RECLAMATION OF A STONE QUARRY IN A PONDEROSA PINE/GRASSLAND
ECOTONE
Mary Peterson
INTRODUCTION
Gravel and stone quarry operations result in extensive manipulation of
the landscape and of the ecosystems indigenous to their sites.
Disturbance to the natural contour of the topography has repercussions,
not only for those communities in the immediate vicinity, but also for
those adjacent. Quarrying presents prime conditions for accelerated
erosion because the topsoil environment required for establishment of
stabilizing vegetation is eliminated. Once quarry resources are
exhausted or operations cease, the landscape has often been degraded to
an extent that recolonization by pre-disturbance communities is
difficult, if not impossible. The cultural perception of such degraded
land is highly unfavorable for several reasons, spanning a range of
safety, ecology, and aesthetics-related concerns. The intrinsic legacy
of quarrying is the exposure of bare soil and underlying strata which
vary in stability, do not support vegetation, and which contrast sharply
with adjacent undisturbed landscape features. The reclamation of Conda
Rock Quarry on the front range of the Rocky Mountains in Colorado is an
example of a project motivated by public concern.
DESCRIPTION OF SITE AND MOTIVATION FOR RECLAMATION
The quarry is located at approximately 6300 feet on the northeast face
of Eldorado Mountain, twenty-five miles northwest of Denver, Colorado. General
opposition by the public in the nearby communities of Eldorado Springs
and Boulder to the noise and landscape scarring from the mine reached a
peak in 1986, when Wesley Conda & Sons proposed extending its operation
further up the face of the mountain. A local organization, People for
Eldorado Mountain, attempted to legally halt the expansion of the quarry,
which is readily visible from Eldorado Springs, but the county court to
which they brought the case had no jurisdiction over the private permit
nor the state-owned land. City of Boulder Open Space, saw the
opportunity to fund the purchase of both the lease permit from the
operator and the land from the state of Colorado, as the site in question
was contiguous to lands which were already part of the City of Boulder
Open Space and Natural Areas system. The acquisition would not only
extend its holdings, but also reduce the impact of the quarry on adjacent
areas and prevent further scarring of the mountainside. Reclamation
became the subject of public debate as the land changed hands in 1992.
In its acquisition of the mining rights, the City of Boulder also
became subject to the preexisting regulations, set forth in the Colorado
Mined Land Reclamation Board (CMLRB)-approved mining permit, for minimum
legally required reclamation of the site. The guidelines essentially
stipulated revegetation and suggested prevention of public access.
However, many of the site conditions presumed by the CMLRB reclamation
guidelines had changed over time due to continued mining operations. The
City therefore commissioned an outline and cost estimate of alternative
plans for the current conditions of the site. Through the cooperation of
the community, experts from multiple disciplines, the Open Space board
and private contractors, a plan for the site was adopted which ultimately
exceeded the minimum requirements. The goals emphasized public safety
and terrain stability foremost, with revegetation directed mainly toward
support of these goals.
The City of Boulder and surrounding area, including the quarry, is
situated in a transition zone where high plains and mountains interface,
creating a mountainous ponderosa pine (Pinus
ponderosa) community/grassland ecotone. Fire suppression had allowed
encroachment of the pines into ecotone areas surrounding the mined land,
and overgrazing had limited the competitive advantage of native grass
species.
Twenty-three years of quarry activity had left the site with a
substantially undercut talus slope on its southwest side and a bare cut
rock face along its west side. From an aesthetic standpoint, the bare
highwalls were severely cut and pinkish tan in color, contrasting sharply
with the well-oxidized, greyish-pink of the crustose-lichen covered
native rock outcrop. Approximately 122,000 cubic yards of material were
estimated to have been removed from the site by mining, and no topsoil
had been salvaged. Thus, the preexisting CMLRB reclamation plan, which
called for grading of overburden and spoils into the extraction corridor,
regrading of bordering highwalls into "gently sloping hills to harmonize
with the surrounding topography," and spreading stockpiled topsoil over
the pit and its haul roads, was deemed not feasible, mainly because of
the absence of suitable quantities of material on site.
The water table within the quarry had been substantially lowered as a
result of the upper strata removal and the porosity of the coarse
material below. Two small flows coming off the north and northeast
slopes had been interrupted by the mined area, but were deemed to pose
little threat for erosion except during isolated peak flow from major
storm events, which might cause redeposition of mined materials.
INTENDED RESULTS
As stated in the alternative conceptual reclamation plans, the
feasibility of complete restoration to match the visual and ecological
characteristics of the surrounding terrain would be very low due to
prohibitive cost and the inherent instability when attempting to
reconstruct original steep slopes from loose fill. Such fill would
mostly have to be obtained from a remote similar site, which would only
add to the cost, without contributing a useful solution to the main
concern, stabilization.
The goals for reclamation were ordered by priority: ensure public
safety by eliminating the threat of falling rock from the talus slope and
stabilizing its rock face of Fountain formation composition; assess the
threat of erosion and minimize its impact on the site; revegetate,
primarily to assist in success of the first two goals, but secondarily to
achieve ecological harmony with adjacent natural areas; and finally, halt
further aesthetic degradation, a result which planners hoped would be
incidental if the first three goals were achieved. Land use was intended
to be wildlife habitat and light public access.
INTERVENTIONS
Since stabilization of the site was the primary goal, the first stage
of the reclamation was to prevent rockfall by buttressing the undercut
talus slope with a reconstructed toeslope. Since on-site loose material
was limited, recontouring of the toeslope required overexcavation of the
existing quarry floor to achieve enough fill to match the original slope
of approximately 2:1. Steep sided piles were removed, as well as
interior pit dropoffs. The previous quarry floor was regraded to match
the grade of the surrounding native slope. Regrading the highwalls
would have caused more disturbance upslope, which was undesirable.
Assessment by a consultant from the Colorado School of Mines judged the
stability of the walls to be approximately equal to the stability of
adjacent native steep slopes. Regrading would not have substantially
changed the falling rock hazard. In addition, although the revegetation
plan suggested that woody species planted on the rock faces would assist
in stabilization as well as enhance aesthetics, the impracticality of
accessing the individual crevices, coupled with low expectation for
successful establishment in those areas due to limited available
groundwater, led to eventual abandonment of that portion of the plan.
Through the public review process, little interest was shown in chemical
use to speed oxidation of the exposed rock face solely for aesthetic
reasons, even though the scar has visibility from several points in the
Boulder County area. A railroad grade further upslope, excavated in the
early 1900's, had weathered over time to be indistinguishable from the
adjacent native rock, thus, the prospective natural weathering of the
current excavation was favored over immediate intervention.
Revegetation of the remainder of the site required the reconstruction
of suitable subsoil and topsoil to support native species. Analysis of
the on-site Lykins Formation material by Colorado State University Soil
Testing Laboratory gave evidence that, although low in organic matter,
the clay texture of the material would make it appropriate for use as a
subsoil. A layer approximately six inches in depth was used to cover the
rough fill on the talus slope and quarry floor areas. Since no topsoil
had been stockpiled during quarry operation it was necessary to obtain it
from some other source. Although the pre-existing CMLRB plan and the
tentative suggestions of the adopted revised plan both called for sewage
sludge mixed with other material for use as topsoil, investigation into
other sources led to eventual discovery of an alternative in the form of
filter fines from the City of Boulder Betasso Water Treatment Plant.
Filter fines are sediments, consisting mostly of mountain topsoil that
washes into the clean water pipeline en route to the treatment facility.
A 3% organic matter content and excellent sandy loam texture made it a
superior choice to sewer sludge. The material was used to cover the clay
subsoil at a depth of three to six inches.
The revegetation strategy of the adopted plan differs substantially
from the preexisting CMLRB plan, since the original plan did not take
into account the extent of regrading necessary for stabilization, the
lack of stockpiled topsoil, nor the subsequent poor edaphic conditions.
Because the encroachment of mountain pine species into the ecotone was
deemed to be more advanced than typical of its natural state before fire
suppression, and because biologists consulting on the project felt the
ecotone was being lost, the priorities for revegetation were changed to
emphasize more grassland and transitional species, rather than trees.
The main thrust of revegetation efforts centered around reestablishment
of cool season native grasses, with the addition of native forbs and
shrubs. Seed from local collecting was used as available, but to achieve
the desired planting density, additional supplies of native species seed
were obtained from a commercial source in Greeley, CO, approximately
fifty miled away.
The first seeding was done in the fall of 1994 and consisted mainly of
Pascopyron smithii (western wheatgrass) and Elytrigia dasystachya
(thickspike wheatgrass). Seed was spread by hand and raked into the
talus slope area, since the 2:1 slope precluded the option of equipment
use. To protect the seeded area, Weyerhauser Soil GuardTM bonded fiber
matrix was applied at a rate of 3500 lbs/acre. Those areas with less
than 2:1 slope, including the quarry floor, were hydromulched after
seeding. The Soil GuardTM successfully held during high winter winds,
but record high spring rainfalls in 1995 caused some slumping of the
material and rilling where slopes were particularly steep. However, due
to the favorable precipitation levels, germination and establishment of
seedlings was better than expected, both in the intact areas and the
eroded spots. During dry summer conditions, areas with a more shallow
topsoil layer were observed to have better seedling survival rates,
presumably because it permitted better contact of newly established plant
roots with the water-holding subsoil. Areas with deeper topsoil dried
out more in late summer. Areas with exposed clay subsoil also did not
perform as well, presumably because of the absence of suitable organic
matter provided by the topsoil dressing of filter fines.
Previously unseeded areas were seeded in the fall of 1995, along with
an additional seeding of the entire area, using a mixture containing
native grasses and forbs. Good germination of this second seeding has
been reported in the spring of 1996. Also in the spring of 1996, a group
of volunteers consisting of local citizens and members of People for
Eldorado Mountain participated in the planting of 160 shrubs, grown from
locally collected seed at local nurseries. The shrub species were mainly Cercocarpus montanus
(mountain mahogany), Rhus trilobata (three-leafed sumac), Crateagus sp. (red stem hawthorne), Ribes aureum (golden currant)
and Rubus deliciosus (Boulder raspberry), and their positioning on site was primarily around
sediment control structures. Seeding and weed maintenance will likely be
ongoing throughout the first few establishment years, as local seed
becomes available, and as needed to repair areas that may fail due to
weather conditions.
ASSESSMENT OF SUCCESS
There is no quantitative performance standard in place for the Conda
reclamation overall. However, beginning in 1997, assessments will be
made as to relative success of revegetation. By choosing the plan option
that called for buttressing the unstable talus slope, Open Space board
members and public reviewers seem confident that the best choice was made
to meet the goal of public safety preservation. Because the Boulder
community places high value on its natural areas, the success of the
project will remain closely monitored by its citizens.
REVIEW OF CONDA PROJECT
The main emphasis of the Conda project centers on the stabilization of
physical features as it pertains to safety and erosion control, with some
attention to aesthetic benefits. Clearly, although ecological concerns
are not specifically mentioned in the plan, through personal conversation
with consultants to the project Tamara Naumann and David Buckner, the
intent to reestablish ecotone structure and function to the area has
underlain much of the decision-making process. The utilization of
locally-collected seed for grasses, forbs and shrubs is an intentional
measure to preserve the integrity of ecotone-typical vegetation. The
decision to veer from the published plan by restricting the plant list
exclusively to grassland species and eliminating tree seedlings is an
effort to partially mitigate the loss of ecotone in adjacent areas.
These measures, if successful, should help to protect the transitional
zone as a distinct ecological community.
The plan does not address wildlife recovery specifically, but wildlife
integration is expected to naturally occur over time if vegetation
establishment is achieved. One shortfall of the project is its overall
lack of specifications for follow-up assessment of success in any
quantitative measure. Nor does it include guidelines for maintenance of
the area in the future, such as sustaining the intended vegetation mix
and keeping out invasives.
Only a brief reference to hydrology is made with regard to directing
surface runoff so as to minimize the movement of loose material from off
the site. Without more detailed hydrology information, comparison of the
site to adjacent natural areas to predict species suitability in terms of
water needs is difficult. Plan authors considered hydrology only as it
pertained to erosion. However, the success of the first year's
cool-season grass germination and establishment appears to be at least
partly linked to water availability. Should weather prove uncooperative
in the future, monitoring of the site may be necessary to ensure that
intended species are sustained.
Aesthetics were given only minor consideration in the reclamation plan,
which is surprising considering that the revegetated area makes up less
than one third of the readily visible landscape from most viewponts, with
the highwall scars remaining prominent. However, the plan allows for
future embellishment to the basic outline as the reclamation reaches its
final stages. The timeline for actual "completion" of the project
appears to be somewhat open-ended, although those activities specifically
set down by the documented plan have been accomplished. Recovery can
only be truly measured over the long term.
In many repects, every reclamation is a unique undertaking, since site
conditions cannot be expected to absolutely conform to previously
attempted projects. In this particular venture, it is encouraging to
find that consultants, officials, and the community were willing to go
beyond the "minimum legal requirements" with thoughtful consideration of
issues specific to their site. These extensions of the basic
recommendations will be likely to produce more rewarding long-term
results, and will give precedent to the use of materials and technique
that may be applicable to similar projects in the future.
REFERENCES
Buckner, David. 1995. Interim Results from Reclamation of a Rock Quarry
Near Eldorado Springs, CO. Text from poster paper presented at High
Altitude Revegetation Workshop.
Buckner, David. April 1996. Personal conversation.
Cameron, Wally. May 1996. Personal conversation.
Hatt, Kathleen. 1992. No Topsoil, No Mulch: A Dozer Makes the
Difference. Land and Water, 36:1. Pages 8-9.
Knapp, Eric E. and Kevin J. Rice. 1994. Starting from Seed: Genetic
Issues in Using Native Grasses for Restoration. Restoration and
Management Notes, 12:1. Pages 40-45.
Naumann, Tamara. April 1996. Personal conversation.
Ryan-Murphy Inc. 1993. Reclamation Plan Options, Conda Rock Quarry.
Zaslowsky, Dyan. 1995. The Battle of Boulder. Wilderness, 58:209. Page 25.
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