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Bert E. Van Voris - 8 - 25 February 2005 Supervising Engineer increased soil salinity levels. Musco cannot simply dismiss the data that show substantial increases in salinity from 2002 to 20047 as a certified laboratory performed the analyses. The elevated concentrations of waste constituents (including nitrate) in Musco's "background" location,which are comparable to that exhibited in soils within Park West proper, is inconsistent with the low concentrations of waste constituents in soil collected in 1999 from South Ridge from an area described as "never been irrigated." This soil was characterized as having nitrate- nitrogen(mg/kg) of 9 at surface, 1 at 36" bgs, and 7 at 60" bgs. Soil collected by Regional Board staff on property adjoining Musco owned by Mr. Paul Harpainter was characterized by similarly low concentrations of nitrate-nitrogen. The addendum does not provide any data on the quality of other soils in the discharge vicinity that have not been influenced by Musco's discharge to support that the existing background location is adequately representative of background conditions. Unless convincing evidence is submitted to support continued rise of the existing background location, the proposed WDRs should reject this location as representative of background conditions. The addendum presents data on soil collected in Park West in September 2004. In September 2003, soil sampled in this area was found to contain elevated concentrations of nitrate-nitrogen (i.e., 636 mg/kg at surface, decreasing to about 100 mg/kg at depth). The more recent sample, collected in a "wet drainage area" had lower concentrations (i.e., 55 mg/kg at surface, decreasing to 2 mg/kg at depth). The addendum admits that Park West soils may have significant temporal or spatial variability in nitrate concentrations, but dismisses the possibility of nitrate impacts to groundwater due to assumed nitrate attenuation in the soil profile. September 2003 data shows nitrate-nitrogen concentrations of around 100 mg/kg at depth. The WDRs should require further investigation to evaluate the extent to which nitrate accumulations in Park West soils represent a threat to groundwater. Water Balance The addendum includes revised water balances for onsite irrigation of 170 acres with a rotating unirrigated area of 34 acres and offsite irrigation of 160 acres with a rotating unirrigated area of 32 acres using rainfalls of both average and 100-year return frequencies. The addendum requests that new WDRs permit monthly daily average and daily maximum discharge flows of 0.5 million gallons per day(mgd) and 1.1 mgd, respectively, until completion of the treatment facility, after which time the addendum requests monthly daily average and daily maximum discharge flows of 0.535 mgd and 1.3 mgd, respectively. Flow data used in the water balances (e.g.,process wastewater flows, irrigation flows, tailwater return flows) are estimates based on projections from raw data. Precipitation data is from the Tracy Pumping Plant and evaporation data is from the CDMS Tracy Station. The irrigation efficiency of 0.8 is an estimate based on the average crop coefficient for staggered planting of ryegrass, Bermuda grass,barley, For example,the sodium content(in meq/L)in surface soil samples increased substantially in Field 95 from 2002 to 2004. Sample 1 increased from 109 to 235;Sample 2,from 56 to 103;and Sample 3, from 65 to 591. In contrast,the sodium content of surface soils collected from Field 95 in 1999 ranged from 5 to 21.