1. SCOPE OF WORK
   The work consists of supplying all necessary supervision, qualified labor, materials, plant and equipment to carry out the construction of the [ ] drain trench(es) as specified herein and as shown on the Drawings. Trenching will proceed from elevation [ ] to the depth shown on the drawings or to a minimum penetration of [ ] feet in the [ ] layer. A BP slurry will be used at all times to support the trench walls. After proper bottom preparation, a drainpipe, properly ballasted will be placed at the bottom of the trench and covered with the specified filter gravel. Riser pipes will be connected to the drainpipe at specified intervals and connected to surface piping. The top 2 feet of the gravel in the trench will be removed and covered with a filter fabric, itself being covered with a compacted cohesive soil.



2. RELATED WORK
   Refer to other specifications:
   
   1. Health and Safety Plan
   2. Owner’s Quality Assurance Plan



3. SUBMITTALS
   1. CONSTRUCTION MEANS AND METHODS The specialty contractor will provide a detailed description of the construction steps, BP slurry management, ballasting methods, trenched spoils, and development fluids management. The specialty contractor will also indicate the features and procedures for trench maintenance.
   2. CONSTRUCTION SEQUENCE AND SCHEDULING If not specified elsewhere, and in the case of multiple trenches, the specialty contractor shall indicate his intended construction order and progress. He will indicate if the trenches are to remain open overnight and how he will assure the safety of the site and the trench(es) at night.
   3. INCORPORATED MATERIALS The specialty contractor will submit certificates of compliance for all materials that will become part of the final product: drainpipe, ballasting devices, bedding material, filter gravel, riser pipes, stand pipes, and feeder header pipes.
   4. BIO-POLYMER The specialty contractor will indicate the name, type, and characteristics of the BP he intends to use and its management, including life cycle and disposal characteristics. The submittal shall indicate whether the polymer is natural or synthetic, its chemical origin, its molecular weight, its viscosifying curve with demineralized water, expected useful life, odor during and after biodegradation, Biological Oxygen Demand (BOD) count of degraded slurry, and percentage of degradability with eventual residues. The specialty contractor will also communicate the compatibility results between his BP and the contaminated groundwater.
   5. QUALITY CONTROL The specialty contractor shall provide a detailed quality control program covering all aspects of construction (i.e., slurry preparation and processing trenching, bottom cleaning, trench sounding method and intervals, drainpipe placement method, filter gravel placement and sounding, extraction flow rate measurement during development, and developed drawdown regime uniformity measurement.)
   
   
4. BIO-POLYMER SLURRY
   The slurry will be prepared with a water quality compatible with the BP and its intended use. The pH will be adjusted to the required lifetime of the slurry. Slurry viscosity will provide optimum trench walls stabilization. Viscosities with an unnecessary high solid content will be discouraged. Viscosities between 35 and 45 Marsh cone seconds are acceptable. The BP slurry must be able to be pumped out of the drain, preferably before bio-degradation occurs; in order to minimize possible bacteriological infestation of the drain. Only the polymer combined with fines in the cake matter within the trench walls must be left to biodegrade in-situ. A mineral colloid can be used as an additive to minimize slurry loss. Colloid fines will be removed during the development process. The slurry level shall be maintained within the top 2 feet of the work pad regardless of the groundwater depth.
   
   The in-trench slurry properties will be monitored following standard bentonite slurry practice, but with greater frequency for the pH and filtrate. The BP slurry must be capable of being desanded and desilted using standard desanding apparatus. Surplus BP slurry can be reused from one trench to another provided it has been cleaned and is still usable.
   
   Excess slurry will be analyzed for contaminants to determine whether the slurry is within the public discharge permit or whether it needs treatment. The Owner will provide storage onsite until the slurry is ready for disposal.
   
   
5. TRENCHING UNDER BIO-POLYMER SLURRY
   Hydraulic excavators will generally be acceptable for trenching. When the depth of the excavation exceeds the digging depth of the excavator, a clamshell operation will need to follow the excavator to keep the trench bottom free of droppings and maintain specified grades. When disposal of the excavated material or supplying filter gravel is a major cost component, the trench can be excavated solely with a clamshell, possibly as narrow as 18 inches. The specialty contractor must elect the most cost effective trenching method in order to maximize the value of the end product.



6. TRENCH BOTTOM CLEANING
   Since all pure polymer slurries are only viscous fluids with little or no gel strength, all suspended solids will settle at the bottom of the trench. The sand fraction will cause a reduction in available trench depth and the silt fraction will create a sludge-like matter that can potentially clog the porosity of the filter gravel. The specialty contractor must implement a trench bottom cleaning procedure. The method of removing the suspended solids and bottom sediments from the BP in the trench shall be capable of maintaining the BP density within the specified limits. The equipment should include clamshells, air lift pumps, mud shakers, settlement ponds, pipes hoses, fittings, or other equipment necessary to show evidence of a clean bottom ahead of the drain pipe installation.
   
   The Contractor’s/Owner's representative in the field must accept the bottom of the trench prior to starting the pipe and gravel placement. Soundings of the trench will be made at no more than ten feet intervals and successive soundings will be made at the same locations.
   
   
7. BEDDING MATERIAL
   If a bedding layer is specified, the specialty contractor will place and grade the coarse gravel material as soon as possible after cleaning a segment of the trench bottom.



8. DRAINPIPE INSTALLATION
   The drain pipe will be slotted as specified in order to permit adequate drain development. Approved ballasting and centering methods will be used to lower and sink the pipe to the bottom of the trench. The specialty contractor will attach depth gauges every 25 feet to assure the Contractor/Owner that the pipe is resting at the correct depth and location until covered by the filter gravel. Once the filter gravel is above the water table, the excavated material, (if acceptable) can be used to fill the trench. Otherwise, clean material must be imported for backfill.
   
   Connections between pipe segments or riser pipes must be as strong as the pipe and must be approved before installation. The drainpipe must emerge at the surface at one end of the drain. This will be used as an access for development and future maintenance. The extraction well pipe will not be perforated. Should the specialty contractor require a slotted well pipe to help develop the drain, he will select an oversized dimension allowing the specified plain well to ultimately fit tightly inside the slotted pipe.The connection will have both a sump and a large radius elbow permitting the entry of cleaning devices.
   
   
9. STAND PIPES
   In order to monitor the effectiveness of the drain and to collect leachate samples, slotted 2-inch diameter PVC or compatible plastic pipe will be installed inside the trench. The pipe should extend the full depth and be spaced every 50 feet of the trench. Precautions shall be taken during the introduction of the filter gravel backfill to secure the pipes. The same stand pipes may be used to help breakdown certain types of BP and to develop or maintain the drain.
   


10. FILTER GRAVEL BACKFILLING
    The specialty contractor will exercise caution and control when placing the filter gravel around areas where the drainpipe is not yet at grade. The placement method will be approved by the Contractor/Owner. Prior to installation, the filter gravel shall be thoroughly washed to remove any fines. The filter gravel can be dropped through the slurry by using a short trench hopper to avoid trench erosion. Depending on the end product of the drain, the filter gradation was selected to either avoid segregation or to have a beneficial segregation. The maximum filter gravel porosity must be found at the bottom of the drain. Vertical placement is preferable to longitudinal placement when standpipes might be deformed or broken. To displace the slurry, the gravel will extend to the surface.



11. DRAIN DEVELOPMENT
    As soon as the filter gravel has been placed over the entire trench, development will proceed. The bio-degradable slurry will be pumped out of the drain as fast as possible and processed to remove the suspended silts and fines. Depending on the aquifer yield and depth, the drain will either be left to equalize and then pumped out in cycles similar to water well development or the cleaned slurry will be recycled after eventual neutralization and seeding with enzymes or bacteria rich soil (top soil).
    
    The specialty contractor will have a means of measuring the volumes and flow rates coming out of the trench. The volume extracted the first time will provide an indication, by comparison to the theoretical open porosity, of the level of effort required to clean the drain. All successive drawdowns will be measured and repeated until the specified amount of water is reached and water coming out is clear.
    
    The drawdown resulting from the specified service flow rate will be measured in each stand pipe for uniformity evaluation. The specialty contractor will use the drainpipe and the stand pipes to flush the water, steam, or surfactant foam to areas that do not conform.
    
    The specialty contractor will exercise caution when using either enzymes to stimulate biodegrading or strong oxidizers like bleach as a disinfectant or as a breaker solution. When chlorine is used, the specialty contractor will rinse the drain with a solution of sodium thiosulfate, or similar, to remove the remnant chlorine. All chemicals and procedures for drain development will have received the Contractor’s/Owner's approval before being implemented.



12. DRAIN PROTECTION
    Upon completion of a trench, the specialty contractor will remove 2 feet of filter gravel and place a filter fabric in the trench. Then cover it with a cohesive soil, applied in compacted lifts, as specified. Care will be exercised to avoid damaging the standpipes and the riser pipes.



13. RESIDUAL BIO-POLYMER SLURRY AND DEVELOPMENT WATER
    The specialty contractor will store, in acceptable containers, the liquid products of the BP drain trench construction. Chemical analyses of the various batches will be performed and compared with the Owner’s discharge permit. When the liquid waste is under the allowable limits, the specialty contractor will be responsible for the discharge and removal of the storage facilities. In the contrary, the Contractor/Owner will take possession of the storage facilities until the liquids can be processed and disposed.



14. DRAIN MAINTENANCE
    (If provided by the contract) At the request of the Contractor/Owner, the specialty contractor shall periodically return to the project site to perform pumping evaluation tests to determine if maintenance is needed. Since this work cannot be planned in advance, actual work shall be compensated on a forced account basis.



15. TRENCH SOIL DISPOSAL
    The specialty contractor will dispose the excavated materials [off, on] site. The Contractor/Owner will determine the disposal location, based on the classification of the materials. Payment for disposal of the materials will based on the unit price list in the contract.



16. SITE RESTORATION
    The specialty contractor will restore the site to its original appearance or as specified. Secured wellhead and drain pipe covers with specified identification marking will be installed. In traffic areas, these will be encased in concrete and have cover plates flush with the surface.



17. BIO-POLYMER SLURRY TRENCH DESIGN CONSIDERATION
    A BP trench is an interceptor trench constructed using synthetic biodegradable polymer water based slurry to support the walls of the trench. The versatility of this type of construction versus conventional trenching machines is the depth of the excavation is virtually unlimited. A second advantage is the BP stabilizes the excavation walls resulting in a safer project. This technique offers a wide variety of different recovery trenches due to the biodegradability of the polymer slurry.

RECON, a specialty contractor, has prepared the following list of information necessary to prepare a comprehensive quote to perform the construction of BP trenches. With this information, RECON can best provide you with the highest quality and assurance for the trench construction estimate.

1. Sample of water that will be available for mixing of BP (for compatibility testing with BP);
2. Sample of leachate from areas where trenches will be constructed (for compatibility testing with BP);
3. Sieve analysis of each major lithologic unit that will be intersected by a trench;
4. Liquid limit and plasticity limit analysis of each major lithologic unit that will be intersected by a trench;
5. As-built drawings of any foundations adjacent to the trenches including loads;
6. Geologic logs of borings completed on the centerline of the trench with groundwater elevations and grade elevations;
7. Grain size of the filter sand backfill material; and
8. Operating flow rate of the recovery system.