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Austin Road Landfill Appendix D Contaminant Plume Characterization Report Aquifer Test Methods Semi-log plots for each test phase and for each observation well are provided in this appendix. The plots show the water level data recorded directly by the Trolls(Raw Data)and the water levels that have been adjusted for trends seen in the background well MW-12(Corrected Data). Adjustment for Superposition Effects As described above,superposition of water levels trends from preceding aquifer test phases must be factored out of the data. Because pumping from wells EW-1 and EW-2 had been ongoing for about a year prior to the start of the subject aquifer test it was assumed that pumping-based water levels had reached a steady-state condition. The data adjustments for superposition effects therefore were implemented in all but the initial aquifer test(Recovery-1)phase. Adjusting for superposition was a two step process. The first step involved evaluating the drawdown curves,that had been corrected for background trends,for each well and each test phase with time equal to zero at the start of a given test phase,and manually selecting straight-line portions from each of these curves. Equations describing the linear trend lines from each of the drawdown curves were calculated using the line-slope equation of the form y=mx+b,where y is the y-intercept value(water level)at a given point,m is the slope of the straight line curve,x is the x-intercept(log time)value at the given point,and b is the y-intercept value when x equals zero. The equation was solved for each observation well and test phase. This was accomplished by selecting a point on the linear trend line to get values for x and y,calculating the slope of the line to get m,then solving for the y-intercept b. The second step in the adjustment process was to use the line-slope equations from a given well and test phase to calculate water level(y)values that would extend forward in time through the duration of the next test phase. The projected water level values were then subtracted from the actual water level values of the subsequent test phase,to get adjusted water level values for the subsequent test phase. For example,the line-slope equation from the Recovery-1 (Rl)phase for a given well was used to determine water level values that would have existed if this test phase had continued through the time period of the Recovery-2(R2)phase. These projected RI water levels were subtracted from the R2 water levels to get R2 water levels adjusted for the effects of superposition. The same process was used to obtain adjusted Pumping-1 and Pumping-2 water level values. The adjusted water level values from the R2,Pl and P2 test phases were then plotted on semi-log plots and fits were made to the linear portions of the adjusted data as depicted in the attached plots. The slope of line from the linear portions of the adjusted curves was used in the Cooper Jacob equation to calculate aquifer T and S. Calculated values from each well and test phase are summarized in Table D-2. - Analysis Results The pumping and recovery test water level data were used to calculate aquifer T and S values. Assuming an average aquifer saturated thickness of 45 feet in the uppermost aquifer and 60 feet in the deeper aquifer(screened by wells MW-6 and MW-7),approximate values of hydraulic conductivity(K)were also calculated,using the relationship T=K"b(Fetter,1988). Aquifer storage CDM Camp Dresser&McKee D-11 W.\REPORTS\STOCKTOMARLPLUME.gMPPD.WPD CS 010858 City of Stockton 190855.0006