And the ground collapsing beneath Otis.
She had been dangerously close to making a much worse mistake.
Then she opened another page.
A list of water-level readings from the weeks before the 1988 failure showed an unsettling pattern.
The pond rose during dry weather.
Then fell suddenly.
Then rose again.
The intervals became shorter as the failure approached.
Naomi stared.
The pattern resembled her own measurements.
Not perfectly.
But enough to be alarming.
She took out her current field book.
Placed it beside Ruthie's.
And began comparing them.
For nearly two hours, she worked without noticing the time.
Then she reached one of her grandmother's final observations.
Pressure changes were strongest during work at the northern excavation.
Naomi looked toward the window.
The distant hills were dark.
Beyond them lay Ridgeline Materials.
For the first time, she had a historical example suggesting that activity near the quarry could affect the old waterworks.
It wasn't proof of the present cause.
But it gave Claire Morgan and Benjamin Mercer something specific to examine.
The following morning, Naomi called Claire.
She explained the letter and notebooks.
The engineer asked whether the original documents were available for review.
Naomi said yes.
Then she contacted Benjamin.
When he arrived, she placed Ruthie's letter on the kitchen table.
He read it slowly.
For several minutes, he didn't speak.
Then he removed his glasses.
His eyes were wet.
"She kept everything."
Naomi nodded.
Benjamin looked toward the old notebooks.
For a moment, he smiled sadly.
"Your grandmother never believed a promise was complete until somebody wrote down what had been done."
Naomi laughed softly.
"That sounds like her."
Then the older engineer turned serious.
"The retirement records may help establish what the county agreed to do with the old line."
He pointed toward the maps.
"And these measurements could help us understand whether the current pattern resembles the earlier failure."
Claire arrived later that afternoon.
Together, they examined the historical records and Naomi's observations.
The engineer noticed something especially important.
Ruthie's notebooks didn't merely document pond levels.
They included dates when the old excavation operated certain drainage equipment.
During the late 1980s, the strongest irregular water-level changes coincided with periods when industrial water movement was recorded near the northern quarry.
Naomi studied the entries.
Then looked toward Claire.
"Can we compare that with current operations?"