WASTEWATER TREATMENT DURING TUNNEL CONSTRUCTION ON BUREAU OF RECLAMATION PROJECTS. By Dr. John C. Peters* INTRODUCTION

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1 WASTEWATER TREATMENT DURING TUNNEL CONSTRUCTION ON BUREAU OF RECLAMATION PROJECTS By Dr. John C. Peters* INTRODUCTION In recent years, a number of papers have been written concerned with water pollution control during dam construction (McCullough and Nicklen, 1971; Sciandrone, 1974; Peters, 1975). These papers described treatment measures undertaken to minimize water pollution from point and nonpoint sources during dam construction. They suggest ways to avoid pollution problems related to haul roads, borrow areas, stream diversion, foundation excavation, aggregate processing, hatching of concrete, and reservoir clearing. Often tunnel construction results in water pollution problems quite different from dam construction. This paper describes wastewater treatment used during tunnel construction on Bureau of Reclamation projects and discusses its effectiveness. Further, it discusses legal requirements to meet State and Federal water pollution laws and regulations. LEGAL RESPONSIBILITIES The Federal water pollution law was amended in 1972 (Federal Water Pollution Control Act Amendments of 1972) and requires permits for all wastewater discharges from point sources into receiving waters. * Environmental Specialist, Bureau of Reclamation, Office of Design and Construction, Engineering and Research Center, Denver, Colorado 106

2 WASTEWATER TREATMENT 107 These permits are part of the National Pollutant Discharge Elimination System and are referred to as NPDES or Section 402 permits. According to the regulations (40 CFR 125) promulgated to carry out the Act, a point source is defined as "any discernible, confined, discrete conveyance including but not limited to a pipe, ditch, channel, tunnel, conduit, well, discrete fissure, container, rolling stock, concentrated animal-feeding operation, or vessel or other floating craft from which pollutants are or may be discharged." NPDES permits are required for all facilities that exceed a discharge of 50,000 gallons on any day of the year. An NPDES permit is obtained either from the U.S. Environmental Protection Agency or a state water pollution agency. EPA has turned the administration of the NPDES program over to those states who have received legislative authority and who have demonstrated technical competence. Upon application for an NPDES permit, the administrative agency must publish in the local newspapers a notice of an application for a permit to discharge wastes. This gives the public sector an opportunity to request a public hearing and formally comment on the conditions of the permit regarding the treatment of wastewater. An NPDES permit is issued specifying the amount of wastes that can be discharged into a water body. Contract specifications must provide the prospective bidders information on water quality standards for a particular water body impacted by construction. Specifications may define methods that are acceptable to the Government to treat wastewater to meet existing water quality standards. Records must be kept on the wastewater discharge and

3 108 SHOTCRETE FOR GROUND SUPPORT regularly transmitted to either the Environmental Protection Agency, the state water pollution agency, or both agencies. Because of public notice requirements and appeal procedures, it may take 180 days to process the permit application. For construction activities, Short or Standard Form C must be used to apply for an NPDES permit. The maximum civil penalty for failure to have an NPDES permit to discharge wastewater is $10,000 per day. When time limits require action on Reclamation construction projects, we have applied for an NPDES permit for an unnamed contractor. The permit is then transferred over to the successful bidder for that project. In conclusion, a contractor must have an NPDES permit to discharge construction wastewater from a point source into a receiving water body to be in compliance with the law. An NPDES permit must be obtained either from a state water pollution agency or a regional office of the Environmental Protection Agency, depending on who has jurisdiction. In the future, the permit program will be administered entirely by the states. Typically, Reclamation tunnel projects discharge a sufficient quantity of wastewater to require NPDES permits. WATER POLLUTION CONTROL METHODS During the construction of a tunnel, the most significant water pollution problem arises from the discharge of turbid or sedimentladen tunnel water. In addition to turbidity, tunnel water may also carry other pollutants such as oil and grease from a tunneling

4 WASTEWATER TREATMENT 109 machine and high ph from concrete hatching and/or tunnel lining. The discharge of untreated wastewater from a tunnel into a watercourse can significantly affect a municipal drinking water supply, disrupt irrigation activities, impact commercial or sport fisheries, and impair recreational uses such as fishing or boating. From a legal viewpoint, unauthorized or untreated wastewater can affect state water quality standards placed on a watercourse to protect water quality, natural resources, and other uses. Thus far, Reclamation has used two methods to treat tunnel wastewater: (l) settling ponds, and (2) filters. Typically, chemical precipitating agents have been used in conjunction with both methods to facilitate the treatment process. The following is a brief discussion of the technology used and the effectiveness of each method. Settling Ponds. One or more ponds approximately one-quarter acre in size have been used on Reclamation projects to settle out suspended particles from tunnel water. Typically, small earth dikes are built near the construction site in intermittent tributaries to impound water. Sedimentation occurs in these ponds when the action of turbulent flow is reduced in magnitude until suspended particles settle out by gravitational pull and are not resuspended by scour. The settled substances are known as sludge and must be periodically removed from the ponds for disposal. These settling ponds have not been particularly effective for

5 110 SHOTCRETE FOR GROUND SUPPORT several reasons. First, sludge must be removed frequently to maintain pond capacity so that suspended particles are given sufficient time to settle out. Second, the dikes built to impound water often do not withstand freezing and thawing and will breech periodically. Third, they do not effectively treat finely suspended material unless large quantities of chemical precipitating agents are used. Finally, they require a sizeable amount of land area for their layout. Effective use of settling ponds during construction is more an art than a science. A rather substantial amount of labor often is required to properly operate and maintain settling ponds. Also, precipitating agents must be carefully controlled to work effectively. Filters. Multimedia pressure filters have been used on Reclamation projects to separate suspended material from tunnel water by passing it through porous media. These pressure filters have anthracite and sand media and underdrains installed in a closed steel tank (Figure 1). Wastewater is pumped through the filter under pressure and the media washed by reversing flow through the bed, flushing out impurities. The filtration operation involves straining by interfacial contact combining to transfer suspended matter onto grains of coal and sand. The accumulated sediment is flushed from the filter media singly or in combination by water and air mechanical rakes. At high elevations in temperate latitudes such as the Fryingpan Arkansas Project's collection system, the filter is h6used

6 WASTEWATER TREATMENT Ill in a heated metal building in the winter so that the equipment operates under extremely harsh climatic conditions. The filter can be installed on a relatively small amount of land. Site preparation for the treatment plant can be accommodated in steep terrain. The wash water is a by-product of water filtration and must be disposed of properly. The wash water can be discharged_ into a sludge pond. The filter can be moved from job to job and can be reused. DISCUSSION Typically, Reclamation specifications have required treatment of 1,000 gallons of water per minute (approximately 2 ft 3 /s) for a tunnel project. There is no way of accurately predicting the volume of wastewater that may be discharged from a tunnel. Thus far, tunnels have not discharged more water than the specifications estimated. Oil and grease discharged from tunnel wastewater can be controlled by using skimmers as a first step of the treatment process. High ph can be controlled by use of concentrated hydrochloric or sulphuric acid to buffer water close to neutral. Most treatment methods require the use of chemical precipitating agents to facilitate the wastewater treatment process. These precipitating agents must be selected so that they do not contaminate drinking water supplies or impair aquatic life. Only nontoxic

7 112 SHOTCRETE FOR GROUND SUPPORT chemicals that are listed safe by the Environmental Protection Agency should be used. The methods available to treat tunnel wastewater must consider topographic features of the job site. The amount of space available in a canyon, an urban environment, or the rugged relief of a hillside can limit the choices available for wastewater treatment. Further, the proximity of the job site to a municipal water supply, a blue ribbon fishing stream, or a high-use recreation area, might warrant additional safeguards so that the water treatment system can operate under extreme conditions. Monitoring wastewater discharge is a requirement of an NPDES permit. Instruments should be used that monitor treated tunnel water instantaneously at the treatment unit outfall such as a recording turbidimeter. Most permits are issued with maximum and average allowable discharges of wastes based on state classification for existing water uses for each water body. The maintenance and care of equipment is important. After start-up and establishment of operating procedures, dual-media filters require only routine inspection by an operator. Alarms can be installed and automatic shutoff devices used if the equipment fails to operate properly. Generally, settling ponds require considerably.more time and labor to keep them operating properly than filters. Sludge must be removed periodically. It is important to locate

8 WASTEWATER TREATMENT 113 AOL'L t ~;. IBYO>E 5) FIGURE I Cunning hem Tunnel Water Treatment System

9 114 SHOTCRETE FOR GROUND SUPPORT waste areas for sludge and wash water so that they do not result in water pollution. Reclamation specifications are written with two or more acceptable Governmental methods for wastewater treatment with a provision for accepting a contractor's treatment method. Bidders are required to bid on a line item basis for water treatment. Recently, contractors working through consultants have submitted treatment techniques other than Governmental methods listed in the specifications. After review by the contracting officer, the contractor's method is either accepted or rejected. Whether a contractor selects a Government method or adapts one of his own, he is required to present a detailed layout describing his water treatment facility before being allowed to proceed with construction. REFERENCES 1. Federal Water Pollution Control Act Amendments of Public Law , 86 STAT McCullough, C. A. and R. R. Nicklen. Control of Water Pollution During Dam Construction. Journal of the Sanitary Engineering Division, ASCE, Vol 97, No. SAl, Proc. Paper 7927, February 1971, pp Peters, J. C. Water Pollution Control During Dam and Tunnel Construction. Proc. Second World Congress, International Water Resources Association, New Delhi, Vol V, December 1975, pp Sciandrone, J. C. Environmental Protection Measures at Martis Creek Lake, California. Civil Engineering-ASCE, March 1974, pp

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