TOWN OF SILVERTON WETLAND INVENTORY UPDATE

Wetland delineation data, historical and high-resolution imagery and existing data from local, state and federal sources

Ironwood Consulting

August 26, 2024

Preliminary Observations

The Silverton Wetlands Inventory (SWI) focused on the following:

• Ironwood mapped extensive, natural wetland complex associated with Shrine Hill. • Several wetland features were mapped on disturbed sites that are believed to be supported by artificial water (runoff). • Ironwood noted evidence of groundwater daylighting/discharge from the Shrine Hill area. • Several evaluated wetland complexes that were previously mapped would likely not fall under federal jurisdiction under the 2023 Conforming Rule. • Ironwood noted several areas supporting natural wetlands that are degraded due to historic mining impacts – these areas may be suitable for remediation/restoration actions in the future.

Project Objectives

The development of a comprehensive baseline inventory of wetland resources within the Town of Silverton:

First Priority – delineate previously unmapped wetlands. Second Priority – evaluate previously mapped wetlands that may no longer be under federal jurisdiction under the 2023 Conforming Rule (post-Sackett). Third Priority – evaluate previously mapped wetlands that are likely to be under federal jurisdiction (waters of the U.S.).

Methodology

The Town retained a consultant team to map the location and extents of wetlands within the town limits using aerial and field-based methods. Below is a summary of the sources the consultant team review and their field and desktop approaches which supported the development of the Silverton Wetland Inventory.

Data Sources

• National Wetland Inventory (NWI) • Recent high-resolution wet season landscape imagery (CDOT 2022) • Historic imagery • Parcel and Town boundaries • Hydrologic Units (watershed boundaries) • National Hydrography Dataset (NHD) • Approved Jurisdictional Determinations (JD) from the U.S. Army Corps of Engineers (USACE)

Collection of wetland data points using the methods outlined in the USACE's Regional Supplement to the USACE’s Wetland Delineation Manual: Western Mountains, Valleys, and Coast Region (Version 2.0).

Vegetation, soils, and hydrology were used to determine wetland/upland boundaries and classified sampled wetlands based on hydrogeomorphic (HGM) type and the Cowardin Wetlands and Deepwater Habitats Classification system.

High-resolution aerial imagery from the 2022 wet season was used to analyze where potential wetlands may be, and to refine wetland boundaries based on detectable greenness" and field verification. Wetlands that are small in size, fall within forested areas, or have experienced multiple years of extreme drought conditions may not have been detected during coarser scale aerial wetland mapping efforts, such as the NWI.

Private and Public Land access

Data was collected on public right-of-ways (allies, streets) and on private parcels where landowner permission was granted. Wetland boundaries on private parcels were mapped using high-resolution wet-season aerial imagery and ground-truthed where access/permission was granted.

Results

Wetlands by Hydrogeomorphic Classification

Classification method developed by USACE; incorporates geomorphic setting, water source, and hydrodynamics to understand physical, chemical, and biological functions of wetlands.

• Riverine - associated directly with or by overbank flooding from the Animas River, Mineral Creek, or Cement Creek, some groundwater influence. • Slope - associated with groundwater discharge and often associated with stream headwaters, Shrine Hill and Cemetery Hill wetland complexes. • Depression - associated with runoff, subsurface, or groundwater sources or combination thereof, usually closed topographic depressions and may have a perched water table.

HGM classification is based on the observed primary water source: groundwater (slope), surface water (depression) or river floodplain overflow (riverine). Secondary water sources may also contribute to the hydrology. Secondary sources may include precipitation, stormwater runoff, snowmelt, and/or point source discharges.

Wetlands by Cowardin Classification

Classification system developed by United States Fish and Wildlife Service (USFWS); used to categorize wetlands in NWI; based primarily on vegetation cover and habitat system.

• PEM – Palustrine Emergent (Inland, freshwater wetland dominated by herbaceous wetland plants). • PSS – Palustrine Scrub-Shrub (Inland, freshwater wetland dominated by scrub-shrub wetland plants).

Wetlands by Potential Clean Water Act Jurisdiction

• Pre-Sackett (Rapanos) wetlands • Post-Sackett (2023) wetlands

Pre-Sackett (Rapanos) Jurisdiction (left) vs. Post-Sackett (2023) wetlands (right)

Potential Waters of the State

House Bill 24-1379 directs the Colorado Department of Health and Environment (CDPHE) to develop a dredge and fill program for impacts to waters of the state and to establish permitting and mitigation rules by December 25, 2025. HB24-1379 will go into effect on January 1, 2025. Waters of the state include all waters and wetlands subject to federal Clean Water Act Section 404 jurisdiction in addition to waters and wetlands excluded from CWA jurisdiction post-Sackett decision, and isolated waters and wetlands. Categories of excluded waters and exempted activities are described in: HB24-1379.

Silverton WOTS

Potential Waters of the State

No* - Denotes - Wetland feature is subject to current/valid Approved Jurisdictional Determinations (AJD) which is applicable to portion of wetland feature/complex that overlaps subject property only, Waters of the State (WOS) jurisdiction is assumed after expiration of AJD; or feature contains or overlaps constructed ditch but drains a natural wetland system, may require site specific determination.

Discussion

Roughly 85 acres of wetlands were mapped within the Town limits. • The majority of wetlands within the town limits are supported by a natural water source (groundwater or overbank flooding). • There are approximately 5.4 acres (6.4 percent) of depression wetlands that are primarily supported by surface water including stormwater runoff and precipitation. Some slope and riverine wetlands may also be supported in part by surface water as a secondary source.

Acreage of wetlands by hydrogeomorphic classification

Wetland Jurisdiction • Roughly 8.8 acres of wetlands that were likely considered protected under the Clean Water Act Section 404 Program may no longer be under federal jurisdiction post-Sackett. • Nine prior approved Jurisdictional Determination have been issued for wetlands on private lands within the Town limits. Those issued within the past 5 years are still valid. • The State of Colorado may exercise enforcement discretion for discharges of dredge/fill material into wetlands that lost federal protection post-Sackett under Policy CW-17; a project notification process is in place in absence of a state permitting program. Policy CW-17 will remain in effect until January 1, 2025, at which time HB24-1379 will go into effect. • A landowner that is seeking to develop a property supporting a known or suspected wetland should request an Approved Jurisdictional Determination from the USACE and seek guidance to determine if their project meets the state notification requirement guidelines.

Acreage of 404 and Non-404 wetlands Pre and Post Sackett

Current regulatory guidance

Approved Jurisdictional Determination/Preliminary Jurisdictional Determination

Approved Jurisdictional Determinations (“AJD”) is a process used by the US Army Corps to make a definite, official determination whether aquatic resources in the review area are or are not jurisdictional (33 CFR 331.2).
The only USACE process for determining that an aquatic resource is NOT jurisdictional is an AJD
AJDs are valid for 5 years from the date of issuance and cannot be extended. A valid AJD holder may request that the Corps reassess a review area and issue a new AJD before the 5-year expiration date
Preliminary Jurisdictional Determinations (“PJD”) is a USACE determination that does not address questions of jurisdiction thereby treating all aquatic resources within the review area that could be jurisdictional as if they are jurisdictional for the purposes of permit processing
More information on AJDs and PJDs can be found here: https://watersgeo.epa.gov/cwa/CWA-JDs/FAQ/
To request an AJD, inquire with the Colorado USACE offices at: SPA-RD-CO@usace.army.mil

Clean Water Act Section 404 Program

The Clean Water Act of 1977 is a federal law enacted to maintain the chemical, physical, and biological integrity of the Nation’s waters, including wetlands
Section 404 of the Clean Water Act establishes a program to regulate the discharge of dredge or fill material into waters of the United States, including wetlands
Section 404 requires a permit be issued before dredge or fill material may be discharged into waters of the state unless the activity is exempt from Section 404 regulation; the Program does not prevent a discharge unless 1) a practicable alternative exists that is less damaging to the aquatic environment or 2) the nation’s waters would be significantly degraded (Section 404(b)(1) guidelines)
The program is jointly administered by the U.S. Army Corps of Engineers (USACE) and the Environmental Protection Agency; proposed discharge activities are regulated through a permit review process administered by USACE.
Compensatory mitigation may be required for impacts on waters of the U.S. to offset unavoidable impacts authorized through issuance of a Section 404 permit to meet the longstanding national goal of “no net loss” of wetland acreage and function (40 CFR Part 230, Compensatory Mitigation for Losses of Aquatic Resources under CWA Section 404, Final Rule)

Current Definition of Waters of the U.S. Following Sackett v Environmental Protection Agency and Effects on Colorado Waters

On August 29, 2023, the US EPA and USACE issued a rule revising the definition of waters of the U.S. conforming with decision in the case of Sackett v. Environmental Protection Agency
Under the current definition, changes were made to the jurisdictional category of waters and limited federal protections of certain waters categories of waters.
These changes place an estimated 60 percent of wetlands at risk due to the loss of federal protections under the CWA Section 404 Program
Additionally, many streams in Colorado would not be considered relatively permanent and may no longer fall under federal jurisdiction. An estimated 26 percent of streams flow only in response to rainfall and 59 percent flow seasonally.

Colorado State Waters

Colorado’s Water Quality Control Act defines “state waters” as “any and all surface and subsurface waters which are contained in or flow in or through this state” C.R.S. 25-8-103(19)
This definition has always been broader than the federal definition of “waters of the U.S.”
Subsequent to the SCOTUS Sacket Decisions, the Colorado Department of Public Health and Environment (CDPHE) – Water Quality Control Division (WCQD) and in accordance with the Water Quality Control Act, which requires that no person shall discharge a pollutant into state waters from a point source without having first obtained a permit from the division (§ 25-8-501(1), C.R.S.), the WQCD implemented Policy Number CW-17.
CW-17 authorizes the WQCB to exercise enforcement discretion for discharges of dredge or fill material into state waters that are not subject to federal Section 404 permitting.
HB24-1379 was signed into law on May 30, 2024, which directs CDPHE to develop a dredge and fill program for waters of the state and to establish permitting and mitigation rules by December 31, 2025. The program will go into effect on January 1, 2025.

Historic wetland areas and impacts

Historic Context

Review of imagery from the past century indicates wetlands in Silverton have been dynamic, and in some areas, groundwater supported wetland systems appear to withstand some disturbance and recover, and even expand, over time. While review of historical imagery does not give a precise understanding of the location and characteristics of historic wetlands, it is assumed that darker areas of vegetation in black and white photos and darker green areas in color photos indicate densely vegetated and wetter locations where wetlands potentially were located.

1912 panorama photos of Southwest and Northeast Silverton

1912 – A west-facing image taken from Kendall Mountain, showing the Shrine Hill, Animas River and valley bottom wetlands. Houses dot the areas on the fringe of the Shrine Hill wetland complex, which appears to be larger than the current wetland area. The wetland complex near the present-day Visitors’ Center appears to be more expansive than the current wetland. The Animas River wetland complex is typical of a free-flowing low-gradient river, with rapid and often dramatic changes over time from scour and inundation across a wide floodplain.

Silverton 1923 - viewing Kendall Mountain

1923 – An east-facing view from the Shrine Hill toward Town, with the Silverton School in the center. The Shrine Hill willow wetland complex (far right) appears to have been mowed or grazed down with willows mostly absent and houses along the margins that are no longer present.

c. 1950s – Aerial image of Silverton showing the Animas River wetland complex and the Shrine Hill wetlands. The Shrine Hill willow wetland complex appears to have recovered from 1923, with a potentially larger footprint than the current wetland. The brick factory site and historic disturbance on the south end of town is apparent.

1990 view of Silverton from Kendall Mountain

c. 1990s – A west-facing image taken from Kendall Mountain shows the Shrine Hill and the Animas River and valley bottom wetlands in color. The Shrine Hill wetland appears to have a larger footprint, with emergent wetlands (grasses, sedges, forbs, and rushes) encircling the willow wetland complex. The brick factory disturbance is seen on the southern edge of the image. The Animas River and valley bottom wetlands appear to include areas where development in the floodplain is encroaching, as indicated by dark green vegetation.

Next Steps

1) Assess wetland conditions using CNHP Ecological Integrity Assessment (EIA) Rapid Assessment protocol (Level 2 – Field Based Assessments). 2) Develop a wetland protection program that is consistent with best available wetland conservation science to support a resilient and functional "urban"-ecological interface that:

a) Is consistent with the Town's Master Plan and implementable through a land use planning code. b) Identifies opportunities for wetland impact mitigation that prioritizes protection of rare and hard to replace ecosystems. c) Considers a wetland's ability to provide ecosystem services that benefit human health and well-being.

3) Develop a robust stormwater and runoff management plan that considers functions that are currently being performed by wetlands that are primarily supported by stormwater/surface runoff.

4) Identify areas where wetland restoration could improve function of existing slope wetlands and reduce the risk damage from flooding and runoff events to private property.