Linking Water Treatment with Wetland Restoration - Restorative Redevelopment of Devastated Ecocultural Landscapes - page 372

Laguna Niguel, southern California, concerns irrigation overflow from residential
neighborhoods that was adding a significant coliform bacteria load to the stream
which, because of extremely low rainfall and high evaporation, reached high concen-
trations. The system built by CH2MHILL was a simple series of successive ponds
down the drainage gradient that within a year was completely vegetated and within
three years had also developed a bordering riparian shrub forest. Importantly, treat-
ment performance has been spectacular in these wetlands with coliform reductions
of over 99 percent, thereby achieving levels that are far below the public health stan-
dards. This case study provides wonderful proof that wetlands can indeed be used to
disinfect and improve water quality, an issue of obvious significance to the situation
in southern Iraq (Bays 2004).
Another small project that CH2MHILL is presently working on in Oxnard, south-
ern California, addresses the salinity question, another issue of pressing concern in
the restoration of the southern Iraqi marshes (France 2011). The city Water Division
was expanding its water supplies with a new reverse-osmosis membrane treatment
facility and although outfall to the nearby ocean was possible, local interest in wet-
land restoration prompted the question of suitability for treatment restoration. The
project takes reverse-osmosis membrane and treatment concentrate and applies it
to a series of constructed marshes in which six different technologies are examined
side by side. The idea was to create a new water source of about 4,000 mg/L TDS
and to select those brackish and natural saltmarsh plants tolerant of brine concen-
trate and then see how well they performed. The six different technologies included
a high marsh that was shallowly flooded, a low marsh that was flooded to a foot
or two or so in depth, a gravel-based subsurface flow wetland, and a peat-based
vertical-flow system. Inflow nitrate concentrations were very high (40-50 mg/L) due
to the source of water initially being groundwater with a consequent long legacy of
agricultural contamination. Both the surface-flow low marsh and the vertical-flow
systems significantly reduced nitrates down below the World Health Organization
standard of 10 mg/L due to having the right kind of habitat and low-oxygen condi-
tions to encourage denitrification. The chemical constituent of most concern with
known ecotoxicological properties is selenium, also an issue in the Iraqi marshes.
Only the vertical-flow wetland was found to do a good job in removing selenium
due to the anaerobic environment which reduced it to an inorganic form that was
essentially bound in sediments in the system, thereby being unavailable to wildlife
(Bays 2004).
Another CH2MHILL project with useful comparisons for Iraq is the Sweetwater
Wetlands in the desert city of Tuscon, Arizona (Bays 2002). High-strength wastewa-
ter, not unlike what would be expected in some parts of Iraq, is received from a tra-
ditional wastewater treatment plant and the quality improved by movement through
the wetland prior to its use for recharging the local groundwater. This system is also
designed to function as a park that provides and sustains wildlife habitat at the same
time as providing educational and recreational amenities through the construction
of numerous landscape features to encourage use of the site. The project is also a
good example of where progress toward vector control has been a significant issue
(Bays 2004). High densities of mosquito larvae were initially present (up to eight
thousand individuals caught per trap night) because biological predators had not