In the northern german lowlands north west of Bremen and south west of river Weser a factory wants to extract 70 cubic meters of groundwater per hour. They want to pump clean water despite of a landfill as contaminant source south of the well (=upstream of the ground water flow). The well is very close to the western one of two parallel faults within the middle layer, with conductivities between 1 and 1E-9 m/s and is strongly influenced by them. The uppermost layer (= Saale) has the highest conductivity and is therefore most important for the flow regime. A MODFLOW model with 3 layers, given elevations and heads in the river and in the rim of the area was run many times to check if and how the well can can deliver the 70 cubic meters per hour of clean water.
Lowering pumping rate, displacement of the well away from the fault, is only sufficient for the case of low conductivity (closed) faults. For open (high conductivity) faults these measures are not sufficient and a cleaning well north of the landfill is necessary. By trying lower and lower pumping rates of the cleaning well the minimum extraction rate for the cleaning well was found.
Table of Contents
1 Executive Summary
2 Project Description
2.a Introduction
2.b Site Description
2.b.i Hydrologic Setting
2.b.ii Site description – more data
3 Data Assimilation
4 Description of the groundwater model
4a Spatial discretization
4b Temporal discretization
4c Heterogeneity and layering
4d Solver
4e Boundary Conditions
5 Discussion of Flow Model Results
6 Description of scenarios
6.1 Scenarios without cleaning well
6.2 Scenarios with a cleaning well
7 Conclusion
8 Recommendation for further work
8.1 Faults
8.2 Contaminants
8.3 Seasonal data
Objectives and Topics
The primary objective of this project is to model groundwater flow and contaminant transport in an area south west of the river Weser in Bremen. The research addresses whether a proposed industrial well can extract 70 cubic meters of water per hour without drawing in contaminants from a nearby landfill site, and identifies potential mitigation strategies using cleaning wells.
- Groundwater flow modeling using USGS MODFLOW.
- Impact of geologic fault conductivity on flow regimes.
- Advection-based contaminant transport analysis.
- Scenario testing for well placement and extraction rates.
- Optimization of a cleaning well to prevent aquifer contamination.
Excerpt from the Book
2.a Introduction
The purpose of the groundwater model for an area south west of river Weser in Bremen is to check if and how a well in the midst of the model area can pump 70 cubic meters per hour for a new factory without getting contaminated water from a landfill site at the southern (lower) border of the area. The well is located at the more western one of two parallel faults in the middle layer running south to north east (perpendicular to river Weser). The conductivity of these faults can vary between two extremes: 1 m/s for the open water filled fault and 1E-9 m/s for the closed fault filled with very fine sediments. Well location, depth and pumping rate can be changed a little bit. If unavoidable also a cleaning well can be placed to catch contaminated water. With ModelMuse, MODFLOW and other USGS-tools the flow of contaminants must be checked and visualised and a combination of parameters found that enables the factory to get clean groundwater in a suitable way. The task is described in more detail in [4a] and [4b].
Summary of Chapters
1 Executive Summary: Provides an overview of the hydrogeological site conditions and the challenge of preventing landfill contamination of a production well.
2 Project Description: Details the site location, geographic coordinates, and the hydrologic setting of the Bremen region.
3 Data Assimilation: Explains the integration of borehole data and digital elevation models into the MODFLOW software environment.
4 Description of the groundwater model: Describes the spatial and temporal discretization, boundary conditions, and solver parameters used in the model construction.
5 Discussion of Flow Model Results: Analyzes the head distribution and water balance for different conductivity scenarios in the identified faults.
6 Description of scenarios: Compiles various model runs with different well locations, pumping rates, and the implementation of a cleaning well.
7 Conclusion: Summarizes the findings, proposing that a cleaning well is necessary to secure clean water extraction given specific fault conditions.
8 Recommendation for further work: Suggests future investigations regarding fault variability, long-term contaminant tracking, and seasonal data integration.
Keywords
Groundwater modeling, MODFLOW, Bremen, Contaminant transport, Hydrogeology, Aquifer, Fault conductivity, Pumping rate, Cleaning well, Advection, ModelMuse, MODPATH, Water budget, Spatial discretization, Well placement.
Frequently Asked Questions
What is the primary goal of this research?
The main goal is to determine if an industrial well in Bremen can extract clean groundwater without drawing in contaminants from a nearby landfill, and to design a system (such as a cleaning well) to mitigate such risks.
What software tools were used for the simulation?
The study utilizes USGS MODFLOW for groundwater flow modeling, ModelMuse as the graphical user interface, and MODPATH for particle tracking to simulate contaminant movement.
Which factors most significantly influence the simulation results?
The conductivity of the faults in the middle aquifer layer and the pumping rate of the production well are the most critical parameters determining whether the production well becomes contaminated.
What methodology was applied to assess contamination risks?
The author performed multiple steady-state model runs under varying conditions, using MODPATH to track particles from the landfill site to verify if they reach the production well.
How does the model handle boundary conditions?
The model uses the WEL-package for the production well and the RIV-package to simulate the river Weser, as well as general head boundaries (GHB) based on regional topographic and piezometric data.
What are the primary themes discussed in this paper?
The core themes include hydrogeologic characterization, numerical groundwater modeling, contaminant advection, and scenario-based engineering optimization for water quality protection.
Why are the faults considered a critical component of the model?
The faults act as potential high-conductivity pathways for contaminant transport; their conductivity levels (open vs. closed) dictate the flow path of groundwater and whether contaminants bypass or enter the production well.
What is the practical conclusion regarding the installation of a cleaning well?
The study concludes that a cleaning well positioned north of the landfill is an effective strategy to capture contaminants and safeguard the water quality of the production well, particularly in scenarios with open faults.
- Arbeit zitieren
- Dipl.-Ing., MSc, Rainer Stickdorn (Autor:in), 2015, Ground water and contaminant flow modelling in Bremen area, München, GRIN Verlag, https://www.grin.com/document/433459
