I live in Pasco off Rd 100, but I've lived in all three cities since I moved here 16yrs ago. It's a nice area with quick access to the bike path along the Columbia. There is a nice, gentle loop along both sides of the Columbia which makes for a relaxing ride. There's a great number of good routes around.
Try poking around the Chinook club website. There's club organized "training rides" which translates to club races (seasonal TT series, a spring rode race series and a fall MTB series). The Kennewick Court Club has evening rides which are popular with a variety of abilities including club riders on Mo, Wed & Fri. Weekend Chinook rides are available. The Saturday ride from a local coffee shop is usually good for ripping the legs off.
http://www.chinookcyclingclub.com/
I haven't ridden with the Tri City Bicycle Club in many years. I think they ride more leisurely. They do sponsor a spring century ride which is fun.
Enjoy!
[edit: court club rides are mon, wed, fri (not tues)]