Ambient-Based Thresholds Effective in Calendar Years 2014-2015 (Based on 2003-2012 RMP Data)

Contaminant 90% UTL of 
90th percentile		 DMMO BTs 90% UTL of 
99th percentile 
(TMDL Disposal Limits)		 Notes
Hg (mg/kg dry wt.) 0.332 0.33 0.470 Total Mercury
PCB (μg/kg dry wt.)3 18.3 18 29.6 Sum of 40 congeners2
PAH (μg/kg dry wt.) 4,511 4,500   Sum of 25 PAHs2

Ambient-Based Thresholds Effective in Calendar Year 2013 (Based on 2002-2011 RMP Data)

Contaminant 90% UTL of
90th percentile		 DMMO BTs 90% UTL of
99th percentile
(TMDL Disposal Limits)		 Notes
Hg (mg/kg dry wt.) 0.336 0.34 0.469 Total Mercury
PCB (μg/kg dry wt.) 17.4 17 28.7 Sum of 40 congeners2
PAH (μg/kg dry wt.) 4,446 4,400   Sum of 25 PAHs2

Ambient-Based Thresholds Effective in Calendar Year 2012 (Based on 2002-2010 RMP Data)

Contaminant 90% UTL of
90th percentile		 DMMO BTs 90% UTL of
99th percentile
(TMDL Disposal Limits)		 Notes
Hg (mg/kg dry wt.) 0.341 0.34 0.471 Total Mercury
PCB (μg/kg dry wt.) 16.8 17 26.41 Sum of 40 congeners2
PAH (μg/kg dry wt.) 4,735 4,700   Sum of 25 PAHs2

Ambient-Based Thresholds Effective in Calendar Year 2011 (Based on 2002-2009 RMP Data)

Contaminant 90% UTL of
90th percentile		 DMMO BTs 90% UTL of
99th percentile
(TMDL Disposal Limits)		 Notes
Hg (mg/kg dry wt.) 0.334 0.33 0.472 Total Mercury
PCB (μg/kg dry wt.) 15.7 16 19.51 Sum of 40 congeners2
PAH (μg/kg dry wt.) 4,847 4,800   Sum of 25 PAHs2

1The difference in the PCB TMDL limit from 2011 to 2012 resulted largely from three PCB values that were identified statistically as outliers in the 2002-2009 data set, but that are no longer statistical outliers in the 2002-2010 data set. Specifically, some of the data collected in 2010 filled in gaps at the higher end of the PCB distribution, causing the former outlier data to now be included in the calculations (histogram of 2002-2010 PCB values).

2The RMP reports total PCBs and PAHs using slightly different analyte lists and/or analytical methods than those shown in the DMMO's “Guidelines for Implementing the Inland Testing Manual in the San Francisco Bay Region”. For PCBs, instead of the Aroclor mixtures, the RMP reports a sum of 40 PCB congeners. For dredged material testing, the DMMO recommends USEPA Method 8082 which employs gas chromatography/electron-capture detection (GC/ECD) capable of achieving per congener detection limits in the 0.1 – 0.6 μg/kg range and reporting limits in the 0.5 – 1.0 μg/kg range. Alternative analytical methods may be acceptable as long as the detection and reporting limits are comparable to those of Method 8082. For PAHs, the RMP reports a slightly expanded list of PAH compounds (25 compounds vs. the previous DMMO list of 16). Since all the PAHs in this expanded list are measured by the same analytical method most commercial laboratories already use when analyzing sediment samples (EPA 8270 SIM), there should be little or no cost increase for reporting the additional PAHs.

3 The ambient-based thresholds for PCBs are based on 2002-2003 and 2007-2012 RMP data. The 2004-2006 PCB data are not included in the analysis because of a recently identified issue with sample processing at the laboratory. PCB results for 2004-2006 passed routine laboratory and RMP Quality Assurance; however, were censored in 2014 due to a low bias identified in the extraction method. The 2002-2003 samples were re-analyzed alongside the 2010 samples; therefore, the 2002-2003 data are unaffected.