5-10 bet river vs. soft opponents?

[Inthacup]

5-10 game that is very loose passive.

I'd say preflop avg. is around 50-60% for 1 bet, occasionally for 2 bets.

5 limpers to me in LP, I call with 9 [img]/forums/images/icons/spade.gif[/img] 10 [img]/forums/images/icons/spade.gif[/img] , CO and Button fold, SB folds, BB checks. 7 see flop for 1 bet.

Flop: 6 [img]/forums/images/icons/spade.gif[/img] 3 [img]/forums/images/icons/diamond.gif[/img] 8 [img]/forums/images/icons/spade.gif[/img]

I have many many outs, 18 to be exact. BB bets, 3 call, MP to my immediate right raises, I cold-call, everyone calls.

Turn: 9 [img]/forums/images/icons/heart.gif[/img]

BB bets out again, all call to me, I raise, everyone calls. 15 BB pot.

River: K [img]/forums/images/icons/club.gif[/img]

Everyone checks to me. What should I do and why?