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Evaluation Work Plan for 3 1 October 2009 Septic Systems and Percolation Pits Order No. R5-2008 0148 Lawrence Livermore National Laboratory Site 300 San Joaquin County concentrations and/or current concentrations. • The work detailed in the Work Plan will be completed one year from the date the plan is approved and a report with the final evaluation will be submitted to the Central Valley Water Board one year and 30 days after the plan is approved. Central Valley Water Board staff concurs with the work plan contingent that you revise the work plan to address following comments: 1. Remove monitoring requirements for the septic systems at Building 899, Building 850, Building 834 and Building 812 from the Work Plan and include these septic systems in the site wide septic system evaluations specified in the Work Plan. 2. Central Valley Water Board staff is skeptical about LLNL's proposal to model transport in the vadose zone followed by fate and transport modeling of the saturated zone. As stated in the Order, LLNL well need to propose installation of groundwater monitoring wells at sites Where discharges from the percolation pits or septic systems have the potential to cause groundwater quality to exceed background water quality. 3. Propose to demonstrate that impermeable zones beneath the septic systems (e.g. 10 to 20 feet of clay) impede groundwater impacts from the septic systems and therefore did not require evaluation of potential to impact groundwater. 4. Propose to determine if attenuation of potential contaminants of concern exists beneath septic systems and how much soil is necessary for adequate attenuation. 5. State that in the final evaluation report to be submitted 1 November 2010, LLNL will include the following: a. A discussion of how the percolation pits and septic systems were grouped, which groupings have adequate monitoring wells and which require additional monitoring wells. b. For percolation pits and septic systems excluded from the evaluation, LLNL must describe the geology below the percolation pits and septic systems and substantiate the conclusion that hydraulic barriers are sufficient to prevent downward migration of and that impacted groundwater in perched zones will not impact groundwater in deeper zones over time. c. A discussion of how analytes were grouped. d. A discussion of available attenuation below the different groups of percolation pits and septic systems. e. A table with text discussing the reasons particular percolation pits and septic systems have been removed from further investigation,