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3.4 Wetlands 0610083.4 Wetlands   This section summarizes the findings and recommendations of the Wetlands Inventory, Impacts and Mitigation Recommendations for the Thurston Highlands Master Planned Community (Coot Company 2008B). A detailed description of each wetland is provided in Appendix I of that report. Wetland characteristics are described according to the U.S. Fish and Wildlife Service Cowardin Classification System (1989). Field review of the Thurston Highlands property for wetland conditions was performed over many days between November 2005 and December 2006. Over this period of time, all areas of the property were traversed on foot while searching for wetland conditions. In addition, topographic maps were used to locate depressional areas, and aerial photographs were used to identify unusual vegetation signatures. All such features were specifically reviewed on the ground for wetland conditions. Wetland delineation followed a Routine Methodology based on the Washington State Wetland Identification and Delineation Manual (Ecology 1997), requiring positive indicators for wetland soil, hydrology, and plants: Wetland hydrology was determined by water conditions in pits. Presence of hydric soil was determined by soil conditions in pits dug around suspected wetlands. Soil inspection included comparison with the Munsell Color Charts (1992). General soil characteristics were derived from information contained within the Soil Survey of Thurston County, Washington (1990). Occurrence of wetland vegetation was determined through species identification, estimation of dominance, and then assignment of wetland indicator status. Indicator status was assigned based upon the National List of Plant Species That Occur In Wetlands (Reed 1988), and Supplement (Reed 1993). The Washington State Wetlands Rating System for Western Washington Revised (Ecology 2004) was used to establish Category Ratings for the wetlands (Ecology Publication #04-06-025). Streams were typed per WAC 222-16-031 within the Washington State Forest Practices Act, prepared by the Washington Department of Natural Resources. Affected Environment A total of 35 individual wetland systems were identified throughout the property. Most of these occur in the southern half of the site (see Figure 3.4-1). Many of these wetlands are small, isolated systems in the bottom of kettle basins that have no outlet. The largest wetlands onsite occur in the southeast and northeast areas. These systems represent the headwater beginnings to drainage routes that eventually connect to the off-property Thompson Creek channel, approximately one-half mile to the east. Only a single, short (approximately 200 foot), Type Ns stream, connecting two wetlands, occurs within the entire project area, emphasizing the depressional topography prevalent throughout the landscape. This is unusual for such a large piece of property in a climate with 40 inches of average annual precipitation. Where any other flowing surface water occurs, it is a seasonal condition confined within a wetland swale but not a scoured stream channel. Only three drainage routes occur within the Thurston Highlands property that have a direct, connected outlet to Thompson Creek (see Figure 3.5-2 in Draft EIS Section 3.5). The two largest of these occur in the southeast portion of the property. One of these drainage routes (Wetlands A5, A7, A8) has its headwater beginnings within Thurston Highlands, while the other (Wetland F) begins well to the south and simply flows through a corner of the property. These two drainages eventually combine off-property into a single drainage route that connects to Thompson Creek. The off-property portions of this combined drainage route have been severely ditched in the past, which has significantly reduced the levels of persistent surface water within adjacent wetlands. The third drainage route, that also begins within Thurston Highlands, occurs in the far northeast corner of the property where a ditched, headwater basin drains to a linear wetland drainage that eventually connects to Thompson Creek. Category ratings for Thurston Highlands wetlands cover the whole range from Category I to Category IV using the Washington State Wetlands Rating System for Western Washington, Revised (Ecology 2004). Category III systems are most common (24), and include most of the isolated systems (B, C, D, E and G wetland groups). Category II systems are a distant second in number (8), and include most of the A wetland group plus F. Three Category I conditions occur based upon Special Features (2 Mature Forests and 1 Bog), and there is one Category IV wetland. Small kettle basin wetlands are common within this property. Most of these are located in the southwest portion of the landscape where underlying soils seem to have an impervious condition that perches water. Although similar kettle structures occur in other portions of the property, these are all well-drained and do not support even marginal wetland conditions like those occurring within almost all significant kettles in the southwest area. Regulatory jurisdiction varies widely between the wetlands. Some are too small for regulation by the City of Yelm under its Critical Areas Code, and some are isolated and thus not subject to Federal regulation. All wetlands on the site, however, regardless of size and isolation, are subject to Washington Department of Ecology regulations. Wetlands described for the Thurston Highlands project were separated into eight different groups (A through H) based on location, proximity, and/or similarities in structure and function (see Table 3.4-1). This was done to help consolidate text descriptions and avoid repetitive duplication while simultaneously providing a better overall review of the wetland conditions. Insert Figure 3.4-1. Surveyed Wetlands Map. Table 3.4-1. Thurston Highlands wetlands summary (Coot Company 2008B). Wetland Size/ Acres Category Rating/ Habitat pts  Recommended Buffer  Jurisdiction  A1 0.55 II / 19 100 ft Yelm, Ecology  A2 1.10 II / 17 100 ft Yelm, Ecology, ACOE  A3 1.28 II / 21 100 ft Yelm, Ecology, ACOE  A4 0.49 II / 17 100 ft Yelm, Ecology, ACOE  A5 14.01 I and II / 24 160ft / 250ft Bog Yelm, Ecology, ACOE  A6 2.33 on-site II / 18 100 ft Yelm, Ecology, ACOE  A7  3.06 on-site III / 20 100 ft Yelm, Ecology, ACOE  A8 23.66 on-site I / 23 140 ft Yelm, Ecology, ACOE  B 4.54 on-site II / 21 100 ft Yelm, Ecology, ACOE  C1 0.47 III / 17 100 ft Yelm, Ecology  C2 0.30 III / 17 100 ft Yelm, Ecology  C3 0.03 III / 18 75 ft Yelm, Ecology  D1 0.66 III / 14 100 ft Yelm, Ecology  D2 0.23 III / 18 100 ft Yelm, Ecology  D3 0.07 III / 18 75 ft Yelm, Ecology  D4 0.06 III / 18 75 ft Yelm, Ecology  D5 0.07 III / 18 75 ft Yelm, Ecology  D6 0.04 III / 15 75 ft Yelm, Ecology  D7 0.05 III / 17 75 ft Yelm, Ecology   D8 0.04 III / 17 75 ft Yelm, Ecology  D9 0.02 III / 17 No Buffer Ecology  D10 0.02 III / 17 No Buffer Ecology  D11 0.02 III / 17 No Buffer Ecology  D12 0.01 III / 17 No Buffer Ecology  D13 0.07 III / 17 75 ft Yelm, Ecology  D14 0.06 IV / 7 50 ft Yelm, Ecology  E1 0.30 III / 17 100 ft Yelm, Ecology  E2 0.01 III / 17 No Buffer Ecology  E3 0.04 III / 17 75 ft Yelm, Ecology  F 2.42 on-site II / 19 100 ft Yelm, Ecology, ACOE  G1 0.52 III / 18 100 ft Yelm, Ecology  G2 0.18 III / 18 100 ft Yelm, Ecology  H1 8.47 III / 23 140 ft Yelm, Ecology, ACOE  H2 0.55 III / 19 100 ft Yelm, Ecology, ACOE  H3 1.89 on-site I / 21 100 ft Yelm, Ecology, ACOE   Wetland buffer widths for regulatory purposes, as recommended in Table 3.4-1 (above) using best professional judgment, were developed by following the Washington Department of Ecology Guidance for Protecting and Managing Wetlands: Volume 2 (Ecology April 2005). Specifically, buffers were determined using the “Graduated Scale” of Alternative 3A as listed in Table 8C-9, with slight modification. Wetlands less than 4,000 square feet in size with low Habitat Function points (<20) are assigned 75-foot buffers for Category III systems, and a 50-foot buffer for the Category IV system. In addition, wetlands below 1,000 square feet in size are interpreted as “non-jurisdictional” to the City of Yelm, and do not require buffers. Potential Impacts During Construction Full Build-Out Conceptual Land Use Alternatives Upland Clearing/Grading and Erosion Potential. Clearing and grading activities within areas to be developed would leave large expanses of bare, disturbed ground exposed to the elements. It is estimated that approximately 100 acres would be cleared for each 300 to 400 dwelling units, under any conceptual land use alternative. As these lots are sold and construction is underway, the next ( 100 acres would be cleared for development. In this manner, only approximately 100 to 300 acres would be cleared, undergoing development, and/or awaiting landscaping at any one time (personal communication with Doug Bloom, Thurston Highlands, L.L.C., May 29, 2007). The potential for erosion of sediments by precipitation will be high during upland clearing and grading. However, potential impacts to property wetlands from any such erosion is expected to be minimal. Existing wetlands are fully vegetated and do not support anadromous fish. There would be very little distinction in clearing, grading and erosion potential impacts between the conceptual land use alternatives. It is possible that with more concentrated development in the Urban Village Alternative and a larger amount of open space to be preserved that wetland and wetland buffer impacts may be avoided to a greater degree, and/or that it may be easier to preserve larger wetland buffers within this alternative. High Value Wetlands Mostly Avoided. Any of the conceptual land use plans for the overall Master Planned Community would avoid and preserve all significant, high-value wetland systems identified herein. It is anticipated that a landscape approach to project layout would be used to protect areas where significant wetlands occur within close proximity to natural geographic boundaries and/or elements or proposed development. Protective buffers may go beyond the simple linear dimension recommended to incorporate distinctive upland features. For example, buffer protection of the large Wetland A complex could extend to the top of a prominent ridge along the western aspect, rather than simply stopping at the recommended 250 or 140-foot buffer width. Wetland Crossings by Roads. Extension of Tahoma Boulevard through the Thurston Highlands Master Planned Community under any conceptual land use alternative would result in unavoidable wetland crossings at two locations (see Figure 3.4-2). This will be necessitated by perimeter access point limitations coupled with the long, linear configuration of wetlands that occur as connected drainages in the northeast and southeast areas of the site. The fixed access points severely restrict options for roadway realignment, and the linear wetland structure precludes the option to “go around” the systems and thereby avoid wetland fill. Insert Figure 3.4-2. Boulevard Wetland Crossings. Wetland Buffer Adjustments. Minor adjustments to wetland buffers recommended herein may be necessary within the overall project to accommodate a proportioned lot layout design. The generally straight alignment of roads and the generally rectangular shape of lots often conflict with the usually irregular boundaries of wetland buffers. Buffer averaging of the outer 25 percent of on-site wetlands would not induce a significant increase in impacts. Buffer reductions of the outer 25 percent of all isolated wetlands would also avoid any significant increase in impacts, provided some type of compensatory mitigation is implemented (such as fencing or plantings). However, buffer reductions should not occur on the larger, high-value wetland systems: the Wetland A and H complexes, as well as Wetland B. The one exception to this “no reduction” recommendation would involve the buffers east of Wetlands A5, A6 and A7, facing the proposed commercial zone. If substantial effort were put forth to shield these wetland systems from potential impacts, especially human access and nighttime lighting, buffer reductions to 100 feet could be considered in these locations. Isolated Wetland Fill. There are an unusually high number of isolated wetlands on the Thurston Highlands site (23 of the 35 wetlands identified herein). This is due primarily to the landscape structure in certain areas that supports a large number of kettle basins formed in glacial outwash conditions. Many of these wetlands are small, low-function systems that would be appropriate to fill and compensate the impacts elsewhere on-site by expanding and enhancing one or more of the high-value wetland complexes. Preserving all of these low-value systems within the landscape would be difficult in an urban environment, and would most likely be unsuccessful. To assist with project design, Table 3.4-2 lists all of the low-value isolated systems that may be acceptable to impact. The list is arranged in prioritized order. Table 3.4-2. Isolated low-value wetlands that may be filled (Coot Company 2008B). Impact can mean either direct fill, or use of the wetland for stormwater detention and/or infiltration.  Wetland Approximate Total Area (in square feet)  D2 through D14 30,000  E2, E3 2,500  C3 1,100  G2 8,000  D1 29,000  E1 13,000  G1 22,500  Total: 106,100 sf (2.43 ac)   Phase 1 Development Concept Upland Clearing/Grading and Erosion Potential. The Phase 1 development area is approximately 351 acres in size. It is possible that most of this site area may be devoid of vegetation at some period of time over the 3- to 4-year period during which development would occur in Phase 1. Potential wetlands impact from erosion within this project area would be especially low. The primary, high-value wetlands within the H complex would be protected with a wide, fully-vegetated upland buffer that exceeds the recommended width due to the proposal to preserve the Mature Forest habitat adjacent to these wetlands (see Figure 3.4-3). High Value Wetlands Mostly Avoided. The Phase 1 development area contains a large, connected wetland complex (Wetland H) that is a headwater drainage basin to a minor tributary to Thompson Creek. Except for a single, unavoidable road crossing to provide access to an adjacent property (described below), Thurston Highlands Phase 1 development would completely avoid this wetland complex, and protect it by retaining the existing buffer, mostly far in excess of the recommended buffer width. This larger buffer would be preserved in the Mature Forest upland habitat adjacent to the west side of the wetland complex (see Figure 3.4-3). Wetland Crossings by Roads. To comply with the City’s “connected streets” policy, a roadway is required to provide access between Thurston Highlands Phase 1 and adjacent residential property to the east. This roadway cannot avoid crossing the high-value Wetland H complex that lies perpendicular to the road alignment (see Figure 3.4-3). This road will impact approximately 3,286 square feet of wetland. Because the road is required to serve the adjacent (Purvis) property, permit applications for the wetland crossing will be submitted to the appropriate federal, state, and local agencies associated with development applications for that property. Wetland Buffer Adjustments. Minor buffer averaging may be used along the southern edge of the Wetland H complex to create a straight edge along the back side of proposed residential lots, if the actual subdivision application is submitted as shown on (or similar to) the Phase 1 conceptual land use plan. The recommended wetland buffer dimension of 140 feet could be reduced by up to 25 percent at the rear of some lots. Isolated Wetland Fill. Three isolated wetlands within Phase 1 would be impacted by construction if development is proposed as shown on the Phase 1 conceptual land use plan. Wetlands D14, G1 and G2 may be completely eliminated as a result of grading to create uniformly level building areas for single-family homes. If this were to occur, the total wetland impact within Phase 1 would be approximately 32,900 square feet (0.76 acre). Alternatively, if City decision makers determine that small isolated wetlands should be preserved within Thurston Highlands, the grading plan would need to be revised to avoid these features, with the result that a reduced number of lots could be developed within the Phase 1 project area. No Action Alternative Under the No Action Alternative, there would be no potential construction-related impacts to wetlands, as no development would occur in the near-term. Insert Figure 3.4-3. H-Complex Wetland Buffers. Potential Developed-Condition Impacts Full Build-Out Conceptual Land Use Alternatives Stormwater runoff from urban environments can adversely affect wetlands in two primary ways. Stormwater can deliver an array of chemical and biological pollutants to downstream wetlands that are washed away from the developed environment. These may include nutrients and herbicides associated with lawn care maintenance, and petroleum product residues associated with automobile use on the site. Additionally, large volumes of stormwater runoff can overwhelm native wetland and stream systems, causing excessive erosion, drowning nest sites, and creating a tendency for non-native, invasive plant communities to develop. However, within this development, both aspects of these primary potential impacts will be largely avoided by site design and existing habitat structure. All stormwater runoff from development areas will be infiltrated, with treatment prior to infiltration. The treatment systems and infiltration through soils will remove potential contaminants (petroleum, hydrocarbons, phosphates and heavy metals) except nitrates. Wetland habitat structure will also negate potential impacts from increased shallow groundwater inputs to the systems. The majority of project wetlands are seasonal systems with “flashy” annual water regimes that fluctuate in direct response to precipitation. Wet years have a longer persistence of hydrology, while dry years have a shorter one. This sort of variable regime pre-adapts wetland vegetation, particularly woody vegetation, to annual changes in hydrology. Therefore, additional shallow groundwater inputs from stormwater infiltration should not adversely impact any seasonal wetland habitat, and would more likely provide a potential improvement by increasing hydrology so that organisms would have a better chance of completing their life cycles before the systems dry out. The only wetland system where the above scenario would not apply is Wetland A5, a permanent surface water condition with minimal water level fluctuation. This wetland has a water control feature in the form of a wide outlet berm that naturally regulates water levels. Any hydrology increases due to stormwater infiltration will not cause an increase in water levels in Wetland A5 because the excess will simply overflow the wide berm and “escape” downstream. Shallow groundwater inputs to Thompson Creek are discussed in the Draft Thurston Highlands Infiltration Effects Assessment (Pacific Groundwater Group 2008). Some of the isolated kettle basin wetlands within the Thurston Highlands property could serve as excellent stormwater detention/infiltration ponds because of their depressional structure relative to the surrounding landscape. While the bottom of these kettles is relatively impervious, resulting in wetland conditions, the sides are porous and would allow detained stormwater to infiltrate laterally. Site development could easily create downhill flow from developed areas that would deliver stormwater to these basins. While this situation would not eliminate the kettle basin wetlands, it would greatly diminish their functions (as described above), requiring full compensation for the area impacted. A hierarchical listing of potential isolated wetlands that could be used for stormwater management under any conceptual land use alternative is provided in Table 3.4-2. About one-third of the property wetlands are very small (less than one-tenth of an acre), isolated systems scattered about the landscape. Preserving all of these wetlands in place, with buffers, would be difficult in an urban environment. Even if they were preserved, they would not necessarily retain their existing functions. Given that these systems would be completely surrounded by a developed, urban environment, they would become “postage stamps” of preserved habitat. Wildlife habitat values would mostly disappear as the areas would become overrun with the presence of domestic pets and children. Because these systems are closed depressions, they would likely accumulate wind-blown or discarded trash that could easily find its way into the wetlands. Rather than occurring as attractive, functioning wetland habitats, they would more likely just become degraded systems within an otherwise managed landscape. For these reasons, it is recommended in the Wetlands Inventory, Impacts, and Mitigation Recommendations report, for the City’s consideration, to fill these small wetlands and provide compensatory mitigation in the form of new and/or enhanced wetland habitat associated with the much larger systems on the property ( wetland complexes that can be protected with upland connections to significant, undeveloped landscape ( for a net gain in habitat function. Phase 1 Development Concept Infiltration of stormwater runoff within the Phase 1 development area, if it could be designed to drain to the Wetland H complex, would produce beneficial effects. This system is a drained wetland/shallow marsh that is primarily degraded by lack of surface water in spring and early summer. This condition prevents full life-cycle activities by a wide array of wetland organisms, such as birds, amphibians and invertebrates. Introducing more surface water to the Wetland H complex as a result of site development would serve to improve this degraded function. The potential adverse effects of preserving isolated wetlands within the overall Master Planned Community, or using them for stormwater detention/infiltration basins, could also occur within the Phase 1 development area. No Action Alternative If the Thurston Highlands site were to temporarily remain in its existing condition, there would be no wetland fill for road construction, and no urban encroachment on the large number of kettle wetlands within the landscape. Mitigation Measures Incorporated Plan Features. Best Management Practices (BMPs) for erosion control will be implemented during construction activities with any of the conceptual land use alternatives. Silt fencing will be installed along all development edges bordering wetland buffers and upland areas to be preserved. Temporary stormwater basins will be employed throughout the construction area to detain stormwater runoff and allow sediments to settle out. The Thurston Highlands Grading, Drainage and Utilities Technical Engineering Report (KPFF 2008) describes proposed Best Management Practices during construction in more detail. The phased development proposal under any conceptual land use alternative would limit the amount of cleared and disturbed land at any one time to minimize the potential for sediment-laden runoff to reach wetlands. Applicable Regulations. If a decision is made to use some of the isolated kettle basin wetlands for stormwater detention and infiltration, stormwater runoff from developed areas will have been treated in accordance with the Washington Department of Ecology Stormwater Management Manual for Western Washington prior to release to landscape wetlands. There are numerous locations within the Thurston Highlands site where compensatory mitigation for wetland fill could occur to comply with the Development Agreement between the City and the applicant, and with applicable State and federal regulations. In general, compensatory actions would involve the creation of new wetland habitat by expanding the perimeters of some existing wetlands through excavations. Figure 3.4-4 depicts the preferred areas for potential wetland creation, with a rough estimate of potential square footage. Table 3.4-3 lists the wetlands in the suggested order of use for creating new wetlands. Total potential compensatory mitigation through creation and restoration could approach approximately 9.5 acres in these areas, which would be more than adequate to offset the maximum potential for the total area of wetland impacts if all isolated systems were filled. Other Possible Mitigation Measures. If it would be feasible to design stormwater infiltration in shallow spreaders at a location that would maximize input to the Wetland H complex through the month of June, this source could be used to increase the temporal duration of standing water in this wetland. This condition would be beneficial to shallow marsh wildlife - to extend the duration of favorable conditions during the breeding season. Insert Figure 3.4-4. Potential Wetland Mitigation Compensation Sites. Table 3.4-3. Potential wetland mitigation compensation sites (Coot Company 2008B). Wetland Creation Total Area (in square feet) Total Credit (in square feet)  A3-A4 Connection 15,290 15,290  A4 7,690 7,690  A7 7,310 7,310  F 21,630 21,630  B 74,460 74,460  H1 22,420 22,420  D11 45,460 45,460  A1 33,500 33,500  Subtotal:  227,760  Wetland Restoration/ Enhancement Total Area (in sq ft) Total Credit (in sq ft)  H1 368,895 184,447  Total:  412,207 sf (9.5 ac)   Compensatory mitigation for wetland impacts within the Thurston Highlands Phase 1 development area will entail enhancement, restoration and creation of wetlands within Wetland H1 as compensation for road construction to provide access to an adjacent property. The primary mitigation concept includes restoration through construction of a water control structure on the existing outfall ditch that would enable reflooding the drained system. Enhancement would entail excavation of small pockets of existing reed canarygrass (Phalaris arundinacea) within the existing wet meadow habitat, and wetland creation activities would involve excavations of upland ground around the wetland perimeter, primarily in an area dominated by Scot’s broom (Cytisus scoparius), to lower ground elevations and allow wetland hydrology to occur. Details of this activity will be provided in a separate report to be prepared at the time development approvals are sought for the Purvis property (adjacent to the Thurston Highlands east boundary). Other Possible Mitigation Measures. Wetland crossings by roads should be aligned to avoid as much direct impact (i.e., fill) as possible, under any conceptual land use alternative. However, site-specific situations regarding upland habitat features (e.g., mature trees) should also be taken into consideration. Consideration should also be given to incorporating an elevated structure across wetland crossings by roads in the southern portion of the project area (Wetlands A7 and F), capable of allowing animal passage beneath the roadway. The roadway crossing of the Wetland H complex to access the Purvis property to the east should be designed to avoid and minimize wetland impacts to the extent practicable. Consideration has been given for the alignment to cross the continuous drainage feature Wetland H3 at the narrowest point while simultaneously avoiding several, small wetland systems east of the drainage on property not within Thurston Highlands. It should be a requirement of the Thurston Highlands Homeowners’ Association to maintain kettle wetlands free from windblown (and other) debris, whether or not these features are used for stormwater management. Significant Unavoidable Adverse Impacts A small amount of wetland fill (approximately 2.43 acres) will be required to construct Tahoma Boulevard through the Thurston Highlands site, and a connecting roadway to serve adjacent property (to comply with the City of Yelm Connectivity Policy). Given that this amount of fill would constitute less than 0.2 percent of the total site area, less than 0.4 percent of total wetland area on the property, and would be offset by compensatory mitigation in the form of new wetland creation or enhancement of existing wetland complexes on the property, the unavoidable wetland impacts of the proposed development are not expected to reach a magnitude that would be considered significant or adverse.