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FEB-I8-99 THU 10:05 AM P. 01 <br /> FEB. -1.' 99 MU-1 15:20 UNOCAL 'FORTH RE TEL:510 '94k../81 P, 015 <br /> In this particular case, as discussed above TPH-g and STEX in the shallow <br /> groundwater in irnmediace contact with the limited msidu7d peaoleum hydrocarbon <br /> constituents adsorbed to soft viii&ciy ramn alxwrft and thus violate, rhe Hash Plan's <br /> objectivcs in a localized voiuma of surramofing Smuedwaet Sbr a slganiticatrt period of <br /> time. ThiS time period could be anywhere from a few decades for STEX to degrade <br /> below MCLa to hundreds of years for thM Iitnited volume of groundwater in kmwdme <br /> coatact with longer drain, itnaaobile residua]pebroieum oonstitumu adsorbed to sods to <br /> mea the commor4y accepted 5 ppb Use and odor thrrMOK <br /> Nonetheies-k &=g this tote thew msxdtaal co»ceutra�ioas in coats of Basin PIan <br /> objectiv%wM trot pose a threat to au=or fimm beneficial uses. It is mgW unlikeiy <br /> that petrolemn hydrocarbon constituents detected in localized area in to irtm agate area <br /> of the release will mute siibsb=mIly beyond current Hmrmd spatial•extera. Though the <br /> longer chain lrydrocad , - F oongwising wemlered TPH-g biodegrade mare siawly thm <br /> certain petroleum aonstitnents,such as brazeae, they are also more recalcitrant(Ir-,less <br /> volatde, less soluble and highly absorbent)=d much las mobile. It is also highly Unftely <br /> d=oris pmt=dar very hm led pociat of shallow gmundwata will be used dirm*as a <br /> source of drinking water. Thus,the significm period of time drat n wM take for water <br /> gttr ky in this wed aru to meet all Basin Plan objectives is a ramble time frame. <br /> Closure of the site, given the facts in this partioalar case,is appropriate. <br /> III. SlMday ION <br /> I. There is no evidence of MME at ibis site. Corrective actions indudbg sod <br /> vapor mon and removal of an estimated,950 cubic yards of coni rninatod sort'have <br /> removed a significant maw of residual petroleum hydrocarbons at petitioner's site. <br /> 2. The plume of dissolved pie hydrocarbons is stable, concentrations of <br /> constituents are decfiring, and nmirally neutering biodegradaiom of residual petroleum <br /> hydrocarbons adsorbed to soil and pmmu in groundwater is oem rring. <br /> 3. Ten years after the release was stopped, groundwater meets Basin Plan <br /> objectives with telt to ETEX constituents within about 70 feet of the site;with respect <br /> to TPM-g, groundwater meets Basin Plan objectives witWn 150 feet of the site. <br /> 12 <br />