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Starleaf PS Task 1 Site Study 12-07-2015  Technical Memorandum    (Starleaf Pump Station Study, Task 1 – Site Study) Page 1 of 5 To: Jamie Brierton, CIP Coordinator Keith Marvin, PE; Assistant Director of Public Works From: Bryant Caswell, PE (Texas PE # 91721) Dorian French, PE, RPLS, DWRE (Texas PE #40453) Date: December 7, 2015 Subject: Starleaf Pump Station – Site Study As part of the Starleaf Pump Station Study, Brown & Gay Engineers Inc., (BGE) has performed an evaluation of the site on Starleaf Street for a proposed 25 MGD Pump Station (PS) and 6 million gallon (MG) Ground Storage Tank (GST). This evaluation considers the physical and administrative site constraints for the proposed pump station project. Physical constraints include items such as the roadway and underground infrastructure such as existing pipelines. Administrative constraints include easements, building setbacks, architectural development codes and Texas Commission on Environmental Quality (TCEQ) regulations. Other constraints include the Federal Emergency Management Agency (FEMA) 500 year floodplain and the United States Army Corps of Engineers (USACE) flood inundation mapping. SITE EVALUATION   Building Area  The site is to consist of two lots, A and B, separated by Starleaf Street. Lot A on the north side is 1.94 acres and bounded on the West by the Irving ISD and the North by the Saint Joseph Village development. Lot B on the south side is 2.18 acres and is bounded on the East by a power line easement and to the West by the City of Coppell’s MacArthur Park. As shown in Exhibit 1, with multiple easements and setbacks on each lot the usable acreage for a structure is reduced to 1.15 acres for Lot A and 0.80 acres for Lot B. Although drainage and sewer easements on each lot reduce the space available for a tank or building, the space may available for paving for vehicular access or parking. Floodplain and Inundation Mapping  The most current FEMA Flood Insurance Rate Map (FIRM) from July 2014 includes the Starleaf site within the 500-year floodplain, but outside of the 100-year floodplain (Exhibit 2). The North Central Texas Council of Governments, as part of the Trinity River COMMON VISION Program, has developed a floodplain development permitting process in cooperation with nine municipalities including the City of Coppell. A permit called a Corridor Development Certificate (CDC) must be applied for by any development within the 100 year floodplain of the Trinity River, in this case the Elm Fork. As the project site does not lie within the 100 year floodplain, a CDC does not appear to be required.   Technical Memorandum (Task 1 – Site Study) Page 2 of 5 In May 2015, the U.S. Army Corp of Engineers performed a study on the impact of flood events and the related dam release flooding downstream of Lake Lewisville. During a high flow scenario, defined as a 30,000 cfs release, there is potential flooding along the property boundaries and is shown on Exhibit 2. However, the potential inundation area per the USACE mapping is outside the easements and setbacks except for a small section in the northwestern corner of Lot A. Tank Size & Location  Considering easements and set back constraints, the approximate maximum tank diameters were determined for both Lot A and B. Table 1 – Approximate Maximum Tank Sizes Lot Max Interior Tank Diameter (ft) Tank Capacity (MG) Approximate Head Range (ft) A 200 6.0 26 B 140 6.0 52 Lot A would allow up to a maximum diameter of 200 ft providing a draft less than 30 feet for a 6 MG tank (Exhibit 3). Lot B is less suited for the tank as the maximum diameter is limited to 140 feet, which would require a tank height of over 50 feet for a 6 MG tank (not shown). For more consistent pump suction conditions, a wider shallower tank is desired. In addition to improved pump suction conditions, a lower tank profile may be aesthetically desirable and it is common to bury taller tanks at least partially to improve their appearance. However, TCEQ rules require that tanks are not to be buried below the groundwater level and no storage tank or clearwell located below ground level is allowed within 50 feet of a sanitary sewer. Although the exact groundwater level at the site is unknown until borings can be made, per the discussion below on the anticipated geologic conditions and the proximity to low lying areas that flood, groundwater is expected which may limit the depth of bury available for the tank. Also, the proximity of the sanitary sewer force main along the West boundary of the site may affect the ability to bury the tank as well. Considering these limitations on Lot B, in contrast with the availability of Lot A, we recommend that the tank be located north of Starleaf St. on Lot A (Exhibit 3). Pump Station Footprint  An approximate maximum size of 75 feet by 100 feet is assumed for the pump station footprint. This footprint includes space for the pump suction and discharge headers as well as the electrical and control room, but does not include added office or storage space. A horizontal split case pump station, similar to the Village Parkway Pump Station, may require most of this footprint to be the building footprint where pipe headers, valves, and ancillary equipment are within. A vertical turbine pump station may allow a much smaller building, but the space required for the supporting yard piping would require approximately the same footprint.   Technical Memorandum (Task 1 – Site Study) Page 3 of 5 Although both lots have sufficient space for the assumed footprint we recommend the pump station be located on lot B per the discussion above regarding tank location. As shown on Exhibit 3, Lot B appears to have sufficient space for the pump station, emergency generator, vehicle fueling station and adequate vehicular access. There also appears to be space to accommodate a slightly larger footprint for additional office and shop space. The piping layout shown in the exhibit is conceptual and only shown for feasibility. Multiple site layout arrangements will be developed as part of the preliminary site layout (Task 5). In general, the size of the site will require close proximity of large buried structures and pipe. Strong consideration for the maintenance and repair of these improvements will be required during design and construction. ARCHITECTURE  Quorum Architects, Inc. evaluated the site for applicable development codes and planning and zoning requirements, including discussions with City staff. The proposed pump station will likely be designed primarily as a load bearing masonry construction, type II-N construction per the 2012 International Building Code, in which the walls and roofs are constructed of non- combustible materials. Specifically, the primary walls will likely be reinforced masonry while roofs will likely have steel structural members and decking. Depending on the final design, a simulated stone or full depth masonry veneer (brick or stone) will likely be used around the exterior perimeter walls. Per discussion with the City staff, the zoning designation PD-114R S-7 will require 80% masonry and no stucco will be allowed. The roof will be designed either as a pitched standing seam metal roof or a low slope modified bitumen roof. All occupied areas of the building will be designed to conform to the current International Energy Conservation Code (IECC) requirements for envelope, lighting and mechanical, and therefore will likely need perimeter studs filled with insulation along with extra insulation on the underside of the roof deck in the occupied areas. The 2012 International Building and Plumbing Code requires one water closet, one lavatory in a toilet room and allows for a single uni-sex toilet room for occupancy under 15. This will need to be confirmed during design by a local building official since some Cities have an amendment that requires a minimum of one for each sex. Screening walls (6-8 feet high) will be required per City development code. However this will be 8 feet per TCEQ as a minimum of 8 feet is required to avoid a barbed wire topping. The City requires this to be double width masonry or CMU with a brick or stone veneer. No split face CMU is allowed for the screen wall per development standards. Landscaping, in the form of trees and shrubs, shall be used to break up long continuous lengths of wall. In general, a minimum of 15 percent of the wall elevation should be screened with vegetation. Off street parking will be required at one space per 300 square feet for office space and one space per 1,000 square feet for the storage/industrial area. One (1) accessible parking space and access aisle will be required. All off-street parking areas for nonresidential uses in a nonresidential district which is used after dark, shall be illuminated beginning one-half hour after sunset and continuing throughout the hours of use or until midnight, whichever is earlier. In case only a portion of a parking area is offered for use after dark, only that part is required to be illuminated in accordance with these standards. However, the portion offered for use shall be clearly designated. No intermittent or flashing lights are permitted.   Technical Memorandum (Task 1 – Site Study) Page 4 of 5 Site plan submittal will be required for review and approval from the Design Review Committee, then Planning and Zoning, as well as City Council. The site may also require a replat. ANTICIPATED GEOLOGIC CONDITIONS  The Starleaf Pump Station and Ground Storage Facility is proposed along Starleaf Street, east of MacArthur Boulevard in Coppell, Texas. Reed Engineering Group has experience with projects adjacent to this site (Exhibit 4). Information about the adjacent sites and the anticipated geologic conditions for the proposed Starleaf site are provided below. Church Property at the Corner of Starleaf Street and MacArthur Boulevard  Reed Engineering Group performed a site investigation for the Church of the Apostles site located at the corner of Starleaf Street and MacArthur Boulevard in September, 1996. The subsurface conditions consisted of terraced and recent alluvial soil overlying the Cretaceous Eagle Ford Formation. Recent alluvial soil associated with Holocene deposition in the floodplain of the Elm Fork Trinity River were encountered. These deposits consisted of low plasticity sandy clay and extended to the 30-foot termination depth of the borings. The sandy clay was overlain by eight feet of high plasticity clay fill with a trace of gravel and sandy clay. One of the borings encountered terraced alluvial soil associated with Pleistocene deposition in the former floodplain of the Elm Fork Trinity River and its tributaries. The terrace deposits consisted of 1-1/2 feet of high plasticity clay overlying low plasticity sandy clay. Low plasticity clayey sand was encountered below 13-1/2 feet, grading into dense, gravelly sand and gravel with increasing depth. The terrace deposits extended to a depth of 20-1/2 feet and were underlain by severely weathered shale. Dark gray, unweathered shale was encountered below 21 feet and extended through the termination depth of the boring. Groundwater was encountered during drilling at depths of eight to nine feet (approx. Elev. 438 to 441). Groundwater had risen to within three to six feet of the surface at completion of drilling, and to within one foot of the ground surface after two days. The groundwater is perched above the unweathered Eagle Ford shale within the overlying alluvial soil. There appears to be a slightly descending groundwater gradient to the east, toward the Elm Fork Trinity River. The depth to groundwater will fluctuate with variations in seasonal and yearly rainfall. Rehabilitation Facility on Sandy Lake Road, Northeast of Starleaf Site  Reed Engineering Group performed a site investigation for a rehabilitation facility located on Sandy Lake Road, northeast of the Starleaf site in December, 2011. The subsurface conditions consisted of fill overlying Holocene alluvial soil, overlying weathered shale of the Cretaceous Eagle Ford Formation. The alluvial soil encountered below the fill consisted of high to moderate plasticity (CH to CL) clay and sandy clay containing varying amounts of sand and gravel. The alluvial soil extended through the termination depths of all the deeper borings except for one boring. One boring encountered dark gray and olive, hard, fissile, weathered shale below the alluvial soil at a depth of 23-1/2 feet and extended through the 25-foot termination depth of the boring.   Technical Memorandum (Task 1 – Site Study) Page 5 of 5 Groundwater seepage was encountered during drilling at a depth of 12-1/2 feet in one boring. Based on post-drilling observations, groundwater was present at depths of 12-1/2 to 24 feet in November-December 2011. The groundwater was perched within the alluvial soil above the relatively impermeable, unweathered shale (not encountered in the borings). The depth to groundwater will fluctuate with variations in seasonal and yearly rainfall. Anticipated Geologic Conditions Summary   Subsurface conditions in the area of the project are anticipated to consist of fill and Holocene alluvial soil overlying unweathered shale of the Cretaceous Eagle Ford Formation. The alluvial soil in the area typically consist of high plasticity clay grading with depth into clayey sand and sandy clay with some coarse sand and fine gravel at the base. The alluvial soil is anticipated to extend to depths of about 25 to 30 feet. Historical aerial photographs show that a detention pond was present on the southern portion of the site, south of Starleaf Street, in 2001. Later aerial photographs indicate that the pond was backfilled with soil to match adjacent grades. Unweathered shale is anticipated below the alluvial soil at depths of approximately 25 to 30 feet. Due to the potential for seasonal movement of the alluvial soil, it is anticipated that remedial earthwork will be required to allow the proposed ground storage tank and pump station to be constructed with a ground supported slab. The type of foundation for structures will be dependent on the tank and building configuration and site specific soil. REFERENCES  1. RG-195 70, Revised June 2012, Title 30, Texas Administrative Code (30 TAC), Chapter 290, Subchapter D: Rules and Regulations for Public Water Systems 2. Federal Emergency Management Agency, Flood Insurance Rate Map, Number 48113C0155K, Revised July 2014 3. USACE Inundation Mapping, Elm Fork Trinity River Downstream of Lewisville Lake, May 2015 Brown & Gay Engineers, Inc. Tel: 972-464-4800 Ɣ www.browngay.com STARLEAF PUMP STATION STUDY Brown & Gay Engineers, Inc. Tel: 972-464-4800 Ɣ www.browngay.com STARLEAF PUMP STATION STUDY Brown & Gay Engineers, Inc. Tel: 972-464-4800 Ɣ www.browngay.com STARLEAF PUMP STATION STUDY PLATE 1Proposed Starleaf Pump Station SiteCoppell, TexasGEOLOGIC MAPENVIRONMENTAL CONSULTANTSGEOTECHNICAL ANDGROUPENGINEERINGREEDNOT TO SCALE:CHURCH SITEPROPOSEDSTARLEAF SITEREHAB SITE