PD-17-00001 Marian Meadows Full Record with Index (2)

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Marian Meadows Rezone and Subdivision Final Environmental Impact Statement 1-25 This high cost would necessitate rates that build a reserve of funds for replacement that would be half to three-quarters of the cost of the initial system. In addition, key mechanical components such as the influent grinder would require relatively frequent replacement of key components.  Risk of upset and failure to meet effluent standards as outlined above. There are a number of steps in the treatment process where mechanical failure or the failure to operate the system properly may result in not meeting effluent standards. This occurrence would subject the public using wastewater for reuse to potential risks from coming into contact with effluent that does not meet proposed standards. Moreover, this untreated wastewater could affect the groundwater aquifer used for public water supply. In the worst case, discharge of untreated wastewater would cause the average nitrate concentration in groundwater to increase beyond water quality standards to approximately 15 milligrams of nitrogen per liter (mg-N/L) within a plume that would migrate downgradient from the infiltration pond. All alternatives can be served by on-site sewage disposal systems with provision of public water supply under current regulations. The major limitation for suitability of an on-site system is the character of the soil. Many soils in mountainous areas are not deep enough, are not permeable enough, or are too permeable, or have restrictive layers, or have high groundwater tables. The soils deposited in the flat valley bottom in the Easton area are generally too permeable to permit standard drainfield systems and require “sand-lined trenches” to provide a layer of soil that provides for adequate retention time for treatment. The general lack of suitable soils on the steeper eastern portion of the site is likely to result in use of community drainfields on the flatter eastern portions of the site for allowed development in those areas. The higher flows from such systems with the permeable soils in the area poses greater risks to groundwater quality. Detailed soil assessment and engineering design of such systems is required, as well as separate environmental review. Utilities – Stormwater Adverse impacts of stormwater conveyance generally would be experienced at downgradient locations. It is possible that during severe storm events in the area, especially rain-on-snow events with frozen ground, the Sparks Road conveyance capacity could be exceeded and surface water would flow generally to the southwest across the gently sloping topography and carve new channels in the path of least resistance. The worst-case potential impacts would be from debris flow, which have occurred on the site in the past as evidenced by alluvial fans and high-capacity channels. Future debris flows and runoff could have catastrophic effects on residents in the development and off site. The most effective mitigation for alluvial fans and debris flows is to avoid any human occupancy or improvements on the fan and its downstream conveyance area as well as providing channels or other measures such as berms to direct high lows away from developed areas.