diff --git a/chicago/permit_cleaning.py b/chicago/permit_cleaning.py
index 8cc62fe..290344c 100644
--- a/chicago/permit_cleaning.py
+++ b/chicago/permit_cleaning.py
@@ -8,9 +8,9 @@
 in separate Excel workbooks in separate folders. Data that need review are split into two categories and corresponding folders/files:
 those with quick fixes for fields over character or amount limits, and those with more complicated fixes for missing and/or invalid fields.
 
-The following environment variables need to be set before running this script:
-    AWS_ATHENA_S3_STAGING_DIR=s3://ccao-athena-results-us-east-1
-    AWS_REGION=us-east-1
+The following optional environment variables can be set:
+    AWS_ATHENA_S3_STAGING_DIR: S3 path where Athena query results are stored
+    AWS_REGION: Region that AWS operations should be run in
 
 The script also expects two positional arguments:
     * start_date: The lower bound date to use for filtering permits
@@ -21,6 +21,7 @@
 """
 
 from datetime import datetime
+import decimal
 import math
 import os
 import sys
@@ -241,21 +242,67 @@ def flag_fix_long_fields(df):
     return df
 
 
-def deduplicate_permits(cursor, df):
-    cursor.execute("""
-        SELECT
-            parid,
-            permdt,
-            amount,
-            note2,
-            user21,
-            user28,
-            user43
-        FROM iasworld.permit
-    """)
+def deduplicate_permits(cursor, df, start_date, end_date):
+    cursor.execute(
+        """
+            SELECT
+                iasw_id,
+                parid,
+                permdt,
+                amount,
+                note2,
+                user21,
+                user28,
+                user43
+            FROM iasworld.permit
+            WHERE permdt BETWEEN %(start_date)s AND %(end_date)s
+        """,
+        {"start_date": start_date, "end_date": end_date},
+    )
     existing_permits = as_pandas(cursor)
-    # TODO: Antijoin df to existing_permits
-    return df
+    workbook_to_iasworld_col_map = {
+        "PIN* [PARID]": "parid",
+        "Issue Date* [PERMDT]": "permdt",
+        "Amount* [AMOUNT]": "amount",
+        "Applicant Street Address* [ADDR1]": "note2",
+        "Applicant* [USER21]": "user21",
+        "Local Permit No.* [USER28]": "user28",
+        "Notes [NOTE1]": "user43",
+    }
+    new_permits = df.copy()
+    for workbook_key, iasworld_key in workbook_to_iasworld_col_map.items():
+        new_permits[iasworld_key] = new_permits[workbook_key]
+
+    # Transform new columns to ensure they match the iasworld formatting
+    new_permits["amount"] = new_permits["amount"].apply(
+        lambda x: decimal.Decimal("{:.2f}".format(x))
+    )
+    new_permits["permdt"] = new_permits["permdt"].apply(
+        lambda x: datetime.strptime(x, "%m/%d/%Y").strftime(
+            "%Y-%m-%d %H:%M:%S.%f"
+        )[:-5]
+    )
+    new_permits["note2"] = new_permits["note2"] + ",,CHICAGO, IL"
+    new_permits["user43"] = new_permits["user43"].str.replace(
+        "(", ""
+    ).replace(")", "")
+    new_permits["user43"] = new_permits["user43"].str.slice(0, 261)
+
+    # Antijoin new_permits to existing_permits to find permits that do
+    # not exist in iasworld
+    merged_permits = pd.merge(
+        new_permits,
+        existing_permits,
+        how="left",
+        on=list(workbook_to_iasworld_col_map.values()),
+        indicator=True
+    )
+    true_new_permits = merged_permits[merged_permits["_merge"] == "left_only"]
+    true_new_permits = true_new_permits.drop("_merge", axis=1)
+    for iasworld_key in workbook_to_iasworld_col_map.values():
+        true_new_permits = true_new_permits.drop(iasworld_key, axis=1)
+
+    return true_new_permits
 
 
 def gen_file_base_name():
@@ -321,8 +368,14 @@ def save_xlsx_files(df, max_rows, file_base_name):
 
 if __name__ == "__main__":
     conn = connect(
-        s3_staging_dir=os.getenv("AWS_ATHENA_S3_STAGING_DIR"),
-        region_name=os.getenv("AWS_REGION"),
+        s3_staging_dir=os.getenv(
+            "AWS_ATHENA_S3_STAGING_DIR",
+            "s3://ccao-athena-results-us-east-1",
+        ),
+        region_name=os.getenv(
+            "AWS_REGION",
+            "us-east-1",
+        ),
     )
     cursor = conn.cursor()
 
@@ -357,7 +410,12 @@ def save_xlsx_files(df, max_rows, file_base_name):
             "Number of permits prior to deduplication: "
             f"{len(permits_shortened)}"
         )
-        permits_deduped = deduplicate_permits(cursor, permits_shortened)
+        permits_deduped = deduplicate_permits(
+            cursor,
+            permits_shortened,
+            start_date,
+            end_date
+        )
         print(
             "Number of permits after deduplication: "
             f"{len(permits_deduped)}"