Groundwater Management and Governance - Coping with Uncertainty - BGR
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Groundwater Management
and Governance
Coping with Uncertainty
Proceedings of IAH2019, the 46th Annual Congress of the Interna onal Associa on of
Hydrogeologists, Málaga (Spain), September 22-27, 2019
Spanish Chapter of the Interna onal Associa on of Hydrogeologists (AIH-GE)
J. Jaime Gómez Hernández & Bartolomé Andreo NavarroParallel / 412
Dealing with seawater intrusion in the Chtouka Aquifer, Morocco
Henrik Schreiber1 ; Fatima Abourrig2 ; Oussama Ait Raoui2 ; Leonard Stöckl1
1
Bundesanstalt für Geowissenschaften und Rohstoffe
2
Agence du Bassin Hydraulique du Souss Massa
Corresponding Author(s): henrik.schreiber@bgr.de, aitraoui.oussama@gmail.com, leonard.stoeckl@bgr.de,
fatima.abourrig@gmail.com
The joint technical cooperation project CREM (Coopération régionale pour une Gestion Durable des
Ressources en Eau au Maghreb) of OSS (Observatoire du Sahara et du Sahel), BGR (Federal Institute
for Geosciences and Natural Resources), and GIZ (German Society for International Cooperation) is
funded by BMZ (German Federal Ministry for Economic Cooperation and Development) and fosters
the exchange of groundwater management strategies between the three countries Morocco,
Algeria, and Tunisia. The strategic focus in the pilot area of Souss-Massa, Morocco, by BGR is on
saltwater intrusion.
The Souss-Massa Basin is the country’s most important agricultural area. Groundwater from the
coastal Chtouka aquifer is the main source for irrigation. The heavy exploitation of groundwater
leads to declining water level in the sub-basin, with the effect of intruding seawater from the
ocean. Several measurement campaigns were launched together with the ABHSM (Agence de
Bassins Hydrauliques Souss-Massa) and the University of Agadir. Wells and monitoring boreholes
along the coast were visited, altitudes and water level data were gathered, and depth specific
electrical conductivity profiles were taken.
Results show an average groundwater depletion of up to 1.5 m per year in several locations. Due to
this depletion, a change of the general flow direction in the Chtouka Aquifer was found. The
mobilisation of high saline water from the south of the plain and the marine intrusion threaten
the irrigated zones. The hydrochemical analyses identified a zone of wells with marine influence.
Additional monitoring wells were drilled. A three dimensional density dependent numerical model is
used to simulate groundwater flow and the development of salinities in the Chtouka aquifer.
Countermeasures are already in progress, e.g. the construction of a water desalination plant for
agricultural purposes and a so-called aquifer contract. In international workshops, the project’s
results, as well as strategies are discussed with the aim to transfer the achievements to other
OSS member countries, i.e. Tunesia and Algeria.
64Parallel / 54
Exploration of deep groundwater systems in mega-fans Example from
Northern Namibia
Author(s): Georg J Houben1
Co-author(s): Paul Königer 1 ; Christoph Lohe 1 ; Stephan Kaufhold 1
1
BGR
Corresponding Author(s): georg.houben@bgr.de
Mega-fans are inland riverine deltas occuring in endorheic basins. Their potential as hosts of major
aquifer systems has only been recognized rather lately.
The Cubango Mega-fan in Northern Namibia contains three aquifer systems, of which the deep
one was only found at the end of the 1990s. Due to its thickness of up to 100 m, its large size
and good water quality it is a game changer for the arid North of Namibia. Its spatial distribution
and sedimentological background was investigated through core drilling and both geophysical and
hydrogeological techniques. Due to the large size of the system, data scarcity is a constant issue
affecting the exploration and management of this resource.
Core drilling revealed that the system comprises two major formations of Tertiary age, originating
from different source Areas. The cores also contain an archive of the development of the climate of
southwestern Africa. The sedimentary background defines the hydrogeological structures.
Groundwater modeling was applied to investigate the rate and location of groundwater
recharge. Recharge rates are as low as 2-3 mm/a and limit potential extraction. This needs to be
considered in management plans. Remote sensing (satellite radar altimetry) was applied to
confirm the recharge areas. They are found in Southern Angola, making it a transboundary aquifer
system.
Similar mega-fan systems can be found in other parts of Africa and worldwide. Their
hydrogeological potential is high but needs to be investigated in the future. The Namibian case
can serve as a blueprint.
81Parallel / 322
Reassessing groundwater resources in the southern Iullemmeden Basin:
Combining archival data and current monitoring
Matthias Heckmann1 ; Kolja Bosch1 ; Stefan Broda1 ; Sara Vassolo1
1
Federal Institute for Geosciences and Natural Resources (BGR)
Corresponding Author(s): matthias.heckmann@bgr.de
Groundwater resources in Sub-Saharan Africa are promoted by development organisations as
reliable alternatives to ensure water supply for human consumption and agricultural use. National
efforts to map and monitor groundwater quality and quantity, however, are not adequate to promote
sustainable groundwater management. Within a technical cooperation project, the Federal Institute
for Geosciences and Natural Resources (BGR) supports the intergovernmental Niger Basin Authority
(NBA) and its nine member states to establish groundwater-monitoring networks, map the quality
and quantity of the groundwater resources, and elaborate tools for groundwater management.
The paper presents a reassessment of the groundwater resources of the southern Iullemmeden
Basin derived from the combination of archival data and recent measurements within the AGES
monitoring network. To improve the limited coverage of national databases, the technical
cooperation project strives towards the valorization of so-far neglected grey literature and archival
data including, among others, the groundwater appraisals of the mid-20th century as well as available
reports of (inter-) national development projects.
A major challenge for the harmonization process is the differentiation of the multi-layered aquifer
system of the Iullemmeden and the assignments of wells to one of the aquifer storeys of the
Continental Terminal (Ct1-3) and the Continental Intercalaire/Hamadien. Unreliable lithological and
technical profiles together with the usual tapping of multiple aquifer storeys to increase productivity
limit the use of both archival and contemporary measurement data for the characterization of
defined groundwater levels.
To create a consistent conceptual (hydro-)geological model, a general reassessment/revision of
borehole lithology and stratigraphy became necessary. We explore the geostatistical approaches to
discriminate groundwater bodies based on water chemistry, hydraulic head, and isotope data to
improve the original lithostratigraphic classification.
Valorization of archival data – with the respective thorough quality checks – is underestimated
provides necessary baseline data for groundwater management.
132Parallel / 216
What hydrogeology can learn from data science in terms of reproducible
research
Maximilian Nölscher1
1
Federal Institute for Geosciences and Natural Resources (BGR)
Corresponding Author(s): maximilian.noelscher@bgr.de
Programming and machine learning play an increasingly important role as part of research methods
in most scientific disciplines, including geosciences, as the volume of data collected increases
exponentially. In hydrogeology, it is used for data pre-processing, analysis, prediction, or
visualization. However, when trying to apply or adapt promising methods to one’s own data, it is
often difficult or even impossible because of poor documentation. Therefore, it is essential to make
use of state-of the-art methods for the documentation of research methods that include code to
maximize reproducibility, transparency and the ability of collaboration in hydrogeology. The quality
of the documentation is also fundamental for a fast transfer of knowledge, methods and related
errors.
This state-of-the-art documentation has been developed and applied for several years mainly in
computer science and data processing. At the lowest level, this includes the supplementary
publication of well-named and structured script files according to ideally existing conventions and at
the highest level the publication of a socalled Jupyter notebook on a development platform such as
Bitbucket, Github or others. Easily reproducible research not only requires high-quality
documentation, it begins with a shift from hard-to-document analysis tools such as spreadsheets to
programming languages for data science and geospatial data processing. The most common
documentation tools from neighbouring disciplines will be presented and discussed to make
hydrogeological research more accessible and accelerate knowledge transfer. Especially because
speed in gaining new insights into the consequences of climate change is a key component.
159Poster / 259
Determining the apparent age of old groundwater of the deeplying
Ohangwena aquifer in the Kalahari Basin, Northern Namibia
Roland Bäumle1 ; Torsten Krekeler1 ; Paul Koeniger1
1
Federal Institute for Geosciences and Natural Resources
Corresponding Author(s): paul.koeniger@bgr.de, torsten.krekeler@bgr.de, roland.baeumle@bgr.de
In arid areas, underground reserves of water from deep sedimentary aquifers containing old
groundwater, probably recharged thousands of years ago, have been recognized as a valuable
additional source of drinking water. The recently discovered, deep-seated groundwater reservoir of
the Ohangwena (KOH-2) aquifer forms part of the north-south trending Cubango Megafan
deposited in the border area between Angola and Namibia. It has been explored at depths between
about 250 to 350 meters in northern Namibia in an area between 17.3 and 18 degrees southern
latitude and 16 and 17.3 degrees eastern longitude. The amount of stored groundwater in the KOH-
2 aquifer on Namibian territory is conservatively estimated at 20 billion cubic meters. A proper
understanding of the origin, history and dynamics of the presumably very old groundwaters found
in the KOH-2 aquifer is a key for the assessment of the reliability and potential of this aquifer as a
strategic resource for supply of drinking water into the future.
The objective of the study is to determine the apparent age of the groundwater in the KOH-2 and
to improve the understanding of the hydrogeological setup of the multilayered aquifer system
developed within the Cubango Megafan. An overall aim is to investigate the use of long-lived
radionuclides, particularly 4He and 81Kr, to assess their reliability as age tracers of old groundwaters.
The use of the radioactive 81Kr and 36Cl isotopes, with a half-life of 229,000 and 301,000 years,
respectively, allows an estimation of recharge over timescales ranging from 50,000 to several
hundred thousand years, a range beyond the reach of radiocarbon. Concentrations of radiogenic
4He derived from the decay of uranium and thorium in deep groundwater may be used as a
qualitative or semiquantitative age proxy.
A comprehensive sampling campaign was carried out during March 2019, which comprised eight
deep boreholes of the KOH-2 aquifer. The apparent groundwater ages will be determined from gas
and water samples using radionuclide dating techniques comprising 85Kr/81Kr, 4He, 14C and 36Cl.
In order to extract bulk gas from groundwater, a new field-gas extraction device was developed
comprising a commercially available hydrophobic semipermeable membrane contactor, a membrane
vacuum pump, a compressor and a memograph to record gas pressure and water flows. For each
well, the gas was collected in a 12.3 L evacuated stainless steel cylinder and compressed to 1.5 bar.
Krypton separation from the bulk gas acquired in the field is currently performed at the University
of Bern, Switzerland. Krypton abundances are determined using atom trap trace analyses (ATTA) by
the National Laboratory Argonne, U.S.
The research is carried out as under the international Coordinated Reseach Programme “Use of
Longlived Radionuclides for Dating Very Old Groundwaters” (F33023) initiated and coordinated by
the International Atomic Energy Agency (IAEA).
315Parallel / 348
A quantitative appraisal of groundwater head time-series measurement:
How well are we doing?
Vincent Post1 ; Gabriel Rau2 ; Margaret Shanafield3 ; Eddie Banks3 ; Philipp Blum4 ; Torsten Krekeler1
1
Federal Institute for Geosciences and Natural Resources (BGR), Hannover, Germany
2
Karlsruhe Institute of Technology (KIT), Institute of Applied Geosciences (AGW), Engineering Geology, Karlsruhe, Germany
and Connected Waters Initiative Research Centre, School of Civil and Environmental Engineering, UNSW Sydney,
Sydney,Australia
3
National Centre for Groundwater Research and Training and College of Science and Engineering, Flinders University, Adelaide,
Australia
4
Karlsruhe Institute of Technology (KIT), Institute of Applied Geosciences (AGW), Karlsruhe, Germany
Corresponding Author(s): vincent.post@bgr.de
Accurate determination of subsurface water levels is essential for the reliable quantification of
hydraulic head gradients from which groundwater flow is inferred. Head measurements also
underpin the quantification of hydrogeological properties based on aquifer pumping tests or tidal
propagation analysis. While measuring a water level seems an easy task, the collection of water level
time-series data is by no means trivial and there is a high potential for errors and misinterpretation.
In this contribution we comprehensively analyse the individual measurements required to determine
hydraulic heads and gradients: (1) geo-spatial positioning, (2) manual water depth, (3) automated
pressure, and (4) spatial reference point for the head. For each component we determine the
systematic and random errors based on our own data sets and field experience, as well as data from
the literature. We assessed the effects of instrument and clock drift, variable density inside the
piezometer, borehole inclination, well aging and instrument performance. By propagating the
minimum achievable random measurement errors for horizontal and vertical hydraulic gradient
calculations we evaluated the accuracy with which groundwater flow processes can be quantified
using current best practice. The largest errors contributing to hydraulic head and gradient
uncertainty originate from borehole inclination and manual water depth measurement, respectively.
Our analysis demonstrates that resolving head gradients, which are smaller than 0.01 for boreholes
that are closer than 10 m, requires extraordinary effort.
444Parallel / 654
Are 253 samples better than 65 samples? Urban groundwater monitoring
in developing countries – Lessons learnt in N’Djamena, Chad
Mélanie Ronelngar Ndedje-Allah1 ; Maike Groeschke2 ; Khazali Abdoulayhi3 ; Sara Vassolo2
1
BGR Chad
2
Federal Institute for Geosciences and Natural Resources (BGR)
3
CBLT BGR Chad
Corresponding Author(s): sara.vassolo@bgr.de, maike.groeschke@bgr.de, cblt.bgr.hydrogeologie@gmail.com
In the frame of a technical cooperation project between the Lake Chad Basin Commission and the
German Federal Institute for Geosciences and Natural Resources, four groundwater sampling
campaigns were conducted in the Chadian capital N’Djamena in 2013, 2016, 2017, 2018. 253
samples were taken from 67 private bore wells equipped with handpumps and 16 large-capacity
production wells of the public water supplier. The first campaign was designed to get an overview
of the chemical and bacteriological groundwater quality and included samples from 52 private wells
from across the entire city area and 13 production wells within the city. The subsequent sampling
campaigns were conducted for monitoring purposes. Many 2013 sampling points were broken or
inaccessible in the following campaigns and were replaced by wells in the vicinity. Only 32 private
and nine production wells were sampled in all four campaigns.
The 2013 campaign identified bacteriological contamination, elevated nitrogen, and fluoride
concentrations as the main areas of concern. While 40 % of the private and 23 % of the production
wells contained fecal bacteria, nitrogen species and fluoride were found (with one exception) to be
below the WHO guideline values. Although the subsequent sampling campaigns confirmed this
general picture, the overall benefit of the additional 188 samples was limited to the finding that
nitrogen concentrations were increasing in some points. In 2016, 2017, 2018 two, five, and four
samples, respectively exceeded the WHO guideline value of 50 mg NO3/L. However, the
distribution of the nitrate hot spots were somewhat random and it was not possible to draw more
than general recommendations (e.g. protection zones around wells) from these findings.
In 2019, a survey was started to measure the total depths of all sampled wells and to make an
inventory of possible sources of contamination. Re-evaluating the collected data in the light of this
additional information leads to some insights on contaminant pathways, but most importantly, clearly
shows that the monitoring network needs to be optimized. (1) Before choosing a sampling location,
the well depth must be known and the future accessibility ensured: Replacing a broken well by any
random well in the proximity does not help, unless both wells are filtered in the same depth and
additional sources of pollution can be out ruled. (2) The construction of new observation wells is
inevitable, as our data proves that random wells close to production wells cannot be used for
monitoring purposes. (3) An additional focus on mapping of the sewerage system (design and
construction years) is necessary to make predictions about the future development of nitrogen
concentrations. In technical cooperation projects, baseline samplings are an important tool to identify
problems, but groundwater monitoring needs more careful planning to be cost effective
449Poster / 676
Transport modelling of Chloridazon-metabolites in soil and groundwater
Christoph Neukum1 ; Knut Meyer2
1
Federal Institute for Geosciences and Natural Resources
2
State Authority for Mining, Energy and Geology
Corresponding Author(s): knut.meyer@lbeg.niedersachsen.de, christoph.neukum@bgr.de
The occurrence of Metabolites (European Commission 2003) in groundwater resources, which are
used for drinking water, has become increasingly the focus of attention in recent years water
resource management. Currently, the use of approved herbicidal active substances, their metabolites
in increased concentration, which have been detected in 20 water conservation areas (WSG) of
Germany are prohibited according to the application restriction NG 301 (BAnz 2018). The
prohibition applies mainly on the since 1964 in Germany approved herbizide Chloridazon. It is mainly
applied during cultivation of beets but also for beetroot and mangold (chard). Chloridazon degrades
into the metabolites desphenyl-chloridazon (B) and methyl-desphenyl-chloridazon (B1) during
transport through soil. The Health Related Indication Value (HRIV) for both metabolites is 3μg/l. A
coupled flow and transport model of the vadose and phreatic zone is used to estimate the long-term
solute concentration in groundwater and the related consequences for drinking water quality of a
gravel aquifer used for water supply. Parameterization of the models is based on data from long-
term soil monitoring in Lower Saxony, on monitoring data from a drinking water abstraction wells
and on published environmental fate properties of Chloridazon and its metabolites. The modelling
results show the spatial-temporal evolution of solute concentration and related uncertainty of the
model predictions.
724Poster / 737
Uranium and arsenic in groundwater on Fogo Island, Newfoundland,
Canada
Leonard Stoeckl1 ; Paul Dean2 ; Shawn Duquet3 ; Dorothea Hanchar3 ; Sara Vassolo1
1
Federal Institute for Geosciences and Natural Resources, Hannover, Germany
2
Fogo Island Geology Center, Newfoundland, Canada
3
Municipal Affairs and Environment, Newfoundland and Labrador, Canada
Corresponding Author(s): leonard.stoeckl@bgr.de
Fogo is an island with a surface of around 237 km², located in the northeast of central
Newfoundland. Around 2,400 people live on the island. The geology mainly consists of granites with
an age of around 410 million years. Some dolerite intrusions as well as ash-flow tuffs appear locally.
It is known that a statistically high number of residents on Fogo Island suffer from cancer (personal
communication with the local hospital), although the cause for high cancer rates is not confirmed.
However, it is assumed that consumption of untreated water might be the cause, if high uranium (U)
and/or arsenic (As) levels are present. This assumption justifies the investigations presented here.
A water sampling campaign was conducted in August/September 2018 to assess concentrations in
different water supply wells on Fogo. Analysis revealed that 6 out of 20 groundwater samples in
Central Fogo and Joe Batt´s Arm show exceedances of the maximum admissible concentration (MAC
= 10 ppb) and 3 out of them exceeded 20 ppb. Additionally, the MAC for uranium (20 ppb) is
exceeded in 9 out of 20 groundwater samples. Except one sample, all wells with high arsenic
concentrations show concurrently elevated uranium concentrations. No arsenic or uranium
exceedances, however, are found in any of the surface water samples from brooks and springs or in
Joe Batt´s Arm in the north. In Central Fogo, As is elevated east of Highway No 333, while samples
in the west do not show values exceeding MAC, potentially indicating different groundwater flow
paths, here.
Curie (2003) as well as Sandemann and Malpas (1993) analyzed uranium concentrations in 53 and
9 rock samples (mainly granites), respectively, in different areas on Fogo Island. In contrast to
concentrations found in groundwater, these measurements reach maximum values of 9 ppb in Shoal
Bay granite and 7 pbb in ash-flow tuffs, only. Different processes are known to enhance
accumulation of radionuclides in groundwater (physical recoil, chemical weathering and milieu
changes, e.g. low redox potential fronts). Long groundwater residence times, and thus contact times
with the bedrock, are crucial for these processes.
The wide range of As and U concentrations over a short distance of around 2 km in Central Fogo
suggests that different groundwater flow paths exist within this limited area. Despite no MAC
exceedances were found in treated water samples, e.g., by reverse osmosis, it cannot be concluded
that such water samples are always free from As or U. Monitoring of U and As on Fogo island in
drinking water is strongly recommended in future.
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