What was found
5:22 INTO FLIGHT, HEARD A LOUD THUMP WITH AN ASSOCIATED PITCH CHANGE WATER SYS, PRESS LOW LIGHTS ILLUMINATED AND SYS 2 QTY REDUCED TO 0. 7:22 INTO FLIGHT, HEARD 2ND LOUD THUMP WITH ASSOCIATED PITCH CHANGE. NO ADDITIONAL ABNORMAL INDICATIONS WERE NOT. FOUND DAMAGE AT LT NR 1 SLAT CRUISE AERODYNAMIC FILLET AND LT HORIZ STAB L/E; REMOVED AND REPLACED LT NR 1 SLAT IAW AMM 27-80 CKS GOOD AND INSTALLED INTERIM REPAIR IN LT HORIZ L/E IAW ERA NR 5530-711 ERA; DRAINED POTABLE WATER SYS 1, 2, AND 3.