Session 5: Shallow groundwater as a water supply resource
* Speakers are indicated in bold type.
* 2 Training Contact Hours are available for this session.
Morning Session – Washington Room (2nd floor)
Co-Chairs: Ryan P. Gordon, Maine Geological Survey; Daniel B. Locke, Maine Geological Survey; Joseph D. Ayotte, US Geological Survey
Groundwater resources in New England are typically extracted from fractured bedrock or relatively thick glacial deposits of sand and gravel. Thin deposits of glacial drift, however, contain a large amount of stored water that is currently underutilized. Shallow groundwater has historically been accessed through dug wells, which have gone out of favor due to concerns about yield and water quality, but new well techniques (and old techniques reapplied) are opening up opportunities to use shallow groundwater more safely and reliably. Shallow aquifers can be an especially useful resource in cases where traditional bedrock wells or surface water have problems of poor quality or low yield, especially for rural homeowners or farms. New research has also shown that increasing long-term water levels may mean additional storage is available in thin upland aquifers.
8:30AM – 8:55AM
Ground Water and Public Health: a New Shallow Well Technology to Provide Safe Drinking Water for Private Wells
Ian Carlisle1, Marcel Belaval2, Ryan P. Gordon3, Julia Bryce4, Joseph D. Ayotte1
1 U.S. Geological Survey, Pembroke, NH
2 US Environmental Protection Agency, Boston, MA
3 Maine Geological Survey, Augusta, ME
4 University of New Hampshire, Dept. of Earth Sciences, Durham, NH
* Presentation not available. Please contact Ian Carlisle with any questions.
In northern New England, about 40 percent of the population uses private domestic groundwater wells. These wells draw primarily from bedrock aquifers where high concentrations of naturally-occurring arsenic are common. In contrast, water in shallow glacial deposits that commonly overlie bedrock typically produce water with little or no naturally occurring arsenic. They exhibit groundwater geochemical conditions that inhibit arsenic solubility. However, these glacial aquifers have been under-utilized in the last few decades due to outdated and unsanitary dug well technology. A low-maintenance shallow well design recently patented by the USGS could eliminate many of the concerns associated with the use of shallow, low-permeability aquifers and could provide safe drinking water to a large fraction of the New England population that would otherwise rely on arsenic-contaminated bedrock wells. The USGS well design comprises a single vertical riser with a sanitary well cap and pitless adapter. It also includes horizontal collectors that extend outward from the bottom of the riser within a trench that is backfilled with crushed stone. The length of the horizontal collectors, and therefore the approximate length of the trench, is determined by the hydraulic conductivity of the aquifer material and the depth of the trench relative to static groundwater levels. A geotextile fabric and native fill material overly the crushed stone in the trench to prevent surface contaminants from reaching the well. In 2017, the USGS, the University of New Hampshire, the Maine Geological Survey, and U.S. Environmental Protection Agency launched a new project to install and test the well design at two pilot sites in northern New England. Monitoring is underway for yield and water quality 6 times per year. Preliminary results indicate that yields and water levels are favorable. Water chemistry and microbiological data will be presented in this talk.
9:00AM – 9:25AM
Castine’s thin sand and gravel aquifer tapped by two unique well designs
Peter Garrett1, Annaleis Hafford2
1 Emery & Garrett Groundwater Investigations, LLC, Winslow, ME
2 Olver Associates, Winterport, ME 04496
Castine Neck is a rocky peninsula capped by a thin sand spit deposited as sea levels retreated about 12,000 years ago. This sand has been tapped for groundwater supply in two very different settings.
The Battle Avenue Ponds were constructed as reservoirs in the 1800s in an area of springs above the town center. The Ponds were used for unfiltered water supply until the Drinking Water Act required filtration in the 1980s. Detailed geological investigation delineated a local sand and gravel aquifer, 10’ thick (5’ saturated), overlying marine clay. A horizontal test well demonstrated feasibility. Water quality was excellent, except that, due to infiltration of Pond water, micro-particulate analysis failed. A horizontal production well, 440 feet long, was installed in 2015. It gravity-drains to the site’s manhole, from which it is pumped for treatment as a source of groundwater under the influence of surface water.
The Spring Street Wellfield was originally tapped by four driven point wells that were replaced in 2012 by a gravel-packed well having a sump set into the clay below the screen. This unusual design allows considerably greater withdrawal volumes with less maintenance than the point wells that have been abandoned.
These two groundwater sources now provide approximately 50% of the water needs of the Town.
9:30AM – 9:55AM
An Overview of Shallow Well Construction in New Hampshire
Andrew Koff
New Hampshire Department of Environmental Services
In the State of New Hampshire, the Water Well Board and New Hampshire Department of Environmental Services (NHDES) regulate the construction of all water wells. A license is required of a business or individual engaged in constructing drilled gravel wells, dug wells, point wells and wash wells. While not as common as drilled bedrock wells, many New Hampshire residents rely on shallow wells installed in overburden aquifers as their drinking water sources. NHDES oversees the well records database that has collected well construction information since 1984. In addition to describing these well construction practices and regulations, this presentation will include a summary of lessons learned from well inspections and highlight publicly available resources from the NHDES Water Well Program.
10:00AM – 10:25AM
Panel Discussion