Add a Letter #3 Mystery Cache

Add the same letter to each of the four sets of letters below to create four common, uncapitalized English words. Arrange the new four words in alphabetical order and submit as one giant keyword to reveal the cache coordinates.

*This puzzle cache is based on a cache in Texas created and hidden by DFW Challenger, who gets credit for the puzzle idea.

Add a Letter has now become a mini-series. Here is a link to the first and second in the series if you haven't solved them and want to check them out as well. 

You can validate your puzzle solution with certitude.