D.2 Case 2

Arsenic in groundwater.

Environmental Science & Technology (January 2005) reported on a study of the reliability of a commercial kit to test for arsenic in ground-water. The field kit was used to test a sample of 328 ground-water wells in Bangladesh. In addition to the arsenic level (micrograms per liter), the latitude (degrees), longitude (degrees), and depth (feet) of each well were measured. The data are saved in the file.

Write a first-order model for arsenic level (\(y\)) as a function of latitude, longitude, and depth.