REGIONAL INFORMATION:
Friuli-Venezia-Giulia / Italy

The aim of Integral Pumping Tests application in the Pilot Area in Arcade is to identify the source of groundwater pollution (PCE), previously detected in local groundwater in a single well named AR3. The potential source was identified on the basis of the IPT tool application, consisting in some pumping cycles in No. 4 wells, 3 of whom are new executed. All the hydrogeological system is also monitored by a specific monitoring network, set up with suitable piezometers, some of whom drilled during the Foks Project.

Pilot area is located in Arcade and the survey has been focused on a limited area in the southern part of the municipality territory, with the aim to identify the PCE contamination pattern in the area immediately upgradient of the AR3 well. At the moment the narrow monitoring network is made up by MW1, MW2, MW3, MW4, AR3, AR16, AR17.

What has been realized:

The investment action of the Province of Treviso was characterised by 3 main phases:
– First phase: acquisition of knowledge about the hydro-geological situation of the pilot area and of the spread of the contamination in the groundwater; in this phase, the following activities were carried out: video-inspection in the AR3 well, drilling of the MW1 and MW2 piezometers and part of the chemical analysis in the groundwater
– Second phase (characterized by the main activity in the pilot area): first pumping cycle with IPT in the AR3 well and, on the basis of the results of the chemical analysis, it was possible to define the location of the wells for the IPT (P1, P2 and P3); drilling of 3 wells and same number of pumping cycles with additional water analysis;
– Third phase: the information acquired during previous activities were used to better identify the source of contamination; for this reason, the MW5 piezometer was drilled and chemical analysis with passive sampling and low-flow methods were performed; the aim was to determine the spread of the concentration (in depth) and suppose the “distance” and the
characteristics of the source.
Total count: n° 155 chemical analysis of which 100 only of chlorinated solvents and 55 complete analysis; n° 32 chemical analysis with passive sampling and n° 32 chemical analysis with active lowflow sampling.

The study area is located in Veneto alluvial plain and is characterized by sandy gravel alluvium deposits with high values of hydraulic conductivity (10-1- 10-3 cm/sec) where an unconfined aquifer exists (groundwater depth = 20-30 m below ground level).

Locally there are some aquitards composed by silty – clay layers or cemented gravel.

The stratigraphic and hydrogeological model has been improved in the macroscale field since it was not clear or exhaustive enough and for this reason all the borehole information on the area has been acquired.

During the monitoring campaign a submersible pump (Grundfos MP1) with an inverter device for pumping rate regulation has been used in all the wells and all sampling has been performed at low-flow, in order to minimize aquifer disturbance and to avoid resuspension of settled solids. Every time sampling followed a purging step in order to collect a representative sample of the aquifer physical and chemical characteristics. Samples have been stored in bottles of appropriate material, labelled, in refrigerated container and then delivered to the laboratory.

The analysis plan defined by the laboratory concerned these parameters:

• 1,1,1-trichloroethane
• trichloroethylene
• tetrachloroethylene (PCE)
• chloroform
• carbon tetrachloride
• dibromochloromethane
• 1,2-dibromoethane
• bromoform
• 1,2-dibromo-3-chloropropane
• chlorinated solvents

The chemical status of the aquifer is summirized by the following table, indicating PCE concentrations determined by well sampling in the period May – September 2010. Concentration above the groundwater regulatory threshold value (1,1 μg/L), stated by the annex 5 to the fourth part of the Legislative Decree n. 152/2006, are marked.

Data evaluation leads to some conclusions:

• AR3, MW1 e MW2 show the excess of the regulatory limit;
• even the other wells of the narrow monitoring network show presence of PCE although below the limit;
• all the other parameters are below the regulatory applicable limit and sometimes even below the detection limit;
• the vertical PCE concentration pattern, resulting from the 08/07/2010 GW sampling in MW3 and MW4, did not show any differentiation in relation to the depth: the average concentrations, showed in table 1, are, respectively, 0.35 μg/L and 0.12 μg/L;

A preliminary IPT test has been performed in the existing AR3 well in the period from 08.09.10 to 13.09.10. The planned 3 new IPT wells (P1, P2, P3) are currently going to be drilled, the IPT tests are scheduled to start on December 2010.

IPT planning

The first Integral Pumping Test was conducted in a single well (AR3) for 83 hours of continuous pumping (Q = 0.02 m3/s) with 15 time steps of sampling.

During the planning of IPT it was made an estimation of maximum capture area of the pumping well and calculation of time steps for groundwater sampling, on the basis of previous hydrogeological information derived from the WP3 activities conducted in the first periods of the Foks Project .

The results of IPT from the well AR3 were evaluated for PCE concentration by using the analytical software developed in the frame of the Project MAGIC (INTERREG IIIB CADSES) – the MAGIC Software tool.

The hydrogeological context was sufficiently well-known and the parameters used as inputs for the interpretation tool MAGIC are the following:

• k (hydraulic conductivity) = 2.2 e-3 m/s
• ne (effective porosity) = 0.2
• i (hydraulic gradient) = 0.0017
• b (saturated aquifer thickness) = 20 m

With a pumping rate of 20 l/s the width of the capture zone at the end of the test is estimated to be around 42.7 meters.

Based on these data, the MAGIC tool analytical model calculate the width of the capture zone and the increase of width at each sampling interval. The final sampling intervals have been chosen in order to achieve an equal increase of width for each step. This results has been obtained foreseeing 15 samples with increasing time gap (the first one after 0.4 hours from the beginning of pumping, the second after 1.6 hours, the third after 3.6 hours and so on).

The result of this estimation has been compared with a numerical solution (Modflow 2000), to confirm the extension of the capture area and the validity of the hydrogeological parameters. This way the analytical model included in MAGIC has been calibrated with a finite difference model, gaining more accuracy and reliability.

IPT implementation

The IPT test in AR3 well has been performed with a submergible pump placed in the well after the removal of the equipment used by the owner for garden irrigation. Pumping rate has been hold constant and equal to 20 L/s for 83 hours during which the samples have been collected.

The groundwater withdrawn from the well has been discharged in an artificial irrigation ditch through a provisional tube.

IPT test followed a calibration step of the pumping regulation system, pumping rate has been measured with a Woltmann volumetric flowmeter. A sampling cock has been installed directly on the tube in order to collect GW samples causing the least disturbance. Before the beginning of the IPT test groundwater depth has been measured in AR3 and also in MW1, MW2, MW3, MW4 and AR16 wells with data logger for continuing GW level
measurement and registration.

Results

Times of taking sample during IPT in AR3 are stated in the following table, with PCE values detected:

The chemical results have been processed with the Circle Method interpretation included in MAGIC software tool; it was assumed left or center plume passage, obtaining the following values of measured and calculated PCE concentration in relation to the distance from the pumping well:

The graphical representation of the “time vs. concentration” data series is shown in the next two pictures:

Both left and center plume passage interpretations indicate a decreasing trend of PCE concentration, reaching at the end of the test a value included in the range of 1.4 – 2.8 μg/L, equivalent to the 5-8 % of the initial concentration.

So, according to the IPT interpretation theory, we can consider that in the beginning of the test we detected the center of the PCE plume and later, increasing the radius of the capture area, we came close to the lateral bounds of the plume.

Data interpretation is not unambiguous because a single IPT test does not allow to locate the plume on the left or on the right of the well. Anyway the IPT test helps to identify the spatial distribution of contamination inside the investigated area and the probable position of the plume IPT performing in 3 new wells upgradient AR3 named P1, P2 and P3, currently under execution, will give a better definition of the contamination plume.

Besides chemical results, also GW level data, recorded in MW1 MW1, MW2, MW3, MW4 e AR16 during IPT test, have been elaborated.

The following graphic shows the trends of data from September the 5th to 13th. The maximum equilibrium drawdown recorded in AR3 was about 1.6 m.

Monitoring wells did not show any influence of the pumping test. In fact the general decrease of the water level, as shown in the graphic, is the same regardless the pumping action in AR3.

As a consequence the actual position of monitoring wells did not allow to collect useful data for the hydrogeologic characterization of the aquifer during IPT because the nearest well, MW1, is out of the capture zone of AR3.

The recovery curve shows an almost instantaneous recovery of the groundwater level right after the switch off of pumping, thus confirming a grat capacity of recharge of the aquifer.

The capital is Trieste and the territory comprises mountains (42.5 %), hills (19.3 %) and plains (38.2 %). The region’s economy is diverse and includes agriculture, manufacturing and building industries, commerce, tourism and others.

The Region has a high energy dependence, importing solid and liquid fuels, as well as natural gas that in 2003 amounted to 94.8 % compared to the national level of 91.3 %. However the growth of renewables has lowered energy imports at regional level, although they still remain rather high compared to other EU countries.

RES play a relevant role at regional level: hydro power is the first renewable energy source, followed by biomass and solar PV. RES at regional level increased remarkably in the last years, in particular solar PV supply and bioenergy consumption. The overall RES-E installed capacity amounts to 1 078 MW, 31 % of the total electricity capacity. The breakdown of total final energy consumption at regional level shows that energy demand in 2008 was primarily driven by the industrial sector (44 %), followed by transport (21 %), household (18 %) and finally commerce and public sectors (17 %). Regarding energy carriers, natural gas (methane) was the main one in 2008, followed by electricity, liquid fuels (oil), solid fuels and renewables. Natural gas is used in the industrial sector, in thermo-electrical installations and distributed into regional grids.

Hydro power will retain a dominant position