HomeMy WebLinkAbout3338; Agua Hedionda & Calavera Creek Dredging; Agua Hedionda Creek Emergency Dredging; 2006-06-01CLOSE-OUT REPORT ENVIRONMENTAL COMPLIANCE MONITORING FOR THE AGUA HEDIONDA CREEK EMERGENCY DREDGING PROJECT CARLSBAD, CALIFORNIA Prepared for: City of Carlsbad 1635 Faraday Avenue Carlsbad, California 92008 Attention: David Hauser, Deputy City Engineer Prepared by: EDAW, Inc. 1420 Kettner Boulevard, Suite 620 San Diego, California 92 10 1 Phone: (619) 233-1454 Fax: (619) 233-0952 June 2006
TABLE OF CONTENTS Section Page .............................................................................................. 1. PROJECT BACKGROUND 1 ............................................................................... 11. PRECONSTRUCTION ACTIVITIES 2 .............................................................................................................. Biological Services 2 111. TURBIDITY MONITORING ............................................................................................ 2 N. DREDGING ACTIVITIES ................................................................................................. 5 ........................................................................................ V. COMPLIANCE MONITORING 6 APPENDICES Appendix A Biological Resources Survey Results - Bird Nesting Survey Report - Field Survey Report for Light-Footed Clapper Rail Appendix B Data Reporting and Results Attachment 1 - Ambient Turbidity Measurements Attachment 2 - Hourly Turbidity Measurements Attachment 3 - Comparison of Upstream and Downstream Turbidity Measurements during Emergency Dredging Attachment 4 - Ambient Turbidity and Creek Level in Agua Hedionda Creek Appendix C RWQCB Correspondence and Photo Documentation Close-out Report Agua Hedionda Creek Emergency Dredging 06080058 Agua Hedionda Clareour.doc 5/22/06 Page i
LIST OF FIGURES Figure 1 Table Turbidity Monitoring Plan, Agua Hedionda Creek Channel Emergency Dredging........... 3 r I LIST OF TABLES r r 1, Page 1 TurbidiF/ Measurelnent Statistics, Agua Hedionda Creek Emergency Dredging, March 2006 ......................................................................................................................... 7 1 Page ii Close-out Report Agua Hedionda Creek Emergency Dredging 06080058 Agua ffediondo Closeout.& 5n2RW6
I. PROJECT BACKGROUND The City of Carlsbad (City) obtained expedited permit approvals from various regulatory agencies to conduct emergency dredging activities within Agua Hedionda Creek and portions of Calavera Creek. Channel dredging within Agua Hedionda and Calavera creeks was conducted under emergency circumstances to maintain adequate flood protection for the adjacent residential coininunity of Rancho Carlsbad. Rancho Carlsbad is an existing residential mobile home coininunity located east of El Cainino Real and south of Cannon Road, in the northeastern section of Carlsbad, California (Figure 1). Because over 50 percent of the homes in Rancho Carlsbad are located within the existing limits of the 100-year floodplain and are subject to flooding during inajor storm events, emergency channel dredging was deemed necessary to regain appropriate interim flood protection while ongoing channel designs are completed. Channel dredging activities were deemed necessary if the channel capacity was not regained. Channel dredging occurred between the downstream edge of the Rancho Carlsbad Bridge to the upstream edge of the Cannon Road Bridge (Figure 1). Agua Hedionda and Calavera creeks are earthen channel watercourses that have historically been subject to significant sedimentation. Due to increased peak discharge from development within the watershed and the accumulation of up to 6 feet of sediment in the channel, the creeks were dredged to avoid flooding hazards and improve public safety in the event of a significant storm event. The regulatory authorizations that were issued by the U.S. Army Corps of Engineers (ACOE), the Regional Water Quality Control Board (RWQCB), and the California Department of Fish and Game (CDFG) to allow the emergency dredging activities to occur included: ACOE Section 404 permit (200600 15 1-KJC) RWQCB Clean Water Act (CWA) Section 401 Water Quality Certification (06C-007) CDFG Streambed Alteration Agreement (1 600-2006-0060-R5) To assist the City during implementation of the dredging activities, EDAW, Inc. (EDAW) was retained to provide general environmental compliance monitoring, including turbidity and water quality monitoring per the conditions outlined in the issued permits. The EDAW team also included the services of Konecny Biological Services to address monitoring efforts for the light-footed clapper rail and to conduct a general preconstruction biological survey. This report summarizes these monitoring efforts from the initiation of the project on March 4,2006, through Close-out Report Agua Hedionda Creek Emergency Dredging 06080058 Agua Hedionda Closeou~.doc 5/22/06 Page 1
completion of dredging activities on March 25, 2006. Copies of the survey results are included in Appendix A. 11. PRECONSTRUCTION ACTIVITIES Biological Services Biological monitoring services were provided by wildlife biologist John Konecny of Konecny Biological Services and EDAW's environmental monitor, Jeff Warner. Biological monitoring occurred between March 3 and March 9,2006, during vegetation removal and dredging activities between the Cannon Road and El Camino Real bridges. Results of the biological surveys are included in Appendix A of this report and summarized below. In accordance with the ACOE 404 Permit (20060015 1-KJC) Special Condition la, and CDFG Streambed Alteration Agreement (1600-2006-0060-R5) Condition 14, a biological monitor conducted a preconstruction survey of the project alignment prior to the beginning of vegetation reinoval between the Cannon Road and El Camino Real bridges. The survey was conducted on March 3, 2006. No active bird nests were detected at the site. The biological monitor was present during vegetation removal between the bridge structures on the morning of March 4, 2006. Biological monitoring continued during vegetation removal and dredging activities that occurred between the bridge structures through March 9, 2006. Exclusionary fencing was provided near the edge of the Cannon Road Bridge to prevent dredging activities from extending outside the project limits and into the environmentally sensitive area downstream of Cannon Road Bridge (Figure 1). The fencing also served as a buffer to keep the clapper rails from entering the active construction site. Although the City was permitted to conduct dredging and vegetation clearing to the downstream portion of Cannon Road Bridge, no actual disturbance occurred in this area. No vegetation removal occurred on the south side of the banks between the two bridges. 111. TURBIDITY MONITORING In accordance with the requirements of the CWA Section 401 Water Quality Certification (401 Certification), EDAW conducted the following turbidity and water quality monitoring services: Page 2 Close-out Report Agua Hedionda Creek Emergency Dredging 06080058 Agua tledionda CIoreouf.doc 3/22/2W6
Turbidity Control Plan (TCP) - per Condition B.l of the 401 Certification, EDAW prepared a turbidity monitoring plan that described the dredging process, the turbidity control best management practices (BMPs), and the turbidity monitoring approach. Turbidity Compliance Monitoring - turbidity monitoring was conducted throughout the emergency dredging process, including: o Collection of water samples within the active flow to measure turbidity levels, o Measurement of creek velocity at the point of measurement, and o Recording of visual observations. IV. DREDGING ACTIVITIES To document ambient water quality prior to dredging, turbidity measurements were taken at 10 locations along the creek alignment. Ambient Turbidity monitoring locations are shown in Figure 1 and the field measurements are shown in Appendix B (Attachment 1). Prior to dredging activities, vegetation removal began on March 4, 2006, between Cannon Road Bridge and El Camino Real Bridge. In accordance with the TCP, a series of gravel-bag check dain structures were constructed under the Cannon Road Bridge to create stilling pools for capturing sediment and controlling turbidity downstream of the project limits. Dredging activities commenced on March 6,2006, but were limited to the area between the Cannon Road Bridge and El Cainino Real Bridge. Dredging between the Cannon Road Bridge and El Camino Real Bridge was isolated from the active stream flow via a diversion channel created along the northeast side of Agua Hedionda Creek. At the upstream edge of the Cannon Road Bridge where the diversion channel terminated, a desilting basin was created to promote sediment settling and capture prior to coming in contact with the gravel-bag check dams downstream. The creation of the diversion channel and desilting basin provided an isolated and relatively dry earthen platform from which dredging was conducted. The dredging crew carefully removed sediment within the perimeter of the earthen platform, leaving approximately 1 to 2 feet of natural creekbed in place as a protective berm between the active creek flow and dredging operations. Dredging activities between the bridge structures were completed ahead of schedule. Permit conditions required that work be completed between the Cannon Road Bridge and El Camino Close-out Report Agua Hedionda Creek Emergency Dredging 06080058 Agua Hediondo Closeout.doc 5/22/06 Page 5
Real Bridge by March 15, 2006 (to avoid the active nesting season). Work activities at this location were completed on March 9,2006. Following a temporary work stoppage due to a storm event, creek dredging was reinitiated on March 14, 2006, upstream of El Camino Real Bridge, beginning with the construction of a similar desilting basin at the upstream edge of the bridge and a diversion channel along the southwestern edge of the creek. The diversion channel was overexcavated (to an approximate depth of 6 feet) to provide extra capacity for capturing additional sediment traveling downstream. By isolating the creek within the diversion channel, the remaining creekbed was accessible for dredging equipment. A roadway was created along the northeastern edge of the creek to allow the dredging excavator and dump trucks to travel the length of the creek without disturbing water quality. A stream crossing, consisting of a 50-foot steel pipe was placed in Calaveras Creek at the junction with Agua Hedionda Creek and covered with creekbed sand to create a water quality bypass underneath the access route to Agua Hedionda Creek. Emergency dredging in Agua Hedionda Creek upstream of the El Camino Real Bridge was completed by March 25,2006. Dredging underneath the south side El Camino Real Bridge began on March 27,2006. The 50- foot section of pipe used for the Calaveras Creek bypass was used to divert the creek's watercourse and allow the creation of an access road across the creek. Once the material from the south side of El Cainino Real Bridge was removed and the area settled from the disturbance, flow was returned to the south side such that work under the central and north sections could take place. With dredging completed, dredging equipment was demobilized and gravel-bag check dams were removed on March 28,2006. V. COMPLIANCE MONITORING As required in Condition B.2.d of the 401 Certification, any exceedances of turbidity limits that occurred during emergency dredging were to be reported to the RWQCB within 48 hours and immediate action was taken to reduce turbidity downstream to the maximum extent practicable. Throughout the emergency dredging in Agua Hedionda Creek, there were a number of occasions when downstream turbidity levels "spiked" due to inadvertent berm sloughing, leakage, and failures that exceeded permit limitations. As these conditions occurred, they were communicated to the RWQCB within 48 hours and, when applicable, BMPs were adjusted to improve turbidity controls and water quality downstream. Turbidity monitoring data and data histograms are provided in Appendix B (Attachments 1, 2, 3, and 4), and project correspondence to the Page 6 Close-out Report Agua Hedionda Creek Emergency Dredging 06080058 Agua Hrdionda CI~seouI.& 5R2nW6
RWQCB and photo documentation are provided in Appendix C. Additional photo documentation is available upon request. The emergency dredging activities were completed ahead of schedule, under extreme rainy conditions. The implementation of BMPs was conducted in accordance with the project's Storm Water Pollution Prevention Plan, which was amended when necessary (Section 207). All BMPs required by the TCP were implemented and were adjusted to adapt to the morphology of Agua Hedionda Creek. It should be noted that throughout dredging operations, water quality controls were monitored and modified to achieve the best practicable water quality conditions at the downstream monitoring location. As shown by the hourly monitoring data (Appendix B - Attachments 2 and 3), there were short episodes of elevated measurements. Overall, the ranges of turbidity measurement statistics were not notably different among upstream and downstream monitoring locations (Table 1). Table 1 Turbidity Measurement Statistics, Agua Hedionda Creek Emergency Dredging, March 2006 Downstream Median Its important to note that observations made and measurements taken during the course of the emergency dredging also indicated that upstream turbidity was periodically higher than downstream values. This was particularly true following rainfall and subsequent runoff events. To demonstrate the effects of storm water runoff, turbidity data from the Agua Hedionda Creek Monitoring Project (Pacific REMS), as measured at the El Camino Real Bridge, shows that significant turbidity effects can be caused by natural conditions (Appendix A - Attachment 4). As shown in Appendix B (Attachment 4), Pacific REMS turbidity data recorded during a storm event in early January 2006 shows in-creek turbidity reaching 3,000 NTUs (nephelometric turbidity units) on two occasions. Average turbidity during this record of measurement was 333 NTUs. As illustrated in Appendix B (Attachment 4), the rise in creek level from local runoff significantly affects water clarity in the creek and substantially exceeds any levels that were Close-out Report Agua Hedionda Creek Emergency Dredging 06080058 Aguo Hedionda Closeout.doc 5/22/06 Page 7
measured during the emergency dredging project (which also experienced rainfall on two occasions). Overall, the BMPs installed were effective in controlling turbidity. Flocculent was also proposed (and approved by the RWQCB) for use on this project to supplement the physical BMPs installed but was not used because the project finished ahead of schedule. In lieu of the very stringent turbidity limits set by the 401 Certification and the documentation of hourly turbidity at upstream and downstream monitoring locations, water quality was controlled to the maximum extent practicable and was maintained well below conditions that have been documented to occur naturally. Page 8 Close-out Report Agua Hedionda Creek Emergency Dredging l 1 06080058 Aguo fledion& CIoscour.doc 5/22/2006 n