diff --git a/data_validation/config_manager.py b/data_validation/config_manager.py
index 010d18a96..f7b5ac11b 100644
--- a/data_validation/config_manager.py
+++ b/data_validation/config_manager.py
@@ -14,7 +14,7 @@
 
 import copy
 import logging
-from typing import Optional, Union
+from typing import Optional, Union, TYPE_CHECKING
 
 import google.oauth2.service_account
 from ibis_bigquery.client import BigQueryClient
@@ -26,6 +26,10 @@
 from data_validation.validation_builder import ValidationBuilder
 
 
+if TYPE_CHECKING:
+    import ibis.expr.types.TableExpr
+
+
 class ConfigManager(object):
     _config: dict = None
     _source_conn = None
@@ -718,17 +722,19 @@ def _strftime_format(
             return "%Y-%m-%d %H:%M:%S"
         return "%Y-%m-%d"
 
-    def _apply_base_cast_overrides(self, column: str, col_config: dict) -> dict:
+    def _apply_base_cast_overrides(
+        self,
+        column: str,
+        col_config: dict,
+        source_table: "ibis.expr.types.TableExpr",
+        target_table: "ibis.expr.types.TableExpr",
+    ) -> dict:
         """Mutates col_config to contain any overrides. Also returns col_config for convenience."""
         if col_config["calc_type"] != "cast":
             return col_config
 
-        source_table_schema = {
-            k: v for k, v in self.get_source_ibis_table().schema().items()
-        }
-        target_table_schema = {
-            k: v for k, v in self.get_target_ibis_table().schema().items()
-        }
+        source_table_schema = {k: v for k, v in source_table.schema().items()}
+        target_table_schema = {k: v for k, v in target_table.schema().items()}
 
         if isinstance(
             source_table_schema[column], (dt.Date, dt.Timestamp)
@@ -762,9 +768,11 @@ def _apply_base_cast_overrides(self, column: str, col_config: dict) -> dict:
 
     def build_dependent_aliases(self, calc_type, col_list=None):
         """This is a utility function for determining the required depth of all fields"""
+        source_table = self.get_source_ibis_calculated_table()
+        target_table = self.get_target_ibis_calculated_table()
+
         order_of_operations = []
         if col_list is None:
-            source_table = self.get_source_ibis_calculated_table()
             casefold_source_columns = {
                 x.casefold(): str(x) for x in source_table.columns
             }
@@ -819,7 +827,9 @@ def build_dependent_aliases(self, calc_type, col_list=None):
                     if i == 0:
                         # If we are casting the base column (i == 0) then apply any
                         # datatype specific overrides.
-                        col = self._apply_base_cast_overrides(column, col)
+                        col = self._apply_base_cast_overrides(
+                            column, col, source_table, target_table
+                        )
 
                     name = col["name"]
                     column_aliases[name] = i