Since the Environmental Sciences are interdisciplinary in nature and depending on your topic, other subject areas such as Political Science (Public Policy), Law, Chemistry, etc., may also help.
GE Environmental Sciences
GB Physical Geography
GF Human Ecology
K 3581 -- K 3598 Environmental Law
QC 851 -- QC 999 Climatology, Meterology
QE Geology and Earth Sciences
QH Life Sciences (endangered species, rain forests, etc.)
S Agriculture, Forestry, Aquaculture
TD Environmental Technology and Sanitation Engineering (recycling, waste treatment, etc.)
For a more detailed breakdown, see: https://www.loc.gov/catdir/cpso/lcco/
eBooks may also be searched in WorldCat Discovery.