OR/17/007 Appendix A3. 1 - Bucharest urban groundwater monitoring system
| Bonsor, H C, Dahlqvist, P, Moosmann, L, Classen, N, Epting, J, Huggenberger, P, Garica-Gil, A, Janźa, M, Laursen, G, Stuurman, R and Gogu, C R. 2017. Groundwater, geothermal modelling and monitoring at city-scale: reviewing European practice and knowledge exchange. British Geological Survey Internal Report, OR/17/007. |
Bucharest City area covers around 240 km2 (6 districts). Hydrological features, playing an important role in the water balance of the city, must be mentioned. Two rivers are crossing the city, both having gone through extensive modifications. The northern river (Colentina) is landscaped in a series of lakes communicating directly with the shallow aquifer. The southern river (Dambovita — crossing the center of the city) is channelized thus interrupting the communication with the aquifer. This river is connected to an important artificial lake (Lacul Morii), located in the western part of the city, constructed in the ‘70 for flood management and urban landscape improvement. Also, a significant number of artificial and natural lakes comprising around 11 km2 are spread on the city surface.
The geological setting is represented by Quaternary sediments (clay, loam, marl, loess, sands and gravel) either fluvial, lacustrine or eolian. From the Lower Pleistocene (200–150 bgs) to the latest Holocene deposits, three important aquifer formations are representative for the Bucharest area: (1) the deeper aquifer — used for water supply, (2) the medium depth aquifer — also used for water supply in some cases, and in a direct (natural and anthropogenic) hydraulic connection with the (3) shallow aquifer (in direct connection with the underground infrastructure).
The Urban Groundwater Monitoring System (UGMS) of Bucharest City tries to capture the most important urban hydrogeological characteristics. The development of the UGMS took into account several constrains and requirements specified in Table 1.
| Requirements | Type | Solution |
| Coverage area | Geometry — Location |
The distribution of the UGMS points covers around 110 sq km (Figure 1), almost a half of the administrative area of Bucharest City. |
| Target aquifers | The UGMS is a monitoring system defined for the urban aquifer system. In this sense, the impact upon the deeper aquifer can be considered in relationship with water extraction and in some cases with pollution, due to inadequate drilling procedures. Considering these arguments and taking into account the development costs, UGMS focuses only on the first two aquifer layers (Colentina — shallow aquifer and Mostistea — medium depth aquifer). The number of monitoring points for the shallow aquifer is larger (116 points) than for the medium depth aquifer (only 30 points), due to the fact that the shallow aquifer shows a strong interaction with the urban infrastructure. | |
| Special urban infrastructure features | The specificity of an urban groundwater monitoring system is to capture the impact of urban infrastructure effect upon groundwater. To accomplish this task, many of the monitoring points are located in the vicinity of the Dambovita lined-up channel and of the Lacul Morii lake. Other special urban infrastructure elements (subway line, deep foundations, others) also have monitoring points in their surrounding areas. | |
| Parameters and tests | Data | Each project involves a limited budget. In order to optimize it, a certain balance between the drilling procedure, well equipment, laboratory and in-situ tests must be taken into account. The UGMS developed in two different phases, using two different drilling procedures. In the first phase the wells were done using hydraulic rotary drilling (around 34 monitoring points) and in the second one, using auger drilling with protective casing. The parameters and the data collected during and after the development of the monitoring wells are described in Table 2. |
| Monitoring parameters | Hydraulic head data, water sampling and laboratory analysis represent the needed information. In order to reduce the costs and to maximize the data benefit, several monitoring boreholes were equipped with double tubing targeting both aquifers. The sealing between the two aquifers was made of a mixture of clay, bentonite and cement. | |
| Constrains | Type | Solution |
| Security and well integrity | Geometry — Location |
Security of the monitoring points is a key aspect in an urban environment. There are several areas of social triggers that need careful attention: (1) scrap iron black market — in this case the metallic components (well head protection) must be eliminated or somehow hidden — for UGMS most of the metallic components (well cover) are found at ground level in public places, (2) vandalism — there is no real solution regarding the public places (ex. UGMS lost around 6 monitoring points due to vandalism — wells were filled with stones and other materials, the well casing broken and the cover stolen). The general solution, to avoid these risks, was to set up (as much as possible) the monitoring points in private locations belonging to the municipal water company. |
| Budget | Data | The budget limitation is a constrain for any project. Within the available budget, the UGMS had to respond to two needs: (1) characterization of the aquifer media — around 10 hydrogeological cluster points, located in key points of the city and (2) hydraulic head monitoring points (double tube wells). |
| No. | Parameters – Data – Test | Hydraulic rotary drilling | Auger drilling |
| 1 | Lithology description | + | +++ |
| 2 | Granulometry | + | +++ |
| 3 | Electric resistivity (16, 64 Ωm) | +++ | - |
| 4 | Natural Gamma (Api) | +++ | + |
| 5 | Temperature | +++ | + |
| 6 | Hydraulic pumping test | ++ | +++ |
| 7 | Slug test | + | ++ |
| 8 | Level measurements | +++ | +++ |
| 9 | Chemical parameters | ++ | +++ |
| Legend – Not applicable | + Satisfactory | ++ Good | +++ Excellent | |||
The urban groundwater monitoring system in Bucharest is composed (end of 2014) by a total number of 145 monitoring points/stations. The distribution of the monitoring points (Figure 2) is concentrated in the center of the city, along the channelized Dambovita River. This can be explained by the high density of urban underground infrastructure elements found in the area: (1) the channel of the Dambovita river, (2) the main sewer collector of Bucharest City located under the channel, (3) 2 major wastewater conduits located in parallel to the Dambovita river, (4) the subway line, (5) Dambovita channel left bank drain and (6) a new drainage system that will be implemented (currently under construction) on the channel right bank.
The monitoring stations/points are divided in three types (Figure 1).
- Single point monitoring well — this type is a simple hydraulic head monitoring well with an outer diameter (OD) between 90–114 mm. For almost all of these monitoring points, geophysical logging and hydraulic testing (pumping tests for 114 mm OD and slug tests for 90 mm OD) have been performed. In some cases, samples from the aquifer strata (sand and gravel) were collected to determine the granulometry.
- Double tube monitoring well — this type of monitoring station is designed to measure the hydraulic head for both Colentina and Mostistea aquifer strata. There are two installed tubes in the borehole: 90 mm and 32 mm. For both, slug tests as well granulometric analyses were performed.
- Hydrogeological cluster — this type of monitoring station is composed by a well (140 mm OD) and a piezometer (90 mm OD) targeting the same aquifer unit (the distance is between 5 to 15 m). This type of monitoring station was designed to give a proper description on the hydrogeologic parameters by performing pumping tests.
