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July 25, 2022 Jim Simon, District Manager Gallatin Solid Waste Management District P.O. Box 461
Three Forks, MT 59752 RE: Gallatin Waste Management District Landfill Task Order No. 6 Annual Compaction, Capacity and Performance Evaluation
Dear Jim:
Per Task Order No. 6 of the 2022 On-Call Engineering Services Contract, we conducted a
GPS topographic survey on June 29, 2022, to estimate the remaining life of the landfill and
evaluate the landfill performance.
The following data was used to perform this work:
1) Field surveys conducted every six months to a year,
2) As-built surveys of completed Phase 3 cell,
3) As-built surveys of completed Phase 4 cell,
4) As-built surveys of construction projects at the landfill,
5) Soil usage data provided by the District,
6) Waste quantity data provided by District, and
7) Master Plan for landfill.
Class II Waste Area Performance Evaluation (Phases 2, 3, and 4)
Topographic information from the field survey was used to generate a computer model and a
contour map of the landfill area on June 29, 2022. Great West Engineering compared the new
model to previous topographic surveys to evaluate the landfill performance over the period.
Table 1 shows the Phase 2 landfill performance calculated with GPS surveys over each period
the Phase 2 cell was open and the total since we have been involved in the landfill operation.
Portions of the Phase 2 cell were closed in 2013 and has not received any waste since
December 2011. Great West Engineering has not surveyed the Phase 2 cell since December
2011. The Phase 2 Closure area was surveyed for the purposes of record drawings that were
submitted to the Montana DEQ.
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Table 1 Gallatin County Landfill Municipal Solid Waste Phase 2 Cell Performance Analysis Summary
05/18/05-10/15/05 10/16/05-03/30/06 03/31/06-11/08/06 11/09/06-10/29/07 10/30/07 – 8/21/08 8/22/08-4/16/09 4/17/09 – 11/25/09 11/26/09 – 6/28/2010 6/29/2010-4/11/2011 4/12/2011-12/8/2011 Phase 2 Total
Total Fill
Volume 41,836 CY 56,005 CY 123,015 CY 218,970 CY 57,555 CY 68,969 CY 67,018 CY 61,328 CY 81,190 CY 66,261 CY 842,147 CY
Soil Volume 0 0 18,732 CY 38,500 CY 9,844 CY 17,789 CY 14,634 CY 10,526 CY 15,014 CY 9,738 CY 134,777 CY
Waste to Soil
Ratio NA NA 5.6:1 4.7:1 4.85:1 2.88:1 3.58:1 4.83:1 4.41:1 5.80:1 5.25:1
Tonnage
Accepted 28,720 Tons 43,646 Tons 77,587 Tons 116,490 Tons 31,498 Tons 36,893 Tons 41,560 Tons 42,254 Tons 60,187 Tons 53,484 Tons 532,319 Tons
Compacted
Waste
Density 1,373 LB/CY 1,559 LB/CY 1,488 LB/CY 1,291 LB/CY 1,320 LB/CY 1,442 LB/CY 1,587 LB/CY 1,663 LB/CY 1,819 LB/CY 1,892 LB/CY 1,505 LB/CY
Volume Per
Ton Ratio 1.46 CY/Ton 1.28 CY/Ton 1.59 CY/Ton 1.88 CY/Ton 1.83 CY/Ton 1.87 CY/Ton 1.61 CY/Ton 1.45 CY/Ton 1.35 CY/Ton 1.24 CY/Ton 1.58 CY/Ton
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Table 2 (1) Gallatin County Landfill Municipal Solid Waste Phase 3 Cell
Performance Analysis Summary
4/17/09-11/25/09 11/26/09-12/8/2011 12/9/2011-10/10/2012 10/11/2012-3/20/2014 3/21/2014-3/5/2015
3/6/2015-4/10/2016 4/11/2016-3/24/2017 3/25/2017- 4/11/2018 4/12/2018-6/13/2019
6/14/2019-6/25/2020
6/26/2020-7/7/2021
7/8/2021-6/29/2022
Phase 3 Total to Date
Total Fill
Volume 24,465 CY 0 118,087 CY 181,494 CY 131,209 CY 158,173 CY 138,082 CY 169,187 CY 192,661 CY 210,766 CY 267,452 CY 92,825 CY 1,828,153 CY
Soil Volume 3,708 CY 0 23,759 CY 27,506 CY 21,786 CY 33,760 CY 31,940 CY 33,588 CY 28,764 CY 49,398 CY 58,140 CY 19,836 CY 365,319 CY(2)
Waste to
Soil Ratio 5.6:1 NA 3.97:1 5.60:1 5.02:1 3.69:1 3.32:1 4.04:1 5.69:1 3.27:1 3.60:1 3.68:1 4.00:1(2)
Tonnage
Accepted 13,458 Tons 0 65,028 Tons 115,075 Tons 91,371 Tons 103,490 Tons 97,766 Tons 113,160 Tons 139,465 Tons 120,901 Tons
169,514 Tons 65,873 Tons 1,173,874 Tons
Compacted
Waste
Density 1,297 LB/CY NA 1,379 LB/CY 1,495 LB/CY 1,670 LB/CY 1,664 LB/CY 1,842 LB/CY 1,669 LB/CY
1,701 LB/CY 1,498 LB/CY
1,620 LB/CY 1,805 LB/CY 1,605 LB/CY
Volume Per
Ton Ratio 1.82 CY/Ton NA 1.82 CY/Ton 1.58 CY/Ton 1.44 CY/Ton 1.53 CY/Ton 1.41 CY/Ton 1.50 CY/Ton 1.38 CY/Ton 1.74 CY/Ton
1.58 CY/Ton 1.41 CY/Ton 1.56 CY/Ton
(1) Performance analysis data prior to 2009 has been omitted from Table 2. This data can be found in previous Annual Compaction Reports.
(2) Individual soil volume quantities do not add up to the total quantity to date. This is because "recycled soil" is counted during the individual time periods but not in the overall total. 8,352 CY of “recycled soil” has been reported to date.
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The Phase 3 and Class IV fill areas have overlapped. With consultation from the District, the
Class II and Class IV waste volumes will be combined. All waste placed in Phase 3 and Class
IV area will be tracked in the Phase 3 Cell and reported in Table 2.
The District began tracking recycled soil in 2019. Recycled soil is generally counted in
individual periods but not in the overall total. Removing the recycled soil from the soil usage
increases the waste to soil ratio to 4.00:1 in the Phase 3 cell. Recycling soil ultimately
increases the life of the site by utilizing less airspace with soil. The District should continue to
try to recycle as much soil as possible. Recycled soil was not used in Phase 3 during this time
period.
Table 2 shows the Phase 3 landfill performance and the overall average of that cell. The
Phase 3 cell did not receive any waste for three time periods due primarily to finishing filling
the Phase 2 cell. Performance analysis data prior to 2009 has been omitted from Table 2.
This data can be found in previous Annual Compaction Reports, or can be provided upon
request. Table 4 shows the overall landfill performance for Phases 2, 3, and 4 and the overall
landfill performance for Phases 2, 3, and 4 combined.
As measured by the volume per ton ratio, the overall space utilization for the Phase 3 cell over
the last period was 1.41 CY/Ton. This was 10.8% less air space utilization than last time
period. The overall performance of the landfill is measured by the volume per ton ratio. The
two components which directly impact the overall landfill performance are the compacted
waste density and the waste-to-soil ratio.
Phase 4 achieved a compacted waste density of 1,805 pounds per cubic yard over the last
period. The staff should be commended for the continued excellent compaction. The industry
standard for compacted waste density at landfills that operate 826-equivalent compactors is
1,200 lb/cy. The District staff is exceeding that metric with the operation. This high
compaction is due to the dedicated and consistent application of compaction techniques with
quality equipment and operators. The District needs to continue with the compaction
techniques it currently uses on the site.
The overall waste-to-soil ratio for the period was 3.68:1. This is a 2% decrease in soil usage
over the previous period. The District needs to continue to utilize the approved alternative
daily cover as often as possible in place of soil.
In summary, the industry standard for landfills this size is a compacted waste density of 1,200
lb/cy and a 3:1 waste-to-soil ratio, resulting in an overall volume per ton performance of 2.22
CY/Ton. The overall performance measured by GPS over this last period was 36.5% better
than standard landfill performance metrics. The landfill staff should be commended for
obtaining this outstanding waste density and overall landfill performance, ensuring the landfill
life is maintained and, in this case, actually extended via excellent performance criteria. This is
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especially true in this instance because the landfill has begun to commingle Class II and Class
IV waste streams. Class IV materials are more difficult to obtain high compaction levels
because of the nature of the waste.
Table 3 Gallatin County Landfill Municipal Solid Waste Phase 4 Cell
Performance Analysis Summary
6/14/2019-6/25/2020 6/26/2020-7/7/2021 7/8/2021-6/29/2022 Phase 4 Total to Date
Total Fill
Volume 102,186 CY 25,624 CY 210,275 CY 338,085 CY
Soil Volume 21,800 CY 4,662 CY 39,348 CY 65,108 CY(1)
Waste to Soil
Ratio 3.69:1 4.50:1 4.34:1 4.19:1(1)
Tonnage
Accepted 47,847 Tons 9,844 Tons 112,371 Tons 170,062 Tons
Compacted
Waste Density 1,190 LB/CY 939 LB/CY 1,315 LB/CY 1,246 LB/CY
Volume Per
Ton Ratio 2.14 CY/Ton 2.60 CY/Ton 1.87 CY/Ton 1.99 CY/Ton
(2) Individual soil volume quantities do not add up to the total quantity to date. This is because "recycled soil" is counted during the individual time periods but not in the overall total. 702 CY of “recycled soil” has been reported to date.
Phase 4 began accepting waste in the Spring of 2019. Table 3 shows the Phase 4 landfill
performance to date. As measured by the volume per ton ratio, the overall space utilization for
the Phase 4 cell over the last period was 1.87 CY/Ton. This is 28.1% less airspace utilized
than last time period, and 15.8% less airspace utilized than the industry standard. The large
airspace utilization swing can mostly be attributed to previous periods using large amount of
gravel and soil used to construct access roads in the Phase 4 cell, not compacting the waste
as much to prevent waste from puncturing the liner, and placing soil cover over a thin layer of
waste and not achieving a full lift thickness.
The Phase 4 area achieved a compacted waste density of 1,315 pounds per cubic yard over
the last time period. The industry standard for compacted waste density at landfills which
operate 826-equivalent compactors is 1,200 lb/cy. Landfill staff exceeded this metric in the last
year by 9.6%.
The waste-to-soil ratio for this time period is 4.34:1. This is 44.7% less soil usage than
industry and less soil usage than is typical for the landfill. The District needs to use the
approved alternative daily cover as often as possible instead of soil. While ADC was not
practical for the first lift in Phase 4, ADC should be used in the future.
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Overall, the landfill is performing exceptionally well, and landfill staff should be commended. If
landfill staff places waste in Phase 4 as they have done historically throughout other phases of
the landfill, performance metrics will return close to where they have been historically.
Table 4 Gallatin County Landfill Municipal Solid Waste Phase 2, 3, and 4 Cells Performance Analysis Summary
Phase 2 Total Phase 3 Total to Date Phase 4 Total to Date Phases 2, 3 and 4 Total to Date
Total Fill Volume 842,147 CY 1,828,153 CY 338,085 CY 3,008,385 CY
Soil Volume 134,777 CY 365,319 CY 65,108 CY 565,204 CY
Waste to Soil Ratio 5.25:1 4.00:1 4.19:1 4.32:1
Tonnage Accepted 532,319 Tons 1,173,874 Tons 170,062 Tons 1,876,255 Tons
Compacted Waste
Density
1,505 LB/CY 1,605 LB/CY 1,249 LB/CY 1,536 LB/CY
Volume Per Ton Ratio 1.58 CY/Ton 1.56 CY/Ton 1.99 CY/Ton 1.60 CY/Ton
Class IV Area Performance Evaluation
Great West has also measured Class IV performance since the Class IV area opened. Class
IV materials are much more difficult to obtain high compaction levels because of the nature of
the waste. Industry standard metrics for Class IV landfills are 750 lb/cy compacted waste
density and a waste-to-soil ratio of 6:1. This results in an overall volume per ton ratio of 3.1
CY/Ton. Table 5 shows that the landfill has historically exceeded industry metrics with the
Class IV operation. Considering the landfill has begun commingling Class II and Class IV
waste streams, the Class IV area performance is being accounted for with Phase 3
performance.
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Table 5 Gallatin County Landfill
Class IV Performance Analysis
4/17/2009-11/25/2009 11/26/2009-7/7/2010 7/8/2010-4/14/2011 4/15/2011-12/8/2011 12/9/2011-10/10/2012 10/11/2012-3/20/2014 3/21/2014-3/5/2015 3/6/2015-4/10/2016 4/11/2016-3/24/2017 3/25/2017- 4/11/2018 4/12/2018-6/13/2019 Total
Total Fill
Volume 33,767 CY 20,768 CY 46,752 CY 51,699 CY 28,538 CY 69,737 CY 58,665 CY 65,472 CY 61,868 CY 74,763 CY 111,849 CY 523,878 CY
Soil Volume 3,780 CY 2,285 CY 6,432 CY 6,977 CY 6,225 CY 13,739 CY 8,465 CY 13,940 CY 13,960 CY 15,624 CY 21,834 CY 113,261 CY
Waste to Soil
Ratio 7.93:1 8.09:1 6.27:1 6.40:1 3.58:1 4.08:1 5.93:1 3.70:1 3.43:1 3.79:1 4.12:1 4.51:1
Tonnage
Accepted 14,557 Tons 9,175 Tons 29,381 Tons 27,577 Tons 14,622 Tons 25,957 Tons 21,787 Tons 27,197 Tons 26,721 Tons 33,105 Tons 46,921 Tons 277,000 Tons
Compacted
Waste
Density 970 LB/CY 993 LB/CY 1,457 LB/CY 1,233 LB/CY 1,310 LB/CY 927 LB/CY 868 LB/CY 1,056 LB/CY 1,116 LB/CY 1,120 LB/CY 1,042 LB/CY 1,084 LB/CY
Volume Per
Ton Ratio 2.32 CY/Ton 2.26 CY/Ton 1.59 CY/Ton 1.87 CY/Ton 1.95 CY/Ton 2.69 CY/Ton 2.69 CY/Ton 2.41 CY/Ton 2.32 CY/Ton 2.26 CY/Ton 2.38 CY/Ton 2.25 CY/Ton
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Life Estimates
The performance data, tonnage and the Landfill Master Plan were used to estimate the
remaining life of Phase 3, the Class IV area, Phase 4, and the overall landfill. To estimate
the remaining life of Phase 3, the first step is to calculate the remaining air space in the cell.
The computer-generated land surface model from the June 29, 2022 survey was compared
to the interim fill plan for Phase 3 to determine the remaining air space. The interim fill
slopes for Phase 3 in the master plan were designed at a 5:1 grade. The slopes, thus far,
have been built at a 4:1 grade. To accommodate this change, Great West Engineering, with
consultation from the District, changed the interim fill slope design to a 4:1 grade. This does
not impact the overall life of the facility but changes the life expectancy of the Phase 3 cell.
This meets the requirements of the seismic design demonstration.
In order to estimate the remaining life of Phase 3, we needed to project the waste generation
throughout the remaining life of this cell. Currently 180,000 tons/year is the best estimate of
the annual tonnage for projections on remaining site life. This has increased from 160,000
tons/year from the previous estimates.
The total air space includes the final cover for the portion of Phase 3 fill which reaches the
final proposed elevations, so this is subtracted out of the air space available for waste and
daily/intermediate soil cover. The overall performance of Phases 2 and 3 is the best
estimate of how much daily and intermediate cover will be utilized at the site. However, the
District must continue to use alternative daily cover (ADC) to the extent possible to minimize
the landfill's air space usage. We estimate that the landfill will be able to utilize soil long
term at a 4:1 waste to soil ratio. The landfill nearly achieved this goal this period. To date,
the landfill is slightly above this ratio and needs to continue reducing the soil usage to
achieve a 4:1 waste to soil ratio consistently. The estimated daily and intermediate soil
cover usage is then subtracted from the available air space to determine the volume
available for waste.
The last variable to determine is the compacted waste density. The landfill averages 1,536
lb/cy historically. The industry standard for compacted waste density for a landfill of this size
with an 826 equivalent compactor is 1,200 lb/cy. It appears from the last 19 periods that the
District should be able to consistently achieve waste densities of 1,280 lb/cy and above. The
landfill staff does an excellent job of placing the waste in thin lifts and compacting the waste
with multiple equipment passes in both directions. For the basis of these life estimates, we
used a 1,280 lb/cy waste density.
The life estimate analysis is summarized in Table 6. The estimates assume there will be no
large “one-time” disposal projects. An example would be a large hailstorm or earthquake
generating a great deal of construction and demolition wastes. The capacity estimate also
assumes that the District will not expand its service area during the remaining landfill life. If
the District does expand its service area in the future, the life estimate would need to be
updated. The ultimate life of the site will be highly dependent on the waste tonnage received
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at the site and the landfill performance. If the tonnage increases over this estimate or the
landfill performance drops, the District will have less life than predicted.
In September 2010, an Addendum to the Landfill Master Plan was designed to include the
Class IV Expansion. During this Master Plan update, a new life estimate was developed.
Table 6 uses the updated Master Plan numbers to determine life projection estimates. The
volumes used to create Table 6 were calculated using CAD applications.
The Class IV area has been built with slightly steeper slopes (~3.5:1) than 4:1 which
increased height and the capacity of the Class IV area. To accommodate this change, Great
West Engineering, with consultation with the District, redesigned the remainder of the final fill
slope of the Class IV area to a 4:1 slope from the current elevation. The redesign of the final
fill for the Class IV was combined with the final fill for the Phase 3 cell to determine the life
expectancy. The redesign was completed July 23, 2019.
Based on the waste streams received prior to combining Class IV waste and Class II waste
volumes, the landfill accepts approximately 20% Class IV waste and 80% Class II waste on
average.
An effective combined density will be used to estimate the remaining life. Therefore, the life
was estimated using 80% of 180,000 tons/year (144,000 tons/year) for Class II waste and
20% of 180,000 tons/year (36,000 tons/year) for the Class IV waste estimates.
The life of each area was calculated and is shown in Table 6. The life estimates for the
waste accepted in Phases 3 and 4 shown in Table 6 are based on an effective volume per
ton ratio of Class II and Class IV wastes. The Class II wastes are estimated at a 1,350 lb/CY
compacted waste density, 4:1 waste-to-soil ratio and an overall volume per ton ratio of 1.85
CY/Ton. The Class IV waste are estimated with a 1,000 lb/CY compacted waste density,
5.5:1 waste-to-soil ratio and an overall volume per ton ratio of 2.36 CY/Ton. An effective
volume per ton ratio of Class II and Class IV wastes based on 80% Class II and 20% Class
IV equals 1.95 CY/Ton.
The Phase 3 and Phase 4 cells will accept both Class II and Class IV waste streams at
180,000 tons/year. The Phase 3 cell will reach capacity in 0.17 years and the Phase 4 cell
will reach capacity in 3.43 years. Therefore, the total life of the landfill is 3.6 years (Phase 3
– 0.17 years + Phase 4 – 3.43 years).
Table 6 Gallatin County Landfill Life Projection Estimates (July 2022)
Phase 3 and Class IV Life (Based on 180,000 Tons/Year) 0.17 years
Phase 4 Life (Based on 180,000 Tons/Year) 3.43 years
Total Life (Based on 180,000 Tons/Year) 3.6 years
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Thank you for the opportunity to assist the District in the operation and planning of the
landfill. If we can be of any further assistance or you have any questions or comments,
please contact me at my office.
Sincerely,
Great West Engineering, Inc.
Stephanie Beckert, PE Project Manager