The United States Geological Survey (USGS), the New Hampshire Department of Environmental Services (DES) and the New Hampshire Geological Survey at DES (NHGS) have completed a study to assess why ground water levels measured in wells constructed in bedrock aquifers declined by more than 13 feet on average from 1984 to 2006.

The results of the study indicate that there are multiple factors that are related to the lowering of observed water levels in newly constructed wells in New Hampshire. “Over 50 percent of the citizens in New Hampshire obtain their drinking water supply from wells drilled in bedrock. Yet, the depth of water in bedrock aquifers has not been adequately monitored in the State,” according to Brandon Kernen, Hydrologist with DES.

The study of reported water levels, measured during well construction, was conducted as a preliminary effort to assess bedrock water level trends across New Hampshire. “Land development, water use and climate trends all can affect the availability of ground water,” according to Brandon Kernen at DES. “The study was conducted because observed average annual water levels in new wells have shown a steady decline over the past two decades, and we need to identify the reasons for this trend so that the State can make well-informed decisions about managing ground water.”

“The study found that primary factors related to trends of deeper average water levels are concurrent increases in overall well depths and the use of new well construction practices,” according to Joseph Ayotte, hydrologist with the USGS. “These changes may result from homeowners needing more water or from improvements in drilling technology – allowing wells to be drilled deeper more quickly and using longer casing to protect the well. The result of these practices is that the amount of available water in wells has increased due largely to the increased well depths.”

The study also found that wells located on hillsides or steep slopes, especially those that are south-facing, are more likely to experience deeper water levels than wells not in these areas. The reasons for these results are unclear. The study also notes that a lack of information on changes in water use over time meant that it was not possible to determine whether potential increased water demand and use impacted water levels state-wide.

The USGS, NHGS and DES have developed and are implementing a strategy to improve routine monitoring of water levels in bedrock aquifers. Representative bedrock wells throughout New Hampshire are being equipped with water-level monitoring devices to measure current water-level trends, utilizing automated equipment on long-term loan from other federal agencies and grants obtained from state and federal agencies. The data will used to assess whether available ground water supplies are being affected by changes in factors such as climate, land use or water use. The data also should improve our understanding drought conditions and of the timing and degree to which precipitation replenishes the drinking water supplies of the majority of the residents in New Hampshire.

The report and data from existing ground water monitoring wells may be found on USGS’ New Hampshire Web site.