I am stuck on this question:

In a study of the amount of contaminants in drinking water, six samples were ran through a lab. The six readings, in parts per million, were $9.8, 9.43, 8.97, 9.33, 9.14,$ and $9.55$. Estimate the population variance $\sigma^2$ for readings by deriving a $90$% confidence interval using a pivotal quantity.

I'm not sure how to approach this question. Finding the sample variance should be straightforward using the six samples, but I'm not sure if I can assume the sample follows a Normal Distribution, as it doesn't state that in the question. Therefore I'm not sure if I can use a pivotal quantity of the Z-Score formula, or $\frac{\bar{x} - \mu}{\frac{\sigma}{\sqrt{n}}}$. 

It'll be great if I can get some pointers as to how to determine the pivotal quantity for similar types of questions. Thanks!