anaerobic digestion and energy recovery project

7/29/2019 Anaerobic Digestion and Energy Recovery Project

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Anaerobic Digestion and Energy Recovery ProjectLewiston Auburn Water Pollution Control Authority, Maine

October 2009

http://www.lawpca.org/Anaerobic%20Digestion/Conceptual%20Design%20Report.pdf

6.3.2.3 VibrationDesign will be performed for the effects of vibration to provide appropriate protectionagainst structural deterioration, mechanical deterioration, and significant occupantdiscomfort. Under normal circumstances, the guidelines below will generally befollowed. If deemed necessary by the supervising structural personnel, a dynamicanalysis of the system will be performed.Mechanical Vibration

Concern for mechanical vibration is greatest for equipment such as blowers,generators, compressors, steady bearings at pump shafts and centrifuges. Operatingfrequencies, unbalanced loads, and specific design recommendations will be obtainedfrom the manufacturer by the discipline specifying the equipment.To avoid resonant vibration, the ratio of the structures natural frequency to the operating frequency of the equipment will be restricted to less than 0.50 or greaterthan 1.50. Where practical, the latter will be used to avoid resonance duringequipment startup and shutdown. Consideration will be given to applicable modesof vibration, including vertical, lateral, and rotational.Design will be performed in accordance with the following guidelines for equipmentwhich produce significant vibrational effects, where possible and appropriate.Equipment will be mounted on concrete foundations or supporting systems ratherthan metal supporting systems.A foundation mat will be provided with a mass equal to ten times the rotatingmass of the equipment or three times the gross mass of the equipment (minimum),whichever is greater.Major equipment foundations and supporting systems will be isolated byexpansion joints or independent supports from the remaining structure tominimize vibrational transmission.Vibration isolators, dampeners, and/or inertia blocks will be provided whereappropriate.Anchorage to foundations will be provided by embedded anchor bolts. Drilledanchors will not be used.Transient VibrationFor elevated steel walkways or platforms, beams will be provided with a depth

greater than or equal to 1/20 of the span.

6.3.3 Foundation Design6.3.3.1 ScopeCriteria will be established for the design of structure foundations in coordinationwith the geotechnical recommendations. Permanent structure foundation elementswill be designed to distribute loads to the supporting soil in accordance with theirallowable loads, and to accommodate predicted deformations of the structure caused
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by settlement or movement of the supporting elements. Structure foundationelements will be designed to resist effects of groundwater, including buoyancy.

6.3.3.2 Frost ProtectionProtection will be provided for structures against excessive heave or settlement due tothe action of frost. In most cases, the bearing level of frost-susceptible foundationelements will be established below the frost depth as provided in the geotechnical

report. For minor structures that are tolerant to some movement, bearing level maybe established above the frost depth, provided that frost formation can be inhibited inthe zone between the bearing level and frost depth by providing a layer of freedrainingmaterial.

6.3.3.3 Shallow Foundation SupportDesign of shallow foundation elements (footings and mats), including excavation andbackfill limits and details, will be performed in accordance with the recommendationsof the geotechnical report.To the extent possible, buried piping and ductbanks will be maintained outside theinfluence zone of the foundation elements. Limits of this zone will be establishedbased on bearing materials characteristics as documented in the geotechnical report.

A reinforced concrete encasement or other appropriate protection will be provided forany utilities extending into this zone.

6.3.3.4 Retaining WallsThe stability of retaining walls will be confirmed for appropriate lateral soil andgroundwater pressures, surcharges and other applicable loads. Passive pressuresfrom the soil in front of the wall or footing keys will not be used to reduce loads,stresses, or overturning and sliding effects, unless measures are taken to ensureagainst erosion or removal of the soil and approved. Design will be performed for thefollowing factors of safety.Overturning: 2.0Sliding: 1.5

For design of retaining walls with portions below the design groundwater level, theeffects of uplift pressures will be considered in stability analyses.

6.3.4.2 Codes and StandardsConcrete structures will be designed in accordance with the following, as appropriate.General structures: ACI 318Environmental engineering structures: ACI 350Reinforcing steel, welding: AWS D1.4

Structures that convey, store or treat liquid, are subjected to severe exposures, or haverestrictive leakage requirements will be designed as environmental engineeringstructures.Design of miscellaneous roadway structures, such as culverts and headwalls will beperformed in accordance with the state highway standards and the AASHTOSpecification.

6.3.4.3 Materials and Design Strengths

Design will be performed for concrete with the following minimum 28-daycompressive strengths (fc).Structural concrete: 4,000 psiConcrete topping: 4,000 psiPrecast concrete: 5,000 psiPrestressed concrete: 5,000 psi

Design will be performed for the strengths and properties of the following materials.Deformed reinforcing bars: ASTM A615, Grade 60Deformed reinforcing bars, welded or field bent: ASTM A706Welded wire fabric, plain: ASTM A185


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Welded wire fabric, deformed: ASTM A497

Section 9Preliminary Geotechnical, Civil and SiteDesign Recommendations9.1 General

As part of the current preliminary design process, CDM has developed the followingdiscussion summarizing conceptual geotechnical, site improvements and site designrecommendations and standards associated with the LAWPCA AnaerobicDigestion/Energy Recovery Project.

9.2 Conceptual Geotechnical Recommendations

9.2.1 Existing ConditionsThe existing Lewiston Auburn Water Pollution Control (LAWPCA) Facility is locatedat 535 Lincoln Street in Lewiston, Maine. The site is bounded to the west andnorthwest by Androscoggin River, to the south by a wooded area, and to the east byLincoln Street. The gated access road on the north side of the plant connects thefacility to Lincoln Street. There are a few commercial buildings located immediatelyto the east of the plant off Lincoln Street.The existing site is relatively flat, sloping gently from El. 135 to El. 137 over ahorizontal distance of 120 feet. The facility mixes and stores compost on the west sideof the property. The compost is available for public purchase. Piles of compost werenot shown on the recent ground surface survey.

9.2.2 Proposed ConstructionThe proposed construction for the anaerobic digestion and energy recover project

includes two 0.8-million-gallon digester tanks, a combined digester gas holding andsludge storage tank, a digester equipment building, above and below grade utilitiesand several at-grade pads for equipment.Two locations are being considered for the new structures. The first location(Option 1) is outside the existing fence line to the south of the existing chlorine contactchamber. The second location (Option 2) is within the existing facility to thenorthwest of the existing clarifiers, between the existing chlorine contact chamber andprocess building.Two different configurations have been proposed for the proposed digester tanks.The first option is a 50-foot diameter tank with side wall of 52 feet in height. This typeof tank will extend about 20 feet below ground surface (bgs) at the side wall and havea foundation bearing load of approximately 5 kips per square foot (ksf). The second

option is a 65-foot diameter tank with side wall of 30.5 feet in height. This type oftank is proposed to extend approximately 15 feet bgs at the side wall of the tank. Weunderstand that the second type of tank will have a foundation bearing load of about2.5 ksf.

The proposed combination digester gas and sludge storage tank has a diameter ofabout 50 feet and will extend about 15 feet below grade.We understand the new pump house building is a one story structure above grade


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with one level below grade. The structure is about 40 feet by 50 feet in plandimensions

A new cogeneration equipment pad is also proposed. The proposed pad has plandimensions of 70 feet by 25 feet.Existing conditions as well as approximate location of the new facilities for the twooptions are shown on Figure 9-1 and Figure 9-2.

9.2.3 Purpose and ScopeThe purpose of this study was to investigate the subsurface conditions at the twoproposed areas for the digester tanks and to provide conceptual geotechnicalengineering recommendation for foundation design and construction considerationsas required for the project. Specifically, the scope of work included the following:Review existing drawings and available subsurface information;Conduct a subsurface exploration program (Phase 1) consisting of two test borings(CDM-1 and CDM-3) to investigate subsurface conditions and obtain soil samplesfor geotechnical laboratory testing;Conduct laboratory tests on select soil samples to assist with classification of soilsencountered and determine engineering properties;Develop preliminary geotechnical recommendations for design and construction;Present CDMs preliminary recommendations, including the data collected as part of previous and recent subsurface investigations; andMake recommendations for additional investigations (Phase 2).

9.2.4 Subsurface InvestigationsPrevious Test Boring ProgramsPreviously a geotechnical exploration program was conducted at the site for the initialconstruction of the facility. Twelve test borings (L-1 through L-6, L-9, L-10, L-12, L-14,L-15 and L-17), were drilled between April 21 and May 6, 1969 by Jon J. Boyle ofMilton, Massachusetts. The test borings were drilled to depths ranging from 15 to 64feet below ground surface. The previous test boring locations in the vicinity of theproposed structures are shown on Figure 9-1. Previous test boring logs are providedin Appendix A.

Recent Test Boring ProgramRecent test borings were conducted at the two proposed locations for the digestertanks. Two test borings, CDM-1 and CDM-3, were drilled by Maine Test Boring, Inc.of Orrington, Maine between September 9 and 10, 2009. The test borings wereconducted with a truck-mounted drill rig using four-inch inside diameter flushjointedcasing with drive and wash drilling techniques. Test borings, CDM-1 andCDM-3, were drilled to depths of 59.7 and 65 feet below the existing ground surface,respectively.Split spoon sampling was typically conducted in soils at five-foot intervals inaccordance with ASTM D1586 (using a 2-inch-outside-diameter sampler driven24 inches by blows from a 140-pound safety hammer falling freely for 30 inches). The

number of blows required to drive the sampler each 6-inch increment was recordedand the Standard Penetration Resistance (SPT) N-value was determined as the sum ofthe blows over the middle 12 inches of penetration. Representative soil samples fromeach split spoon were collected, logged and stored in jars from later review andgeotechnical laboratory testing. Undisturbed tube sampling of fine-grained (cohesive)soils was conducted at select locations in general accordance with ASTM D-1587 usinga pushed Shelby tube sampler. The Shelby tube samples were trimmed and both endsof the tube samples were sealed with plastic caps, tape and wax for subsequentreview and laboratory testing. A CDM representative visually classified the soil


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samples recovered in the field using the modified Burmister classification system.When possible, groundwater levels at the test boring locations were estimated fromthe condition of the samples obtained and by the observed water levels within theborehole at the time of drilling. However, with the drive and wash drilling method,measured ground water level readings are not considered stable due to theintroduction of the drilling fluids in the borehole. Each borehole was backfilled with

drill cuttings upon completion.The recent borings were located in the field by taping and line of sight from existingsite features. The as-drilled locations are shown on Figures 9-1 and 9-2.Test boring logs prepared by CDM are included the Appendix B. The locations of thetest borings are shown on Figures 9-1 and 9-2.

9.2.5 Geotechnical Laboratory TestingGeotechnical laboratory tests were performed on select split spoon samples obtainedfrom the recent test borings. Gradation analyses were performed on six samples inaccordance with ASTM D422. Atterberg Limit tests were performed on two samplesin accordance with ASTM D-4318. The purpose of these tests was to assist with soilclassification, to assign soil parameters to use in engineering analyses and to assessthe reuse potential of the soils to be excavated.Results of the geotechnical laboratory testing are summarized in Table 9-1. Thecomplete geotechnical laboratory test results are included as Appendix C.

Subsurface ConditionsIn general, subsurface conditions encounter during the recent test boring programconsisted of a sequence of silty sand, clay, silt and sand underlain by a sand layer.Silty sand was encountered at both test boring locations. Typically, the silty sandlayer consisted of dry to wet, loose to medium dense, brown, gray, and orange, fineSAND, with varying amounts of silt and occasionally trace gravel. The silty sand isabout 8 to 19 feet in thickness at CDM-1 and CDM-3 respectively. SPT N-valuesranged from 8 blows/foot (bl/ft) to 16 bl/ft at the recent exploration locations.Below the silty sand, a layer of clay was encountered. The clay stratum consisted of

wet, soft to medium stiff, gray, silty CLAY with occasionally little to trace sand andtrace gravel. The clay layer was approximately 12.5 and 9 feet in thickness at CDM-1and CDM-3, respectively. SPT N-values ranged from 3 bl/ft to 8 bl/ft.Below the clay stratum, silt and sand was encountered at test boring CDM-3 with athickness of 35 feet. Typically, the silt and sand consisted of wet, loose to very dense,gray, SILT with little fine sand. SPT N-values ranged from 6 bl/ft to 52 bl/ft at therecent exploration location.

A sand layer was encountered below the clay layer at CDM-1 and below the silt andsand layer at CDM-3. Typically, the sand layer consisted of wet, medium dense tovery dense, brown or gray, fine to coarse SAND, with some to trace gravel and tracesilt. This layer was not fully penetrated at either test boring location. SPT N-valuesranged from 11 bl/ft to 53 bl/ft at the recent exploration locations. Refusal wasencountered at 59.7 ft below ground surface at test boring CDM-1.

A summary of the subsurface conditions encountered at our recent test boringlocations is presented in Table 9-2.Groundwater ConditionsGroundwater was observed in all of the recent test borings at the completion ofdrilling. Groundwater levels measured in the boreholes ranged from 16.5 to 17 feetbelow existing ground surface (approximately El. 118.4 to El. 118.8). However,stabilized groundwater levels can be difficult to obtain in borings drilled using driveand wash drilling methods due to the introduction of drilling fluid in the borehole. Inaddition, due to the sites close proximity to the Androscoggin River, the


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groundwater level is likely influenced by the river level.Variation in Subsurface ConditionsInterpretation of general subsurface soil conditions presented herein is based on soiland groundwater conditions observed in the recent test boring program and testboring logs of previous explorations conducted by others. However, subsurfaceconditions may vary between exploration locations. If conditions are found to be

different than assumed, recommendations contained in this report should bereevaluated by CDM and confirmed in writing.

.2.6Conceptual-Level Geotechnical EvaluationGeotechnical Engineering EvaluationGeotechnical engineering evaluations have been made related to the subject project.In general, these evaluations have been based on results of subsurface investigations,published correlations with soil properties and the minimum requirements of theMaine Model Building Code (MMBC), which references to the International BuildingCode. In addition, recommended design criteria are based on performance tolerances,such as allowable settlement, as understood to relate to similar structures.

Primary Foundation ConsiderationsThe primary foundation considerations related to the design and construction of theproposed tanks and structure include (but are not limited to):The presence and depth of the soft compressible clay layer:Based on the recent test boring data, the soft clay layer extends to a depth ofapproximately 21 feet bgs at the Option 1 location and 27 feet bgs at the Option 2location.The presence of loose silt and sand underlying the clay layer at the Option 2 location:

A loose silt and sand layer is underlying the soft clay layer at the Option 2 locationwhereas a well graded and denser sand layer is below the soft clay layer at theOption 1 location.The depth and foundation bearing load of the proposed structure foundations:The relatively large loads of the proposed 50-foot diameter sludge tanks (5 ksf) are

anticipated to induce larger settlements than are typical considered tolerable forstructures.The distance from and potential impact on nearby existing structures at the Option 2location.The proposed structures at the Option 2 location are located within approximately4 feet of the existing TWAS tank No. 4 and 13 feet off the existing sludge thickenertanks. Since the existing structures are understood to be supported on matfoundations on loose to medium dense silt and sand, those existing structures willbe susceptible to construction vibration-induced settlements. In addition, theexcavation for the 50-foot diameter digester tank extends at least 6 feet below theadjacent TWAS tanks. The excavation will extend within the zone of influence ofthe TWAS tank, potentially causing settlement/deformation of the existing tank.

9.2.7 Conceptual-Level Foundation RecommendationsLayout Option 1Based on our understanding of the proposed structures and the anticipatedfoundation loads, the proposed digester tanks, gas holding/sludge storage tank andpump house structure can potentially be supported on shallow foundation providedthe underlying soft compressible clay layer is overexcavated and replaced withcompacted structural fill. Based on conditions encountered at test boring CDM-1,


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between 1 and 6 feet of additional overexcavation will be required for the proposedtanks and pump house structure at this location.For the 65-foot diameter tank alternative, preliminary settlement estimates indicatetotal settlements of approximately 1 inch. However, total settlements are anticipatedto be up to 2 inches for the for the 50-foot diameter tank alternative. If theseanticipated settlements cannot be tolerated, deep foundations may be required.

Additional explorations and evaluations will need to be conducted to verify thesuitability of shallow foundation support for Option 1.Layout Option 2Due to the deeper extent of the soft clay layer and the presence of loose silt and finesand below the clay layer, deep foundations will likely be required for support of thetanks and associated structures at the Option 2 location.For the 50-ft diameter tank alternative, the proposed digester 2 will extend within thezone of influence of the existing TWAS Tank No. 4. To minimize the risk of impactingthe TWAS tank during construction, a stiff excavation support system with braces willbe required for the construction of the new digester tank. In addition, underpinningof the adjacent TWAS tank may be required to prevent excessivesettlement/deformation of the existing tanks.Earthquake Considerations

For purposes of determining design earthquake forces for the structures in accordancewith the Code, Site Class should be considered as D, provided the soft clay layer isover excavated and replaced with structural fill or the structures are founded on deepfoundations.Based on previous and recent subsurface investigation, the soils encountered at thesite are not considered susceptible to liquefaction.Ground Water ElevationFor the purpose of design, the groundwater level should be assumed to be at the 100-year flood elevation, which we understand to be at El. 136.

Deep Foundations

Based on the considerations discussed above, deep foundations may be required tosupport some structures depending on the location, the type of structure selected andsettlement tolerances.Option 1. Although a number of pile types are considered feasible, for the purpose ofconceptual design, we recommend that precast prestressed concrete (PCP) pile beassumed for any structures requiring foundations at the Option 1 location. TypicalPCP piles sizes include 12- and 14-inch square piles with approximate structuralcapacities of 99 and 134 tons, respectively.Option 2. Due to the close proximity of the proposed structures to the existingshallow-supported structures and the susceptibility of the existing structures tovibration induced settlements, we recommend the structures at the Option 2 locationbe supported on drilled, cast-in-place reinforced concrete piles.Based on the limited deep boring information, the required pile lengths are not

known at this time. However, piles are anticipated to extend to a depth of at least of65 to 70 feet bgs. Final design recommendations regarding foundation type and othergeotechnical design recommendations are pending additional test borings, finalfacility layout and loading information for the tanks and structures.

9.2.8 Recommended Phase 2 Exploration ProgramWe recommend an additional five borings be drilled after the final selection of tankand structure locations. The additional borings should be located at the proposedtanks, structures and equipment pad locations. Depending on the final choice oflocation and design of the tanks and structures, the borings should be drilled to a


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depth from 30 to greater than 75 feet in order to facilitate design of the anticipatedfoundation elements.The borings should be conducted using drive and wash techniques. Sampling shouldtypically be conducted at 5-foot intervals using a standard split spoon sampler (SPT).Split spoon sampling should be conducted in accordance with ASTM D1586.Representative samples should be taken from each split spoon and stored in jars for

later review and laboratory testing. Up to ten feet of rock should be cored at selectedborings if encountered to confirm the competence of the rock and assist incharacterizing the engineering properties rock. A CDM geotechnical engineer orgeologist should monitor the borings in the field and classify the samples recoveredusing the Burmister soil classification system.

9.3 Site Design Considerations9.3.1 Codes and StandardsThe site design will conform to the requirements outlined in the applicable nationaland/or local standards and codes. Codes primarily outline design requirements andconstruction details. It is not intended in the scope of this memo to list every code andstandard. Proper recognition of the applicable standards for a project is essential to awell-engineered, coordinated and constructed system. Listed below are those national

institutes and associations that publish the most widely accepted related U.S. codesand standards.American Association of State Highway and Transportation Officials (AASHTO);Maine Department of Transportation Standard Specifications for Highways andBridges (MHSSHB);American Society of Testing and Materials (ASTM); andMaine Dept of Environmental Protection, Maine Erosion and Sediment ControlLaw.New structures and roadways should be located using a coordinate system based onMaine State Plane Coordinate System or dimensioned from existing structures.Dimensions will be to column lines, outside face of building corner walls, or center ofcircular tanks. New roadways will be established based on centerline dimensions.Minimum width for new roadways will be 20 feet for two-way traffic with thepreferred width of 24 feet. Access driveways and one-way roadways will have aminimum width of 15 feet. Minimum radii at roadway intersections will be 35 feet toaccommodate turning requirements of 30-foot fixed wheel or 55-foot semi-truck typevehicles. New paved areas are anticipated around the proposed Digester Facility andGas Safety Equipment Buildings. Final dimensions will be determined based onaccess requirements and anticipated vehicle type. New pedestrian walkways willhave a minimum dimension of 5 feet.

9.3.2 Site PreparationIn order to maintain access to existing facilities and minimize impacts on dailyactivities construction routes will be identified. Limits of construction will beestablished to protect existing structures and staging areas. Existing facilities andnatural resource areas/lawn areas will be protected in areas not impacted by

proposed improvements. Temporary construction access ways may be required toprotect existing paved roadways. A temporary construction fence may be installedaround new work during the various phases to protect existing facilities andemployees and visitors.

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