2006-08-10_REVISION - M1977306

• Permit No: M1977306
• IBM Index Class Name: Revision
• Doc Date: 8/10/2006
• Doc Name: Monitoring Well map
• From: Cotter Corporation
• To: DRMS
• Type & Sequence: TR4
• Media Type: D
• Archive: No

(see Figure 2) illustrates that it is easier to remove water from a
sandy soil with 10% moisture, than it is to remove water from a
clay soil with 30% moisture. This is because the water in the clay
sail is held in very small capillary spaces within the soil particles
under a higher soil suction, whereas the sandy soil holds water in
large capillary spaces under a lower soil suction.
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SOIL SUCTION BARS
Figure 2.
Soilmoisture's Soil Water Samplers allow water to be removed from
the soil by creating a vacuum (negative pressure or suction) inside
the sampler greater than the soil suction holding the water in the
capillary spaces. This establishes a hydraulic gradient for the wa-
ter to flow through the porous ceramic cup and into the sampler.
Note: when evaluating soil suction ratings of a ceramic plate or
cup, a positive pressure rating is used. Water can be held at ten-
sions far greater than 1 atm (the limit for vacuum-type measure-
ments). Positive pressure can force water out of capillary pores
equivalently as negative pressures, and is the practical method
for evaluation of soil suction.
In practice, a vacuum is drawn in the Soil Water Sampler that
exceeds the soil water tension. Then liquid water will flow to the
ceramic cup due to the potential gradient (i.e. water will move from
less negative potential to more negative potential). The practical
limit for water flow in soils is about 65 cb (centibar) (although in
some soils, the value can approach 85 cb). When soil moisture ten-
sions exceed 2 bars, the wetted meniscus in the ceramic pores will
break and the Soii Water Sampler will appear to be unable to hold
vacuum. The ceramic cup will have to be rewetted to hold a vacuum
and soil moisture tensions will have to decrease to less than 85 cb
before water can again be moved toward the ceramic cup.
Additional information on the advantages and disadvantages of
Soil Water Samplers in general can be found in Chapter 19, "Com-
SOILMOISTURE EQUIPMENT CORP. 5 /~®
P.O. Box 30025. Santo Borboro, Colifornio 93105 USA
Phone: [phone] • Fox: [phone] SOILMOISTURE
e-moil: solesQsoilmoisture.com ~ Web: http: //wwwsoilmoisturacom