Volume 2: Draft Gorst Planned Action Environmental Impact Statement

GORST PLANNED ACTION EIS | AFFECTED ENVIRONMENT, SIGNIFICANT IMPACTS, AND MITIGATION MEASURESThe following is a description of each model for evaluating stormwater-related impacts. The watershedcharacterization model used is described in Ecology publication #10-06-05, “Puget Sound WatershedCharacterization Project: Description of Methods, Models and Analysis”. The document provides guidance on howto conduct a coarse-scale characterization for multiple watershed processes. Application and analysis of the GorstCreek Watershed Characterization was undertaken by a project team from the Department of Ecology. The initialstep involves identifying the geographic area upon which the analysis was run, and selecting GIS map units thatcorrespond to the area of interest. The GIS model brings together the attributes that contribute to water flow inthe landscape where stormwater runoff is a factor in the model.Another model developed for the specifically for the Gorst Watershed as a tool to improve stormwater relatedimpacts is a HSPF Model. HSPF is a mathematical model designed to simulate the hydrology and movement ofcontaminants in a basin (Bicknell et al. 2000). Runoff from a basin is quantified by the continuous simulation of thehydrologic response to rainfall and other meteorological records. In HSPF, a basin is represented by a collection ofhydrologically similar areas referred to as hydrologic response units (HRUs) that drain to a stream network. HRUsreflect areas of similar land use, soil, subsurface geology, and other factors that respond the same wayhydrologically to climatic conditions. Runoff is predicted separately for each HRU (inch per hour per acre) androuted to obtain the total runoff for the watershed. This output for this model is a quantified discharge rate thatcan be used with different land use scenarios to predict stormwater runoff and optimize investment stormwaterinfrastructure. These models are used in identifying opportunities for improving stormwater deficiencies. TheSUSTAIN model would be built after a preferred alternative has been determined from the Draft EIS process. Thegoal of this SUSTAIN model would optimize the BMPs that could be used in conjunction with the final land usealternative. The results of the model would provide data to support development of the stormwater plan.Impacts related to stormwater are predicted based on these models in combination with comparing future landuse designations and description for each alternative. Because specific project-related changes in impervioussurface area are not available, an approximation of proportional changes in stormwater runoff relative to eachland use is used to evaluate of potential effects. Specific new development standards such as the limiting theamount of impervious surface are not capture in this analysis. Impacts are generalized and based onapproximations of impervious surface and related stormwater impacts relative to land use classifications asdocumented in Hill et al. 2003 technical report, A Rapid Land Cover Classification Method for Use in UrbanWatershed Analysis.The impact analysis for water (drinking) and wastewater systems addresses both physical impacts on infrastructure(i.e., impacts that could disrupt service or require facility relocations because of proposed development) andcapacity impacts (i.e., the ability of existing infrastructure to accommodate the projected growth in park visitor,employee, and/or residential populations).IMPACTS COMMON TO ALL ALTERNATIVESWatershedUnder all project alternatives and as described in Section 2.0 Alternatives, areas planned land uses outside of theGorst UGA but within the watershed would remain the same as at present. These areas include the City ofBremerton’s CULs and SKIA, the City of Port Orchard’s McCormick Woods, and remaining rural unincorporatedKitsap County lands. In addition, over the next 20 to 30 year jobs would substantially increase from 264 to 2,305primarily due to economic development in the SKIA. The added jobs in the SKIA area would be subject the SKIASubarea Plan. Population growth is projected to increase from 1,810 to 2,659. These changes in the watershedwould increase demand in utilities services. The CFPs for the specific growth areas in the watershed would ensureadequate utility services matched the new demand and reduce the potential for disruption of utility services.The Kitsap County Final EIS for the UGA Sizing and Composition Remand (Kitsap County 2012b) found that withimplementation of the Kitsap County Preferred Alternative Comprehensive Plan, including growth in the cities,Draft | June 2013 3-226