Glossary

Aquifer – An aquifer is defined as an underground bed or layer yielding groundwater for wells and springs. It may occur at any accessible depth below the ground surface and may or may not require pumping to reach the surface. Aquifer productivity depends upon permeability, or the ability of the water to move, in the aquifer. Permeability is primarily controlled by the size and interconnectedness of pore spaces or fractures. The quality of water from an aquifer typically depends upon the chemistry of the geologic unit comprising the aquifer, and the chemistry of the water as it may have been influenced in its path to the aquifer. For example, an aquifer with fractured limestone typically produces harder water, due to a higher concentration of calcium and magnesium, than water from an alluvial aquifer composed of unconsolidated gravels and sands. A number of aquifers may exist below a given location at varying depths and may be stratified (one above the other). If geologically isolated by a "confining layer" (typically clay or some similarly impermeable material), each aquifer may have its own unique water quality. Without a confining layer, intermixing may occur.

Primary and Secondary Metals – The U.S. Environmental Protection Agency has identified Primary Drinking Water Standards for a number of constituents with associated health risks.  These are legally enforceable  standards that apply to public water systems and are designed to protect the public from ingesting potentially toxic levels of chemicals. The following metals can be found on this list and have been requested for analyses of residential well samples submitted by PPL.

Antimony (Sb), Arsenic (As), Barium (Ba), Beryllium (Be), Cadmium (Cd), Chromium (Cr), Copper (Cu), Lead (Pb), Mercury (Hg), Selenium (Se), and Thallium (Th).

The EPA also has identified Secondary Drinking Water Standards for drinking water constituents that may cause cosmetic (skin or tooth discoloration) or aesthetic effects (such as taste, color or odor) in drinking water. For these constituents, EPA has established unenforceable guidelines that may or may not be adopted by individual states as enforceable standards. Metals listed in this category by the EPA are:

Aluminum (Al), Copper (Cu) [both lists], Iron (Fe), Manganese (Mn), Silver (Ag), and Zinc (Zn)

Naturally-Occurring in Groundwater – Because nearly all rocks are composed primarily of inorganic constituents, these metals and other inorganics appear in groundwater. Their concentrations are determined by a complicated set of conditions, including concentration in host rocks or former host rocks, solubility (a function of temperature, acidity and conductivity, competing ions, etc.). Because these are elemental constituents they do not naturally degrade to other simpler constituents. Their concentrations may, however, change due to a change in solubility or other factors. Some inorganic constituents are very common and occur in all groundwater (such as calcium, potassium, magnesium and sodium), while others are more rare and/or in much lower concentrations. Some are considered to present a health risk at low concentrations (such as arsenic, mercury, cadmium and lead), while others are considered good for the body and are included in mineral supplements (zinc, copper, selenium, calcium and magnesium). To understand the health risks and benefits associated with naturally occurring metals, one should compare the EPA MCL or MCLG (see definition 10 below) with concentrations in your drinking water. The challenge for environmental specialists is often to determine the contribution of metals due to naturally-occurring background versus those contributed by anthropogenic (man-induced) processes.

Hydrogeology – Hydrogeology is the study of groundwater and the geologic formations through which it travels or resides. It is important to the understanding of water quality in many ways. For example, aquifers in limestone bedrock and in unconsolidated alluvial sands may have very different chemical signatures. Water that results from the mixing of several aquifers may have characteristics of both, or a unique balance of its own water quality features. Water samples from one well should not be compared to water samples from another well unless the wells draw from the same aquifer and are expected to present comparable water quality characteristics.

Primary Constituents of Concern in Fly Ash - Fly ash is a material that remains after the combustion of coal. The process of combustion removes most organic (combustible) constituents and leaves a highly concentrated solid containing many naturally occurring metals within an aluminosilicate matrix. Typically the metals in aluminosilicates do not dissolve ("leach") into the water, but "leachability" may be variable under certain geochemical conditions. Thus, most important to understanding the risks to residential drinking water quality, is understanding which inorganic constituents are leaching from the fly ash into groundwater and whether any such contaminated groundwater has a pathway to flow to your tap . The most common inorganic constituents that might leach from fly ash under normal hydrogeologic conditions include arsenic, selenium and mercury.

Milligams per Liter (mg/L) - Is a standard unit of measure for reporting the concentration  of constituents in water. A milligram (mg) is one-millionth of a kilogram (kg). One liter of water weighs approximately 1 kg (if you ignore the very small density differences between pure water and most drinking water samples). Therefore, one milligram is one-millionth of the mass of 1 liter of water (I kg),and equals 1 part per million parts, or 1 ppm by weight.

Micrograms per Liter (ug/L) – Similar to the above description of Milligram per Liter, 1 microgram per liter (ug/L) is equivalent to 1 part per billion parts, or 1 ppb by weight.

Corrosion of Pipes – Corrosion of pipes can affect the color and taste of supplied water, cause stained fixtures or possibly cause health impacts due to the transfer of toxic metals in drinking water. The most notable metal directly attributed to health impacts is lead. Homes built before 1986 are more likely to leach lead from distribution pipes, fittings or fixtures than newer homes. Current regulations for piping still allow for up to 8 percent lead. Most common lead problems are attributed to leaching from brass- or chrome-plated faucets. The more common metals attributed to leaching from piping and fixtures are lead, copper, iron and manganese with lead generally posing the most serious health risk.

Maximum Contaminant Levels (MCLs) and Maximum Contaminant Level Guidelines (MCLGs) The EPA has established nationwide enforceable standards for certain constituents of drinking water that are believed to pose certain health risks. These numbers are called MCLs and are the highest level of a listed constituent that is allowed in drinking water. MCLGs are the level of a constituent below which there are no known or expected health risks. MCLGs are more conservative and allow for a margin of safety. They are nonenforceable health goals, unless adopted as regulatory standards by individual states.