TEST RESULTS SHOW DRAMATIC IMPROVEMENTS

Under Environmental Protection Agency regulations, homes that are likely to have high lead levels - usually older homes likely to have lead service lines or lead solder – must be tested. Also, only first flush samples, water most likely to have lead, are sampled. The EPA rule requires that 90% of these sampled homes must have lead levels below the Action Level of 15 parts per billion (ppb).

Lead levels in sampled worst case homes have steadily dropped since 1992. Average lead levels at sampled worst-case homes have dropped nearly 90%. In this most recent sampling round (September 2008), the MWRA 90th percentile was 8.1 ppb, well below the Action Level of 15 ppb.

The following charts show the dramatic drop in lead levels in tap water since improvement in corrosion control were begun in 1996.  In the first pie chart showing 1992 data before improvements were made to corrosion control, the number of samples that were above the Action Level of 15 ppb (the red, over 50 ppb and pink sections, between 15 and 50 ppb) take up almost half of the chart.  The 90th percentile value was 71 ppb.

June 1992 Larger Image

After MWRA implemented effective corrosion control in 1996, the lead levels started to drop dramatically. The 90th percentile value had dropped to 11.3 ppb. The fraction of samples in the September 2002 rounds that were above the Action Level of 15 ppb is much lower (less than 10%), while the number of results that were less than 5 ppb or non-detected (the light blue and dark blue sections) now represent  nearly three-quarters of the samples. 

September 2002 Larger Image

With continued fine-tuning of the corrosion control, levels have continued to drop.  In the latest sampling round, September 2008, the number of non-detects has increased and the combination of non-detects and those less than 5 ppb is now 80 percent of the total chart, and the number of samples above 15 is nearly 90% less than the 1992 sampling round.  The fraction of samples over high values, over 50 ppb, has dropped from about 20% to zero. The 90th percentile value is 8.1 ppb.