Chris, Thanks for the update. I'd be curious to know if your date analysis of the stratification in the deposit justifies your assertion that the cistern was open and receiving deposits over a twenty year period. Kent Schneider reported that a local informant told him that the majority of the deposit was created by a single clean-out event of the basement at the time the house was hooked up to city water. Don't know if he documented this, l but sometimes it's hard to sort out the baloney from the Spam (tm). Either way the safety advice is still good. Tim T.