Could you tell us which multiplexer IC you are using? This way, we can help you better. Also, why do you need the 8 second cycle? Does it matter if it's a little shorter or longer? If timing does not have to be very precise it would make things a lot easier.
By the way: you say there are 30 sensors, but your table has 32...
The following pseudocode will not work on your Arduino, but you can use the same structure.
int sensorArray // we will store our 32 sensor values here
// these pins control the multiplexer chips
int selectPinZero = 8;
int selectPinOne = 9;
int selectPinTwo = 10;
// these pins will receive the sensor values from the multiplexer chips
int inputPinOne = 0;
int inputPinTwo = 1;
int inputPinThree = 2;
int inputPintFour = 3;
// make sure the correct pins are inputs and outputs
// all done, now keep reading the sensors
// set selectPins so that each Multiplexer will output its first channel
digitalWrite(selectPinZero, HIGH); // or low, depending on your Multiplexer IC
digitalWrite(selectPinOne, HIGH); // or low, depending on your Multiplexer IC
digitalWrite(selectPinTwo, HIGH); // or low, depending on your Multiplexer IC
// start reading sensors
int i = 0;
sensorArray[i] = analogRead(inputPinOne);
i++; // variable i was 0, now 1
sensorArray[i] = analogRead(inputPinTwo);
i++; // variable i was 1, now 2
sensorArray[i] = analogRead(inputPinThree);
i++; // variable i was 2, now 3
sensorArray[i] = analogRead(inputPinFour);
i++; // variable i was 3, now 4
use digitalWrite() on all the selectPins to make the Multiplexer IC output the next channel
delay(1000); // wait 1000 milliseconds
this will repeat until all 32 sensors are read and stored in the array
This code is by no means optimized, but written to make it easy for you to understand. Good luck!