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Bert E. Van Voris - 9 - 17 September 2004 Supervising Engineer RWD/RWR should, therefore, thoroughly characterize the irrigation supply in both proposed use areas and attempt to project the concentrations of IDS and IDS constituents in leachate released to groundwater as a result of the recycled water project, even if it will take over 50 years for this release to reach groundwater. The RWD/RWR should provide data in support of its determination that storm water diverted to the reservoir will contain IDS and other waste constituents in concentrations less than in processing wastewater discharged to the reservoir. Due to the ongoing discharge's IDS loading to LTU soils, stone water running off the LTU has the potential to transport substantial IDS and other waste constituents (including sediment). The criteria governing the release of stone water runoff from the LTU are very strict and will Rely require all stone water runoff from the LTU be collected for years, and possibly decades, to come. The amount of flow this represents, especially in a rainfall year of 100-year return frequency, is necessary to evaluate the project's water balance and the adequacy of its wastewater and storm water storage for the proposed discharge flow (discussed below). Proposed Reservoir Use. The proposed use of the reservoir as a treatment reactor is problematic. First,the delivery of water for flood irrigation, as proposed, is typically accomplished by discharges of large volumes ("runs") and not as steady small flows. The proposal appears to rely on the currently available long detention time to achieve the proposed target BOD levels. Detention time may be less than current levels during the summer irrigation season when potentially large volumes of recycled water are provided to use areas in irrigation runs. Second, the impounded wastewater may release to groundwater oxygen-demanding substances in sufficient mass to cause groundwater to contain higher concentrations of total organic carbon and decomposition byproducts, including,but not limited to, iron, manganese, calcium,magnesium, and alkalinity.7 Musco has not submitted, nor is it apparently capable of submitting, a report showing construction details of a liner adequate to prevent wastewater impounded within the reservoir from impacting the groundwater. Due 15 August 2002 pursuant to Task 16 of the TSO,this submittal has never been provided. Shortly after wastewater impoundment, the dam's blanket drain began discharging at a reported rate of about 5 gpm, a rate that has reportedly decreased during this summer. Musco has disagreed with the determination by Regional Board staff—based on a chloride mass balance analysis—that impounded wastewater comprises a significant portion of the dam's blanket drain discharge.8 Chloride is a widely used tracer constituent in groundwater evaluations due to its low reactivity with soil.9 However, in a 10 June 2004 letter to the Executive Officer, Mr. Drago, questioned the analysis, stating the "chloride ion is not necessarily conservative under all conditions, based on some other groundwater studies with which we are familiar." On 22 June,I telephoned Mr. Drago to ask what studies he was referring to. He replied studies done by Kennedy/Jenks Consultants for the Wine Institute. I am familiar with the reports documenting these studies, and none question or otherwise dismiss the use of chloride as a tracer constituent.