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j Updated Human Health Risk Assessment Natural Attenuation Analysis and Additional Site Investigation Work Plan Tabow California Tank Lines , Inc. since 1956 3105 South EI Dorado Street, Stockton , California 2.4 . 1 Grab Groundwater Samplina and Analysis Grab ground water samples will be collected from each boring new disposable bailers . [ First groundwater is expected at between 35 to 40 ft. bgs . The samples will be placed into laboratory-supplied sample containers, labeled , packed in an iced sample container, and transported under chain-of-custody to a California certified laboratory for analysis of TPG- D, and �j TPH - MO using LUFT GC/MS and TPH-G using EPA method 8260B, benzene, toluene , ethylbenzene, and total xylenes ( BTEX) , methyl tertiary butyl ether (MTBE) , di-isopropyl ether r ( DIPE) , tertiary amyl methyl ether (TAME), tertiary butyl alcohol (TBA) and 1 ,2-dichloroethane ( 1 , 2- DCA) using EPA method 82608. I 3 .4.2 Boring Abandonment I Upon completion , the soil borings will be sealed with neat cement grout for their entire l depth in accordance with State of California and SJEHD regulations . The surface will be �. . J restored to its pre-drilling configuration . 2.5 Absorbent Socks Free product has been removed from MW-2 at each quarterly groundwater sampling ff 1 event through 2008 , and semi-annually events beginning in 2009. Free product has been removed using a standard bailer prior to groundwater sample collection . Taber Consultants proposes to use specialized bailers and/or socks to remove the oil on a continuous or semi- l � continuous basis, to speed up its removal . This will involve securing a number of specialized f products , such as socks filled with "Carphene" or 'Peatwick". Carphene is a Highly Reactionary Carbon Mixture ( HRCM) which has the ability to absorb various products from water; Peatwick is a hydrophobic organic material which draws hydrocarbons through capillary action until it ` reaches saturation . Taber Consultants will suspend the socks into the groundwater within the well . Following saturation , Taber Consultants will withdraw the socks for proper disposal . It will be necessary to experiment to determine how long each takes to become saturated , and to develop a program to remove the waste oil as rapidly and completely as possible . The socks will be set at a depth that will consider seasonal groundwater fluctuations. More detailed I� I information on the adsorbent socks can be provided to SJCEHD upon request . i2.6 Monitoring Well MW-1 Depth Assessment The total depth of MW-1 has been reported to be approximately 45 to 46 ft. since i 1 9/12/05, suggesting that significant silting has occurred compared to a constructed depth of approximately 50 feet, and that the well should be redeveloped . However, the total depth measurement on 02/11 /10 (annual monitoring) was 50 ft. , which brings into question earlier measurements. MW-4 exhibited similar results for total depth measurements . Depth fmeasurements were 44.8 ft . from 9/12/05 through 11 /25/08, and 49 . 84 ft. on 02/13/09 and 09/02/09. Thus there appears to be a need for greater care in securing this measurement. In any case , well depths will be re- measured and confirmed in the presence of SJCEHD representatives before any action is taken regarding redeveloping the well . 4 Taber Project No. 051087 LJ