@misc{indiciaecef0647f37aa,
  title = {Puerto Rico ground-water quality},
  author = {A. L. Zack and Teresita Rodrigues-Alonso and Angel Roman-Mas},
  year = {1987},
  doi = {10.3133/ofr87749},
  url = {https://pubs.usgs.gov/publication/ofr87749},
  note = {Source identifier: ofr87749}
}