Is it Possible to get a negative piezometer reading ??

[nagatalluri]

Hi All:

Is it Possible to get a negative piezometer reading ?? Which means the water level rose above the grade level. In our case we tried to dig few trial pits to see if the WT is @ ground surface. We could not see any water at GS. What could be the reason for negative piezometer readings ? Please let me know.

Thanks

NT

 

[GeoPaveTraffic]

If by negative piezometer reading you mean is it possible to have a ground water reading in a piezometer that is higher than the ground surface at the piezometer, the answer is yes. This is known as an artesian condition. There are many situations where this can occur, but the most common is when the piezometer is installed into a confined aquifer.

Also, not seeing water in a shallow test pit does not mean that the piezometer is not working correctly. You have to penetrate the same material that the piezometer is reading to verify the data and even then it could depend on the permeability of the aquifer material.

Mike Lambert

 

[nagatalluri]

Dear Mike

Thanks for the input. I believe the artesian could be the reason.

 

[oldestguy]

One more. Your site has received a loading, as a new fill or surcharge and the measurement is down in a zone that is compressing. For instance suppose there is a sand fill that is placed in a lake for a new road embankment, only partly done and the subsoils are soft clays that undergo compression. If you are using the standpipe measurement method, you will see that level somewhat above the lake surface. I once had a job with that situation where we read the devices using a boat. Then comes what to do in freezing weather???

 

[aeoliantexan]

Artesian conditions are common at the downstream toe of a dam, especially in a deeper confined aquifer. I know of one dam where clear tubes were connected to the standpipes and attached to old telephone poles to accommodate piezometric levels nearly 20 feet above the ground surface. Scales were attached to the poles, and readings were taken with binoculars.