UNB, Chuadanga :Four construction workers, including father and son, were killed as a septic tank collapsed on them at Boidyanathpur village in Jibannagar upazila on Wednesday.The deceased were identified as Hashem Ali, 52, his son Sujon, 32, Jalal Uddin, 25, son of Kawsar Ali, of Boidyanathpur village, and Jewel, 25, of Gangadaspur village in the upazila.Police said, the four were constructing a new septic tank by an old one at the house of Rustam Ali, an engineer of Dhaka Electric Supply Authority (DESA),in the afternoon. Suddenly, the old septic tank collapsed on them around 4:15pm, leaving all of them dead on the spot, said police super of Chuadanga Rashidul Hasan.