SEWAGE

STANDARD OF REVIEW

According to the CBJ Mining Ordinance (49.65.135(a)), the CBJ shall require that:

Also, the Juneau Coastal Management Program (CBJ 49.70.955) incorporates the state water quality standards, as follows:

Sewage treatment and disposal in Alaska are regulated by both the Alaska Department of Environmental Conservation (ADEC) and the U.S. Environmental Protection Agency (EPA). Plans for sewage treatment and disposal systems must be approved by ADEC under the Wastewater Disposal Regulations (18 AAC 72). Discharge of treated sewage to surface waters must also comply with state water quality standards. ADEC sets water quality standards (18 AAC 70) subject to approval by EPA. EPA issues wastewater discharge permits (National Pollutant Discharge Elimination System -- or NPDES permits) for discharges to surface water. Under section 401 of the Clean Water Act, ADEC must certify that the permits issued by EPA will result in compliance with state water quality standards. ADEC 401 certifications may contain stipulations to ensure that discharges will comply with standards.

This staff report analyzes the potential impacts that sewage from the Kensington Gold Project would have on water quality, proposed measures to contain and dispose of sewage, proposed measures to control and to mitigate water quality impacts due to sewage discharge, and the extent to which water quality will be maintained in accordance with federal, state, and city and borough law.

BACKGROUND

Sewage is a specific type of wastewater derived from primarily domestic (or non-industrial) sources such as lavatories, sinks, laundry facilities, and showers. Sewage is also referred to as sanitary or domestic wastewater. The applicant's proposed operation includes collecting and treating sewage generated at two locations: the marine terminal complex; and the process and camp area. Sewage from the marine terminal complex will be treated and discharged via an existing outfall to Lynn Canal. Sewage from the process and camp area will be treated and discharged to subsurface soil via a leach field. In both cases, sludge resulting from the treatment process will be managed offsite.

Sewage poses well-known microbial threats to humans. Concentrations of "fecal coliform bacteria" -- a particular type of bacteria found in the intestinal tract of mammals -- are used as indicators of microbial contamination. Sewage can also adversely impact aquatic life by imposing an oxygen demand on receiving waters that reduces the amount of available oxygen. A common measure of the oxygen-robbing capacity of sewage is called biochemical oxygen demand, or BOD. Sewage also contains solids that can settle on the bottom and impact benthic life, reduce the amount of light available for photosynthesis, and cause a number of other effects. The amount of solids in sewage is usually measured as "total suspended solids," or TSS. Sewage can contain a number of other contaminants, of course. Small amounts of dissolved metals from the water supply or from dissolution of piping and storage materials, surfactants and nutrients from laundry soaps, reacted disinfectants, ammonia, oils and grease, and other contaminants may also be present.

Modern sewage treatment technology and regulation focuses on controlling levels of TSS, BOD and fecal coliform bacteria. Experience has shown that health and water quality impacts can usually be minimized with proper control of these three parameters.

Permitting Status. Treated domestic sewage from the marine terminal area is currently discharged via an outfall to Lynn Canal under an NPDES permit issued in 1991 (SRK, 1996d). On February 24, 1997, EPA issued a draft NPDES permit for all wastewater discharges from full-scale operations as proposed by the applicant. That permit would authorize discharge of an increased amount of treated sewage to Lynn Canal via the existing outfall (identified as Outfall No. 003).

Because treated sewage from the process and camp area is to be discharged to subsurface lands, no NPDES permit is needed. Instead, a waste disposal permit is required from ADEC. The applicant has an existing ADEC waste disposal permit to discharge 4,000 gallons per day to a leach field. In November 1996, Coeur applied to ADEC to increase the permitted discharge to an average of 40,000 gallons per day to accommodate full-scale operations.

ANALYSIS

Mill Process and Camp Area. Sewage from this area will be collected in an 8-inch gravity main and routed to three 16,000-gallon septic tanks for treatment. Septic tank effluent will discharge to a 50,000 square foot leach field. Flow would be distributed to the leach field using 4-inch perforated drain pipe placed on about 2-foot centers (Montgomery Watson, 1996).

In general, ADEC regulations (18 AAC 72) require that sewage treatment and disposal systems of the proposed size and type be designed by a professional engineer using standard practices. The preliminary design report prepared by Montgomery Watson, Inc. (1996) complies with this requirement.

ADEC regulations require that domestic wastewater (sewage) to be discharged to subsurface land receive primary treatment (18 AAC 72.040(a)(2)). The proposed use of septic tanks will comply with this requirement.

ADEC regulations require that soil absorption systems and other components of sewage collection, treatment and disposal systems be greater than 100 feet from surface waters (18 AAC 72.015(f)). The proposed leach field area is approximately 700 feet from the Ophir Creek diversion, 700 feet from Ivanhoe Creek, and 600 feet from Sherman Creek.

ADEC regulations require that designs for soil absorption systems with flows equal to or greater than 2,500 gallons per day include calculations prepared and sealed by a registered engineer demonstrating that nitrate concentrations in groundwater will not exceed 5 mg/l beyond a point specified by the department (18 AAC 72.265(a)(5)). Mean background nitrate concentrations from monitoring well SH-23 in the vicinity of the proposed leach field are 0.07 mg/l (SAIC, 1997). Given low background nitrate levels, and no drinking water use of area groundwater, staff conclude that the proposed discharge will comply with this limit.

Marine Terminal Complex. Sewage from the marine terminal complex will be collected in sewer lines and routed to a sewage treatment plant providing secondary treatment. Treated effluent from the sewage treatment plant will be discharged to Lynn Canal via an existing 8-inch outfall that discharges approximately 800 feet offshore, and at a depth of approximately 20 feet below mean lower low water. The collection, treatment and disposal system will be designed to process an average flow of 30,000 gallons per day. (Montgomery Watson, 1996).

In general, ADEC regulations (18 AAC 72) require that sewage treatment and disposal systems of the proposed size and type be designed by a professional engineer using standard practices. The preliminary design report prepared by Montgomery Watson, Inc. (1996) complies with this requirement.

ADEC regulations require that domestic wastewater (sewage) to be discharged to subsurface land receive secondary treatment (18 AAC 72.040(a)(4)). The applicant's proposed treatment will comply with this requirement.

The draft NPDES permit sets out a number of conditions to ensure compliance with EPA regulations and ADEC water quality standards. The permit limits flows and concentrations of pollutants in the treated effluent as follows:

"

Effluent Parameter Daily Maximum Weekly Average Monthly Average
Total Flow (gal per day) 60,000 --- 30,000
BOD5 (mg/l) 60 45 30
TSS (mg/l) 60 45 30
Fecal Coliform (#/100 ml) 43* --- 14*
pH (std units) 6.5-8.5    

*These limits are based on Alaska Water Quality Standards without dilution afforded by an authorized mixing zone."

These limits are standard for discharge of secondary treated sewage effluent. For example, they are the same limits that would apply to the CBJ wastewater treatment discharges. A large number of pre-built (package) secondary treatment plants are available and capable of meeting the BOD, TSS and pH limits set out in the draft permit. The applicant's proposal will comply with these requirements.

The limits on fecal coliform bacteria cannot be met without disinfecting the effluent or providing a mixing zone. Concentrations of fecal coliform bacteria in secondary treatment plant effluent are on the order of hundreds of thousands of colonies per 100 ml. Disinfecting the effluent is usually discouraged by the Alaska Department of Fish & Game and other agencies as standard disinfectant processes not only reduce the number of viable bacteria, but result in residuals that are toxic to marine life. Coeur Alaska applied to the ADEC for a mixing zone to allow dilution of the hundreds of thousands of colonies of fecal coliform bacteria per 100 ml in the treated effluent to the 14 colonies per 100 ml specified by the permit. The applicant conducted modeling to predict the size of the required mixing zone (Klepfer, 1997a). The applicant's modeling effort was reviewed by the ADEC, and the agency conducted independent modeling. The applicant and ADEC agree that a mixing zone configured as a 200- by 600-meter rectangle centered on the end of the outfall in about 60 feet of water 1200 feet from shore will be sufficient to provide the required dilution (see attached figure). ADEC intends to specify the mixing zone for outfall 003 in its 401 certification of the NPDES permit (Stambaugh, 1997).

An alternative that could reduce the size of a mixing zone would be to disinfect the wastewater stream using ultra-violet light, or another method that does not produce a toxic residual.

The NPDES permit also requires:

Discussion of SEIS Alternatives. The applicant's original dry tailings proposal (Alternative B) and the U.S. Forest Service's preferred alternative (Alternative D) do not differ with respect to sewage.

STAFF FINDINGS

STAFF RECOMMENDATION

Staff recommends approval of this aspect of the project.


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Last revised on 06/28/99 - bgb