In order to evaluate the extent to which sewage treatment plant effluent (STPE) irrigation reduces or eliminates the entrance of endocrine disrupting compounds (EDCs) into groundwater, studies on the fate and transport of selected EDCs in the Penn State spray-irrigation system are ongoing. This study reports the variations in the occurrence of 17 β-estradiol (E2), estrone (E1) and 17 α-ethynlestradiol (EE2) in the Penn State STPE during high (>7000 m3/d) and low (approximately 4000 m3/d) flow and at different time periods during the day. Effluent samples were collected throughout the year at times when school was in session (high flow) and also when school was out of session (low flow). The samples collected were cleaned up and concentrated by solid phase extraction followed by detection and quantification using liquid chromatography tandem mass spectrometry. The estrogens, E1, E2 and EE2 concentrations found were 33.2 ng/L (6.1- 235.4); 48.13 (<BDL - 420.9 ng/L) and 0.36 (BDL - 3.28), respectively. It was observed that estrogen concentrations were generally higher during periods of high flow. Of the three estrogens, E1 was the most commonly detected while EE2 was the least observed. In agreement with previous studies, the estrogen concentrations were generally higher in the effluent samples during colder periods than in warmer months.