LOUISIANA DEPARTMENT OF ENVIRONMENTAL QUALITY | Secretary Aurelia S. Giacometto
A DEPARTMENT OF THE STATE OF LOUISIANA
A Source Water Protection Area defines the zone through which contaminants, if present, are likely to migrate and reach a drinking water well or surface water intake. Every public water system obtains its water from either a ground water source (aquifer) or a surface water source (stream, river, reservoir or lake). Delineation of source water protection areas is based on the source of the water supply.
Delineation for Ground Water Systems
For assessment and protection of ground water supplied public water systems, the Arbitrary Fixed Radius Method of delineation will be used. The Arbitrary Fixed Radius Method is the established method for the State's U.S. EPA approved Wellhead Protection Program, a protection program for ground water systems implemented since 1991. This method is most appropriate for Louisiana due to the highly variable nature of river laid deposits across the state and the lack of site-specific hydrogeologic data (aquifer data). Radius sizes based on vulnerability of the well in order of priority are as follows:
Delineation for Surface Water Systems
Delineation of Source Water Protection Areas for surface water bodies will include the entire watershed upstream of the public water supply intake structure up to the boundary of the state borders. However, for the purpose of assessment, a database assessment will be done for potential sources of contamination over the portion of the watershed contributing to the water intake that is outside of the field assessment area, the non-critical area. The field assessment will be conducted in the critical area which is defined as the upstream portion of the watershed within 5 miles of the intake.
A Source Water Protection Area Inventory consists of regulated and unregulated potential sources of contamination and associated contaminants of concern identified within the source water protection area or any known existing contamination in the area. The contaminants of concern include those raw water contaminants regulated under the Safe Drinking Water Act (SDWA) (those contaminants with a maximum contaminant level or "MCL"), contaminants regulated under the Surface Water Treatment Rule (SWTR), and the microorganism Cryptosporidium. The SWTR is designed to minimize risks from only a subset of microbial contaminants (Giardia, Legionella, and viruses). In addition, states may include those contaminants that are not federally regulated under the SDWA, but which the state has determined may present a threat to public health. The state does test for some unregulated organic chemicals and these are included in the list of contaminants of concern.
The U.S. EPA defines a Significant Potential Source of Contamination as any facility or activity that stores, uses, or produces, as a product or by-product, the contaminants of concern and has a sufficient likelihood of releasing such contaminants to the environment. The release would be at levels that could contribute significantly to the concentration of these contaminants in the source water of public water supplies. DEQ has developed a list of significant potential sources of contamination for ground water and surface water and ranked the potential sources into high, medium, and low risk categories based on sources of public water supply contamination in the past and experience of the staff. This is in essence a vulnerability analysis. Examples of significant potential sources of contamination include, but are not limited to, industrial facilities, underground storage tanks, auto repair shops, oil and gas activity, dry cleaners, abandoned water wells, and agriculture. Locations of significant potential sources of contamination within each source water protection area will be determined by field surveys and available databases.
Potential for Contamination by Significant Potential Sources of Contamination
Potential contamination sources are facilities that use, produce, or store contaminants of concern (those regulated under the Safe Drinking Water Act) which, if improperly managed, could find their way into a source of public drinking water. It is important to understand that a release may never occur provided they are using best management practices. Many are regulated at the federal level, state level, or both to reduce the risk of a release. There are a number of methods that water systems can use to work cooperatively with such facilities. These often involve educational visits and inspections of stored materials. Many owners of such facilities may not even be aware that they are located near a public water supply well or intake.
A Potential Susceptibility Analysis is a determination of the susceptibility of the public water supply to contamination by significant potential sources identified within the source water protection area. The potential susceptibility analysis consists of a sensitivity analysis, which includes factors inherent to the system and source water, and a vulnerability analysis, which is the number and types of significant potential sources of contamination identified. Therefore, the potential susceptibility analysis combines a hydrogeologic or hydrologic sensitivity analysis with a vulnerability analysis within the delineated areas. The results of the analysis can be used as a basis for determining appropriate new protection measures or reevaluating current protection efforts.
Potential Susceptibility Analysis for Ground Water Systems
Factors considered in determining sensitivity for ground water systems include:
The types and quantity of significant potential sources of contamination found and their distance from the well(s) will influence the degree of vulnerability for the water system.
Potential Susceptibility Analysis for Surface Water Systems
Factors considered in determining sensitivity for surface water systems include:
The types and quantity of significant potential sources of contamination found and their distance from the surface water source (stream, river, reservoir or lake) will influence the degree of vulnerability for the water system.