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asked the SWRCB to issue a stay of the May 4th directive pending SWRCB action on <br /> Petitioner's request for closure. However, since this order considers the petitions on their merits <br /> the issuance of a stay order is now moot. Because both petitions raise similar issues, we have <br /> consolidated them and will deal with both in this order. <br /> By letter dated July 22, 1999, the Chief of the Division of Clean Water Programs, State <br /> Water Resources Control Board, informed the County that sufficient data were available to <br /> conclude that further assessment of site conditions was not warranted and that he would <br /> recommend closure if the results of four additional quarters of sampling remained consistent with <br /> the historic data. In responding to the letter, the County expressed disagreement with the <br /> Division Chief s conclusions and contended that declining concentrations of dissolved phase <br /> hydrocarbons in site groundwater was a consequence of natural attenuation via dispersion and <br /> dilution and that the occurrence of biologic degradation was not supported by available data. <br /> The County also contended that down-gradient monitor wells do not monitor the depth interval <br /> where the highest concentrations of dissolved phase hydrocarbons were detected at the site, <br /> hence the need for continued investigative activities. <br /> II. CONTENTIONS AND FINDINGS <br /> Contention: Petitioner contends its case should be closed because soil and groundwater <br /> assessment is complete and corrective actions conducted have diminished the presence of <br /> residual petroleum hydrocarbon constituents to a point where they pose a"low risk"to public <br /> health and safety, the environment, and to current or probable future beneficial uses of water. <br /> The County concedes that natural attenuation is occurring at the site but it argues that <br /> biologic degradation is not a factor in the observed decline of petroleum hydrocarbon . <br /> constituents in groundwater and contends that down-gradient monitor wells do not extend to the <br /> depth interval where the highest documented concentrations of dissolved phase hydrocarbons <br /> have been detected at the site. <br /> Findings: Petitioner's contention has merit. As explained below, the facts in the record <br /> support the finding that additional soil and groundwater investigation or additional remediation is <br /> not necessary, and that residual petroleum hydrocarbon constituents at Petitioner's site do not <br /> pose a threat to human health and safety, or the environment, and do not adversely affect, or <br /> 8 <br />