diff --git a/autotest/en_tests.py b/autotest/en_tests.py
index f0faafb54..5270c008d 100644
--- a/autotest/en_tests.py
+++ b/autotest/en_tests.py
@@ -592,7 +592,7 @@ def mixed_par_draw_test():
     #phi_vector_test()
     #add_base_test()
     #nz_test()
-    # deviations_test()
+    deviations_test()
     # as_pyemu_matrix_test()
     # dropna_test()
     #enforce_test()
diff --git a/autotest/utils_tests.py b/autotest/utils_tests.py
index f5fec372c..9bfd3b2a7 100644
--- a/autotest/utils_tests.py
+++ b/autotest/utils_tests.py
@@ -1787,6 +1787,27 @@ def run_test():
         raise Exception("should have failed")
 
 
+def maha_pdc_test():
+    import pyemu
+    l1_critical_value = 6.4 #chi squared value at df=1,p=0.01
+    l2_critical_value = 9.2 #chi sqaured value at df=2,p=0.01
+    pst = pyemu.Pst(os.path.join("la", "pest.pst"))
+    en = pyemu.ObservationEnsemble.from_gaussian_draw(pst=pst,num_reals=20)
+    level_1,level_2 = pyemu.helpers.get_maha_obs_summary(en)
+    assert level_1.max() < l1_critical_value
+    assert level_2.sq_distance.max() < l2_critical_value
+
+    # pst = pyemu.Pst(os.path.join("pst","zoned_nz_64.pst"))
+    # en = pyemu.ObservationEnsemble.from_gaussian_draw(pst=pst, num_reals=20)
+    # level_1, level_2 = pyemu.helpers.get_maha_obs_summary(en)
+    # level_1.sort_values(inplace=True)
+    # level_2.sort_values(by="sq_distance",inplace=True)
+    # print(level_1)
+    # print(level_2)
+    # assert level_1.max() < l1_critical_value
+    # assert level_2.sq_distance.max() < l2_critical_value
+
+
 if __name__ == "__main__":
 
     #run_test()
@@ -1805,13 +1826,13 @@ def run_test():
     # sfr_obs_test()
     #sfr_reach_obs_test()
     #gage_obs_test()
-    setup_pp_test()
+    #setup_pp_test()
     # sfr_helper_test()
     # gw_sft_ins_test()
     #par_knowledge_test()
     # grid_obs_test()
     #hds_timeseries_test()
-    postprocess_inactive_conc_test()
+    #postprocess_inactive_conc_test()
     #plot_summary_test()
     # load_sgems_expvar_test()
     # read_hydmod_test()
@@ -1856,4 +1877,5 @@ def run_test():
     # ok_grid_test()
     # ok_grid_zone_test()
     # ppk2fac_verf_test()
-    #ok_grid_invest()
\ No newline at end of file
+    #ok_grid_invest()
+    maha_pdc_test()
\ No newline at end of file
diff --git a/pyemu/utils/helpers.py b/pyemu/utils/helpers.py
index 2d0e712c1..d85d0123a 100644
--- a/pyemu/utils/helpers.py
+++ b/pyemu/utils/helpers.py
@@ -5970,3 +5970,74 @@ def _set_vertices(self):
 #                   "instead.", category=DeprecationWarning)
 # 
 #     return get_spatialreference(epsg, text='proj4')
+
+def get_maha_obs_summary(sim_en):
+    """ calculate the 1-D and 2-D mahalanobis distance
+
+    Args:
+        sim_en (`pyemu.ObservationEnsemble`): a simulated outputs ensemble
+
+    Returns:
+
+        tuple containing
+
+        - **pandas.DataFrame**: 1-D subspace squared mahalanobis distances
+        - **pandas.DataFrame**: 2-D subspace squared mahalanobis distances
+
+    Note:
+        Noise realizations are added to `sim_en` to account for measurement
+            noise.
+
+
+
+
+    """
+
+    if not isinstance(sim_en,pyemu.ObservationEnsemble):
+        raise Exception("'sim_en' must be a "+\
+                        " pyemu.ObservationEnsemble instance")
+    if sim_en.pst.nnz_obs < 1:
+        raise Exception(" at least one non-zero weighted obs is needed")
+
+    # process the simulated ensemblet to only have non-zero weighted obs
+    obs = sim_en.pst.observation_data
+    nz_names =sim_en.pst.nnz_obs_names
+    # get the full cov matrix
+    nz_cov_df = sim_en.covariance_matrix().to_dataframe()
+    nnz_en = sim_en.loc[:,nz_names].copy()
+    nz_cov_df = nz_cov_df.loc[nz_names,nz_names]
+    # get some noise realizations
+    nnz_en.reseed()
+    obsmean = obs.loc[nnz_en.columns.values, "obsval"]
+    noise_en = pyemu.ObservationEnsemble.from_gaussian_draw(sim_en.pst,num_reals=sim_en.shape[0])
+    noise_en -= obsmean #subtract off the obs val bc we just want the noise
+    noise_en.index = nnz_en.index
+    nnz_en += noise_en
+
+
+
+    #obsval_dict = obs.loc[nnz_en.columns.values,"obsval"].to_dict()
+
+    # first calculate the 1-D subspace maha distances
+    sim_mean = nnz_en.mean()
+    obs_mean = obs.loc[nnz_en.columns.values,"obsval"]
+    simvar_inv = 1. / (nnz_en.std()**2)
+    res_mean = sim_mean - obs_mean
+    l1_maha_sq_df = res_mean**2 * simvar_inv
+
+    # now calculate the 2-D subspace maha distances
+    onames1,onames2,l2_maha_sq_vals = [],[],[]
+    for i1,o1 in enumerate(nz_names):
+        r1 = res_mean[o1]
+        print("{0} of {1}".format(i1+1,len(nz_names)))
+        for i2,o2 in enumerate(nz_names[i1+1:]):
+            c_inv = np.linalg.inv(nz_cov_df.loc[[o1,o2],[o1,o2]].values)
+            r2 = res_mean[o2]
+            r_vec = np.array([r1,r2])
+            l2_maha_sq_val = np.dot(np.dot(r_vec,c_inv),r_vec.transpose())
+            onames1.append(o1)
+            onames2.append(o2)
+            l2_maha_sq_vals.append(l2_maha_sq_val)
+    l2_maha_sq_df = pd.DataFrame({"obsnme_1":onames1,"obsnme_2":onames2,"sq_distance":l2_maha_sq_vals})
+
+    return l1_maha_sq_df,l2_maha_sq_df