In the case when groundwater contamination is detected, it becomes essential to determine the extent, level and source of contamination. Conventionally, among many others, determination of the extent and level of contamination is undertaken by taking as many samples as possible from several points . In general, this requires the installation of several observation wells. As a result, the cost of such operations can be very high, especially when high sampling resolution is required. Moreover, drilling of a large number of monitoring wells could also be constrained by geological and land-use factors. Other methods such as forward mathematical models require knowledge of source parameters. But in many cases, especially in complex industrial areas, the origin of contamination is not known and determining it could require costly investigations.

Follow up:

Alternatively, contaminated sites can be screened out and the extent and level of groundwater contamination can be determined by inverting the pumped concentration-time series curves obtained during pumping tests. Employing concentration measurements through pumping tests help to screen-out and localize hot spot zones for further analysis on the state of groundwater pollution, health risk studies, remediation design studies, etc. Moreover, aquifer parameters can simultaneously be determined so as to use them for other hydro-geological studies.

Most of the previous studies are based on analytical inversion solution under homogeneous, isotropic condition with circular well capture zones. However, in many cases, the real geo-hydrological systems are complex and, therefore, the aquifer media must be characterized by heterogeneous media . Depending on the local permeability values, the well capture zone geometry can vary from that of a circular capture zone. Therefore, total mass flow to be calculated in homogeneous and isotropic conditions can correspondingly differ from that of the heterogeneous formation.

Hence, with the newly developed volume-based mathematical model (VINMOD), the inversion of pumped concentration can take into account heterogeneous flow fields in the vicinity of the pumping well. VINMOD helps to calculate the transversal concentration distribution of undisturbed contaminant plume and quantify the corresponding mass flow rate at a predefined imaginary control plane (ICP), a plane which is perpendicular to the prevailing direction of groundwater flow. Practical applications of VINMOD are, for instance, groundwater pollution evaluation, health risk studies, remediation design studies.

The advantage of VINMOD is its flexibility in handling irregular well capture zones and, therefore, it can be applied for both heterogeneous and homogeneous conditions. Under homogeneous conditions, VINMOD calculates streamtube areas from circular capture zones and straight streamlines. For non-circular capture zones, which is a case under heterogeneous conditions and/or when the effect of groundwater flow velocity is not neglected, streamtube areas can be easily calculated using EDigitizer.

Allelign Zeru (Ph.D)

09 August, 2007
Hydroxpert Press Vol. 1-9