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Fcneountersthewater <br /> nalysis <br /> ade to the encountered groundwater table at 11 feet below existing grade. This shallow <br /> able may induce a phenomenon known as the"mounding effect"by which percolating effluent <br /> water table,or restrictive stratum and cannot disperse laterally in a certain time frame.a mound forms under the disposal field creating saturated flow conditions and decreasing the <br /> distance the effluent must travel under unsaturated flow for effluent treatment to occur. An equation <br /> developed by Finnemore and Hantzsche (1983) is used below to predict the long-term maximum rise of the <br /> mound: <br /> h=H+Zm+2 <br /> where: h=distance from boundary to mid-point of the long-term mound, in ft <br /> H=height of stable groundwater table above impermeable boundary, in ft <br /> Zm=long-term maximum rise of the mound, in ft <br /> Substituting known and estimated values for the variables,we find the following: <br /> H=The height of stable groundwater above an impermeable boundary is unknown since there are no on-site <br /> or adjacent well logs to determine an impermeable boundary. Therefore, it will be assumed that a boundary <br /> exists at 100 ft bgs,H= 100 - 11(Existing water table)= 89 ft. Long-term maximum rise of mound is estimated at <br /> 1 ft plus the apparent water table elevational rise as determined in the monitoring wells(11 ft- 8 ft(Highest depth <br /> to grounddwwaatter) =3 ft+ 11 ftI rise of the mound=4 ft). Therefore, h= 89+(4=2)=91 <br /> Zm 1 A (4 h, <br /> Kh/os� I Sy'1.0.5o <br /> where: Q=average daily flow in ft'/day <br /> A=area of disposal field in ft' <br /> C=mounding equation constant <br /> L=length of disposal field in ft <br /> K=horizontal permeability of soil in ft/day <br /> n=mounding equation exponent <br /> Sy=specific yield of receiving soil in percent <br /> t =time since the beginning of wastewater application in days <br /> Substituting known constants for the variables,we find the following: <br /> Q =2,108 gpd(From Max.flow volume calcs.,Page 12)=7.48 gals/ft'=281.8 ft'/day <br /> A =3,400 ft'(From filter bed sizing calcs,Page 16) <br /> C=Length to width ratio = 3.3,therefore, C= 1.75 <br /> L= 102ft <br /> K=Using average vertical permeability as most conservative=38 min/in: 1440 min/day_38=3.2 ft/day <br /> h=7(See above) <br /> n=Length to width ratio =3.3,therefore,n= 1.700 <br /> SY= 12% <br /> t =3,650 days(10 yrs) <br /> Zm =0.145 x 246 x 0.008043 x 2.35=0.674 ft <br /> It appears that the maximum mound height that may occur under the filter bed, and above the highest <br /> anticipated depth to the water table of 8 ft is 0.67 feet. This would leave a marginal distance of <br /> approximately five feet between the soil/effluent interface and the top of the theoretical mound: <br /> soil/effluent interface =2 ft below existing grade+ 5 ft separation distance= 7 ft below grade. <br /> 8 <br /> Chesney Consulting <br />