## 4 Results and Discussion  
The development of a 3D geospatial database of former mining activity allowed us to map the location and geometry of underground workings with respect to the present-day topography of the study area. The GIS-based geodatabase stores features representing individual vertical, horizontal, and inclined drifts, with information on their depth below the surface, heading, and geometry. The archival documentations, and thus the resulting database, cover the entire area of test field three. These were used to set out test field three and tests sites within its border. Interpreting the gravimetry results, the areas at the greatest risk of post-mining deformations, related to the consolidation of the ground caused by mining, are associated with the occurrence of negative gravity anomalies resulting from the shortage of mass in the substratum. The results of microgravity data interpretation (Figure 7) show that the Bouguer anomaly has a streaked, alternating pattern visible in the central and northern parts of the test field. From the center of the area to the south, there is a larger, relatively negative anomaly, reaching a minimum of \(-14.21\) mGal at the southern border, near the anthropogenic lake above the excavated coal deposit. There are three streaks of relatively negative  
Figure 6: Scheme of ERT measurement with a three-electrode system method. anomalies from the center in the NE part. These negative anomalies are associated with the lighter formations, also of anthropogenic origin, that fill the depressions. The positive anomalies of the SW-NE direction run from the center and continue beyond the northern and north-eastern boundaries of the area. The positive anomalies are probably caused by tertiary formations, with a higher bulk density in relation to the anthropogenic formations marked in the picture of Bouguer anomalies, in the form of relatively negative anomalous forms. The picture of the Bouguer anomaly in, test field three, is shown in Figure 7a. To focus on anomalies associated with shallow sources, separation of gravity Bouguer anomalies into residual components was done in the frequency domain, using the Butterworth high-pass filter. This filter rejects regional components resulting from deeper geological structures. The image of residual anomalies is dominated by alternating positive and negative anomalous forms running from the central part of the area towards the north-east (Figure 7b). The two larger forms in the central part merge into one anomaly towards the SW (A). The anomaly near the NE border has three maxima, the largest of which reaches 0.28 mGal. In the southern part, near the anthropogenic lake (B), there are several small positive anomalies with values that do not exceed 0.15 mGal. There are three negative bands between the positive bands with a minimum value of \(-0.27\) mGal (C). The sequences of positive values (in the central and north-eastern part) are contoured by distinct densities separating the areas of positive and negative anomalies. This is probably related to the difference in density between the heavier Miocene formations and lighter anthropogenic formations and brown coal outcrops. In the central and southern parts of test field three, the density contrast is slightly lower, and may indicate transformation of the original environment as a result of the brown coal mining and appearance of anthropogenic deposits (sand, gravel, peat, or silt). With respect to the particular test sites, the one located in the NE part of test field three is covered by a relatively negative residual anomaly, with a minimum of \(-0.055\) mGal (D), located near the south-eastern border of the site. The positive anomalous forms are visible mainly at the edges, and partially in the central part, of this area.