diff --git a/public/java/src/org/broadinstitute/sting/gatk/walkers/bqsr/ContextCovariate.java b/public/java/src/org/broadinstitute/sting/gatk/walkers/bqsr/ContextCovariate.java
index 89a30e4f5..a1ab73341 100644
--- a/public/java/src/org/broadinstitute/sting/gatk/walkers/bqsr/ContextCovariate.java
+++ b/public/java/src/org/broadinstitute/sting/gatk/walkers/bqsr/ContextCovariate.java
@@ -26,10 +26,12 @@
 package org.broadinstitute.sting.gatk.walkers.bqsr;
 
 import org.broadinstitute.sting.utils.BaseUtils;
+import org.broadinstitute.sting.utils.MathUtils;
 import org.broadinstitute.sting.utils.exceptions.UserException;
 import org.broadinstitute.sting.utils.sam.GATKSAMRecord;
 
 import java.util.Arrays;
+import java.util.BitSet;
 
 /**
  * Created by IntelliJ IDEA.
@@ -43,10 +45,6 @@ public class ContextCovariate implements StandardCovariate {
     private int insertionsContextSize;
     private int  deletionsContextSize;
 
-    private String mismatchesNoContext = "";
-    private String insertionsNoContext = "";
-    private String  deletionsNoContext = "";
-    
     // Initialize any member variables using the command-line arguments passed to the walkers
     @Override
     public void initialize(final RecalibrationArgumentCollection RAC) {
@@ -57,29 +55,26 @@ public class ContextCovariate implements StandardCovariate {
         if (mismatchesContextSize <= 0 || insertionsContextSize <= 0 || deletionsContextSize <= 0)
             throw new UserException(String.format("Context Size must be positive, if you don't want to use the context covariate, just turn it off instead. Mismatches: %d Insertions: %d Deletions:%d", mismatchesContextSize, insertionsContextSize, deletionsContextSize));
 
-        // initialize no context strings given the size of the context for each covariate type
-        mismatchesNoContext = makeAllNStringWithLength(mismatchesContextSize);
-        insertionsNoContext = makeAllNStringWithLength(insertionsContextSize);
-        deletionsNoContext  = makeAllNStringWithLength( deletionsContextSize);        
     }
 
     @Override
     public CovariateValues getValues(final GATKSAMRecord read) {
         int l = read.getReadLength();
-        String[] mismatches = new String [l];
-        String[] insertions = new String [l];
-        String[]  deletions = new String [l];
+        BitSet[] mismatches = new BitSet[l];
+        BitSet[] insertions = new BitSet[l];
+        BitSet[] deletions  = new BitSet[l];
 
         final boolean negativeStrand = read.getReadNegativeStrandFlag();
         byte[] bases = read.getReadBases();
-        if (negativeStrand) {
-            bases = BaseUtils.simpleReverseComplement(bases); //this is NOT in-place
-        }
+        if (negativeStrand)
+            bases = BaseUtils.simpleReverseComplement(bases);
+
         for (int i = 0; i < read.getReadLength(); i++) {
-            mismatches[i] = contextWith(bases, i, mismatchesContextSize, mismatchesNoContext);
-            insertions[i] = contextWith(bases, i, insertionsContextSize, insertionsNoContext);
-            deletions[i]  = contextWith(bases, i,  deletionsContextSize,  deletionsNoContext);
+            mismatches[i] = contextWith(bases, i, mismatchesContextSize);
+            insertions[i] = contextWith(bases, i, insertionsContextSize);
+            deletions[i]  = contextWith(bases, i,  deletionsContextSize);
         }
+
         if (negativeStrand) {
             reverse(mismatches);
             reverse(insertions);
@@ -90,7 +85,7 @@ public class ContextCovariate implements StandardCovariate {
 
     // Used to get the covariate's value from input csv file during on-the-fly recalibration
     @Override
-    public final Comparable getValue(final String str) {
+    public final Object getValue(final String str) {
         return str;
     }
 
@@ -100,29 +95,28 @@ public class ContextCovariate implements StandardCovariate {
      * @param bases           the bases in the read to build the context from
      * @param offset          the position in the read to calculate the context for
      * @param contextSize     context size to use building the context
-     * @param noContextString string to return if the position is not far enough in the read to have a full context before.
      * @return
      */
-    private String contextWith(byte [] bases, int offset, int contextSize, String noContextString) {
-        return (offset < contextSize) ? noContextString : new String(Arrays.copyOfRange(bases, offset - contextSize, offset));
+    private BitSet contextWith(byte [] bases, int offset, int contextSize) {
+        if (offset < contextSize)
+            return null;
+        
+        String context = new String(Arrays.copyOfRange(bases, offset - contextSize, offset));
+        if (context.contains("N"))
+            return null;
+        
+        return MathUtils.bitSetFrom(context);
     } 
-    
-    private String makeAllNStringWithLength(int length) {
-        String s = "";
-        for (int i=0; i<length; i++)
-            s += "N";
-        return s;
-    }
 
     /**
      * Reverses the given array in place.
      *
      * @param array any array
      */
-    private static void reverse(final Comparable[] array) {
+    private static void reverse(final Object[] array) {
         final int arrayLength = array.length;
         for (int l = 0, r = arrayLength - 1; l < r; l++, r--) {
-            final Comparable temp = array[l];
+            final Object temp = array[l];
             array[l] = array[r];
             array[r] = temp;
         }
diff --git a/public/java/src/org/broadinstitute/sting/gatk/walkers/bqsr/Covariate.java b/public/java/src/org/broadinstitute/sting/gatk/walkers/bqsr/Covariate.java
index b99cd3c3c..80d8cff5d 100755
--- a/public/java/src/org/broadinstitute/sting/gatk/walkers/bqsr/Covariate.java
+++ b/public/java/src/org/broadinstitute/sting/gatk/walkers/bqsr/Covariate.java
@@ -53,7 +53,7 @@ public interface Covariate {
      */
     public CovariateValues getValues(GATKSAMRecord read);
 
-    public Comparable getValue(String str); // Used to get the covariate's value from input csv file during on-the-fly recalibration
+    public Object getValue(String str); // Used to get the covariate's value from input csv file during on-the-fly recalibration
 }
 
 interface RequiredCovariate extends Covariate {}
diff --git a/public/java/src/org/broadinstitute/sting/gatk/walkers/bqsr/CovariateValues.java b/public/java/src/org/broadinstitute/sting/gatk/walkers/bqsr/CovariateValues.java
index dd3a44fb5..09aa1e5b8 100644
--- a/public/java/src/org/broadinstitute/sting/gatk/walkers/bqsr/CovariateValues.java
+++ b/public/java/src/org/broadinstitute/sting/gatk/walkers/bqsr/CovariateValues.java
@@ -12,25 +12,25 @@ package org.broadinstitute.sting.gatk.walkers.bqsr;
  * @since 2/8/12
  */
 public class CovariateValues {
-    private Comparable[] mismatches;
-    private Comparable[] insertions;
-    private Comparable[] deletions;
+    private Object[] mismatches;
+    private Object[] insertions;
+    private Object[] deletions;
 
-    public CovariateValues(Comparable[] mismatch, Comparable[] insertion, Comparable[] deletion) {
+    public CovariateValues(Object[] mismatch, Object[] insertion, Object[] deletion) {
         this.mismatches = mismatch;
         this.insertions = insertion;
         this.deletions = deletion;
     }
 
-    public Comparable[] getMismatches() {
+    public Object[] getMismatches() {
         return mismatches;
     }
 
-    public Comparable[] getInsertions() {
+    public Object[] getInsertions() {
         return insertions;
     }
 
-    public Comparable[] getDeletions() {
+    public Object[] getDeletions() {
         return deletions;
     }
 
diff --git a/public/java/src/org/broadinstitute/sting/gatk/walkers/bqsr/CycleCovariate.java b/public/java/src/org/broadinstitute/sting/gatk/walkers/bqsr/CycleCovariate.java
index a5795c018..292fc720d 100755
--- a/public/java/src/org/broadinstitute/sting/gatk/walkers/bqsr/CycleCovariate.java
+++ b/public/java/src/org/broadinstitute/sting/gatk/walkers/bqsr/CycleCovariate.java
@@ -198,7 +198,7 @@ public class CycleCovariate implements StandardCovariate {
 
     // Used to get the covariate's value from input csv file during on-the-fly recalibration
     @Override
-    public final Comparable getValue(final String str) {
+    public final Object getValue(final String str) {
         return Integer.parseInt(str);
     }
 }
\ No newline at end of file
diff --git a/public/java/src/org/broadinstitute/sting/gatk/walkers/bqsr/QualityScoreCovariate.java b/public/java/src/org/broadinstitute/sting/gatk/walkers/bqsr/QualityScoreCovariate.java
index b48e486ac..373210bdb 100755
--- a/public/java/src/org/broadinstitute/sting/gatk/walkers/bqsr/QualityScoreCovariate.java
+++ b/public/java/src/org/broadinstitute/sting/gatk/walkers/bqsr/QualityScoreCovariate.java
@@ -2,8 +2,6 @@ package org.broadinstitute.sting.gatk.walkers.bqsr;
 
 import org.broadinstitute.sting.utils.sam.GATKSAMRecord;
 
-import java.util.Arrays;
-
 /*
  * Copyright (c) 2009 The Broad Institute
  *
@@ -67,7 +65,7 @@ public class QualityScoreCovariate implements RequiredCovariate {
 
     // Used to get the covariate's value from input csv file during on-the-fly recalibration
     @Override
-    public final Comparable getValue(final String str) {
+    public final Object getValue(final String str) {
         return Integer.parseInt(str);
     }
 }
diff --git a/public/java/src/org/broadinstitute/sting/gatk/walkers/bqsr/ReadGroupCovariate.java b/public/java/src/org/broadinstitute/sting/gatk/walkers/bqsr/ReadGroupCovariate.java
index 74aead9b0..6076a7a20 100755
--- a/public/java/src/org/broadinstitute/sting/gatk/walkers/bqsr/ReadGroupCovariate.java
+++ b/public/java/src/org/broadinstitute/sting/gatk/walkers/bqsr/ReadGroupCovariate.java
@@ -55,7 +55,7 @@ public class ReadGroupCovariate implements RequiredCovariate {
 
     // Used to get the covariate's value from input csv file during on-the-fly recalibration
     @Override
-    public final Comparable getValue(final String str) {
+    public final Object getValue(final String str) {
         return str;
     }
 }