Sentence:  Research at Fayette , Missouri on oxidation ponds has shown that the BOD in the treated effluent varied from 30 to 53 mg / l with loadings from 8 to 120 lb BOD / day / <WSD>acre</WSD> . 
Meaning of the word marked with <WSD> tags:  a unit of area (4840 square yards) used in English-speaking countries