Complex sentence: Wastewater from the field was once allowed to drain directly into the streams dissecting the region, and thence into the Kern River; this practice ended in in the 1960s and 1970s when more stringent environmental regulations were enacted both on federal and state levels.
Split into simpler sentences: Wastewater from the field was once allowed to drain directly into the streams dissecting the region, and thence into the Kern River. This practice ended in in the 1960s and 1970s when more stringent environmental regulations were enacted both on federal and state levels.