142 research outputs found
Evaluation of Analytical Methods to Study Aquifer Properties with Pumping Tests in Coastal Aquifers with Numerical Modelling (Motril-Salobreña Aquifer)
Two pumping tests were performed in the unconfined Motril-Salobreña detrital
aquifer in a 250 m-deep well 300 m from the coastline containing both freshwater and
saltwater. It is an artesian well as it is in the discharge zone of this coastal aquifer. The two
observation wells where the drawdowns are measured record the influence of tidal fluctuations, and the well lithological columns reveal high vertical heterogeneity in the aquifer. The
Theis and Cooper-Jacob approaches give average transmissivity (T) and storage
coefficient (S) values of 1460 m2
/d and 0.027, respectively. Other analytical solutions,
modified to be more accurate in the boundary conditions found in coastal aquifers,
provide similar T values to those found with the Theis and Cooper-Jacob methods,
but give very different S values or could not estimate them. Numerical modelling in a
synthetic model was applied to analyse the sensitivity of the Theis and Cooper-Jacob
approaches to the usual boundary conditions in coastal aquifers. The T and S values
calculated from the numerical modelling drawdowns indicate that the regional flow,
variable pumping flows, and tidal effect produce an error of under 10 % compared to results
obtained with classic methods. Fluids of different density (freshwater and saltwater) cause an
error of 20 % in estimating T and of over 100 % in calculating S. The factor most affecting T and
S results in the pumping test interpretation is vertical heterogeneity in sediments, which can
produce errors of over 100 % in both parameters.This research has been financed by Project CGL2012-32892 (Ministerio de EconomÃa y
Competitividad of Spain) and by the Research Group Sedimentary Geology and Groundwater (RNM-369) of the
Junta de AndalucÃa
Unconfined Aquifer Flow Theory - from Dupuit to present
Analytic and semi-analytic solution are often used by researchers and
practicioners to estimate aquifer parameters from unconfined aquifer pumping
tests. The non-linearities associated with unconfined (i.e., water table)
aquifer tests makes their analysis more complex than confined tests. Although
analytical solutions for unconfined flow began in the mid-1800s with Dupuit,
Thiem was possibly the first to use them to estimate aquifer parameters from
pumping tests in the early 1900s. In the 1950s, Boulton developed the first
transient well test solution specialized to unconfined flow. By the 1970s
Neuman had developed solutions considering both primary transient storage
mechanisms (confined storage and delayed yield) without non-physical fitting
parameters. In the last decade, research into developing unconfined aquifer
test solutions has mostly focused on explicitly coupling the aquifer with the
linearized vadose zone. Despite the many advanced solution methods available,
there still exists a need for realism to accurately simulate real-world aquifer
tests
Characterization of a fluvial aquifer at a range of depths and scales: the Triassic St Bees Sandstone Formation, Cumbria, UK
Fluvial sedimentary successions represent porous media that host groundwater and geothermal resources. Additionally, they overlie crystalline rocks hosting nuclear waste repositories in rift settings. The permeability characteristics of an arenaceous fluvial succession, the Triassic St Bees Sandstone Formation in England (UK), are described, from core-plug to well-test scale up to ~1 km depth. Within such lithified successions, dissolution associated with the circulation of meteoric water results in increased permeability (K~10−1–100 m/day) to depths of at least 150 m below ground level (BGL) in aquifer systems that are subject to rapid groundwater circulation. Thus, contaminant transport is likely to occur at relatively high rates. In a deeper investigation (> 150 m depth), where the aquifer has not been subjected to rapid groundwater circulation, well-test-scale hydraulic conductivity is lower, decreasing from K~10−2 m/day at 150–400 m BGL to 10−3 m/day down-dip at ~1 km BGL, where the pore fluid is hypersaline. Here, pore-scale permeability becomes progressively dominant with increasing lithostatic load. Notably, this work investigates a sandstone aquifer of fluvial origin at investigation depths consistent with highly enthalpy geothermal reservoirs (~0.7–1.1 km). At such depths, intergranular flow dominates in unfaulted areas with only minor contribution by bedding plane fractures. However, extensional faults represent preferential flow pathways, due to presence of high connective open fractures. Therefore, such faults may (1) drive nuclear waste contaminants towards the highly permeable shallow (< 150 m BGL) zone of the aquifer, and (2) influence fluid recovery in geothermal fields
- …