Draft terrestrial resources biological assessment

5.2.1 Estimate of Indirect Impact to Vernal Pool Complex Habitat

As indicated in Table 5-3, a maximum of 3.56 acres of vernal pools will be indirectly affected by the DI full build-out and 1.43 acres will be affected by JTA Option C. However, note that JTA Option A would impact the maximum amount of high value vernal pools (0.53 acres).

5.2.2 Habitat Fragmentation and Hydrologic Separation

Indirect effects resulting in alteration or disruption to the hydrologic regime that supports vernal pool complexes may occur, depending on the stormwater elements incorporated into the project design. At the time of this assessment, stormwater design was still being developed. Curb and gutter systems, should they be incorporated, will capture runoff from new impervious surfaces and direct them to treatment facilities prior to discharge. These systems have the potential to remove direct surficial hydrology into adjacent VP wetlands. This may cause the complex to receive a decreased amount of water, have lower ponding depths, and shorter wet seasons. This may impact the life cycle of the shrimp, which depends on this wet / dry cycle to breed and lay eggs.
Certain construction methods, such as excavation, bulldozing or movement of heavy equipment in general, may fracture the hardpan soils under the wetlands, allowing cracks to develop and drainage of groundwater to occur.
Habitat may become fragmented with the loss of hydrologic connection. Without an medium the VPFS can negotiate to access adjacent pools and different populations of shrimp, they may no longer find wider sources of genetic material. Populations may become less viable to the point of extinction.

5.2.3 Spread of Invasive Species / Noxious Weeds

Selection of any of the Design Options would likely increase development in the local area. Spread of noxious weeds may be likely through errant transmission through construction or transportation activities should an aggressive management plan not be enforced. As stated previously, construction of the Build Alternatives may increase the pace of future development in the area. Spreading noxious weed seed or plant parts offsite or to new areas within the proposed footprint on vehicle carriages, tire treads, or on clothing is also possible. Should adjacent parcels not enforce aggressive weed management programs, adjacent populations of weeds may spread into vernal pool habitat within the project action area and outcompete ESA-listed species and alter habitat quality.
Vernal pools have a narrow range of tolerance for hydrology; alteration of this range may inadvertently dry up wetlands and further degrade vernal pools. Loss of hydrology may also affect flora species. Should the complexes begin to become drier through the alteration of hydrology, invasive species may invade and become established. Non-native species are listed as a threat to the conservation and recovery of both Cook’s lomatium and Large-flowered woolly meadowfoam (USFWS 2011).

5.2.4 Sedimentation

Construction activities in proximity to vernal pool wetlands may create the potential for erosion of soils and generation of airborne dust and particulate matter. Potential indirect effects associated with such fugitive sediment migration include possible increased sedimentation of the adjacent mound-vernal pool habitat complexes. Heavy sediment loads, if untreated, may cover the bottoms of vernal pools, where algae, bacteria and nutrients that VPFS require, is found. Additional sedimentation may also decrease pool depth, which may decrease the amount of surface area VPFS have to forage and breed.
Potential vectors of fugitive sediment migration may include precipitation induced stormwater runoff from construction equipment and action area surfaces, the absence of or inadequate erosion controls, vehicle-generated dust from traffic on unpaved surfaces, and construction in or adjacent to surface water conveyances. Should BMPs not be implemented, direct sheet flow from disturbed surfaces would degrade VPC habitats.
Impacts from sedimentation due to stormwater events will be avoided or minimized through the implementation of a project ESCP, implementation of structural and operational BMPs, construction monitoring, and timing restrictions. With proper implementation of the proposed avoidance and minimization measures, incidence of sedimentation should occur infrequently, be appropriately contained, be short in duration, and be detected and corrected prior to posing a risk to vernal pool fairy shrimp or degrading critical VPC habitat complexes. Given the avoidance and minimization measures proposed, impacts should be of limited duration and not rising to the intensity to result in take.

5.2.5 Stormwater-Induced Surface Water Contamination

Impacts to receiving waters from stormwater discharges within the project area are a function of the amount of impervious surface and the degree of treatment and flow control runoff receives through appropriately designed and located stormwater detention and treatment facilities. Pollutant loads are also a function of traffic volumes, such that greater traffic volumes per unit of impervious surface result in higher pollutant loads. The standard of significance for impacts from ODOT highway projects is whether there are predicted exceedances of water quality standards after implementation of stormwater BMPs in accordance with ODOT guidance (ODOT 2006). Stormwater runoff from impervious roadway surfaces can transport toxic levels of automotive-derived pollutants, including petroleum-based compounds and heavy metals, into adjacent vernal pool wetland habitat if left uncaptured and untreated or undertreated.
ODOT is required to manage stormwater according to a stormwater management plan to remove pollutants to the maximum extent practicable. This is done using a variety of stormwater treatment facilities and maintenance activities, collectively known as BMPs.
Preliminary stormwater treatment design has only been completed for a portion of the project corridor. Further stormwater design is awaiting completion of the DEIS and selection of a Preferred Alternative, as committing resources to produce preliminary engineering for alternatives and options that will not be built would be an inappropriate use of limited project funds. Currently, stormwater would sheet flow off new impervious surfaces and transport roadway-related contaminants into wetlands. Vernal pool fairy shrimp are sensitive to water quality; consequently, introduction of these pollutants could result in mortality of individuals, decreased population viabilty, and displacement of species by rendering suitable habitat less suitable. Crowding of individuals trying to escape poor quality water may overburden existing resources and create a die off, affecting population viability.
Pollutants may also affect food sources within the wetland by being trapped or taken up by algae or bacteria within the water and later consumed by fairy shrimp. This may create acute and/or chronic toxic conditions for the fairy shrimp, similarly resulting in mortality, reduce viability, or displacement from suitable habitat.
ODOT has committed to design all portions of the Preferred Alternative to the level and performance standards demonstrated for the portion of the JTA phase described herein, including all contributing impervious area (CIA) associated with the Project. Should there be areas where stormwater treatment is not feasible or possible due to site constraints, ODOT will provide treatment to untreated impervious surface area located outside the project area as mitigation.

5.2.6 Disruption to Vernal Pool Complex Hydrology

As discussed partially under Section 5.2.2, hydrologic disruption to vernal pool wetlands may come from either addition or depletion of existing sources (runoff from adjacent upland areas that is either increased through the addition of impervious surface, or reduced through curbing or other stormwater capture designs). Depletion may also come from construction activities that alter soils and the underlying hardpan aquatard, providing drainage for perched groundwater and creating a long term drying condition. The proper implementation of Project construction BMPs is expected to limit potential indirect effects resulting from construction methods. .
Design of the stormwater system so that complete removal or, on the other extreme, heavy additions of stormwater does not occur may also mitigate impacts of a new roadway.

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Terrestrial BA -> Draft Terrestrial Resources Biological Assessment oregon highway 62 corridor solutions project

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