Hawaii Department of Health, Safe Drinking Water Branch
04/23/04 - 06/28/05
A WRRC team headed by Dr. Aly El-Kadi has recently completed the task of conducting an assessment of the State's 450-odd drinking water sources for the State Department of Health (DOH). The work implemented the state's source water assessment program (SWAP) plan that the EPA approved in November 1999.
For each drinking water source in the State the WRRC team performed modeling of the source's capture area based on elements of hydrogeology at each site and the rate and pattern of withdrawal at each source. Much of this work drew upon data obtained from studies conducted by the U.S. Geological Survey. The sofware employed in this modeling was Modflow, a commercially available 2-dimensional groundwater flow model that is widely used. Two capture areas were defined using this software; a 10 year travel time zone, and a two year travel time zone. In addition to these two zones a third area, the well site control zone with a diameter of 50 m around each source was established. The logic of these travel time zones is that chemical contaminants can be expected to last 10 years in the environment, microbiological contaminants can be expected to last two years, and all types of activities within the 50 m well site control zones will be closely examined. The two-year zone ties into the provisions of the soon to be implemented groundwater disinfection rule which mandates disinfection for all groundwater sources. Together the three zones are referred to as Well Head Protection Areas (WHPAs).
Once the WHPAs were established team members identified potentially contaminating activities (PCAs) within these zones. This involved acquiring and analyzing existing GIS data layers showing land use, searching of business directories, maps, and telephone records, and undertaking a limited number of site visits to the WHPAs to clarify questions which arose from analysis of the collected datasets.
Each PCA was assigned a score depending on the seriousness of the threat it posed, a function of it's extent and character.
Finally each source was assigned a score based on the cumulative scores of the PCAs identified within that source's WHPA.
Reports that include maps of each WHPA, lists of PCAs located therein, and scores for each WHPA have been delivered to the State Department of Health and have been distrubuted to each water utility to aid them in their wellhead protection efforts. If you would like to view this information please contact the appropriate water utility.