4.1 INTRODUCTION

Information discussed in this chapter has been collected from several sources, including, but not limited to, the following:

• 1990 US Census Data
• Douglas County Master Plan, 1997
• Douglas County Parks, Trails and Open Space Master Plan, 1998
• Douglas County 2015 Transportation Plan
• Douglas County Master Plan Land Use Map, September 2000
• Douglas County Zone District Map, April 2000
• Douglas County Population and Development Report, 1999
• Colorado Department of Labor and Employment, December 1999
• I-25 and US 85 Environmental Surveys and Studies, Sugnet & Assoc, 1998
• Castle Rock Town Wide Transportation Plan, 1994
• State Highway 85 Environmental Assessment: C-470 to I-25 at Castle Rock, 1994
• Colorado State Parks: Chatfield Web Site, 2000
• Town of Castle Rock Generalized Zoning Map, October 2000
• Chatfield Reservoir Clean Lakes Study, 1984
• Historic Resources Technical Report, May 2000

This chapter discusses the existing social, economic, and physical environment of the I-25 Corridor and US 85 Corridor. The project limits along I-25 are from C-470 to Douglas Lane and along US 85 from C-470 to Meadows Parkway.

4.2 SOCIOECONOMICS

Socioeconomics information was obtained from the Douglas County Population and Development Report, 1999, which provides current and forecasted population estimates and income. Information from the US Census Bureau and the Douglas County Master Plan, 1997 provided supplemental data.

Douglas County has had substantial population growth and development during the past 20 years, and has had the distinction of being the fastest growing county in the United States. In the late 1970s, Douglas County, including Castle Rock and the project corridors, was a rural county with approximately 12,000 residents. In 1998 Douglas County had a population of more than 150,000 and the second highest per capita and median family income of all 63 counties in Colorado.

For additional information on socioeconomics, see the Socioeconomic Technical Memorandum South I-25 Corridor and US 85 Corridor, May 2000, amended November 2000, in the Technical Reports Volume of the South I-25 Corridor and US 85 Corridor FEIS.

4.2.1 Demographics

According to figures from the Douglas County Population and Development Report, 1999, the county’s population was estimated at 221,774 for the low-growth scenario and 248,184 for the moderate-growth scenario in the year 2005. The two growth scenarios provide the envelope for the projected growth. Table 4.1 shows the projected growth rate for the county from 2005 to 2020. The 2005 population estimates represent a 260 percent increase for the low-growth scenario and a 304 percent increase for the moderate-growth scenario over the 1990 census, projecting Douglas County to be one of the nation’s fastest growing counties during that period.

In 2010 there is a projected population increase from the year 2005 of an additional 23 percent for the low-growth scenario and an additional 25 percent for the moderate-growth scenario. In 2020 there is projected population increase from the year 2010 of an additional 31 percent for the low-growth scenario and an additional 25 percent for the moderate-growth scenario.

The Town of Castle Rock has a current population of 18,000, based on town figures from March 1999. Table 4.2 shows the 1999 average labor force in Douglas County.

The median age of the Douglas County population on January 1, 1997, was 33.2 years, with 5.7 percent of the population being 60 years and older, and 18.3 percent being under 10 years and under.

4.2.2 Environmental Justice

In February 1994 President Clinton issued Executive Order 12898 requiring federal agencies to incorporate consideration of environmental justice into the National Environmental Policy Act (NEPA) evaluation process. The purpose of the order is to ensure that minority communities and low-income communities do not suffer a disproportionate share of adverse environmental impacts resulting from federal actions that are not offset by project benefits. The order also requires that these parties have had adequate access to and opportunity for participation in project planning.

4.2.2.1 Minority Populations

The United States Department of Transportation (USDOT) defines minorities in its guidelines on implementation of the Environmental Justice Order, to be persons who are (1) Black (a person having origins in any of the black racial groups of Africa); (2) Hispanic (a person of Mexican, Puerto Rican, Cuban, Central or South American, or other Spanish culture or origin, regardless of race); (3) Asian American (a person having origins in any of the original peoples of the Far East, Southeast Asia, the Indian subcontinent, or the Pacific Islands); or (4) American Indian and Alaskan Native (a person having origins in any of the original people of North America and who maintains cultural identification through tribal affiliation or community recognition).

In 1990 the US Census determined the racial composition of Douglas County. As shown on Table 4.3, minority populations represent a much smaller percentage of the county population than is typical for the State of Colorado. Colorado’s minorities represent 19.1 percent of the state’s population. In contrast, minorities comprise only 5.2 percent of the Douglas County population.

Figure 4.1a and Figure 4.1b illustrate the distribution of minority and Hispanic populations within Douglas County. Due to Census data limitations, maps depicting the geographic distribution of total minority populations are not available. As Figure 4.1a and Figure 4.1b indicate, percentages of minorities tend to be slightly higher along C-470 and within the US 85 Corridor. The area is characterized by slightly higher concentrations of minority residents to the west of I-25 and slightly higher levels of Hispanics to the east.

4.2.2.2 Income

Per capita income in Douglas County has more than doubled since the early 1980s. Table 4.4 shows the increase in the per capita income for Douglas County over the last several years.

4.2.2.3 Low Income Populations

The USDOT draft guideline addressing the Environmental Justice Order defines low income as "...a person whose median household income is below the US Department of Health and Human Services (HHS) poverty guidelines." These guidelines provide a formula based on the number of persons in a household or family and their annual income. The US Census provides population data based on these guidelines.

According to the State of Colorado, 1997 Douglas County per capita income was $34,264. This represents a 38 percent increase over the 1990 level of $24,740. In comparison, the annual per capita income for the area has traditionally been characterized by high per capita income, and recent increases in population have corresponded with higher incomes.

The 2000 national poverty level, according to HHS, was reported to be $17,050 per family. The median family income and per capita income for the residents of Douglas County was reported to be $77,000 and $34,264, respectively, by the Colorado Department of Labor and Employment in 1997. Table 4.5 provides the Douglas County poverty level as compared to the State of Colorado.

Figure 4.1c illustrates the distribution of individuals living below poverty levels in 1990. Concentrations of people living in poverty are slightly higher along the US 85 Corridor and to the east of I-25. As Figure 4.1d illustrates, median incomes are highest to the west of I-25 and in areas along State Highway (SH) 83 in eastern portions of the county.

4.2.3 Lifestyle

Residents adjacent to I-25 between Lincoln Avenue and the Town of Castle Rock enjoy a semi-rural lifestyle. The only commercial development in this section is residential-supported (e.g., grocery stores and service stations). Homes are situated on large lots, with golf courses within short driving distance. Employment for residents in this area is primarily to the north in the Denver metropolitan area. Commuters going to and from the employment centers in the South East Business District (SEBD) and downtown Denver use I-25.

The Town of Castle Rock continues to maintain a small town ambiance while incorporating a growing low-density suburban fringe. Employment opportunities exist in the town in retail and in county government services. Castle Rock, the small communities along US 85, and residential areas along both corridors serve as bedroom communities for the Denver metropolitan region and to Colorado Springs to the south. Commuters use both I-25 and US 85 as their primary routes to work.

The east side of the US 85 Corridor is lined with large, open space areas and large ranches. The west side of the corridor has two communities, Sedalia and Louviers. US 85 parallels the Union Pacific Railroad and Burlington Northern Santa Fe Railroad. The west side of US 85 is paralleled by the Plum Creek floodplain that passes through a low-density developed area. The northern half of the US 85 Corridor is in close proximity to segments of strip commercial development and heavy industrial development.

The Douglas County Master Plan states that no additional urban development (beyond what is already approved) is planned in the valley, west of US 85, within the 2010 timeframe because of the existing inventory of approved development, and the major cost to provide infrastructure and service to this area.

4.2.4 Neighborhoods

Distinct neighborhoods and/or subdivisions are located adjacent to I-25 and US 85. Each of these neighborhoods is confined to one side of the existing highway. There are no neighborhoods or subdivisions that are spilt by the highway.

Along I-25, from the north to south, the following neighborhoods and municipalities currently exist: Surrey Ridge, Oak Hills, Castle Pines North, Castle Pines Villages, Happy Canyon, Silver Heights, Castle Rock, Yucca Hills, Twin Oaks and Bell Mountain Ranch. Along US 85, from the north to the south, the following neighborhoods and municipalities currently exist; Highlands Ranch, Chatfield Acres/Chatfield East, Louviers, and Sedalia. Table 4.6 displays information about these neighborhoods in terms of location and size.

Many of these neighborhoods are considered rural or large lot neighborhoods, and have a significantly lower density than neighborhoods such as Highlands Ranch. These neighborhoods include Surrey Ridge, Oak Hills, Castle Pines Villages, Happy Canyon, Yucca Hills, Twin Oaks, Bell Mountain Ranch, and Chatfield East.

For planning purposes, Douglas County has identified incorporated towns and municipalities, primary urban areas and subareas of growth, defined with boundaries. Within the confines of this project, only the Town of Castle Rock is considered a municipality and Highlands Ranch is part of the Primary Urban Area. Subareas in the project include the Chatfield Valley Subarea, High Plateau Subarea, the Castle Pines Subarea, West Plum Creek Subarea and the Cherry Valley Subarea. The specific neighborhoods in these subareas that are adjacent to either I-25 or US 85 are included in the table above.

4.2.5 Economics

Douglas County is strategically located between Colorado’s two largest cities, Denver and Colorado Springs. The county actively plans for, and pursues, well-managed, quality commercial development to provide local employment opportunities and to diversify its tax base. The county’s strength as the centerpiece of the Denver/Colorado Springs Development Corridor comes from a blend of quality lifestyle and business environment.

4.2.6 Development

Douglas County continues to undergo rapid growth in both population and construction. Total building permit value rose 18.5 percent in 1998, with commercial construction value up a phenomenal 59 percent. New housing starts were down slightly (2 percent) from the 1997 all-time high, attributable to a high number of apartment starts in 1997. Unincorporated Douglas County’s single-family unit permits were up nearly 8 percent in 1998.

Building trends have been consistent for many years in Douglas County. The total number of residences by the end of 1999 totaled 60,502, an 11.2 percent increase over 1998. Since 1993, Douglas County has experienced housing growth rates more than 10 percent every year. Over 21 hectares (52 acres) of new commercial construction began in unincorporated Douglas County in 1999. Employment in the County has increased 268 percent since 1990.

To serve the growing population, retail growth has been explosive, with more than 278,710 square meters (3 million square feet) built in recent years. Just north of the I-25 Corridor, Park Meadows Town Center opened in Douglas County in August 1996, bringing scores of new retail shops to the area. Surrounding the mall, numerous complementary stores have opened. In 1997 Prime Outlets along I-25 at the Meadow/Founders Interchange completed a 9,290 square-meter (100,000 square-foot) expansion.

The county continues to seek quality commercial development. 1996 was a record year for commercial development, and included the start of the Merrill Lynch business campus, the 139,350 square-meter (1.5 million-square-foot) Park Meadows Town Center, and adjacent retail power centers. 1997 saw continued expansion of the Park Meadows Town Center and power centers, as well as office development along the northern I-25 Corridor.

Commercial development for 1998 focused on the Meridian International Business Center, with the new AT&T Cable Services, American Family Insurance headquarters, and First Data Corporation headquarters. In total, more than 185,810 square meters (2 million square feet) of commercial development occurred in the county in 1998. With commercial development proceeding, in 1999 the SEBD emphasized the development of 1,500 dwelling units for local employees earning less than the county’s median family income level.

The County is actively planning to preserve quality of life through planning and zoning. The preservation of open space is a critical component in maintaining quality of life and quality of environment. The county has been aggressive in purchasing open space and conservation easements, particularly along the I-25 Corridor and the US 85 Corridor. The county has a goal of protecting areas of visual significance and of wildlife habitat to preserve the quality of life for the residents and to protect the image and identity of Douglas County. Several studies have been conducted on this issue, including the High Plateau Conservation Area Study and the Douglas County Open Space Plan. These plans will aid in managing of growth and development. Large areas recently purchased or acquired in the program include the Cherokee Ranch along US 85 and the Greenland Ranch near Larkspur. Additionally, 3,320 hectares (8,200 acres) south of the developed portion of Highlands Ranch was planned by Mission Viejo for open space and recreation at the inception of the Highlands Ranch Development. The county supports planning for Open Space Conservation Area (OSCA) to ensure its preservation.

4.2.7 Recreation

The rapid population growth in Douglas County creates an increasing demand for recreational facilities, while at the same time depleting the available land for recreation areas. To maintain the area’s natural environment, local, state, and federal agencies, as well as community volunteers and organizations, are working together to retain recreation areas, trails, and open space throughout the county.

I-25 and US 85, between C-470 and Castle Rock, provide access to many popular recreation areas adjacent to and beyond the project area. These recreation areas include Pike National Forest, Chatfield State Park, Spring Gulch Equestrian Facility, Roxborough State Park, and Daniel’s Park as well as other county, municipal, and local parks and trails. In addition, several public golf courses are close to the project area. These recreation areas are shown on Figure 4.2a and Figure 4.2b. Open space properties exist within the project area, but are not open to public recreation. For the purpose of this section, only trails and recreation areas adjacent to, or within the project area, are reviewed in detail; they are listed in Table 4.7 and illustrated in Figure 4.2c and Figure 4.2d.

For additional information on recreation, see the Recreation Technical Report, May 2000, amended November 2000, in the Technical Reports Volume of the South I-25 Corridor and US 85 Corridor FEIS.

4.2.7.1 Hiking/Bike Trails

Hiking and biking are popular activities in Douglas County. Governmental agencies, private citizens, and local organizations have attempted to preserve and improve existing trails, as well as plan for future trails in the area. The Douglas County Parks, Trails and Open Space Master Plan, 1998 provides a design for future interconnected trails throughout the project area.

In addition, other agencies and organizations including Chatfield Basin Conservation Network, Colorado State Parks, US Army Corp of Engineers (USACE), Highlands Ranch Metropolitan District, Denver Water Board, and South Suburban Park and Recreation District have set similar goals to improve existing trails and increase the number of interconnecting trails within the area.

Currently, four maintained trails exist within the project area: East Plum Creek Trail, Front Street Trail, Centennial Bike Trail, and High Line Canal Trail.

• East Plum Creek Trail in Castle Rock is a multi-use, paved trail extending south from Wolfensberger Road for approximately 0.9 kilometer (0.6 mile) along East Plum Creek on the west side of I-25. The trail crosses beneath I-25 at Third Street and continues southeast to the Douglas County Fairgrounds. Future Douglas County plans will extend the trail to the west through Plum Creek Valley to Titan Road.
• Front Street Trail in Castle Rock is a multi-use trail extending along the west side of Front Street for approximately 1.9 kilometers (1.2 miles). A short segment of the trail, directly south of the Liggett Road overpass on I-25, is within the project area.
• Centennial Bike Trail is paved and publicly owned. It is a multi-use trail extending approximately 40 kilometers (25 miles) along C-470 from Belleview Avenue to near the Town of Parker. The trail crosses US 85 at-grade immediately south of the US 85/C-470 Interchange. A spur of the trail also extends southwest from the main trail, ending on the east side of US 85 at approximately milepost (MP) 200. The Centennial Bike Trail also crosses the northern terminus of the I-25 Corridor at C-470.
• High Line Canal Trail is approximately 120 kilometers (75 miles) long, and runs alongside the High Line Canal. It includes both paved and unpaved segments and is used for walking, running, biking, and horseback riding. The trail crosses US 85 at-grade approximately 1.1 kilometers (0.7 mile) south of C-470 (approximately MP 199.5.) The trail begins approximately 1.6 kilometers (1.0 mile) south of Highlands Ranch Parkway, extending to I-70 and Tower Road.

In addition to the above four trails, Highlands Ranch Metro Districts, Douglas County, Chatfield State Park, Denver Water Department, and South Suburban Park and Recreation District maintain a series of trails in Douglas County that are outside the US 85 right-of-way (ROW). These groups and the Chatfield Basin Conservation Network are in the process of developing a trail plan that includes existing trail locations and identifies new trails and trail connections.

4.2.7.2 Recreation Areas

Four recreation areas are adjacent to or within the project area: Castle Rock Baseball Fields and Park Complex, Chatfield State Park, Spring Gulch Equestrian Facility, and Chatfield East Park. Each area offers unique recreational activities to the general public.

• Castle Rock Baseball Fields and Park Complex, located on the east side of I-25 in Castle Rock, includes approximately 17.4 hectares (43.0 acres). The park is currently under construction and is adjacent to a future middle school site. When completed, the park will have four baseball fields, two inline hockey rinks, picnic tables with shelters, a small amphitheater, two playgrounds, a concession stand, and restrooms. The park is owned and maintained by the Town of Castle Rock and is designed for public use.
• Chatfield State Park is located on the west side of US 85. One of two entrances into the park is through Titan Road via US 85. The recreation area includes 2,853 hectares (7,050 acres), of which 2,266 hectares (5,600 acres) is ground surface and 586.8 hectares (1,450 acres) is water surface. Chatfield State Park offers a wide range of recreation opportunities including horseback riding, hiking, biking, camping, picnicking, wildlife viewing, water sports, fishing, and an area specifically designed for flying model airplanes and launching hot air balloons. Nearly 1.5 million people visit the park annually.
• Spring Gulch Equestrian Facility encompasses 42.5 hectares (105.0 acres), and is operated and maintained by Chatfield State Park through a lease with the USACE. In 1999, 8,565 visitors used the facility. The area is open to the public for equestrian training and competition-related activities. Access to the facility is from US 85.
• Chatfield East Park is located on the east side of US 85 at MP 196. The property was dedicated to the Douglas County Commissioners in 1978 by the developers of Chatfield East Subdivision. The property includes approximately 19.8 hectares (49.0 acres). A small playground and a horse arena are on the easternmost part of the property. The remainder of the property is open and undeveloped.

4.2.8 Land Use and Zoning

The study area is undergoing abundant growth and development. Rapid economic development and land use changes can accelerate the need for transportation improvements. The following discussion focuses on the existing conditions for land use and zoning. Land use is defined as how the property is used today. Figure 4.3a and Figure 4.3b show existing land uses in the I-25 Corridor and US 85 Corridor, respectively. This information was taken from the Douglas County Master Plan Land Use Map, September 2000. Zoning reflects the particular development purpose that has been approved by the appropriate governmental entity (Douglas County, Town of Castle Rock, or City of Lone Tree). Zoning information was taken from the Douglas County Zone District Map, April 2000, and the Town of Castle Rock Generalized Zoning Map, October 2000. Denver Regional Council of Governments (DRCOG) developed a comprehensive guide for future development that combines the separate plans for growth, development, transportation, and water quality for the eight-county region served by DRCOG into a single integrated plan. The implementation strategies and how they may affect future land use in this project is discussed in Section 5.3.2.6, Land Use and Zoning Impacts. Figure 4.3c and Figure 4.3d show the zoning in the I-25 Corridor and US 85 Corridor, respectively.

4.2.8.1 I-25 Corridor Land Use and Zoning

Land Use

At the northern limit of the project near Lincoln Avenue, land use is defined as primary urban area; this includes residential in the vicinity of Yosemite, office parks in Meridian, and the currently undeveloped land in Rampart Range. Land use surrounding the Schweiger Interchange is classified as municipal planning area inclusive of county planned developments. Further south along I-25, in the vicinity of Surrey Ridge Road and Castle Pines Parkway, the land use definition changes to predominantly non-urban areas (primarily large ranches or large single-family lots), with some separated urban area (primarily residential). Through Castle Rock, the land use is primary urban service area. South of Castle Rock, the land use reverts to primarily urban area. Heading south, land uses quickly start to thin out from the urban nature of Castle Rock and move more into a rural theme where they are categorized by Douglas County as extended and remote urban service areas, secondary urban service areas, and non-urban areas.

Zoning

The area surrounding the C-470/I-25 Interchange consists of various zoning such as commercial, light industrial, incorporated towns, and planned development. The I-25 Corridor from C-470 to just north of Surrey Ridge Road is zoned as planned development land. The west side of I-25 from Surrey Ridge Road to Castle Pines Parkway is zoned rural residential and estate residential land. The east side is zoned agricultural. The area between Happy Canyon Road and Meadows/Founders Parkway along I-25 is predominantly rural residential and suburban residential. In the Town of Castle Rock between US 85 and 5th Street, the east side of I-25 is predominantly zoned as single-family and multi-family with a public school (Douglas County High School) and open space along Front Street. On the west side of I-25, the area is zoned primarily general and integrated commercial. South of 5th Street to Plum Creek Parkway, the land to the east of I-25 is zoned general and integrated commercial, and land to the west of I-25 is zoned single-family. South of Plum Creek Parkway to Douglas Lane, land is zoned general commercial to the west and business/commercial to the east. At Douglas Lane, land is zoned planned development.

4.2.8.2 US 85 Corridor Land Use and Zoning

Land Use

At the northern limit of the project near C-470, the Douglas County Master Plan Land Use Map, September 2000, depicts primarily urban area (Highlands Ranch) to the east and preserved land (Chatfield State Recreation Area) to the west. This area of Highlands Ranch is currently undergoing development. From just north of Lakeside Drive through the towns of Louviers and Sedalia, land use is primarily non-urban area (large ranches and large single-family lots) on both sides of US 85, along with a substantial number of low-density, general industrial uses. The Douglas County map also lists Louviers and Sedalia as rural town centers. The east side of US 85 in the vicinity of Sedalia has preserved land uses, which cover about 2 miles; this preserved land is part of the Cherokee Ranch. The southern portion of US 85 is shown as a separated urban area near Castle Pines, which is mostly single-family residential. South of that, the land use is shown as urban service area (Town of Castle Rock).

Zoning

The west side of US 85 from C-470 to Highlands Ranch Parkway is zoned general industrial land. West of this industrial area from C-470 to Titan Road is zoned parkland. The east side of US 85 begins as general industrial land at C-470 and continues to Highlands Ranch Parkway. Douglas County has planned development land beginning along the east side of US 85 that becomes estate and rural residential areas until reaching Titan Road. Along both sides of US 85 south of Titan Road to south of Louviers Avenue, zoning is general industrial. Just north of County Road (CR) 16, on the east side of US 85, is an area of rural residential and planned development land. Sedalia and its surroundings are made up of various zoned parcels such as general industrial, rural residential, planned development, agricultural, and business. South of Daniels Park Road is planned development land to the east and agricultural and planned development land to the west. At the southern end of the US 85 Corridor, zoning is comprised of integrated and general commercial to the east and open space to the west.

4.2.9 Applicable Transportation Plans

Transportation plans adopted by governing bodies in the study area include the DRCOG Metro Vision 2020 Plan, the 1999 Regional Transportation Plan (RTP), 1994 Castle Rock Town Wide Transportation Plan and the Douglas County 2015 Transportation Plan. Impacts to each of the plans are outlined in Section 5.3.2.6, Land Use and Zoning Impacts.

DRCOG Metro Vision 2020 Plan

The DRCOG Metro Vision 2020 Plan is the Denver region’s plan for addressing future growth of the metropolitan area. The plan outlines strategies and implementation steps to preserve the region’s quality of life while also positioning the region to benefit from growth. The plan is organized around six core elements addressing the development pattern of the region, the necessary transportation system, and the actions needed to preserve air quality and water quality. The six core elements are:

• Extent of urban development
• Open space
• Free-standing communities
• Balanced/multi-modal transportation system
• Urban centers
• Environmental quality

Regional Transportation Plan

The RTP is the fiscally constrained version of the DRCOG Metro Vision 2020 Plan. It includes those elements of the Metro Vision that can be provided through the year 2020, based on reasonably expected revenues.

Elements included in the DRCOG RTP along the I-25 Corridor include:

• Eight lanes from C-470 to Meadows/Founders Parkway
• Six lanes from Meadows/Founders Parkway to MP 178
• Car pool lot

Elements included in the DRCOG RTP along the US 85 Corridor include:

• Six lanes from C-470 to Highlands Ranch Parkway
• Four lanes from Highlands Ranch Parkway to Meadows Parkway

Castle Rock Town Wide Transportation Plan

The Castle Rock Town Wide Transportation Plan, completed in 1994, outlines recommended transportation improvements for the Town of Castle Rock.

The Douglas County 2015 Transportation Plan is an element of the Douglas County Master Plan completed in 1997. The plan outlines transportation improvements that will be needed in Douglas County in 5-year increments for the next 15 years. Douglas County is about to start updating the current transportation plan.

4.3 PHYSICAL ENVIRONMENT

4.3.1 Air Quality

The U.S. Environmental Protection Agency (EPA) has established National Ambient Air Quality Standards (NAAQS) for six criteria pollutants to protect the public from the adverse health effects associated with air pollution. These six criteria pollutants are carbon monoxide (CO), ground level ozone (O₃), oxides of nitrogen (NO_x), sulfur dioxide (SO₂), fine particulate matter (PM₁₀), and lead (Pb).

4.3.1.1 Meteorology and Climate

The geographical and meteorological characteristics of Douglas County contribute to the air quality conditions within the study area. Douglas County is located at the foot of the Rampart Range of the Rocky Mountains. It is the subdrainage basin of Plum Creek, which drains into the Platte River Basin north of Douglas County.

The climate is moderate with average monthly temperatures ranging from –1.8° C (28.7° F) in January to 29.9° C (85.8° F) in July, with low relative humidity. Prevailing winds are from the south at an average of 12.9 kilometers per hour (km/h) (8.0 miles per hour [mph]). The average annual precipitation is 43.7 centimeters (17.2 inches).

4.3.1.2 Air Quality Levels

Douglas County is a part of the Central Front Range Air Quality Control Region along with Boulder, Gilpin, Clear Creek, Adams, Arapahoe, Denver, and Jefferson counties. The Denver metropolitan area consists of Boulder, Adams, Arapahoe, Denver, Jefferson, and Douglas Counties. The Denver metropolitan area is currently classified as non-attainment for CO and PM₁₀. The project area is the northern portion of Douglas County. No violations of the NAAQS in the project area have been reported for the last 11 years. According to the Colorado Air Quality Control Commission Report to the Public, 1998-1999, there are no monitors in the project area to provide CO, NO_x, hydrocarbons (HC), and O₃ air quality data; therefore, actual levels of these pollutants are not available. PM₁₀ monitoring in the Town of Castle Rock has shown no PM₁₀ violations in the last 11 years in Douglas County. Emission inventories projected for the Denver non-attainment area are represented in Table 4.8.

It is predicted that motor vehicle operation on paved and unpaved roads will contribute approximately 90 tons per day of PM₁₀ of the total projected emissions of 112 tons per day or about 80 percent. About 95 percent of these emissions are contributed by road dust, sand, and unpaved roads. Actual vehicle PM₁₀ emissions are 5 percent of the total motor vehicle operation.

4.3.1.3 State Implementation Plan

Colorado Air Quality Control Commission Regulation No. 10, "Criteria for Analysis of Conformity" requires that a transportation improvement plan (TIP), or RTP (a long-range plan) must conform to the state implementation plan (SIP). As part of the SIP development process, an emissions budget for CO is established for non-attainment and maintenance areas to maintain the NAAQS. Because the Denver Metropolitan Area is currently classified as non-attainment for CO and PM_10, projected emissions of these pollutants resulting from the TIP or RTP must not exceed the emissions budgets set forth in the SIP. The CO emissions budget for the Denver Metropolitan Area in the horizon years (2010 and 2020) is set at 800 tons per day. The PM₁₀ emissions budget for the Denver Metropolitan Area in the horizon years is set at 60 tons per day.

In addition, Regulation No. 10 sets the requirements for air quality analysis for regional and "hot-spot" air quality on a project level. This includes the requirements for modeling and screening analysis of the selected project. These requirements have been incorporated in the air quality analysis for the South I-25 Corridor and US 85 Corridor EIS.

4.3.1.4 Conformity Requirements

Section 176 (c) of the Clean Air Act (CAA) and related requirements of the Transportation Equity Act for the 21st Century (TEA-21) and the Federal Transit Act, require that transportation plans, programs, and projects that are developed, funded, or approved by USDOT and by metropolitan planning organizations or other recipients of funds under TEA-21 or the Federal Transit Act, must demonstrate and assure conformity of such activities to the applicable SIP. The provision related to conformity applies in all non-attainment and maintenance areas for transportation-related criteria pollutants for which the area is designated non-attainment or has a maintenance plan.

An RTP is the official intermodal metropolitan transportation plan that is developed through the metropolitan planning process for the metropolitan planning area. A TIP is a staged, multi-year, intermodal program of transportation projects covering a metropolitan planning area, which is consistent with the metropolitan transportation plan. The RTP specifically describes the transportation system envisioned over the next 20 years. The RTP quantifies and documents the demographic and employment factors influencing expected transportation demand, including land use forecasts. Additions and modifications to the transportation network must also be sufficiently specific to show there is a reasonable relationship between expected land use and the envisioned transportation system. It is a requirement that the RTP, TIP, and their approved projects respond to anticipated growth, showing the relationship of these projects to land use, population growth, and employment.

Table 4.9 and Table 4.10 summarize the results of the emission inventory and dispersion modeling analyses on the 2001-2006 DRCOG TIP conformity transportation networks.

4.3.1.5 Other Pollutants of Concern

Toxic Air Constituents

In addition to the NAAQS set forth by EPA for the six criteria pollutants, EPA has also established a list of 33 urban hazardous air pollutants. These pollutants include air toxics emitted from stationary (factories), non-road (lawnmowers, airplanes, etc.), and road (cars, trucks, and buses) sources.

To better understand the harmful effects road sources have on human health, the EPA has also developed a list of 22 mobile source air toxics (MSAT), such as benzene, formaldehyde, diesel exhaust, lead, and 1,3 butadiene. People are exposed to these MSATs in six basic ways: airborne emissions from burning of fuel; airborne emissions from partially burning the fuel; emissions from evaporating fuel primarily at filling stations; chemical reactions that transform MSATs once they are released to the air into other MSATs; airborne exposure to worn engine parts, tires or brakes, and direct exposure to toxics from leaking underground fuel storage tanks through drinking water sources.

The EPA is currently conducting studies to better understand the rates at which these MSATs are emitted. They are also developing an air toxics model called the Assessment System for Population Exposure Nationwide (ASPEN). The ASPEN will help predict areas where toxics may be concentrated based on emission estimates of toxic air pollutants and meteorological data from the National Weather Service.

Greenhouse Gas

Carbon dioxide (CO₂) is a greenhouse gas of global concern. The Colorado Air Pollution Control Division (APCD) has developed a list of CO₂ reduction strategies and will be considering CO₂ reduction options that will affect point, area, and mobile sources on a region-wide basis.

For additional information on air quality, see the Air Quality Analysis South I-25 Corridor and US 85 Corridor, November 2000, in the Technical Reports Volume of the South I-25 Corridor and US 85 Corridor FEIS.

4.3.2 Water Quality and Quantity

4.3.2.1 Surface Water

The I-25 Corridor and US 85 Corridor are located in portions of two watersheds: Upper South Platte and Middle South Platte-Cherry Creek. Both watersheds eventually drain into the South Platte River and can be characterized by high plains and rolling foothills, with elevations ranging from approximately 1,676 meters above mean sea level (amsl) (5,500 feet amsl) to 2,134 meters amsl (7,000 feet amsl). Groundcover in these watersheds is largely grass, although some forested areas do exist. Drainages in the corridors can be characterized as sandy washes with streambanks populated by upland vegetation species. Drainages in both corridors flow intermittently, typically in response to spring snowmelt or high-intensity precipitation events. The Upper South Platte watershed includes the entire US 85 Corridor and portions of the I-25 Corridor occurring south of Happy Canyon Road.

The US 85 Corridor parallels, but does not include, the northerly banks of Plum Creek and East Plum Creek between Castle Rock and Highlands Ranch Parkway. Surface water drainage between Highlands Ranch Parkway and C-470 flows into either Spring Gulch or Marcy Gulch (see Figure 4.6b in Section 4.3.8, Floodplains). Spring Gulch discharges into a reservoir situated between US 85 and Chatfield Reservoir, and Marcy Gulch discharges into the South Platte River. Thirty-three ephemeral or intermittent tributaries of Plum Creek or East Plum Creek flow under US 85 including Highlands Gulch and Haskins Gulch.

East Plum Creek flows under I-25 in the Town of Castle Rock and also flows through Castle Rock northwesterly, discharging into Plum Creek near Sedalia (see Figure 4.6a in Section 4.3.8, Floodplains). I-25 crosses eight drainages including Hangman’s Gulch and seven unnamed drainages that are tributary to East Plum Creek. Plum Creek continues northwesterly, discharging into Chatfield Reservoir. Chatfield Reservoir was completed in 1976 for flood control, silt control, recreation, fish and wildlife, and water supply storage. The High Line Canal, constructed in 1883 as an irrigation ditch, flows under US 85 to the northeast.

A segment of I-25, north of Happy Canyon Road, occurs in the Middle South Platte-Cherry Creek watershed. Seven natural, ephemeral, or intermittent drainages flow through this portion of the study area into Cherry Creek or Cherry Creek Reservoir: Cottonwood Creek, Newlin Gulch, Happy Canyon Creek, and unnamed tributary drainages. The Arapahoe Canal Pipeline also flows through the study area. Cherry Creek flows to the north, approximately 8.0 kilometers (5.0 miles) east of the I-25 project corridor, and discharges into Cherry Creek Reservoir, a water supply and flood control reservoir completed in 1950.

For additional information on surface water drainageways, see the Floodplain and Drainage Assessment Technical Report, May 2000, amended November 2000, in the Technical Reports Volume of the South I-25 Corridor and US 85 Corridor FEIS.

4.3.2.2 Groundwater

Groundwater quality is generally considered good in the project area, although population growth may be causing a decline in aquifer levels. Groundwater pumped within the project corridors is primarily used for domestic and agricultural purposes, although commercial and industrial uses predominate within the Town of Castle Rock.

Groundwater underlies the project corridors in a series of unconfined and confined aquifers. The Plum Creek alluvial aquifer is the primary aquifer in the vicinity of US 85. The vertical extent of the Plum Creek aquifer saturated zone occurs at an elevation slightly higher than that of Plum Creek, or between 6 and 24 meters (20 to 80 feet) beneath US 85, depending on the proximity to Plum Creek or East Plum Creek. The Plum Creek alluvium is about 30 meters (100 feet) thick and is underlain by the 60- to 70-million-year-old semi-confined Dawson Formation.

The I-25 Corridor follows a ridge north from Castle Rock. Groundwater under this corridor occurs in the Dawson Formation at depths of 61 meters (200 feet) or greater. Some saturated alluvium does occur adjacent to the surface water drainages. These alluvial aquifers have small yields and are of limited use for water supply purposes.

4.3.2.3 Water Quality

Urbanization is affecting water quality in both corridor watersheds. The increase in impervious surfaces brought about by urbanization generates elevated stormwater flows. As the natural vegetated land surface is replaced with roads, parking lots, houses, sidewalks, golf courses, and other landscaped areas, the area of soil available for stormwater infiltration diminishes and storm-related runoff increases, thus resulting in three primary impacts to water quality:

• Release of pollutants. Runoff from developed areas typically contains pesticides, herbicides, fertilizers, hydrocarbons, salts, volatile and semivolatile organics, heavy metals, bacteria, and other contaminants.
• Erosion. Gully erosion occurs when increased overland flows are concentrated in drainageways.
• Sediment loading. Sediment loading to surface waters occurs when snowmelt or precipitation contacts disturbed lands laid bare from construction activities.

East Plum Creek, Plum Creek and Cherry Creek receive runoff from residential and commercial development. Gully erosion and sediment inflows can result in large quantities of sediment being delivered to East Plum Creek, Plum Creek, and Cherry Creek. Suspended solids will be transported downstream until the material settles out in a dormant reach, such as Chatfield Reservoir and Cherry Creek Reservoir.

The mainstems of East Plum Creek and Plum Creek are classified by the CDPHE Water Quality Control Division (WQCD) as Cold Water Aquatic Life, Class 1; Recreation, Class 2; Water Supply; and Agriculture.

The Cold Water Aquatic Life, Class 1 designation is applied to waters capable of sustaining a wide variety of cold-water biota, including sensitive species. The Recreation, Class 2 secondary contact designation is applied to those surface waters that are suitable or are intended to become suitable for recreational uses on or about but not in the water. Recreation, Class 2 generally results in a standard of 2,000 fecal coliforms per 100 milliliters.

All tributaries of the East Plum Creek system, including all lakes and reservoirs not on National Forest lands, are classified by CDPHE WQCD as Warm Water Aquatic Life, Class 2; Recreation, Class 2; and Agriculture. Warm Water Aquatic Life, Class 2 waters are not capable of sustaining a wide variety of warm water biota, including sensitive species, due to physical habitat, water flows or levels, or uncorrectable water quality conditions that result in substantial impairment of the abundance and diversity of species.

Waters that flow through and along the US 85 Corridor are not currently listed on either the state 303(d) list of impaired waters or the state monitoring and evaluation list. However, some reaches of East Plum Creek and Plum Creek outside of the project corridor are included on the state monitoring and evaluation list. Identified impairments for these reaches include sediment, temperature, and aquatic life. Reaches of East Plum Creek and Plum Creek adjacent to and through the project corridor exhibit many of these same characteristics. Sections of Plum Creek, for example, have obvious sediment deposition problems. Sediment build-up is changing the nature of the stream, possibly making this reach uninhabitable for aquatic species. Continued degradation of the streams in and along the project corridor may lead to 303(d) listing in the future and additional restrictions on projects adjacent to the impaired waters.

The Chatfield Reservoir Clean Lakes Study, 1984, presented the following water quality findings relevant to the Plum Creek drainage:

• Concentration of total and dissolved phosphorus are generally greater in Plum Creek than the other two streams discharging into Chatfield Reservoir: Deer Creek and the South Platte River
• The average concentration of total suspended solids (TSS) is high in Plum Creek flows; this condition is attributed to the fine sediments that occur on the channel bottom
• Concentrations of all contaminants are higher during storm flow events

In 1985, following the Clean Lakes Study, DRCOG established the Chatfield Basin Task Force (Task Force) to make recommendations regarding water quality issues in drainages upstream from Chatfield Reservoir, including Plum Creek. The Task Force collects and disseminates ambient water quality data for Plum Creek at Titan Road. Total phosphorus, nitrate, and nitrite concentrations in 1999 were similar to the 1986 through 1999 average values of 0.13 mg/l, 0.50 mg/l, and 0.01 mg/l, respectively. Annual average phosphorus concentrations ranged from a high of 0.42 mg/l in 1987 to 0.05 mg/l in 1996, the 1998 and 1999 average concentrations were 0.16 mg/l and 0.13 mg/l, respectively. The Chatfield Reservoir Control Regulation has set the goal of a 50 percent reduction in phosphorus loading from non-point sources, including stormwater runoff. Specific conductance, an indicator of dissolved solids and total suspended solids, were higher in 1998 and 1999, compared to the 1986 through 1999 averages of 274.8 microsiemens/centimeter (m s/cm) and 161.6 mg/l. It is difficult to draw any conclusions from the limited data points; however, these studies suggest that Plum Creek water quality has not changed significantly since 1986.

Middle South Platte-Cherry Creek

All tributaries to Cherry Creek, including all lakes and reservoirs, from the source of East and West Cherry Creeks to the confluence with the South Platte River, are classified by CDPHE WQCD as Warm Water Aquatic Life, Class 2; Recreation, Class 2; and Agriculture. None of the project corridor streams in the Middle South Platte-Cherry Creek Basin are currently listed on the state 303(d) list or in the state monitoring and evaluation list.

Land use in the Middle South Platte-Cherry Creek basin is changing from agrarian to suburban residential, with associated development. Urbanization is accompanied by changes in water quality and water quality concerns. Forest and rangeland are sources of nutrients, suspended sediment, dissolved solids, and metals in surface water. Suburban environments typically generate greater volumes of stormwater as homes, yards, roads, and other impervious surface areas replace undeveloped land. Increased stormwater can result in higher quantities of sediment and nutrients (e.g., phosphorus and nitrogen) discharged into surface waters as well as increased levels of HC and VOCs.

Cherry Creek Reservoir, like Chatfield Reservoir, is susceptible to eutrophication from upstream point and non-point source pollutant loading. Eutrophication is the process by which a body of water becomes enriched in dissolved nutrients that stimulate the growth of aquatic plant life, usually resulting in the depletion of dissolved oxygen. Phosphorus is the nutrient most responsible for causing eutrophication in reservoirs and aquatic plant growth in streams. The most significant source of phosphorus in Cherry Creek Reservoir is stormwater runoff, as identified in the 1984 Cherry Creek Reservoir Clean Lakes Study. The Water Quality Control Commission (WQCC) set a phosphorus standard for Cherry Creek Reservoir in August 1984.

The narrative standard states the goal of achieving a 50 percent overall reduction in non-point source phosphorus discharges for the entire Cherry Creek Basin, including the Middle South Platte-Cherry Creek, through the use of detention and rapid infiltration basins for the treatment of stormwater runoff. The Cherry Creek Basin Authority (CCBA) is using this narrative standard as a target for development of point and non-point source pollution control strategies. The CCBA was established specifically to develop a water quality program to control pollutant loading upstream of the reservoir.

4.3.3 Vegetation

Several factors influence the distribution and abundance of plants across a landscape, including latitude, elevation, aspect, slope, soils, precipitation, and land use. Within the APE, latitude and precipitation differences are minimal; therefore, differences in the remaining factors primarily influence the composition and distribution of plant species within the I-25 Corridor and US 85 Corridor. The topography of the APE consists of rolling hills, with elevation increasing from north to south. Elevations in the study area generally range from 1,646 meters (5,400 feet) at C-470 and US 85 and 1,798 meters (5,900 feet) at C-470 and I-25 to approximately 1,890 meters (6,200 feet) in Castle Rock.

Wetland vegetation types are discussed in the wetland section of this document. Dominant upland vegetation types in the APE include:

• Grasslands
• Shrublands
• Woodlands
• Riparian
• Urban

These vegetation types were mapped from aerial photography along I-25 within a range of 150 to 245 meters (500 to 800 feet) from each side of the highway (Table 4.11). Along US 85, plant communities were mapped within a range of 30 to 305 meters (100 to 1,000 feet) from each side of the highway. Although the APE is likely to be 30 meters (100 feet) from the existing ROW for US 85 and 60 meters (200 feet) from the existing ROW for I-25, the larger vegetation type mapping area provides context for impact analysis. Due to rapid urbanization in Douglas County, acreage estimates may vary slightly from those presented in Table 4.11.

For additional information on vegetation, see the Vegetation Technical Report, May 2000, amended November 2000, in the Technical Reports Volume of the South I-25 Corridor and US 85 Corridor FEIS.

4.3.3.1 Grasslands

The grassland vegetation type dominates (65 percent of total area mapped) much of the landscape along both highway corridors. Immediately adjacent to both highways, introduced grasses such as smooth brome (Bromopsis inermis) and crested wheatgrass (Agropyron cristatum) are common. Weeds such as Japanese brome (Bromus japonicus), musk thistle (Carduus nutans), Canada thistle (Breea arvense), yellow sweetclover (Melilotus officinale), and diffuse knapweed (Acosta diffusa) are also prevalent. Japanese brome is also common further from I-25 in historically grazed areas and is often indicative of depleted rangeland from livestock grazing or other land use. Of the above-mentioned weeds, Canada thistle, diffuse knapweed, and musk thistle are among the top 10 weed species in Colorado.

Native grasses such as buffalograss (Buchloë dactyloides), blue grama (Chondrosum gracile), side-oats grama (Bouteloua curtipendula), and little bluestem (Schizachyrium scoparium) are more common further from I-25. Other native species common in upland grasslands along I-25 are Alyssum spp., yucca (Yucca glauca), and prickly pear (Opuntia spp.).

Sand dropseed (Sporobolus cryptandrus) is the dominant native grass along much of US 85. Other native grass species include buffalograss, blue grama, side-oats grama, little bluestem, and big bluestem (Andropogon gerardii). Additional plant species observed includes yucca and prickly pear.

4.3.3.2 Shrublands

Shrublands occur in mesic draws and on hillsides within the project area of both highways (8 percent of the total mapped area). These areas are dominated by a Gambel oak (Quercus gambelii) overstory. Though not dominant, ponderosa pine (Pinus ponderosa) is found in some areas, scattered among the Gambel oak. The mid-canopy is composed of mixed shrubs such as skunkbrush (Rhus aromatica trilobata spp.), hawthorn (Crataegus spp.), snowberry (Symphocarpus occidentalis), and wild rose (Rosa woodsii). The herbaceous understory is typically depauperate; some western wheatgrass (Pascopyrum smithii), bluegrass (Poa spp.), and Oregon grape (Mahonia repens) occur along the interface between grasslands and shrublands. Some shrubland communities located near the tops of hills with northern aspects are dominated by mountain mahogany (Cercocarpus montanus) and have a grass understory with some Oregon grape.

4.3.3.3 Woodlands

Woodlands are dominated by ponderosa pine and occur primarily along I-25 between Happy Canyon Road and Meadows/Founders Parkway (6 percent of the total mapped area). Some ponderosa pine woodlands also occur along the southern section of US 85 near Daniels Park Road. Woodlands are typified by a ponderosa pine overstory and a patchy mid-canopy layer comprised of Gambel oak. In the understory, patches of snowberry, wild rose, and yucca are common. Grasses typically found with this association include little bluestem, big bluestem, smooth brome, and Canada wildrye (Elymus canadensis).

4.3.3.4 Riparian

Riparian areas occur primarily along Happy Canyon Creek, East Plum Creek, Marcy Gulch, Spring Gulch, and Plum Creek (3 percent of the total mapped area). Where an overstory occurs, it is dominated by cottonwood (Populus spp.), with some crack willow (Salix fragilis) and boxelder (negundo aceroides). The shrub canopy is primarily coyote willow (Salix exigua) and shining willow (S. lutea). The understory is mixed and includes patches of snowberry, wild rose, smooth brome, Canada wildrye, and Kentucky bluegrass (Poa pratensis). Herbaceous hydrophytic species, such as sedges (Carex spp.) and rushes (Juncus spp.), generally occur in wetter locations and are discussed in Section 4.3.4, Wetlands.

4.3.3.5 Urban

The urban vegetation type represents landscaped areas associated with residential and commercial development (18 percent of the total mapped area). Area estimates include both impervious surface (e.g., buildings and parking lots) and landscaped areas (e.g., lawns). Non-native grass (e.g., bluegrass) and ornamental shrubs and trees are the dominant vegetation in these areas.

4.3.4 Wetlands

Wetlands are defined using three criteria:

Much of the northern portions of the I-25 Corridor from C-470 to the Happy Canyon Interchange are designated as areas containing unstable or potentially unstable slopes. In these areas, evidence exists of past slope movement or geologic conditions favorable to slope failure. An area of potential rockfall or rockslide and debris avalanche hazard is located along I-25 from an area near the Happy Canyon Interchange south for about 3.2 kilometers (2 miles). These areas are subject to falling, sliding, or avalanching of individual blocks of rock or accumulations of blocky material, usually during heavy rainstorms. In addition to these classifications, most of the I-25 Corridor is designated as moderate to high erosion susceptibility, which include areas that are susceptible to erosion due to slope, composition, poor consolidation of surficial materials, sparse vegetation cover, or proximity and similarity to areas already undergoing accelerated erosion. A small portion of the corridor to the north of Newlin Gulch is classified as a low erosion susceptibility area. These areas are often characterized by materials that are difficult to excavate and by poorly defined surface drainage.

During construction of additional southbound climbing lanes approximately 0.8 kilometer (0.5 mile) south of Lincoln Avenue in the spring of 2000, the contractor triggered two landslides. The slides propagated uphill and daylighted outside of the CDOT ROW at the crest of the steep natural slopes located above the existing cut slopes. The contractor had decreased the proposed lower slope angles and pushed the toe of the new cut slope further to the west, in order to generate more fill material. The cause of the slides, although not specifically defined in the report, Engineering Geology for Proposed Cuts to Widen Interstate 25, CDOT Project No. IM 02052-038, August 19, 1998, appears to be the result of general unloading of the toe of the steep upper slope.

These slope failures, although not catastrophic, emphasize the need for detailed geologic and geotechnical investigations prior to any slope modifications along the I-25 Corridor. The constructed slopes in question were less steep than the 2:1 slopes present along a majority of this corridor, and they were still subject to failure because of the presence of weak shear zones in the Denver Formation. The Engineering Geology for Proposed Cuts to Widen Interstate 25, CDOT Project No. IM 02052-038, document states: "The potential for triggering possible landslide movements should be carefully considered in performing evaluations for future roadway projects and private developments on the west and east side of the highway adjacent to and within the project vicinity."

4.3.5.2 US 85 Corridor Geology

A survey of available geologic reports along the US 85 Corridor was made to identify subsurface geology within the area affected by roadway, major structure, and drainage construction. Soil information generated from research allows a determination of how drainage structures and erosion control can be impacted by soil conditions.

The US 85 Corridor is located in Seismic Risk Zone I of the Seismic Zone Map of the United States as indicated on Figure 16-2 of the 1997 Uniform Building Code.

The review of these reports indicated that the soil and subsurface conditions of US 85 are as follows.

Northern Area

The northern area begins at the US 85 and C-470 Interchange and extends south approximately 5.2 kilometers (3.3 miles) through the Lakeside Drive and US 85 Intersection.

Geomorphology

Surficial geologic conditions in the northern area were mapped by the USGS as eolian (wind-blown) sand and Broadway Alluvium. For this portion of the US 85 Corridor, the roadway parallels Plum Creek in a southerly direction, remaining on the east side of the creek. The eolian sand deposit is described as fine to medium sand derived mainly from alluvium of streams and distributed east of the source area by the wind. The Broadway Alluvium is described as gravel, sand, silt and clay that forms an alluvial terrace above the present creek level. Deposits of major streams east of the South Platte River are mostly sand. This deposit is a source of sound aggregate. The Broadway Alluvium is commonly less than approximately 7.6 meters (25 feet) thick.

Bedrock

Bedrock underlying the surface units consists of the Dawson, Denver, and Arapahoe Formations of Paleocene to Upper Cretaceous age. The formations are all described as containing sandstone, siltstone, claystone, and conglomerate and are highly locally variable. It should be realized that the information presented in this FEIS is of a generalized nature and local variations are possible. No large exposures are present in highway cuts along this section of the alignment.

Swell Potential

Swell potential of the subsoils in this area is low, although a significant risk of collapse is present with eolian soils, present over a significant portion of this area.

Groundwater

Shallow local groundwater is expected in unconsolidated alluvial deposits at this portion of the alignment, at or slightly below the water level in Plum Creek.

Slope Stability

Existing slopes on the east side of the highway are very flat and range from 40:1 (horizontal: vertical) or slightly flatter to 8:1 and up to 39.6 meters (130 feet) high. The topographic relief present to the east is located a significant distance from the present alignment which can be described as flat to very flat with some slight rolling hills toward the south of this area.

The central area begins at the Lakeside Drive and US 85 Intersection, and extends south approximately 10 kilometers (6.3 miles) to 1.6 kilometers (1.0 mile) north of the intersection of SH 67 and US 85 in Sedalia.

Geomorphology

Surficial geologic conditions in the central area were mapped by the USGS as Broadway, Louviers, and Piney Creek Alluvium. For this portion of the US 85 Corridor, the roadway parallels Plum Creek in a southeasterly direction, remaining on the east side of the creek. The primary surficial materials are the Louviers and Piney Creek Alluvium, described as gravel, sand, silt, and clay of modern stream plains and slightly older low terraces less than 6 meters (20 feet) above stream level. The Piney Creek Alluvium is present in the northern portion of this section and in fingers that extend eastward from the main Plum Creek drainage in small valley fan drainages. In streams east of the South Platte River, the Piney Creek deposits are mainly sand. Sand, silt, and clay compose the deposits in small streams and tributaries. The Post-Piney Creek and Piney Creek Alluvium are commonly less than approximately 6 meters (20 feet) thick. Present to a lesser degree is the Broadway Alluvium, described above as gravel, sand, silt, and clay.

Bedrock

Bedrock underlying the surface units consists of the Dawson and Arapahoe Formation of Paleocene to Upper Cretaceous age. The formation is described as containing sandstone, siltstone, claystone, and conglomerate and is highly locally variable. It should be recognized that the information presented in this FEIS is of a generalized nature and local variations are possible.

Two large exposures of the bedrock are present approximately 3.2 kilometers (2.0 miles) north of Sedalia on the east side of the existing highway. These cut slopes are between 6 and 12 meters (20 and 40 feet) high and are cut almost vertically. Weathering and raveling of the slope is evident from the small piles of loosened material present at the base of these cuts. The predominant material exposed in these cuts is a tan to orange sandstone with bands of claystone up to 0.9 meter (3.0 feet) in thickness. Capping the exposure is an alluvial deposit with sand, gravel, cobbles, and large boulders up to 1.5 meters (5.0 feet) in diameter.

An additional exposure is located approximately 1.6 kilometers (1.0 mile) north of Sedalia on the east side of the highway. Sandstone is again the predominant material in this almost vertical road cut. Also present was a very hard capping layer of highly cemented sandstone that had resisted weathering and raveling and showed relief from the remaining cut.

Slope Stability

Existing slopes on the east side of the highway are more steep in this section and range from 10:1 (horizontal: vertical) or slightly flatter to 4:1 and up to 40 meters (140 feet) high. The topographic relief present to the east is located adjacent to the present alignment. Two major and one minor cut slopes, described above in the geology discussion, are close to vertical in slope and range in height up to 12 meters (40 feet).

Swell Potential

Vegetation consists of native rangeland grasses, yucca, other shrubs, herbs, small cactus, and brush. Most of the existing near-vertical cut slopes are devoid of vegetation. Mapping completed by the Colorado Geological Survey indicates this central portion of the US 85 alignment is in an area of low to high swell potential. Potentially expansive materials in this area include bedrock, weathered bedrock, and surficial deposits. The swell potential of the claystone present in isolated layers in the Arapahoe formation is high. The swell potential of the subsoils and bedrock along this section is high, dependent on the presence of clay lenses in the alluvial materials, weathered bedrock zones, and whether the alignment intersects the expansive claystone bands in the Arapahoe Formation.

Groundwater

Shallow local groundwater is expected in unconsolidated alluvial deposits at this portion of the alignment, at or slightly below the water level in Plum Creek.

The southern area begins 1.6 kilometers (1.0 mile) north of the intersection of SH 67 and US 85 in Sedalia, and extends approximately 11.6 kilometers (7.3 miles) south of the US 85/I-25 Interchange.

Geomorphology

Surficial geologic conditions in the south area were mapped by the USGS as Slocum, Louviers, and Piney Creek Alluvium. For this portion of the US 85 Corridor, the roadway parallels Plum Creek in a southeasterly direction, remaining on the east side of the creek, turning almost eastward at Sedalia. The primary surficial materials are the Slocum and Louviers Alluvium. The Louviers Alluvium is described as gravel, sand, silt, and clay of modern stream plains and underlies much of the Piney Creek Alluvium in channels of major streams. It is a major source of commercial sand and gravel. The Slocum Alluvium is described as bouldery cobble gravel near the mountain front, decreasing in grain size eastward away from the mountains. The Piney Creek Alluvium is present in fingers that extend eastward from the main Plum Creek drainage in small valley fan drainages. In streams east of the South Platte River, the Piney Creek deposits are mainly sand. Sand, silt, and clay compose the deposits in small streams and tributaries. The Piney Creek Alluvium is commonly less than approximately 6 meters (20 feet) thick.

Bedrock

Bedrock underlying the surface units consists of the Dawson and Arapahoe Formation of Paleocene to Upper Cretaceous age. The formation is described as containing sandstone, siltstone, claystone, and conglomerate and is highly locally variable. It should be recognized that the information presented in this FEIS is of a generalized nature and local variations are possible. No large exposures are present in highway cuts along this section of the alignment.

Slope Stability

Existing slopes on the east side of the highway are very flat and range from 20:1 (horizontal: vertical) or flatter to 40:1. The topographic relief present to the east is located at least 305 meters (1,000 feet) from the present alignment, which can be described as flat to very flat with some slight rolling hills.

Swell Potential

Vegetation consists of native rangeland grasses, yucca, other shrubs, herbs, small cactus, and brush. Mapping completed by the Colorado Geological Survey, indicates this southern portion of the US 85 alignment is in an area of low to high swell potential. Potentially expansive materials in this area include bedrock, weathered bedrock, and surficial deposits. The swell potential of the claystone present in isolated layers in the Arapahoe Formation is high. The swell potential of the subsoils and bedrock along this section is highly dependent on the presence of clay lenses in the alluvial materials, weathered bedrock zones, and whether the alignment intersects the expansive claystone bands in the Arapahoe Formation.

Groundwater

Shallow local groundwater is expected in unconsolidated alluvial deposits at this portion of the alignment, at or slightly below the water level in Plum Creek.

Soil conditions along the US 85 Corridor are characteristic of the loamy, alluvial land of the Sampson association. These soils are deep, nearly level to gently sloping, loamy, and sandy soils located on the floodplains and terraces of Plum Creek. Flooding is a hazard in these areas, especially in lower lying areas. Gullies are common in areas of alluvial land. In areas near Riverside and Sedalia, the corridor crosses the Bressler-Newlin-Stapleton association. These are deep, gently sloping to moderately steep sandy and gravelly soils. Most of the soils in this association have good bearing strength for foundations. Table 4.15 describes characteristics of the specific soil types found along the US 85 Corridor.

Through most of the corridor, US 85 follows the border between an area of low-erosion susceptibility to the west and south, and an area of medium to high erosion susceptibility with unstable or potentially unstable slopes to the east and north. The northern and eastern slopes show evidence of past slope movement or display geologic conditions favorable for slope failure. Areas to the south and west along Plum Creek are subject to occasional flooding and deposition of sediment. In many locations, stream bottomlands are aggrading by deposition of sediment produced by accelerated modern erosion in uplands.

4.3.6 Wildlife

The APE for the I-25 Corridor and US 85 Corridor encompasses an area 60 meters (200 feet) from either side of the existing I-25 ROW and an area 30 meters (100 feet) from either side of the existing US 85 ROW. The following wildlife and habitat descriptions are based on surveys of the APE. A broader level of analysis and description is also provided for landscape adjacent to the APE.

The APE and surrounding landscape occur within the western edge of the Great Plains – Palouse Dry Steppe Province. Native habitats within the APE include grasslands, shrublands, woodlands, and riparian areas. Steppe is synonymous with short-grass prairie and describes a class of short grasses usually bunched and sparsely distributed. Common native short grasses in this ecoregion include blue grama (Chondrosum gracile) and buffalograss (Buchloё dactyloides). Other grasses include western wheatgrass (Pascopyrum smithii), needle and thread grass (Heterostipa comata), fescue (Festuca spp.), and bluegrass (Poa spp.). The grasslands east of the Rockies have scattered trees and shrubs, such as plains cottonwood (Populus deltoides), ponderosa pine (Pinus ponderosa), rabbitbrush (Chrysothamnus nauseosus), and Gambel oak (Quercus gambelii).

Vegetation along streams within the APE is dominated by plains cottonwood, box elder (Negundo aceroides), and an understory of crack willow (Salix fragilis), peachleaf willow (Salix amygdaloides), and sandbar willow (Salix exigua). These riparian habitats may represent the most important wildlife habitats in the APE and the adjacent landscape due to the abundance and richness of species they support. Riparian areas also provide excellent wildlife movement corridors.

Most wildlife habitat within the APE is dominated by human activity due to its past use as a transportation corridor; associated residential, commercial, and industrial development; and historic cattle ranching. Despite human impacts on the landscape, Douglas County maintains an abundance of wildlife and wildlife habitat. In the Douglas County Parks, Trails, and Open Space Master Plan (1998), preservation of wildlife was stated by the public as a high priority. Identification of wildlife use areas was an important criterion in determining suitable or priority areas for conservation.

Douglas County has more than 15,000 hectares (37,000 acres) of open space within the county, which is managed by Douglas County Division of Open Space and Natural Resources. Douglas County Parks currently manages 120 hectares (293 acres) of developed parkland, and more than 970 hectares (2,400 acres) of unimproved open space.

In addition to County-managed open space, nearby protected areas such as Chatfield State Park, Plum Creek Riparian Corridor, Roxborough State Park, Pike National Forest, Woodhouse State Wildlife Area, Cherokee Ranch Foundation, and Highlands Ranch Open Space Conservation Area also exist. These areas serve as refuges for wildlife and become increasingly important as surrounding lands are converted from agriculture and natural landscape to developed areas. Additionally, much of the project area between Daniels Park Road and Titan Road along US 85 is relatively undeveloped. A recent wildlife tracking study indicated that wildlife regularly moves across and under US 85 within the undeveloped area.

For additional information on wildlife, see the Wildlife Technical Report, May 2000, amended, November 2000, and the Wildlife Tracking and Habitat Connectivity Study US Highway 85 Corridor, October 2000, in the Technical Reports Volume of the South I-25 Corridor and US 85 Corridor FEIS.

4.3.6.1 Mammals

Big game species found within the APE and adjacent landscape include elk (Cervus elaphus), mule deer (Odocoileus hemionus), white-tailed deer (Odocioleus virginanus), pronghorn (Antilocapra americana), black bear (Ursus americanus), and mountain lion (Felis concolor). A resident elk population uses habitat west of I-25 to the foothills west of US 85. In addition, a foothills population of elk uses severe-winter range within the northwest portion of the project area. The primary east-west elk movement corridor across I-25 is south of the Town of Castle Rock, outside the APE. Elk activity within the study area along US 85 appears to concentrate near South Pollock Gulch in the northern portion of the study area and on Cherokee Ranch and adjacent properties in the southern portion of the study area. Cherokee Ranch has a year-round elk population of approximately 400. Winter field surveys of the APE revealed elk movement south of Cherokee Ranch across Daniels Park Road into adjacent developed areas north of Castle Rock and east toward the interstate. According to the CDOW, elk cross I-25 primarily south of Castle Rock; however, evidence of unsuccessful elk crossing on I-25 has been recorded north of Castle Rock near the Castle Pines Parkway Interchange. (See Wildlife Technical Report for elk range map.)

Mule deer travel and forage within the APE and are abundant in adjacent winter and severe-winter range along US 85 and summer range to the west. Mule deer concentrate on winter and severe winter range due to the availability of resources, particularly forage that is scarce or inaccessible in other portions of their range. Winter range condition and availability can be a limiting factor for ungulate species survival within a population. Therefore, threats to connectivity between ungulate winter range and other seasonal ranges can have serious negative consequences at the population level. White-tailed deer are relatively common along riparian corridors and adjacent uplands within the APE. (See Wildlife Technical Report for mule deer range map.)

Pronghorn occur east of US 85 in the northeast section of the project area near Highlands Ranch. Pronghorn also occur east of I-25; however, numbers are few because both corridors are undergoing rapid development. Pronghorn have been observed on several occasions during winter surveys near South Pollock Gulch on the east side of US 85. (See Wildlife Technical Report for pronghorn range map.)

Black bears in Colorado are most common in sub-alpine forests at moderate elevations, montane forests, and shrublands and within well-developed stands of oakbrush or berry-producing shrubs such as chokecherry (Padus virginiana) or serviceberry (Amelanchier alnifolia). Black bears likely use oak and mountain mahogany shrublands during their hyperphagic phase in late summer and fall, when abundant nuts and berries allow them to gorge prior to hibernation.

Mountain lions are common in rough, broken foothills often in association with montane forests and shrublands. Evidence from wildlife tracking stations includes a mountain lion crossing beneath US 85 between Louviers and Sedalia.

Other mammalian predators exist within the project area, including coyote (Canis latrans), red fox (Vulpes vulpes), bobcat (Lynx rufus), raccoon (Procyon lotor), badger (Taxidea taxus), long-tailed weasel (Mustela frenata), western spotted skunk (Spilogale gracilis), and striped skunk (Mephitus mephitus). These predators have all been detected crossing tracking stations set up in culverts under I-25 and US 85 within the APE.

Gray fox (Urocyon cinereoargentus) habitat occurs throughout Douglas County in broken terrain, montane shrublands, riparian areas, and weedy margins of fields; however, their presence may be limited by competition with red fox. Swift fox (Vulpes velox – State Species of Concern and candidate species for federal protection under the Endangered Species Act [ESA]) reside in Colorado on the eastern plains in flat or very gently rolling topography and its presence is documented in eastern Douglas County. However, the highly eroded terrain interspersed with gullies and washes east of I-25, and the brushy habitat west of I-25 are not likely swift fox habitat (see Section 4.3.9, Threatened, Endangered, and Other Special-Status Species).

Other carnivores whose range includes Douglas County are ringtail (Bassaricus astutus), short-tailed weasel (Mustela erminea), black-footed ferret (Mustela nigripes – State Endangered and Federal Endangered) (see Section 4.3.9, Threatened, Endangered, and Other Special-Status Species), and mink (Mustela vison).

Upland grasslands within the project area contain colonies of black-tailed prairie dogs (Cynomys ludivicianus – State Species of Concern and Federal Proposed Candidate Species). Desert cottontails (Sylvilagus audubonii) are often associated with black-tailed prairie dog colonies and grassland habitat with scattered shrubs. Grasslands also provide habitat for the thirteen-lined ground squirrel (Spermophilus tridecemlineatus). Black-tailed jackrabbits (Lepus californicus) may use areas east of I-25. Mountain cottontails (Sylvilagus nuttalii) are found within the shrubland (oak and mountain mahogany) habitats west of US 85, as are rock squirrels (Spermophilus variegatus). Golden-mantled ground squirrels (Spermophilus lateralis), least chipmunks (Tamias minimus), and Colorado chipmunks (Tamias quadrivittatus) are found in mountain shrublands and ponderosa pine communities. Abert’s squirrels (Sciurus aberti) are dependent upon ponderosa pine for nesting and food. Abert’s squirrels were observed within the APE during field surveys. Eastern cottontails (Sylvilagus floridanus) and fox squirrels (Sciurus niger) inhabit riparian areas within Douglas County, as do beavers (Castor canadensis) and muskrats (Ondatra zibethicus). Beavers and their dams were observed in East Plum Creek in Castle Rock.

Small mammal sign is abundant along the I-25 APE and US 85 APE, particularly deer mouse (Peromyscus maniculatus) and bushy-tailed woodrat (Neotoma cinerea). The five general habitat types within the APE likely support a diverse, small mammal population. Grasslands are habitat for the northern grasshopper mouse (Onychomys leucogaster) and the prairie vole (Microtus ochrogaster). Gambel oak and mountain mahogany shrublands contain small mammals such as Mexican woodrat (Neotoma mexicana) and brush mouse (Peromyscus boylii). Montane vole (Microtus montanus), longtailed vole (Microtus longicaudus), and heather vole (Phenacomys intermedius) are all found in ponderosa pine woodlands. Riparian areas within the project area provide habitat for the threatened Preble’s Meadow Jumping Mouse (Zapus hudsonius preblei – State Threatened and Federal Threatened) (see Section 4.3.9, Threatened, Endangered, and Other Special-Status Species) and the meadow vole (Microtus pennsylvanicus).

The western small-footed myotis (Myotis ciliolabrum) occurs in all the habitat types present within the project area. Little brown bats (Myotis lucifugus) would likely occur within wooded habitats (cottonwood and ponderosa) of the project area. Mountain shrublands provide habitat for the fringed (Myotis hysanodes) and long-eared myotis (Myotis evotis), big brown bat (Eptesicus fuscus), and Townsend’s big-eared bat (Plecotus townsendii).

4.3.6.2 Birds

Breeding birds found in upland grass communities within the APE and surrounding landscape include horned lark (Eremophila alpestris), meadowlark (Sturnella neglecta), lark sparrow (Chondestes grammacus), common night hawk (Chordeiles minor), Swainson’s hawk (Buteo swainsoni), northern harrier (Circus cyaneus), and burrowing owl (Athene cunicularia – State Threatened). Common breeding birds within Gambel oak and mountain mahogany shrublands include the spotted towhee (Pipilo maculatus), green-tailed towhee (Pipilo chlorurus), Virginia’s warbler (Vermivora peregrina), orange-crowned warbler (Vermivora ruficapilla), scrub jay (Aphelocoma coerulescens), black-headed grosbeak (Pheucticus melanocephalus), and wild turkey (Meleagris gallopavo). Ponderosa pine forests provide breeding habitat for the Stellar’s jay (Aphelocoma coerulescens), chipping sparrow (Spizella passerina), mountain chickadee (Parus gambeli), white-breasted nuthatch (Sita carolinensis), and flammulated owl (Otus flammeolus). Low-elevation riparian areas are breeding habitat for Bullock’s oriole (Icterus graduacauda), yellow warbler (Dendroica petechia), black-billed magpie (Pica pica), northern flicker (Colaptes auratus), house wren (Troglodytes aedon), and great horned owl (Bubo virginiana).

An active golden eagle (Aquila chrysaetos) nest is on the Cherokee Ranch south of Sedalia, approximately 1 kilometer (0.6 mile) from US 85. The nest site was active in March 2000 and has been consistently active in past years. Raptors observed within the APE and surrounding landscape during site visits include northern harrier (Circus cyaneus), ferruginous hawk (Buteo regalis – State Species of Concern), red-tailed hawk (Buteo jamaicensis), golden eagle (Aquila chrysaetos) and American kestrel (Falco sparverius). Other raptors that may be present within the study area include bald eagle (Haliaeetus leucocephalus – State Threatened and Federal Threatened) (see Section 4.3.9, Threatened, Endangered, and Other Special-Status Species), peregrine falcon (Falco pereginus – State Species of Concern), prairie falcon (Falco mexicanus), and rough-legged hawk (Buteo lagopus), a winter resident in Colorado’s grasslands. Sharp-shinned (Accipiter striatus) and Cooper’s hawks (Accipiter cooperii) may occupy woodland habitats adjacent to the APE.

Chatfield Reservoir is a production area for breeding waterfowl and a staging area for migratory waterfowl. The South Platte River below the Chatfield Dam is winter range for waterfowl. Canada geese are commonly observed in agricultural fields and other habitats within the APE and adjacent landscape.

4.3.6.3 Tracking Study

Results from a wildlife tracking study in the I-25 and US 85 APE indicate that a variety of wildlife use bridges and culverts to cross under highways. Tracking stations that identify wildlife species crossing under bridges and through culverts, and quantify the number of crossing events, were established at four locations in November 1999 and at two additional stations in January 2000 along the I-25 Corridor and US 85 Corridor (Figure 4.5a and Figure 4.5b). Table 4.16 summarizes the crossings at each station.

From November 15, 1999, through May 31, 2000, 943 crossing events were detected for 11 wildlife species (excluding mice). Eight of these were carnivores (bobcat, mountain lion, coyote, red fox, badger, weasel, skunk, and raccoon), and three were small mammals (woodrat, squirrel, and cottontail). Mice and voles were also recorded at the six tracking stations; however, the high number of records may be skewed by individuals living within the structure. One hundred and sixty-six domestic crossings were also recorded including dogs (39), domestic cats (45), all-terrain vehicles (ATV) (5), and human (77). No ungulate crossings were detected at any of the tracking stations; however, elk and deer were recorded crossing at grade.

Several factors that may affect ungulate and other wildlife use of bridges or culverts within the study area were noted during tracking surveys. Human occupation or related effects (e.g., noise, lighting, pets) may inhibit wildlife crossing. Artificial substrate (e.g., concrete) size (i.e., openness factor), structural barriers (e.g., riprap, fencing), and adjacent landscape features could also limit suitability of underpasses for some species.

An underpass may also appear long and confining so as to preclude passage by ungulates. Relative openness of an underpass, described as the "openness factor," may be a primary stimulus to ungulates approaching a potential crossing. The openness factor is calculated as (height x width)/length. A CDOW study indicates that