Developing Water Supplies in Challenging Environments

SESSION F: Developing Water Supplies in Challenging Environments: Case Studies and Innovative Solutions

Session Chair: Mike Abbott, Maine CDC Drinking Water Program

Session Description: Although Maine has an abundance of clean water, there are many locations where finding adequate yield and/or water quality can be very difficult due to the geologic characteristics of a particular site or impacts from human activities. This session will focus on techniques that have been used in Maine and elsewhere in New England to tackle these problems and provide reliable drinking water supplies. Case studies will include alternative well construction and treatment techniques utilized to address low-yielding bedrock formations, saltwater intrusion, road salt and other contamination issues, naturally elevated minerals and radionuclides.

Presentations Available

Session Overview

8:30-8:55 am
Regulatory Impacts of Water Supply Development in Challenging Environments
David Braley, Hydrogeologist, State of Maine, MeCDC, Drinking Water Program

Many factors can result in difficulties developing water supplies including limited water availability, current land use and potential future development allowed by existing municipal zoning, past land uses that may have resulted in groundwater contamination and naturally occurring contaminants. The State of Maine has programs to regulate the development of both private and public water supplies. Private wells are required to meet specific setback distances from subsurface wastewater disposal system components. Public water supplies must complete a comprehensive application which includes identification of potential sources of contamination, delineating wellhead protection areas and plans to manage or mitigate for potential or existing sources of contamination. Information submitted for both private and public water supplies is used by the State of Maine to make decisions regarding appropriate levels of risk and proper mitigation. All water supply development is subject to the requirements of several State and Federal laws and regulations intended to protect public health and the environment. Navigating these regulatory requirements can be as challenging as the cultural and environmental difficulties encountered during water supply development.

9:00-9:25 am
S
queezing More Water from Maine’s Bedrock Aquifers
Ike Goodwin, President of Goodwin Well & Water, Inc.

According to the 2010 US Census information, 60% of Maine’s residents rely on ground water to supply their homes. However, only 3.4% of the land area in Maine is covered by significant sand & gravel aquifers. Another 12.8% is covered by surface water. The remaining 83.8% of the state must rely on bedrock aquifers to supply their ground water.

Ground water in Maine’s bedrock aquifers is found only in fractures in the bedrock. Our bedrock has no primary porosity to absorb and hold ground water. In some locations, these fractures are abundant and provide good to excellent water yields. More frequently the bedrock fractures are few and far between and provide very low water yields, if any at all.

For many years drillers realized if they could create new bedrock fractures that would radiate out from a bedrock borehole they might be able to connect to existing adjacent water bearing fractures and increase the yield of their new well.

After many attempts using dynamite and dry ice, with only limited success, we found a way to modify the “hydrofracking” process, common to the oil and gas industry, and use it successfully and economically to increase the yield of bedrock wells in Maine with an 85% – 90% success rate for single family residential homes.

Using various hydrofracking techniques it is now possible to not only make “dry” bedrock wells produce water but also significantly increase the capacity of those wells that already produce water naturally.

9:30-9:55 am
Identifying potential yield collapse in bedrock wells and shallow springs by Inverse Step Testing

Bruce Fowler, Andrew Gobeil, Sevee and Maher Engineers

For the past decade, we’ve been fortunate to witness favorable recharge conditions across most of Maine’s bedrock wells and shallow springs, but we can remember the cries of “drought” or “dry well” that filled the headlines in the early 2000s. A purveyor’s understanding of how bedrock wells respond to challenging recharge or demand conditions is critical to maintaining a safe well yield and, in turn, maintaining a reliable water supply system.

The safe yield of these often sensitive water sources is governed by the hydraulics of groundwater moving through bedrock fracture systems into bedrock wells or shallow springs. With the exception of some karst wells, which can exhibit high yields across a wide range of drawdown conditions, the yield within bedrock wells is typically non-uniform and declines as critical water-bearing fractures are dewatered. The safe yield in bedrock wells and shallow springs is commonly not identified through testing for critical threshold limits. Yet once these thresholds are exceeded, the well yield collapses.

Sevee and Maher Engineers, Inc. has developed an innovative way to assess bedrock well and fracture fed spring safe yields through a methodology called Inverse Step Testing. In our experience, Inverse Step Testing is a relatively inexpensive means for assessing well yield limits, and identifying and targeting drawdown thresholds that cannot be exceeded. Monitoring of identified drawdown thresholds has the benefit of avoiding a well yield collapse through controlled water use and the well damage that can occur with extreme drawdown events.

10:00-10:25 am
Reducing human exposure to arsenic in domestic drinking water by use of a novel design for shallow wells in the glacial aquifer
Joseph Ayotte, U.S. Geological Survey, New England Water Science Center

Domestic drinking water supplies in New England are dominated by wells drilled into fractured crystalline bedrock aquifers, which can contain geogenic arsenic. These wells are capable of providing reliable water supply by intersecting water-bearing fractures and providing storage of water in the borehole. However, water from many tens of thousands of these wells contains concentrations of arsenic that are harmful for human health – that is, greater than the U.S. Environmental Protection Agency’s Maximum Contaminant Level of 10 micrograms per liter. Recent studies related to high arsenic concentrations in private bedrock aquifer wells suggest that as long as home owners are responsible for treatment to reduce concentrations, many wells will go untreated and there will always be human exposure.

A new shallow well design can potentially provide sustainable yields from surface glacial deposits, reduce concentrations of arsenic, and protect against exposure to harmful bacteria. The new design helps ensure sustainable yield by expanding the surface area through which water is collected; infiltration-limiting fill material above the well limits the downward movement of surface runoff. The size and shape of the well is governed by the hydraulic properties of the local glacial aquifer and the hydraulic gradient. Importantly, the geochemistry of groundwater in the shallow glacial aquifer (generally oxic and slightly acidic) inhibits the mobility of arsenic, resulting in low concentrations of arsenic in the groundwater. This novel design can reduce human exposure to arsenic in drinking water for thousands of private well owners without the need for sustained chemical treatments.

Poster Session & Lunch Break

1:30-1:55 pm
Riverbank Filtration in New England: The Groundwater/Surface Water Hybrid
Greg Smith, Hydrogeologist; Jeffrey Musich

High yield groundwater sources have historically been developed adjacent to large water bodies. Riverbank filtration is a relatively new approach to developing high yield groundwater sources in New England where the well is constructed in close proximity to a surface water body instead of a direct surface water intake or a conventional vertical well. Multiple well technologies are applicable for bank filtration approach including horizontal wells, angle wells, and radial collector wells and can be used in soil formations where conventional vertical wells are not applicable. We will examine two case studies for Bank Filtration on the Merrimack River: The Hooksett West River LLC Site in Hooksett New Hampshire; and the Hill Site in Haverhill, MA. Well technologies, groundwater exploration including geophysical survey techniques, water quality, and regulatory issues will be discussed.

2:00-2:25 pm
A Horizontal Well in a thin sand and gravel aquifer adjacent to an existing reservoir, Castine, Maine
Peter Garrett, Emery & Garrett Groundwater Investigations, LLC

Castine has been challenged to provide a water supply due to its location on a rocky peninsula almost separated from the mainland. The Battle Avenue Ponds were constructed as reservoirs in the 1800s in an area of springs located on a hillside above the town center. The Ponds were used as a source of unfiltered water supply until the Drinking Water Act required filtration in the 1980s. Since then groundwater, primarily from bedrock wells, has been the source of supply. Stricter regulation of arsenic and radionuclides in the 2000s made operation of several of the bedrock wells problematic.

Detailed investigation of the geology of the Battle Avenue Pond property demonstrated the local existence of a sand and gravel aquifer, 10’ thick (5’ saturated), overlying marine clay. A 20’ long horizontal test well was installed at the base of this aquifer in a trench excavation oriented parallel to one of the Ponds. The test well produced 10 gpm with 2’ of drawdown. Water quality was excellent, except that, due to infiltration of Pond water, bacteria were persistent and micro-particulate analysis failed.

A horizontal production well, 440 feet long, was later installed in a separate trench excavation using construction materials approved for drinking water sources. It will serve as a collection gallery, gravity-draining to the site’s pumping station. There it will be subject to treatment as a source of groundwater under the influence of surface water. The treatment plant is now in design and permitting.

Afternoon Break

3:00-3:55 pm
Forty-four years of advancement in groundwater studies
Robert Gerber, PE, CG, Ransom Consulting

This is a review of how methods and tools for finding and studying groundwater have changed over the past 44 years. It is a review of the changes that have occurred broadly within the field of groundwater studies as well as the changes in the author’s skill set with time. The presentation gives examples from each decade of work, illustrating how the new tools and computer programs of the decade made it possible to provide more complex analyses. The author’s career progressed through 1) finding high yield wells in sand and gravel; 2) determining the “safe yield” of these wells; 3) finding high-yield bedrock wells; 4) dealing with a variety of water quality issues including natural and man-made. The EPA made wellhead protection a major issue in the late 1980’s and the issue became one of defining how much of the area of contribution to protect. A succession of water quality issues became topics of study and learning with the current hot topic being arsenic. Most recently, the DEP’s Ch. 587 In-stream flow rule has made the study of well water withdrawal on stream flow depletion a major focus of study. Although the cost of field data gathering has generally increased with time, the cost of data analysis and prediction have decreased, with the result that fewer field data are collected, more office analysis is performed with the aid of public domain data, and the overall cost of studies has decreased in real dollars.