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✓-�` <br /> . anticipated to present significant risks to human health and safety Shallow Geomatrix <br />! groundwater below the Site has no current or anticipated future beneficial use See <br /> Discussion No 16 in Section 2 0 and Section 3 2 3 <br />' 6 The plume size is stable and sufficiently limited in extent. The plume size is <br /> stable and limited to less than 200 feet in length and less than 150 feet in width See <br /> Section 3 2 1 for further discussions <br />! 3.2 NFAR CRITERIA FOR CASES EXCEEDING WQOS <br />! RWQCB staff believe that in some cases it is reasonable to issue a NFAR letter for a site that <br /> does not meet WQOs but presents a low risk and is expected to meet WQOs in the near future <br /> (TRR—Appendix A) One example is when incremental cost for mass removal exceeds the <br />! incremental benefit for a site RWQCB staff currently require the following information to <br /> support requests to issue a NFAR letter at UST sites with contaminant concentrations above <br /> WQOs (Section 6 5 of the TRR—Appendix A) <br /> • demonstration that the plume is stable, <br />! • estimated time when WQOs will be achieved, and <br /> • verification that there are no current or anticipated uses of impaired water within the <br /> timeframe projected to meet WQOs <br />' This information is presented in the following three subsections <br />' <br /> 3.21 Demonstration That the Plume is Stable <br /> The petroleum release at the Site was discovered in 1988 when the USTs were removed, which <br /> means that the release occurred at least 18 years ago The current plume size is estimated to be <br />' less than 200 feet long and about 100 feet wide (Figure 1) The concentrations of BTEX and/or <br /> TPHg in the groundwater samples collected from four of the six existing monitoring wells at <br />' the Site have exceeded the WQOs (Table I of the TRR—Appendix A) These four wells are <br /> MW3-1, MW3-2, MW3-3, and MW3-6 Groundwater monitoring data in wells MW3-1, <br />' MW3-2, and MW3-3 (7 years of data since groundwater monitoring began at the Site in 1999) <br /> and well MW3-6 (3 years of data since installation in 2003) indicate stable concentration trends <br />' and no apparent upward trends (Figures 5, 6, and 7) <br /> Biodegradation of petroleum constituents is well documented (Rice, et al , 1995, Wiedemeier, <br />' et al , 1999) These studies concluded that petroleum hydrocarbons plumes typically do not <br /> extend more than 250 feet from the source The extent and stability of the plume at the Site are <br />' consistent with the findings of these studies <br />' I16000s16437 0001Archive16437-041 doc 8 <br />