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Home My WebLink AboutCD 2019-0020; PACIFIC RIM; INFILTRATION FEASIBILITY LETTER, PROPOSED RENOVATIONS; 2019-12-30Leighton and Associates, Inc. A LEIGHTON GROUP COMPANY December 30, 2019 Rra' 1 ID To: Xenia Hotels & Resort, Inc. JAN 13 2C20 200 S. Orange Ave. Suite 2700 Orlando, FL 32801 LAND DEVELOPMENT Attention: Mr. Stephen Long ENGINEERING Subject: Infiltration Feasibility Letter, Proposed Renovations to the Park Hyatt Aviara Resort, Carlsbad, California References: Leighton Consulting, 2019a, Geotechnical Investigation Report, Exterior Renovations, Park Hyatt Aviara Resort Golf Club & Spa, Carlsbad, California, Project No. 12493.001, dated October 23, 2019. Leighton Consulting, 2019b, Addendum - Additional Field Percolation Testing for New Bio-filtration Basin Location, Proposed Renovations to the Park Hyatt Aviara Resort, Carlsbad, California, Project No. 12493.001, dated November 21, 2019. As requested, we have prepared this letter to discuss the infiltration feasibility of the proposed Drainage Management Areas associated with the renovation project at the Park Hyatt Aviara Resort, located in Carlsbad, California. The site is currently occupied by existing hotel buildings, pool areas, an event lawn courtyard, and associated landscape and hardscape areas. As shown on the attached Fuscoe Engineering exhibit, there are three proposed Drainage Management Areas (DMAs) for the project. As background, Leighton Consulting, Inc. (Leighton) has performed a geotechnical study for the proposed project, which included field percolation testing at four potential Bio-filtration areas for determining the feasibility of on-site near surface storm water infiltration in general accordance with the County of San Diego Storm Water Standards (County of San Diego, 2019). 3934 Murphy Canyon Road, Suite B205 • San Diego, CA 92123-4425 858.292.8030 • Fax 858.292.0771 • www.leightongroup.com I 12493.001 For an assessment of the overall feasibility of infiltration of the DMAs, we have utilized the seven items that are key in determining feasibility in our professional opinion. Note that these items are also used by the City of San Diego in determining infiltration feasibility (Section C.1.1, of San Diego Storm Water Standards, 2018). I The phase of the project in which the geotechnical engineer first analyzed the site for infiltration feasibility. As encountered during our field exploration (Leighton, 2019a), the site is underlain by artificial fill extending to varying depths up approximately 13 feet below the existing ground surface (bgs). The fill soil was derived from on-site excavations that was placed and compacted during the original grading of the site in the late 1990s. As part of our geotechnical investigation, three proposed BMP locations for the project were first analyzed for infiltration feasibility during the field investigation for the geotechnical report dated October 23, 2019. Subsequently, a four proposed BMP location was analyzed for infiltration feasibility, as documented in our addendum letter, dated November 21, 2019. In summary, field percolation testing was done to determine the feasibility of on-site near surface storm water infiltration in general accordance with the County of San Diego Storm Water Standards (County of San Diego, 2019) using section D.2.1, Borehole Percolation Test Method. Based on the field percolation testing, the four proposed BMP sites were categorized as "Partial Infiltration" condition, as determined by the County of San Diego Infiltration Form 1-8, Categorization of Infiltration Feasibility Condition. However, based on further assessment by the project civil engineer, Fuscoe Engineering, the proposed BMP sites were subsequently eliminated due to parcel boundaries and a Deed Restriction (Environmental Restricted Area) issues. It should be noted that localized infiltration within the existing hotel pool areas, an event lawn courtyard, and associated landscape and hardscape was not considered feasible for storm water infiltration due of the existing underlying fill soil. 2 Results of previous geotechnical analyses conducted in the project area, if any. As discussed above, the artificial fill beneath the site was encountered and extended to varying depths up approximately 13 feet below the existing ground surface (bgs) (Leighton, 2019a). The artificial fill consists of moist, light-yellowish brown, loose to medium dense, silty sands and was derived from on-site excavations and the original grading of the site. In general, the existing artificial -2- Leighton 12493.001 fill beneath the project area has a high potential for preferential pathways and transmitting groundwater/seepage down gradient. 3 The development status of the site prior to the project application (i.e., new development with raw ungraded land, or redevelopment with existing graded conditions). This is a renovation project with existing hotel buildings, pool areas, an event lawn courtyard, and associated landscape and hardscape. The site was developed prior to the 2000's. Currently, storm water infiltration at the site does not occur. 4 The history of design discussions for the project footprint, resulting in the final design determination. We were not involved in design discussions related to project footprint and final design determination. 5 Full/partial infiltration BMP standard setbacks to underground utilities, structures, retaining walls, fill slopes, and natural slopes applicable to the DMA that prevent full/partial infiltration. As shown on the attached Fuscoe Engineering exhibit, there are three DMAs for the project: DMA I is an existing courtyard area which is underlain by fill. Immediately south and down gradient of DMA I is a facility access road with a service entry that would be adversely affected by infiltration of storm water. DMA 2 is generally an existing pool area, which is underlain by fill and has numerous existing underground utilities. These utilities include wet utilities such as storm drain and sewer lines that can act as preferential pathways and adversely affected by infiltration of storm water. DMA 3 is an existing pool area, which is underlain by fill and has numerous existing underground utilities. These utilities include wet utilities such as storm drain and sewer lines that can act as preferential pathways. Of particular concern is an existing Keystone Retaining wall along the eastern boundary, which is an up to 28 feet high that would be adversely affected by infiltration of storm water. 6 The physical impairments (i.e., fire road egress, public safety considerations, etc.) that prevent full/partial infiltration. Immediately south and down gradient of DMA I is a facility access road with a service entry that would be adversely affected by infiltration of storm water. Leighton 12493.001 7 Conclusion or recommendation from the geotechnical engineer regarding the DMA's infiltration condition. As previously mentioned above, all of the DMAs are underlain by up to 13 feet of existing fill. In accordance with County of San Diego Storm Water Standards (County of San Diego, 2019) Section B.2.2, these fills (i.e., greater than 5 feet in thickness) should therefore be considered for an Infiltration Restriction by the SWQMP preparer. Of particular concern is the existing facility access road with a service entry down gradient of DMA 1, the existing underground utilities within DMA 2, and existing Keystone Retaining wall along the eastern boundary of DMA 3 that would all be adversely affected by infiltration of storm water. It is therefore our professional opinion that storm water infiltration at DMAs 1, 2, and 3 is not feasible (see attached Fuscoe Engineering exhibit for DMA locations). If you have any questions regarding our letter, please do not hesitate to contact this office. We appreciate this opportunity to be of service. Respectfully submitted, LEIGHTON CONSULTING, INC. CO fls No. 45283 \\* Exp.'V30/20 * 2 d -ofIO51 William D. Olson, RCE 45283 Associate Engineer Attachments: Fuscoe Engineering - Attachment 1 - DMA Exhibit Distribution (1) Digital Copy -4- Leighton 3' tVVU2SR' V-N 0.50 EASING 15 N AS L'S NS TOtT.AR'S "3., N .'N• 7Sf / SET EXISTING G EST WING EXISTING GUEST WING - I / v/- '•—-- LEGEND BIOP]LTRATION BASIN PROPERTY LINE UNIT OF WORK (DISTURBED AREA) - - - - STREET CENTERUNE - - — EXISTING CONTOUR PERVIOUS AREA £015590 STORM DRAIN —st— ARTIFICIAL TURF PROPOSED STORM DP"JP) — — - DMA UNFIX GRASSCRETE I DIRECTION OF FLOW DMA DESIGNATION DMA 1 POOL AREA PROJECT SITE NFO UNDERLYING ITF'DROLOGIC SOIL! D APPROXIMATE DEPTH TO GROUNDWATER; > 20 Fl EXISTING NATURAL HYDROLOGIC FEATURES (WATERCOURSES, SEEPS, WETL9A4DS)! NONE CRITICAL COARSE SEDIMENT TOLD AREAS TO BE PROTECTED NONE EXISTING IMPERVIOUS AREA. 59,910 SF DISTURBED AREA: 97,169 SF PROPOSED IMPERVIOUS AREA: 16,643 SF PROPOSED PERVIOUS AREA, 543,302 SF (INCLUDES POOL AREA 7.363 SF) PERMANENT STORM WATER BMP NOTES Q BIOFILTRA'TlON BASIN BEEP (BF-1) DMA SUMMARY TABLE MWS MI PERVIOUS GRASSCRETE IMPERVIOUS POOL TREATMENT TREATMENT DMA TOTAL TOTAL AREA AREA AREA- AREA METHOD OF FLOWRATE FLOWEATE MI AREA (AC) AREA (SF) (SF) (SF) ASPEUSLT. (SF) TREATMENT 98013960 PROVIDED MODEIM CONCRETE ISP) (GPO) (CFS) 1.1 065 28,340 0 S 23,340 BMP 1)MWS) 0.187 0 230 L-8-8 1.2 0,91 39,706 22,368 4,936 12,802 I 21 013 5,478 0 0 5,473 0 BMP 2 (MWS) 0.176 0230 L-8-3 2.2 0/2 31452 7,903 2,2132 16,223 5126 3 060 26,064 5,321 0 18,ORR 2,624 BMP3(MWS) 0.132 0.144 L-4-53 PARK HYATTAVIARA ATTACHMENT 1a- 35 0 5' 35 DMA EXHIBIT SCALE: 1 = 30' JOB NO. 1111 DATE REVISION 883-001 FUSCOE ENNUI III Ull L.S 6390 Gr..nwirh Dr., OMit. 170 Son Di.go, Colifoosro 92122 SHEET to) 858.554A 500 fox 856.097.0335 x,.,.w.fx,xx..xxn, 1 of 1