Rapid City – Background to the Problem
Part 1
Questions
1. Rapid City is located on the banks of a river and its population is growing. It
attracts tourists and businesses and industries.
2. This area is probably facing an increase in pollution because the population is
growing and industries and factories add to the pollution.
3. Bridgeland and Springford are experiencing problems with pollution in their
water.
4. Since they are downstream from Rapid City they are blaming Rapid City for their
problems.
5. The politicians of Rapid City are worried they won’t get reelected if there is too
much negative publicity about their waste water treatment.
6. The city doesn’t want to upgrade the phosphate removal equipment because they
are not sure that Rapid City is responsible for all the problems and the upgrade is
very expensive.
7. Effluent means the water leaving the treatment plant.
8. The owners of the fertilizer plant would prefer that the city acquire phosphateremoving equipment and then they would pay the city to remove its phosphates.
9. If the city does not install phosphate removing equipment then the fertilizer plant
would have to clean up its own waste, making it too expensive to run the plant
and they would have to shut down.
10. The detergent manufacturer suggests that people in Rapid City use their
phosphate-free detergent so there will be less phosphates added to the water.
11. They are proposing this solution because they want to sell lots of detergent and
make lots of money.
12. Farmers and ranchers contribute to the problem of phosphates by using large
amounts of phosphate containing fertilizer. When it dissolves in rainwater the
phosphates run off their fields and into the river.
13. A catch basin could collect runoff water so the phosphates wouldn’t enter the
river.
14. I think that everyone should pay for the additional phosphate removing equipment
but the bigger sources of phosphates should pay more.
Part 2
Questions
1. The purpose of Site 1 is to see the condition of the water before it passes Rapid
City to see if Rapid City is totally responsible for the pollution.
2. The purpose of Site 5 is to see the condition of the water after it has passed Rapid
City and the two towns.
3. Site 4 had the highest concentration of suspended solids.
4. Site 1 had the lowest concentration of suspended solids.
5. Five sources of suspended solids are: the sewage from Rapid City, the fertilizer
plant, the farmers, the ranchers, and erosion.
6. The normal concentration of phosphate in the waterways surrounding Rapid City
would be 10 micrograms per litre because that is the level before the water goes
by Rapid City and any phosphates are added.
7. The largest changes are from Site 1 – 2 and from Site 4 – 5.
8. Five sources of phosphates are: the sewage from Rapid City, the fertilizer plant,
the farmers, the ranchers, and phosphates naturally found in the river.
9. The normal concentration of oxygen in the water would be 10 mg/L because that
is what is in the water before it flows past Rapid City.
10. At Sites 2, 3, and 4 the oxygen concentration shows a decrease.
11. Possible sources of pollution are: the sewage from Rapid City, the fertilizer plant,
the farmers, the ranchers, erosion, and too many organisms found in the water.
12. a) Phosphates – sewage and the fertilizer plant.
b) Undissolved suspended solids – erosion and sewage
13.
Indicator
water plants and algae
Your Prediction
(increase or decrease)
Increase
Reason
Because algae and plants
use phosphates as nutrients
bacteria and other
Increase
Because where there is a
decomposers
large amount of organic
matter, the decomposers
and bacteria multiply
dissolved oxygen in water
Decrease
Because the plants, algae,
bacteria and decomposers
would use up the available
oxygen
insects
Decrease
Because the plants, algae,
bacteria and decomposers
would use up the available
oxygen
fish
Decrease
Because there wouldn’t be
enough oxygen for them to
live
14. Two human activities that could cause the water to be turbid would be sewage and
industrial waste.
15. Turbidity is caused by undissolved solids suspended in the water and these solids
block sunlight, preventing it from penetrating into the water. This reduces the
ability of plants and algae to carry out photosynthesis, which returns oxygen to
the water.
Part 3
Questions
1. Biodiversity describes the numbers and types of organisms living in an area.
Biological indicators are organisms whose presence or absence can be used to
indicate how polluted and environment is.
2. At 3.0mg/L you would expect to find midge larvae.
3. The level of oxygen and this invertebrate would tell me that the water was below
critical level.
4. The highest level of 8.0mg/L and above would have the greatest biodiversity.
5.
Mayfly larvae
300
250
200
150
100
50
0
Series1
Site Site Site Site Site
1
2
3
4
5
Stonefly larvae
140
120
100
80
60
40
20
0
Series1
Site Site Site Site Site
1
2
3
4
5
Caddisfly larvae
50
40
30
20
10
0
Series1
Site
1
Site
2
Site
3
Site
4
Site
5
Beetles
20
15
10
Series1
5
0
Site 1 Site 2 Site 3 Site 4 Site 5
Midgefly larvae
300
250
200
150
100
50
0
Series1
Site Site Site Site Site
1
2
3
4
5
Leeches
120
100
80
60
40
20
0
Series1
Site
1
Site
2
Site
3
Site
4
Site
5
Other w orm s
150
100
Series1
50
0
Site Site Site Site Site
1
2
3
4
5
6. Immediately downstream from the sewage treatment plant there must be a lot less
oxygen in the water and only midges and worms can survive.
7. a) mayfly larvae – cannot survive below 6.0mg/L of oxygen so at Sites 2, 3 and 4
the oxygen level must be below that.
b) midgefly larvae – can survive at the lowest levels of oxygen so they increase at
low levels because nothing else can survive.
8. Yes the biological indicators support the data. The worms survive at very low
oxygen levels and they increased when the oxygen levels were low. The stonefly larvae
only survive above 6.0mg/L and at Sites 2, 3 and 4 the levels were below 6 and there
were no stonefly larvae. Leeches can survive in low level oxygen waters and they
increased at the sites where the oxygen levels were low.
9. a) I would expect worms and midge larvae to be numerous downstream from a
sewage treatment plant because there would be less oxygen in the water and only these
organisms could survive.
b) I would expect that the mayflies and stoneflies to be more numerous in water
upstream from a large industrialized city because the water hasn’t been polluted yet and
all organisms would thrive.
c) I would expect mayflies and stoneflies to be more numerous in a mountain
river that is tumbling over many rocks and waterfalls because it would not be polluted
and have lots of oxygen in it.
d) I would expect worms and midge larvae to be numerous in a turbid, slow
moving river on the prairies because it would lack oxygen and these organisms would
thrive.
10. This river has a water quality problem between Sites 2 and 4. The pollution is
robbing the water of oxygen and organisms are dying. The two towns don’t add any
pollution and then the water quality picks up again further downstream.