Groundwater Elevation

[AAEC]

We have an existing cesspool that we wanted to replace with other types of wastewater system. In order to identify what type of system we need, we need a groundwater elevation reading first. Is it appropriate to take groundwater elevation inside the existing cesspool? Could you explain reasons if either okay or not okay?

Thanks,
Nelson

 

[bimr]

You probably should get a topographic map of the surrounding area within a 150-200 feet radius.

A traditional cesspool is most likely an absorptive pit constructed of loose fitting bricks. While this may provide the elevation of the ground water, over a long period of time, the cesspool outlet water path may have become plugged. If the outlet path is plugged, the cesspool water elevation may not be the same as the ground water.

If the cesspool is a holding tank that drains to a septic field, then the holding tank water level will also not be the level of the ground water. In a holding tank, the water level in the holding tank will be maintained by an outlet weir.

http://en.wikipedia.org/wiki/Cesspit

 

[GoldDredger]

I think you would need a boring test pit and groundwater monitoring to really find out. Remember gw elevation can be seasonal. Also the permiability of the soil will affect how fast the water gets into the test hole from surrounding soil (ie how long it takes water to reach static level.)

 

[Spartan5]

For the purposes of designing an onsite wastewater system, you need to evaluate the historical seasonal high water table. In Michigan, the typical protocol is to dig test pits to allow for observation of redoximorphic features (mottling) or other visual indicators of the seasonal high water table (SHWT). These test pits are usually no more than 4 feet deep and generally no deeper than the observed SHWT.

As far as soil permeability goes, we rely on textural analysis of the soil and estimate.

The SHWT and texture dictate whether we go with a raised system, pretreatment, or a combination of the two.

 

[Ron]

Agree with Spartan5...in addition, you can do an in-place "percolation" test....no real accurate, but indicative.