Baildown test

Baildown testing is a widely used field method to evaluate the actual thickness of LNAPL product in a monitoring well. Baildown testing involves the rapid removal of fluids from the well, and subsequent monitoring of fluid levels, both the water level or potentiometric surface (oil-water interface) and NAPL level (oil-air interface), with time. Such testing was originally used as a preliminary field method to evaluate recoverability of NAPLs and thus to determine potential locations for recovery wells. All monitoring wells at a site that exhibited a measurable thickness of LNAPL were typically tested. Whether or not all the LNAPL product could be 

FIGURE 6.12 Representative baildown testing curve results using Hughes et al. (1988) method where depth to top of product layer vs. time is produced. 

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FIGURE 6.11 Representative baildown testing curve results using Gruszenski s (1987) method. Graphs of depth to product and depth to the product-water interface vs. time (a), and product thickness vs. time (b) are produced. 

Baildown test results do not always conform to the theoretical response anticipated. This is evident from Figure 6.12, which shows much fluctuation as a result of borehole effects. In these instances, maximum theoretical values can be determined by subtracting the static depth-to-product from the corrected depth-to-water. Thicknesses provided in this manner are conservative in that true thicknesses must be less than or equal to these values and, thus, this method overestimates the actual thickness by an amount equal to the thickness of the capillary zone. 

The recharge test has the advantage of yielding results regardless of the location of the mobile LNAPL-water interface in relation to the potentiometric surface. Although more accurate than a baildown test, it is also more complicated to conduct. 

Baildown tests have been used for decades during the initial or preliminary phases of LNAPL recovery system design to determine adequate locations for recovery wells and to evaluate recovery rates. Baildown tests involve the rapid removal of fluids from a well with subsequent monitoring of fluid levels, both the LNAPL-water (or oil-water) interface and LNAPL-air (or oil-air) interface, in the well with time. Hydrocarbon saturation is typically less than 1, and commonly below 0.5, due to the presence of other phases in the formation (i.e., air and water). Since the relative permeability decreases as hydrocarbon saturation decreases, the effective conductivity and mobility of the LNAPL is much less than that of water, regardless of the effects induced by increased viscosity and decreased density of the LNAPL. 

Validity of baildown tests for estimation of true thickness ... 

Huntley, D., 2000, Analytic Determination of Hydrocarbon Transmissivity from Baildown Tests GroundWater, Vol. 38, No. 1, pp. 46-52. 

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