Breaking the Water Barrier
4/2/2009
Planning an On-Site Groundwater System
By Michael Shortell
Shelton, Connecticut
Water flows over almost three quarters of Earth's surface, yet it can form an all-too-solid barrier to a new project or expansion of an existing development when a municipal water supply system is inaccessible or insufficient to meet the demand. As development moves farther afield from a municipal center, it becomes increasingly expensive to connect with an existing water main. And, with water-main installation costs potentially ranging from $100 to $250 per linear foot, cost implications can be a major factor. In these cases, a developer must be prepared to provide an on-site water supply using a groundwater well supply system. Here is a look at the issues and process involved in planning, siting, testing and permitting an on-site groundwater system.
A typical on-site groundwater system comprises one or more groundwater wells supplying water to an atmospheric storage tank. Re-pressurization transfer pumps push the water from the atmospheric storage tank into the distribution system. Most state and local building codes require a minimum of two water supply wells to provide for redundancy; that is, the system must be capable of meeting demand with the most productive well out of service. If this is insufficient to meet demand, either because the two wells do not have adequate yield, or because output is restricted as a result of sanitary set-backs, then additional wells may be necessary.
Importance of Early Investigation
A developer considering a site for a new project is wise to conduct a water supply investigation early in the planning process. Municipal planning boards will not issue a building permit without establishing that there is adequate well yield to meet water demand. While supply generally is not an issue for small scale residential, office and retail projects in the Northeast, for example, a golf course project is another matter because it entails a high irrigation-water demand that may be difficult to satisfy if the only water supply sources are bedrock wells.
U.S. Geological Survey information has some predictive value for well yield, but one never knows for sure how much water is available until a test well is drilled. One test well may yield 40 gallons per minute (gpm), and another just 50 feet away may yield 1 gpm. In addition, the developer wants to complete this investigation before the architect sites a structure on top of the optimum location for a water well!
Of course, the type(s) of occupancy and population determine the appropriate per-capita and/or per-bedroom water usage rate(s) and thus, target yield. For a phased project, a determination of the total population and target yields for all phases of the project should be completed before the investigation begins.
Average daily demand will also be used to calculate the number of wells and the sizes of the well pumps, atmospheric storage tank(s), transfer pumps and pressure tank(s).
Targeting Cost-Effective Well Sites
The first step in the groundwater supply investigation is to obtain or develop a site plan that shows all potential sources of pollution on the property. These sources of pollution include storage tank (fuel oil, diesel etc), septic tanks, septic systems, storm sewers and surface water features, which have set-back requirements from proposed water supply wells.
On large properties, the water resources consultant often performs a fracture-trace analysis, which enables the consultant to identify a specific area of the property that offers the greatest potential to find water within the constraints of the set-back requirements. The depth of the water bearing fractures can vary considerably over the area of the property, and typical bedrock wells are drilled from 300 feet to 400 feet deep; however, it is not uncommon for wells to be as great as deep as 800 feet.
Potential well sites are indicated on the site plan and submitted with a well-site application to the health department with jurisdiction. After review and approval, a truck-mounted drilling rig is brought on-site to drill a test well(s).
Testing for Yield
After the well is drilled, a pumping test is conducted to determine the yield of the wells and collect water samples for laboratory analysis. A submersible pump, often generator-powered, is lowered into the well shaft and operated for a period of time as determined by state regulations. The state of Connecticut, for example, determines the length of the pump test according to the target yield; if target yield is less than 10 gpm, then the state requires an 18-hour pumping test; 10-50 gpm requires a 36-hour pumping test; above 50 gpm requires 72-hour pumping test. In New York, a 72-hour pumping test is required regardless of target yield.
Water Quality Issues
Toward the end of the pumping test, water samples are collected for laboratory analysis for the parameters identified in the state’s public health code. The parameters include, but are not limited to, coliform bacteria, volatile organic compounds (VOCs), semi-VOCs, metals, pesticides and herbicides.
Natural contaminants, relatively benign and/or hazardous in nature, also may be present in groundwater. The presence of minerals, such as iron, magnesium and calcium, typically creates “hard water,” which can be treated with relative ease. However, contaminants such as arsenic, radon, and radionuclides such as radium and uranium, are health hazards. Treatment options are available; however, the options may be more complex. The options could include filtration, aeration or ion exchange.
It is worth noting that just as yield varies between nearby well sites, groundwater quality on a given site can vary from that of existing wells on nearby properties and in nearby towns.
If this is an expansion project, the consultant should review existing objective water quality analyses and subjective user comments, including customer complaints. For example, current occupants of the property can provide information about fixture staining or odor which could be indicators of water quality issues.
Other aspects that need to be considered are the condition and functionality of the existing storage tanks and pumping equipment. As part of any upgrades to a faculty, the water supply storage and treatment equipment (if any) may need to be upgraded.
A Sustainable Water Supply
Developers, planners and architects who are striving for environmental sustainability may propose the use of water conservation practices which include water saving fixtures within the facility. Conservation practices can also be practiced with timely operation of irrigation wells These issues should be raised early in the planning process as the water resources consultant may recommend drilling one or more wells dedicated to irrigation in addition to those for the population.
Breaking the water barrier, development of an on-site groundwater system where municipal water is inaccessible or insufficient, has a significant impact on a project’s viability, schedule and cost. Consider the issues early to ensure that there is adequate water to meet current and projected demand.
