Method for slender tube, multi-level, subsurface borehole sampling system

Abstract

Methods and systems for allowing the use of very small-diameter sample tubing, with a flexible borehole liner, in multi-level water sampling systems deployed in subsurface boreholes. Methods are disclosed for determining depth distances to a ground water table, in a borehole, without the need to lower a pressure transducer into a sampling tube.

I claim: 
     
         1 . A method for determining groundwater condition in a borehole beneath the earth's surface, comprising:
 defining a sleeve on a flexible liner;   disposing in the sleeve at least a portion of a slender tube thereby to hold upon the liner at least the portion of the slender tube, the slender tube having a tube first end and a tube second end;   defining a port in the liner;   placing the slender tube in fluid communication with the port;   everting the flexible liner into a borehole below the surface;   situating the tube first end and the tube second end above a ground water table in the borehole;   allowing ground water to flow from the port through the check valve into the slender tube;   permitting the ground water to rise in the slender tube to a first level corresponding to the ground water table;   closing the tube first end;   changing a condition of a gas within the slender tube between the tube first end and the ground water in the slender tube to affect a change of a ground water level in the slender tube from the first water level to a second water level; and   determining, from the condition of the gas or from the change of the ground water level in the slender tube, the depth of the ground water table.   
     
     
         2 . The method of  claim 1 , wherein placing the slender tube in fluid communication with the port comprises:
 locating a check valve adjacent to and in fluid communication with the port; and   placing the slender tube in fluid communication with the check valve.   
     
     
         3 . The method of  claim 1 , wherein situating the tube first end and the tube second end above a ground water table in the borehole further comprises situating the tube first end and the tube second end above the surface. 
     
     
         4 . The method of  claim 1 , further comprising providing a pressure transducer near the tube first end. 
     
     
         5 . The method of  claim 4 , wherein the step of closing the tube first end comprises sealably disposing the pressure transducer on the tube first end. 
     
     
         6 . The method of  claim 4 , wherein the step of changing a condition of a gas within the slender tube between the tube first end and the ground water in the slender tube comprises applying a gas pressure to the tube second end, causing an increase the gas pressure within the slender tube between the tube first end and the ground water in the slender tube. 
     
     
         7 . The method of  claim 6 , wherein the step of determining the depth of the ground water table comprises:
 measuring the gas pressure applied to the tube second end; and   measuring with the transducer the increase the gas pressure within the slender tube between the tube first end and the ground water in the slender tube.   
     
     
         8 . The method of  claim 7 , wherein the step of determining the depth of the ground water table further comprises calculating the depth of the ground water table using the formula:
   WT=( Po ΔPbn/ΔPs+ΔPbn−Ps )/2,   
       wherein WT is the depth of the ground water table, Po is an initial gas pressure, ΔPbn is the pressure increase applied at the tube second end, Ps is the final pressure measured within the slender tube between the tube first end and the ground water in the slender tube, and ΔPs is the gas pressure increase measured with the transducer. 
     
     
         9 . The method of  claim 4 , wherein the check valve is a normally open check valve, and the step of changing a condition of a gas within the slender tube between the tube first end and the ground water in the slender tube comprises injecting with a syringe a known number of moles of gas into the slender tube between the tube first end and the ground water in the slender tube. 
     
     
         10 . The method of  claim 9 , wherein the step of determining the depth of the ground water table comprises measuring with the transducer a change in the gas pressure within the slender tube between the tube first end and the ground water in the slender tube. 
     
     
         11 . The method of  claim 10 , wherein the step of determining the depth of the ground water table further comprises calculating the depth of the ground water table using the formula:
   WT= Po Vs/ (Δ Ps At )− Ps,  
   
       wherein WT is the depth of the ground water table, Po is an initial gas pressure, Vs is the volume of the syringe, ΔPs is the gas pressure increase measured with the transducer, At is the cross sectional area of the slender tube, and Ps is the final pressure measured within the slender tube between the tube first end and the ground water in the slender tube. 
     
     
         12 . The method of  claim 4 , wherein the check valve is a normally closed check valve, and the step of changing a condition of a gas within the slender tube between the tube first end and the ground water in the slender tube comprises injecting with a syringe a known number of moles of gas into the slender tube between the tube first end and the ground water in the slender tube. 
     
     
         13 . The method of  claim 12 , wherein the step of determining the depth of the ground water table comprises measuring with the transducer a change in the gas pressure within the slender tube between the tube first end and the ground water in the slender tube. 
     
     
         14 . The method of  claim 13 , wherein the step of determining the depth of the ground water table further comprises calculating the depth of the ground water table using the formula:
   WT= Po Vs/ (Δ Ps At )− Ps/ 2,
   
       wherein WT is the depth of the ground water table, Po is an initial gas pressure, Vs is the volume of the syringe, ΔPs is the gas pressure increase measured with the transducer, At is the cross sectional area of the slender tube, and Ps is the final pressure measured within the slender tube between the tube first end and the ground water in the slender tube.