Featured Project

Hawaii’s Source Water Assessment Program (SWAP) 

This project, headed by Dr. Aly El-Kadi, completed the task of conducting an assessment of Hawaii’s 450-odd drinking water sources for the Department of Health. The work implemented Hawaii’s source water assessment program (SWAP) plan that the EPA approved in November 1999.  



The SWAP team and the reports produced for the project

Groundwater

Groundwater source delineation

For each public drinking water well 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 for each source. Much of this work drew upon data obtained from studies conducted by the U.S. Geological Survey (USGS). The software employed in this modeling was MODFLOW, a USGS three-dimensional groundwater flow model that is widely used in conjunction with MODPATH, a USGS groundwater particle tracking model. The models are integrated in the commercially available Groundwater Modeling System (GMS), which was used as a vehicle for data preparation and results presentation. GMS facilitates the modeling process by utilizing geographic information system maps. Two capture areas were defined using this software: a 10-year travel time zone, and a 2-year travel time zone. In addition to these two zones, a third area, the “well site control zone” with a diameter of 50 meters 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 2 years, and all types of activities within the 50-meter well site control zones naturally warrant close examination. The 2-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 Capture Zone Delineations (CZDs). In addition a 25-year time-of-travel zone was delineated for the groundwater sources on Molokai in accordance with Hawaii’s Well-Head Protection Demonstration Project performed in 1992.

Surface Water

Similar to the groundwater CZDs surface water CZDs were delineated using the following three-part formula; Zone A – 200 foot radius around the water intake point; Zone B – 400 feet from the perimeter of reservoirs and lakes and 200 feet from the banks of rivers, canals and ditches; and Zone C – the watershed area upstream of and contributory to the intake point and a 400-foot corridor along any open channel portions of the transmission system. For Zone C, Watershed Management Software (WMS) was used to delineate watershed boundaries based on available digital elevation maps. Watersheds thus generated were compared to those developed by the Hawaii Coastal Zone Management Program of DBEDT in 1994.

Under this scheme, Zone A (direct chemical contamination zone) corresponds to the well site control zones for wells, intended to assess the source’s vulnerability to tampering, vandalism and direct introduction of contaminants. Zone B (microbial contamination zone) designates the area that may introduce pathogenic microorganisms directly into the water source. Zone C represents the area from which indirect chemical contamination of a source could originate.

Source areas for water development tunnels were treated as groundwater under the direct influence of surface water (GWUDI) and modeled using the watershed approach because of the complexity of the geology where these types of sources occur.  

Once the CZDs were established, team members identified potentially contaminating activities (PCAs) within these zones. This involved acquiring and analyzing existing data layers showing land use; searching of business directories, maps and telephone records; and undertaking a limited number of site visits to the CZDs to clarify questions which arose from analysis of the collected datasets.

Each PCA was assigned a score (low, medium, high or very high), depending on the relative seriousness of its potential to contaminate the source water.

Finally, each source was assigned a score based on the cumulative scores of the PCAs identified within that source’s CZD.

Reports that include maps of each CZD, lists of PCAs located therein and scores for each CZD have been delivered to the Hawaii Department of Health and are being distributed to all the water utilities in the state to aid them in their drinking water source protection efforts.

As a follow up project, the research team has been awarded other grants to update and maintain the SWAP. The main tasks include updating the information based on new data, correcting errors, and addressing model and data uncertainty.