B. Hakim et al.
1. Introduction
Prior to the construction and the operation, by Andra (French Agency for Radioactive Waste), of the future deep
geological repository for high and intermediate long lived radioactive waste, an analysis and evaluation of pre-
dictive hydraulic impacts which could be induced by the underground structures (shafts and tunnels) linking
surface installations to the rad waste disposal located in the clay formation of Callovo-Oxfordian age (160 My)
at depth of 500 m.The clay host formation of Callovo-Oxfordian age is found throughout the multilayered sedi-
mentary fill of the Paris basin. The Callovo-Oxfordian layer is located between an overlying limestone of Ox-
fordian (Jurassic) age and an underlying limestone of Dogger (Jurassic) age. The potential repository emplace-
ment is located in the Meuse/Haute-Marne sector which includes two nested zones: 1) transposition zone ZT and
2) the ZIRA. The transposition zone has been chosen as a suitable host domain based on 20 years of site inves-
tigations results; it extends over an area of approximately 250 km2. In the transposition zone, the Call-
ovo-Oxfordian formation is encountered at a depth of roughly 500 m, with a minimum thickness of approxi-
mately 130 m and a very small hydraulic conductivity (less than 10−12 m/s). Andra has carried out several inves-
tigation campaigns considering the chosen host domain and its surroundings and also carried out extensive site
descriptive modelling. The aim of the site-descriptive modelling is to develop a discipline-integrated description
of the past and present conditions at the site, by analysing, assessing, and modelling the data obtained from the
investigation campaigns. “ZIR A” is an area extending over 30 Km2 selected for further investigations, will be
emplaced, five shafts with a diameter of 5 m to access the repository. Two access tunnels represented in the
model by one ramp of over 5 Km length, 13 m of diameter and with a slope of about 12. This ramp will join the
shafts in the host formation of the Cal lo vo -Oxfordian at about 500 m of depth.
2. Conceptual Model and Mathematical Formulation
2.1. Geological Model, Engineered Structures and Data Monitoring
The hydrogeological conceptual model consists of 27 layers from the Triassic to Tertiary at the scale of the Paris
basin and the 28 layers of the Triassic to Neocomian/Berriasian on the sector scale. The geological conceptual
model represents the multilayered system including regional local faults and fracturing zone mainly located south
west of the “ZI R A” which is the potential emplacement for the future repository. The construction of this geo-
logical concept was based on over 3300 drill holes data and about 2800 Km of seismic profiles.
Modelled domain is extracted from an integrated hydrogeological region-sector model which consists of the 1)
27 layers from the Triassic to the Quaternary on the scale of the Paris basin and 2) the 28 layers from the Trias-
sic to the Portlandian on the scale of the sector. Lateral extend covers an area of about 3000 Km2 which large
enough to contain the hydraulic perturbation of repository construction. Vertically, only the geological layers
above the Callovo-Oxfordian host formation which will host the underground structures (shafts and access tun-
nels) are represented. The first formation overlying the Callovo-Oxfordian is the Oxfordian formation consi-
dered as an aquifer and consists of limestones of Oxfordian age and early Kimmeridgian age and with a mean
thickness at the repository potential emplacement of about 290 m. In the area of interest, this aquifer is split into
two aquifer units separated by a marl layer called “sériegrise”. Macro-pores zones identified through drill holes
data and seismic survey results were characterized as relatively water productive with hydraulic conductivity
ranging from 10−9 m/s to 10−7 m/s. Marne and limestone hydraulic conductivity are of 10−12 m/s and 10−9 m/s to
10−10 m/s respectively.
The 7 identified macropores zones are represented in the model by four relatively productive units:
• Hp1-4: lower unit located in deep Oxfordian with a mean thickness of 55 m;
• Hp5 confined by the marl;
• Hp6 and Hp7 belong to the Upper Oxfordien. Hp5, Hp6 and Hp7 have a mean thickness of about 5 m.
Kimmeridgianmarl layer overlying Oxfordian has men thickness of about 100 m and hydraulic conductivity
estimated to 10−12 m/s. Measured specific storage values of the macro-pores zones ranges from 2.3 × 10−6 m−1 to
3.0 × 10−6 m−1
For the simulations of the hydraulic impact of the access shafts to the Underground Research Laboratory
(URL), it has been supposed that the perturbations of the flows will not affect the host formation northe under-
lying layers. It has thus been decided to uniquely model the layers on top of the Callovo-Oxfordian as a surface
that comprises the sedimentary structures of the Oxfordian (the porous horizons and gray marl series).