Environmental Setting May 2007 species, including the bald eagle (Haliaeetus leucocephalus), wood stork (Mycteria americana), and timber/canebrake rattlesnake (Crotalus horridus) exist within the proposed DART Rail to Rowlett Corridor. The USFWS Arlington Field Office was contacted to verify known occurrences of threatened or endangered species within the proposed DART Rail to Rowlett Corridor (personal communication, June 9, 2006). According to the agency, no known occurrences of any of the listed species are documented within the proposed DART Rail to Rowlett Corridor. In addition, no threatened or endangered species were detected during the site reconnaissance.
2.7 Water Resources and Floodplains
2.7.1 Water Resources
Surface Waters
The DART Rail to Rowlett Corridor primarily lies within a portion of the Trinity River Basin which receives an average of 30 to 40 inches of rainfall per year (TPWD 2004). The Trinity River Basin has the largest population of any river basin in Texas. It includes parts of 34 counties and has a total drainage area of 17,969 square miles. This includes the DFW region, which encompasses more than five million people (USCB 2000). There are ten major reservoirs within the basin including Lavon Lake and Lake Ray Hubbard on the East Fork and eleven other reservoirs on the smaller tributaries, most of which are located in the DFW region (Texas Council on Environmental Quality [TCEQ] 2007).
Surface water flow in the proposed DART Rail to Rowlett Corridor is generally to the east- southeast. The proposed DART Rail to Rowlett Corridor lies north-northwest of Lake Ray Hubbard. Lake Ray Hubbard, an impoundment of the East Fork of the Trinity River, and its tributaries are the major surface waters found in northeastern Dallas County. Among these tributaries are Mills Branch, Rowlett Creek, and Longbranch Creek. From west to east, the proposed DART Rail to Rowlett Alignment passes through the floodplain of Mills Branch, which parallels the proposed DART Rail to Rowlett Alignment to the south; crosses a tributary of Rowlett Creek; crosses Rowlett Creek, the largest creek in the area; crosses two additional smaller tributaries of Rowlett Creek; and crosses Longbranch Creek, just before entering downtown Rowlett.
The majority of surface water runoff in the DART Rail to Rowlett Corridor would be intercepted by either storm water drains or surface waters and carried to Lake Ray Hubbard. Descriptions of the surface waters intersected by the proposed DART Rail to Rowlett Alignment are provided below.
• Mills Branch Tributary: This tributary is an intermittent stream with an average Ordinary High Water Mark (OHWM) of 13 feet that is culverted under the existing rail. The stream originates just north of the existing rail and flows to the southeast, emptying into Rowlett Creek. Vegetation mainly consists of black willow (Salix nigra), hackberry (Celtis laevigata), American elm (Ulmus americana), Texas swampprivet (Forestiera angustifolia), and roughleaf dogwood (Cornus drummondii). The bottom of the channel is bedrock with no emergent or edge vegetation within the OHWM. During the time of the
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field survey, the channel was dry except for a small ponded area at the outfall, south of the existing rail.
• Rowlett Creek Floodplain Tributary #1: This is a stream located approximately 1,300 feet west of the main branch of Rowlett Creek within its 100-year floodplain, just east of the DORBA trail. This water originates just south of SH 66 and empties into Mills Branch before connecting with Rowlett Creek. This water is perennial south of the existing rail, but exhibits intermittent characteristics upstream where it has an OHWM of 16 feet. The portion of the creek that crosses under the existing rail has an OHWM of 130 feet as the tributary is ponded at this location (0.19 acre). Four emergent wetlands associated with this water were delineated, three adjacent and one in-channel. Vegetation within these wetlands consists mainly of swamp smartweed (Polygonum hydropiperoides), balloonvine (Cardiospermum halicacabum), ragweed (Ambrosia artemisifolia), and black willow. A bottomland hardwood system surrounds these waters and contains species such as green ash (Fraxinus pennsylvanica), American elm, sugar hackberry, poison ivy and Indian woodoats (Chasmanthium latifolium).
• Rowlett Creek: The creek is a perennial creek that crosses the proposed DART Rail to Rowlett Alignment approximately 0.5 miles east of Centerville Road. The creek originates in west central Collin County and flows south into Lake Ray Hubbard. The creek is characterized by steep banks with exposed roots. The OHWM of this stream as it crosses under the existing rail is 88 feet. Adjacent vegetation lies within a bottomland hardwood system and consists of pecan (Carya illinoinensis), American elm, hackberry, cottonwood (Populus sp.), poison ivy (Toxicodendron radicans), barley (Hordeum vulgare), ragweed, saw greenbrier (Smilax bona-nox), and chinaberry (Melia azedarach).
• Rowlett Creek Floodplain Tributary #2: This is a stream located approximately 800 feet east of the main branch of Rowlett Creek within the 100-year floodplain. It originates just north of SH 66 and flows south into the western reach of Lake Ray Hubbard. This water is perennial south of the existing rail, which is bridged over this crossing, but exhibits intermittent characteristics upstream where it has an OHWM of 15 feet. The OHWM at the rail crossing is 112 feet where the water is ponded (0.24 acre) with a small island located near the east bank. A small (0.0003 acre), emergent wetland exists in- channel as the ponded area narrows to an intermittent stream, north of the existing rail. Around the ponded area, the banks of the water rise steeply from the water, and vegetation located above the OHWM is within a bottomland hardwood system and includes ragweed, poison ivy, annual marshelder (Iva annual), saw greenbrier, balloonvine, cedar elm (Ulmus crassifolia), and pecan.
• Rowlett Creek Floodplain Tributary #3: This is a stream located approximately 630 feet west of Dexham Road within the Rowlett Creek 100-year floodplain. This water begins as an ephemeral drainage north of the existing rail and exhibits intermittent characteristics south of the rail where it flows west and connects with Rowlett Creek Floodplain Tributary #2. The tributary has an average OHWM of 9 feet and is culverted under the existing rail. Existing vegetation along the banks of this stream include
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ragweed, saw greenbrier, black willow, green ash, poison ivy, American elm, and sugar hackberry.
• Longbranch Creek: This is an intermittent stream located at the intersection of Main Street and the existing rail with an average OHWM of 22 feet. This creek originates approximately 0.37 miles north of SH 66 and flows southeast into Lake Ray Hubbard. Within the project area, the water crosses the proposed DART Rail to Rowlett Alignment through a pipe that extends under Main Street and outfalls just south of the roadway. North of the existing rail during the field survey, the channel was dry and heavily impacted by trash and debris. Vegetation existing at this creek included roughleaf dogwood, Johnson grass, pecan, American elm, box elder, green briar and Chinese privet.
Table 2-25 provides current designated use and impairment information for some of the larger water bodies near the proposed DART Rail to Rowlett Corridor, namely Muddy Creek and Lake Ray Hubbard, which are tracked by the TCEQ.
Table 2-25: Summary of Surface Waters Identified by TCEQ Designated Use Impaired Water Summary Segment Domestic Parameter Segment # Aquatic Pollution Name Recreation Water Priority of Life Source* Supply Concern Public Lake Ray Contact 0820 High Water ------Hubbard Recreation Supply Bacteria levels sometimes exceed the Muddy Contact criterion 0820C High --- Low PS, NPS Creek Recreation established to assure the safety of contact recreation. Source: TCEQ, 2005 Note: *PS – Point Source; NPS – Nonpoint Source
Designated uses for water bodies are defined by the TCEQ as required by the CWA. Muddy Creek (Segment 0820C), which is located approximately two miles northeast of the proposed DART Downtown Rowlett LRT Station, has been designated for contact recreation and high aquatic life use. Lake Ray Hubbard (Segment 0820), which is located approximately one mile east of the proposed DART Downtown Rowlett LRT Station, has been designated for contact recreation, high aquatic life use, and domestic water supply, as well as fish consumption.
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Contact recreation use is determined by measurements of three organisms including elevated fecal coliform, E. Coli (freshwater), and Enterococci (tidal water) bacteria levels. Aquatic life use designation is based on assessment of dissolved oxygen criteria, toxic substances, ambient water and sediment toxicity, and characteristics such as desired use, sensitivity of aquatic communities, and local physical, chemical, and biological characteristics. Domestic water supply use is designated for all sections used as the supply source for public water systems (TCEQ 2003). Lavon Lake is the primary municipal water source for the cities of Garland and Rowlett.
The Texas 2004 CWA Section 303(d) list identifies Muddy Creek (Segment 0820C) as an impaired water body, not meeting the water quality standards as required by Section 303(d) of the CWA (TCEQ 2005). The primary water quality issues for surface water in the Trinity River Basin are effluents from large municipal WWTP in the DFW region and stormwater runoff from urbanized areas (TCEQ 2007). Surface water issues relating to nonpoint source (NPS) pollution and impairment of water quality include runoff that picks up pollutants from soils, vegetation, roadways, parking lots, etc., and carries them to streams or infiltrates into the groundwater. Water quality issues associated with NPS pollution include reductions in dissolved oxygen and increases in nutrients, fecal coliform, metals, elevated temperature, and algal growth. The proposed DART Rail to Rowlett Alignment is south of Muddy Creek and therefore, not within five miles upstream of the impaired waterbody.
Groundwater
Aquifers within the DART Rail to Rowlett Corridor include the Trinity Aquifer, which is the major groundwater aquifer underlying the proposed DART Rail to Rowlett Alignment, and the minor Woodbine Aquifer. The Trinity Aquifer encompasses about 41,000 square miles consisting of 68 counties from the southernmost county in south-central Texas (Kinney County) to the northernmost county in southeastern Oklahoma (McCurtain County). The Woodbine Aquifer follows a north-south direction from McLennan County in north-central Texas north to Cooke County, and east to the Red River (Texas Water Development Board 1999).
The Trinity Aquifer consists of sandstone, sand, silt, clay, conglomerate, limestone dolomite, shale, and marl from the Cretaceous age formations. The formations are the Paluxy, Twin Mountains (formerly Travis Peak), Antlers (resulting from the coalescence of the Paluxy and Twin Mountains), and the Woodbine formation (Nordstrom 1982). The Paluxy is the upper formation around DFW and consists of 400 feet of predominantly fine to coarse-grained sand interbedded with clay and shale (Ashworth and Hopkins 1995; Eckhardt 2003). The Twin Mountains formation consists of medium to coarse-grained sands, silty clays, and conglomerates and is the most prolific of the Trinity aquifers in north-central Texas even though the water quality is poor compared to the Paluxy formation. The Antlers formation consists of up to 900 feet of sand, gravel, limestone, and clay beds, and the Woodbine consists of shale and clay. As a result of the aquifer being made up of fine-grained, clayey, and locally cemented materials, its transmissivity is low (Ryder 1996). The Trinity Aquifer recharges very slowly. Only four to five percent of the water that falls as rain over the area ends up recharging the Trinity Aquifer (Eckhardt 2003).
The Trinity Aquifer has had water-level declines of several hundred feet in east-central and northeast Texas, Dallas County and several other neighboring counties. Low permeability and ______
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2.7.2 Floodplains
The 100-year floodplain is defined as the area that would be inundated by the level of flooding which has a one percent chance of occurring in a given year. Table 2-26 shows areas in which the proposed DART Rail to Rowlett Alignment encroaches on or crosses the 100-year floodplain. The table also highlights several areas where the alignment is adjacent to the 100- year floodplain. Figure 2-24 displays the areas that may be potentially flooded along the alignment according to the Federal Emergency Management Agency (FEMA) Flood Insurance Rate Maps.
Table 2-26: Floodplain Locations Water Feature Location Length Mills Branch MKT between downtown ~6,250 feet (parallels the Tributary Garland and Centerville Road existing rail) MKT between Centerville Road Rowlett Creek ~2,600 feet and Dexham Road MKT at Main Street, west of Longbranch Creek ~700 feet Rowlett Road Source: FEMA, 2006
The 1988 Spring Creek and Rowlett Creek Floodplain Management Study was referenced to determine the existing conditions of the Rowlett Creek floodplain. The study served as a guide for the local Floodplain Administrator to prepare for the future development of the Rowlett and Spring Creek watershed areas in the City of Garland. The actual determination of floodplain status was based on the current FEMA floodplain maps. The goal of the study was to determine and evaluate alternative floodplain management methods and recommend a comprehensive floodplain management plan for Rowlett Creek and Spring Creek in the City of Garland. The management plan is used by the City of Garland, landowners, developers, planners, and engineers to coordinate development along the creeks. Rowlett Creek connects to Spring Creek downstream from the proposed DART Rail to Rowlett Corridor. Therefore, only information on the Rowlett Creek floodplain from the Floodplain Management Study was analyzed for the proposed DART Rail to Rowlett LEA.
The limits of Rowlett Creek for the purposes of the Floodplain Management Study were from Miller Road in southeast Garland, near the confluence of Rowlett Creek with Lake Ray Hubbard, to the city limits of Richardson just upstream of Blackburn Road. The headwaters of Rowlett ______
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Lake Ray Hubbard Proposed Downtown Rowlett Station
Existing Downtown Garland Station Figure 2-24 DART LRT Northeast Corridor
Floodplains DART Rail to Rowlett 0 1,000 2,000 DART Rail to Rowlett LEA Feet Data Source: Aerials - NCTCOG, 2003; Floodplain - FEMA, 1996. Environmental Setting May 2007
Creek lie near Frisco, Texas north of State Highway 121. The creek flows south to its confluence with the East Fork of the Trinity River at Lake Ray Hubbard. The Rowlett Creek watershed has a total drainage area of 139 square miles at Lake Ray Hubbard and is approximately 23 miles long and eight miles wide. The main stem has a length of 26.4 miles above Miller Road. The channel has been straightened from the lake to a point about 0.5 miles downstream of Ben Davis Road. A portion of this straightened channel is within the DART Rail to Rowlett Study Area. This portion of the channel is small, but the floodplain is broad and flat, varying from 1,700 to 5,000 feet in width. Parts of the floodplain are extensively wooded, while others have been reclaimed for residential development. According to the floodplain management study, during a 100-year flood event, the MKT railroad within the project area that crosses the Rowlett Creek floodplain is severely and relatively frequently inundated. The railroad is overtopped by 5.6 feet by the 100-year water surface elevation.
2.8 Noise and Vibration
2.8.1 Noise Methodology
Noise is typically defined as unwanted or undesirable sound, where sound is characterized by small air pressure fluctuations above and below the atmospheric pressure. The basic parameters of environmental noise that affect human subjective response are • Intensity or level • Frequency content • Variation with time The first parameter is determined by how greatly the sound pressure fluctuates above and below the atmospheric pressure and is expressed on a compressed scale in units of decibels (dB). By using this scale, the range of normally encountered sound can be expressed by values between zero and 120 dB. On a relative basis, a 3-decibel change in sound level generally represents a barely noticeable change outside the laboratory, whereas a 10-dB change in sound level would typically be perceived as a doubling (or halving) in the loudness of a sound.
The frequency content of noise is related to the tone or pitch of the sound and is expressed based on the rate of the air pressure fluctuation in terms of cycles per second (Hz). The human ear can detect a wide range of frequencies from about 20 Hz to 17,000 Hz. However, because the sensitivity of human hearing varies with frequency, the A-weighting system is commonly used when measuring environmental noise to provide a single number descriptor that correlates with human subjective response. Sound levels measured using this weighting system are called “A-weighted” sound levels and are expressed in dB notation as “dBA.” The dBA is widely accepted by acousticians as a proper unit for describing environmental noise.
Because environmental noise fluctuates from moment to moment, it is common practice to condense all of this information into a single number, called the equivalent sound level (Leq). Leq can be thought of as the steady sound level that represents the same sound energy as the varying sound levels over a specified time period (typically one hour or 24 hours). Often the Leq values over a 24-hour period are used to calculate cumulative noise exposure in terms of the Day-Night Sound Level (Ldn). Ldn is the A-weighed Leq for a 24-hour period with an added 10- ______
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