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.