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ENV.. <br /> AMERICA <br /> Mr. Duane White <br /> California Department of Toxic Substances Control <br /> September 24, 2004 <br /> Page 4 of 6 <br /> Based on these reasons, the Site is a low-risk groundwater case even though <br /> concentrations of COCs in the groundwater samples collected from some monitoring wells <br /> at the Site exceed the numerical RAOs. <br /> PROPOSED REVISED GROUNDWATER MONITORING PROGRAM <br /> Analytical data collected to date from each monitoring well are evaluated using the <br /> Groundwater Monitoring Decision Tree. Since the Site is a low-risk groundwater case, a <br /> reduced (frequency and number) groundwater monitoring program is proposed: <br /> Monitoring Field Laboratory Analyses <br /> Zone Well Frequency Parameters 0_A_Hs4 BTEX TPHg4 TPHd Bio <br /> A MW4 Annual X X X X X X <br /> A MW8 Annual X X X X <br /> A MW9R Annual X X X X X X <br /> A MW18 Annual X X X X <br /> B MW6R Annual X X X X <br /> B MW19R Annual X X X X X X <br /> B MW23R Annual X X X X <br /> BMW26R Annual X X X X <br /> C MW13 Annual X X X X X X <br /> C MW24 Annual X X X X X X <br /> Notes: <br /> 1. Field parameters include measurements of depth to water, electrical conductivity, pH, and <br /> temperature. <br /> 2. PAHs = polycyclic aromatic hydrocarbons analyzed using EPA Method 8310- <br /> 3. BTEX= benzene, toluene, ethylbenzene, and xylenes analyzed using EPA Method 8021. <br /> 4. TPHg = total petroleum hydrocarbons quantified as gasoline analyzed using EPA Method <br /> 8015M. <br /> 5. TPHd =total petroleum hydrocarbons quantified as diesel analyzed using EPA Method <br /> 8015M. <br /> 6. Bio = bioremediation indicator parameters for evaluation of natural attenuation of COCs in <br /> groundwater. Sample should be collected for measurements/analysis of these parameters <br /> once every 5 years, starting in 2009. Bio parameters include: <br /> - dissolved oxygen (field measurement) <br /> - oxidation-reduction potential (field measurement) <br /> - dissolved iron using EPA Method 6010 <br /> - dissolved manganese using EPA Method 6010 <br /> - sulfate using EPA Method 300 <br /> 7. Annual monitoring is proposed to be conducted during the first quarter when groundwater <br /> level is usually higher than other times of the year. <br /> C:\Documents and Settingsknjavier\Local Settings\Temporary Internet Files\OLK860TSC response Itr Sep2004—revised.doc <br />