Click here to view the Interim Report (August 2005)
Can Gravel Mining and Water Supply Wells Coexist?
John M. Peckenham, Senior Research Scientist
Teresa Thornton, Graduate Student
Senator George J. Mitchell Center for Environmental and Watershed Research
5710 Norman Smith Hall, University of Maine, Orono, Maine 04469
Table of Contents
Results (field observations, lab results, statistical associations)
In 2002, the members of the Lamoine Conservation Commission approached researchers at the Senator George J. Mitchell Center for Environmental and Watershed Research (Mitchell Center) at the University of Maine because they were increasingly concerned about how sand and gravel mining was affecting the local aquifer. Citizens observed the activities associated with development: land being sold; new developments being established; lots getting cleared; and, sand and gravel trucks leaving the town filled with material from the aquifer. Were these activities going to harm the town’s water supply? The commission worked with the Mitchell Center to design a project to collect data about gravel pits and groundwater in the area. The project objectives were as follows:
- Inventory drinking water supplies near active pits to update existing information;
- Inventory drinking water supplies near large reclaimed pits;
- Assess changes in water quality using existing information from selected locations;
- Develop a methodology to assign risk rankings to groundwater resources;
- Assess how well current regulations protect the water resources; and,
- Provide the results of this study to towns, concerned citizens, and regulators to help them manage local resources more effectively.
This study produced answers to two main questions. The first was – How does mining affect the hydrology of the underlying sand and gravel aquifer? Based on interviews with well owners and observations of surface water features there was no evidence of significant changes in surface or groundwater hydrology. Water level measurements and observations made during the field study can now serve as a reference for future measurements. The absence of significant changes in hydrology is encouraging in that short term disruptions are seemingly rare. Repeated water level measurements in future years will address the question of long-term disruptions.
The second major question answered was – Does mining make the underlying aquifer more vulnerable to contamination? Based on the data collected, water quality has been degraded by salt and nitrate. Degradation of water quality occurs in different areas; however directly linking changes in water quality with gravel pit operations goes beyond the limits of the data. There may be an increase in nitrate in surface waters near gravel pits, but the number of samples analyzed is too small to make this a certainty.
One of the questions asked was – How does the water chemistry vary across the aquifer. We answered this question by plotting the chemistry results on a map. There are indications that there is some consistency in chemistry across the aquifer. It can also be noted that there is confirmation of the effect of salt on water quality. There is not a systematic change in the chemistry of the aquifer in any one direction. The greatest concentrations of chloride appear to occur near major roadways. Road salting in the winter is a likely source of this chloride. Elevated concentrations near the coast may reflect the influence of the nearby bay. There was not a strong spatial relationship between ‘salt-affected’ wells and gravel pits. There also was no statistical association between the distance from a sample point to a gravel pit and chloride concentrations. More detailed studies are needed to understand why the chemistry changes by location.
The water quality data must be interpreted with care. Chemistry results may change in concentration by location due to seasonal precipitation amounts and transport of substances into ground water. Presently field data indicate that water quality degradation is limited in both magnitude and occurrence location. Further studies will generate more data on groundwater chemistry to demonstrate how water quality changes across the whole aquifer and surrounding towns.
Some of the gravel pits in this study have been in operation for more than eighty years. Unfortunately, there are very few documents or much institutional memory of historical activities. Activities have been inferred from field observations and interviews. Quantifying future impacts on local hydrology will be possible now that some baseline measurements have been made. The baseline water elevation data will be updated on an annual basis to map out changes over longer periods of time.
An added concern that was outside of the project scope was how pits were managed and prepared for disuse. Mining below the water table was noted in at least one pit and maintenance of separation distances above the water table was not always apparent. Old inactive pits were observed to be used for storage of a variety of construction equipment, vehicles, and debris. Some pits were obviously being used as small dumps. Former community landfill sites located in disused gravel pits have been documented to affect water quality in many towns throughout the state. Lamoine continues to experience poor water quality in some wells located near Berry Cove due to an old landfill in the aquifer. Reclamation of inactive pits is essential to prevent degradation of groundwater by illicit and unregulated debris dumping.