| Groundwater Studies
An extensive data-gathering program was initiated to determine
whether bacterial contaminants in groundwater were responsible for the contaminants
found in the Huntington Beach surf zone. An initial survey of the area used instruments
that measured: a) one- or two-dimensional patterns in subsurface conductivity; b) subsurface
metals; and c) conductivity in boreholes. A series of wells around TM and in other potentially
strategic regions were monitored for bacterial contamination and nitrogen. Data from
the wells were used to refine models of groundwater movement. These models showed that
groundwater moves toward the beach in a shallow layer that rests above a salt-water
intrusion zone. It was thought that although some contaminated groundwater flowed into
local surface waters, such as TM, the impact was minimal. The magnitude of the transport
was small compared to contaminant levels associated with beach closure events.
Panel Comments:
The presenters suggested that groundwater was not a significant source of beach contamination;
however, the presenters did not show data supporting this conclusion, though they
did allude to the fact that observed beach contamination patterns (i.e., the relationship
to spring tides, the short temporal extents, and the high contaminant levels) did
not match current groundwater process models. In addition, it appeared that shallow
groundwater in the region is influenced by surface water contamination. Therefore,
the Panel believes that the data supports the above conclusion and that further groundwater
studies are not necessary.
Additional information may be obtained from the data already collected.
Patterns in nitrates measured in the groundwater could be used to determine if the
nitrates were from a local source, such as sewage, or were linked to the generally
high nitrate levels associated with historical farming patterns. The presenters also
suggested that bacteria levels in the core samples were not stratified by depth. A
subsequent presenter suggested that bacteria from cores in TM were concentrated in
the upper few centimeters of the core sediment. This conflict should be resolved.
The objectives of the geophysical investigations were unclear. The
Panel could not determine how the results of these studies enhanced the understanding
of groundwater contaminant pathways to Huntington Beach.
Some of the hydrogeologic figures from the model were misleading.
In particular, the groundwater flow diagrams near TM were inaccurate. The presenters
should rethink and redraw the conceptual model of hydrogeologic flow patterns because
the public may view conceptual models of flow patterns as actual conditions.
Coastal Ocean Process Studies
A variety of physical oceanographic data in the near-coastal zone was collected during
the common study period of May 3-17, 2000. In particular, currents, directional wave
data, and sea level and wind records were obtained at several sites in the near-coastal
ocean. Similar sets of records were collected in the Santa Ana River (SAR) channel
and at several sites within TM. Only a limited selection of the data was presented
to the Panel. It appeared that this extensive data set would be used primarily to
calibrate a two-dimensional numerical model that predicts contaminant transport through
the SAR, TM, and coastal ocean. The model seems to be driven mainly by processes associated
with tides and waves, but neither the details of the model nor model-calibration procedures
were presented to the Panel.
Panel Comments:
An extensive analysis of the data should be undertaken to determine the major processes
that transport contaminants in the local region.
The coastal-ocean numerical model may be an important tool to help
determine regulations for future beach-closure issues. Sufficient information on this
nested model was not presented for the Panel to evaluate the potential validity of
the model. The general impression is that a two-dimensional numerical model will not
represent contaminant-transport patterns in complex near-shore environments because:
- If the model is a commercial product, it is possible that
a lack of access to the model's code will limit the ability to mimic local events.
- If a commercial model is chosen, it might be useful to hire one
of the developers to customize it.
However, if a model is developed for this region and has an open
code, the local research or university community might be used to improve model performance.
It would be useful to determine if models similar to the ones under
consideration have helped identify sources of pollution in the near-coastal ocean.
A concerted effort should be made to validate any model using the collected data sets
described above. It is recognized that these data sets are too limited to validate
extreme or unusual events. Hence, models may never mimic extreme events.
Dye Studies for Plumes from Talbert Marsh
and the Santa Ana River
Dye was injected into the channels joining the TM and SAR to the coastal ocean. Dye
was injected for a specified period of time over a relatively short section across
each channel. The path of the dye was followed with local water samples and with remote
monitoring from an aircraft. Limited data were presented to the Panel.
Panel Comments:
The Panel recognizes that the dye path determined in this project represents conditions
at one specific point in time. This particular path may not represent general conditions,
though it may represent a particular portion of the spring/neap tidal cycle.
The total amount of dye released and the flow rates in the channels need to be quantified
to determine initial dye concentrations.
It is unfortunate that dye concentration data were lost at 3N, a
critical site. Data from this site would have been useful to calibrate dispersion
models. However, the data did show the following important results:
- Water from central portion of the SAR bypassed the littoral
zone.
- Rip tides moved water from the littoral zone into the
coastal ocean.
- High transport speeds of up to 1 kilometer per hour (kph)
were found in the littoral zone
The Panel noted that the dyes were released sequentially within
the two channel systems. The second dye release was near the end of the ebb tidal
cycle. Hence, the patterns in the two systems cannot be directly compared.
In future dye studies, two injection systems could be used to inject
dye simultaneously into TM and SAR. Perhaps each system can use a different color
dye. If possible, the dye would be injected across the full channel width at narrow,
defined sites, leaving wide spaces between the injection sites. This dye pattern might
represent flow streamlines. The resulting data would be particularly helpful in understanding
how wider coastal inlets, such as the SAR, exchange with the coastal ocean. In particular,
water flowing through the central portion of a wide channel may bypass the littoral
zone, while water in the slower flowing regions near the channel edges may turn into
it and travel parallel to the beach. This water may contain higher concentrations
of bacteria because dry areas near the channel edges are inundated during spring tides.
A fair number of birds that deposit fecal matter are often seen when the shore is
dry or only covered with a small amount of water.
Talbert Marsh Investigations
Two investigations were carried out to determine if bacteria from either TM or urban
runoff into the TM are carried into the coastal ocean during ebb tidal flows. The
initial winter 1999 study monitored hourly bacterial concentrations in the channel
between TM and the coastal ocean for a 2-week period. These initial investigations
suggested that high levels of bacteria did occasionally pass from TM into the coastal
ocean. This information led to additional data collection. Hourly bacterial samples
were collected during the intensive 2-week sampling period in May 2000 at the head
of TM and in the channel connecting it to the coastal ocean. The oceanographic conditions
during this second study were more similar to conditions during the closure period
in 1999 in that the water was warmer and the timing of the tidal cycles was closer
to summer conditions. During the first week, several of the pump stations were in
a diversion mode while in the second week they were connected to the storm channel
system. During the same two-week period the gravity flow channels were never diverted
to the sewage system.
Only some of the data from the second study was presented to the
Panel. The initial results suggest that high bacterial counts are found in the ebb
tidal waters exiting TM. Because the strongest ebb flows occur during the late night
and early morning hours, bacteria may survive to enter the coastal water before sunlight
possibly destroys them; therefore, TM (or the SAR, which was not monitored) could
be a source for bacterial contamination.
Panel Comments:
The Panel could not determine the contamination patterns at sites 3N and 9N from the
data sets presented. These sites need to be added to the study plan.
The Panel was under the impression that the techniques used to determine
contaminant levels in TM were different from those used in surf-zone studies. If so,
the techniques need to be inter-calibrated. In particular, are there any methodological
conflicts?
Recognizing that this study is still underway, the Panel would like
to see more comparisons between the TM data sets and those collected in the surf zone
or the coastal ocean. These comparisons will help determine whether the releases from
TM coincide with elevated contamination in the surf zone. One could sort the OCSD
historical data set by tidal stage and/or by day/night cycles. This sorted data could
be compared to the TM data. The resulting information might help increase our temporal
understanding of bacterial contamination cycles.
 
|
OC
Sanitation District - Huntington Beach Closure Investigation Phase
I 
PFRD
Medium Range Strategy
