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Mr. Ken Price - 2 - 3 July 2003 treated water is expected to damage tree saplings, so Geomatrix proposes to dilute the treated water with municipal water to lower the concentrations before irrigating with it. When diluted, the concentrations of chloride, nitrate, and ammonium will still be above water quality objectives. However, the underlying groundwater contains nitrate in concentrations ranging from 350 to 600 mg/l, ammonium ranging from 3 to 265 mg/l, and chloride ranging from 200 to 464 mg/1. Therefore, we concur with the use of the carbon-treated runoff water as an irrigant provided the following conditions are met: • Irrigation will occur at rates that do not exceed estimated consumptive water use of the irrigated trees (as previously stated our 12 July 2002 Approval of Amended Phytoremediation Work Plan letter); • The applied nitrogen loading shall not exceed the seasonal consumptive uptake of nitrate by the trees; and • Nitrogen loading data shall be provided in regular phytoremediation reports. GROUNDWATER CLEANUP CRITERIA In the 26 February 2003 comment letter, Geomatrix states that several of the entries listed in the 21 January 2003 Groundwater Cleanup Criteria Table are incongruous with the Water Quality Control Plan for the Sacramento River and San Joaquin River Basins, 4rh Edition (Basin Plan). In particular, Geomatrix discusses the following three items and requests that staff revise the Groundwater Cleanup Criteria Table. Background Concentrations We determined the background concentrations identified in our 21 January letter based on the monitoring record(July 1997 through July 2002) from upgradient MW-16. Based on this record, we determined if a constituent was routinely present in the upgradient groundwater. The following table presents the constituent, the range of background concentrations Geomatrix identified in the record, Board staff s assessment of background, and the supporting reasoning leading to staff s assessment. Background Concentration Comment Table Constituent Range of RWQCB RWQCB Response Background Background Chloride 30.3 to 55 mg/L 30 to 55 mg/L We rounded 30.3 to 30 for simplicity. The 1% difference between the two values is insignificant. Nitrate-N <2 to 24 mg/L <2 mg/L Nitrate concentrations in MW-16 have been declining over the five year period of record,and nitrate has not been detected for the past six consecutive monitoring events from March 2001 through March 2003. Therefore,we believe that<2 mg/L is representative of background concentrations at this site. Total Kjeldahl <0.5 to 1.3 mg/L <0.5 mg/L TKN was detected at or below 0.5 mg/L for 12 of the Nitrogen(TKN) 13 monitoring events for which this constituent was analyzed. It was detected at 1.3 mg/L only once. We believe that 0.5 mg/L is more representative of background concentrations than 1.3 mg/L