Environmental Impact

The effects of surface subsidence due to longwall mining under the conditions observed in Belmont County, Ohio, are very subtle on surface terrain and not observable in upland forest vegetation. Subsidence is likely to cause transient effects on the surface water regime of some of the area that is undermined. The hydrologic regime of the generally shallow root zone from which both large and small trees draw their water is influenced by precipitation and evapotranspiration. Longwall mining obviously has no influence upon either of these two factors. The impact of longwall mining upon tree growth has now been extensively studied, and previous studies also suggest that mining does not appear to impact growth of either sapling or larger size trees. Since Dysart Woods is managed for natural processes rather than value accretion, uncertainty over growth should not represent a significant issue.

From a mechanistic viewpoint, considering the functional relationship of trees and their root systems to the soil and hydrologic processes, it is unlikely that subsidence due to longwall mining will adversely effect the overall forest health of Dysart Woods.
(read longwall study part 1, PDF file 9,628KB)
(read longwall study part 2, PDF file 11,993KB)
(read longwall study part 3, PDF file 4,176KB)
(read longwall study part 4, PDF file 8,487KB)

The groundwater models discussed in this report are simple representations of the area modeled. Model parameters such as boundary conditions, transmissivity, storativity, and areal recharge are not based on site specific data. No attempt was made to calibrate any of the models to observed water levels, either before or after mining operations were conducted. In addition, no data were available from which site specific boundary conditions could be developed.

The model simulations performed were all two-dimensional planes, conceptual in nature, and do not match the complex three-dimensional stratigraphy of the system being modeled. It is probable that for this application, even with site specific data, realistic numerical representations of the real three dimensional system cannot be achieved with a two-dimensional plane model.

Assuming a two-dimensional plane model could be used, the two-dimensional model developed by Dr. Ahmad is both conceptually and numerically flawed, as demonstrated in the body of this report.
Recent pump tests completed by P2T indicate transmissivity values assumed for these simulations may be too high. The results of the pump tests performed near well areas 5 and 6 are presented in a summary report. For Well Area 5, transmissivity estimates range from about 1.6 to 5.4 ft.² a day. For Well Area 6, transmissivity estimates range from about 14 to about 16 ft.² a day. These values, while limited to the areas cited, are significantly lower than the assumed transmissivity value of 133.7 ft.² a day adopted by Dr. Ahmad and used for most of the simulations described in this report.

To our knowledge, the development of a predictive groundwater modeling tool sufficiently accurate to allow simulations of the area near Dysart Woods in Belmont County, Ohio, has not yet been accomplished by Ohio University or anyone else. Such development is well beyond the scope of any efforts which have been conducted to date, and indeed may not be practical. (read full study, PDF file 9,321KB)

(read full study, PDF file 833KB)

The sample of trees included in this study is typical of the most mature cohort of second-growth forests in Belmont County, Ohio. They represent a typical variety of sites and the species chosen were selected to represent the species mixture in nearby Dysart Woods. Initial examination of the tree growth data showed that a few significant differences existed between the radial growth of trees after mining when compared with the previous five-year average, either directly over the longwall mine or at a distance from the mine. Multiple regression analysis was used to determine if the independent variables used, explained the variations in radial growth. With the exception of red oak, the explained variability was generally less than 20%. Only in the case of white oak did distance from the mine explain the variations in ring growth, and in this case, the effect appeared to be delayed for at least five years after mining. This relationship was not simply due to a reduction in growth of trees directly over or near the mine, but rather appeared to take the form of increased growth of certain trees far from the mine. A closer inspection showed that in some cases alternative explanations were more plausible for the significant relationship of distance with growth than one based on mining impact such as, the impact of adjacent logging operations.
(read the full study, PDF file 3,855KB)

Longwall mining related subsidence produced no general impacts on soil moisture in the present study. Longwall mining related subsidence produced no general, consistent impacts on tree growth rates in the present study. Overall, vegetation does not seem to be affected by longwall mining. Instead of general effects, the potential impacts of longwall mining seem highly specific and localized. Vegetation dependent upon a specific spring will be affected if that spring dries up for even a couple of years. The reappearance of the water downslope may not be sufficient to maintain the spring-dependent species if dispersal between the old and the new spring sites is difficult. Local land slippage can disrupt individual trees, especially on steep slopes. Where individual trees are especially significant due to their size or rarity, such impacts might be important.
(read the full study, PDF file 859KB)