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Home My WebLink AboutBio_Alternatives Analysis_LSA (07-28-19)LSA is a business name of LSA Associates, Inc. CARLSBAD FRESNO IRVINE LOS ANGELES PALM SPRINGS POINT RICHMOND RIVERSIDE ROSEVILLE SAN LUIS OBISPO 20 Executive Park, Suite 200, Irvine, California 92614 949.553.0666 www.lsa.net July 28, 2019 Mayuko Nakajima Associate Planner City of Diamond Bar, Planning Division 21810 Copley Drive Diamond Bar, California 91765 cc: Robert Chiang, Project Manager Subject: Biological Resources Alternatives Analysis for the Proposed Crooked Creek Residential Development Project Dear Ms. Nakajima: LSA has prepared this letter to present the impacts to biological resources associated with three (3) alternative site development plans for the proposed Crooked Creek Residential Development Project (project) located on Assessor’s Parcel Number (APN) 8714-028-003 in the City of Diamond Bar, Los Angeles County, California (subject property; refer to the attached Figure 1). BACKGROUND In July 2019, LSA prepared and submitted a Biological Resources Assessment Report (Report) covering the subject property. The Report presents an assessment of potential impacts on biological resources associated with subdividing the existing 13-acre parcel to create 11 new residential lots (preferred alternative). The impact limits were determined based on one of three preliminary grading exhibits prepared by Michael Baker International (dated March 12, 2019), and the Report notes that the project description and footprint presented therein are subject to refinement and approval. This letter provides an analysis of potential impacts on biological resources associated with the other two preliminary grading exhibits which include impact limits for 10 and 9 residential lots, respectively. These alternative designs and associated impacts are provided in relation to the preferred alternative to inform the project planning and approval process. For resource definitions and detailed information regarding specific biological resources associated with the subject property, please refer to the original Report. Project Description and Alternatives The project, as currently proposed, involves subdividing the existing 13-acre parcel to create up to 11 new residential lots ranging in size from 7,500 square feet (sf) to 9,000 sf, with each home averaging approximately 4,000 sf. Each home would include a driveway and garage, above- and below-grade utility connections, and site finishes (e.g., fenced yards and landscaping). The three alternative site plans presented herein include (1) an 11-lot alternative (preferred by applicant), (2) a 10-lot alternative, and (3) a 9-lot alternative. Under all proposed alternative designs, annual vegetation adjacent to the new homes would be maintained for fuel modification/firebreaks, consistent with current practices (or as otherwise required by the Fire Department). All alternatives would also involve a southward expansion of the 7/28/19 (P:\CVD1901\Alternatives Analysis\Crooked Creek_Bio_Alternatives Analysis_072819.docx) 2 existing Crooked Creek Drive, with new retaining walls and slope contouring (with terrace drains) to stabilize and protect the new residential lots and extended roadway. The amount of slope contouring and retaining walls varies slightly between alternatives. Under all alternatives, a new Fire Department access road and turnaround area would be constructed at the northern end of the preliminary development footprint. Up to 40 percent of the 13-acre parcel (the western most portion of the parcel) would be permanently impacted due to mass grading activities and retaining wall construction, with the remaining land and natural resources on the parcel left undisturbed. Mapped vegetation communities and other land cover types existing on the subject property are shown on Figure 2. This letter presents the impacts on mapped vegetation communities as well as the amount of undisturbed/preserved vegetation associated with each alternative. IMPACT ANALYSIS As shown on Figures 3 through 5, each of the analyzed alternatives would result in permanent impacts to nonnative grassland as well as coast live oak (Quercus agrifolia) woodland and southern California black walnut (Juglans californica) groves. Coast live oak woodland and southern California black walnut groves are considered sensitive natural communities, and, if unmitigated, permanent impacts to these vegetation types associated with any of the alternatives would be considered potentially significant. LSA recommended mitigation measures in the Report, including compensatory planting for the loss of sensitive natural communities and preservation of the existing stands of coast live oak and California walnut trees on the remainder of the parcel, to reduce impacts associated with the 11-lot alternative to less-than-significant levels. The same mitigation measures would be recommended for each of the alternative designs. Table A, below, presents the total acreages of impacts to and preservation of mapped vegetation communities based on the preliminary grading limits associated with each alternative. Table A: Alternative Grading Impacts and Preservation Acreages Alternative Impacts to Vegetation within the Preliminary Grading Limits Preservation of Existing Oak and Walnut Woodland (Outside Grading Limits) Annual Brome Grassland California Walnut Groves Coast Live Oak Woodland 11-Lot 2.25 ac 1.23 ac 0.11 ac 5.58 ac 10-Lot 2.11 ac 1.23 ac 0.10 ac 5.59 ac 9-Lot 2.02 ac 1.00 ac 0.10 ac 5.82 ac ac = acres It should be noted that the precise designs of ancillary development components (such as utility connections, drainage systems, retaining walls, etc.) are subject to refinement, and the precise number of trees required to be trimmed or removed may change during final project design. Furthermore, it is difficult to definitively quantify all potential detrimental effects on individual trees adjacent to the grading limits (based on preliminary designs) that often manifest over a period of many years following construction or development activities conducted near the root zones of individual trees. Sometimes the trees can adapt or recover, and other times they cannot. Therefore, the acreages presented in Table A are considered approximate, and the number of individual trees 7/28/19 (P:\CVD1901\Alternatives Analysis\Crooked Creek_Bio_Alternatives Analysis_072819.docx) 3 impacted under any alternative should be assessed when project designs are finalized, as recommended in the Report under Mitigation Measure BIO-1. CONCLUSION While the amount of impacted coast live oak and southern California black walnut trees would be slightly less than the preferred alternative under the 10-lot and 9-lot alternatives, all California Environmental Quality Act (CEQA) impact determinations regarding biological resources would be the same as what is presented in the Report for each alternative. With the recommended mitigation measures contained in the Report, the 11-lot, 10-lot, and 9-lot alternatives would not result in unmitigated significant impacts to sensitive vegetation communities or special-status plant or animal species. Impacts to jurisdictional aquatic resources and wildlife movement and habitat connectivity would be considered less than significant, and the project would not conflict with regional conservation plans or local policies related to biological resources. Differences in impacts to biological resources associated with each alternative are considered negligible. If you have any questions regarding the contents of this letter or would like to discuss the project in further detail, please contact me at Bo.Gould@lsa.net or at (949) 553-0666. Sincerely, LSA Associates, Inc. Bo Gould Senior Biologist Attachment: Figures 1-5 SOURCE: USGS 7.5' Quad., Yorba Linda, CA (1981) I:\CVD1901\GIS\MXD\AlternativesAnalysis\ProjectLocation.mxd (7/26/2019) FIGURE 1 Crooked Creek Diamond Bar DevelopmentAlternatives AnalysisRegional and Project Location 0 1000 2000 FEET LEGEND Project Parcel Boundary ProjectLocation SanBernardinoCounty OrangeCounty LosAngelesCounty ÃÃ142 ÃÃ19 ÃÃ241 ÃÃ72 ÃÃ55 ÃÃ90 ÃÃ22 ÃÃ39 ÃÃ71 ÃÃ91 ÃÃ60 ÃÃ57 §¨¦105 §¨¦405 §¨¦210 §¨¦5 §¨¦605 §¨¦605 §¨¦10 Project Vicinity RUNNINGBRANCHSILVE R B U L L E T CASTLE ROCKCROOKED CREEKBREACANYONRDÄÆ57 SOURCE: Nearmap (06/2019) I:\CVD1901\GIS\MXD\VegetationMap.mxd (7/12/2019) FIGURE 2 Crooked Creek Diamond Bar Development Alternatives Analysis Vegetation Map LEGEND Project Parcel Boundary Vegetation Type Annual Brome Grasslands (6.07 Ac) California Walnut Groves (3.42 Ac) Coast Live Oak Woodland (3.50 Ac) Developed (0.01 Ac) 0 100 200 FEET 1 2 3 4 5 6 7 8 9 10 11 Fire DepartmentTurnaround Access Slope Contouring Area RUNNINGBRANCHSILVER BULLET CASTLE ROCKCROOKED CREEKBREACANYONRDÄÆ57 SOURCE: Nearmap (06/2019) I:\CVD1901\GIS\MXD\AlternativesAnalysis\SitePlan_11Lot_VegetationImpacts.mxd (7/26/2019) FIGURE 3 Crooked Creek Diamond Bar DevelopmentAlternatives Analysis 11 Lot AlternativeVegetation Impact Map LEGEND Project Parcel Boundary Preliminary Site Plan Preliminary Grading Limits* Vegetation Within Grading Limits Annual Brome Grasslands (2.25 Ac) California Walnut Groves (1.23 Ac) Coast Live Oak Woodland (0.11 Ac)0 100 200 FEET * Limits are approximationsbased on preliminary site plansand are subject to refinement 1 2 3 4 5 6 7 8 9 10 Fire DepartmentTurnaround Access Slope Contouring Area RUNNINGBRANCHSILVER BULLET CASTLE ROCKCROOKED CREEKBREACANYONRDÄÆ57 SOURCE: Nearmap (06/2019) I:\CVD1901\GIS\MXD\AlternativesAnalysis\SitePlan_10Lot_VegetationImpacts.mxd (7/26/2019) FIGURE 4 Crooked Creek Diamond Bar DevelopmentAlternatives Analysis 10 Lot AlternativeVegetation Impact Map LEGEND Project Parcel Boundary Preliminary Site Plan Preliminary Grading Limits* Vegetation Within Grading Limits Annual Brome Grasslands (2.11 Ac) California Walnut Groves (1.23 Ac) Coast Live Oak Woodland (0.10 Ac)0 100 200 FEET * Limits are approximationsbased on preliminary site plansand are subject to refinement 1 2 3 4 5 6 7 8 9 Fire DepartmentTurnaround Access Slope Contouring Area RUNNINGBRANCHSILVER BULLET CASTLE ROCKCROOKED CREEKBREACANYONRDÄÆ57 SOURCE: Nearmap (06/2019) I:\CVD1901\GIS\MXD\AlternativesAnalysis\SitePlan_9Lot_VegetationImpacts.mxd (7/26/2019) FIGURE 5 Crooked Creek Diamond Bar DevelopmentAlternatives Analysis 9 Lot AlternativeVegetation Impact Map LEGEND Project Parcel Boundary Preliminary Site Plan Preliminary Grading Limits* Vegetation Within Grading Limits Annual Brome Grasslands (2.02 Ac) California Walnut Groves (1.00 Ac) Coast Live Oak Woodland (0.10 Ac)0 100 200 FEET * Limits are approximationsbased on preliminary site plansand are subject to refinement