SITE INFORMATION AND CORRESPONDENCE

Home Browse Search

ST Services Stockton Terminal - 3 - 26 March 2008 Mr. Joe Aldridge 1998 through 2002, when the well did not contain SPH. The EPA Guideline is included as an attachment to the Response Letter. This method predicted that the WQO of 5 pg/L for TPHg will be attained in about 18 years in ST/MW-1 and that a concentration of 1 ,000 pg/L of TPHg will be attained in MW-15 in about 26 years. Using only the 1998-2002 monitoring data to determine a first-order attenuation rate constant ignores the gasoline and diesel releases of March, April, and June 2002. These releases reverse any attenuation that might have occurred prior to 2002, as evidenced by the appearance of about two feet of SPH in well ST/MW-1 following the April 2002 spill. Regional Water Board staff prepared a first-order attenuation rate model which incorporates only post-2002 data. Consistent with our previous results, the post 2002 spill model also showed that despite the disappearance of SPH from source area well ST/MW-1 in 2005, dissolved petroleum hydrocarbon concentrations would continue to show an increasing trend. This model demonstrates that decay is not occurring naturally in the source area. As stated in the EPA Guideline, biodegradation does not occur without source area decay. Thus, NuStar will have to perform active remediation in order to attain WQOs. 2. The Response Letter includes a plot for PS/MW-15 using the EPA Guideline and predicts that a concentration of 1,000 pg/L will be achieved by 2034. However, as discussed in the 9 July 2007 meeting and acknowledged by NuStar in the Report, the WQO for TPHg is 5 pg/L. Regional Water Board staff used the EPA Guideline to project out to 5 pg/L for PS/MW-15 and found that this level cannot be achieved by natural attenuation until about 2090 or 80 years from now. This finding shows that MNA is not a feasible option for achieving the WQO for TPHg in a reasonable time. 3. The EPA Guideline for determining a first-order attenuation constant combines non- destructive attenuation processes such as dispersion, sorption, and dilution with biodegradation. In the absence of a distinction between attenuation processes there is no way to verify that petroleum hydrocarbon in groundwater are being destroyed by biodegradation as opposed to being displaced by non-destructive processes. The EPA Guideline confirms this concern in Appendix III by showing that attenuation occurs in the absence of biodegradation and that sorption is the most influential variable in attenuating contaminant concentrations without biodegradation. Therefore, without determining a first- order biodegradation rate constant, NuStar cannot claim that biodegradation is occurring at this Site. 4. The text on page 11 of the Report states, "The anaerobic microbial degradation of petroleum hydrocarbons (such as benzene) commonly utilize sulfate as the electron acceptor and generate methane as a degradation byproduct." Regional Water Board staff could not verify that this metabolic pathway has been documented in published literature. The stoichiometry that describes sulfate reduction with benzene degradation is described as 3.75 SO42- (sulfate) + 7.5 H' (hydrogen) + C6 H6 (benzene) ----4 6 CO2191 (carbon dioxide) + 3 H2O (water) + 3.75 H2 S° (sulfide) This redox equation shows that the byproduct of sulfate reduction is sulfide. Methane is generated (methanogenesis) using CO2 as an electron acceptor. This pathway has not been verified for this Site. NuStar's 2007 data provide no documentation that there is any