From TK's Nature paper:
"If the previous experiments and investigations rule out diatom infiltration while buried, then the findings suggest that diatoms found their way onto the bills during water immersion. As shown in Fig. 4, a stack of bills once saturated, will fan out in water exposing all surfaces to micro-particles in the water environment. The exposure of the fanned out stack to the river, suggests the simplest way for large, intact but fragile diatoms to be found alone interior to the bill stack. This would have occurred prior to burial and be in the water long enough for fan out to occur."
Second, to be clear, I'm not dismissing dredging. I'm merely asking how a money bag could rest on the bottom of Columbia for years, but only have spring diatoms on them? Also, the bills had to have fanned out for a period of time for exposure to occur. How could that happen in the rather rapid process of dredging?