SITE INFORMATION AND CORRESPONDENCE

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Mr. Benson Cuthbertson - 3 - 19 March 2013 2. Figure 3D of the 2 October 2012 Third Quarter (Semi-Annual) Groundwater Monitoring Report shows the approximate range of historic groundwater gradients. Figure 3D also shows that there are no monitoring wells located downgradient of the spill. Therefore, the downgradient extent of the contaminant plume is not defined. 3. The previous site investigations failed to identify the on-going groundwater extraction and treatment system at the former Occidental Chemical site. This system has multiple extraction points at multiple depths, and data available from the Geotracker website shows that the PNA release lies within the capture zone of the Occidental groundwater extraction system. Furthermore, data suggest that the extraction system induces downward gradients at the site. Therefore, site hydrogeology and groundwater flow patterns are not defined and pollution from the PNA site may be migrating downward. Groundwater Section 3.2 of the Closure Report states that the maximum detected TPHd during the August 2012 monitoring event was 6,200 ug/I. However, the pattern did not match the standard for diesel. Section 3.2 goes on to state that the plume above water quality objectives does not exceed 250 feet, free product has been removed to the maximum extent practicable, that the plume does not extend offsite, that it has been stable for at least 5 years, and the closest water supply well is greater than 1,000 feet from the plume boundary and that the contamination does not pose a risk to human health or the environment. Regional Board staff do not concur for the following reasons: 1. As stated previously, the downgradient extent and the vertical extent of contamination at this site are not defined, therefore it cannot be determined from the available data whether the plume, particularly the dissolved plume, extends offsite. 2. PNA has not attempted to implement any enhanced methods to recover diesel, beyond bailing the 4-inch wells, since 1999. Therefore, it has not been demonstrated that additional diesel recovery is not possible. 3. The dissolved TPH detected in the SW sump during the August 2012 monitoring event was the highest concentration of TPH ever detected in the sump. Therefore, the dissolved plume may not be stable. 4. The construction, purpose, operation and maintenance of the two interior sumps have never been reported to Regional Board staff. A review of the monitoring data shows that dissolved TPHd is routinely found in the SW sump. However, ground water in the sump also contained motor oil constituents 17 times since August 2000. Because motor oil was not one of the constituents released during the 1996 leak, there may be an additional source of pollution being released to groundwater from the facility. Finally, the Closure Report, in Section 3, provides a Low Risk Closure Evaluation. Currently, the State Water Resources Control Board Low-Threat Underground Tank Case Closure Policy applies only to underground storage tanks regulated under Chapter 6.7 of Division 20 of the Health and Safety Code, Underground Storage of Hazardous Substances. State Water Resources Control Board Resolution 68-16 prohibits any