Volume 2: Draft Gorst Planned Action Environmental Impact Statement

GORST PLANNED ACTION EIS | AFFECTED ENVIRONMENT, SIGNIFICANT IMPACTS, AND MITIGATION MEASURESGorst UGAUnder all alternatives, most impacts to soils would occur within the Gorst UGA, where the majority of planneddevelopment would be focused. Within the UGA, development could occur within the 281 parcel acres identifiedin Table 3.1-1 Soil Types in the Gorst Creek Watershed and Gorst UGA, and Their Associated ConstructionLimitations and Erosion Hazard Potential, although the types of development would vary by alternative.Additionally, it is unlikely that all currently developed areas would be redeveloped within the next 20 to 30 years.Potential impacts associated with construction activities within the UGA would be similar to those described forthe watershed, although creation of new impervious surface would be a smaller factor in the UGA. The potentialfor loss of soil through erosion, soil compaction, and soil contamination would be present, all of which would havethe potential to be minimized, to varying degrees by pertinent plans and BMPs.Planned development within the UGA would potentially result in a long-term loss of soil functions over a smallarea if currently undeveloped areas are developed in the future. It is expected that the total area of impervioussurface could increase within the UGA, leading to increased soil erosion. Future development within the UGAwould have the potential to impact slope stability in steep areas.Alternative 1Based on the information in Table 2-7 Growth Comparison by Gorst UGA Alternative, a total of approximately 41developable acres within the UGA have been identified under Alternative 1. In addition to these developableparcel acres, some land would be modified in existing or future rights of way or on lands for public purposesTherefore, in addition to future projects on already developed parcels, sites that currently do not supportdevelopment would likely be altered. Creation of impervious surface would result in the loss of soils on up to 41acres, as well as the functions that they provide (e.g., ability to support native plant species and other vegetation,and infiltration of water), and could contribute to increased erosion of soils.Under this alternative, sand, gravel, and rock deposits would continue to be mined from the area identified withthe mineral resources overlay in Figure 3.1-1 Gorst Creek Watershed: Geology. This ongoing activity would result inthe permanent loss of these mineral resources from the region.Under this alternative, existing regulations and plans to minimize soil erosion, impacts to steep or unstable slopes,and soil contamination would continue to be tied to permitting for new development/redevelopment projects inthe watershed and the UGA (discussed under Applicable Regulations and Commitments in the MitigationMeasures discussion for this section). These regulations and guidelines are effective at minimizing impacts tosteep/unstable slopes, preventing contamination of soils, and minimizing loss of soil from construction sites.Additionally, adoption of the LID guidance manual will help guide new development such that the amount ofeffective impervious surface on a site is reduced. Within the UGA, redevelopment would likely result in an overallreduction in effective impervious surface. On a larger scale, however, shortcomings that have been identified instormwater management throughout the watershed would continue to have a negative impact on surface waterand stormwater flows, leading to ongoing erosion and removal of soil from the watershed.As the Watershed Characterization & Framework Plan would not be implemented under this alternative, therewould be no watershed-level plan for future development identifying protection and restoration zones andassociated actions/restrictions to limit flooding, water erosion, and movement of soil. Development within thewatershed would continue to be haphazard, and despite existing regulations and guidance, soil erosion within thewatershed may increase as a result of new development.Alternative 2A total of approximately 70 developable acres have been identified for Alternative 2. In addition to thesedevelopable parcel acres, some land would be modified in existing or future rights of way or on lands for publicpurposes. Therefore new development on currently undeveloped parcels would result in the long-term loss of soilsand their functions on up to 70 acres, which is greater than that under Alternative 1. However, this alternativeDraft | June 2013 3-8