Soldier Pile/precast plank lagging Mole wall repair

[Jc67roch]

I was called out to review a mole/breakwall that the client fears is being undermined. The location is on an inland Finger Lake in New York. It is constructed of steel soldier piles at 10 feet on center with 16" high precast plank lagging between. Then capped with cast in place concrete walks. See photos. It was constructed in 1961 by private contractor. I suspect that it was not excavated very far down into the lake bottom (typically bedrock or loose gravel), and as you can see over time some of the planks have shifted - probably due to shifts in bearing surface under the bottom planks. I think this is allowing water/waves to additionally wash material out from behind the lagging. I am looking for ideas on how to stabilize the situation. Concrete pollution in the water is a major concern. My thoughts thus far are: 1) Steel sheet pile wall either in front of or directly behind the existing wall, or 2) new cast in place wall, Or 3) replacement precast panels that are larger with keyed joints. Does anyone have other thoughts or suggestions? What methods would be appropriate to keep wet concrete out of the lake water if using tremie pours behind the existing wall?