Geosynthetics October/November 2019 - 19

Case Study

Remediation of a uranium
ore residues settling basin
By Laura Carbone, Ole Syllwasschy and Lilma Schimmel

n the past, the Soviet-German stock company Wismut carried out an intensive
uranium mining operation resulting in a large amount of polluted tailings
containing daughter nuclides of uranium (Koß 1997) that were released into
industrial sediment ponds (named IAA). The tailings "Pond 4" was built in 1957
and worked as a settling basin for residues of uranium ore treatment from January
1958 to December 1960. Due to its morphology, the pond acted also as a rainwater retention basin, and in 2006, the regional Authority of Water Management
declared Pond 4 as a contaminated site to be remediated.
Generally, the management of tailings ponds consists of three main steps:
solid-liquid separation, sludge dewatering and disposal (Zinck 2005).
For Pond 4, the remediation concept consisted of an impermeable capping,
which mainly aimed at 1) isolating the residues and therefore reducing the exposure of uranium radiation, and 2) preventing new leakage formation by limiting
the infiltration of water into the pond.
In Pond 4, despite the very soft subgrade, the construction of the cover system
has been made possible thanks to the introduction of geosynthetics into the system
combined with the use of vertical drains in some areas of the pond (Figure 1). In
this article, the remediation of Pond 4 in Freital, Germany, through an impermeable
capping is presented. Particular attention is given to the use of geosynthetics in the
system. Thus, a detailed description of the use and design of the geosynthetics for
the Pond 4 capping system is presented. The stability analysis, the selection of the
materials and the installation phases are described.

Capping system of impoundments: Main generalities
Impermeable capping systems mainly aim at:
* isolating the residues and therefore reducing the exposure of the contaminated materials
* preventing new leakage formation by limiting the infiltration of water into
the pond
An impermeable cover system for pond closure is composed of a sealing layer,
a drainage layer and topsoil. The layers and their thicknesses may vary according

PROJECT HIGHLIGHTS
CAPPING A URANIUM ORE
RESIDUES BASIN
OWNER

WISMUT GmbH, Chemnitz
LOCATION

Freital, Germany
GENERAL CONTRACTOR

Heitkamp Erd- und Straßenbau
DESIGN ENGINEER

G.E.O.S. Ingenieurgesellschaft
mbH, Halsbrücke
GEOSYNTHETICS PRODUCT

Base 40, nonwoven E 250
K4 and E 150 K3, Basetrac
woven PP 80, 2 SoilTain
dewatering tubes
GEOSYNTHETICS MANUFACTURER

HUESKER Synthetic GmbH

Laura Carbone, Eng., Ph.D., is
senior engineer with HUESKER
in Gescher, Germany.
Ole Syllwasschy, Eng., is expert engineer
with HUESKER in Gescher, Germany.
Lilma Schimmel, MSCE, P.E., is
engineering department head with
HUESKER in Charlotte, N.C.
All figures courtesy of the authors unless otherwise noted.

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Geosynthetics October/November 2019

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