Locator column is actually a text. Here are the Explain Plan data.

Code:
PLAN_TABLE_OUTPUT
----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

| Id  | Operation                          |  Name                       | Rows	 | Bytes | Cost  |
--------------------------------------------------------------------------------------------------

|   0 | SELECT STATEMENT                   |                             |     1 |   205 |    40 |
|   1 |  SORT AGGREGATE                    |                             |     1 |   205 |       |
|   2 |   NESTED LOOPS                     |                             |     1 |   205 |    40 |
|   3 |    NESTED LOOPS                    |                             |     3 |   543 |    37 |
|   4 |     NESTED LOOPS                   |                             |     3 |   438 |    31 |
|   5 |      NESTED LOOPS                  |                             |     3 |   237 |    25 |
|   6 |       NESTED LOOPS                 |                             |     1 |    38 |    22 |
|   7 |        NESTED LOOPS                |                             |     3 |    84 |    16 |
|*  8 |         TABLE ACCESS BY INDEX ROWID| CLG_ASSESSMENT_RESULT       |     3 |    54 |    13 |
|*  9 |          INDEX RANGE SCAN          | IDX_ASMNTRES_COMPDATE       |    38 |       |     3 |
|  10 |         TABLE ACCESS BY INDEX ROWID| CLG_ASSESSMENT_INSTANCE     |     1 |    10 |     1 |
|* 11 |          INDEX UNIQUE SCAN         | PK_ASSESSMENT_INSTANCE      |     1 |       |       |
|* 12 |        TABLE ACCESS BY INDEX ROWID | CLG_USER                    |     1 |    10 |     2 |
|* 13 |         INDEX UNIQUE SCAN          | PK_USER                     |     1 |       |     1 |
|  14 |       TABLE ACCESS BY INDEX ROWID  | CLG_ITEM_RESULT             |    13 |   533 |     3 |
|* 15 |        INDEX RANGE SCAN            | PK_ITEM_RESULT              |    13 |       |     2 |
|* 16 |      TABLE ACCESS BY INDEX ROWID   | CLG_ITEM                    |     1 |    67 |     2 |
|* 17 |       INDEX UNIQUE SCAN            | PK_ITEM                     |     1 |       |     1 |
|* 18 |     INDEX RANGE SCAN               | IDX_CORR_ASSET_CONTENT_MLO  |     1 |    35 |     2 |
|* 19 |    TABLE ACCESS BY INDEX ROWID     | CB_STANDARD                 |     1 |    24 |     1 |
|* 20 |     INDEX UNIQUE SCAN              | PK_CB_STANDARD              |     1 |       |       |
--------------------------------------------------------------------------------------------------


Predicate Information (identified by operation id):
---------------------------------------------------

   8 - filter("CAR"."STATUS"=20)
   9 - access("CAR"."COMPLETED_DATE">=TO_DATE('2006-09-05 00:00:00', 'yyyy-mm-dd hh24:mi:ss') AND  "CAR"."COMPLETED_DATE"<=TO_DATE('2006-10-13 00:00:00', 'yyyy-mm-dd hh24:mi:ss'))
  11 - access("CAR"."ASSESSMENT_INSTANCE_ID"="CAI"."ASSESSMENT_INSTANCE_ID")
  12 - filter("U"."ORG_UNIT_ID"=21296)
  13 - access("CAI"."ASSIGNOR_ID"="U"."USER_ID")
  15 - access("CAR"."ASSESSMENT_RESULT_ID"="CIR"."ASSESSMENT_RESULT_ID")
  16 - filter("CI"."ANCESTOR_LOCATOR" IS NOT NULL)
  17 - access("CIR"."ITEM_LOCATOR"="CI"."LOCATOR")
  18 - access("CORR"."ASSET_TYPE_ID"=113 AND "CORR"."CONTENT_ID"="CI"."ANCESTOR_LOCATOR")
  19 - filter(SUBSTR("CBS"."LOCATOR",1,6)='1.1026' AND BITAND("CBS"."INTERNAL_GRADE_LEVELS",2)>0)
  20 - access("CORR"."CBS_ID"="CBS"."CBS_ID")

Note: cpu costing is off