CONSULTANCY

NOLDOR S.R.L. offers assessment, developments and studies related with hydrology and environment. In these fields its main tools are radiotracers and isotopic indicators included the environmental ones. A complement for these techniques is the application of mathematical models to simulate the behaviour of water bodies and  to evaluate extreme situations.

In this framework NOLDOR has capabilities to envisage studies on surface water and groundwater pollution, determination of leakage in lakes and reservoirs, hydrological studies, analysis of natural or human induced extreme events and assessment in all of these fields.


 Hydrological contamination

For the sake of sustainability of hydrological resources is necessary and convenient to have suitable techniques and methods for the control and surveillance of the  biosphere pollution. The environmental impact of each hydroelectric complex, industry, village or navigable water body cannot be considered as an isolate or located fact. They should be taken into account as a result of concatenated effects generated not only in the own basin but also in the neighbour ones.

In such a context, NOLDOR offers  heavy metal determinations, radioactive material measurements, toxic products analyses and evaluation of any factors that contribute to degrade the environment. This proposition is addressed to national agencies and private companies related with the treatment of industrial, mineral or urban wastes.

Proposed indicators

All the dynamic tracers and indicators as well as the methods and techniques suggested here have very high sensitivity, specify and reliability. They are suitable for detection, measurement and control of inadequate practises for waste management in the basin under study.

At present, there are more than 5,000 known atoms (isotopes) being radioactive around of 95% of them. Radioactivity is present in almost every material or biological organism in concentrations that depends on the physical, chemical or biological characteristics of the considered material.

Regarding the maximum accepted radioactive contamination level in solid materials, the criteria are not equal in different countries. As a general rule the limit for commercialisation, importation or exportation, rounds 400 Bq / kg.

The atmospheric nuclear tests that ended in the sixties made the radioactive contamination levels increase, especially in the cases of tritium (3H) in water and cesium-137 (137Cs) in sediments. The North hemisphere was more affected than the South hemisphere.

On the other hand, natural radioisotopes, mainly potasium-40 (40K) and those belonging to uranium-235 (235U), uranium-238 (238U) and thorium-232 (232Th) series can be found in some materials such as flying ashes and phosphates in high specific activities.

The contribution of fossil fuels (coal, oil, gas) to increase the environmental radioactivity level is very well known. The generation of one electric gigawatt from coal releases to the environment between 109 y 1011 Bq of radon (220Rn and 222Rn) in a year as well as lead-210 (210Pb), radium- 226 (226Ra), radium-228 ( 228Ra) and polonium-210 (210Po) among other radioisotopes in a range from 108 to 1010 Bq in a year. These effluents  are mainly discharged to the atmosphere and the hydrosphere and their release rates are comparable to those generated by nuclear power plants operating in standard conditions.

Some other human duties make the radioactivity level in the hydrosphere grow, such as accidents or incidents whose probability of occurrence is very low but not totally negligible.

Finally, the natural water molecule belonging to any basin or water body has a characteristic mixture of stable isotopes and some traces of tritium. These environmental isotopes (stable or radioactive) make part of natural water and its detection in very low concentrations is possible. For these reasons,  they are considered the most sensitive, reliable and effective tools to follow the dynamic behaviour of the most important physic, biological and ecological water parameters.

 Proposed techniques

NOLDOR offers the following techniques to measure or to evaluate the contamination level in surface water, groundwater and sediments: alpha, beta and gamma spectrometry, mass spectrometry, X-ray diffraction, atomic absorption, nuclear activation analysis chromatography and "in situ" determinations.

Leakage from lakes and reservoirs

Leakage in water storage and conveyance systems may influence the economic value of a project and create serious problems related to the stability of the hydraulic works. Therefore, to find the rate of leakage and its preferential paths it is important to identify as precisely as possible the regions where the leakage occurs. Various isotope techniques can be applied with that purpose.

Tracer application is one of the better methods to investigate leakages in huge reservoirs. The information got in preliminary studies allow to elaborate hypothesis about  the location of the areas where infiltrations are likely. Artificial tracers can be applied to test the validity of such hypothesis, being iodine-131(131I) the most commonly radioisotope used to accomplish this task.

Preliminary studies should include the collection of as much information as possible in terms of the available time and resources to solve the problem. The most important data to collect should include: geological information, inventory of the outflows possibly connected with the reservoir, modifications in the outflows, precipitation regime, changes in the reservoir level, vertical thermal profiles in the lake, water geochemistry and borehole information. The behaviour of many of these variables should be followed along a complete hydrological cycle.

Once the suspicious regions have been found, radiotracers can be injected. The trajectory of the "radioactive cloud" should then be followed by means of submerged detectors carried by small motor boats. Simultaneously, the presence of radioactivity in certain neighbour points should be controlled in order to correlate the tracer concentration curves in these locations with the trajectory of the radioisotope in the reservoir.

Generally, the combination of different techniques and collected data allows the researchers to gather enough reliable information to locate the infiltration point with good accuracy.

 Hydrological studies

Whenever any kind of facilities have to be sited in a river bank or in the proximities of a water body  the knowledge of the hydrological behaviour of a basin is a previous condition

A hydrological study gives invaluable information not only with regard to the past or present but also is useful to predict the trends of the variables involved in the project.

The collection of historical data, its analysis and interpretation are the basic tools for any hydrological study. This data is used later to feed mathematical models which will produce reliable results and valuable forecasts.

The climatic, hydrological and geological aspects are analysed through the information obtained regarding temperatures, pressures, precipitations, flow rates, soil composition, aquifer interconnections and recharge sources.

Floods

The knowledge of meteorological variables (winds, pressures, temperatures, rains) and hydrological variables (flow rates, water levels) related with their daily changes as well as with their historical evolution along months and years is on the basis of the understanding of the behaviour of any water body.

This information makes it possible not only the evaluation of standard situations but also the foresight of extreme floods and water shortages with the help of mathematical models.

In this framework, the human induced events have also  to be considered, such as construction of new hydroelectric works, dams and canals as well as different kind of accidents that could generate extreme hydrological events.

The deterministic analysis of historical flow rates is based upon a set of mathematical equations and logic operations that can be gathered in a suitable software. Deterministic models are generally supported by objective bases and a deep knowledge about the system under study. They lead to the determination of the maximum probable flood.
The statistical analysis consists in the fitting of historical data (as random variables) by distribution functions that assign a probability value to each original datum. Once a suitable theoretical distribution function has been selected its parameters are calculated from the historical data and the quality of the approximation is evaluated by means of some statistic test.  The hypothesis is then accepted or rejected according to the test results. In case of acceptation the confidence intervals are determined

When working with extreme values the results are exposed as the probability to exceed some reference flow rate in a given time (generally a year). In practise, it is better to determine for a reference probability the corresponding flow rate. Another  and very common way to show the results is using the recurrence interval that is the reciprocal value of the probability and is usually expressed in years.

On that subject, a complete theoretical work (more than one hundred pages) titled in Spanish "Análisis estadístico de valores extremos. Aplicaciones en hidrología" ("Extreme Value Statistical Analysis. Applications in Hydrology") can be freely downloaded in this site.  Download the file.

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