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2-12 <br />a <br />permeability should be greater than the vertical permeability if all <br />flow was by primary or interstitial means. Since4the vertical; pe,rme= <br />ability# isegual'tolor' greater than the =horizontal permeability, the <br />potential for secondary flow mechanisms is great. The existence of high <br />tensile stresses in the soil, as evidenced by the piezometer test <br />results, indicate that secondary flows may be occurring in small <br />fractures caused by these stresses. <br />2.2.3 Additional Readings and Measurements at Existing Monitoring <br />Points <br />The piezometers installed during previous investigations, the seep <br />locations, and the other monitoring points have been monitored at the <br />site by D'Appolonia and Homestake personnel. Piezometer and pond levels <br />versus time are presented in Figure 2. The piezometer readings are <br />■ relatively constant, with the exception of some fluctuations associated <br />11 with grouting activities or installation' of downstream cutoff and <br />collection systems. Most of: the piezometers generally .respond to <br />- changes in pond level elevation, although fluctuations of pond level and <br />piezometer readings was not significant during the investigation. <br />2.2.4 Changes in Downstream Seepage Conditions <br />During the piezometer testing on Decembers 19 19�82�5- a'1sand boil -was <br />J noticed near Sampling Point 13 downstream of the toe (see Figured ). A <br />sand boil is a point of concentrated seepage where the material is <br />suspended by upward flowing water. The .-sand!(boil.ad acent,.Rto Sampling <br />Point -13 had,R,Aa measured ° pfezometric '� . a e of the : boil <br />approximatel}±'1.5c#eet above the ground surface. <br />Also, the pump -back rate increased from about 80 to 110 gpm in late <br />November 1982. The rate increased briefly again in the middle of <br />December to 125 gpm and then decreased to 115 gpm as shown on Figure <br />i <br />2. The rates shown on Figure 2 are average values over the time periods <br />indicated. The actual rate during the same time periods could have been <br />higher or lower than the indicated average value. <br />