Loading...
HomeMy WebLinkAboutCT 98-14; Thompson/Tabata; Tentative Map (CT) (83)Investigative Science and Engineering 3511 Cam/no Del Rio South, Suite 302 Phone/Fax: €19-640-9379/619-640-0763 San Diego, CA 92108-4003 www.ise-advantage.com July 13, 1999 Ms. Melissa Allen Jack Henthom & Associates 5375 Avenida Encinas, Suite D Carlsbad, CA 92008 Re: Standard Pacific Poinsettia Property Addendum Analysis (ISE Report #98-017a) Dear Ms. Allen: At the request of Standard Pacific Properties and Jack Henthom and Associates, Investigative Science and Engineering (ISE) has performed a brief comparative analysis of our acoustical report for the proposed Poinsettia Properties residential development located in Carlsbad, California (ISE Report #98-017) and an earlier study prepared for the Mariners Point Tentative Tract 91-12 (Source: Robert Kahn, John Kain & Associates, 1/24/92). The purpose of the analysis was to reconcile differences in proposed mitigation measures for the two projects along Aviara Parkway for City staff. The results of the analysis are presented in this letter report. Introduction and Definitions The Standard Pacific Poinsettia Properties project site consists of 74.9 acres located in the central portion of the City of Carlsbad in San Diego County, California. The site resides on both sides of Poinsettia Lane, approximately 1 mile east of Interstate 5. The lots are bound by Aviara Parkway to the east, single-family residential housing to the north, and high-density single-family housing to the west and south (including the Mariners Point project site). The site is currently zoned L-C and R-1- 10000 with a proposed zoning of R-1-7500 and RD-M-Q. The eastern portion of the project site contains moderate westward facing slopes while the western half of the site contains gentle slopes with minor relief. Elevations on the site range from approximately 308 feet above mean sea level (MSL) at the northeastern portion of the property to approximately 195 feet MSL at the southwestern comer of the property. Ms. Melissa Allen Standard Pacific Poinsettia Property Addendum Analysis ISE Report #98-017a July 13, 1999 PageS 3. The Mariners Point project was analyzed using a proprietary computer program developed by the consultant based upon the FHWA's RD-77/108 Noise Abatement Methodology. The Poinsettia Property project was analyzed using the Caltrans Sound 32 Traffic Noise Prediction Model which was developed by Caltrans and is used statewide. 4. The Mariners Point project set the receptor height at 6.0 feet AGL. The accepted standardized receptor height for acoustical modeling is 5.0 feet AGL. This value is used in the Poinsettia Property report. 5. Finally, the Mariners Point report set the receptor point at 5.0 feet from the slope edge. The Poinsettia Property report sets the rear yard receptor point approximately midway within the back yard area or approximately 10 feet back from the slope edge. This methodology is consistent with the City's Noise Guidelines Manual. Conclusion Based upon our findings, the future sound levels expected within Lots #235 through #240 (inclusive) reflect the conditions present at the proposed project site and are consistent with the expected levels present at a 10 foot setback from the top of the proposed slope edge. No additional modifications are necessary. Should you have any questions regarding the above findings, please do not hesitate to contact me at (619) 640-9379. Sincerely, RickTavares, REA, INCE Project Principal Investigative Science and Engineering Cc: Gregg Linhoff, Standard Pacific Homes Glen Laube, ISE Ms. Melissa Allen Standard Pacific Poinsettia Property Addendum Analysis ISE Report #98-017a July 13, 1999 Page 2 Comparison Findings A review of the two reports found several differences consistent with individual modeling strategies and analytical techniques. Both reports were fashioned using the FHWA's RD-77/108 Noise Abatement Methodology which is consistent with the guidelines outlined in the City of Carlsbad Noise Guidelines Manual. Both reports utilized correct noise impact thresholds per noise element guidelines. Specific concern expressed by the City centers around six lots within the Poinsettia Property (Lots #235 through #240 inclusive) and the lack of recommended mitigation measures. Past mitigation measures (in the form of a six-foot high AGL masonry wall) were recommend for the Mariners Point project site Lot #56 which is directly adjacent to Poinsettia Property Lot #235. The following observations were made which clarifies the differences: 1. The principal reason for the differing opinion of mitigation design on the affected lots is that the Mariners Point project report assessed impacts to the project site based upon an acoustical model, which did not include the attenuating effects of local existing topography. The Poinsettia Property project report includes the effects of topography per City and ISE's standard modeling guidelines. Comment: This fact was verified through examination of the Poinsettia Property acoustical model at Lot #235. With the attenuating effects of topography (and a receptor point 10 feet from the edge of slope) the calculated peak hourly sound level is 57.2 dBA, which is below the City's impact threshold. Upon removal of the local topography (a non-realistic configuration), the peak hourly level increases to 63.7 dBA. The future sound level identified in the Mariners Point project report for Lot #56 (directly adjacent to Poinsettia Property Lot #235) is 65.7 dBA. The difference of 2.0 dBA is directly attributable to differences in future traffic volumes (below), the conversion between peak hour Leq and CNEL, and modeling differences. 2. The traffic volumes used in the Mariners Point project report for Aviara Parkway (formerly College Boulevard) was 23,000 ADT with a mix of 97.42 percent automobiles, 1.84 percent medium trucks, and 0.74 heavy trucks (or 97.42/1.84/0.74). The peak hour percentage was taken at 10 percent and the speed was set at 45 MPH. These levels are based upon a June 1991 traffic study performed by Wilden and Associates. The traffic volumes utilized in the Poinsettia Property report for the same roadway segment was 19,000 ADT with a mix of 98/1/1. The peak hour percentage was taken at 8 percent and the speed was set at 40 MPH. These levels are based upon a 1998 traffic report prepared for the project site by Urban Systems Associates.