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A <br /> PUBLIC MEALTH SERVES q�,N <br /> P <br /> SAN JOAQUIN COUNTY �0.V!N <br /> ENVIRONMENTAL HEALTH DIVISION a ,. <br /> Ernest M. Fujimoto, M. D., M.P.H., Acting Health Officer <br /> 304 E. Weber Ave., Third Floor • P. O. Box 388 • Stockton, CA 95201-0388 °4tiFaQN`" <br /> 209/468-3420 <br /> TINA BERRY MAILED JUN 14199E <br /> UNOCAL CORPORATION <br /> 2000 CROW CANYON PALCE STE 400 <br /> SAN RAMON CA 94583 <br /> RE: former UNOCAL#5098 SITE CODE: 2162 <br /> 5606 Pacific Ave. <br /> Stockton, CA 95207 <br /> San Joaquin County Public Health Services, Environmental Health Division (PHS-EHD) has reviewed your <br /> correspondence dated May 22, 1996 and has the following comments. <br /> Your site has been on quarterly monitoring and sampling since the groundwater investigation began. The <br /> most recent quarterly report, First Quarter-1996, for the sampling event on March 11, 1996 was <br /> incomplete and did not include groundwater sampling data for monitoring wells 10, 11, 12, 13, 14, or 15. <br /> Instead a notation that these wells are "sampled semi-annually"was inserted in the report. This change in <br /> your sampling frequency was not approved by PHS-EHD. <br /> In your May 22, 1996 correspondence you propose to reduce the sampling and monitoring frequency to <br /> either annually or semi-annually commencing June 1996. The first quarter-1996 report dated April 17, <br /> 1996 by MPDS Services submitted to PHS-EHD on May 20, 1996 appears to already reflect a change in <br /> sampling frequency. <br /> Also included in your proposal were references to policies and guidance documents for low-risk sites, that <br /> as of this date, have not been accepted, passed, or adopted, and as such, will not be evaluated by PHS- <br /> EHD. <br /> Although UNOCAL contends that soil remediation has been completed at this site, PHS-EHD has <br /> concerns that soil in the area of Monitoring Wells 11 and 12 is impacting the groundwater. Due to the <br /> limits of the over-excavation and slope-wall safety requirements, the soil in the area of MW-11 and MW-12 <br /> was not removed. Vapor extraction wells that were constructed in this area were never placed into active <br /> service and were destroyed prior to any vapor extraction remediation effort. <br /> PHS-EHD is also concerned that the groundwater recharge in this area has caused the depth to <br /> groundwater to rise to levels that exceed the screened interval of the well casings by over seven (7) feet. <br /> The reducing trend you mentioned in your letter for groundwater hydrocarbon concentrations since 1992 <br /> may be attributed to dilution, and since Fall 1995, the inability of the monitoring wells to allow the <br /> groundwater above the screened interval to enter the casings so an accurate representation of the <br /> groundwater could be sampled. <br /> Plan C of your proposal includes placement of Oxygen Reducing Compound (ORC) into monitoring wells <br /> 11 and 12 as an interim remedial measure. After discussions with REGENESIS BIOREMEDIATION <br /> PRODUCTS COMPANY (RBP), the folder you supplied, PHS-EHD has determined that the placement of <br /> ORC socks in only these two wells will be inadequate to effect any significant change in groundwater <br /> hydrocarbon levels or stop the migration of on-site contamination to off-site areas. <br /> A Division of San Joaquin County Health Care Services <br />