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*400, r./ <br /> Central Valley Construction <br /> 146 Klo Road, Lathrop - 2 - 15 May 2002 <br /> at appropriate detection limits. Based on this information,no additional soil investigation work is necessary at <br /> the former AGT area. <br /> JCA concluded in the Q1-2002 Report that two additional quarterly monitoring events will be completed(for a <br /> total of four monitoring events), and if the remaining sampling events show stable or decreasing groundwater <br /> contaminant trends, file closure would be recommended. Board staff concur with JCA that TPHd at this site is <br /> relatively low, and a no further action required(NFAR) determination is probable for the site. <br /> However,prior to Board staff issuing a NFAR letter for the subject site, Central Valley Construction must show <br /> through groundwater monitoring and fate and transport calculations that constituents remaining at the site will not <br /> continue to degrade groundwater resources. The water quality objectives for TPHd in groundwater are based on <br /> the taste and odor threshold of TPHd, which is set at 100 µg/1. At a minimum, cleanup at the Central Valley <br /> Construction site must approach this goal to be protective of beneficial uses of groundwater in this area. <br /> For future quarterly monitoring events,which are due by the last day of the month following the quarter when <br /> samples were collected(e.g. 31 July, 31 October, 31 January, and 30 April),please complete the following items: <br /> 1. Analyze groundwater samples from the three monitoring wells and the on-site domestic well for TPHg and <br /> TPHd by EPA Method 8015M, and for BTEX constituents by EPA Methods 8020/8021 or 8260B. As <br /> discussed above,you may discontinue analyzing water samples for fuel oxygenates,lead, and volatile organic <br /> compounds. <br /> 2. Collect and analyze a water sample from the domestic water supply well identified as "Well No. 2"in the <br /> well receptor survey. Besides the on-site domestic well,Well No. 2 is the closest down gradient water <br /> supply well to the site, and as reported, it is completed to a total depth of 80 feet. Please analyze the sample <br /> for the same constituents as listed in Item No. 1 above. <br /> 3. Please correct Table 6 in the Q1-2002 Report to show that TPHd was identified in monitoring well MW-2 at <br /> 56 micrograms per liter(µg/1) during the November 2001 sampling event. <br /> 4. Submit isoconcentration maps for all petroleum hydrocarbon constituents identified in future monitoring <br /> events. <br /> Please notify me at least five business days prior to any site work or sampling. If you have any questions or <br /> comments,please call me at(916)255-3115. <br /> Marty Hartzell,R.G. <br /> Associate Engineering Geologist <br /> cc: Mr. Sam Savig, San Joaquin County Public Health Services, Stockton <br /> Mr. John Cummings, John Cummings &Associates,Fremont <br />