Unsaturated zone sampling

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. 

Wood, W. 1973. A technique using porous cups for water sampling at any depth in the unsaturated zone. Water Resources Research, 9, 486-488. 

Kerfoot [6] examined the performance of a grab sampling technique for soil-gas measurement analyses, at a site with groundwater known to be contaminated with chloroform. The study assessed the correlation between soil-gas and groundwater analyses with chloroform as a model volatile organic compound. Chloroform concentration in soil gas increased linearly with depth in the unsaturated zone. 

Based on the successful reactor study, a 1-acre field demonstration was performed to evaluate the potential for full site remediation of the unsaturated zone. The selected area was surveyed to be exactly 1 acre (circular), carefully sampled to determine the quantity of residual hydrocarbon, and place counts were made to... 

The U.S. Department of the Interior is conducting research under the U.S. Geological Survey to determine the impacts of highway de-icing chemicals on the groundwater quality of shallow, unconsolidated aquifers in Ohio, and to determine the salt concentration present in the soil and unsaturated zones. This research will include some analyses for dissolved cyanide in monthly samples from eight sites across Ohio. 

DBCP has been found In ground water In Hawaii, California, Arizona, South Carolina, and Maryland (5-7,19,77-79). Typical positives are 0.02-20 ppb. Areas with the highest frequency of positives and the highest well concentrations are the San Joaquin Valley In California and the region southwest of Phoenix, Arizona. The Hawaii contamination has occurred despite several hundred feet of overburden between the basal aquifer and the surface. One set of California soil core results show that ppb amounts of DBCP has leached about 15 m through the unsaturated zone ( ), whereas DBCP was not detected In another set of California soil cores sampled as deep as 10 m and five years after the last application (80). The latter results can possibly be explained by rapid movement of DBCP down the soil profile to depths greater than 10 m. 

Figure 10. Air pressure at land surface and three depths in the unsaturated zone as a function of time for the August and October 1996 sampling events. Symbols are only used to help distinguish between lines and do not necessarily represent actual data points. Actual data points were collected at 5-minute intervals for all subsurface depths and hourly for surface pressure.

Collection of Soil and Water Samples. Soil sampling provides information on unsaturated zone pesticide migration, and as such, is the most critical data that will come out of a prospective field study. For this reason, soil sampling programs should adequately describe pesticide fate horizontally, vertically, and temporally (over time). 

Luhdorff, G. Scalmanini, J. "Ground Water and the Unsaturated Zone Monitoring and Sampling," National Water Well Assoc. unpublished training manual, 359-365. 

Unsaturated Zone Studies. These experiments began in 1980 at special interest areas in the United States. In each area, two to five locations, which were grower-treated fields, were sampled once or twice after application. Soil cores were taken by hand auger at three sites per location with sampling of strata from 0-0.3,... 

Laboratory Studies. A variety of laboratory studies have been performed including degradation rate studies with actual samples from the saturated and unsaturated zones, oxidation mechanism studies, saturated zone degradation mechanism studies, potential for sulfoxide or sulfone reduction studies, and distilled water hydrolysis studies. The experimental methodology in these experiments varied according to the study objectives. 

No. of Samples So11 Mater Unsaturated Zone Application Rate Half-L1fe Maximum Leaching kq/ha (months Deoth (ml ... 

The primary gaseous carrier for transport of C from the low-level radioactive-waste disposal site (lat. 41 20 N, long. 89 47 W), near Sheffield, Bureau County, Illinois is C02 (1). Production of the gas is caused by aerobic microbial decomposition of organic waste buried in waste-disposal trenches. This results in steep gradients in P C02 in undisturbed glacial and eolian sediments adjacent to the site. To collect samples of unsaturated zone gases, nests of gas piezometers were installed along a cross section in boreholes located at distances of 12,29, and 46 m from the end wall... 

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