A lysimeter monitoring system was installed to gather soil-water samples at the field sites. The system consists of ceramic cup tension lysimeters that enable the collection of soil water from the vadose zone. Ceramic suction cups and plates have to a large extent replaced the classical zero-tension drainage lysimeter (van der Ploeg and Beese, 1977). The tension systems are cheaper and do not destroy the soil structure as much as the larger area zero-tension systems. They can be placed at various depths allowing for the detection and monitoring of groundwater pollutants as they travel from the surface towards the water table. When installed beneath a contaminant source, a porous cup sampler can be used to detect a contaminant as it moves towards the groundwater (Morrison and Lowery, 1990). This allows for an earlier detection of contaminants over standard monitoring well systems, which sample the saturated zone. Lysimeters may also be used to monitor any chemical changes that the contaminant may undergo as it travels through the vadose zone.
Literature studies have indicated that there is concern over the validity of the soil water sampled via tension lysimeters as being representative of the true soil water composition. Clearly the application of a vacuum to the vadose zone in the vicinity of the ceramic cup will have a noticeable effect on the kinetics of soil water movement. This altering of the time the soil water spends in contact with soil particles may have an effect on the soil solution if equilibrium conditions are not met as it passes around the soil particles.
The study used two different lysimeter designs, although both operated on the same principle. One design uses a sealed 1.9” O.D. PVC body housing, which is fitted with two ports which allow application of a vacuum or pressure and the other to delivery of collected water samples to the surface (Figure 6). The sealed unit, which is 17.5” in length, is connected to a head assembly that enabled a clean and easy application of vacuum/ pressure and sampling via pressure dual pressure ports. The head assembly also contains a pressure gauge that allows the operator to apply the proper vacuum/pressure and monitoring the rate at which the vacuum dissipates as soil-water enters the system. The system was built by the Monoflex Division of Campbell Manufacturing, makers of groundwater sampling equipment.
lysimeter design, consists of a 1” O.D. acrylic tube again with a ceramic cup
at the sampler bottom and a rubber stopper with access port at the top
(Figure 7). The system was simpler
in design than that previously mentioned, and was used to collect the uppermost
samples that were too shallow to be collected with the PVC units.
Both lysimeter units are designed for either the head assembly or rubber stopper above the ground or at grade. However, at both sites minimal disturbance of landscaping practice was the goal, and the units were installed beneath grade. This allows for the plots to be landscaped in much the same manner they would be, if the monitoring system
Figure 6 – PVC Lysimeter (Image courtesy Monoflex Brochure)
Figure 7 – Acrylic Lysimeter (Image courtesy Fetter, 1999)
had never been installed. It also enables the plots to give off a fairly undisturbed appearance. This is important at the SUNY site, which is located alongside a fairly heavily traveled foot-path.
The units were encased in commercially-made round, plastic sprinkler control valve boxes with green plastic covers that blended with the turf. These boxes were set with the cover at grade. Upon a quick inspection, it is difficult to notice that a sampling system has been installed at either plot. These boxes can be locked to eliminate vandalism.