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ESTABLISHMENT OF A LEVELLING NETWORK FOR THE MONITORING OF POSSIBLE VERTICAL 
MOVEMENTS IN THE AREA OF PISA - SAN GIULIANO TERME-PONTASSERCHIO-MIGLIARINO PISANO (ITALY) 
G. Caroti (*), E. Mengali (*), A. Rossi (**), C. Scalese (*) 
(*) DIEIT, University of Pisa, Italy 
(**) HRG - CNR, Pisa, Italy 
ISPRS Commission VI, Working Group 3 
KEYWORDS: Compaction, Geothermics, Levelling, Subsidence 
ABSTRACT 
One of the wavs of inspection expected for the monitorig of the possible environmental alterations caused by the utilization of 
thermal underground waters in the heating of the buildings and laboratories of the CNR Research Campus in Pisa is the supervision 
of the surroundig district subsidence. 
Taking into account the well-known information about the extension and location of reservoir - rocks to be exploited we have located 
the area to be monitored: it consists of a broad part of Pisa, opening like a fan towards the north stretches to reach Migliarino Pisano 
and San Giuliano Terme, through a benchmark network by meshes which are narrower near the CNR complex and wider in more 
distant areas. 
1. INTRODUCTION: 
GEOTHERMAL SPACE-HEATING OF THE CNR 
RESEARCH CAMPUS IN PISA: 
PROBLEMS IN ENVIRONMENTAL MONITORING 
The joint venture project by ENEL and CNR proposes to heat 
the buildings and laboratories of the CNR Research Campus in 
Pisa, utilising thermal waters (60-70°C) by means of a doublet 
of wells. The project has been partly sponsored and funded by 
the European Union (Research Project U.E., ЕЮ XVII), the 
Regional Council of Tuscany, and the Italian Ministry for 
Industry. 
Right from the start the proponents were aware that they would 
have to overcome public distrust and suspicion for the use of 
this type of non-conventional energy'. 
Therefore the project is aimed at fostering the development of 
similar initiatives, in order to save fossil fuel and reduce the 
amount of air pollutants discharged into the atmosphere. 
The promotional effect of the Pisa CNR project could be further 
enhanced by demonstrating the benefits that can be achieved 
with the direct use of low-temperature geothermal energy, also 
in the residential part of such an old town as Pisa. 
Арап from its technical feasibility and innovative solutions, the 
most challenging aspect of the Pisa project will be to show the 
emironmental benefits, and to verify' the sustainability of 
geothermal development with time, provided an effective 
system of integrated networks is set up all over the Pisa area to 
monitor environmental natural parameters and improbable 
induced effects of this activity. 
The reservoir of the geothermal fluid is expected to he at a 
depth of 800-1200 m below ground level, with temperatures 
around 70°C, within the Mesozoic carbonate complex that is 
present throughout a large pan of Tuscany (Bellani et al., 1995). 
A production/reinjection doublet of directional wells will be 
drilled from the same drilling pad. The distance between the 
two well-bottoms will be about 1000 m. The geothermal fluid 
will circulate in a "closed loop" (carbonate formations, 
production well, heat exchangers, reinjection well, carbonate 
formations) as all the extracted fluid will be reinjected after use. 
There will be no direct contact with shallow aquifers, surface 
waters and atmosphere, thus preventing any pollution. 
The Pisa geothermal project is based on a very conservative 
analysis of the safety parameters, in order to prevent any risk. 
Nevertheless the Pisa plain cannot be considered a safe area in 
steady-state condition from the environmental point of view. It 
is a flat lowland area (2-3 m a.s.l.) that was flooded a few times 
by the Amo river in the past, and affected by natural historical 
subsidence. Precision levelling data show negative ground-level 
variations at a maximum rate of 1 cm per year during the period 
1969-1983 (Palla, 1988). This high rate of subsidence can be 
explained by a combination of natural and man-induced effects. 
The Pisa plain rests on a thick sequence of soft Quaternary 
unconsolidated sediments, and has been a marsh land since the 
Holocene; its reclamation was not complete until the first half of 
this century. Drainage of surface waters and pumping from 
shallow aquifers, in particular, increased the compaction rate of 
the shallower layers. The recent intensive urbanisation has 
further compromised the delicate equilibrium of the foundations 
of the city' buildings. 
Subsidence is commonly caused by the settlement and 
compaction of recent sediments and does not affect the deep 
Mesozoic carbonate substratum, at least on a human time-scale. 
The production-reinjection process will be developed through a 
closed loop between the surface heat exchangers and the deep 
carbonate formations without interacting with the cover 
formations, from which the wells will be completely isolated. It 
must be stressed that hydrothermal exploitation will not entail 
any extraction of mass, but only of heat. 
The draft programme of an integrated system of monitoring 
networks has therefore been carefully studied to answer the 
demanding questions on the various environmental aspects of 
the geothermal development The svstem consists of: 
1. A topographic network for monitoring the vertical ground 
movements by means of periodical surveys with precise 
levelling and Global Positioning System methods. 
2. A microgravity network, utilising about 30 % of the 
benchmarks of the topographic network, will help to 
detect, with periodical surveys, any crustal mass variation, 
fluid displacements, and water level changes in surface 
acquifers. 
3. A hydrogeochemical monitoring network of the 
unconfined and confined shallow aquifers in 5 existing