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Response to ODEQ

19 January 2017

Mr. James Chabot, P.E. Riverbend Landfill Company 7227 NE 55th Avenue Portland, Oregon 97218 Subject: Response to Memorandum dated 6 December 2016 from the Oregon Department

of Environmental Quality – Review Comments on Final Grading Plan Modification Permit Application Report, Riverbend Landfill, SWD Permit #345

Dear Mr. Chabot:

Geosyntec Consultants, Inc. (Geosyntec) reviewed the comments received from the Oregon Department of Environmental Quality (ODEQ) on the Final Grading Plan Modification Permit Application Report (Modification Report) prepared by Geosyntec and dated 14 November 2016. Attachment A to this letter includes the memorandum with the comments by ODEQ. Below each comment is copied (in bold) followed by the response.

Comment 1: Page 7, proposed final cover system geomembrane. The proposed final cover system includes a “Super Gripnet geomembrane (Agru)”. I assume this would be a 60-mil HDPE geomembrane? I believe Agru makes this product in both HDPE and LLDPE. Because you propose to replace existing LLDPE with HDPE because of HDPE’s superior chemical resistance, this is should be clearly stated.

For the proposed final cover system, the thickness of the geomembrane will be 60-mil and the material would be linear low density polyethylene (LLDPE).

In those areas where the existing final cover system will function as a base liner for the new overlying waste and currently includes an LLDPE geomembrane, the LLDPE geomembrane will be replaced with a 60-mil-thick high density polyethylene (HDPE) geomembrane.

Comment 2: Page 8, alternative final cover system. The document refers to an alternative final cover system. Is there a reason why you are proposing two alternatives? Are the properties assumed in the slope stability calculations applicable to both alternatives?

The current final cover system includes an Agru Super Gripnet geomembrane which has one side with studs and the other side with spikes or texturing. The Agru Super Gripnet geomembrane is

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deployed with the studs facing up and a nonwoven geotextile is deployed above the studs. This system functions as a drainage layer for the overlying vegetative soil of the final cover. The drainage system also includes perforated drainage pipes in gravel-filled trenches.

Agru Super Gripnet geomembrane is a proprietary system (i.e., only one manufacturer controls the price); therefore, alternatives would be to use a double-sided textured geomembrane overlain by a drainage geocomposite supplemented with perforated drainage pipes in gravel-filled trenches or a blanket gravel layer instead of a geocomposite.

Yes, the properties assumed in the slope stability calculations will be applicable to both alternatives. For reference, a stability analysis of the final cover system was presented by Geosyntec in December 20141; the required interface strength of the final cover system would be the same regardless of the alternative selected.

Comment 3: Figures 4 and 5, boundary of current permitted area. The currently permitted waste disposal boundary should be shown for reference, so that the location of the proposed interior berm relative to the perimeter berm is easier to see.

The currently-permitted waste disposal boundary is shown in the revised Figures 4 and 5 attached to this response letter.

Comment 4: Appendix G, Specifications. Page 02219-2 states, “2.04 VEGETATIVE SOIL A. Soils obtained from on-site excavations that meet the requirements of Section 02249 for vegetative layer in the final cover system.” Please note that section 02249 of the specifications does not refer to vegetative soil.

We agree. Please refer to the replacement Section 02249 in Attachment B of this response letter.

Comment 5: Size of various areas. The report should identify the size of the FGPM area, and the size of the currently permitted area.

We agree. The size of the Final Grading Plan Modification (FGPM) area is 19.7 acres and is within the currently-permitted area. The currently-permitted area is 87.4 acres.

Comment 6: Identification of areas with LLDPE cap and with HDPE cap. Which portion of the currently capped area is capped with LLDPE (and must therefore be replaced by HDPE)

1 See Appendix E in Final Engineered Site Closure and Postclosure Plan, Riverbend Landfill, McMinnville, Oregon; prepared for Riverbend Landfill Company; WG1915; 30 December 2014.

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and which area is capped with HDPE? Can this be identified on a drawing? Review of Appendix F drawings 4, 7 and 10 indicate that the LLDPE was used on the eastern portion of Module 3, but a drawing showing the exact area where LLDPE geomembrane was used would be helpful.

The exact limits are not confirmed. The limits will be verified by performing a field investigation prior to construction.

Comment 7: Proposed HDPE liner and settlement. I did not find calculations showing that the proposed HDPE geomembrane will be able to withstand deformation due to settlement. The slope stability calculations are based on normal and shear strength. However, I believe this is a different issue having to do with tensile strength and the geomembrane’s ability to withstand deformation resulting from differential settlement.

Calculations that evaluated the tensile strain in the liner were performed for the Module 11 waste fill grades.2 The Module 11 waste fill grades are higher than for the FGPM grades; thicker waste results in higher loads and higher tensile strains. For the Module 11 waste fill grades, the tensile strains were acceptable (see Attachment C); therefore, the tensile strains caused by the FGPM grades, which are lower than the Module 11 grades, will also be acceptable.

Comment 8: Appendix F, drawing 3. What is the significance of the 105-foot and 50-foot offsets to stream banks? Are these regulatory requirements or zoning requirements?

The offsets are shown in the drawings to address County planning requirements.

Comment 9: Appendix F, drawing 10. Detail F does not specify the thickness of the existing foundation soil. What is the minimum required thickness for this layer?

According to Riverbend Landfill: Partial Closure of Modules 1, 2, and 3 Engineering Design Report prepared by EMCON Northwest, Inc. dated 6 June 1994 (see Attachment D):

“The area designated for closure (Appendix A, Drawing No. C-2) was considered using existing interim cover for use as a foundation layer. The interim cover soils were evaluated as part of this design, and also in a separate study as part of the 1993 permit renewal requirements.

2 See Appendix C (Settlement and Tensile Strain Evaluation) in Response to comments from Hart Crower dated October 9, 2015 on behalf of Oregon Department of Environmental Quality (ODEQ) regarding Riverbend Landfill Document Review, 27 October 2015, prepared by Geosyntec Consultants, Inc.

ATTACHMENT A 6 December 2016 Memorandum from ODEQ

State of Oregon Department of Environmental Quality Memorandum _____________________________________________________________________________________ Date: December 6, 2016

To: Jim Chabot, Waste Management From: Bob Schwarz, Oregon DEQ Subject: Riverbend Landfill, SWD Permit #345; Review comments on Final

Grading Plan Modification Permit Application Report Following are some comments on the Final Grading Plan Modification Permit Application Report, prepared by Geosyntec and dated November 14, 2016. Hart Crowser plans to complete their review within the next week. I will forward any comments they have at that time. Settlement calculations. Hari Sharma provided settlement calculations by email on November 22. I have a few questions I would like to discuss with Geosyntec by phone. Page 7, proposed final cover system geomembrane. The proposed final cover system includes a “Super Gripnet geomembrane (Agru)”. I assume this would be a 60-mil HDPE geomembrane? I believe Agru makes this product in both HDPE and LLDPE. Because you propose to replace existing LLDPE with HDPE because of HDPE’s superior chemical resistance, this is should be clearly stated. Page 8, alternative final cover system. The document refers to an alternative final cover system. Is there a reason why you are proposing two alternatives? Are the properties assumed in the slope stability calculations applicable to both alternatives? Figures 4 and 5, boundary of current permitted area. The currently permitted waste disposal boundary should be shown for reference, so that the location of the proposed interior berm relative to the perimeter berm is easier to see. Appendix G, Specifications. Page 02249-2 states, “2.04 VEGETATIVE SOIL A. Soils obtained from on-site excavations that meet the requirements of Section 02249 for vegetative layer in the final cover system.” Please note that section 02249 of the specifications does not refer to vegetative soil. Size of various areas. The report should identify the size of the FGPM area, and the size of the currently permitted area. Identification of areas with LLDPE cap and with HDPE cap. Which portion of the currently capped area is capped with LLDPE (and must therefore be replaced by HDPE)

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and which area is capped with HDPE? Can this be identified on a drawing? Review of Appendix F drawings 4, 7 and 10 indicate that the LLDPE was used on the eastern portion of Module 3, but a drawing showing the exact area where LLDPE geomembrane was used would be helpful. Proposed HDPE liner and settlement. I did not find calculations showing that the proposed HDPE geomembrane will be able to withstand deformation due to settlement. The slope stability calculations are based on normal and shear strength. However, I believe this is a different issue having to do with tensile strength and the geomembrane’s ability to withstand deformation resulting from differential settlement. Appendix F, drawing 3. What is the significance of the 105-foot and 50-foot offsets to stream banks? Are these regulatory requirements or zoning requirements? Appendix F, drawing 10. Detail F does not specify the thickness of the existing foundation soil. What is the minimum required thickness for this layer?

ATTACHMENT B Technical Specifications –

Section 02249 – Replacement

Geosyntec Consultants, Inc.

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SECTION 02249 EARTHFILL

PART 1 GENERAL 1.01 SECTION INCLUDES

A. Placing and compacting soil for earthfill at locations shown in the Construction Drawings, which includes: 1. anchor trench backfill 2. engineered fill 3. vegetative layer soil for final cover

B. Work includes the excavation, moisture-conditioning (disking, drying, etc.), segregation, stockpiling, placing and handling of soils to allow the construction of the project. The Contractor shall use soils from sources previously approved by the Owner.

1.02 RELATED SECTIONS

A. Section 02219 – Stockpiling and Soil Management B. Section 02221 – Excavating and Trenching C. Section 02223 – Refuse Removal D. Section 02225 – Subgrade Preparation E. Section 02710 – Polyethylene Pipe F. Section 02778 – HDPE Geomembrane

1.03 REFERENCES

A. Construction Quality Assurance (CQA) Plan. B. ASTM D422 - Standard Test Method for Particle-Size Analysis of Soils. C. ASTM D1556 - Standard Test Method for determining soil density in-place by Sand Cone

Method. D. ASTM D1557 - Standard Test Method for moisture-density relations of soils and soil

aggregate mixtures using a 10-pound rammer and an 18-inch drop. E. ASTM 2216 - Standard Method for laboratory determination of water (moisture) content of

soil and rock F. ASTM D2488 - Standard Practice for Description and Identification of Soils (Visual-Manual

Procedure). G. ASTM D4318 - Standard Test Methods for Liquid Limit, Plastic Limit, and Plasticity Index

of Soils. H. ASTM D 6938 Standard Test Method for In-Place Density and Water Content of Soil and Soil-Aggregate by Nuclear Methods (Shallow Depth)

PART 2 PRODUCTS 2.01 ANCHOR TRENCH BACKFILL

A. Anchor trench backfill shall consist of excavated on-site soils free from landfill waste,

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organic materials, and other materials, which may be highly compressible or which cannot be properly compacted.

B. Shall not contain blocks, broken concrete, masonry rubble, debris, expansive soil, or other deleterious material.

C. Maximum particle size of 3/8 in. in largest dimension. 2.02 ENGINEERED FILL

A. Shall consist of excavated on-site soils free from landfill waste, organic materials, and other materials which may be highly compressible or which cannot be properly compacted.

B. Shall not contain blocks, broken concrete, masonry rubble, debris, and other deleterious material.

C. Shall have a maximum particle size of 3 inches except where in contact with geosynthetics where maximum particle size shall be 3/8-inch.

D. Shall have an undrained shear strength (Su) of at least 1,600 psf at 10 percent strain when tested in accordance with ASTM D2850 at a confining pressure (not the consolidation pressure) of 8,000 psf; samples for strength shall be remolded to 95 percent of the maximum dry density determined in general accordance with ASTM D1557 and optimum moisture content plus 2.

2.03 VEGETATIVE SOIL (FINAL COVER)

A. The vegetative soil is the organic soil placed above the final cover geosynthetics for the purpose of supporting vegetation.

B. Soil shall be natural (i.e., not recycled or from waste materials), from on-site sources, and free of excess moisture.

C. Soil shall be free of wood, rubble, broken concrete, trash, and other objectionable materials that can damage the underlying geosynthetics.

D. The maximum particle size shall not exceed 2 inches in largest dimension. PART 3 EXECUTION 3.01 PREPARATION

A. Verify soils meet requirements for compacted soil before commencing work. B. Where excessive moisture is encountered, consider installing a dewatering system before

placing any material above areas of the subgrade. C. Contractor shall be prepared to shore the excavations. D. Liquids from dewatering shall be disposed as required by the State of Oregon regulations. E. Dewatering and shoring shall be designed by a Registered Professional Engineer in the State

of Oregon and submitted to the Owner. F. If required by Owner, prior to beginning soil placement, demonstrate that placement

techniques will not damage the adjacent geosynthetic materials. 3.02 PLACEMENT – GENERAL REQUIREMENTS

A. Scarify, moisture condition, and compact surfaces that will receive fill to a minimum of 90 percent of maximum dry density in accordance with ASTM D1557.

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B. Scarify and moisture condition the top of each compacted lift before placing subsequent lift. C. Bench or key compacted soil into existing subgrades and side slopes. Provide bench widths

equal to or greater than the compaction equipment. D. Areas inaccessible to large compaction equipment shall be compacted with small mechanical

or vibratory compactors. E. Do not place fill under water. F. Repair all eroded and desiccated soil areas before placing subsequent lifts. G. Compacted lift thickness shall not exceed 6 inches. H. Grade final compacted soil surfaces to remove ruts and gouges. Finish compacted soil above

grade by track-walking perpendicular to slope contours so that track marks are parallel to the contours.

I. Tolerances: 1. Horizontal ≤ 0.5 foot 2. Vertical ≤ 0.1 foot

3.03 PLACEMENT - ANCHOR TRENCHES (AND TERMINATIONS) A. Place geosynthetic materials in the anchor trenches as shown in the Construction Drawings. B. Compact backfill to a minimum of 90 percent of maximum dry density and at moisture

contents between -3 and +3 of the optimum moisture content as determined by ASTM D1557.

C. Do not place fill if anchor trench has water in it. D. Scarify the top of each compacted lift before placing subsequent lift. E. Place and compact fill to the lines, grades, cross sectional requirements, and dimensions

shown on the Construction Drawings. F. Grade final fill surfaces to remove ruts and gouges. G. Finish fill above grade by wheel-rolling along the length of the anchor trench.

3.04 PLACEMENT

A. Contractor shall sequence the work so that the various materials can be placed in tandem. B. Engineered Fill shall be placed and compacted to at least 95 percent of the maximum dry

density and at moisture contents between -2 and +2 of the optimum moisture content as determined by ASTM D1557.

C. Backfill surface shall be graded to avoid ponding or overtopping by storm-water runoff. At the end of each day’s work, the fill shall be worked such that positive drainage off the working platform is maintained.

D. Surfaces that will receive liner components need to meet the requirements for subgrade preparation in Section 02225.

3.05 PLACEMENT – FINAL COVER MATERIALS (VEGETATIVE LAYER SOIL)

A. Vegetative Layer Soil shall be placed and compacted to 85 percent of the maximum dry density and at moisture contents between -5 and +3 of the optimum moisture content as determined by ASTM D1557.

B. Construction equipment shall not be operated directly upon geosynthetics - see Part 3.07 of this Section for more details.

Geosyntec Consultants, Inc.

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C. A loose soil thickness of at least 12 inches shall be maintained over the geosynthetics in order to operate tracked vehicles. Turning of tracked vehicles should be kept to a minimum to prevent tracks from displacing the soil and damaging the underlying geosynthetics.

D. Backfill surface shall be graded to avoid ponding or overtopping by storm-water runoff. E. Soils shall be placed over the geosynthetics in such a manner that minimizes the

development of wrinkles in and/or movement of the geosynthetics. At the end of each day’s work, the fill shall be worked such that positive drainage off the working platform is maintained.

3.06 OTHER STRUCTURES AND IMPROVEMENTS A. All connections between storm drains, catch basins, drop inlets, drainage pipes, etc. shall be

water tight. Joints shall be kept at a minimum. B. Installation of other components (e.g., pavement, storm-water management improvements,

etc.) shall not damage the geosynthetics.

3.07 EQUIPMENT FOR PLACING SOIL OVER GEOSYNTHETICS A. Equipment used for placing soils shall not be driven directly over geosynthetics. A minimum

thickness of 1 ft of material is required between a low ground pressure dozer (such as a Caterpillar D-3C LGP bulldozer or equivalent) and underlying geosynthetics. A minimum thickness of 3 ft of material is required between rubber-tired vehicles and underlying geosynthetics. Equipment shall place material without braking. In areas of heavy vehicle traffic, such as access ramps, the material thickness should be at least 3 ft. In any case, the following table shall be complied with during construction:

Maximum Equipment Ground Pressure

(psi)

Initial Lift Thickness

(ft) 5 1.0 10 1.5 20 2.0

>20 >3.0

3.08 FIELD CONSTRUCTION QUALITY ASSURANCE (CQA)

A. The OWNER will perform CQA testing during earthfill placement in accordance with the CQA Plan.

B. CONTRACTOR shall cooperate fully with the OWNER in scheduling and performing field CQA tests and inspections. Include costs for coordination and assistance in unit prices.

***END OF SECTION***

ATTACHMENT C Module 11 – Settlement and Strain Evaluation

of Geosynthetics

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Text Box

Excerpt from Response Letter to ODEQ dated 27 October 2015

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Highlight

ATTACHMENT D Excerpt of EMCON Report dated 6 June 1994