So long story short, we had a geological survey done (three borings) done our property (10,000 sqft) a few years ago and basically for the first 10-13’ we have “clean silt” (US CS ML) and then “silty sand” (US CS SM). One of the borings showed free ground water at ~12’. This is very atypical for our area, but seems to be related to the creek which used to run about a block away. Theory is that it used to flood and when it did so, deposited silt on our lot (the report specifically calls out some overbank deposits in the silt).
Anyways, I looked up our AOI info on the WSS site and none of the soil descriptions of the samples match what our report says (all are some kind of loam soil). That said, the Available Water Storage based on the WSS report in our area seems to be around 8-9.5". Not sure if that number is also effectively wrong?