t-test of Fecal Coliform Data
In this activity, you will be performing a t-test
on the
fecal coliform counts collected from Blackwater Creek in
Lynchburg, Virginia. Blackwater Creek is known to have a problem
with fecal coliforms due to sewage overflow from an old sewer
system that mixes storm drainage and
Fecal coliforms are often found in the mud in the
bottom of rivers and streams. When it rains, the increased flow
of water disrupts the bottom sediments and fecal coliforms are
released into the water. This study was designed to determine
if fecal coliforms reside in the sediments of Blackwater Creek.
Water samples were taken in three locations along the creek; Sandusky
This data exists in three files; one is in Excel Data
format and one is in Text
format, and one is in TI-83 Group format. If you want to perform the t-test using the TI-83, you
will have to import
the text data into the calculator from the computer after you
have downloaded the file.
Were the results of the t-test a surprise? Eliminate
the 4200 and the 1200 readings from the "Before Disruption"
data set and the 7300 and the 8400 readings from the "After
Disruption" data set and redo the t-test? Can you explain
the results?
sewage. Hence, when it rains, sewer pipes back up and sewage is
dumped into the creek. Several studies are being conducted by
students at the Central VA Governor's School for Science and Technology to quantify the extent of the fecal coliform concentration in
the creek associated with rainfall. 
Park, Blackwater Athletic Area and Hollins Mill. First, a water
sample was taken, then the sediments at the bottom of the creek
were disrupted with a shovel and a second sample was immediately
taken downstream. Samples were collected over a four week period
in the fall of 1995. The data represents 12 samples taken before
disruption and 12 samples taken after disruption. Using either
Excel or the TI-83
graphing calculator, conduct a t-test to determine if there is
a significant difference between the two samples.
Original work on this document was done by Central Virginia Governor's School student Crystal Peery (Class of '97).
Copyright © 1997 Central Virginia Governor's School for Science and Technology Lynchburg, VA