My intention was that the player would roll the chord and while it was sustained, roll another chord on top. As you can see, when I added the arpeggio mark to the top chord, it included the lower chord that was being held.
This might confuse the player into thinking he/she was supposed to play the lower notes again.
How would I add the arpeggio line to the top triad only?
Note that this is a piano part and the sustain pedal is down so it is not a practical problem in this case. I am just trying to notate it correctly. There could be cases where the first chord is held down with one hand while another chord is added.
You could also keep it in one voice and shorten the second arpeggio in Engrave mode, but I think @Janus’s suggestion is clearer notation. It also lets you use a whole note for the first chord in bar 32 and a dotted half for the first chord in bar 33.
Thanks, guys!
Oddly, although I grew up as a pianist, working on concertos and all that, I find piano music much more complicated to notate. 
