Overlapping Prefabs

i have a permanent terrain rendering set up, it randomizes the hills and stuff aswell but when the next "chunk" shall we say is rendered it will be fine until you walk to a new "chunk", at which point it will spawn a new "chunk" were a previous one would be, i have tried a few different ways to delete the newly rendered chunk if it overlaps an exsisting one.

 #pragma strict
 var terrainpplane:Transform;
 private var colliderr:boolean = false;
  var spawn:boolean = false;
  var boom:boolean = false;
 function Update () {
 var boxCollider = gameObject.GetComponent(BoxCollider);
 if (colliderr == false)
 do{
 boxCollider.size = Vector3(500, 30, 500);
 boxCollider.isTrigger = true;
 colliderr = true;
 }while(colliderr == false);}
 function OnTriggerEnter (other:Collider)
 {
 if (other.CompareTag ("Plane"))
 Destroy (gameObject);
 if (other.CompareTag ("Player"))
 {
 if (boom == false){
 do{
 yield(WaitForSeconds(5));
 var instancesnow1 = Instantiate(terrainpplane, Vector3(transform.position.x + 500, 0, transform.position.z), Quaternion.identity);
 var instancesnow2 = Instantiate(terrainpplane, Vector3(transform.position.x - 500, 0, transform.position.z), Quaternion.identity);
 var instancesnow3 = Instantiate(terrainpplane, Vector3(transform.position.x  , 0, transform.position.z + 500), Quaternion.identity);
 var instancesnow4 = Instantiate(terrainpplane, Vector3(transform.position.x  , 0, transform.position.z - 500), Quaternion.identity);
 spawn = true;
 boom = true;
 Destroy (this);
 }while (!other.CompareTag ("Player"));}}}

NOTE i have tried using sphere collider but it doesnt work and instead deletes itself even when it's not touching anything and it is the only thing in the scene -- It spawns plane prefabs which randomly changed with other scripts -- "snowprefab" is from a previous game i made, i will change it later