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Epvirouwept , Inc.
LARRY E. O'BRIAN 7985 VANCE DRIVE. SUITE 205A
FOUNDER ARVADA,COLORADO 80003
303-423-7297
FAX 303-423-7599
May 22, 2001
4L''_. _/-<I
Clerk to the Board
Weld County Commissioners Office
915 10th Street, 3rd Floor
Greeley, Colorado 81003
Re: Application for a Mined
Land Reclamation Permit
Dear Sir/Madam:
We are delivering to you here with a Technical Revision
adequacy review response packet for the S & H Mine to be operated
by Platte Sand & Gravel LLC. This copy of the adequacy review
packet is delivered to you pursuant to 34-32 .5-112 (9 ) (a) , Colo-
rado Revised Statutes 1995, as amended.
This packet must be kept with the original book, for public
review until the permit has been approved by the Division. We
will contact you once it is and make arrangements to pickup this
copy.
Please acknowledge receipt of the copy of this packet by
signing in the appropriate space provided below and returning one
copy of this letter to the person delivering the book. This will
be submitted to the Division of Minerals and Geology to prove
this packet was delivered to your office.
Yours truly,
ENVIRONMENT, INC.
Stevan L. O'Brian
enclosure
RECEIVED THIS-Y DAY OF /''(c rf-. , 2001, one
copy of an D.M.G. Adequacy review pieket for above mine.
Wel County Clerlcto the Board
By / [' ,2F a ' A/2'L
17.," „_ a �cvl- 35'1
- / / Pi/54/5
• •
•Epvirouweut , Inc.
LARRY E. O'BRIAN 7985 VANCE DRIVE,SUITE 205A
FOUNDER ARVADA, COLORADO 80003
303-423-7297
FAX 303-423-7599
May 22, 2001
Ms . Erica Crosby
Division of Minerals and Geology
1313 Sherman St. , #215
Denver, CO 80215
Dear Erica;
RE: Platte Sand & Gravel LLC
S&H Mine, Permit # M-2000-158
Continuance of hearing date
On behalf of Platte Sand & Gravel LLC (PS&G) , I am responding to
the Technical Revision review sent to Mr. Hoffschneider last week.
This response addresses and expands on the plan submitted on April 20,
2001 . It specifically addresses the four bullets on the first page of
your review. During design and installation of the armoring, whether
on the lake banks or river, PS&G will follow the guidelines in the
INSTREAM AGGREGATE AND RECLAMATION GUIDANCE DOCUMENT. If subsequent changes are
required to be made to this plan, PS&G will submit the proposed
changes to the Division of Minerals and Geology review and approval.
Initially the site was looked at to identify areas of excessive
scour, the depth and velocity of floodwaters across the mined area and
along the river banks that might cause problems . Identified were
areas along the river and on gravel pit slopes that are either lateral
berms or peninsulas perpendicular to the river, where flood water
could erode the banks and cause damage to structures . These areas are
where armoring will take place as mining progresses .
In addition, there may be areas on the river side of the bank
that may need armoring to protect the site. Prior to mining within
400 feet of the river Platte Sand & Gravel will prepare a map showing
the area where potential erosion could cause the river to enter the
excavation area. For example, there are three possible areas that may
be subject to erosive flows during a flood. They are the outside
edges of sharp bends in the river channel, adjacent to Meadow Lake,
Sharkey's Lake and Longhorn Lake. The map will be submitted to the
Division for review and approval.
•
ENVIRONMENT, INC. • PAGE 2
MAY 22, 2001
In the areas where armoring is necessary, the gradation of the
soil and subsoil (sand and gravel) will be examined along with vegeta-
tion characteristics to determine if the erosive power of the flood
will cut into the vegetation and soil. In those areas were it is
determined that erosion will occur the operator will place riprap
material, that cannot be lifted and moved by floodwater. This will
prevent erosion and down cutting on those slopes subject to scour. As
noted in the Division's review, we will use a D,p = 24 to fulfill this
requirement.
For this mine Pickett Engineering opted to use a 100-year event
as the design criteria for the plan. This is consistent with the
standard national procedures adopted by the Federal Emergency Manage-
ment Agency as the base flood for purposes of floodplain management.
PS&G recognizes that the erosion controls installed are only intended
to be effective up to the flow rate associated with the design event.
There may be residual losses from extreme flood events, above and
beyond those for which mitigation is cost effective.
As noted in the original flood plain information the 100-year
floodwater velocity at the south end of this mine will be from 1 .5 to
2 . 0 feet per second up to 3 .6 feet per second at the north end of the
site. The increased flows and velocity on the upper end are north of
the confluence of the South Platte River and St. Vrain Creek. These
velocity estimates are on a macroscopic scale, and were the average
velocity of the large volume of water flowing through the mine reach
during a 100-year flood. Since no specific velocities are known, the
operator will follow the general guidelines and conservative formulas
outlined in the guidance document.
The map in the Pickett study has been revised to include the
areas that may be affected by a 100-year flood. These areas incorpo-
rate the areas outlined in the division letter, in addition to those
shown previously. While the original plans were based on a qualita-
tive analysis of the river and floodplain, the operator will begin to
develop the qualitative analysis as mining progresses . Using the
information provided in the review letter, the map was revised to
extend the armoring around the south side of the slope in Meadow Lake.
Pit slopes that intersect with natural swales, abandoned tail water
ditches, et cetera, will also be armored. These areas do not readily
show on the map so as the site is developed, they will be identified
and armored using the design criteria outlined in this plan. The last
areas of concern are the gaswell pads and access road alignments in
Sharkey's Lake where they are in close proximity to the River.
•
ENVIRONMENT, INC. • PAGE 3
MAY 22, 2001
Attached are typical cross sections that will be used to design
the bank armoring. They are from the Division of Minerals and Geol-
ogy's Instream guidance document (Figure D-5, Figure D-7 , and D-8 ) .
Proposed armoring plan
Pickett Engineering used a D90 equal to 24 inches and the Divi-
sion suggested the minimum thickness should be D90 x 2 .0 for the pit
banks and D50 x 1 .75 to DSO x 3 .0 on the river banks . These guidelines
will be followed. If a change is necessary, revisions will be submit-
ted to the Division for review and approval. Armoring will be doubled
on each end of a reach whether in a lake or on the river, if it ends
on a natural bank.
Pit Slopes
The pit slope armoring will be placed on slopes no steeper than
2 .5H to 1V as shown on the guidelines. The thickness will be calcu-
lated by using D50 x 2 .0 to determine the thickness. The applicant
proposes using concrete rubble as riprap material. This material is
readily available to Platte Sand & Gravel and has been proven effec-
tive on other mines throughout Colorado. The concrete rubble is
angular, durable, and non-slaking in nature, but physical testing and
documentation showing that it meets the requirements and the gradation
specification will be conducted on the material prior to use on each
500-foot section. Physical testing will include a slake test and an
abrasion test to be sure the rubble is suitable for riprap. Any
unsuitable material will be used as fill as explained in the permit
application. The records of the test results will be kept in the
corporate offices for review.
Prior to placing the riprap the applicant will conduct at least
one gradation test for each 500 linear feet of riprap installation to
determine if the in situ material is suitable for the bedding. This
will be done to demonstrate and document that the filter bedding is
compatible with the riprap. This bedding will be a filter blanket of
gravel, or sand and gravel that will prevent soil movement into or
through the riprap. It is possible that the in situ materials will
create suitable bedding, particularly on the pit slopes since pit run
sand and gravel usually makes a good filter blanket. The armoring
will cover a band from the existing ground surface to an elevation 3
feet below the river invert on any gives section and will be keyed in
or doubled per the design specifications provided in the Division' s
guidance document. On the ends of the armored pit banks the depth
• • PAGE 4
ENVIRONMENT, INC.
MAY 22, 2001
will be doubled in accordance with the guidance document's recommenda-
tions.
River bank armoring
The armoring will be done along the river channel side of the
bank, but only where mining is within 400 feet of the river. A map
will be prepared and submitted to the Division showing the areas of
concern for review and approval prior mining within 400 feet of the
river. In the areas where armoring is required, Platte Sand & Gravel
will follow the guidelines published by the Division. In general, a
D50 x 1 .75 to 3 .0 will be used depending on the site specific require-
ments in each reach being armored. If an armored reach ends on a
natural riverbank, the Division' s published guidance for riprap end
protection will be followed. This calls for doubling the riprap
thickness at the ends of an armored reach that begin and end on
natural banks or extending them to non erosive areas .
The riverbank armor will be keyed five feet below the river bed
or, alternatively, extension of a thicker (doubled) layer of riprap
into the channel bed will be done as suggested in the guidance docu-
ment. (Figures D-5 and D-8, DMG, 1998, copies attached) . There may
be areas where keying the toe into the river bottom is not practical
so both methods may be used depending on what is encountered in a
reach. A granular bedding and filter will be placed under the rip
rap. As noted above the in situ material will be tested at each site
to determine if it is acceptable. Prior to installing riprap into
areas of a cut bank, it will be graded to no steeper than 2 .5 : 1 and
granular bedding and filter subgrade will be placed.
On the areas of riprap above the normal highwater line the
applicant will use a method of slope protection measures found in
section 2 .3 .2 of the Urban Drainage and Flood Control guideline
document. In general, a cover of dirt will be placed over the riprap
and willow stakes and grass will be planted to lock the dirt in place.
The willows will eventually spread and create a vegetation blanket
that slows flood water along a bank reducing erosion.
The timetable for riprap installation
The timing for rip-rap placement depends on how fast the mine
develops . The operator will make every reasonable effort to complete
final lakeshore protection measures for all such areas prior to April
1st of each year. The lakeshore sensitive areas are those areas
depicted in green on the map included with this response. Map Exhibit
C-1 show how the mine will look approximately 15 years after mining
ENVIRONMENT, INC. PACE S
MAY 22, 2001
starts . A line has been added showing when planning for riprap work
will begin. Prior to Platte Sand & Gravel reaching this line a map
showing where river bank armoring will need to be done will have been
submitted and approved by the Division. Also at that time, the bond
will be evaluated to determine the cost to rip-rap the lake banks that
will be created in the near future. At no time will mining take place
within 400 feet of the river without first having armored the banks on
the riverside that are subject to erosion and less that 400 feet from
the excavation area.
This line is at least 430 feet from the closest structure that
would be affected by down cutting if the river flooded. Note that
there are no lake banks next to a structure that could be affected if
flood water entered the excavation area and that mining will not be
within 400 feet of the river.
Armoring on pit side banks will begin once 500 feet of final
shore line has been created in an area needing armoring. No more that
500 feet of erosion sensitive final pit perimeter, will be exposed
without armoring, at any one time during the life of the mine.
Armoring will be done concurrent with reclamation so PS&G stays within
the 500-foot limitation. The bank sloping will be done prior to
armoring, the gradation test will be done to see if the in situ
material is acceptable, and the riprap will be placed. Resoiling and
revegetation will then take place according to the proposed plan.
Mining is not expected to reach an area where armoring of lake banks
will be necessary for 10 or more years .
Armoring will be completed prior to mining within 400 feet of the
river where the armoring is needed. The areas that need to be armored
will be identified on a map that will be submitted to the Division for
review and approval. The operator will continue to monitor the river
banks as mining progresses and if additional areas are identified
after the first map is submitted a revised map will be prepared and
submitted for Division review. On a conservative side mining is not
expected to reach the river area within the first 10 years of the
mines life.
The estimated cost
Review of the Division cost estimate and methodology is accept-
able to the applicant. While they believe they can do it at a lower
cost, it is understood that the cost for the Division to do the job is
greater than the applicant's cost. The applicant is choosing to use
concrete rubble but that material may not be available to the Divi-
sion. Thus, using quarry rock is the only alternative when calculat-
ENVIRONMENT, INC. • • PAGE 6
MAY 22, 2001
ing the bond. No bond change will be necessary for river bank armor-
ing since it will be completed before mining is within 400 feet of the
section needing armoring. Under the plan presented above, calculating
a bond to increase to build armor on lake banks will not be necessary
for at least 5 years and costs will have changed over that time. I
have repeated the Division's rational for bonding, but choose to leave
material and delivery costs out of the formula so they can be included
when the time comes to recalculate the bond to cover bank armoring.
Base line data for bond calculation:
Cost of Rip Rap = C„
Cost of bedding = C,,
Placement cost of Rip rap = Prr
Haul cost Rip rap = H, = Haul distance x per ton cost
Haul cost bedding = H,, = Haul distance x per ton cost
Rip rap volume per linear foot 11.4 tons
Bedding volume per linear foot 2.9 tons
Riprap Haul distance = 60 miles (one way)
Bedding Haul distance = 10 miles
Formula: (Crr x 11 . 4T)+(H, x 11 .4T)+(P,: x 11 .4T)+(Cb x 2 .9T)+(Hb x 2 . 9T)
If, as mining progresses, the locations and amount of riprap
needed in a particular area differs from the commitment PS&G is making
in this response they will submit a revision to the Division for
review and approval .
Thanks for your help and if you have any questions call me at
303-423-7297 .
Respectfully Submitted,
Environment, Inc.
Stevan L. O'Brian
President
enclosures
cc Platte Sand & Gravel LLC .
Weld County Clerk
file
a)TYPICAL CHANNEL RIPRAP SLOPE PROTECTION
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Figure D-7
Plan Views of End Protection Configurations:
a) Extension. Out of the Zone of Erosion with a Potential Reduction in Thickness,
s.naasn..F7r,.px and b) an Increase in the Thickness at the Ends of the Revetment
Rfprap•
Water Lever E:r'/ —Filter
BackilEl to Original .•.•
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for S^ix,r
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Figure 0-6
Cross-Sections of Toe Protection. Configurations:
a) Extension of the Riorap Below the Dry Bed and Balling, and
b) Placement of Extra Maters! Along the Bed to Launch itself into Developing
Scour Hares
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