Preseted at the 2010 TESNAR COnference.

1. Determining Indirect Impacts to Wetland Plant
Communities resulting from Mine-induced changes to
Groundwater Hydrology
The Crandon Mine
Experience
Jim Arndt, Ph.D., Westwood
Professional Services
John Almendinger, Ph.D., Mn Dept.
Natural Resources
History: 7 years Scoping, 20 years data collection
Exxon, Crandon Mining Company, Nicollet Minerals
COE Lead Agency, EPA, WiDNR, Tribes, Public Interveners

2. National Environmental Policy Act
• Promote informed federal agency decision-making by
ensuring that detailed information concerning significant
environmental impacts is available to both agency leaders
and the public.
• An EIS is the most detailed NEPA instrument that is reserved
for projects that have a substantial potential for adverse
environmental impact.
• Lead and reviewing agencies identify and evaluate the
likelihood and magnitude of significant impacts.
• If potential impacts cannot be identified or their
magnitude determined, informed decisions regarding the
nature of the impacts, and the potential for avoidance,
minimization, and mitigation cannot be made

3. Mine Facilities
Mine Infrastructure
• Facilities (119 acres)
• Access Roads
• Power Transmission
• Pipelines
• Tailings Management
Area (292 acres)
• Soil Absorption System
(SAS)
• Surface Water
Supplementation
• Rail lines
Proposed Action: 3 years construction, 28 years mining, 4
year reclamation

4. Wetland Resources
Analysis Plan: Issues
• Direct and indirect impacts on
wetland hydrology, plants, soils,
and functions
• Direct fill impacts
• Indirect impacts on wetlands and
wetland plant communities from
mine de-watering,
supplementation well(s), and SAS
operation, reclamation and
recovery of watertables.

5. Significance
Criteria (Easy):
Hydrology,
Vegetation, Soils
• Wetland hydrology is removed (WT not > 12 inches for
greater than 5% of the growing season.
• Wetland vegetation removed. Hydrophytes less than
50 percent (aerial coverage) using vegetation
assessments stipulated in the 1987 Wetlands
Delineation Manual.
• Wetland soils removed. Would no longer have the
moisture regime required of hydric soils
Result in change in wetland jurisdictional status

6. Significance Criteria
(Hard): Wetland
Functions
• Percentage reduction or increase in raw
scores of functional assessments
performed on wetlands that could be
affected by the project
• Percentage to be determined from
distribution of wetland functions in
individual wetlands and throughout the
impact area of influence
Indirect impact, losses and gains in functions

7. Impact Area of Influence
• Most conservative estimate of
0.25-
0.25-foot contour of estimated
steady state water table
drawdown with mine de- de-
watering and supplementation
well using USACE model
• Most conservative estimate of
0.25-
0.25-foot contour of estimated
steady state water table rise in
the SAS area using USACE
model

8. Methodology: Define Baseline Conditions
• Existing wetland
delineations, wetland
hydrogeologic settings, and
wetland function
assessments
• Baseline conditions assumed
to represent No Action
conditions
• Baseline data entered into a
database for GIS analysis

9. Impacts on Wetland Plant Communities
Baseline Plant Community Data
• 46 detailed semi-quantitative samples (PEC)
• 9 Detailed Species Lists (Foth & Van Dyke)
• 15 quantitative transects (Normandeau)
• 158 Functions Assessments (Normandeau)
• ~ 20 wetland delineations
• ~100 photo-interpretations to class

10. Site
Characteristics
• Sub-glacially molded
till
• Lots of outwash,
complex stratigraphy
• Underlying sandy
unit (layer 2) of
concern
• Wetland at varying
elevations
• Wetlands of varying
characteristics
• Three recharge types
with respect to
interactions with
layer 2
• Five condition classes
with respect to inlets
and outlets, surface
water interactions.

11. PEC Functions Database (Demo, Output)

12. Hydrology
– Determine impacts of groundwater drawdown and
mounding on wetland hydrology
– Compare baseline hydrologic regimes to steady state
cone of depression or groundwater mound from
USACE groundwater model (controversial)
• Impact assessment performed in a GIS

13. Groundwater Drawdown Modeling (per EarthTec)

14. Step 1: Assignment of Wetlands to NPC
Classes: Reclassification
• Compare existing plant communities to those adapted to
conditions under the Proposed Action
• Existing plant data from ecological plot studies in
Minnesota and Wisconsin were used to rank native plant
species and the Crandon wetlands by affinity for specific
hydrologic regimes
Ordination Example

15. Minnesota Native Plant Classification System
WFn53a
WFn53a Northern Wet Cedar Forest Class Code
WFn53a
Ecological System – Wet Forest
Floristic region – Northern
Moisture (0 driest – 9 wettest)
Nutrients (0 poorest-9 richest)
Type (a driest/poorest in class)
– Other Similar Classes
• FPn63 – Northern Cedar Swamp, wetter, peat
dominated, different understory plants.
• WFn64 – Very Wet Ash Swamp, more ash, wetter,
richer.

16. Portion of Class
Description

17. Fieldwork: Crandon Wetlands to Mn NPC Classes

18. PEC Project Field Database (Demo, Output)

19. Air Photo Interpretation and Field Verification
Used to Place Crandon Wetlands In Minnesota’s
NPC Classification

20. Step 2: Ordination (DCA Decorana)
– Non-metric, multi-dimensional ecological statistics. Similar samples
are near each other and dissimilar objects are farther from each other.
– These relationships are then characterized numerically and/or
graphically.
– John Almendinger (MnDNR) very familiar with DCA ordination and
used extensive dataset developed on 1,079 (now over 2000) releve plots
in Minnesota to develop classifications on wetlands for which we had
detailed Crandon Data
• MnDNR data with functional understanding of how the vegetation
relates to water-table, nutrient status, substrate, and hydrology.
• Representative wetlands in the Crandon Mine Project
• Data accumulated, plant community numbers/distribution, soils,
hydrology, classification
• Placed in a relational database

21. MnDNR Data with
Wetlands
in Crandon Area

22. Ordination FAQs
http://ordination.okstate.edu/

23. Step 3: Assessment of Indirect
Impacts to Plant Communities
• Estimate new plant
community composition
assuming the rate of the
change agent (e.g.,
groundwater drawdown)
would result in converting
one adapted native plant
community to another

24. Watertable Data for Wetland Classes in the Crandon
Area

25. Hydrologic Impact Sensitivity Groups
• None-to-Slight HSIG. Monitoring or mitigation is not anticipated.
Sufficient habitat variability exists for most plants to persist within a wetland
basin subject to falls or rises in WT position and variance. Changes in species’
abundance may occur, but significant loss of species or invasions of weedy
species capable of dominating the wetland are unlikely.
• Moderate HISG. Monitoring is recommended, and mitigation would depend
upon the monitoring results. Turnover in species (losses and invasions) or
changes in physical site properties are likely to cause slow recovery to the
community’s initial state. Permanent changes in site properties or the invasion
of ecologically dominant plants are possible. Wetlands sensitive to modest
changes in mean WT position or altered variance were placed in this category
when these modest changes were small compared to the predicted accuracy of
the groundwater model.
• Severe HSIG. Mitigation likely required. Class-level, System-level, or
irreversible changes in the vegetation are expected, even after restoration of the
groundwater regime. Permanent alteration of physical site properties, high
turnover in species and invasion of ecologically dominant plants expected. Not
applicable to recharge or supplemented wetlands.

26. Example: WFn53, Northern Wet Cedar Forest
– Vegetation: Patchy to interrupted canopy (25-75% cover) dominated by
white cedar. Black ash may also be abundant. The groundlayer is herb-
dominated and very rich, with 50-100% cover in a typical stand.
– Soils: Layer of well-decomposed organic material 25-150 cm deep over
mineral soil. Underlying mineral soil can be of almost any texture, but
medium and fine textures are common.
– Hydrology: wet throughout most of the growing season, but dry
sufficiently often to prevent further accumulation of peat. Frequently in
areas of groundwater discharge evident as seepage areas, spring runs,
or cold-water streams. (Mean WL 2.2 feet +/- 2.4 feet)

27. Example: WFn53, Northern Wet Cedar Forest
Sensitivity to Groundwater Drawdown
• None-to-Slight HSIG; < 2.0 foot drawdown; remains in WFn53
– Class has sufficient habitat variability for most plants to persist within
a wetland basin subject to falls in WT position under 56cm (~2 feet).
• Moderate HISG; 2-4 foot drawdown, conversion to Northern
Wet Ash Swamp (WFn55)
– WFn55 has similar variance in WT compared to Northern Very Wet
Cedar Forest but the mean WT position is significantly deeper.
• Severe HSIG; > 4 foot drawdown, conversion to Wet-Mesic
Hardwood Forest
– The mean WT position at top of gray (gleyed) horizons at about
150cm with bright iron-rich mottles, which indicate soil aeration,
were used to estimate the variance in WT position as about 130cm.
This would be sufficient to convert most very wet cedar forests to a
community that is essentially terrestrial.

28. Demonstration: Appendix B

29. Step 4: Summarize Data:
Hydrologic Impact
Sensitivity Classes for
Discharge Wetlands

30. Hydrologic Impact
Sensitivity Classes for
Recharge Type 3 Wetlands

31. Hydrologic Impact
Sensitivity Classes for
Soil Absorption
System Wetlands
(Groundwater Rise)

32. Suggestions, Issues
• Groundwater hydrology: variability, scale,
accuracy
• Function and value assessments: limited
categories, resolution, not available for all
wetlands
– Use accepted model, incorporate recent literature, new
data, airphoto interpretation, interpolation
• Plant community assessments: Need for
quantitative data
– Detailed assessment of representative wetlands
– Monitoring plots