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This paper shows how important the historical contaminant boom, 1975 to 2005, has been to hydrogeology. Its role in this respect has never been well documented or appreciated. We use text mining and machine learning to extract information describing research trends in subsurface hydrology (SH), groundwater plus the vadose zone. The analysis, using articles from Water Resources Research (WRR) and Environmental Science and Technology, shows how SH grew from a small niche area within broader hydrologic sciences in the 1960s to become the dominant area of research by 1995. Subsequently, the performance of SH has declined, as other areas of hydrologic sciences have emerged. These patterns reflect the growth and decline of research related to contaminant topics in SH. Thus, the decline is economic-less money leads to less research. The boom in contaminant hydrogeology was effectively a 1000-year flood of money for SH. It let us outcompete the non-SH areas for a while. From 1991 to 2000, SH research in WRR was dominated by papers on contaminant-related themes. More recently, these themes and all other areas of SH except one have declined significantly in WRR. All major topics related to non-SH areas are growing except one. This evidence points to a continuing decline in competitiveness of basic research in SH. The fact that critical problems or social needs for research still exist has not changed this basic trend. The focus of research has clearly shifted away from SH to areas of hydrology associated with climate change, water cycle modeling and similar themes.