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BALTIMORE COUNTY DEPARTMENT OF ENVIRONMENTAL

PROTECTION AND RESOURCE MANAGEMENT

FACTS ABOUT WELL YIELDS IN BALTIMORE COUNTY

Based on frequently asked questions about well yield requirements, the Department of Environmental Protection and Resource Management (DEPRM) has prepared the following information.

The minimum well yield requirements for approval of a domestic water supply is a state regulation that has been in effect since 1981. The state regulation requires that new well systems must be able to yield at least 1 gallon/minute over a six-hour period. In addition, new well systems must be constructed such that they can deliver at least 500 gallons over a 2 hour period. In other words, lower yielding wells must be drilled deep enough to provide a reservoir of water available for immediate use.

A minimum well yield requirement for property conveyance has been in the Baltimore County Code since 1980. The County Code also requires that domestic water supplies yield a minimum of 1 gallon/minute, however, the buyer of an existing property has the right to accept a yield less than I gallon/minute. In addition, there is no storage requirements for existing wells. A yield test, conducted to determine the well yield, is valid for three years.

These laws are intended to provide reasonable assurance that residents of properties served by private water supplies have adequate water supplies for typical domestic purposes. They are not a guarantee of water well yield.

Theoretically, the minimum well yield (I gallon/minute) equates to 1,440 gallons/day, which is over 4 times the average consumption for a family of four (300 gallons/day or 75 gallons/day/person).

DEPRM has recorded well replacement statistics in Baltimore County since 1989. The data indicates that each year approximately 165 wells (or <1 % of the 30,000+ wells on record) are drilled to replace a previously existing water supply. This includes new wells drilled to replace substandard water supplies such as hand dug wells and springs. The number of wells drilled per year to replace a well due to "insufficient yield" is approximately 60.

It is DEPRM's experience that most of the replacement wells drilled due to "insufficient yield" are discovered when the property owner decides to sell the house and is required to conduct a yield test. The reason for this becomes evident if you consider the average consumption for a family of four (300 gallons/day) equates with a yield less than 1/4 gallons/minute. In other words, the minimum yield requirement of a 1 gallon/minute acts as a conservative estimate for most domestic users.

While it is not uncommon for a well yield to exhibit seasonal variation, there is generally not a wide fluctuation over the lifetime of a well. The ability of a well in bedrock aquifers to produce water is dependent on the number and size of fractures intercepted during drilling. Occasionally, wells may "go dry" due to drought conditions, or natural siltation (clogging) of the water bearing fractures.

Some formations are known to be "good producers" due to the highly fractured nature of the rock, however, there remains a possibility of drilling a "dry hole" if suitable fractures are' not encountered during drilling. In general, it is more likely to drill higher yielding wells in valleys or drainage swales than it is on ridge tops.

Water pressure at the tap is not necessarily dependent on well yield. Proper sizing of the well pump, pressure tank, and distribution lines by a licensed plumber will ensure adequate pressure for the user.

If you have additional questions or want further clarification contact Baltimore County's DEPRM at  410-887-2762.

c:well yield fact sheet-7/99

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Gaylord Brooks Realty Company     410-667-0800
P.O. Box 400, 14346 Jarrettsville Pike     Pheonix, Maryland 21131

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