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Hydraulic conductivity decline from wastewater

Infiltration rate declinefrom wastewater. . Sandy Soil. Smectite (swelling 2:1 mineral). (Borchardt, 1986). Grain coating. . Smectite

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Hydraulic conductivity decline from wastewater

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    1. Problem with on-site systems decrease in hydraulic conductivity (as shown for laundry water) leads to failure.Problem with on-site systems decrease in hydraulic conductivity (as shown for laundry water) leads to failure.

    2. Alternate to slide 1Alternate to slide 1

    3. Smectite (swelling 2:1 mineral) SEM image shows a grain covered with smectite. If such a grain would dislodge, it could plug pore upper left and decrease hydraulic conductivity. (This is actually on a rock, but can illustrate the principle).SEM image shows a grain covered with smectite. If such a grain would dislodge, it could plug pore upper left and decrease hydraulic conductivity. (This is actually on a rock, but can illustrate the principle).

    4. Smectite low hydraulic conductivity micropore network SEM - very small micropores through smectite (leaflets) means very low hydraulic conductivity.SEM - very small micropores through smectite (leaflets) means very low hydraulic conductivity.

    5. Colored image of kaolinite to replace B&WColored image of kaolinite to replace B&W

    6. 1:1 Clay Minerals DELETE THIS SLIDEDELETE THIS SLIDE

    7. 2:1 Clay Minerals CEC ~ 40 meq/100 g non-expanding Colored image - micaColored image - mica

    8. 2:1 Clay Minerals (expanding) CEC: 100 200 meq/100 g (vermiculite) 70 120 meq/100 g (smectite) Colored image vermiculite and smecite (partially and fully expanding minerals)Colored image vermiculite and smecite (partially and fully expanding minerals)

    9. 2:1 Clay Minerals DELETE THIS SLIDEDELETE THIS SLIDE

    10. Laboratory Methods Direct methods ($$$$$$) XRD (all crystalline minerals) Infrared spectroscopy (mainly kaolinite) Thermal analysis (DTA) mainly kaolinite, gibbsite) Indirect methods Atterberg Tests COLE Bulk Density/Ksat CEC Summary of the direct and indirect lab methods; of direct methods, elaborate only on x-ray diffraction.Summary of the direct and indirect lab methods; of direct methods, elaborate only on x-ray diffraction.

    11. X-ray Diffraction (XRD) Identifies minerals based on their crystal structure (repeating planes of atoms), and expansion and contraction of structure following chemical and heat treatments. PrinciplePrinciple

    12. Up front cost of x-ray diffractometer is between $80,000 to $130,000 or greater.Up front cost of x-ray diffractometer is between $80,000 to $130,000 or greater.

    13. Soil sample collected, mineral fractions separated (SEMs show minerals), x-ray diffraction patterns for different treatments. This one shows smectite, mica, and kaolinite in XRD patter.Soil sample collected, mineral fractions separated (SEMs show minerals), x-ray diffraction patterns for different treatments. This one shows smectite, mica, and kaolinite in XRD patter.

    14. X-ray Diffraction (XRD) Pros and Cons Direct measurement of minerals Cost ($175 - $300 for XRD + cost for time-consuming clay separation) Time (2-3 day turnaround for XRD at commercial lab, excluding separation time) Detection limit (approx 5-10%) exactly where cutoff is in taxonomy Semi-quantitative (approx. 10-20%) I got the cost and time numbers from H&M Analytical services in Allentown, NJ. However, the owner would not give me a cost for separating the clay fraction, and he did not seem real keen on getting a bunch of soil samples needing fractionation. He would rather just do the XRD for the $175-$300 cost for treated samples (Mg, Mg-EG, K, K-350, K550)I got the cost and time numbers from H&M Analytical services in Allentown, NJ. However, the owner would not give me a cost for separating the clay fraction, and he did not seem real keen on getting a bunch of soil samples needing fractionation. He would rather just do the XRD for the $175-$300 cost for treated samples (Mg, Mg-EG, K, K-350, K550)

    15. X-ray Diffraction (XRD) Identifies minerals based on their crystal structure, expansion and contraction of structure after chemical and heat treatments. Define the results Picture of Diffractogram Mineral ID Quantify results Pros and Cons Direct measurement of minerals Cost Time Sensitivity (approx 10%) exactly where cut is in taxonomy Semi-quantitative (approx. 10-20%) DELETE THIS SLIDEDELETE THIS SLIDE

    16. Apparent CEC Cation Exchange Capacity (CEC) definition: Sum of exchangeable bases (Na+, K+, Ca2+, Mg2+) plus acidity (H+, Al3+) at a specific pH. (from Soil Sci. Soc. Am., 1997). However, direct extraction of soil cations cannot distinguish between exchangeable cations and cations dissolved from soluble salts. This is the main definition for CEC (not specifically apparent CEC) given by the Glossary of Soil Science terms published by SSSA (I added the cations given in parentheses). Emphasize that direct extraction can introduce errors, and represents the CEC at the soil pH (we had a discussion about this with Steve Bristow. CEC definition differs from how we actually measure CEC.This is the main definition for CEC (not specifically apparent CEC) given by the Glossary of Soil Science terms published by SSSA (I added the cations given in parentheses). Emphasize that direct extraction can introduce errors, and represents the CEC at the soil pH (we had a discussion about this with Steve Bristow. CEC definition differs from how we actually measure CEC.

    17. Apparent CEC (contd) More accurate to first saturate soil with a single index cation (NH4+, Na+, or Ba2+), then displace and measure the amount of that cation adsorbed). In practice, CEC is operationally defined by the procedure used and tailored to the purpose for which the results will be applied (measured CEC depends on the method used). This slide should emphasize that there are a number of different CEC methods used, and the resulting value obtained depends on the method used.This slide should emphasize that there are a number of different CEC methods used, and the resulting value obtained depends on the method used.

    18. First (animated) slide in series illustrating the CEC measurement process displacement of native cations by ammonium at pH 7. First (animated) slide in series illustrating the CEC measurement process displacement of native cations by ammonium at pH 7.

    19. Slide shows that the soil clay particles are now saturated with ammonium and native cations are in the water. To be able to measure adsorbed (exchangeable) ammonium, the excess in water must washed out.Slide shows that the soil clay particles are now saturated with ammonium and native cations are in the water. To be able to measure adsorbed (exchangeable) ammonium, the excess in water must washed out.

    20. Excess ammonium from solution is removed. Now displace exchangeable ammonium with Na+. Excess ammonium from solution is removed. Now displace exchangeable ammonium with Na+.

    21. Ammonium displaced into solution (can be done with NaHCO3/acid for aeration method; or displace by leaching with acid and NaCl and measure ammonium with Kjeldahl (like EPA 9080 essentially).Ammonium displaced into solution (can be done with NaHCO3/acid for aeration method; or displace by leaching with acid and NaCl and measure ammonium with Kjeldahl (like EPA 9080 essentially).

    22. Apparent CEC Methods Wash soil with pH-7 NH4OAc solution to NH4+ saturate the exchanger phase. Emphasize the point that the EPA method uses pH 8.2 Na-saturation (this will likely inflate the measured CEC). Buol and I question 8.2. CEC also depends on saturating cation (NH4 vs Na) because NH4 can be fixed by any vermiculite and high-charge smectite.Emphasize the point that the EPA method uses pH 8.2 Na-saturation (this will likely inflate the measured CEC). Buol and I question 8.2. CEC also depends on saturating cation (NH4 vs Na) because NH4 can be fixed by any vermiculite and high-charge smectite.

    23. Apparent CEC (contd) Because EPA Method 9081 is a pH 8.2 method instead of a pH 7.0 method, it is NOT appropriate for apparent CEC measurements tied a cutoff of 16.3 meq/100 g as used in soil taxonomy. This is a key point the EPA Method saturates the soil at pH 8.2, so the measured CEC may be too high for 16.3 comparison. Next slide shows pH effect.This is a key point the EPA Method saturates the soil at pH 8.2, so the measured CEC may be too high for 16.3 comparison. Next slide shows pH effect.

    24. CEC increases with increasing pH (Data compiled by S. W. Buol) In all cases shown, the CEC increases between the pH 7 and pH 8.2 methods. Explains why it is important to use pH 7 saturation method. The saturation step dictates how much of the index cation present if at pH 8.2, then there is more index ion ending up in the exchanger phase.In all cases shown, the CEC increases between the pH 7 and pH 8.2 methods. Explains why it is important to use pH 7 saturation method. The saturation step dictates how much of the index cation present if at pH 8.2, then there is more index ion ending up in the exchanger phase.

    25. Soil minerals have a range of CEC (chemical compositions vary) kaolinite 2 15 smectite 70 120 vermiculite 100 200 mica 10 40 (organic matter) 150 300 (Sparks, 1995) Emphasize that there is no single CEC value for a given mineral need to take an average for a cutoff value. OM is not a mineral, so given in parentheses.Emphasize that there is no single CEC value for a given mineral need to take an average for a cutoff value. OM is not a mineral, so given in parentheses.

    26. Natural variation in chemical composition and CEC of 47 soil smectites (Borchardt, 1989) These data show that properties of soil smectites vary along a continuum THERE IS NO ONE CHEM. FORMULA OR CEC VALUE; Ideal montmorillonite, beidellite and nontronite fall on the top left, top right, and bottom right corners, respectively.These data show that properties of soil smectites vary along a continuum THERE IS NO ONE CHEM. FORMULA OR CEC VALUE; Ideal montmorillonite, beidellite and nontronite fall on the top left, top right, and bottom right corners, respectively.

    27. Basis for apparent CEC cutoff of 16.3 meq / 100 g for 10% smectite Based in taxonomy to define kandic horizons Assumes kaolinite and smectite are dominant clay minerals Average CEC values used kaolinite 7 meq / 100 g smectite 100 meq / 100 g (90% kaol. x 7) + (10% smect. x 100) = 16.3 meq/100g Shows the calculation (and assumptions) leading to the 16.3 value. Note that other minerals such as mica and hydroxyinterlayered 2:1 minerals are ignored.Shows the calculation (and assumptions) leading to the 16.3 value. Note that other minerals such as mica and hydroxyinterlayered 2:1 minerals are ignored.

    28. Range of apparent CEC for range of mineral CEC Low end (kaolinite 2; smectite 70 meq/100 g) (90% kaol. x 2) + (10% smect. x 70) = 9.8 meq/100g High end (kaolinite 14; smectite 120 meq/100 g) (90% kaol. x 15) + (10% smect. x 120) = 25.5 meq/100g Shows the extremes in calculated CEC cutoffs based on high and low values of kaolinite and smectite.Shows the extremes in calculated CEC cutoffs based on high and low values of kaolinite and smectite.

    29. Apparent CEC Pros and cons Reproducible and precise Relatively cheap ($50) Based on the actual mineral properties that relate to water movement. Should not be used in soils < 35% clay Should not be used on soils >0.5% OC 16.3 meq/100g acec is based on ideal soil sample containing only smectite and kaolinite Most soil labs are not set up to run the correct test Modification of original slide.Modification of original slide.

    30. Assumptions in apparent CEC cutoff of 16.3 meq / 100 g (originally used in taxonomy to Show high end calculation 16.3 is mid point. Show range for different methods and pH. DELETE THIS SLIDEDELETE THIS SLIDE

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