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HomeMy WebLinkAbout3537; Vista/Carlsbad Interceptor Sewer; North Agua Hedionda Intercepter West; 2004-12-01• City of Carlsbad 1635 Faraday Avenue Carlsbad, CA 92008 PREPARED BY; Dudek & Associates, Inc. 605 Third Street Encinitas, CA 92024 FINAL ADDENDUM to the ENVIRONMENTAL IMPACT REPORT for the NORTH AGUA HEDIONDA INTERCEPTOR WESTERN SEGMENT SEWER MAINTENANCE, ACCESS ROAD AND SHORELINE PROTECTION PROJECT SCH # 2003051076 Prcfared by: & ASSOCIATES, INC. Pro/essional Teams for Complex Projects 605 Third Street Encinitas, CA 92024 December 2004 Table of Contents m Section Page No. PREFACE P-1 1.0 INTRODUCTION 1-1 1.1 Purpose of the Addendum 1-1 1.2 Content and Format of the Addendum 1 -5 2.0 PROJECT DESCRIPTION 2-1 2.1 Purpose 2-1 2.2 Location and Setting 2-1 2.3 Project Characteristics 2-2 2.4 Measures Included to Avoid Environmental Impacts 2-6 3.0 DETERMINATION 3-1 4.0 RATIONALE 4-1 4.1 Aesthetics 4-1 4.2 Biological Resources 4-7 4.3 Cultural Resources 4-8 4.4 Geology and Soils 4-8 4.5 Hydrology and Water Quality 4-9 5.0 REFERENCES 5-1 APPENDICES Appendix A Water Quality Technical Report - Dudek, March 2004 December 2004 2798-03 EIR Final Addendum • HM\ Sewer Maintenance, Access Road & Shoreline Protection Project i Table of Contents Page No. LIST OF FIGURES •m Figure 1 Figure 2 m Figure 3 Figure 4 •m Figure 5 m Figure 6A m Figure 6B Figure 7 Figure 8 m Figure 9 Figure 10 Figure 11 «• Figure 12 •m Figure 13 m m m m m m m m «• m December 2004 Regional Map 1-2 Vicinity Map 1-3 Project Components-February 2004 1-6 Project Components - August 2004 1-7 Access Road and Shoreline Protection Wall Section - February 2004 1-8 Access Road and Shoreline Protection Wall Section with Cut Slope & Culvert 1-9 Access Road and Shoreline Protection Wall Section with Cribwall Section.... 1-10 DEIR Cribwall Profile - February 2004 2-4 FEIR Cribwall Profile -August 2004 2-5 Visual Simulations Key Map 4-2 Visual Simulation 1 4-3 Visual Simulation 2 4-4 Plan View of Sight Line from Private Vantage Point 4-5 View of Project Site from Private Vantage Point 4-6 2798-03 ElR Final Addendum • NAHI Sewer Maintenance, Access Road & Shoreline Protection Project PREFACE FINAL ADDENDUM TO THE EIR NORTH AGUA HEDIONDA INTERCEPTOR WESTERN SEGMENT The following document represents the Final Addendum to the EIR for the North Agua Hedionda Interceptor Western Segment. After printing, it was discovered that the Draft Addendum, in two locations, contained an inconsistency between the text of the project description and the supporting graphics. The text indicates the width of the proposed sewer maintenance access road to be 8-feet wide, rather than the actual width of 10 feet. The misinterpretation is based on subtracting the 2-foot wide drainage swale from the road width. The actual proposed project (and graphics) are comprised of a 2-foot wide drainage swale in addition to the 10-foot wide road. The errors have been corrected in the Final Addendum. It should be noted that the analysis of impacts is based on the actual proposed project; i.e., the 10-foot wide access road with an additional 2-foot wide drainage swale. Therefore, no changes to the analysis of potential effects have been made from the administrative draft of the Addendum to the Final Addendum; the only change made includes revision of the text in the Project Description section. December 2004 2798-03 EIR Final Addendum • NAHI Sewer Maintenance. Access Road & Shoreline Protection Project P-1 SECTION 1.0 INTRODUCTION 1.1 Purpose of the Addendum The purpose of this Addendimi is to describe the project design changes made to the North Agua Hedionda Interceptor Sewer (NAHI) Western Segment Sewer Maintenance, Access Road and Shoreline Protection Project after circulation of the Environmental Impact Report (EIR) 03-02 and to discuss why those changes do not trigger a recirculation of the EIR. The City of Carlsbad (City) prepared a FEIR for the NAHI Project in October 2004. Project Background The NAHI Western Segment project consists of six components: (1) re-establishment of the sewer maintenance access road; (2) construction of a shoreline protection wall; (3) sewer pipeline improvements; (4) rehabilitation of existing manholes; (5) future maintenance and operation activities for the sewer pipeline facilities; and (6) development of a portion of the regional trail system. The project is located along the north shore of Agua Hedionda lagoon in the City of Carlsbad (Figures I 2). The FEIR focuses on five issue areas: Aesthetics, Biological Resources, Cultural and Paleontological Resources, Geology and Soils, and Hydrology and Water Quality. The project, based on the Initial Study, was found to have potentially significant in only those five areas. Each of the five focus issue areas have the potential to be significantly impacted by the project; however, with incorporation of mitigation measures set forth in the FEIR, residual impacts are less than significant for all issue areas. The public comment period on the DEIR closed on April 7, 2004 and no comments that require change in the design or evaluation of the project were received. In March 2004 the City requested that Dudek and Associates, Inc. (Dudek) prepare draft applicafions for wetlands impact permits from the U.S. Army Corps of Engineers (ACOE), California Department of Fish and Game (CDFG), Regional Water Quality Control Board (RWQCB), and California Coastal Commission (CCC). As part of those apphcations, Dudek prepared a Water Quality Technical Report (WQTR) to address final design of the drainage features of the proposed project. The WQTR, prepared in May 2004, is attached as Appendix A to this document. December 2004 2798-03 EIR Final Addendum • NAHI Sewer Maintenance, Access Road & Shoreline Protection Project 1-1 Orange County Imperial Beach 1"-8 Miles Tijuana North Agua Hedionda Sewer Western Segment EIR Addendum Regional Map FIGURE BEST ORJGtNAL BASE MAP SOURCE: USGS 7.5 Minute Series, San Luis Rey Quadrangle r -2000' North Agua Hedionda Sewer Western Segment EIR Addendum Vicinity Map FIGURE 2 Introduction The WQTR was prepared in accordance with the City of Carlsbad Public Works Department Standard Urban Storm Water Mitigation Plan (SUSMP). The SUSMP states that Best Management Practices (BMPs) shall be designed to remove pollutants of concerns to the maximum extent practicable. The WQTR identifies sediment as the primary pollutant of concern for this project and recommends long-term BMPs that would remove pollutants of concern to the maximum extent practicable. These long-term BMPs include, among others, use of vegetated swales, planted crib walls, and catch basin filter inserts. Currently, sediment is carried in runoff that sheet flows directly into the lagoon. With implementation of the NAHI proj ect as described in the FEIR, post-construction, sediment/runoff from the adjacent coastal bluffs would continue to flow into the lagoon via culverts. Runoff from the maintenance access road would drain off the road into an 18-inch wide colored concrete gutter located between the roadway and shoreline protection wall. The runoff would then be transported away from the road surface towards catch basins located at low points along the road before entering the lagoon. The FEIR identified four culverts and three catch basins as part of the project design, which would remove debris and material from the runoff Under the original design, maintenance would be conducted quarterly and with each storm event, as necessary. The FEIR concluded that water quality impacts resulting from increased levels of sediment conveyed into the lagoon were significant but mitigable. The proposed mitigation, which would reduce impacts to less than significant, involved complying with the City's Jurisdictional Urban Runoff Management Plan (JURMP). Compliance with the JURMP shall include proper engineering design and construction of drainage control devices to collect and direct surface water runoff Dudek has coordinated the design modifications to the access road with the City to ensure that no new significant environmental impacts are caused by the redesign. Design modifications occurred in an iterative fashion. First, the road slope direction was changed from draining toward the lagoon to draining toward the cut slope/cribwall side of the road, as recommended in the WQTR to improve control of pollutant discharge. Also, a two-foot wide biofiltration, grassy swale replaced the previously proposed 18-inch wide concrete gutter along the entire length of the proposed access road. These design changes initially resulted in greater impacts to upland habitats (approximately 0.2 acre of coastal sage scrub) and aesthetics with approximately 50% larger cut slopes and crib walls. These new additional impacts were reduced to pre-design change levels by decreasing the road width from a 12-foot wide road of decomposed granite plus December 2004 2798-03 EIR Final Addendum • NAHI Sewer Maintenance, Access Road & Shoreline Protection Project 1-4 Introduction an 18-inch wide concrete gutter (total 13.5 feet wide) to an ten-foot wide road of decomposed granite plus a two-foot wide biofiltration, grassy swale (total 12 feet wide). The final design has a different configuration of cut slopes and crib walls when compared to the project design described in the FEIR; however overall impacts to biological resources and aesthetics remain unchanged. Figure 3 illustrates the project components, as presented in the FEIR, over an aerial photograph of the project area. Figure 4 illustrates the new set of project components with the only change being the cribwall locations and dimensions. Figure 5 is the typical cross-section of the access road and shoreline protection wall, as presented in the FEIR. Figures 6 A & 6B dXQ the redesigned cross-sections; two cross-sections have been prepared because drainage features incorporated as recommended in the WQTR differ for cut slopes and crib walls. The City desires to provide CEQA documentation for the access road design modifications. The focus of this Addendum is therefore on the environmental effects associated with implementation of the project with the access road features. This Addendum fiilfills this need and conforms to the provisions of CEQA and CEQA Guidelines, Section 15164, providing for the preparation of an Addendum. The CEQA Guidehnes allow the preparation of an Addendum to a EIR under the following circumstances: 1. Only minor technical changes or additions are necessary to make the EIR under consideration adequate; 2. The changes and additions to the EIR do not raise important new issues about significant effects on the environment; and 3. None of the conditions described in Section 15162, CEQA Guidelines, calling for the preparation of a subsequent EIR have occurred. 1.2 Content and Format of the Addendum This addendum includes the following: Section 1.0, Introduction. Provides an Introduction to and purpose of the Addendum. (Project). December 2004 2798-03 EIR Final Addendum • NAHI Sewer Maintenance, Access Road & Shoreline Protection Project 1-5 I I B D I I I I D I D I I I D U U y u Shoreline Protection Wall Existing Paved Access Road Existing Public Trail Non-Improved Sewer Access Road BASE PHOTO SOURCE: AERIAL ACCESS LLC, JAN/MAR 2002 200 Scale in Feet North Agua Hedionda Western Segment EIR Addendum Project Components - February 2004 FIGURE 3 Sewer System Existing Paved Access Road New Sewer Access Road Existing Public Trail Crib Wall Shoreline Protection Wall Non-Improved Sewer Access Road BASE PHOTO SOURCE: AERIAL ACCESS LLC, JAN/MAR 2002 200 Scale in Feet North Agua Hedionda Western Segment EIR Addendum Project Components - August 2004 FIGURE CALTRANS CABLE RAIL (WHERE REQUIRED) RLL (WHERE REQUIRED) ^^^^^^^^^^^ ALLUVIUM/COLLUVIUM .a 4 4" MIN. CARVED/HAND- SCULPTURED FACE /-TRANSIENT BEACH / SANDS PROPOSED DRILLED PIER WALL A; •V; ' "A TOTAL LENGTH OF DRILLED PIER APPROX. 30' TYPICAL PROPOSED DRILLED PIER WALL - SECTION NOT TO SCALE SOURCE: TERRACOSTA CONSULTING GROUP North Agua Hedionda Sewer Access V\festem Segment EIR Addendum Access Road & Shoreline Protection \Na\\ Section - February 2004 FIGURE I I i i I I I I i I i t I I I i i llllliilfeltllillli PROPOSED SLOPE VARIES 1.5:1 TO 2:1 Onsite CSS Mitigation rl2" MIN. AGGREGATE ROAD SECTION 2% Droinage Swale CULVERT (WHERE SHOWN ON PLAN) PROPOSED DRILLED' PIER WALL Ox SEWER PIPELINE-^ Sewer Access Road NOT TO SCALE CALTRANS CABLE RAIL {WHERE REQUIRED) 2* CARVED/HAND-SCULPTURED FACE MEAN HWL (5.5) Salt Marsh Intertidol Rocky Beoch Intertidol Mudflat 1r North Agua Hedionda Sewer Access Western Segment EIR Addendum Access Road & Shoreline Protection Wall Section with Cut Slope & Culvert - August 2004 FIGURE 6A I J t I ft I t i I I r i s I E 1 I I I ; I I iftliliifciftiiifti Onsite CSS Mitigation RECOMMENDED -BROW DITCH CRIBWALL Crib wall Droinage Swole PROPOSED DRILLED PIER WALL O, SEWER PIPELINE-^ Sewer Access Rood CALTRANS CABLE RAIL (WHERE REQUIRED) CARVED/HAND-SCULPTURED FACE tXJ Salt Marsh MEAN HWL (5.5] Intertidol Rocky Beach Intertidol Mudflat NOT TO SCALE North Agua Hedionda Sewer Access Western Segment EIR Addendum Access Road & Shoreline Protection Wall Section with Crib Wall - August 2004 FIGURE 6B Introduction Section 2.0, Project Description. Provides a description of the proposed access road design changes. Section 3.0, Determination. CEQA GuideUnes Sections 15162 through 15164 set forth the criteria for determining the appropriate environmental documentation, if any, to be completed when there is a pre-existing adopted EIR covering the project. This section addresses the criteria provided in CEQA Guidelines, Section 15162(a) and 15163, and provides a conclusion statement as to the basis for preparing an Addendum to the existing Final EIR pursuant to CEQA Guidelines Section 15164. Section 4.0, Rationale. This section addresses environmental resource areas and provides discussion as to why the proposed project would not create new significant impacts or increase the severity of impacts identified for environmental issues addressed in the Final EIR. The following resource areas are addressed: Aesthetics, Biological Resources, Cultural and Paleontological Resources, Geology and Soils, and Hydrology and Water Quality. For those resource areas for which the Initial Study found no potentially significant impacts, the revised project still would not result in potentially significant impacts. December 2004 2798-03 EIR Final Addendum • NAHI Sewer Maintenance, Access Road & Shoreline Protection Project 1-11 SECTION 2.0 PROJECT DESCRIPTION m 2.1 Purpose The City is pursuing approval for implementation of the North Agua Hedionda Interceptor Western Segment, Sewer Maintenance, Access Road, and Shoreline Protection Project. The purpose of the NAHI project is to protect the sewer pipeline from fiiture failure, collapse, or leakage, provide reliable sewer service to existing and planned development, and to develop a trail consistent with the Agua Hedionda Local Coastal Plan (LCP) and the City General Plan. Following preparation of the FEIR, the access road was redesigned to address recommendations made in the WQTR prepared for the project. The purpose of the project has not changed as a result of incorporation of the WQTR recommendations. 2.2 Location and Setting As shown in Figure 7, Regional Map, the project is located along the northern bank of Agua Hedionda Lagoon within the City of Carlsbad. Figure 2, Vicinity Map, illustrates the location of the project site between Cove Drive and Hoover Street. Agua Hedionda Lagoon is one of three coastal lagoons within the City of Carlsbad and is located in the west-central portion of the City. The lagoon comprises approximately 230 acres of water surface and extends 1.7 miles inland from the coast. At its widest point, the lagoon is 0.5 mile wide. Agua Hedionda Creek enters the lagoon at its easternmost point. The area surroimding the lagoon is characterized by open areas along the northern shoreline with residential development occurring on the bluffs above the lagoon to the north. Active agricultural fields occupy a portion of the slopes along the southern shoreline. Several electrical transmission lines and towers are also present along the southern banks of the lagoon. Interstate 5 and the Atchinson, Topeka & Santa Fe (AT&SF) Railroad cross over the lagoon near its western end. Vegetation cover along the lagoon includes a mixture of coastal sage scrub on the slopes and wetlands habitat types, including rock beach, mudflats and salt marsh. In addition, developed areas associated with residences and boat launches are present, as well as patches of ornamentally landscaped areas. Elevation ranges from 0 feet to 10 feet above mean sea level. December 2004 2798-03 EIR Final Addendum • NAHI Sewer Maintenance, Access Road & Shoreline Protection Project 2-1 Project Description 2.3 Project Characteristics In order to comply with the City's JURMP requirements, reduce long-term maintenance activities and costs, and to address newly adopted permit requirements, several project design changes are warranted. These changes include modifications to the roadway, cut slopes, crib walls, and swale. The following sections describe the differences between the original project design analyzed in EIR 03-02 and the current project design. Roadway Drainage Under the access road design described in the FEIR, runoff from adjacent cut slopes, natural slopes, crib walls, and the access road would flow across the access road toward the shoreline protection wall. At the jxmction of the access road and the shoreline protection wall, a colored concrete swale/gutter would be constructed to transport runoff from the access road towards catch basins (Figure 5). The maintenance access road, as described in the FEIR, would have a 2% cross-slope towards the lagoon for positive drainage. Although the catch basins would be equipped with filters that remove approximately 35% of coarse material (Idaho Department of Environmental Quality 2004), fine sediment would not be removed by the filters and at low flow rates, accumulated material/sediment in the filters would become re-suspended. In addition, a substantial number of maintenance visits would be required to remove/clean coarse material from the filters. Maintenance of the catch basins and filters would be necessary before and after each rain event. By changing the roadway drainage design such that runoff would drain toward the landward side and into a bio-filtration (grassy) swale, the amount of flow across the road would be greatly reduced as the only source of runoff would be from the access road itself (Figures 6A and 6B). The redesigned access road would also have a 2% cross-slope. This minor modification would greatly reduce the amount of sediment entering the catch basins as well as the amount of maintenance required when compared to the level of maintenance anticipated under the FEIR. In addition, the access road width has been reduced from 12 feet of decomposed granite to 10 feet (Figures 5, 6A & 6B). This reduction is necessary, because as a result of modification of the road cross-slope direction, grading cut slopes on the landward side of the road increased. The amount of cut slopes, however, can be reduced by reduction of the road width. December 2004 2798-03 EIR Final Addendum • NW^t Sewer Maintenance, Access Road & Shoreline Protection Project 2-2 Project Description Swale The FEIR includes a swale to be constructed where the access road meets the shoreline protection wall. The swale was proposed to be an 18-inch wide concrete gutter colored to match the shoreline protection wall (Figure 5). With the modified roadway drainage, the swale is proposed to be constructed on the landward side of the road (Figures 6A & 6B), The swale would be grass-lined, two-feet wide and occur wherever the road is present (Figure 4). By changing the type of swale from concrete to grass- lined, approximately 65% of suspended sediment entering the swale could be removed when properly maintained (Idaho Department of Environmental Quality 2004). Maintenance of vegetation estabhshed on the swale floor and side slopes is necessary in order to promote dense turf with extensive root growth which enhances infiltration, prevents erosion and consequent sedimentation, and precludes invasive weed growth. Once turf is well established in the swale, suspended materials are strained out within a few yards of surface water travel. Well-established turf on a swale floor will grow up through sediment deposits forming a porous turf and preventing the formation of an impenetrable layer. Grass planted on swale side slopes will prevent erosion. The planted grass variety will be one which is non-invasive such that adjacent biological communities are not adversely affected. Crib Walls The FEIR identifies two crib walls as part of the project design with a combined length of 562 feet (Figure 3). The two walls would have had a maximum height of seven feet and four and one-third feet (Figure 7). With the modified roadway, crib walls would still be necessary to avoid large cut slopes and minimize impacts to coastal sage scrub. Under the redesign, three crib walls are proposed with a total length of 552 feet (Figure 4). Heights of the crib walls have been reduced as well, with the maximum height of approximately six feet, five feet, and three and one-half feet, respectively (Figure 8). To capture runoff from adjacent slopes, a standard 18" concrete lined brow ditch would be constructed at the top of the crib wall to prevent runoff from flowing over the wall threatening its integrity (Figure 6B). Runoff collected in the brow ditch will be transported to the roadway swale. The brow ditch will occur wherever the crib wall is present (Figure 3). December 2004 2798-03 EIR Final Addendum • NAHI Sewer Maintenance, Access Road & Shoreline Protection Project 2-3 I !! D D D I I T, D C D I I D U u u I I APN 2 36-172-03 I CRIBWALL NO. 1 251 ± LF APN 206-172-05 X < CRIBWALL NO. 2 APN 206^ 82 + X < 172-05'APN 206-172-06 I CRIBWALL NO. 3 Typical Crib Wall CN X < 219+ LF APN 206-200-01 APN 206-200-02 Crib Wall Elevations NOT TO SCALE North Agua Hedionda Sewer Access Western Segment EIR Addendum Profiles of Crib Walls & Typical Crib Wall Photograph - August 2004 FIGURE 8 Project Description The crib walls would still be planted, as described in the FEIR. In areas where the crib wall is less than three feet, only the top of the wall would be planted. Plantings in these areas are expected to drape over the crib wall to help obscure views of the crib wall. 2.4 Measures Included to Avoid Environmental Impacts The City has incorporated into the Mitigation and Monitoring and Reporting Program for the NAHI Western Segment Project a number of measures to reduce or avoid potential environmental impacts associated with implementation of the proposed project. These measures have not changed as a result of the redesign, and are summarized in Section S-9 and discussed in detail in Section 3.0 of the FEIR. The proposed access road redesign would not resuU in any new or intensified significant environmental effects, therefore this project does not include any new or revised mitigation measures. December 2004 2798-03 EIR Rnal Addendum • NAHI Sewer Maintenance, Access Road & Shoreline Protection Project 2-6 SECTION 3.0 DETERMINATION CEQA Guidelines Section 15162 through 15164 set forth the criteria for determining the appropriate environmental documentation, if any, to be completed when there is a certified EIR covering the project. The City provides the following discussion to demonstrate the appropriateness for the preparation of an Addendum for the project design changes. CEQA Guidelines, Section 15162(a) and 15163 state that when an EIR has been certified for a project, no subsequent or supplemental EIR shall be prepared for that project unless the lead agency determines, on the basis of substantial evidence in light of the whole public record, one or more of the following: 1. Substantial changes are proposed in the project which will require major revisions of the previous EIR due to the involvement of new significant environmental effects or a substantial increase in the severity of previously identified significant effects. Discussion: The project design changes would not resuU in new significant environmental effects or a substantial increase in the severity of previously identified significant effects when compared to the environmental impacts considered in the FEIR. As discussed in Section 4.0 Rationale, the project design changes do not change the impact analysis for the all identified potential environmental issue areas (i.e., aesthetics, biology, cultural, geology/soils, and hydrology). 2. Substantial changes occur with respect to the circumstances under which the project is undertaken which will require major revisions of the previous EIR due to the involvement of new significant environmental effects or a substantial increase in the severity of previously identified significant effects. Discussion: No changes to the circumstances under which the EIR was finalized in October 2004, resulting in significant new or increased effects were identified in the environmental review of the proposed NAHI Project. As discussed in Section 4.0 of this document, comparison of the environmental impacts considered in the FEIR with the current proposed project design changes did not identify any change to the impacts associated with the project. Although the City determined that implementation of project design changes would improve water quality of Agua Hedionda Lagoon, this factor does not constitute changes to circumstances which would be considered to be substantial. Consequently, no substantial changes in circumstances have occurred that would require December 2004 2798-03 EIR Final Addendum • NAHI Sewer Maintenance, Access Road & Shoreline Protection Project 3-1 Determination major revisions of the previous EIR due to the involvement of new significant environmental effects or a substantial increase in the severity of previously identified significant effects. 3. New information of substantial importance, which was not known and could not have been known with the exercise of reasonable diligence at the time the previous EIR was certified as complete shows any of the following: a) The project will have one or more significant effects not discussed in the previous EIR or Negative Declaration: or Discussion: As discussed in Section 4.0 of this document, the project design changes would not have a significant or potentially significant effect on the environment that was not previously discussed in the EIR for the North Agua Hedionda Interceptor Project. The visual effects associated with the revised project design would result in less impacts than the original design analyzed in the FEIR because the project design changes would result in an overall decrease in crib wall length and height. These impacts to visual resources are still considered significant and the mitigation provided in the FEIR would reduce impacts to less than significant. For biological resources, permanent and temporary impacts associated with the revised project design would be equivalent to the impacts resulting fi-om the original project design. Mitigation provided for in the FEIR would reduce significant impacts to biological resources to less than significant. For cultural resources, the revised project design would not have an effect on cultural resources that was not previously discussed in the FEIR. For geologic and soil resources, the project design changes would not result in any new or additional impacts that have not been previously analyzed in the FEIR. As such, mitigation outlined in the FEIR would reduce impacts to geologic and soil resources to less than significant. For hydrology and water quality, impacts to water quality would be reduced under the revised project design, which removes more sediment fi-om runoff, when compared to the original design. Mitigation provided in the FEIR would reduce impacts to water quality to less than significant. December 2004 2798-03 EIR Final Addendum • NAHI Sewer Maintenance, Access Road & Shoreline Protection Project 3-2 Determination b) Significant effects previously examined will be substantially more severe than shown in the previous EIR; or Discussion: As discussed in Section 4.0 of this docmnent, based on a review of the Final EIR, no previously examined effects will be more severe than shown in the Final EIR. For aesthetics and water quality, the project design changes would result in less impacts when compared to the original design analyzed in the FEIR. Overall lengths and height of crib walls under the revised project would be less than the original design. Water quality would be improved as a result of the modifications to the access road. For biology, cultural, and geology and soils, the proposed project design changes would not result in any new or additional impacts. c) Mitigation measures or alternatives previously found not to be feasible would in fact be feasible, and would substantially reduce one or more significant effects of the project, but the project proponents decline to adopt the mitigation measure or alternative; or Discussion: As discussed in Section 4.0 of this document, no new information or changes in the project design have been identified or proposed that would change the feasibility of any proposed mitigation measures. The project design changes would not have significant or potentially significant environmental effects, and would not require additional mitigation measures. Measures adopted in the NAHI FEIR are found to be adequate and mitigate for all impacts associated with the proposed project. d) Mitigation measures or alternatives which are considerably different from those analyzed in the previous EIR would substantially reduce one or more significant effects on the environment, but the project proponents decline to adopt the mitigation measure or alternative. Discussion: The project design changes would not have significant, or potentially significant adverse environmental effects requiring additional mitigation measures. Mitigation measures adopted with the EIR in October 2004 are found to be adequate and mitigate for all impacts associated with the proposed project. December 2004 2798-03 EIR Final Addendum • NAHI Sewer Maintenance, Access Road & Shoreline Protection Project 3-3 Determination CEQA Guidelines, Section 15164(b) states that An Addendum to a previously certified EIR may be prepared if only minor technical changes or additions are necessary. Discussion: Only minor changes or additions are required. As discussed in Section 4.0 of this document, the project design changes would not cause any revisions to the mitigation measures identified in the FEIR. In addition, tiie minor technical changes associated with altering the maintenance road slope, drainage features, and crib walls would not meet the criteria set forth in Section 15162(a) and 15163 of CEQA requiring the preparation of a Supplemental or Subsequent EIR. None of the above criteria triggered the preparation of a subsequent or supplemental EIR pursuant to CEQA Guidelines Section 15162(a), 15163. Based on the rationale discussed in Section 4.0 of this document, this Addendum to the FEIR has been prepared pursuant to CEQA Guidelines Section 15164. December 2004 2798-03 EIR Final Addendum • NAHI Sewer Maintenance, Access Road & Shoreline Protection Project 3-4 SECTION 4.0 RATIONALE '•I HI The following discussion demonstrates that tiie project design changes would not result in any new significant environmental effects or increase the severity of the significant effects beyond those previously identified in the FEIR. 4.1 Aesthetics The FEIR concluded that tiie two crib walls would be visible from 1-5, local roadways and the lagoon. The two crib walls would have a combined length of 562 feet witii a maximum height of seven feet for tiie westerly crib wall and a maximum height of five feet for the easterly wall. Figures 9, lOmdll include before and after photographs of tiie project site, as described in the FEIR. Views of the crib walls were considered a significant visual impact because they would change the existing views of tiie coastal bluffs to one that contained several man-made structures along tiie shoreline. Mitigation was provided in the FEIR to reduce visual impacts to less tiian significant and involved seeding the open areas of the crib walls witii native plant species. Figure 7 provides an illustration of a crib wall planted witii native plant species, as specified in tiie FEIR. It is anticipated that views of the crib walls would diminish as native plants tiiat are seeded into the crib wall establish and obscure views of the walls, hi time, the crib walls would blend in witii the bluffs as the plants grow and mature to reduce the wall's visibility. With the proposed project design changes, the number of crib walls would increase to three; however, the length of the crib walls would decrease by 10 feet to a total of 552 feet. The maximum height of the crib walls would be less tiian tiie crib walls described in tiie FEIR. The maximum height of the westeriy wall, approximately six feet tall, would extend over a lengtti of approximately 80 feet, and would occur near MH 11. The maximum height of the center crib wall, approximately five feet tall, would extend a length of approximately 25 feet and occur near MH 12. The maximum height of the easteriy wall, approximately 3.5 feet tall, would extend over a length of approximately 20 feet and would occur near MH 18. Figure 8 provides a profile of the revised crib walls. Views of the crib walls would be available from the same public vantage points as described in the FEIR (Figures 9, 10 (6: U). Although an additional crib wall is required as part of the proposed design changes, views of the crib walls would not be visible from private vantage points and no impact to private views would occur with the proposed design changes. As shown on Figures 12 and 13, crib walls are not visible from private vantage points along Adams Street. December 2004 2798-03 EIR Final Addendum • NAHI Sewer Maintenance, Access Road & Shoreline Protection Project 4-1 SCALE: r=800 North Agua Hedionda Sewer Access Western Segment EIR Addendum Visual Simulation Key Map FIGURE m u u 0 0 Shoreline Protection Wall 3D Simulations Existing View from Northbound 1-5 Existing View Revised Design August 2004 North Agua Hedionda Sewer Access Western Segment EIR Addendum Visual Simulation 1 FIGURE 10 n n Shoreline at Agua Hedionda Lagoon Existing View Shoreline Protection Wall 3D Simulations Original Design February 2004 Revised Design August 2004 North Agua Hedionda Sewer Access Western Segment EIR Addendum Visual Simulation 2 FIGURE 11 SEE FIGURE 13 AGUA HEDIONDA LAGOON North Agua Hedionda Sewer Access Western Segment EIR Addendum Plan View of Site Line from Private Vantage Point FIGURE 12 II ii ftl hi ki hi hi hi il ii hi hi ti II li li li ii i< "^c EXISTING GRADE PROPOSED ACCESS ROAD EXISTING SEWER- PROPOSED DRILLED PIER WALL North Agua Hedionda Sewer Access V\festem Segment EIR Addendum Cross Section of Sight Line from Private Vantage Point FIGURE 13 Rationale Although the proposed design changes would result in a decrease in the overall length of the crib walls, views of the crib walls are still considered significant. Mitigation as provided in the FEIR would reduce visual impacts to less than significant. This mifigation includes seeding the open areas of the crib walls with native plant species. Figures 9, 10 and 11 provide visual simulations of the project site with the proposed design changes and implementation of mitigation. As shown in Figures 9, 10 and 11, views of the crib walls are obscured by native vegetation planted in the open areas of the walls, as well as, on top of the walls. As the plants mature and fill in open areas within and on top of the walls, less of the crib walls would be visible firom pubHc vantage points. Visual impacts associated with the crib walls would be reduced to a level below significant with mitigation as provided in the FEIR. No new mitigation would be necessary to reduce visual impacts to less than significant. No additional visual impacts associated with the modification in the roadway drainage and swale location are expected to occur. These project design changes are proposed to occur within the footprint previously analyzed in the FEIR for the maintenance access road. No previously unidentified impacts or intensification of previously identified impacts to aesthetics would result fi-om the change in roadway drainage and swale location. 4.2 Biology The FEIR discusses impacts to biological resources in terms of direct permanent and direct temporary impacts as well as indirect impacts. Significant impacts were identified for two types of biological resources: vegetation communities and sensitive wildlife. Impacts to sensitive plants and regional connectivity/wildlife corridors were not considered significant. Direct permanent impacts included the shoreline protection wall, crib walls, and access road footprint. Direct temporary impacts included the cut slope area, sewer realignment areas, and temporary construction corridor, where impacts such as stockpiling equipment and vehicular traffic may occur but soil disturbance is expected to be minimal. The project design changes occur entirely within areas previously surveyed and mapped as part of the biological studies for the FEIR. No project impacts would occur to areas outside of those surveyed and analyzed in the Biological Resources Technical Report. Furthermore, no impacts occur outside the temporary construction easement as it was identified in the FEIR. No change in the permanent or temporary impacts to vegetation communities and sensitive wildlife would occur with implementation of the proposed design changes. Therefore, the conclusions in the FEIR and the mitigation measures relevant to permanent and temporary December 2004 2798-03 EIR Final Addendum • NAHI Sewer Maintenance, Access Road & Shoreline Protection Project 4-7 Rationale impacts to vegetation communities and sensitive wildlife are still applicable to the NAHI project. No previously unidentified permanent or temporary impacts or intensification of previously identified impacts to vegetation communities and sensitive wildlife would result from the change in roadway drainage, swale location, or crib wall configuration. 4.3 Cultural Resources The FEIR concluded that the portion of one cultural site, CA-SDI-13701, within the project study area is not significant; therefore, impacts resulting from construction of the NAHI project would be less than significant. However, there is a potential to encounter buried cultural resources during construction, as well as unrecorded Native American cultural sites or human remains. Therefore, mitigation including construction monitoring by a qualified archeologist and an agreement with the San Luis Rey Band of Mission Indians is required to reduce impacts to less than significant. The project design changes would occur entirely within the survey areas previously analyzed in the FEIR. No project impacts would occur to areas located outside of those areas surveyed and analyzed in the Cultural Resoiu-ces Technical Report prepared by Gallegos & Associates. Therefore, the conclusions in the FEIR, which is based on Cultural Resources Technical Report, and the mitigation measures are still applicable to the revised NAHI project. No previously unidentified impacts or intensification of previously identified impacts to cultural resources would result from the proposed project design changes. 4.4 Geology and Soils The DEIR concluded that significant impacts associated with unstable soils, caving of trenches during excavation activities, soil erosion during construction and post-construction, encountering groundwater during dewatering, and liquefiable soils onsite would occur. However, mitigation measures are provided that would reduce impacts to less than significant levels. The project design changes would occur entirely within the project study area analyzed in the FEIR. Therefore, the conclusions in the FEIR and the mitigation measures would still apply to the design, construction, and post-construction phases of the NAHI project. No previously imidentified impacts or intensification of previously identified impacts to geologic resources and soils would result from the proposed project design changes. December 2004 2798-03 EIR Final Addendum • NAHI Sewer Maintenance. Access Road & Stioreline Protection Project 4-8 Rationale 4.5 Hydrology and Water Quality The FEIR concluded that significant impacts to water quality during construction, dewatering and post-construction (long-term) would occur but with implementation of mitigation measures provided in the FEIR, those impacts would be less than significant. The project design changes are located entirely within the project study area analyzed in the FEIR. The design changes would not impede flows associated with the Agua Hedionda floodplain, beneficial uses of surface water, groundwater supply or recharge. The design changes will modify the hydrology of the coastal bluffs adjacent to the maintenance access road. Previously, with implementation of the NAHI project as described in the FEIR, all surface flow from adjacent coastal bluffs would continue to sheet flow across the road, to a 18- inch wide concrete gutter/swale on the seaward side of the proposed access road. With the project design changes, all surface flow from adjacent slopes would flow into brow ditches constructed on top of the crib walls or across cut slopes into a two-foot wide grassy swale located on the landward side of the proposed access road. Under both designs, flows are conveyed along the proposed access road to catch basins which treat runoff before discharging into the lagoon. With the redesign, sediments are trapped in the grassy swale before reaching catch basins where treatment structures are less efficient at removing sediments. The project design changes would result in an improvement in long-term water quality as more sediment/pollutants present in runoff from adjacent slopes can be removed prior to entering the lagoon. All permits and site-specific BMPs, as described in the FEIR, still apply. Storm water compliance measures, as described in the FEIR, will be implemented during construction and post-construction. No previously unidentified impacts or intensification of previously identified impacts to hydrology or water quality would result from the proposed project design changes. December 2004 2798-03 EIR Final Addendum • NAHI Sewer Maintenance, Access Road & Shoreline Protection Project 4-9 SECTION 5.0 REFERENCES Dudek & Associates, Inc. (Dudek) 2004. Water Quality Technical Report for the North Agua Hedionda Sewer Maintenance Access Road, and Shoreline Protection Project. Prepared for the City of Carlsbad, Encinitas, C A Idaho Department of Environmental Quality 2004. Catalog of Best Management Practices. Website accessed: http://www.deg.state.id.us/water/stormwater_catalog/index.asp. December 2004 2798-03 EIR Final Addendum • NAHI Sewer Maintenance, Access Road & Shoreline Protection Project 5-1 NORTH AGUA HEDIONDA LAGOON INTERCEPTOR PROJECT WATER QUALITY TECHNICAL REPORT March 2004 Prepared for: Cit^ of Carlsbad 1635 Faraday Avenue Carlsbad, CA 92008 Prepared by: DUDEK & ASSOCIATES,INC. 605 Third Street Encinitas, CA 92024 Contact: Jim Turpin, P.E. 760-479-4113 M M m m •m NORTH AGUA HEDIONDA LAGOON INTERCEPTOR PROJECT WATER QUALITY TECHNICAL REPORT March 2004 TABLE OF CONTENTS PURPOSE ....1 ••I PROJECT DESCRIPTION • 1 POLLUTANTS AND CONDITIONS OF CONCERN 2 m PERMANENT STORM WATER BMPS 4 - MAINTENANCE AND POST-CONSTRUCTION CONTROL 5 CONCLUSION - - • 5 APPENDICES Appendix A - Site Map « Appendix B - Drainage Study NORTH AGUA HEDIONDA LAGOON INTERCEPTOR PROJECT WATER QUALITY TECHNICAL REPORT March 2004 PURPOSE To describe the permanent storm water Best Management Practices (BMPs) that will be incorporated in the project to mitigate the impacts of urban runoff due to the development. VICINITY MAP TIE X ei.--'^"^-. 3 ^ •PI PROJECT DESCRIPTION The project site is located just east of 1-5 along the north shore of Agua Hedionda Lagoon within the City of Carlsbad, California (see Vicinity Map above). The Pacific Ocean is directly to the west of the project site. The objective of this project is to provide an access road and shoreline stabilization to avert further undermining and/or erosion and to allow routine sewer maintenance, cleaning, rehabilitation and emergency repairs without deleterious environmental impact. The proposed project consists of a 12-foot wide, 2,400-feet long decomposed granite (DG) access road generally paralleling the shoreline with topographic features ranging from sandy beach to sloped hillsides. The DG surface provides a permeable, durable, and renewable surface without the petrochemicals used in standard asphalt concrete paving. There will be a 12-foot wide, 230-foot long gated paved approach road from Hoover Street. Of the proposed 2,400-feet of DG access road. & ASSOCIATES,INC. NORTH AGUA HEDIONDA LAGOON INTERCEPTOR PROJECT WATER QUALITY TECHNICAL REPORT March 2004 approximately 1,800-feet is currently inaccessible. A shoreline protection wall, adjacent to the access road, is proposed along this 1,800-foot long stretch. The proposed wall is a structural drilled pier wall consisting of 24-inch-diameter, structurally-reinforced piers spaced on 6 to 8-foot centers, with the clear space between drilled piers infilled with structural concrete. In areas where the access road would resuh in cut slopes, short (2-4 feet), plantable retaining structures (crib walls) are used in two locations. These structures are placed on the north side of the access road to minimize impact on native vegetation. Upslope drainage will be conveyed across the road to the lagoon via 11 proposed culverts. The maintenance road will be sloped away from the lagoon at 2% to direct surface drainage to proposed vegetated swales and/or gravel shoulders that will carry the flows to the culvert locations. The proposed project will discharge directly to the Agua Hedionda Lagoon, which is an Environmentally Sensitive Area, and is categorized as a Priority Project as outlined in the regional and City of Carlsbad adopted SUSMP. Therefore BMPs Applicable to hidividual Priority Projects will apply and require additional BMP implementation. POLLUTANTS AND CONDITIONS OF CONCERN A. Potential Pollutants Standard Urban Storm Water Mitigation Plan (SUSMP) identifies the followmg categories of pollutants that are anticipated and/or potential to be generated from this development: 1. Sediments - Sediment from scour and erosion will be the primary pollutant of concern from this project. Eroded soils or other surficial materials from site, primarily during construction, may be generated during storm events. 2. Heavy Metals - Heavy metals are anticipated from vehicles after the unpaved maintenance road is constructed. The proposed access road will be used occasionally by maintenance vehicles only and will not generate a significant amount of this pollutant. 3. Organic Compounds - Petroleum hydrocarbons are anticipated after construction. The proposed access road will be used occasionally by maintenance vehicles only and will not generate a significant amount of this pollutant. 4. Trash & Debris - Paper, plastic, polystyrene products, aluminum materials, landscape waste, and food waste are anticipated during and after construction primarily from public trail use. • A550CJATi;5.[NC.| NORTH AGUA HEDIONDA LAGOON INTERCEPTOR PROJECT WATER QUALITY TECHNICAL REPORT March 2004 m 5. Oil & Grease - Motor products from leaking vehicles would be the only potential pollutant of concern for this category. 6. Bacteria & Viruses - Animal waste (particularly from pets) is a minor concern. Although the project is for the construction of a maintenance access road, it is anticipated that the majority of the potential pollutants listed will be generated from public access. The infrequency of a maintenance vehicle accessing the site (1-2 times per year, non-emergency) will not significantly generate the hsted pollutants of concern. B. Receiving Waters The receiving water for each discharge point is the Agua Hedionda Lagoon. The project site is located within Carisbad Watershed Management Area in the Carlsbad Hydrologic Unit (904.00), Agua Hedionda Hydrologic Area (904.30) and Los Monos Hydrologic Subarea (904.31) according to the California Regional Water Quality Control Board, San Diego Region Water Quality Control Plan for the San Diego Basin (9.). (See Appendix A-Site Map) Bacteria Indicators and sedunentation/siltation are the pollutants on the most recent Clean Water Act Section 303(d) impaired water bodies list. The TMDL priority is low. C. Conditions of Concern As stated in the project description, the site is presently undeveloped beach and hillside with several concentration points discharging directly to the lagoon. Two concrete brow ditches on the western end of the proposed alignment and one 18-inch CMP conveying storm water from Hoover Street and above are the only visible drainage structures that discharge directly to the lagoon. Several other discharge points are evident from observed eroded gullies that have formed where flows concentrate and discharge to the lagoon. The remaining upstream runoff is characterized by sheet flow that either concentrates at the gullies or sheets directly to the lagoon. There is currently one area of impervious surface that the proposed alignment will cross and consists of a privately owned asphalt and concrete boat launch located along the eastern portion of the alignment. Existing site conditions based on field reconnaissance indicate mild to severe scour and erosion at several locations along the proposed maintenance access road, all of which are upstream of the proposed alignment. There are two very distinct soil types found along the proposed alignment: Carisbad gravely loamy sand (CbD) on 9% to 15% slopes (hydrologic soil group C) with moderate erosion potenfial; and Marina loamy coarse sand (MIE) on 9% to 30% slopes (hydrologic soil group A) with moderate to severe erosion potential. NORTH AGUA HEDIONDA LAGOON INTERCEPTOR PROJECT WATER QUALITY TECHNICAL REPORT March 2004 The northwestern shoreline of Agua Hedionda Lagoon is largely undeveloped and has naturalized since installation of the existing sewer line in 1965. Native vegetation communities found within the sewer alignment corridor include coastal sage scrub, coastal salt marsh, intertidal mudflat and intertidal rocky beach. The shoreline of the lagoon experiences fluctuations in the water level due to coastal tides. The shoreline is currenfly experiencing erosion as evidenced by a vertical bank adjacent to the flat sandy shore. Whenever a wave-cut bench is not eroded down to a stable equilibrium, continued downcutting of the bench is inevitable. The effective elevation of high water begins to erode the shore and the wave-cut bench develops. A drainage study was prepared for this project following the guidelines of the City's Storm Water Standards Manual and the most recent edition of the San Diego County Hydrology Manual. The analysis concludes that the construcUon of the access road will not significantly increase site runoff and will actually decrease site runoff for smaller storm events due to the placement of DG, which has greater infiltrafion properties than the existing soil. The complete analysis can be found in the Appendix B - Drainage Study. PERMANENT STORM WATER BMPS According to SUSMP provisions, BMPs designed to remove pollutants of concern to the maximum extent practicable (MEP) shall be applied in the following progression: Site Design, Source Control, BMPs for individual Priority Project Categories, and Treatment Control. Because this project has been identified as a prionty project, the project is subject to the Priority Project Permanent Storm Water BMP requirements and must also implement the BMPs applicable to mdividual priority project categories. BMPs that are proposed for the project site are listed below for the three categories in progression, with a brief explanation of the pollutants or conditions of concern mitigated. A. Site Design and Individual Priority Project BMPs • Decomposed Granite is used for most of the access road surface to minimize impervious surfaces and reduce runoff volumes. • Vegetated swales, in Ueu of curb & gutter, will be used to convey surface runoff to collection points. • Cut slopes will be minimized by using planted crib walls. • All cut slopes and disturbed hillsides will be landscaped with deep rooted, drought tolerant native plant species. • Concentrated runoff from top of slopes will be conveyed down proposed slopes with lined ditch. • Gravel will be placed around inlets. k ASSOCIATES,INC. NORTH AGUA HEDIONDA LAGOON INTERCEPTOR PROJECT WATER QUALITY TECHNICAL REPORT March 2004 B. Source Control BMPs • There will be no hazardous materials stored on site. • Temporary landscape irrigafion will employ raia shutoff devices. • Stenciling will be done on all site inlets, where practical, to educate pubHc on storm water pollution prevention. C. structural Treatment BMPs • Drainage inserts will be incorporated into catch basins as indicated on Site Map. Applicable systems include filters manufactured by Downstream Services, hic. or equivalent. This flow- based BMP will be designed to filter to the maximum extent practicable and is intended primarily for trash and debris removal. MAINTENANCE AND POST-CONSTRUCTION CONTROL All long-term maintenance of the BMPs will be the responsibility of the site owner. Long-term maintenance of the proposed BMPs shall include: 1. Clean the access road once per month. 2. Inspection of paved areas for cracks. All identified cracks will be sealed, re-surfaced and/or re- paved, as needed. 3. Disposal of all sediment and inlet debris in accordance with all applicable laws and regulations. 4. Re-stenciling at inlets, as needed. 5. A Client Department-Approved method of storm water BMP maintenance, repair and replacement shall be executed prior to commencement of construction. 6. City shall execute a signed statement accepting responsibility for all permanent BMP maintenance, repair and replacement in a Permanent BMP Maintenance Agreement. The SUSMP does not consider treatment control BMPs effective unless a mechanism is in place that will ensure ongoing long-term maintenance of BMPs. Maintenance schedules for the treatment control BMP's, as stated in the Permanent BMP's Maintenance Agreement, will be filed with the City of Carisbad. Fiscal responsibility to install and maintain all site BMPs is to the owner. CONCLUSION This WQTR has been prepared in accordance with the City of Carlsbad Public Works Department Standard Urban Storm Water Mitigation Plan Stonn Water Standards. This WQTR has evaluated and addressed the potential pollutants associated with this project and their affects on water quality. A summary of the facts and findings associated with this project and the measures addressed by this WQTR are as follows: NORTH AGUA HEDIONDA LAGOON INTERCEPTOR PROJECT WATER QUALITY TECHNICAL REPORT March 2004 • The receiving water has been idenfified, which the developed area would discharge to, is listed on the recent Clean Water Act Section 303(d) impaired water bodies list. • The site has been careftiUy designed by using decomposed granite for the majority of the access road surface to minimize impervious cover, minimize discharge rates and velocities. • Storm water conveyance system will include stenciling and signage to educate public on storm water pollution. • Two stainless steel inlet insert filters will be installed in the two proposed catch basins. They will capture of floatable pollutants (debris and trash) and sediments. The Fossil Rock filter medium pouches allows for the separation of oil and grease from the collected solids (sediment and debris). The BMPs address mitigation measures to protect water quality to the maximum extent practicable. & ASSOCIATtS.lNC. NORTH AGUA HEDIONDA LAGOON INTERCEPTOR PROJECT WATER QUALITY TECHNICAL REPORT March 2004 APPENDICES i, ASSOCIATES.INC. NORTH AGUA HEDIONDA LAGOON INTERCEPTOR PROJECT WATER QUALITY TECHNICAL REPORT March 2004 APPENDIX A - SITE MAP m & ASSOCIAFES.INC. k ASSOCIATES, INC, 605 Third Street tnciniloi, CA 9202* 760.M2.5H7 Foi 7M.fiJZ.016* SITE PLAN SCALE: 1"=250 SHEET 1 NORTH AGUA HEDIONDA INTERCEPTOR f1 i i' n I n n 1 Ml 1 4f k ASSOCIATES, INC. PROPOSED DG ACCESS ROAD (TYP) AGUA HEDIONDA LAGOON PROPOSED CIDH WALL P-1 CULVERT LEGEND 605 Third SIreet Encinilos, CA 91024 760.9W.5147 Fax 760.5JZ.0164 VEGETATED SWALE CONCRETE LINED BROW DITCH FLOW PATTERN DG ACCESS ROAD AC ACCESS ROAD CULVERT PROPERTY LINE PLAN SCALE: 1"-40 HIGH POINT SHEET 4 NORTH AGUA HEDIONDA INTERCEPTOR n Li ^ in LJ LU X {/) LJ LU CO LJ X o & ASSOCIATES, INC. PROPOSED DG ACCESS ROAD AGUA HEDIONDA LAGOON VEGETATED SWALE CONCRETE LINED BROW DITCH FLOW PATTERN DG ACCESS ROAD AC ACCESS ROAD CULVERT PROPERTY LINE P-10 CULVERT PLAN 605 Third Street Encinilos, CA 92024 76B.942.5147 Foi 760.632.0164 SCALE: 1"=40 SHEET 6 NORTH AGUA HEDIONDA INTERCEPTOR NORTH AGUA HEDIONDA LAGOON INTERCEPTOR PROJECT WATER QUALITY TECHNICAL REPORT March 2004 APPENDIX B - DRAINAGE STUDY (. ASSOCIATES,INC- NORTH AGUA HEDIONDA LAGOON INTERCEPTOR PROJECT WATER QUALITY TECHNICAL REPORT March 2004 DRAINAGE STUDY The following outlines the impacts the proposed project would have on water quahty and runoff patterns. Peak flows were determined for existing and proposed conditions using the 2-year, 10-year and 100-year six-hour storm events. Results indicate negligible increase in runoff due to increase in impervious surface. Therefore the proposed project will have negligible impacts on the hydrologic regime. Site Hydrology Rational method and the San Diego County Hydrology Manual are utilized to determine discharge for the site under existing and proposed conditions. Soil type "D" is selected. Existing basin hydrology study from Rick Engineering co. is referenced. Formula to Calculate Runoff Coefficient is: C=0.90 (%Impervious) + Cp (l-%Impervious) Where: Cp=Pervious coefficient runoff value for the soil type (shown in Table 3-1 of San Diego County Hydrology Manual as undisturbed natural terrain/permanent open space, 0% impervious). Formula to Calculate Sheet Flow Time of Concentration is: Tc=1.8*(l.l-C)*(D^0.5)/(S^0.3333) Where: Tc=Time of concentration in minutes C=Runoff coefficient D=Distance in feet, maximum D is 100 feet S-Slope in percent Formula to Calculate Travel Time for Natural Watersheds is: Tc={n.9L^3/AE)^.385 Where: Tc=Time of concentration in hours L=Watercourse distance in miles AE=Change in elevation along effective slope line in feet & ASSOCIATKS.INC Drainage Study -1 NORTH AGUA HEDIONDA LAGOON INTERCEPTOR PROJECT WATER QUALITY TECHNICAL REPORT March 2004 Formula to Calculate Intensity is: I=7.44*P6*Tc^(-0.645) Where: I=lntensity in inch/hour P6=6 hour rainfall depth in inches Tc=Time of concentration in minutes Rational Method: Q=CIA Where: Q=Discharge rate in cfs C=Runoff coefficient A=Drainage area in acres PEAK FLOW RATE 2-YEAR STORM 10-YEAR STORM 100-YEAR STORM Drainage Area Post Q Existing Q PostQ Existing Q Post Q Existing Q cfs cfe cfs cfs cfs cfe PI 21.51 21.52 31.27 31.27 45.99 45.99 P2 2.73 2.75 3.99 3.99 5.87 5.87 P3 6.61 6.62 9.61 9.61 14.14 14.14 P4 2.74 2.74 4.04 3.99 5.94 5.86 EX. CULVERT 11.12 11.12 16.15 16.15 23.75 23.75 P5 11.51 11.54 16.82 16.77 24.73 24.66 P6 2.48 2.55 3.70 3.70 5.44 5.44 P7 4.17 4.22 6.13 6.13 9.02 9.02 P8 8.57 8.67 12.60 12.60 18.53 18.53 P9 0.94 0.96 1.39 1.39 2.05 2.05 P10 7.16 7.18 10.43 10.43 15.34 15.34 P11 0.30 0.30 0.44 0.44 0.64 0.64 & ASSOCIATES.INC- Drainage Study - 2 i 1 I 1 I I I i I I i i ft I I I I i NORTH AGUA HEDIONDA LAGOON INTERCEPTOR PROJECT WATER QUALITY TECHNICAL REPORT March 2004 RUNOFF VOLUME AND RETENTION VOLUME 2-YEAR STORM 10-YEAR STORM 100-YEAR STORM DRAINAGE AREA EXISTING RUNOFF VOLUME RETENTION VOLUME POST RUNOFF VOLUME EXISTING RUNOFF VOLUME RETENTION VOLUME POST RUNOFF VOLUME EXISTING RUNOFF VOLUME RETENTION VOLUME POST RUNOFF VOLUME cf cf cf cf cf cf cf cf cf PI 228.49 -0.15 228.34 331.99 0.00 331,99 488.22 0.00 488.22 P2 28.44 -0.22 28.22 41.32 0.00 41.32 60.76 0.00 60.76 P3 116.47 -0.09 116.38 169.23 0.00 169.23 248.87 0.00 248.87 P4 44.65 -0.06 44,58 64.87 0.85 65.72 95.40 1.25 96.65 EX. CULVERT 215.40 0.00 215,40 312,97 0,00 312.97 460.25 0.00 460.25 P5 178.38 -0.44 177.94 259,18 0,78 259.96 381.15 1.15 382.30 P6 31.31 -0.77 30,54 45.49 0,00 45.49 66.90 0.00 66.90 P7 52.24 -0.67 51.57 75.91 0.00 75.91 111.63 0.00 111.63 P8 82.56 -0.95 81,62 119.97 0.00 119.97 176.42 0.00 176.42 P9 10.38 -0.26 10.12 15.08 0.00 15.08 22.18 0.00 22.18 PIG 79.07 -0.23 78.83 114.89 0.00 114.89 168.95 0.00 168.95 P11 5.79 0.00 5.79 8.41 0,00 8.41 12.37 0.00 12.37 & ASSOCIATr.S,INC. Drainage Study - 3