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state Rea. <br />GYassy Cree]c during ~+Trra,,,t,ar. No discharge has been recorded at <br />NPDFS 002 during September, aryl a small amount of flow was mr~~n-ed <br />at Site SN~S2-1 on 9/5/91 (0.005 cfs), the only flora reoox3ed in <br />September at this site. <br />As stated above, the highest ZDS concentration (3018 mg/1) reoorcied <br />at SW-S2-2 thus far occurred on 9/5/90. An P~m~*~tion of hydrologic <br />oorditions on this date should provide insight regarti:ing conditions <br />required to create high 'IDS levels in gassy Creek. Flow and `IDS <br />ooncexttrations in the SW-S2-2 area on 9/5/90 are stumnarized as <br />follows: <br /> Site 9/5/90 Flora (cfs) 9/5/90 ~D6 (mg/1) <br /> SFT-S2-2 0.036 3018 <br /> SW-S2-1 0.000 <br /> NPDFS 002 0.000 <br /> NPDFS 003 0.027 3302 <br /> Zhe flow data presented above show that Sites SW-S2-1 and NPDES 002 <br /> were not. dicr-hawrirg t,o (Massy CYeek on 9/5/90, arx3 that flow from <br /> NPDFS 003 to CYassy Creek represented only 75 percent of the <br /> dicrlurge at SW-S2-2. 'Ihe difference in flows at these two sites, <br /> 0.009 cfs, can be attributed to d; ~ha* ~e fresu the alluvial aquifer, <br /> a reasonable assumption for the month of Sept°T^}~°r when baseflow <br /> conditions prevail. Zhe data presented above also show that the <br /> discharge fmn NPDES 003 was diluted by the alluvial aquifer <br /> dicrha*'ge since a lower 'IDS value was measured at SW-S2-2. By back <br /> calculating, it can be seen that a mixture of 75 percent NPDES 003 <br /> discharge and 25 percent alluvial aquifer discharge would rm,,; ra <br />I <br />r,\~ that the alluvial grourrl water have a ZD6 concentration of 2164 mg/1. <br />V PWOC currently monitors two wells oong~leted in the alluvial aquifer in <br /> this area, GW-S33 A and GW-S31-A2. Althcix~ water quality sampling <br /> was not oordtncted at these sites during September of 1990, 4D5 <br /> rations of 1694 mg/1 and 2524 mg/1 were measlrred at We1Ls <br /> GW-S33-A and G~1-531-A2, respectively, on 10/27/90. The average of <br /> the 4D6 measurements at these two wells, 2109 mg/1, closely <br /> approximates (within 2.5 percent) the estimated alluvial aquifer 'IDS • <br /> concentration of 2164 mg/1 on 9/5/90. <br /> 7-327 Revised 08/20/93 <br />