Abstract:
A method and apparatus for selecting a filter pack and a well casing slot size for a well which uses soil classification data derived from cone penetrometer test. A user of the method and apparatus utilizes a piezocone or other soil classification sensors to measure soil properties in an area of contaminated soil or non-contaminated soil and then determine the soil type at specific depths within the soil. A multisensor probe generates a laser induced fluorescence intensity plot of the area of soil contamination which is superimposed on a soil boring log identifying the soil type at specific depths within the soil. The soil type for the area of contaminated soil is identified from the load cell data. Contamination within the soil is identified using the laser induced fluorescence intensity plot.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to a method and apparatus for fabricating a well used for monitoring and remediation of contaminated soil and ground water. More specifically, the present invention relates to a method and apparatus for selecting a sand pack mesh for a filter pack and a well casing slot size for a well using soil classification data derived from a cone penetrometer test. 
     2. Description of the Prior Art 
     In a standard well, a bore hole is first drilled into the ground. Normally, the well water is sampled as part of a water quality monitoring program. A well casing is then inserted into the bore hole. Normally, the well casing houses a pumping mechanism or other mechanical components which comprise the operational features of the particular well. 
     The well casing will normally include a portion that is permeable to groundwater. The remainder of the well casing is typically impermeable to insure proper hydraulic flow of the liquids through the well casing at a specific depth intervals, as dictated by the design of the casing. 
     The space in between the exterior surface of the well casing and the interior surface of the bore hole is then filled with an annular fill material. This annular fill material, which operates as a filter or cleaning device, may be a permeable material, such as gravel or sand. 
     Water, which is pumped through the well is directed through a filter or cleaning device placed in the annular space of the well casing. Ground water so directed will capture impurities or contaminants leached or dissolved from the surrounding soils into the groundwater, thus passing impurities or contaminants from the surrounding soils to the filter or cleaning device along the screened portion of the well casing. 
     In the past selection of the filter (also known as the gravel pack or primary filter pack) and well casing slot size which is based on the filter pack was an extremely time consuming, expensive and difficult process requiring soil sampling, sieve analysis, and reference to standard recommendations. What is needed is a relatively simple method and apparatus by which a user can select the sand pack mesh and the well casing slot size when the soil type which is contaminated has been identified. 
     SUMMARY OF THE INVENTION 
     The present invention overcomes some of the disadvantages of the prior art including those mentioned above in that it comprises a relatively simple yet highly effective method and apparatus for selecting a filter pack and the well casing slot size for a well which uses soil classification data derived from cone penetrometer tests. 
     The user of the method and apparatus of the present invention uses a piezocone to measure soil properties in an area of contaminated soil or non-contaminated soil and then determine the soil type at specific depths within the soil. The soil doesn&#39;t always need to be contaminated. Sometimes wells are installed in clean areas to determine background chemistry and hydrologic properties. 
     A multisensor probe, such as a probe that generates a laser induced fluorescence intensity plot of the area of soil contamination which is superimposed on a soil boring log identifying the soil type at specific depths within the soil can lead to a detailed subsurface characterization. The soil type for the area of contaminated soil is identified from load cell data and the contamination is identified by the laser induced fluorescence intensity plot. When the user identifies the soil type for the area of soil contamination, the user accesses one of a pair of lookup tables to select the sand pack mesh and the well casing slot size for the specified zone. The lookup tables sets forth the filter pack and well screen slot size for soil descriptors based on the 9-scale and soil descriptors based on the 12-scale of Robertson and Campanella. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a plain view of electric cone penetration test assembly used with a piezocone or other penetrometer sensors (e.g. load cells) for deriving the soil classification data used in the method of the present invention; 
     FIG. 2 is a view, in partial section, of the piezocone of FIG. 1; 
     FIGS. 3 and 4 are nine scale soil behavior charts; 
     FIGS. 5 and 6 are twelve scale soil behavior charts; 
     FIG. 7 illustrates a laser induced fluorescence intensity plot wherein soil type is superimposed on a chart depicting soil contamination; and 
     FIG. 8 is a grading curve used in the selection of the filter pack. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring first to FIG. 1, there is shown a electric cone penetration test system  10  which may be used during environmental groundwater investigations as an efficient means of hydrogeologic site characterization and subsurface plume tracking. Test system  10  includes a multi-axle truck  12  which has mounted inside its rear compartment  14  a plurality of heaving hydraulic rams (not illustrated). Position at each corner of the rear compartment  14  of truck  12  is a leveling stanchion  15  which provides support for truck  12  and maintains truck  12  in a fixed position relative to the ground  16 . 
     Extending vertically downward from the underside of multi-axle truck  12  into the ground  16  is a string of steel pipes  18 . Attached to the end of steel pipes  18  is a piezocone  20  which is depicted in FIG. 2 in section. Each steel pipe of the string of steel pipes  18  is approximately one meter in length and is generally pushed into the ground at a constant penetration rate of 2 cm/sec, one pipe length at a time. The pushing force exerted on pipes  18  and piezocone  20  is supplied by the hydraulic rams within compartment  14  of truck  12 . The weight of truck  12  provides the reaction force to push against pipes  18  and can be as large as twenty tons. 
     The string of steel pipes  18  has additional pipes added to the upper end of string  18  by means of a tapered threaded joint (not illustrated). 
     The on board data acquisition system  21  of FIG. 2 for test system  10  converts analog electrical signals received from piezocone  20  into digital data, and then stores the data at small depth increments (typically about one inch) on a personal digital computer system  23  also mounted inside compartment  14  of truck  12 . The data is also displayed on a monitor  29  mounted inside of compartment  14  of truck  12 . A printer  27  can also be connected to the computer  23  to provide an automatic log of penetration upon completion of the test. 
     Referring to FIG. 2, there is shown a detailed view of piezocone  20 . Piezocone  20  includes a friction sleeve  22  and a conical tip or cone  24  attached to the lower end of friction sleeve  22 . Conical tip  24  is removable from friction sleeve  22 . Conical tip  24  develops the end bearing component q c  of penetration resistance. Friction sleeve  22  is an isolated cylindrical sleeve positioned above tip  24  which senses the resistance of the soil as sleeve  22  passes through the soil. The Friction sleeve resistance f s  is determined by dividing the soil friction by the friction sleeve area. The cone resistance q c , the friction sleeve resistance f s  and the pore pressure can then be used to generate the soil classification charts illustrated in FIGS. 3,  4 ,  5  and  6 . 
     Mounted within friction sleeve  22  are a pair of strain gauge load cells  25  and  26  which measure the soil bearing resistance acting on conical tip  24  and the soil shear resistance sensed along the cylindrical friction sleeve  22  as piezocone  20  penetrates the ground soil  16 . The pore water pressure is measured by a porous element or filter  28  mounted in conical tip  24  of piezocone  20  and a pressure transducer  30  mounted in cylindrical friction sleeve  22  of piezocone  20 . 
     It should be noted that the porous element or filter may be mounted above the conical tip of the piezocone. 
     In addition, piezocone  20  also has an inclinometer (not illustrated) which is used to monitor the verticality of the environmental groundwater test performed by piezocone  20 . 
     The test performed by piezocone  20  are recorded continuously as a function of depth and transmitted through an electrical cable  32  which extends from the upper end of piezocone  20  through a coupler  34  and pipes  18  (FIG. 1) to the rear compartment  14  of truck  12 . The end of electrical cable  32  is connected to computer  23  of the on board data acquisition system  21  for test system  10  allowing test data from piezocone  20  to be transmitted to the data acquisition system  21  for test system  10 . It is also possible to use wireless to transmit test data from piezocone  20  to computer  23 . 
     The sleeve  22  of piezocone  20  also has at its upper end a quad ring  38  and at its lower end a quad ring  40 . Similarly, there is located near the upper end of sleeve  22  an “O” ring  42 , while there is located near the lower end of sleeve  22  an “O” ring  44 . Quad rings  38  and  40  and “O” rings  42  and  44  function to insure that interior portion of sleeve  22  is water tight. 
     Referring to FIGS. 3 and 4 there are shown soil classification charts or plots for nine scale soil behavior. In the plots of FIGS. 3 and 4, the soil types are as follows: 
     
       
         
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 zone 1 
                 Sensitive, fine grain 
               
               
                   
                 zone 2 
                 Organic, soils-peats 
               
               
                   
                 zone 3 
                 Clays-clays to silty clay 
               
               
                   
                 zone 4 
                 Silt mixtures clayey silt to silty clay 
               
               
                   
                 zone 5 
                 Sand mixtures; silty sand to sandy silt 
               
               
                   
                 zone 6 
                 Sands; clean sand to silty sands 
               
               
                   
                 zone 7 
                 Gravely sand to sands 
               
               
                   
                 zone 8 
                 Very stiff sand to clayey sand 
               
               
                   
                 zone 9 
                 Very stiff fine grained 
               
               
                   
                   
               
             
          
         
       
     
     Referring to FIGS. 5 and 6 there are shown soil classification charts or plots for nine scale soil behavior. In the plots of FIGS. 5 and 6, the soil types are as follows: 
     
       
         
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 zone 1 
                 Sensitive, fine grain 
               
               
                   
                 zone 2 
                 Organic material 
               
               
                   
                 zone 3 
                 Clay 
               
               
                   
                 zone 4 
                 Silty clay to clay 
               
               
                   
                 zone 5 
                 clayey silt to silty clay 
               
               
                   
                 zone 6 
                 Sandy silt to clayey silt 
               
               
                   
                 zone 7 
                 Silty sand to sandy silt 
               
               
                   
                 zone 8 
                 Sand to silty sand 
               
               
                   
                 zone 9 
                 Sand 
               
               
                   
                 zone 10 
                 Gravely sand to sand 
               
               
                   
                 zone 11 
                 Very stiff fine grained 
               
               
                   
                 zone 12 
                 Sand to clayey sand 
               
               
                   
                   
               
             
          
         
       
     
     The cone resistance q c  and the friction sleeve resistance f s , obtained from measurements made by piezocone  20  and other direct push soil measurement devices is used to generate the nine-scale soil behavior charts of FIGS. 3 and 4 and the twelve-scale behavior charts of FIGS. 5 and 6. This soil-behavior data is also used to generate the materials identifier located on the lower right side of FIG.  7 . The materials identifier of FIG. 7 is for contaminated soils and non-contaminated soils having up to twelve soil types. 
     The filter pack for the well consist of a granular material of a selected grain size and gradation that is installed in the annulus between the well screen and the borehole well. The filter pack is usually selected to have a 30% finer (d-30) grain size that is about 4 to 10 times greater than the 30% finer (d-30) grain size of the hydrologic unit being filtered (see FIG. 8 which is an example of a grading curve used in the selection of the filter pack). The filter pack is usually selected to have a low uniformity coefficient, that is less than ten. The grain size and gradation of the filter pack are selected to stabilize a soil section adjacent the well screen and permit only the finest soil grains to enter the well screen. 
     The filter pack is graded and comprised of hard durable siliceous particles washed and screened with a particle size distribution derived normally by multiplying the d-30 size of the finest-grained screened stratum by a factor between 4 and 10. If the stratum is fine and uniform, a number between four and ten is used as the multiplier. When the material has a highly nonuniform gradation and includes silt-sized particles, a number between six and ten is used as the multiplication factor. The grain-size distribution of the filter pack is then plotted using the d-30 size as the control point on the graph. 
     FIG. 8 is representative of a plot for the grain size distribution of a filter pack. The selected filter pack should have a uniformity coefficient of approximately 2.5 or less. 
     Common filter pack materials include coarse  4  to  8  mesh silica sand; standard 20 to 40 mesh silica sand; and ultra-fine 100 mesh silica sand 
     Referring to FIG. 8, the data set forth in the following Tables was obtained from multiple grading curves such as the grading curve illustrated in FIG.  8 . The data in the following tables shows particle size (Grain Diameter-millimeters) verses total percent passing for U.S. Standard seive numbers and other seive numbers and Soil Qualifiers (9-Scale). The only soils considered in formulating the following Tables were Zones 7, 6, 5, 4 and 3 soils. 
     
       
         
               
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                 TABLE I 
               
               
                   
               
               
                 Sieve 
                 Particle 
                   
                   
                   
                   
               
               
                 Type 
                 Diameter (mm) 
                 7-high 
                 7-low 
                 6-high 
                 6-low 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 3″ 
                 76.2 
                 100 
                   
                   
                   
               
               
                 1.5″ 
                 38.1 
                 70 
               
               
                 ¾″ 
                 19.05 
                 45 
                 100 
                 100 
               
               
                 ⅜″ 
                 9.525 
                 23 
                 80 
                 90 
               
               
                 #4 
                 5 
                 0 
                 70 
                 60 
               
               
                 #8 
                   
                   
                 60 
                 37 
                 100 
               
               
                 #10 
                 2 
                   
                 42 
               
               
                 #16 
                   
                   
                 28 
                 17 
                 70 
               
               
                 #30 
                   
                   
                 18 
                 0 
               
               
                 #40 
                 0.4 
                   
                   
                   
                 46 
               
               
                 #50 
                   
                   
                 12 
                   
                 32 
               
               
                 #100 
                   
                   
                 7 
                   
                 28 
               
               
                 #200 
                 0.08 
                   
                 5 
                   
                 20 
               
               
                   
               
             
          
         
       
     
     
       
         
               
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                 TABLE II 
               
               
                   
               
               
                 Sieve 
                 Particle 
                   
                   
                   
                   
               
               
                 Type 
                 Diameter (mm) 
                 5-high 
                 5-low 
                 4-high 
                 4-low 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 3″ 
                 76.2 
                   
                   
                   
                   
               
               
                 1.5″ 
                 38.1 
               
               
                 ¾″ 
                 19.05 
                 100 
               
               
                 ⅜″ 
                 9.525 
                 80 
               
               
                 #4 
                 5 
                 70 
                   
                 100 
               
               
                 #8 
                   
                 56 
               
               
                 #10 
                 2 
                   
                   
                 81 
               
               
                 #16 
                   
                 45 
                 100 
                 67 
               
               
                 #30 
                   
                 37 
                 85 
                 55 
               
               
                 #40 
                 0.4 
                   
                   
                   
                 100 
               
               
                 #50 
                   
                 31 
                 71 
                 45 
                 87 
               
               
                 #100 
                   
                 26 
                 60 
                 37 
                 74 
               
               
                 #200 
                 0.08 
                 21 
                 50 
                 30 
                 65 
               
               
                   
                 0.037 
                 16 
                 42 
                 26 
                 57 
               
               
                   
                 0.019 
                 10 
                 32 
                 23 
                 50 
               
               
                   
                 0.009 
                 7.5 
                 22 
                 21 
                 42.5 
               
               
                   
                 0.005 
                 5 
                 15 
                 20 
                 40 
               
               
                   
               
             
          
         
       
     
     
       
         
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                   
                 TABLE III 
               
               
                   
                   
               
               
                   
                 Sieve 
                 Particle 
                   
                   
               
               
                   
                 Type 
                 Diameter (mm) 
                 3-high 
                 3-low 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 #16 
                   
                 100 
                   
               
               
                   
                 #30 
                   
                 80 
               
               
                   
                 #40 
                 0.4 
               
               
                   
                 #50 
                   
                 65 
               
               
                   
                 #100 
                   
                 50 
                 100 
               
               
                   
                 #200 
                 0.08 
                 40 
                 95 
               
               
                   
                   
                 0.037 
                 35 
                 87 
               
               
                   
                   
                 0.019 
                 31 
                 78 
               
               
                   
                   
                 0.009 
                 27.5 
                 70 
               
               
                   
                   
                 0.005 
                 25 
                 65 
               
               
                   
                   
               
             
          
         
       
     
     The data included in Tables I, II and III was compared with the following data from ASTM (American Society For Testing and Materials) standard D5092-90 entitled “Standard Practice for Design and Installation of Ground Water Monitoring Wells in Aquifers” to generate a Lookup Table which sets forth the filter pack and well screen slot size for soil descriptors 9-scale and soil descriptors 12-scale. 
     
       
         
               
               
               
               
             
           
               
                 TABLE IV 
               
               
                   
               
               
                 Size of Screen 
                   
                 Sand Pack Mesh 
                 30% Passing 
               
               
                 Opening mm (in.) 
                 Slot No. 
                 Size Names 
                 Size mm D-30 
               
               
                   
               
             
             
               
                 0.125 (0.005) 
                  5 
                 100 
                 0.17 to 0.21 
               
               
                 0.25 (0.010) 
                 10 
                 20 to 40 
                 0.5 to 0.6 
               
               
                 0.50 (0.020) 
                 20 
                 10 to 20 
                 1.2 to 1.5 
               
               
                 0.75 (0.30) 
                 30 
                 10 to 20 
                 1.2 to 1.5 
               
               
                 1.0 (0.40) 
                 40 
                  8 to 12 
                 1.7 to 2.0 
               
               
                 1.5 (0.60) 
                 60 
                 6 to 9 
                 2.5 to 3.0 
               
               
                 2.0 (0.80) 
                 80 
                 4 to 8 
                 2.6 to 3.1 
               
               
                   
               
             
          
         
       
     
     The following Table allows the user to select a filter pack and well screen slot size for soil descriptors 9-scale. 
     
       
         
               
               
               
             
           
               
                 TABLE V 
               
               
                   
               
               
                 Soil Descriptor 
                 Recommended Sand Pack 
                   
               
               
                 9-scale 
                 Mesh 
                 Recommended Slot # 
               
               
                   
               
             
             
               
                 3 
                 100 
                 5 
               
               
                 4 
                 100 
                 5 
               
               
                 5 
                 100 
                 5 
               
               
                 6 
                 20 to 40 
                 10  
               
               
                 7 
                 4 to 8 
                 80  
               
               
                   
               
             
          
         
       
     
     The following Table allows the user to select a filter pack and well screen slot size for soil descriptors 12-scale. 
     
       
         
               
               
               
             
           
               
                 TABLE VI 
               
               
                   
               
               
                 Soil Descriptor 
                 Recommended Sand Pack 
                   
               
               
                 12-scale 
                 Mesh 
                 Recommended Slot # 
               
               
                   
               
             
             
               
                 3 
                 100 
                 5 
               
               
                 4, 5, 6 
                 100 
                 5 
               
               
                 7 
                 100 
                 5 
               
               
                 8, 9 
                 20 to 40 
                 10  
               
               
                 10  
                 4 to 8 
                 80  
               
               
                   
               
             
          
         
       
     
     Although screening in soil types 1, 2, 8 and 9 (Soil Descriptor 9-scale) is not recommended, the user may select a 100 or finer sand pack mesh and a 5 or finer slot number when screening is required. Similarly, screening in soil types 1, 2, 11 and 12 (Soil Descriptor 12-scale) is not recommended, the user may select a 100 or finer sand pack mesh and a 5 or finer slot number when screening is required. 
     Referring to FIGS. 1 and 7 there is shown a plot generated by a multisensor probe in which the soil type is identified and an area of contamination is also identified at a depth of from about 2.5 feet to a depth of about 10 feet with significant contamination occurring at a depth of from about 6 feet to about 10 feet. The probe  20 , which may be a multisensor probe, provides for laser induced fluorescence to locate the area of contamination  80  which may be, for example, petroleum contamination. This allows for a plot  80  of the area of contamination after the data from the probe is analyzed by a computer such as computer  23 . The probe  20  also provides load cell data which allows computer  23  to identify the soil type at various depths. After the data has been analyzed by computer  23 , printer  27  generates the plot of FIG.  7 . 
     The plot of FIG. 7 depicts identifies significant contamination at a depth of between 7 and 10 feet where the soil type is silty sand to sandy silt. Silty sand to sandy silt is defined in the twelve-scale soil behavior charts of FIGS. 5 and 6 as a zone 7 soil. For zone 7 soils the lookup table (12-scale) recommends a sand pack mesh of 100 and a slot number of five. 
     Between five and six feet the soil type is identified as sandy silt/clay silt which is a zone six soil. For zone six soils the lookup table recommends a sand pack mesh of 100 and a slot number of five. 
     At this time it should be noted, depth ranges of well screens, which is critical for monitoring and extraction well networks also can be determined by data from the piezocone and load cell sensors. Computer software incorporating Lookup Tables V and VI may be developed and used to determine well specifications in log form in real-time. 
     From the foregoing, it may readily be seen that the present invention comprises a new, unique and exceedingly useful method for selecting a sand pack mesh and a well casing slot size for a well which constitutes a considerable improvement over the known prior art. Many modifications and variations of the present invention are possible in light of the above teachings. It is to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.