Water supply is an important issue in every community, and the City of San Antonio (COSA), Texas, has been proactively evaluating its water policies. COSA and the nearby City of Fair Oaks commissioned the Texas A&M Institute of Renewable Natural Resources to “review and assess factors relevant to implementing water policies.” The Texas A&M report is available here. Among the policies considered was whether COSA should consider a ban on refined coal tar-based pavement sealant (RTS). The report contained the following summary of the RTS-related findings:
Contradictory research results increase the difficulty for developing sound policy regarding the use of coal tar sealants. We recommend COSA policymakers review the available research to determine if coal tar sealants provide a threat to San Antonio water quality, and if an ordinance regulating use of such materials would minimize risk to contamination. Eleven sources of information on the coal tar issue are listed below for review.
Debate continues regarding water quality threats posed by coal tar sealants and the polycyclic aromatic hydrocarbons (PAH) that are released. This report provides a sample of positive and negative references concerning a coal tar sealant ban.
Recommendation – Review the available scientific literature and incorporate goals and actions in the City’s Sustainability Plan on the use of coal tar. [p.89]
Before it was finalized, the Water Policy Report was reviewed by a Science Review Panel (SRP), which reviewed the report and made recommendations. The SRP’s findings are included both in the main body of the Water Policy Report and in two Appendices. The SRP’s comments included the following statement:
The SRP found limitations in both water issue selection and grading, particularly with respect to subjectivity. The SRP determined certain issues should not have been included in the analyses because there was no apparent historical measure based on data provided from which to determine a grade (i.e., coal tar sealant, climate change). [page 21, Comment 4]
The Water Policy Report included “grades” from A to D for actions that COSA might take to improve its water policies. The SRP questioned how the grading system could be translated into actions. On the topic of RTS, the SRP weighed in as follows:
In some cases, the water issues being “graded” did not have any historical activities (e.g., Coal Tar Sealant section). If the grade measure is related to past activities, how can an assigned grade be justified for a potentially future activity that has not occurred? [Appendix A: Science Review Panel Commentary , p. 162]
In response to the recommendation in the Water Policy Report to review available literature, staff of the COSA Office of Sustainability prepared a preliminary research inventory. PCTC reviewed and submitted comments (posted here) on this preliminary document.
COSA had become concerned about RTS because of a USGS report about substances found in sediments in Bexar County, TX. PCTC asked the science consulting firm Exponent® to use environmental forensic techniques to evaluate the USGS attribution of PAHs in Bexar County sediments to RTS. PCTC provided Exponent’s report to COSA. The key finding of the forensic evaluation is as follows:
The City of San Antonio is concerned that refined tar sealers (RTS) may be an important source of polycyclic aromatic hydrocarbons (PAHs) found in sediments of the San Antonio River and its tributaries. This concern is based on the results of a study using an environmental forensic technique called chemical mass balance (CMB) modeling presented in the U.S. Geological Survey (USGS) report, “Assessment of selected contaminants in streambed- and suspended-sediment samples collected in Bexar County, Texas, 2007–09” (Wilson 2011). We evaluated the modeling effort described in the report, and found that the technical findings are subject to significant error due to a failure to include a complete and appropriate list of potential source inputs to CMB. The contribution of PAHs that the USGS report attributed to RTS was associated with a source sample of dust collected from RTS-sealed lots. When we use USGS data from non-sealed parking-lot dust (a source sample that the author did not use), we obtain essentially the same estimated contribution. This finding indicates that prior use of RTS on the parking lots was not a definitive contributing factor to determining PAH sources in sediments. When we replaced parking-lot dust with a source input derived from samples collected from an RTS test plot (therefore, unquestionably related to RTS), CMB-estimated PAHs in San Antonio River sediments contain, at most, a minor contribution from RTS. The conclusion of our evaluation is that USGS’s claim concerning the role of RTS is not supported by the proper application of CMB modeling. No other data set or data analysis in the USGS report indicates that RTS is having a negative effect in the San Antonio River watershed.
Read the full Exponent® report here.