From University Testing to Practical Application—Sequential Aquifer Testing Demonstrates How Hydraulic Tomography Improves Model Accuracy

Hydraulic tomography estimates aquifer properties using data analyses from a sequence of cross-well interference tests or sequential aquifer tests. It is a useful method to determine the distribution of aquifer parameters over a well field with a small number of wells. Hydraulic tomography has been used primarily within academic studies to define aquifer parameter distributions in computer simulations, sandbox experiments and small scale field experiments. This method has been shown to yield more accurate distributions of aquifer properties than classical aquifer testing analysis. Therefore, in a non-academic project, this method was used to help define the distribution of aquifer parameters in a large, complex well field in Placentia, California.

This work differs from previous studies in that the site is larger, the wells are deeper, they have variable depths and screen intervals and the pumping rates are higher–reflecting the characteristics of typical full-scale projects. The drawdown data generated during the sequential aquifer testing was analyzed using classical methods to obtain the initial, depth-averaged aquifer parameters between the pumping well and the observation wells. These initial values were co-kriged using PEST utilities to generate an initial estimated distribution of aquifer parameters across the site, and construct a groundwater model of the site. PEST was used to employ the hydraulic tomographic method by calibrating the model using pilot points with values restricted within the ranges determined from aquifer testing analyses results.

Although acceptable calibration of the groundwater model is possible without using the hydraulic tomography method, it obtains a more accurate representation of hydraulic properties. A more accurate representation of subsurface properties will result in more accurate predictions in the future if conditions change, or more wells are installed in the well field. This paper will discuss an instance where hydraulic tomography is recommended.