Appendix E - Geology and Soils Geotechnical Supporting Information COMBINED

LESTER-SHRINER PROPERTY 132-8-2 Page 17 6.9.3 Fill Drainage A permanent subsurface drainage system consisting of a series of perforated gravity pipes or drainage strips should be constructed between engineered fill placed against a bedrock slope and within all keyways. This system is intended to intercept perched water flowing through the bedrock and transmit it to suitable outlet structures and reduce the potential for hydrostatic pressures building up behind the fills and causing slope instability. The drain lines should be placed at the back of the keyways and benches. A typical subsurface drainage system for engineered fills is shown in Figure 7. All drainage lines should slope towards suitable outlet structures at an inclination of at least ½ percent. Suitable outlet structures may consist of connecting the drainage lines to a storm drain system; if the drain lines will outlet overland at the toe of the slope, an appropriate rock spill pad should be provided; the drain lines should not outlet onto the slope. Cleanouts, or access ports, will likely be required at all upslope ends of the drainage lines and at all 90-degree bends. 6.10 SITE DRAINAGE 6.10.1 General Surface Drainage Surface water runoff should not be allowed to flow over the top of or pond at the top or toe of engineered slopes or retaining walls. Surface water should also not be allowed to pond on or adjacent to pavements or concrete flatwork. Surface drainage should be directed towards suitable drainage facilities such as lined or unlined drainage ditches or drain inlets. If feasible, drainage ditches should be included near the mid-height of fill slopes. All drainage ditches and drain inlets should be sized to accommodate the design storm events for the upslope tributary area. Concrete-lined j- or v-ditches should be reinforced as required and have adequate control and construction joints and should be constructed neat in excavations; backfill around formed ditches should not be allowed. Upslope sources of water should be evaluated. If upslope irrigation is planned, additional surface and subsurface drainage, or construction of drained buttress fills may be needed to protect site improvements. We should further evaluate this issue during the design-level investigation. 6.10.2 Lot Surface Drainage Surface water runoff should not be allowed to pond adjacent to building foundations, slabs-on- grade, or pavements. Hardscape surfaces should slope at least 2 percent towards suitable discharge facilities; landscape areas should slope at least 3 to 5 percent. Roof runoff should be directed away from building areas. Where minimal side yards are planned (10 feet or less), we recommend that area drains collect surface runoff and transmit the runoff to other suitable landscape drainage facilities to prevent ponding adjacent to building foundations. Landscape drainage such as drain inlets and storm water filtration and/or infiltration trenches should be provided to collect and transmit storm water runoff to project storm drains, and/or detention or retention facilities. Ultimately, the proposed foundations will be designed to accommodate some moisture variability within the near-surface soils; however, excessive moisture or desiccation may result in additional differential foundation movement. Ii! CORNERSTONE EARTH GROUP