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ExxonMobil Global Services Colony Shale Oil Project ESR Reclamation Studies Weighing Lysimeter Performance 1990-2003 Project No. 353 Page 15 sublimation is carried away by the atmosphere and is therefore not available for runoff or for percolation into the topsoil layer. Whenever the theoretical Et line is above the precipitation line, as occurs from mid-April until October, the deficit must be made up from water stored in the plant root zone. The deficit will be seen as a net reduction in weight of the lysimeter as water is pulled up from the soil via plant roots to be transpired by the plants, and as water migrates upward due to evaporation in the upper few inches of the soil. Note that on Fig. 4.1 this "summertime" seasonal weight loss is evident every spring (refer to the black line, lysimeter weight, on Fig. 4. I ). The orange line in Fig, 4.3 is the actual evapo-transpiration (Et), as inferred by water balance based on actual measured precipitation, actual weight change in the lysimeter, and the rainfall equivalent (in inches) of actual runoff and percolation collected in the buckets below the lysimeter. On Wymore's Fig 4.4 this line is referred to as "Eta". It can be observed that precipitation, theoretical (potential) Et and actual Et match only for a brief period at Mid-April and later in eazly October. The April point corresponds essentially to the end of the spring melt and the beginning of the growing season. At this time snow pack that has not already sublimed has melted and has begun to runoff, and the plants are beginning to consume water. The potential Et line in the summer months is always much higher than the actual precipitation in this climate. If the plant cover were dense enough, it could easily consume more than the average 1.6" of precipitation that falls each month in an average year. However, in the semi-arid climate at the Colony site, water obviously does become the limiting parameter, and based on Fig. 4.3 it apparently becomes limiting very eazly in the summer. Until about mid-June, the plants are malting up the difference between the theoretical maximum Et and the available rainfall by drawing stored water from within the root zone. At the ESR lysimeter, that would be the upper 20" of topsoil, and apparently also the next 6 inches of "mixed' zone. Soil moisture content each yeaz drops off • significantiy at the 6" and 19" topsoil depths, and also at the 25" `Ynixed zone" depth. By mid-June, LACHEL FELICE & Associates