diff --git a/hydrolib/core/dflowfm/ext/models.py b/hydrolib/core/dflowfm/ext/models.py
index 4bcd476d3..caaa8ef1c 100644
--- a/hydrolib/core/dflowfm/ext/models.py
+++ b/hydrolib/core/dflowfm/ext/models.py
@@ -215,8 +215,6 @@ class SourceSink(INIBasedModel):
 
     salinitydelta: Optional[ForcingData] = Field(alias="SalinityDelta")
     temperaturedelta: Optional[ForcingData] = Field(alias="TemperatureDelta")
-    interpolationmethod: Optional[str] = Field(alias="interpolationMethod")
-    operand: Optional[Operand] = Field(Operand.override.value, alias="operand")
 
     @classmethod
     def _exclude_from_validation(cls, input_data: Optional[dict] = None) -> Set:
diff --git a/hydrolib/tools/ext_old_to_new/converters.py b/hydrolib/tools/ext_old_to_new/converters.py
index b7a1e7fc4..f9f9afd6f 100644
--- a/hydrolib/tools/ext_old_to_new/converters.py
+++ b/hydrolib/tools/ext_old_to_new/converters.py
@@ -499,10 +499,6 @@ def convert(
             "zsink": z_sink,
         }
         data = data | time_series
-
-        data = convert_interpolation_data(forcing, data)
-        data["operand"] = forcing.operand
-
         new_block = SourceSink(**data)
 
         return new_block
diff --git a/tests/dflowfm/ext/test_ext.py b/tests/dflowfm/ext/test_ext.py
index 3d08cfb19..2d660c014 100644
--- a/tests/dflowfm/ext/test_ext.py
+++ b/tests/dflowfm/ext/test_ext.py
@@ -229,8 +229,6 @@ def source_sink_data(self) -> Dict[str, Any]:
             "ycoordinates": [12.950216, 6.350155],
             "zsource": -3.0,
             "zsink": -4.2,
-            "interpolationmethod": "",
-            "operand": "O",
             "discharge": 1.1234,
             "temperaturedelta": [2.0, 2.0, 5.0, 8.0, 10.0],
             "salinitydelta": [3.0, 5.0, 12.0, 9.0, 23.0],
@@ -292,8 +290,6 @@ def test_time_series_discharge_case(self):
             "discharge": [1.0, 2.0, 3.0, 5.0, 8.0],
             "temperaturedelta": [2.0, 2.0, 5.0, 8.0, 10.0],
             "salinitydelta": [3.0, 5.0, 12.0, 9.0, 23.0],
-            "interpolationmethod": "linearSpaceTime",
-            "operand": "O",
         }
 
         source_sink = SourceSink(**data)