Lysimeters

It is often important to quantify the contamination of pore fluid in the unsaturated soil 2one, where monitoring wells are ineffective. In this region, suction cup lysimeters are useful (7). These samplers consist of a porous cup, typically ceramic, having two access tubes which are usually Teflon. One access tube provides a pressure-vacuum, the other discharges the sampled fluid to the surface. The porous cup, typically between 2 and 5 cm in diameter, is attached to a PVC sample accumulation chamber. 

Acid amide herbicides are nonionic and moderately retained by soils. The sorption of several acid amide herbicides has been investigated (369). Acetochlor [34256-82-1] is sorbed more than either alachlor or metolachlor, which are similarly sorbed by a variety of soils. Sorption of all the herbicides is well correlated to soil organic matter content. In a field lysimeter study, metolachlor has been found to be more mobile and persistent than alachlor (370) diphenamid [957-51-7] and napropamide [15299-99-2] have been found to be more readily leached (356). 

Methods for data collection vary from lysimeters to streamwater samples. Additional examples of inputs and losses may be found in Jordan (80), Melillo and Gosz (85) and Vitousek and Sanford (26). 

Albanis TA, Pomonis PJ, Sdoukos AT. 1988b. Movement of methyl parathion, lindane and atrazine through lysimeters in field conditions. Toxicol Environ Chem 17 35-45. 

Stork A, Ophoff H, Smelt JH, et al. 1998. Volatilization of pesticides Measurements under simulated field conditions. In Fuhr F, Hance RJ, Plimmer JR, et al, ed. The Lysimeter Concept Environmental behavior of pesticides. Washington, DC American Chemical Society, 21-39. 

Suction lysimeters are required for some field-scale groundwater monitoring studies to monitor the transport of compounds of interest through the unsaturated zone. Unlike monitoring wells or water supply wells that sample water from the saturated zone, suction lysimeters sample water from the unsaturated zone. This section provides a summary of the installation and sampling procedures for pressure-vacuum suction lysimeters. A detailed discussion of unsaturated zone sampling devices is available elsewhere. 

The reservoir materials may be PVC, stainless steel, or a fluorocarbon polymer, and the porous cup may be constructed of ceramic, stainless steel, or fluorocarbon polymer. Ceramic cups have a smaller pore size, a greater bubble pressure (pressure under which the cup produces bubbles), and a greater operational suction range, and are preferred to other porous cup materials. All materials used for the construction of the suction lysimeter should be tested in the laboratory to determine if any bias in the sample analysis will result from their use. 

Lysimeter assembly and pre-installation testing should be conducted in a clean area, preferably indoors. Careful installation is necessary to ensure proper operation. The components of the lysimeters may need to be decontaminated prior to installation... 

The method to install a lysimeter is dependent on the placement depth. A hand auger may be adequate to advance a shallow borehole (<4.5m), or a hollow-stem auger may be necessary to advance a deeper borehole. If a hollow-stem auger is used. 

After the silica flour or soil mixture has set, add a layer of silica sand as a filter pack, then fill the remainder of the borehole with bentonite or a grout seal (Figure 5). Access lines may be run from the lysimeter reservoir through a protective PVC riser pipe to the land surface. A locking protective casing should be used to secure the abovegrade lysimeter components. If the lysimeter is used immediately after installation, it is necessary to purge any water used to prepare the siiica flour or soil slurry. Remove at least the water volume equivalent to approximately one third of that used to make slurry. 

The sampling of a suction lysimeter is initiated by applying a vacuum (approximately 40-50 cm of mercury) through the vacuum/pressure line with a hand pump or electric pump. The valve on the sampling line must be closed. A constant vacuum may be maintained on the lysimeter using an electric pump. The time required before collecting a sample from a lysimeter will depend on the method of vacuum application, the moisture content of the soil, and the soil type. 

A vacuum may be applied to a lysimeter more than one time. The previous vacuum is lost when an additional vacuum is applied. 

Figure 6 Example of a suction lysimeter sampling form...

Timco Manufacturing Inc., TIMCO Lysimeter Manual , Hmco Manufacturing Inc., Prairie... 

Figure 1 Structure of a lysimeter for a model paddy study...

Prepare a calibration curve in the following manner. Measure 1 mL of control water into a series of 1.8-mL autosampler vials. Fortify each water sample with 200 o.L of the appropriate calibration standard to make a 0.1, 0.5 and 2.5ngmL calibration curve. Mix the sample by vortexing or shaking the vial and analyze 200 iL by LC/ESI-MS/MS. For well and lysimeter water, mix 1 mL of sample water with 200 uL of the lOngmL" mixed internal standard solution in a 1.8-mL autosampler vial, cap the vial, mix the contents and analyze 200 iL by LC/ESIMS/MS. 

Nisbet AF, Shaw S. 1994. Summary of a 5-year lysimeter study on the time-dependent transfer of 137Cs, 90Sr, 239 240Pu and 241Am to crops from three contrasting soil types 1. Transfer to the edible portion. J Environ Radioact 23 1-17. 

TCE residuals have been discovered in an unsaturated soil profile at a depth of 3 m. From lysimeter samples, the soil water concentration is approximately 100 mg/L. Long cuttings of hybrid poplar... 

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