordpress/wp-content/uploads...