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Bert E. Van Voris - 9 - 25 February 2005 <br /> Supervising Engineer <br /> and salt grass, as provided by the Soil Conservation Service National Engineering Handbook. The water <br /> balances assume the root zone soil has the capacity to store 9.5 inches of water. <br /> Figure 1 compares the monthly change in the reservoir's storage volume from November 2002 through <br /> September 2004 using measured freeboard with the monthly change using calculations based on <br /> inflow/outflow and weather data. The results appear to be similar. Musco is planning operational <br /> changes to further improve future measurement accuracy. <br /> Comment: The water balances are still technically deficient. To support the requested <br /> discharge flows, the RWD's water balances must use the appropriate annual daily <br /> average discharge flows (i.e., 0.5 mgd for the interim period of onsite irrigation and <br /> 0.535 mgd for future offsite irrigation) and, to facilitate review and gain concurrence, <br /> provide sufficient technical documentation for all assumptions and calculated values. <br /> They should contain columns documenting all input and derived values. For example, <br /> columns representing evaporation losses from and rainfall contributions to the reservoir, <br /> evapotranspiration from and rainfall contributions to the fields, and captured storm water <br /> runoff volume, should be included. They should be accompanied by a technical <br /> discussion that thoroughly describes the assumptions, calculations and/or estimates used <br /> to obtain values for gross irrigation,return flow coefficient, total return flow, process <br /> water flow,net irrigation inches, and soil water storage. Rainfall contributions to the <br /> reservoir should include all storm water runoff from the 100-year storm, and supporting <br /> calculations for these monthly values, as well as other calculated values, should be <br /> provided. The water balance for offsite irrigation should include storm water runoff <br /> retained from the existing land application area. <br /> Background Groundwater Quality <br /> The current irrigation supply for the proposed offsite use areas is groundwater. The addendum states <br /> that Regional Board staff have indicated that the salinity of effluent discharged to the use areas should <br /> not exceed that in the areas' irrigation supply. Musco proposes to further analyze underlying <br /> groundwater quality beneath the Jepsen Webb Ranch property, a proposed offsite use area, to establish <br /> proposed effluent limitations for salinity. The site has an existing production well and a new <br /> groundwater monitoring well. Kennedy/Jenks will prepare a work plan for the installation and <br /> evaluation of additional groundwater monitoring wells that will include data for the design of the <br /> existing monitoring well. <br /> Comment: Though the addendum did not identify the date by which the work plan will <br /> be submitted, representative data should be submitted in a timely manner for staff to <br /> incorporate this information in tentative WDRs. <br /> Effluent Limitations <br /> The addendum requests that effluent limitations be established based on the information in the <br /> 30 July 2004 Background Groundwater Quality Report prepared by Kennedy/Jenks Consultants. The <br /> addendum states that target IDS concentrations for influent to the reservoir have been established to be <br /> lower than that of the underlying groundwater. The addendum requests effluent quality limitations be <br />