Next aims and future plan for the activities in Arcade:
- Drilling th third IPT well (P3) within the 22nd of December 2010;
- IPT Test in P1 from 16 to 19 of December 2010;
- IPT Test in P2 from 27 to 30 of December 2010;
- IPT Test in P3 from 10 to 15 of January 2011;
- Continuing with the automatic monitoring network of the groundwater level;
- Other campaign of sampling and analysis in January 2011 (maybe in the wells named MW1, MW2, MW3, MW4, AR3, AR17).
Report on IPT application and interpretation in Arcade (Province of Treviso):
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 (formerly designated as well n. 773 belonging to the Arpav monitoring network called SISMAS, operative since 2000, present in the province of Treviso).
The potential source is going to be 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.
Figure 1 – City of Arcade and location of the monitoring wells
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.
Figure 2 – stratigraphic structure
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.
Table 1 – PCE concentrations detected during the last monitoring campaigns
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.
Figure 3 – AR3 well location and groundwater flow direction
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.
Figure 4 – Sensitivity testing for IPT planning
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:
Table 2 – Results of IPT in AR3
Table 3 – Interpretation of results considering the plume passage
The graphical representation of the “time vs. concentration” data series is shown in the next two pictures:
picture
picture
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.
Figure 5 – GW levels measured during IPT in AR3
COST SUSTAINED DURING THE PERIOD: EXTERNAL EXPERTS AND INVESTMENTS
Sinergeo s.r.l.: investigation and environmental research, interpretation of the data, definition of the transport model, definition of the pollutant model; geological assistance to drilling of No. 2 additional surveys / piezometer (MW3 and MW4).
Phreatimetric execution of field surveys and tracking tests. Multiparameter log in the hole. Stratigrafic processing MW3 and MW4. Interpretation tracking tests. Elaboration of multi phreatimetrical data and log in the hole.
Planning, implementation and interpretation of pumping test IPT for 83 hours at the private well AR3. Design through analytical calculation code (Magic) and numerical (Modflow) IPT. Recalibration of the numerical model of steady based on the new phreatimetrical data. Participation in meetings and technical meetings.
WP3: € 14.000,00
Assistance and support for the internal staff of the province of Treviso; managing relationships with other sub contractors (business surveys, well drilling company, a Figura 10 – Livello di falda misurati durante la prova IPT in AR3 laboratory for analysis.) Co Drafting of the procurement for the assignment of the contract for the execution of the investment
WP4: € 1.000,00
Easy Language:
translation of material from English to Italian and VS; translation of IPT handbook in italian for delivering it to an Italian technical audience
WP3: € 1.710,00
Studio A.S.A:
Laboratories and analysis:
16 analysis x 75 euros each one
23 analysis x 15,36 euros each one
WP3: € 1.590,56
Studio ASA has been charged of realizing the water analysis foreseen in WP3 (€ 15.000) and in WP4 (€ 7.000)
Artesia S.p.a.:
Recovery and re-establishment of the private pump, installation of the temporary pump with the extracted water collector in the consortium network, provision and rent out of a generator with 90 hours of functioning, fuel for the generator
WP3: € 4.800,00
The rest of amount of the contract of Artesia (about € 76.000) will be paied as soon as the investment activities is completed. The deadline was foreseen for 30 November 2010, but for the strong rain phenomena of the last period, the execution of the wells and IPT pumping has been postponed.
