Subsurface Environmental Impact in Urban Areas. Shallow Groundwater Composition, Corrosion of Soil-Buried Constructions, and Leachates from Reclaimed Asphalt Pavement

Doctoral thesis, 2004

Worldwide, groundwater represents the largest and most important source of potable water. Usually, urbanisation affects shallow urban aquifers in two ways: by radically changing patterns and rates of aquifer recharge, and by adversely affecting the quality of groundwater. The overall objective of this thesis is to illuminate multiple subsurface environmental problems in urban areas. The urban environment, first described generally, is thereafter treated from three angles: (1) leakage water from stockpile storage of reclaimed asphalt pavement (RAP) as a source of groundwater contamination; (2) urban shallow groundwater quality, exemplified by the conditions in Göteborg; and (3) corrosion of soil-buried structures as an effect of the composition of the soil, soil water and groundwater. In the asphalt investigation both field and laboratory works were included. Several semi-volatile compounds were identified frequently in the leakage water from the field stockpiles. The laboratory column test differs in that the concentrations of the compounds were much lower, and the compounds were fewer and to some extent different. The main reason was the much higher ratio of liquid to solid in the column tests than in the field. The most common semi-volatile compounds found in the leakage water from RAP were also observed in shallow urban groundwater, the quality of which was investigated in eighteen observation wells; it was shown that the quality differs greatly from that of rural areas, normally by greater ion strength and a much higher alkalinity. Although the composition of the filling material caused the high alkalinity, the natural geological material also had an influence. The soil analysis from the field corrosion investigation showed large differences between samples taken from places as close to each other as half a metre, which highlights the heterogeneity of the filling material. Results showed that the heterogeneity of the filling material stimulated the corrosion process of soil-buried panels of carbon steel and zinc; however, the high alkalinity of the soil water and the groundwater and the high total hardness of the filling material both retard the corrosion rate.