A DEPARTMENT OF THE STATE OF LOUISIANA

WATER

Source Water Assessment Program

The Source Water Assessment Program was required by the federal Safe Drinking Water Act Amendments of 1996 to determine the potential susceptibility of public water supply systems to contamination.  The state's source water assessment plan document was submitted to the U.S. Environmental Protection Agency (EPA) in 1999 and the mandated completion date for all assessments was May 6, 2003.  Although the work on the program took place from 2000 - 2003, information obtained during the assessments serves as the foundation for the Drinking Water Protection Program.  Assessments will continue to be conducted for new or expanding water systems.

What is the Source Water Assessment Program?

The Safe Drinking Water Act (SDWA) Amendments of 1996 emphasize pollution prevention to ensure safe drinking water, focusing on the protection of the water sources. In order to achieve such protection, all states are required to develop Source Water Assessment Programs. Once completed, these assessments can be used to focus prevention resources on drinking water protection. The Louisiana Department of Health and Hospitals (LDHH) entered into an interagency agreement with the Louisiana Department of Environmental Quality (LDEQ) to develop and implement the State’s Source Water Assessment Program. The program is funded by a set-aside of the Federal Drinking Water State Revolving Fund Grant awarded to LDHH.

A completed source water assessment for a public water supply must include the following key elements:

  • A delineation of the source water protection area. The delineated area defines the zone through which contaminants, if present, are likely to migrate and reach a drinking water well or surface water intake.
  • A contamination source inventory for that source water protection area. The inventory consists of regulated and unregulated potential sources of contamination and associated contaminants of concern within the area or any known existing contamination. This is in essence a vulnerability analysis.
  • A determination of the public water supply’s susceptibility to contamination by sources identified within the source water protection area. The susceptibility analysis combines a hydrogeologic sensitivity analysis with the vulnerability analysis within the delineated areas.

The Source Water Assessment Program will result in an evaluation of the source water that provides drinking water to each public water supply system in Louisiana. This evaluation will determine the degree to which a public water supply is protected, or at risk from, contamination. Once completed, the assessment results will be used to assist local communities in implementing protection measures such as contingency planning, implementation of best management practices, adoption of local ordinances, and public education.

For more information, please contact the Aquifer Evaluation and Protection Section at (225) 219-3510.

What are Source Water Protection Areas and How Are They Delineated?

Source Water Protection Areas

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:

  • A one-mile fixed radius for wells screened above 1000 feet.
  • A half-mile fixed radius for wells screened below 1000 feet and completed before Louisiana Department of Transportation and Development (LDOTD) regulations promulgated November 1, 1985.
  • A 1000-foot radius for wells screened below 1000 feet and completed after LDOTD regulations were promulgated.
  • A half-mile radius for transient non-community wells in the Terrace Aquifer.
  • A 1000-foot radius for all other transient non-community wells.

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. 

What is a Source Water Protection Area Inventory and What is a Significant Potential Source of Contamination?

Source Water Protection Area Inventory

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.

What is a Potential Susceptibility Analysis?

Susceptibility Analysis

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:

  • Depth of the well (the shallower, the more sensitive)
  • Age of the well (the older, the more sensitive)
  • Average ground water velocity in the aquifer in which the well is screened (the higher, the more sensitive)
  • Soil recharge potential (the higher, the more sensitive)

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:

  • Age of the intake (the older, the more sensitive)
  • Length of streams in the source water protection area (the longer, the more sensitive)
  • Runoff (the higher, the more sensitive) factors - high precipitation, steep slope, low vegetative cover, and low soil permeability contribute to high runoff

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.

 

Source Water Assessment Program Document 

Louisiana Source Water Assessment Program

Appendices A-Z