diff --git a/python/ngen_cal/src/ngen/cal/errors.py b/python/ngen_cal/src/ngen/cal/errors.py
new file mode 100644
index 00000000..c3be7f0b
--- /dev/null
+++ b/python/ngen_cal/src/ngen/cal/errors.py
@@ -0,0 +1 @@
+class UnsupportedFeatureError(ValueError): ...
diff --git a/python/ngen_cal/src/ngen/cal/ngen.py b/python/ngen_cal/src/ngen/cal/ngen.py
index d4f7a4c4..90fdabdb 100644
--- a/python/ngen_cal/src/ngen/cal/ngen.py
+++ b/python/ngen_cal/src/ngen/cal/ngen.py
@@ -28,6 +28,7 @@
 from hypy.nexus import Nexus
 from hypy.catchment import Catchment
 
+
 class NgenStrategy(str, Enum):
     """
     """
@@ -83,7 +84,7 @@ class NgenBase(ModelExec):
     nexus: Optional[FilePath]
     crosswalk: Optional[FilePath]
     ngen_realization: Optional[NgenRealization]
-    routing_output: Optional[Path] = Field(default=Path("flowveldepth_Ngen.csv"))
+    routing_output: Path = Path("flowveldepth_Ngen.csv")
     #optional fields
     partitions: Optional[FilePath]
     parallel: Optional[PosInt]
@@ -288,20 +289,27 @@ def check_for_partitions(cls, values: dict):
             raise ValueError("Must provide partitions if using parallel")
         return values
 
-    @root_validator()
-    def validate_hydrofabic(cls, values: dict) -> dict:
+    @root_validator
+    def _validate_model(cls, values: dict) -> dict:
+        NgenBase._verify_hydrofabric(values)
+        realization: Optional[NgenRealization] = values.get("ngen_realization")
+        NgenBase._verify_ngen_realization(realization)
+        return values
+
+    @staticmethod
+    def _verify_hydrofabric(values: dict) -> None:
         """
-        Validates hydrofabric information is provided either as (deprecated) GeoJSON
+        Verify hydrofabric information is provided either as (deprecated) GeoJSON
         or (preferred) GeoPackage files.
 
         Args:
-            values (dict): configuation values to check
+            values: root validator dictionary
 
         Raises:
             ValueError: If a geopackage hydrofabric or set of geojsons are not found
 
         Returns:
-            dict: Valid configuration elements for hydrofabric requirements
+            None
         """
         hf: FilePath = values.get('hydrofabric')
         cats: FilePath = values.get("catchments")
@@ -313,17 +321,32 @@ def validate_hydrofabic(cls, values: dict) -> dict:
                   "or proide catchment, nexus, and crosswalk geojson files."  
             raise ValueError(msg)
         
-        if hf is not None:
-            try:
-                p = Path(hf)
-                if not p.exists():
-                    raise
-            except:
-                raise TypeError("hydrofabric must be a valid file path")
         if cats is not None or nex is not None or x is not None:
             warnings.warn("GeoJSON support will be deprecated in a future release, use geopackage hydrofabric.", DeprecationWarning)
 
-        return values
+    @staticmethod
+    def _verify_ngen_realization(realization: Optional[NgenRealization]) -> None:
+        """
+        Verify `ngen_realization` uses supported features.
+
+        Args:
+            realization: maybe an `NgenRealization` instance
+
+        Raises:
+            UnsupportedFeatureError: If `realization.output_root` is not None.
+                                     Feature not supported.
+
+        Returns:
+            None
+        """
+        if realization is None:
+            return None
+
+        if realization.output_root is not None:
+            from .errors import UnsupportedFeatureError
+            raise UnsupportedFeatureError(
+                "ngen realization `output_root` field is not supported by ngen.cal. will be removed in future; see https://github.com/NOAA-OWP/ngen-cal/issues/150"
+            )
 
     def update_config(self, i: int, params: 'pd.DataFrame', id: str = None, path=Path("./")):
         """_summary_
diff --git a/python/ngen_cal/tests/test_ngen.py b/python/ngen_cal/tests/test_ngen.py
index ad7f826d..cab77249 100644
--- a/python/ngen_cal/tests/test_ngen.py
+++ b/python/ngen_cal/tests/test_ngen.py
@@ -1,5 +1,15 @@
+import pathlib
+
 import pytest
-from ngen.cal.ngen import NgenExplicit, NgenIndependent, NgenUniform, NgenStrategy
+import pydantic
+from ngen.cal.ngen import (
+    Ngen,
+    NgenBase,
+    NgenExplicit,
+    NgenIndependent,
+    NgenStrategy,
+    NgenUniform,
+)
 
 
 def test_NgenExplicit_strategy_default_value():
@@ -13,7 +23,20 @@ def test_NgenIndependent_strategy_default_value():
     o = NgenIndependent.construct()
     assert o.strategy == NgenStrategy.independent
 
+
 def test_NgenUniform_strategy_default_value():
     # construct object without validation.
     o = NgenUniform.construct()
     assert o.strategy == NgenStrategy.uniform
+
+
+def test_NgenBase_verify_realization(ngen_config: Ngen):
+    # session level pytest fixture. take deep copy to avoid pollution
+    config = ngen_config.__root__.copy(deep=True)
+    assert isinstance(config, NgenBase)
+
+    assert config.ngen_realization is not None, "should have already raised if not None"
+    config.ngen_realization.output_root = pathlib.Path("./output_root")
+
+    with pytest.raises(pydantic.ValidationError):
+        Ngen.parse_obj(dict(config))