The study area is underlain by rocks of the paleontologically sensitive Late Cretaceous and
Paleocene Denver Formation, and surficial deposits of Holocene-aged Post-Piney Creek and Piney
Creek Alluviums (Trimble and Machette 1979). The Denver Formation, which contains locally
abundant and scientifically significant plant fossils and less common vertebrate fossils, has
moderate to high paleontological sensitivity (Class 3 of PFYC). The Post-Piney Creek and Piney
Creek Alluviums have low paleontological sensitivity (Class 2 of PFYC). As described in Section
4.12 Soils and Geology, the Denver Formation underlies the alluvial deposits in this area.
4.13.2 Consequences
Consequences of the No-Action Alternative
No impacts to paleontological resources will occur under the No-Action Alternative.
Consequences of the Proposed Action
Ground disturbance from highway construction activities associated with the Proposed Action may
potentially cause direct impacts (damage or destruction) to paleontological resources. It is not
possible to predict the extent of such impacts due to the unknown specific distribution of fossils
within the geologic units in the study area. The fossiliferous Denver Formation bedrock is of
greatest concern. The Denver Formation could be encountered during excavation.
4.13.3 Mitigation
Monitoring will be conducted during excavation that may encounter Denver Formation rocks. As
project design plans are finalized, the CDOT paleontologist will examine them to determine the
extent of impact to the Denver Formation, and the scope of monitoring work, if any, which is
required.
Although the paleontologic sensitivity of the surficial deposits (primarily alluvium) within the study
area is low because they typically contain few fossils, construction personnel will be made aware of
the potential to encounter fossils while excavating. If any sub-surface bones, leaf impressions, or
other potential fossils are found during construction, the CDOT paleontologist will be notified
immediately to assess their significance and make further recommendations.
4.14
CONSTRUCTION
4.14.1 Roadway Construction Methods
The contractor would determine construction methods during or after development of the final
design and construction plans. In general, roadway construction could likely involve the following
types of actions: bridge demolition and construction, excavation and grading, utility adjustments,
placement of retaining walls, storm sewers and pavement. Sequencing and the overall timeframe of
construction have not been determined and would be based upon minimization of construction
impacts, funding constraints, and coordination with CDOT.
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4.14.2 Construction Impacts
This section discusses construction impacts that may occur with the Proposed Action. Construction
along I-225, Colfax Avenue, Potomac Street and 17th Place presents the potential for decreased
mobility during construction, dust, noise, runoff, traffic congestion, temporary restricted access to
residences and businesses, and visual intrusions to motorists and residents. Additionally,
construction presents the potential for the accidental spill of hazardous materials, such as fuel or
oil.
Construction delays are expected to create short-term impacts to local and regional traffic
circulation and congestion. The traveling public and emergency service vehicles would experience
delays, and study area residents would be inconvenienced. Reduced speed limits, short-term travel
on unpaved surfaces, and temporary lane closures could be expected during construction activities.
No-Action Alternative – The No-Action Alternative involves no additional construction
over what is currently programmed, approved and funded by CDOT and the City of
Aurora. Therefore, the No-Action Alternative would result in no direct or indirect
construction impacts.
Proposed Action – The Proposed Action would include new bridges over I-225,
Potomac Street and Toll Gate Creek at two locations and the widening of the I-225
bridge over Colfax Avenue. The Proposed Action construction activities would include
bridge demolition grading, pile driving, paving, and compaction. Construction of the I225/Colfax Avenue interchange project would require construction phasing, staging
areas, and detours, as well as temporary interruption of traffic along I-225, major
arterials including Fitzsimons Parkway and Colfax Avenue, and local streets including
Potomac Street and 17th Place. There may be temporary access restrictions to
commercial properties along Potomac Street. Retaining walls will need to be
constructed in order to keep the improvements within the right-of-way. This may cause
noise and fugitive dust impacts to nearby businesses and residences along Potomac
Street and Billings Street.
4.14.3 Construction Mitigation
Mitigation for direct impacts will be specified in final design and will include implementation of the
following measures during construction:
Construction of noise walls (as identified in Section 4.5.3) as early as possible in the
construction period (to be determined during final design).
Maintain access to local businesses and residences, especially along Potomac Street
Coordinate detour routes (to be provided on existing streets) to avoid overloading local
streets
Minimize construction duration in residential areas
Minimize nighttime activities in residential areas
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Minimize construction truck traffic on residential streets, in accordance with the traffic
management plan (below)
Combine noisy operations to occur in the same period
Conduct pile driving and other high-noise activities during daytime construction, when
possible. Public notification of high-noise activities will be provided as part of public
outreach.
Develop traffic management plan to include:
•
Maintain traffic flow during peak travel times by minimizing lane closures, if possible
•
Coordinate with emergency service providers to minimize delays and ensure access
to properties
•
Use signage, television and radio announcements to inform and advertise timing of
road closures
•
During peak travel times, keep as many lanes as possible open by temporarily
shifting lanes within the existing framework of the roadway
•
Develop public outreach and public information plan
•
Develop method of handling traffic
•
Estimated work zone delays and mitigation strategies
Public information and involvement prior to and during construction. This will include
public workshop during construction planning to discuss construction details and
mitigation measures.
To address the temporary elevated air emissions that may be experienced during construction,
standard construction mitigation measures will be incorporated into construction contracts. These
could include:
Engines and exhaust systems on equipment in good working order
Equipment maintained on a regular basis, and equipment subject to inspection by the
project manager to ensure maintenance
Fugitive dust systematically controlled through diligent implementation of a dust control
plan
No excessive idling of inactive or unnecessary equipment or vehicles
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Construction equipment and vehicles use higher-grade fuel to reduce pollutant
emissions
Stationary equipment located as far from neighbors as possible
Both the No-Action Alternative and the Proposed Action may affect environmental resources not
regulated at the federal, state, or local level. Such impacts can include the consumption of natural
resources such as fossil fuels and raw materials like gravel. The alternative selected may also
affect social resources such as landfill capacity. In most cases such impacts cannot be quantified,
and cannot be avoided. It is recognized that these impacts need to be minimized to the extent
practicable. Sustainable practices incorporated into the project planning, construction, and
maintenance can minimize impacts, both during and after construction. To this end, CDOT and its
contractors are encouraged, and will be allowed the flexibility, to incorporate the concepts of
sustainability into planning, bidding, contracting, building, and maintaining the Proposed Action.
As part of its environmental ethic and policy, CDOT encourages its staff, consultants, and
contractors to identify opportunities and methods to reduce the impact of projects and programs on
environmental resources through innovative programs and by providing flexibility in project planning
and construction for the use of sustainable processes and materials. This may include such
concepts as natural resource conservation, efficient use of recycled and minimally processed
items, and preference for locally available resources. CDOT encourages the identification and
incorporation of proven materials that are longer lasting, and require less maintenance as long as
such materials do not impact CDOT’s ability to meet its primary obligations for providing a safe and
efficient transportation system.
Finally, CDOT will encourage the application of contractor Environmental Management Systems.
Alternative materials and practices must meet the performance goals of CDOT construction
specifications and be cost-effective, demonstrate legitimate expenditure of public funds, and
comply with all other applicable laws and regulations.
4.15
PERMITS
The following permits or coordination would be required for the Proposed Action and must be
obtained prior to construction:
National Pollutant Discharge Elimination System (NPDES), issued by the Colorado
Department of Public Health and Environment (CDPHE). This storm water discharge
permit is required to assure the quality of storm water runoff.
Municipal Separate Storm Sewer System (MS4) Permit issued by CDPHE. The study
area falls within the CDPHE Phase I Colorado Discharge Permit System and therefore
would follow the requirements of CDOT’s or City of Aurora’s Municipal Separate Storm
Sewer System discharge permit.
Section 402: Construction Dewatering Permit issued by CDPHE-Water Quality
Control Division (WQCD) would be required for dewatering of construction areas, if
necessary. In addition, if contaminated groundwater were anticipated, an Individual
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