The Siloam Association was one of Primitive Baptist Congregations. The name probably derived from the church by that name in Marion County, Oregon. But the ultimate derivation and use of the term comes from the New Testament.
"And as he passed by, he saw a man blind from his birth. 2. And his disciples asked him, saying, Rabbi, who sinned, this man or his parents, that he should be born blind? 3. Jesus answered, Neither did this man sin, nor his parents: but that the works of God should be made manifest in him. 4. We must work the works of him that sent me, while it is day; the night cometh, when no man can work. 5. When I am in the world, I am the light of the world. 6. When he had then spoken, he spat on the ground, and made clay of the spittle, and anointed his eyes with the clay, 7. and said unto him, Go, wash in the pool of Siloam (which is by interpretation, Sent). He went away therefore, and washed, and came seeing "
Siloam Inscription and Hezekiahs Tunnel - http://jeru.huji.ac.il/eb26.htm
Siloam Inscription - http://www.stolaf.edu/people/kchanson/siloam.html
Siloam Pool - http://www.slider.com/enc/48000/Siloam.htm
Pool and Tower of Siloam - http://www.j30ad.org/Siloam.htm