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s <br />It should be noted that there is a risk of finther slope failures occurring during the construction of the drainage <br />systems due to the excavation of relatively steep and unreinforced slopes during the construction of the drain <br />and removal of the unstable soils from the keyway area constructed at the base of the earthen buttress fill. <br />Another alternative would be to construct a driven steel H-pile or a straight shaft drilled concrete pier retaining <br />wall through the failed areas. This type of wall system would consist of the installation of either steel H-piles <br />or concrete piers placed at relatively close spacing and that will penetrate the underlying bedrock materials as <br />least twice the height of the overburden soils being retained. However, due to the variable depth to the <br />underlying bedrock materials, site constraints and access conditions, we do not believe that this type of system <br />will be economically feasible for this project. <br />Regardless of the slope failure mitigation measure used, we strongly recommend that the groundwater and <br />slope conditions at the site be further monitored this summer and fall so that alternatives for a feasible drainage <br />system and stabilization plan can be evaluated. <br />0 Limitations <br />The recommendations given in this report are based on the soil and groundwater conditions encountered in the <br />test holes and test pits, and those exposed during this investigation. The test holes and pits were widely spaced <br />to determine the general subsurface profile in the failed areas at the subject site. We believe that this <br />information gives a high degree of reliability for anticipating the performance of the subject slope; however, <br />our recommendations are professional opinions and cannot control nature, nor can they assure the soils or <br />groundwater profiles beneath or adjacent to those observed. We do not guarantee the performance of the <br />project in any respect, only that our engineering work and judgments meet or exceed the standard of care of <br />our profession at the time they were rendered. <br />It should be stressed that the soil and groundwater conditions encountered at this site were highly variable and <br />seasonal changes in groundwater levels can be expected. Additional dewatering efforts and site grading will <br />be required to stabilize the slope. <br />u <br />Job Number: 08-8099 NWCC, Inc. Page 10