The New River Wetlands

Their role in removing bacteria 

from the river water
The New River

• The New River has been constantly called the 

“most polluted river in the United States. 

Running 66 miles from the US-Mexico border 

to the Salton Sea, Flow at the border is 

approximately 200 ft3/s (6 m3/s), and about 

three times this flow at the Salton Sea 

because of agricultural discharges in the 

Imperial Valley. 

• The pollution of the river comes from chemical 

runoff from the agricultural waste of the 

Imperial Valley irrigation system that accounts 

for about (69.6%), 29% is sewage from 

Mexicali, and waste from manufacturing plants 

is 1.8%. 

• By the time the river crosses the border, it 

carries about 100 different identified 

contaminants, such as volatile organic 

compounds, heavy metals, (like selenium, 

uranium, arsenic, and mercury), pesticides, 

and many types of pathogenic organisms that 

cause tuberculosis, cholera, encephalitis, and 

typhoid. Fecal coliform bacteria has various 

levels ranging from 100K to 16million colonies 

per milliliter, and this is far above the USMexico treaty limit of only 240 colonies. 
History of Pollution • Because of the sewage waste, the New River has 

had large amounts of the bacteria E. Coli since the 

early 1940s. The Water Treaty with Mexico that 

solved the problem of the Colorado River water 

uses included the agreement that both countries 

had to concentrate primarily on sanitation problems 

along the border, and the two countries created the 

International Boundary and Water Comission and in 

1948 this commision decided that they had to build 

a facilitiy to treat the water of the New River at a 

plant in Calexico. 

• After the Mexicali boom in population in the 1960s, 

and the increasing numbers of assembly plants after 

the NAFTA treaty of 1990, the old water plants in 

Mexicali and Calexico were inadequate to treat all 

the water flowing into the New River. 

• In the last years, there have been numerous 

attempts to control the pollutants in the New River. 

After the State Senate Bill 387 which amends state 

law to protect human and the natural environment, 

there are new hopes for the creation of more plants 

and other methods to reduce the amount of 

pollutants and, especially, the E. Coli Bacteria. 

Foam caused by toxic waste 

flows with the New River water 

as it crosses the border. 
What are the “pathogens” in the 

New River?

• Pathogens (from the Greek 

pathos “suffering/emotion” 

and gene “to give birth to”) 

are biological organisms 

that cause illness and 

infectious diseases. These 

pathogens are more easily 

measured by bacteria 

called Coliforms, which are 

rod-shaped, gram-negative, 

non-spore forming 

organisms that are 

abundant in the feces of 

warm-blooded animals. 

They are used to measure 

the presence of other 

pathogenic organisms in a 

certain environment such 

as virus, protozoa, or 

parasites. 
Attempts to Clean the New River

• There have been many attempts to “clean” the New River by many groups of 

“concerned” local citizens and local governmental agencies such as the 

Calexico New River Committee in 2001, the Salton Sea Ecosystem 

Restoration program, and the Citizen’s Congressional Task Force on the 

New River. 

• A proposal from the Citizens Congressional Task Force on the New River 

was to construct a series of wetlands that would act as “nature’s filters” to 

remove the bacteria and the other contaminants carried by the river’s water. 

The project was finally funded by the U.S. Environmental Protection Agency 

and the Bureau of Reclamation.

• The purpose of the construction of wetlands was not to create a wildlife 

habitat but to demonstrate the ability of wetlands to improve the quality of 

water in the New River. 
Wetlands

• Wetlands have been constructed in developed nations to treat water 

that contains industrial, agricultural, and residential waste. These 

wetlands act as natural filters where the contaminants are removed 

through a series of natural processes involving wetland plants and a 

network of causeways that decrease these contaminants as the 

water reaches the outlet and is returned to the rivers. 

• Brawley Wetland Imperial Wetland

• Two wetlands were constructed in 2000, one near Imperial and 

another one near Brawley, with the Imperial wetland receiving 

agricultural waste water and the Brawley wetland receiving water 

directly from the New River. 
Proposal

• As wetlands have been proven to be effective in 

other environments, the proposal of the 

construction of a series of wetlands attempts to 

reduce significantly the percentages of 

contaminants of the New River. If the wetlands 

of Imperial and Brawley demonstrate such 

outcome, there is a solid consideration for future 

wetlands being constructed. In order to 

measure the effects of the wetlands on the 

quality of water, a study of monthly samples 

were taken in the inlets and outlets of the 

wetlands from January 2001 to January 2007. 
How wetlands work with the 

environment

• Regarding removal of bacteria 

and other pathogenic 

organisms, wetlands work in 

different ways,

• Predation: most bacteria are 

food for other organisms, such 

as nematodes, rotifers, and 

protozoa. 

• Solar Disinfection: the solar UV 

rays are a powerful means of 

killing bacteria after it has been 

in the wetlands for several days. 

• Mortality: most bacteria die in 

wetlands after several days, 

depending on the type of 

bacteria and the conditions of 

the water. 
Measuring effectiveness of bacteria 

removal

• Samples of the New River water were collected before reaching the 

Brawley wetland (inlet) and then after the water left the wetland 

(outlet) with samples of Total Coliforms numbers per 100 milliliters ( 

# per 100 ml) in a 50-month period from January 2001 to January 

2005. 
Percentages of Total Coliform 

reduced

• We can also form a graph of the percentages of Total Coliform reduced 

each month by using (((Outlet#)*100)/(Inlet#)). This graph takes the form,

• This graph surely looks different to the other graphs since we are dealing 

with percentages and not with the actual numbers of Total Coliforms in the 

water.
Numbers of Total Coliform reduced

• We can think of the graph ((# in Inlet)-(# in outlet)) as the numbres 

of Total Coliform reduced or eliminated from the New River water 

which takes the form,
How to construct a function of the data

• In statistics, after you have a valid set of data that you obtained from 

experiments, you can use that data to construct a function. This 

function will help you estimate and predict values that you don’t have 

in your set of data. 

• For instance, if you have 

You can find the function of these points in a way that you will get 
Methods

• Interpolation You can create a curve 

to estimate the value of x in other 

points that you don’t have yet on 

your set

• Linear Interpolation This is the 

easiest method, you just have to joint 

each point that you have by finding 

the slope and getting a linear 

equaiton for each segment between 

points,

• Polynomial Interpolation There are 

many algorithms available that help 

you find a polynomial of degree n if 

you have n points on your graph,

• Extrapolation This is the process of 

finding new data points beyond the 

existent data points. This is the 

method that you would like to use if 

you want to predict a future estimate, 
Analyzing numbers of Total 

Coliform reduced

• When measuring the effects of the wetlands, we basically want to 

analyze the numbers of Total Coliform reduced.

• We can take this graph and attempt to find an estimated polynomial 

of the graph using Newton’s Divided Difference that calculates the 

coefficients of the polynomial using the x-axis(time) and y-axis(# per 

100ml). The method looks something like this,

If, Then,
Predicting Future Reductions

• Using only 10 months as samples, the polynomial that we can use to 

predict future reductions in the water is, with x as the number of 

months from January 1, 2001, is of the form,

700+5725(x-1)-85(x-1)(x-5)-79.071(x-1)(x-5)(x10)+30.867(x-1)(x-5)(x-10)(x-15)-.443(x-1)(x-5)(x-10)(x15)(x-20)-.332(x-1)(x-5)(x-10)(x-15)(x-20)(x25)+.04143(x-1)(x-5)(x-10)(x-15)(x-20)(x-25)(x-30)-

.0028(x-1)(x-5)(x-10)(x-15)(x-20)(x-25)(x-30)(x35)+.000128354(x-1)(x-5)(x-10)(x-15)(x-20)(x-25)(x30)(x-35)(x-40)-.000004172272(x-1)(x-5)(x-10)(x-15)(x20)(x-25)(x-30)(x-35)(x-40)(x-45).

We can use this polynomial to predict the Total Coliform reduction of a 

certain month with x=1 being the first month (Jan 2001).
Conclusion

• The ideas of constructing a wetland 

in the Imperial Valley to challenge 

the contaminants in the New River 

ended up being more than what 

was expected with more than 95% 

average of Total Coliforms 

eliminated. After this success, 

there are now more plans to 

construct more wetlands in other 

sites after proving their 

effectiveness in cleaning the 

country’s most polluted river. There 

have been various proposed sites 

such as one in Calexico and also in 

the Alamo River, thanks to the effort 

and ingenuity of the Citizen’s 

Congressional Task Force on the 

New River.