In most cases you should cite the original EIQ paper for methodology. The citation should read:
Kovach, J., Petzoldt, C., Degni, J., and Tette, J. 1992. A method to measure the environmental impact of pesticides. New York’s Food and Life Sciences Bulletin 139:1–8.
If accessing the website, and using newly calculated EIQ values, the website should also be referenced:
Eshenaur, B., Grant, J., Kovach, J., Petzoldt, C., Degni, J., and Tette, J. www.nysipm.cornell.edu/publications/EIQ. Environmental Impact Quotient: “A Method to Measure the Environmental Impact of Pesticides.” New York State Integrated Pest Management Program, Cornell Cooperative Extension, Cornell University. 1992 – 2015.