## 2 Materials and Methods
The authors set the following research theses in the paper:
* drilling liquid is introduced to the environment on a much larger scale than that declared by investors; and
* the scale of the loss of bentonite used for directional drilling depends on the type of soil on which the construction works are conducted. The analyzed area covered a section of the constructed high-pressure gas pipeline, DN1000 Czeszow-Wierzchowice, in the Peciszow village, Trzebnica poviat, Zawonia commune (Poland, Lower Silesian Voivodeship), where the horizontal directional drilling (HDD) method was used in order to protect valuable natural areas. The construction of the Czeszow-Wierzchowice pipeline, along with the realization of other connected investment tasks, is an important element in introducing the concept of a Central European North-South gas transmission corridor in Poland. The land structures, located on the route of the planned Czeszow-Wierzchowice gas pipeline, include, among other areas, Natura 2000 areas and ecological utility areas. The drilling in the area of Peciszow was constructed in order to preserve the lowland ash and alder forest 91E0-3 along a watercourse, which is likely to be a breeding site of the Bluethroat (a species listed in Appendix I DP) and common frog, as well as a site of the protected bush, Guelder rose (Figure 1). The pipeline is constructed from steel pipes (grade L485 MB) of 14.2 mm and 22.2 mm thick walls, provided that the thicker walls are used in sections, constructed using trenchless methods. The installation was constructed using a Normag machine class 3000 kN and an associated fluid segment of a capacity exceeding 3500 L/min. A high-capacity decanter centrifuge was applied for the first time in Poland in a HDD project. The HDD1 boring, with a length of 534 m, located in the village  
Figure 1: Location of the directional drilling HDD on the route of the gas pipeline construction. Peciszow, was constructed during 25 work shifts, including six shifts of pilot drilling. The drilling plan foresaw the construction of a trajectory, with a radius of 1250 m and an average cover of less than 20 m.  
Navigation was performed using the Paratrack 2 system, equipped with a pressure measurement module. Upon the verification of the geological conditions, the contractor of the works decided to widen the borehole from 12 \(\frac{1}{4}\)\" to 52\" in a single step (for the first time in Poland). The quality of the borehole was confirmed by a calibrating march, conducted with an expanded set of tools. The DN1000 pipeline was installed in the borehole on the 8 th of June, with an average recorded traction force of 350 kN. The tests were based on daily reports on the realization of the high-pressure gas pipeline using the HDD method and on field inspections conducted along the route of the gas pipeline construction in Peciszow in June and July 2017. Additionally, the authors performed a literature inquiry, as well as a review of the technical and technological documentation of the drilling works and of the documentation in the possession of the drilling company. Geological analyses are extremely important in the stage of designing investments realized using trenchless technologies. The number of test boreholes in the geological documentation depends on the soil structure and the length of the pipe. The depth of the holes should be 5-10 m deeper than the assumed drilling depth, so as to enable changing the grade line of the pipe in the event of unsuccessful drilling at the planned depth. The soil property analyses (grain size distribution analyses, laboratory and field tests, soil probing and penetration, CPT, SPT, etc.) constitute the basis for selecting the drilling liquid and equipment. In urban areas, it is extremely important to recognize and take an inventory of all elements of underground technological infrastructure and the remains of old development structures. Failure to do so may result in damage to, or the destruction of, the drilling equipment or the failure of the existing systems.