2014-069 - Final Environmental Impact Report No. 2014-01

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HARBOR BLVD. MIXED USE TRANSIT CORRIDOR PLAN FINAL FIR CITY OF SANTA ANA 5. Environmental Analysis HYDROLOGY AND WATER QUALITY Impact 5.7 -2: Development pursuant to the Harbor Corridor Plan would not substantially alter the existing drainage pattern of the project area in a manner that would result in a substantial erosion or siltation on- or offsite. [Thresholds HYD -3] Impact Analysis: Erosion and siltation impacts potentially resulting from individual development projects that would be accommodated by the Harbor Corridor Plan would, for the most part, occur during the construction phase, which would include site preparation and grading activities. However, there is a potential for erosion and siltation to occur during project operation. Construction Impacts Individual development projects that would be accommodated by the Harbor Corridor Plan would be required to prepare and implement a SWPPP pursuant to the GCP during grading and construction. The SWPPP would specify BMPs that individual project applicants would implement prior to and during grading and construction to minimize erosion and siltation impacts on and offsite. Adherence to the 13MPs in the SWPPP would reduce, prevent, or minimize soil erosion from project related grading and construction activities. Therefore, project implementation would not substantially alter the existing drainage pattern of individual development sites or the project area in a manner that would result in substantial erosion or siltation on- or offsite. Operation Impacts The majority of the project area is developed and consists of impervious surfaces (buildings, driveways, and other paved areas). Currently, approximately 11.6 acres of the project area are vacant and consist of bare soil. However, these areas are slated for development under the Harbor Corridor Plan and would not always remain undeveloped bare soil. Additionally, development standards for landscaping outlined in the Harbor Corridor Plan would result in approximately 20 percent, or 50.6 acres, of parcelized area within the project area being landscaped at project buildout. There would be no substantial areas of bare or disturbed soil onsite at project completion that would be vulnerable to erosion. Therefore, implementation of the Harbor Corridor Plan would not substantially alter the existing drainage pattern of the site or area m a manner that would result in substantial erosion or siltation on or offsite. Impact 5.7 -3: Development pursuant to the Harbor Corridor Plan would increase the amount of impervious surfaces in the project area and would therefore increase surface water flows into drainage systems within the watershed. [Thresholds HYDA and HYD -5] Impact Analysis: Implementation of the Harbor Corridor Plan would increase impervious surfaces in the project area through the development of individual project sites. The majority of impervious surfaces would come from development of the existing vacant lots, which make up approximately 11.6 acres of the project area. At project completion, the Harbor Corridor Plan area is estimated to generate 15 percent more runoff than in current conditions; that is, approximately 80 percent of stormwater within the project area would be expected to run off ( 131 2013). With project drainage volumes were forecast by adding 15 percent to existing estimated drainage volumes. Needed storm drain improvements for project generated drainage were identified by comparing with project drainage volumes to existing capacities. Page 5.7 -20 PlaceWorkr