Hawaii’s Source Water Assessment Program (SWAP)
project, headed by Dr. Aly El-Kadi, completed the task of conducting an
The SWAP team and the reports produced for the project
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
Much of this work drew upon data obtained from studies conducted by the
Geological Survey (USGS). The software employed in this modeling was
USGS three-dimensional groundwater flow model that is widely used in
with MODPATH, a USGS groundwater particle tracking model. The models
integrated in the commercially available Groundwater Modeling System
which was used as a vehicle for data preparation and results
presentation. GMS facilitates
the modeling process by utilizing geographic information system maps.
capture areas were defined using this software: a 10-year travel time
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
established. The logic of these travel time zones is that chemical
can be expected to last 10 years in the environment, microbiological
contaminants can be expected to last 2 years, and all types of
within the 50-meter well site control zones naturally warrant close
examination. The 2-year zone ties into the provisions of the
groundwater disinfection rule which mandates disinfection for all
sources. Together, the three zones are referred to as Capture Zone
(CZDs). In addition a 25-year time-of-travel zone was delineated for
groundwater sources on
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.