5. Construction

Construction/Project Manager – Referred to as the Construction Manager or Project Manager. This individual is the official representative of the Owner and is responsible for all construction activities, including oversight and direction during construction. The Project Manager is also responsible for coordinating construction and CQA activities for the project. The Project Manager serves as a liaison between all parties involved in the project to ensure that ongoing communications are maintained and that resolution is reached for all CQA issues that arise during construction. Duties for the Construction/Project Manager may include:

• Review construction drawings and project specifications.
• Coordinate with the Engineer / Engineer of Record prior to construction to ensure that the construction drawings and specifications are integrated with the CQA program.
• Administer the construction contracts, including any associated changes that occur during the course of construction.
• Assure that Engineer of Record receives required information for review, change requests and other information to assure completion of certification report.
• Coordination of all construction activities
• Coordination with regulatory agencies
• Coordination and implementation of project Health and Safety Plan
• Scheduling and coordination of construction activities with required CQA testing and activities

Engineer – Also referred to as Design Engineer or Engineer of Record, this individual is responsible for the design and preparation of the construction drawings and specifications. The Engineer should be a registered professional engineer in the state in which the work occurs. The Engineer should have the authority to stop any aspect of the work that is not in compliance with the CQA Plan. Work would then resume once a corrective action has been approved by the Engineer. In the absence of the Engineer from the work site, the duties and responsibilities of the Engineer are delegated to the CQA Monitor(s). The specific responsibilities of the Engineer may include the following:

• Develop the construction drawings and specifications, and CQA Plan.
• Train CQA personnel on CQA requirements and procedures.
• Schedule, review, coordinate, and approve CQA activities to ensure that testing and documentation are complete, accurate, and in accordance with the site-specific design requirements.
• Review the QC operations performed by the Contractors(s).
• Ensure that required CQA testing has been performed in accordance with this CQA Plan as well as the intent of the construction drawings.
• Confirm that test data are accurately recorded, validated, reducedIn chemistry, having gained electrons. Often gaining electrons is accompanied with gaining protons (hydrogen). As an example, when O₂ reacts with H₂, the oxygen is reduced, forming H₂O., summarized, and interpreted.
• Approve specific corrective measures to be implemented during construction when deviations from the design and this CQA Plan occur.
• Follow Project Manager-approved Request for Information (RFI) and change order procedures.
• Develop a project file to maintain and store originals or copies of originals of all CQA data sheets and reports generated during the course of construction and following completion of the project. A complete file of this documentation is also maintained by the CQA Monitor.
• Oversee preparation of the Certification Report at the completion of the project.
• Provide final certification that the BCR system has been constructed in accordance with the construction drawings and specifications, and related project documents.

Construction Contractor– The group(s) responsible for performing the earthwork, construction, revegetation, and other construction activities associated with the BCR system. The Construction Contractor may employ various subcontractors, approved by the Owner and Engineer, for completion of the work.

Construction Quality Assurance Monitor – Also referred to as the Monitor or CQA Monitor, this is the firm or individual responsible for performing the tasks outlined in this plan. The CQA Monitor reports directly to the Engineer. The following may be included in the CQA Monitor’s duties:

• Review and understanding of all construction drawings, Contractor-provided shop drawings, project specifications, and related guidance documents.
• Review any required Contractor submittals and make appropriate recommendations.
• Observation and documentation of sub-grade preparation, compaction, cover material placement, surface water controls construction, planting materials and methods, and other site work activities.
• Ensure that testing equipment used and tests performed are conducted according to project specifications and industry standards.
• Coordinate development of the Record Drawings.
• Perform or observe documentation and reporting of test results as required to Engineer and Project Manager.
• Report to the Engineer any deficiencies that are not corrected to the satisfaction of the CQA Monitor, including design or project specification changes.

Owner – Company or Agency that pays for the work to be completed.

Project Construction Drawings and Specifications – Includes all project-related construction drawings and specifications, including design modifications, specification changes, and Record Drawings.

Quality Control (QC) – Functions performed by the Construction Contractors or supplier to conform to the construction drawings and specifications. The Construction Contractors and its designated consultants should implement QC procedures to monitor construction methods, survey controls and any other controls as needed by the Construction Contractors to meet the project specifications and requirements.

Record Drawings – Record (as-built) Drawings record the dimensions, details, and coordinates of the final grading, surface water controls and other structures after construction is completed. The Record Drawings may show any design or field modifications or changes from the original design Drawings.

The Construction Contractors is responsible for developing the QC methods and procedures that are used in the construction, and ensuring the methods are consistent with the construction drawings and specifications.

The Construction Contractor performs and keeps a record of all visual and physical checks. Visual checks (such as material integrity, seaming, and overlaps) may include photo-documentation as well as observation notes to document performance and compliance with the Drawings and Specifications. Physical checks involve surveys, grade checks, physical measurements (such as for proper overlaps, lift thicknesses, and structure dimensions) or other data collection activities, as required to document compliance. Examples of the primary QC functions and observations include but are not limited to the following:

• clearing
• keeping inventory of equipment, materials and personnel on site
• testing fill support to CQA (and associated QC testing and surveying)
• surveys for grade control and for submittal and review by Engineer to review for conformance with design requirements and tolerances
• QC testing
• excavation, and fill placement for conformance to Drawings
• proportioning and mixing of sulfate reducing bioreactor organic substrate
• application of bacterial inoculum on the BCR unit surface if manure is not used as seed
• installation of pipelines and associated plumbing for burial depth conformance
• installation of electrical components including power, instrumentation, and alarm systems for functionality conformance
• testing of riprap or other fill materials for conformance with gradation and physical property requirements
• surface water survey controls (e.g. channel construction, conformance with gradient and cross-section design tolerances, erosion protection revetment)
• concrete structures, including performing QC testing of concrete in accordance with the specifications
• BCR cover placement and thickness control (grade stakes or pre-and post-survey that account for potential lightweight fill (LWF) settlement)
• plant growth medium preparation and placement
• seedbed preparation and seeding
• installation of wetland plants in the aerobic polishing cell (APC)A shallow pond which allows for aeration and settling of particles, typically following a BCR.
• record surveys
• submittals to the Engineer for review (for instance, shop drawings and RFIrequest for information forms) and inclusion in Certification Report

Prior to installation of any materials, the Construction Contractor should verify that all construction materials meet the required specifications. The Construction Contractor should provide the CQA Monitor and Engineer with the manufacturer’s QA/QCquality assurance/quality control documentation including, at a minimum: a certificate of analysis for each lot of material supplied; a description of the manufacturer’s QC procedures for verifying final product quality; product identification numbers; and results of standard material properties testing verifying that the materials meet minimum material requirements.

Any substitutions for the specified materials should be requested in advance and receive approval from the Owner and Engineer prior to use. Substitutions should meet the minimum requirements for the specified material for approval. The Construction Contractor is responsible for all materials from the point of shipping until the material is placed consistent with the BCR design specifications. The CQA Monitor should visually inspect, inventory and approve all materials upon delivery.

The Construction Contractor should assist the Engineer and the CQA Monitor with the test fills to attain the required method specifications for compaction. The test fills QC requires survey control per standard Proctor (ASTMAmerican Society of Testing and Materials D-698) compaction testing.

In many cases the design includes an influent control structure (see Section 4.4.2.1). The Construction Contractor determines the construction methods for this structure, including the method applied to bypass MIW from the site during the construction process.

In other cases, the capture and conveyance of the MIW influent requires the design and construction of permanent structures such as spillways, or underground piping that connect the influent flow to the BCR system. Figure 5-1 show one example influent structure that required the use of an underground concrete piping that directs the influent to the headA specific measurement of water pressure above a geodetic datum. It is usually measured as a water surface elevation expressed in units of length. of the BCR system.

Figure 5-1. Example of influent structure on a BCR.

The presence of sediment, either in the MIW influent or resulting from the BCR construction phase, can negatively affect the performance of the BCR and must be managed and controlled using temporary or permanent settling basins or sediment traps.

In addition to MIW local regulations, tribal, state, and federal regulations may apply to storm water management at the site during construction. Stormwater management during construction of the BCR can be as simple as inspecting the stormwater drainage area or basin to ensure that minimum stormwater flows are allowed to the BCR system. In other cases, major stormwater drainage basin modifications would be needed and called for in the design. Implementing these changes may require close coordination with local and state watershed basin stakeholders. Some of the stormwater management practices that are implemented during construction, specifically those aimed at managing soil erosion and controlling the disturbance of sediment and siltation, are also implemented during operation of the BCRs.

Abandoned or active mine sites often have disturbed land areas in which the BCR can be constructed. In this case, minimal clear and grub activities may be required. Many mines are also located in steep or sloping terrain. In these cases, areas must be excavated and re-graded according to the design. In remote areas, road construction may be required as the first scope of work in order to provide access to the site. Additionally, areas disturbed by mining activities may be contaminated by metals or other constituents. If contaminated materials are present, excavated materials must be handled in accordance with the design or other site requirements, such as disposal in an on-site repository or off-site location.

BCR units can be in-ground or above-ground, depending on site conditions. For in-ground units, the unit area is excavated according to the construction plans, and overburdenGeological term for the material above solid rock. Sometimes called "soil". (soil) material may be stockpiled for construction of other components of the overall treatment system. Above-ground units require borrow from a stockpile of overburden already present on site, developed from a nearby area, or brought in from off site in order to construct the unit berm. Some BCR units may also be partially in-ground, where the excavated overburden is used to build a berm on the sides of the unit, thereby extending the overall depth of the unit. It is also possible that a BCR unit is constructed within an area of bedrock, in which case bedrock must be blasted and removed to create the depression necessary for the unit installation.

If deemed acceptable in accordance with the design, excavated overburden material could also be used for construction of several other components such as run-on/run-off control features (such as berms or drainage channels), riprap, influent/effluent channels, pond berms, roads and other access features, growth media for vegetation and erosion control, and cover material for the BCR unit. Importing off-site material for construction may also be required for these various components. Re-use of excavated overburden or other local on-site resources is an important component of the project, as this can reduce overall cost of hauling materials. Since these various uses may require different particle size gradations and/or other soil/rock properties, overburden may need to be screened, separated, and amended in accordance with the design. There is also potential to chip or shred the cleared and grubbed woody vegetation material and incorporate it into the BCR unit substrate, if this material is deemed appropriate as prescribed by the design.

The design determines what site preparation procedures are to be followed. Construction QA/QCquality assurance/quality control procedures must be adhered to during site preparation to ensure the BCR unit size, depth, and grades meet the design requirements, which are critical components for successful operation of gravity fed systems. Surveying should be conducted prior to, during, and after unit construction to ensure the line grades are met. The elevations of the influent, effluent, overflow, and other features must meet the design requirements in order to reduce risk of future potential issues with improper loadingMass of something per time entering a volume (volumetric loading rate) or flowing into an area (areal loading rate). to the system. Issues that could result from poor construction grading could include overloading the system beyond the designed limits and allowing the system to become dried out. These system stresses can lead to issues such as reduction in treatment efficiency, loss of appropriate bacterial community, and plugging as further discussed in Section 4.

Another element of site preparation construction is implementation of proper erosion control practices. As common for earthwork construction, materials such as silt fences, diversion channels and ditches, sediment capture ponds, and similar features may be required. The main purposes of utilizing erosion control practices are to prevent damage to downstream resources, limit loss of material stockpiles or other features as a result of stormwater erosion, and to route stormwater around construction areas to improve the safety of work conditions. For the BCR unit, it is also important to have a storm water diversion and dewatering plan in place in the case of high precipitation events occur during construction. Proper implementation of these features is typically required prior to all land disturbance. An erosion control plan and/or storm water pollution prevention plan should be developed and implemented that defines the approaches for erosion controls.

Since the intent of the BCR system is to treat MIW, an actively flowing source of MIW may be present near the BCR construction area. This MIW should be managed accordingly to prevent it from entering the work area and prevent contamination of otherwise clean soil or granular fill resources used for construction. MIW should be routed around the work area, treated, or stored in a containment pond as required per the design, mine operating plan, or other requirements.

A liner system can be constructed of a number of different materials that are common for dam, pond, or impoundment construction (see Appendix B.13 Copper Basin Mine Case Study). These material types may include PVC, high density polyethylene (HDPE), linear low density polyethylene (LLDPE), and geosynthetic clay liner (GCL). For more information on liner components see Use of Geosynthetics in the Mining and Mineral Processing Industry (http://geosyntheticsmagazine.com/articles/0807_nags_processing.html). These materials are usually laid in place in sections, and sections are heat welded together in the field to create an impermeable seal. Geotex is generally placed over liner prior to gravel placement. Installation of these liner materials must follow strict CQA procedures to ensure that the permeability and other material properties are met as prescribed by the design. These procedures include but are not limited to:

• inspection of liner material for defects
• documentation of sheet material properties and testing to meet the design requirements
• evaluation of proper liner bedding material to prevent liner damage or puncture
• field trial seam development and testing to determine if the field welding process creates seams that meet the design requirements for material properties
• destructive and/or nondestructive field seam testing ensure the continuity and integrity of in-place field seams

For some materials, the liner can be manufactured as one continuous piece. In this ideal situation, field welding of sections would not be required, thereby reducing the amount of construction cost associated with welding and testing. The only field welding that may be required in this case is for pipe penetrations for the influent and/or effluent piping.

After completion of the of the site preparation for the BCR unit, the liner bedding is installed. The bedding material is typically a non-angular sand or fine gravel so as to not damage the liner. Due to the specific particle size and shape requirements for bedding material, it may be imported from an off-site location that has the appropriate processing equipment. Alternatively, on-site resources may be present and could be used. As described for site preparation, use of on-site materials for bedding can help reduce costs. The bedding layer is placed according to the thickness defined by the design (typically 3 to 6 inches) and compacted. The bedding surface should be smooth and free of rocks or other protrusions that can damage the liner. Inspection of the bedding should occur prior to liner installation to ensure the design conditions are met.

The liner is installed after placement and inspection of bedding. Liner installation can proceed by first anchoring one side of the liner sheet into the pond berm, and rolling the sheet across the BCR unit base. The liner may also be laid out over the BCR unit with excess liner temporarily anchored until field welding is completed. Ultimately, the method of liner installation should be per the manufacturers’ and experienced installers’ recommendations. Final anchoring of the liner on all sides of the BCR unit is conducted by excavating a shallow trench (typically 1 to 2 feet deep and up to 1-foot wide), laying the liner along the walls and floor of the trench, and backfilling and compacting soil into the trench. Backfilled trench materials in direct contact with the liner should meet the same typical requirements as for liner bedding.

Field seaming of sheets is conducted in accordance with the design and manufacturers recommendations and should be conducted by qualified personnel. Penetrations through the liner for influent and/or effluent piping may be required. A pipe penetration is installed by cutting the proper size hole in the installed liner, feeding pipe through the penetration, welding a piece of liner material to the sheet around the pipe, and clamping the liner around the pipe to create a seal.

The last component of liner installation is field seam testing of sheets and pipe penetrations to ensure that leakages do not occur and to test the properties of a field seam. Field seam testing can be conducted using destructive or non-destructive methods, depending on the type of material installed, extent of field seaming, and field conditions. Destructive field seam testing involves collecting a sample of the seamed area and submitting to the laboratory for testing. Non-destructive field seam testing involves either vacuum testing (pulls a vacuum on a seemed area) or air pressure testing (inserts air into the enclosed space between a double-track fusion seam). The type of testing method to be used is dependent on the type of liner material and type of field seaming method. Based on the results of field seam testing, repairs to seams may be required, and the area should be re-tested upon completion of the repairs.

For downflow BCR units, effluent piping is installed at the bottom of the unit. Pipe bedding is first installed over the liner to aid in achieving proper grade. Pipe bedding in direct contact with the liner system should be similar to the bedding used for liner installation to prevent liner puncture. Bedding directly around the perforated pipe is commonly a poorly graded gravel to aid in drainage. This material may also be limestone gravel, which can add additional alkalinity to the effluent. Gravel or any other backfill placed over piping should be conducted carefully to prevent damage to the piping system. The depth of gravel over top of the effluent piping should be placed in accordance with the design and confirmed in the field prior to additional backfill of substrate into the BCR unit.

The effluent piping can be configured in a number of ways. For example a gallery of perforated effluent piping may be installed. This consists of several lines of perforated pipe in parallel which are connected a main effluent header that feeds to the effluent pipe through the liner penetration. Assuming the effluent pipe through the liner is installed near the bottom of the BCR unit, effluent piping installation should continue from this point outward, or the gallery should be constructed, graded, and connected to the effluent pipe. All piping, couplings, elbows, and other fittings should be inspected for defects prior to installation. The effluent system may also contain more than one effluent pipe gallery in parallel. In either case, grade checks should be conducted throughout effluent pipe installation to ensure grades are met. All inspections of grade should be documented on appropriate forms or in a logbook. Adjustment to grade can be achieved by adding more or less bedding beneath the piping.

For upflow BCR units, influent piping that evenly distributes the flow to the bottom of the system would be installed similarly to that of an effluent collection piping gallery described above for a downflow system. The key difference would be proper pipe grading in the opposite direction of the effluent piping for a downflow system. For an upflow system, the effluent would typically rise to the surface and overflow into discharge channels or other flow control structures such as an overflow spillway.

Some horizontal flow BCRs have been constructed, but are not as common as downflow BCRs. Flow can be delivered to a horizontal flow system along one side of the BCR unit via a series of influent pipes or a perforated pipe gallery that evenly distributes flow. Similarly, effluent would be drained on the opposite end of the unit using a collection gallery. Perforated influent or effluent galleries would be constructed similar to upflow or downflow BCRs, expect that the piping galleries may be raised off of the unit floor. Suspended piping systems may require adequate anchoring and support systems during construction. In other cases, the flow follows a serpentine pattern through multiple reaction units where the influent to one unit enters at the bottom at one corner and the effluent leaves at the opposite corner of a rectangular or square reactor (see Appendix B.10 Peerless Jenny King Site Case Study), as dictated by space availability.

Piping installed outside of the BCR unit also requires bedding material, although the type of bedding is typically a well-graded sand or gravel, or alternatively on-site overburden materials could be used. Trench excavation would be required for buried piping. Bedding is placed within the trench, and then pipe is installed to grade. Backfill is placed over the piping and compaction is completed with caution to not damage the piping. A common practice to install flagging or a warning tape at least six inches above the piping to prevent potential damage if piping ever requires future maintenance. Above ground piping may require anchoring systems, especially on steep slopes.

Valves are not likely within the BCR unit, but may be found at the effluent or influent of the unit in areas that can be accessed for maintenance. Construction of access to valves or other process control equipment may require construction of an in-ground manhole or vault, and require additional safety precautions during operation of the BCR. Installation of these kinds of structures must also occur with close attention to required grades. Proper bedding for structures should be installed, compacted, and tested for density as required. This bedding is critical to reducing potential for future settling of the structure, which could lead to damage to piping entering or exiting the structure. Below ground structures may also be considered confined spaces and adequate procedures should be implemented to ensure the safety of workers during installation and during future operations and maintenance. Sampling ports or automated monitoring devices may also be present within the structure or near the valve area. Connections to valves, or any other device, to process piping should be conducted by qualified personnel to ensure leakage does not occur. Leak testing of connections or the piping system, as a whole may also be required prior to backfill over piping. All testing should be documented on appropriate forms or a log book.

Installation of the BCR substrate begins with understanding the conversion between volumetric and mass quantities of substrate materials. Bench and pilot studies and design parameters may be developed using either one or the other type of quantity, or both. Purchase and hauling of large quantities of substrate materials may also be measured in either unit. Therefore, the conversion between these units (density) is critical to properly proportioning the substrate materials. Additionally, the percent moisture can have a large effect on materials measured by weight. Prior to construction (if not done during the design), samples of substrate materials can be submitted to a laboratory to test the density and percent moisture of the materials (Section 3.2.1). This step may be conducted during the bench or pilot test phases. Alternatively, this information may already be available from the material supplier or determined based on past experience and/or literature values at the discretion of the Engineer and Construction Contractor. The material properties are then used to properly coordinate with the Construction Contractor on how to blend the materials in the field.

Delivery of each of the substrate materials to the site in truckloads should be placed in separate areas prior to field mixing. Upon each delivery, documentation of the contents volume and properties should be provided in accordance with the CQA Plan. Based on the proportioning of materials in the design, mixing batches of substrate can then commence. This procedure should proceed using a method that is simple using standard earthwork construction equipment. One approach is to proportion the designed substrate mix using excavator bucket loads of each material. The size of the bucket is determined and then fractional amounts of each component are grabbed with the excavator and placed in a pile. The pile is then mixed using the excavator bucket, site workers, and/or tilling equipment. Concrete mixers also have been used. Such mixers mix well but have limited batch sizing.

As part of CQA requirements, the Construction Contractor should create a test batch prior to full-scale mixing. The test batch would use the same approach as described above, but at a smaller volume. Development of the test batch should be observed by construction oversight personnel. This observation allows for calibration of the mixing method used that ensures the designed proportions are met. The mixing procedure should be approved by the oversight personnel prior to full-scale implementation.

After installation of the pipe and gravel bedding, the substrate is installed. A geotextile filter material may be required over the gravel layer prior to substrate placement. The geotextile reduces loss of fine-grained substrate material into the gravel layer, while allowing adequate water flow to the effluent drain system; however, the geotextile should not be too fine that in may cause plugging.

Placement of substrate material within the BCR unit can be conducted in a number of ways, but all should be implemented with caution to not significantly compact materials once placed. Significant compaction of substrate material can cause reduction in permeability in certain areas of the BCR unit and result in reduced treatment efficiency and potential plugging issues. In some cases, the design may call for minor compaction to meet a certain permeability requirement; however, the key for substrate placement is to provide uniform compaction throughout the unit. Non-uniform compaction or excessive compaction is some areas can cause preferential flow pathways in less compacted areas and reduction in treatment efficiency.

Substrate materials can be installed from equipment along the outside of the BCR unit, with light-duty equipment within the unit, or a combination of both methods. Placement depends on whether water flow is vertical or horizontal.

Vertical flow BCRs:  For installation from the outside of the BCR unit, an excavator is used to place substrate into the BCR unit and spread the material without entering the BCR unit. This process proceeds around the entire perimeter of the unit until all material is placed and leveled to the required depth. This approach reduces the issues regarding compaction of the substrate or damage of collection pipes while the substrate is being installed. However, this method is limited to placement at the reach of the excavator. If the excavator reach is less than the geometric radius of the BCR unit, then proper spreading of the substrate cannot be conducted using the excavator. In this case spreading substrate in the center of the BCR unit must be conducted by small track mounted skid loaders that can enter the BCR. Figure 5-2 shows sketches of vertical flow BCRs.

Figure 5-2. Vertical downflow and upflow BCRs.

If equipment can be operated on the gravel bedding layer above the liner, another method of substrate placement is to dump truckloads periodically spaced throughout the unit. The decision to drive trucks over the gravel bedding (portions of which may contain buried pipe) should be made based on the compaction properties and thickness of the gravel placed over the piping gallery. An entrance ramp to the BCR unit should be constructed with a layer of additional protective material over the liner to prevent damage by heavy construction equipment. A small track mounted skid loader should then be used to spread the substrate piles into a uniform depth. The loader should start at the opposite end of the entrance ramp to the BCR unit and work backwards toward the entrance until the entire BCR unit has been graded to a uniform depth.

Horizontal flow BCRs: As with vertical flow BCRs, an excavator is used to place BCR substrate and alternating rows of gravel, but the unit may be constructed from one end to the other while equipment operates on the non-filled portion of the unit. Figure 5-3 shows a sketch of a horizontal BCR, the upper of which is at the Peerless Jenny King site (see Appendix B.10 Peerless Jenny King Site Case Study) and the lower is an example included in the ADTI Handbook (http://wvwri.nrcce.wvu.edu/programs/adti/pdf/adti_handbook_5.pdf).

Figure 5-3. Cross-sections of horizontal flow BCRs.

The method of constructing the rows of substrate and gravel may not be specified and may be labor intensive. An illustration of one such installation is shown in Figure 5-4.

Figure 5-4. Horizontal BCR media placement.

Source: Jeff Schoenbacher Park City Municipal Corporation.

Another alternative for substrate placement regardless of flow direction is construction of a dividing earthen berm between parallel BCR units or sections of a BCR unit. If not in the design drawings, adding berms require the Construction Contractor to obtain concurrence from the Owner and Engineer. The berms provide the benefit of an access route for construction equipment to install substrate and also to perform maintenance on the substrate. The berms can be constructed within the overall lined system. As an example, berms can be constructed that divide a rectangular unit into two or more sections. The berm should be constructed after the liner installation, but prior to or during bedding and effluent pipe installation. The berm height should be equivalent to the BCR unit height at the perimeter of the unit and compacted in lifts as appropriate. In some cases part of the top of the berm is built at a lower elevation to allow for overflow by design or serve as the actual effluent of the BCR. A protective layer of soil should be placed directly over the liner surface prior to placement of other soil materials that may contain angular gravel or other debris that could damage the liner. The segregated areas created by the berms can then be equipped with separate effluent drain systems and appropriate influent/effluent valves. Separating a BCR into units provides opportunity for maintenance of a portion of the system (such as removal of substrate) while the other units continue to treat MIW. Building BCR units in parallel or sections is part of an overall design approach to improve capability and efficiency of maintenance on substrate materials over time. The basis for this approach is discussed further inSection 4.2.5 and maintenance approaches are discussed in Section 6.

The cover system can consist of any number of materials, preferably overburden or other on-site materials leftover from the BCR construction to reduce costs. Placement of cover material must also be carefully conducted to limit compaction to the substrate layer. As such, a higher density material such as gravel or rock may not be preferred. Layers of wood chips have been used at a few sites. The placement and grading of cover material should be installed from the perimeter of the system using excavators. If equipment must be driven onto the BCR unit surface, sufficient cover material should be installed first within the area that the equipment operates.

Cover material generally should be sufficiently sloped to shed stormwater off of the BCR unit surface, assuming the cover extends to the top of the BCR’s containing berm. Grade checks should be conducted periodically to ensure the designed cover thickness and grades are met. The cover should also be graded and tied into runoff/run-on diversion structures along the perimeter of the BCR unit, if present. Routing water from the BCR unit surface towards the influent or effluent areas should be avoided. Otherwise, inflow of runoff water into these areas could increase the amount of water to be treated in the BCR or in subsequent posttreatment steps.

The design may consist of a low permeability cover system, which would involve a material similar to the BCR unit liner that limits infiltration. Placement of this kind of cover should be conducted similar to the methods discussed for liners in Section 5.2.2.2, depending on the type of material. The low permeability liner should have a protective layer placed over the liner and may also have a seeded surface. This layer protects the liner from photodegradation and heave/thaw affects that could damage the liner. Ventilation of gases (hydrogen sulfide) within the BCR unit may be a required component of the cover system. If this is required, vent pipes would be installed through the cover system. Penetrations in the liner for the vent pipes should be installed as described for liners installation in Section 5.2.2.3.

In addition, sometimes it is necessary to cut and extract a vertical transect of the BCR to ensure that the various BCR zones are clearly defined in the cross section. This type of sampling is rare but can be extremely useful during the diagnosis of the BCR performance.

Most MIW BCRs do not contain automatic flow and sampling devices and rely on the manual monitoring performed by experienced personnel, including trained private companies, federal or state personnel as well as local organizations and site stakeholders representatives. The design of the BCRs normally provides sufficient technical information to determine a raw and treated effluent chemical characterization that the samplers are familiar with and compared results such as pH, temperature, ORP, DOdissolved oxygen, and actual water chemistry samples of heavy metals, sulfate, sulfide, alkalinity and other site-specific parameters, as designed (seeSection 6.2.2.2 for a comprehensive list of parameters).

BCR effluent monitoring commonly is comprised of a discharge pipe where effluent sampling using field monitoring equipment such as a stopwatch and bucket for flow determination, pH and ORP meters, and thermometer are used. Samples for off-site analysis can also be collected from the BCR effluent. Figure 5-8 shows a BCR discharge pipe with field equipment being used.

Figure 5-8. BCR effluent monitoring.

Automated monitoring equipment include open channel primary and secondary flow measuring devices as well as automatic samplers that can be programed to collect BCR effluent (and influent) samples based on a predetermined sampling protocol. Section 6 of this guide presents a detailed description of automatic flow monitoring and samplers used for MIW BCRs. The precautions necessary for the installation of primary flow monitoring devices is to provide access and infrastructure for the installation of primary flow monitoring devices, including an open channel and weir system as well as conditioning the site to locate the flow and sampling equipment in a safe, secured and reliable location.

In addition a small wood shed or prefabricated shed is normally useful to keep sampling equipment and consumables needed for flow monitoring and sampling purposes. Sampling equipment may be operated by the use of solar power and solar panels and photocells need to be installed such that direct sunlight is maximized. In addition, sampling devices can be powered by water wheel technology.