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