This is a draft ASTM Test Procedure.

The UFA Method For Extracting Pore Fluids From Relatively Impermeable And Highly Unsaturated Porous Media.

1.1 This test method covers the extraction of pore fluids from relatively impermeable and highly unsaturated porous media, e.g. soil, sediment, rock, concrete and ceramic, either natural or artificial.

1.1.1 A procedure for preparing test specimens is provided in section 8 and a procedure for carrying out the extraction is provided in section 10. Specific instructions for operation of the specific ultracentrifuge should be obtained from the manufacturer of the equipment. The specific equipment discussed in this test method is described in Section 6 and is called the UFA.

1.2 This standard may involve hazardous materials operations and equipment. This standard does not purport to address all of the safety issues associated with its use. It is the responsibility of whoever uses this standard to consult and establish appropriate safety and health practices and determine the applicable regulatory limitations prior to use.

2.1 ASTM Standards

C 702 Methods for Reducing Field Samples of Aggregate to Testing Size, Annual Book of ASTM Standards, Vol. 04.02.

D 420 Practice for Investigating and Sampling Soil and Rock for Engineering Purposes, Annual Book of ASTM Standards, Vol. 04.08.

D 653 Terminology Relating to Soil, Rock and Contained Fluids, Annual Book of ASTM Standards, Vol. 04.08.

2.2 Other References

Conca, James L., and Judith Wright. 1992. "Diffusion and Flow in Gravel, Soil, and Whole Rock." Applied Hydrogeology, vol. 1, p. 5-24.

Klute, A. 1986. Methods of Soil Analysis, Part 1, Physical and Mineralogical Methods, Second Edition, American Society of Agronomy, Inc., and Soil Science Society of America, Inc., Madison, Wisconsin.

Wright, Judith, James L. Conca, and Xiaobing?Chen. 1994. Hydrostratigraphy and Recharge Distributions from Direct Measurements of Hydraulic Conductivity Using the UFA Method, PNL Technical Report PNL 9424, Pacific Northwest Laboratory, Richland, WA, 150 p.

3.1 See ASTM D653 for specific terms relating to soil, rock and contained fluids.

3.2 Porosity -- the percentage of the bulk volume of a rock, soil or porous material that is occupied by air, vacuum or fluid; the non-solid portion of the total volume.

3.3 Permeability (also referred to as Flow Porosity) -- the portion or fraction of the total porosity that is interconnected and contributing to the overall flow of fluid through the sample.

3.4 Water Content -- the amount of water contained in a porous solid or aggregate; generally expressed either as the weight percent, which is the ratio of the weight of water in the sample determined by weight loss upon heating to the total sample weight, or as the volume percent (q), which is the volume of water in the sample divided by the total sample volume. The volumetric water content is the weight percent water multiplied by the dry bulk density (r) of the sample. When the sample is saturated, the water content expressed as the volume percent equals the porosity.

3.5 Matric potential (matric suction; water suction, water potential, etc.) -- The negative pressure potential generated in the pore spaces of the sample resulting from the surface tension of the water and includes all capillary, electric double layer and other water film effects. Matric potential is the negative gauge pressure, relative to the external gas pressure on the soil water, to which a solution identical in composition to the soil water must be subjected in order to be in equilibrium through a porous membrane wall with the water in the soil (Hillel, 1980)

3.6 Unsaturated Flow Apparatus -- in this application, the UFA is a specially adapted ultracentrifuge that can hold soil or rock samples in a configuration that enables pore fluid to be collected. Specific parts are defined as follows:

3.6.1 Sample Holder -- the metal, polysulfone, fiberglass or epoxy shell that contains the soil, rock, cement or aggregate to be tested.

3.6.2 Sample Cup -- the metal canister that contains the sample holder. It has a cap with o-rings to prevent fluid flow around the sides of the sample holder.

3.6.3 Bucket -- the metal shell that holds the sample cup and screws into the rotor.

3.6.4 Effluent Collection Chamber -- the plastic graduated vessel at the end of the sample cup that collects the effluent as it exits the sample cup.

3.6.5 Rotor -- the central aluminum fixture that holds the sample and bucket and spins on the rotating shaft. The Hy-sed 3.0 rotor holds the 3.33 cm diameter samples and the Hy-sed 10.0 rotor holds the 4.44 cm diameter samples. We are in the process of developing a rotor which will be able to hold shelby tube sized samples.

4.1 The UFA Method is effective because it allows the operator to subject a sample to high whole body forces that act on the pore fluid without affecting the solid phases of the material. The driving force is fixed by imposing an acceleration on the sample through an adjustable rotation speed. Only the bulk pore fluid is extracted, no structural water, interlayer water or electric double layer water is extracted. No pressure dissolution occurs as the whole body accelerations do not produce high point pressures. No osmotic gradients occur in the UFA. The operator can impose whatever force is desired or necessary within the operational range of rotation speeds usually between 0 and 14,000 rpm, or approximately 0 to 50 bar of equivalent pressure. Note this is not a real pressure but is a whole body force, so no dewatering of clay interlayers or other adverse pressure effects occur. The yield of fluid will depend upon the water content, matric potential and rotation speed. Because a relatively large driving force is used, extraction of the bulk fluid phases occurs in hours for most geologic materials, even at very low water contents.

5.1 Recent results have demonstrated that extraction of pore fluid using a whole body force are superior to pressure or osmotic techniques because the pore fluid composition is not altered. The extracted fluids can be used for identification of contaminants, major, minor and trace element chemistries for various applications, and for predictive models and geochemical speciation models used to determine phase stabilities and the transport properties of real systems.

6.1 For this application, the UFA instrument consists of an ultracentrifuge that can reach accelerations of up to 20,000 g. Temperatures can be adjusted from -20 degrees to 150 degrees C. Effluent from the sample is collected in a transparent, volumetrically-calibrated chamber at the bottom of the sample assembly. Using a strobe light, an observer can check the chamber while the sample is being centrifuged. The sample assembly is gas tight so that no volatiles can escape. The only commercial UFA is available from UFA Ventures Inc., 2000 Logston Blvd., Richland, WA 99352, and is manufactured for UFA Ventures Inc. by Beckman Instruments, Inc.

6.2 Several variations of the UFA have been developed under the Department of Energy's (DOE) Volatile Organic Compound (VOC) - Arid Site Integrated Demonstration (ID) Program to accommodate the various aspects of multiphase/multicomponent systems in mixed waste environments. Various materials, e.g., teflon, titanium, stainless steel, copolymers, and nylon, address the many chemical compatibility requirements of various applications such as non-aqueous phase liquids and tank waste sludge. Different rotor sizes accommodate samples up to 200 cm^3. Each rotor and sample assembly comes preconfigured. The operator does not need to configure any part for this procedure.

6.3 Materials can be run in the UFA as recomposited samples or as in situ samples subcored directly into the sample UFA chamber from trench, outcrops or drill cores. Whole rock cores and cores of ceramics, grouts, and other solids can also be run.

7.1 In addition to the UFA instrument, various materials are necessary for sample preparation and handling of soils, rock, aggregate, concrete and other porous media (see ASTM D 420 and Section 8). However, once the sample is prepared, all that is needed is a balance accurate to ?0.01 g for weighing the sample for water content determination if that is desired (see ASTM D 2216) and an oven for drying the sample after the final point to obtain the dry weight if that is also desired. Kim-wipes or other dust-free wipes, clean brushes for cleaning threads, various spoons and spatulas, squeeze bottles, distilled water for cleaning, and other basic laboratory implements are essential for smooth operation. As with any precision instrument, it is important to keep the area clean and dirt free because grit can wear or destroy certain moving parts in the UFA. Depending upon the application, sample handling can be performed in a glove box or fume hood. The UFA comes with specific tools necessary for operation, e.g., spanner wrenches.

8.1 Soil and disaggregated materials- Depending upon the specific investigation, samples are obtained in many ways. The best possible sampling is to subcore the outcrop, trench, or undisturbed sample directly into the UFA sample holder using a subcoring device that holds a UFA sample holder. Often, however, undisturbed samples are not available and the sample is simply added to the sample holder in a disaggregated manner. For pore water extraction the sample form is not critical. Care must be taken to prevent or reduce evaporation from the sample, especially with samples at highly unsaturated conditions or for volatile organic compounds.

8.2 Whole rock cores, concrete or ceramics- Solid coherent materials must be broken into a small enough size to fit into the sample holder or cored using a coring bit (see ASTM C 702), usually diamond, that produces cylinders that will fit into the sample chamber. Usually these activities can dry the sample out significantly, unless extreme care is taken.

The UFA should have a manufacturers service contract to maintain calibrations, smooth functioning and long life. Do not attempt to calibrate the UFA manually. The balances used to weigh samples and the oven used for drying samples should be calibrated periodically according to the relevant quality assurance or impact levels for the application.

10.1 The following procedure refers to the commercially available UFA. However, it is applicable to any centrifuge set-up that allows flow out of the sample during centrifugation and collection in an effluent collection chamber.

10.2 The operator will make sure the temperature of the centrifuge chamber is a constant 23 degrees ?1.0 degree C during operation through-out the test period, unless otherwise specified. The operator will note any deviations of the temperature on the data sheet.

10.3 Centrifuge operations are carried out according to standard procedures for each instrument supplied by the manufacturer.

10.4 The sample assembly is prepared according to the following procedure. The sample holder, cup, caps, effluent collection chamber and any other part that contacts the pore fluid during the extraction must be cleaned to whatever level is required. For most aqueous applications requiring major, minor and trace element compositions, use a 10% nitric acid bath for several hours. Rinse in deionized water. Clean O-rings and lubricate with silicon vacuum grease. Assemble the sample cup and effluent collection chamber and fill the sample cup under whatever conditions are appropriate to the application, e.g., an environmental chamber or glove box to reduce evaporation. Proceed quickly to minimize evaporation. Make sure metal cone is in place in the bottom of the cup with the flat, grooved side oriented toward the top of the sample cup. Push metal threaded cap onto the top of the sample holder. Place sample holders inside cups and carefully screw down the caps by hand, taking care that the threads are seated properly. Do Not Overtighten! Push the top cap into the O-ring seal in the metal threaded cap. Weigh both sample assemblies and equalize their weights to ?5 grams to maintain balance. Equalization of weights can be obtained by adding teflon to the effluent collection chamber of the lighter assembly. Alternatively, a equal pre-weighed portion of each sample can be set aside just prior to loading. Push the sample assembly with the letter A marked on the cap into position A in the centrifuge rotor. Gently screw the metal bucket into the rotor over the sample assembly. Place the second sample assembly (marked C) into position C of the centrifuge rotor. Gently screw the metal bucket into the rotor over the sample assembly. After each bucket is tightened, make sure the calibration lines on the effluent collection chamber are visible through the windows in the top of the buckets.

10.5 The centrifuge should be prepared for a sample run by lowering the rotor assembly into the centrifuge chamber. Set the temperature by pressing the "Temp" button, entering the selected temperature, and pressing the "Enter" button. Set the rotor speed by pressing the "Speed" button, entering the selected speed and pressing the "Enter" button. The centrifuge settings must be displayed in order to start the machine, so press "Enter" to display settings, and press the "Start" button to start centrifuging. Carefully follow the operating instructions that will be included with the UFA.

10.6 Depending upon the application, effluent is either removed using a syringe and filtered through a submicron sized filter into appropriate pre-cleaned vials, or decanted directly into vials for subsequent transport to an analytical laboratory.

10.7 Remember to check O-rings frequently to determine if they are damaged. Change O-rings if they show even small nicks or cuts. Remember to grease O-rings to assure proper sealing of sample and lubricate all threads to prevent galling and to reduce wear of threads.

10.8 As an example of some results, Table 1 shows the compositions of pore waters extracted from four unsaturated soils sampled using split-spoon methods from a borehole drilled using cable tool methods from the Hanford Site in Washington State.

TABLE 1. Vadose Zone Water Extracted from Borehole Samples Using the UFA

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