groundwater level in a nested piezo

[DougHole]

I have a nested piezometer that is screened between 5-6 m ("shallow") and 10-11 m ("deep")

The water level is measured at 3.2 m in the shallow piezo and 3.4 m in the deep piezo.

The soil is silty clay down to 20 m.

Does this suggest that we have a hydrostatic porewater pressure profile (10kPa/m) from say 3.4 m? i.e. no perched water level. If it is hydrostatic, why would there be a slight difference in the water levels measured?



Doug Hole
Junior Geotechnical Engineer

 

[L0k]

I though there is an indication of lots of water pumping from the underlying layer.

 

[RobPE]

I've seen the phenomenon you're describing many times, but in very deep installations (>1000'). A significant difference in readings would indicate either a perched aquifer or a hydraulic gradient. I would say that your data indicates more or less hydrostatic conditions for the purpose of your analysis.

I don't think you should be concerned with 0.2m of difference in head. If you factor in the variability in the VWP (each manufacture reports a tolerance) and inaccuracy in the depth of installation, the discrepancy essentially disappears. Otherwise, you may have a very slight upward vertical albeit negligible gradient.

 

[fattdad]

you have a 3.6% gradient vertically upward. That's what the data show. Is there some topograpic relief to either side of the well? Is there a nearby creek? Never rule out a flow-net-type dynamic!

f-d

ípapß gordo ainÆt no madre flaca!