Can Gravel Mining and Water Supply Wells Coexist?
Executive Summary • Introduction • Problem Statement • Objectives • Methods • Results (field observations, lab results, statistical analysis) • Discussion • Acknowledgements • Appendices
The results of this study are organized into three groupings: field observations, laboratory results, and statistical analyses. Field observations include surveys of gravel pits, water supply wells, and other water resources such as springs, streams, and ponds.
Gravel Pits. Gravel pits exist in the mapped sand and gravel aquifer that extends from the southern shore of Graham Lake in T8 SD, through Ellsworth and Hancock and terminates in the town of Lamoine (Figure 4). On average this sand and gravel deposit is 18 kilometers long and up to 2 kilometers wide (11 miles by 1.25 miles) and in excess of 30 meters thick (100 feet). The outline of the sand and gravel deposit was calculated to cover 13 square kilometers (5 square miles). At least 34 active and former gravel pits were located, and it is likely that there are additional small abandoned pits. There were a total of 18 locations with intensive gravel mining. Eleven owners or operators of active pits were identified. Most of the owners were able to provide historical information and granted permission to sample pit sites in the future. Summary information for the gravel pits is contained in Appendix A.
The gravel pits observed ranged in size from 0.8 to 34 hectares (2 to 85 acres). Pit size can be misleading because some pits may lie on adjacent land parcels and the pit sizes, although contiguous, are tallied separately. The total area covered by gravel pits, active and inactive, was estimated to be 3.4 square kilometers (1.3 square miles). This estimate means that approximately 26 per cent of the aquifer surface has been affected by gravel mining.
Most of the gravel pits were run efficiently as simple extraction and screening operations. Used vehicles and construction debris were observed in three of the larger inactive pits. Numerous small abandoned pits have been used for miscellaneous debris dumping. It was noted that gravel pit reclamation was limited. Seemingly, some pits were not abandoned, just mining at very slow rates. It should be noted that the former Lamoine landfill is surrounded by active gravel mining. This former landfill was documented by the Maine DEP to have contaminated local groundwater.
Private Wells. Approximately 200 properties were identified as being near or over the aquifer, as determined from tax maps. A total of 37 landowners allowed us access to document the location and water levels in wells. Some properties had more than one well and some properties shared a common well. It was surprising that only two properties had water quality testing documentation. Water levels were measured in 55 wells within the study area. A summary of private data is presented in Appendix B.
Wells were classified into two groupings: dug wells and drilled wells. Dug wells were typically shallow (<10 m) and often were constructed in well-drained soils such as sand or sandy loam. Drilled wells were consistently deeper (10 m to 150 m) and cased through the soil to open bedrock borings.
The water levels in dug wells ranged in depth from 0.45 to 3.55 meters below the surface (1.5 to 12 feet). The water levels in drilled wells range from 11m to > 30m below the surface (36 to >98 feet) and beyond the range of the water-level gauge. Since water levels in the bedrock wells were consistently lower than in the dug wells, the bedrock aquifer is likely being recharged in part from the sand and gravel aquifer. It is not known how closely the bedrock aquifer is connected to the sand and gravel aquifer. Nevertheless, activities that affect water quality in the sand and gravel aquifer will also affect bedrock water quality.
Surface Waters. Surface waters were sampled from ponds, streams and springs. The objective of this sampling was to develop a regional understanding of water quality. Seepage ponds lie with the sand and gravel aquifer and have no inlet streams; all of their water comes from precipitation and groundwater. The two seepage ponds sampled were Blunts Pond (outlet) in Lamoine and Simmons Pond in Ellsworth.
Several streams discharge from the lateral edges of the sand and gravel deposits. The streams are believed to be fed by water coming from the sand and gravel aquifer. Streams sampled were as follows: Blunts Pond outlet in Lamoine (same as above); Harding Stream in northeastern Lamoine (stream not named on maps); and Spring Brook, to the east of the MacQuinn pit in Lamoine and Hancock. The intent was to sample streams under baseflow conditions when the streams are being replenished by groundwater.
A total of nine springs were located, mapped using GPS, and sampled for laboratory analysis. The springs are considered to be the best indicator of aquifer water quality under natural conditions. Spring sampling was completed for six springs in Lamoine, two springs in Hancock, and one in Ellsworth. Flow rates ranged from seeps to approximately 2.5 l/s (40 gpm).
Public Supply Wells. One spring is also a public water supply, the Cold Spring Water Company. Flow from this spring was measured at 2.5 l/s (40 gpm). Overflow discharge rates varied depending upon how much water was being pumped into the distribution system. As part of this project, four groundwater-monitoring wells were installed around the source spring. The wells were sited to lie between the spring and potential areas of concern to the south-southeast and northwest. These monitoring wells are constructed from two-inch I.D. pvc pipe with locked protective steel risers. These special wells are identified as CSWC-1 through CSWC-4 in this report.
Summary data for the sampling locations are presented in Appendix C. Only locations with field data are listed.