DSPUD Permit Review Meeting Notes

Joe Gray, February 15, 2009

DSPUD held a special board meeting Tuesday February 10, 2009, to review the recently released draft discharge permit from the State Water Quality Control Board. The meeting was held at Sugar Bowl and attended by upwards of 20 people to hear the presentations by the DSPUD board, their general manager (Tom Skjelstad), their plant operator (Jim King), two representatives from the California Regional Water Quality Control Board- Central Valley Region (Ken Landau and Diana Messina), and two representatives of Eco:Logic (Jeff Hauser and Bob Emerick). Eco:Logic is DSPUD's engineering consulting firm for the treatment plant.

The permit, if adopted, specifies the discharge quality limits that DSPUD's wastewater treatment plant must meet in order to discharge into the South Yuba River and to spray on the Soda Springs ski hill in the summer. A copy of the tentative permit, including options and its companion cease and desist order can be found on DSPUD's website at: http://www.dspud.com/documents.php (see the Feb 2, 2009 documents).

The meeting was split into two parts, first a discussion of the tentative permit, followed by what can be done to the treatment pant to meet any new discharge quality requirements.

The Tentative Permit

Ken Landau and Diana Messina of the state water quality control board (State) summarized the key components of the draft permit. The handout they used is: DSPUD 10 February 2009 Meeting Handout. Of primary interest are the changes in the permit which may require improvements to the DSPUD plant or its operation. These are in the area of ammonia and nitrates. There were new limitations on other chemicals, but none likely to cause any plant changes.

The total flow allowed through the plant was not changed, so any expansion to add capacity will require a new permit. At this time additional hookups, beyond the currently available ones, could only come if conservation and sewer repairs lowered the current sewage volume flowing into the plant.

The ammonia limit went down from 5 milligrams per liter (mg/L) to 2.1 mg/L, measured as the monthly average of ammonia levels in the discharge. Ammonia is very toxic to aquatic life in the river and the more stringent limit was expected. The plant was able to meet the 5 mg/L ammonia discharge limit after the last upgrade was completed in 2006. Plant improvements may be needed to meet the new limit.

The nitrate limit was relaxed from 10 mg/L to 18 mg/L, measured as the monthly average of nitrate levels in the discharge. The new limit assumes that the discharge would be diluted by a factor of at least 1.8 to one in the river so that the diluted nitrate level will be below the 10 mg/L limit. DSPUD was hoping for the much higher dilution factor of 24.5 to one, based upon a yearly average river flow. Instead the State used a monthly flow for December for the dilution factor, finding that the lowest amount of dilution came in that month when there were high effluent flows due to skiers, and low river flows due to minimal snow melt. The State justified basing the dilution on monthly flows, rather than yearly flows, because nitrates are considered a short time exposure risk for human and river health.

Members of the audience questioned whether the State should allow dilution using estimates of the river flow at DSPUD, based upon river flow data collected 10 miles downstream at Cisco Grove. The estimate assumes that the flow at DSPUD will reflect the ratio of the watershed area above DSPUD to the watershed above the gage. This estimate may be inaccurate because water from Kidd and Cascade Lakes is released into the river below DSPUD, and Van Norden Dam blocks the flow of water coming from a large portion of the watershed. Comments were made that the river can have no flow in the fall months and into December, raising questions whether there would be any dilution at all, and whether the nitrate limit should remain at 10 mg/L.

The State said they would consider requiring a flow gage at the discharge point in order to accurately measure the amount of dilution. Eco:Logic said that DSPUD had proposed a flow gage in the permit application and would have no objections to the State requiring one. The State also said that they would require DSPUD to monitor the river water 500 feet downstream, and to verify that the nitrates were diluted down to below 10mg/L. It is unclear whether the downstream 10mg/L limit is in the tentative permit, or if the State needs to add it.

Dilution was also granted for dichlorobromomethane at the full 24.5 to one ratio that DSPUD asked for. This chemical is a by-product of the chlorine disinfection process used by the plant, and is considered a long-term exposure (70 years) toxin, so is granted dilution based upon yearly river flows.

The State indicated that preserving the health of the river was an important objective. The State said that there will be more stringent monitoring requirements for algae and other nuisance growth in the river. The audience asked if the State could add something to the permit that would force DSPUD to start discharging the effluent on the Soda Springs ski hill as early as possible, rather than allowing DSPUD to discharge to the river through the end of July. While the permit says the spray discharge should start as early as possible,  and end as late as possible, there are no enforcement mechanisms, and because of the added electricity expenses to pump and spray the effluent, there is a very real economic incentive to delay the start of spraying as much as possible.

Finally, the tentative permit is written with three options: (1) Dilution would be allowed for both nitrates and dichlorobromomethane; (2) dilution will be allowed for dichlorobromomethane but not nitrates; and (3) no dilution will be allowed for either chemical. The State will decide which option is adopted after reviewing all comments and holding a public hearing.

The state also presented a tentative "Cease and Desist" order, which gives DSPUD up to 5 years to make plant improvements to meet the new limits. The tentative order sets higher, more relaxed, limits during that period.

The public hearing will be held on April 23/24 in Rancho Cordova. The notice of the public hearing can be found on the DSPUD website in the link above. Comments on the permit are due by 5PM, March 6th and should be directed to Diana Messina. See the notice for where to send comments.

DSPUD Treatment Plant Upgrades

Mr. Hauser of Eco:Logic described how the treatment plant could potentially be upgraded to remove more ammonia and nitrates. A copy of Mr. Hauser's report can be found on the previously mentioned DSPUD link as "Cost Comparisons for Treatment Plant Improvements".

Mr. Hauser designed the plant in the 1980's. At that time there were minimal or no requirements to remove ammonia and nitrate. In 2002 the State imposed new ammonia and nitrate limits that required plant upgrades. 

The plant was upgraded between 2002 and 2006 to enhance ammonia removal and to add a nitrate removal stage. The upgrade was designed by Brentwood Industries in Pennsylvania. They added what are called AccuWeb modules to the biological processing tanks. These modules contain many layers of fiber meshes that act as artificial "reefs" for the bacteria (bugs) used in the treatment process to grow on. The purpose of the AccuWeb reefs is increase the processing capacity of the tanks and to improve the ability of the bugs to survive and grow at cold temperatures.

The treatment plant removes ammonia ("nitrification") using bugs that convert ammonia to nitrates. The nitrification bugs use oxygen (O2) to convert NH4 (ammonia) to NO3 (nitrate). The nitrification stage is aerobic, with oxygen added to the flow in order to feed the bugs.  

The nitrate is removed ("denitrification") using bugs that strip the oxygen from nitrates (NO3) to release harmless nitrogen gas (N2).These bugs need to work in an anoxic (oxygen deprived, nitrate rich) environment, so no oxygen is injected in the denitrification stage.

The treatment flow is a series of anoxic (denitrifying) AccuWeb frames followed by a series of aerobic nitrifying frames. The denitrifying and nitrifying zones are separated by a baffle to keep the two zones from mixing. The sewage liquid is  continually recycled through the two zones. New sewage enters the anoxic zone and processed sewage exits the aerobic zone and goes to the clarifiers.

Graphs were shown to illustrate that the plant has been able to convert ammonia to nitrates very well from May through December. During the same period, however, the graphs show that the plant did not get rid of the nitrates. From January through May the plant did not remove all of the ammonia, but was able to keep the nitrates under control, mainly because the plant wasn't converting all of the ammonia to nitrates.

Over the last two years DSPUD has accumulated six violations for excessive nitrates (greater than 10 mg/L) and one for excessive ammonia. The ammonia violation may, however, be considered an anomaly, as it was for a single one-hour violation, not a 5 mg/L monthly average violation. These violations illustrate the problems the plant has had in removing nitrates in those summer and fall months when almost all of the ammonia is being converted to nitrates. Note that, if the violation records are correct, the plant met the 5 mg/L ammonia limit all year, even during the winter months when the cold temperatures and highly erratic flows makes it hard to remove ammonia. I.E., while the plant wasn't removing all of the ammonia, it was removing enough to prevent violations.

Mr. Hauser examined four upgrade scenarios: (1) a 5 mg/L ammonia limit but no nitrate limit; (2) a 1 mg/L ammonia limit and no nitrate limit; (3) a 1 mg/L ammonia limit and a 10 mg/L nitrate limit; and (4) a 1 mg/L ammonia limit and a 2 mg/L nitrate limit.

Scenarios (1) and (2): Low ammonia limits, no nitrate limits

Mr. Hauser showed, through simulations, that the existing plant should be able to remove almost all of the ammonia, as required by the first two scenarios, even during the difficult winter months. He showed that by feeding the plant with additional ammonia, slowly increasing the feed during the month prior to Christmas, the population of ammonia removing bugs could be grown in order to absorb the sudden shock of ammonia that hits the plant around Christmas due to the ski season starting. Currently the plant does feed extra ammonia to the plant in November, but apparently not in the gradual ramp Mr. Hauser suggests. This operational change, plus enclosing or covering the processing tanks to retain heat, was shown in simulations to reduce the ammonia discharge down to less than 1 mg/L. Hence the plant, with some minor changes should be able to meet the new 2.1 mg/L ammonia limit.

Scenarios (3) and (4): Low ammonia and low nitrate limits

Mr. Hauser then looked at meeting very low ammonia limits while at the same time meeting very low nitrate limits. Mr. Hauser did not think the existing plant could simultaneously meet low ammonia and low nitrate limits, so he examined replacing the plant altogether with a multi-stage plant design that had multiple nitrification and denitrification tanks as well as a membrane bioreactor stage. Simulations showed that the proposed plant could meet extreme limits  of 1 mg/L ammonia and 2 mg/L nitrate.

Mr. Hauser estimated the cost of the new plant to be at least $10M. He emphasized that these were back of the envelop numbers, and the actual cost would probably be higher. For example, the plant upgrade proposed by Carollo Engineers (for Royal Gorge LLC development plans) was to double the capacity of the plant. Their estimate to double the capacity was over $40M. This would indicate that their plant upgrade estimate, without doubling the capacity, was more like $20M. Either number is much more than the plant upgrade in 2002 which cost $4M.

Mr. Hauser did not look at any other options for upgrading the plant or changing its operation which may be cheaper. He also says he did not get a chance to consult with Brentwood Industries to see if they had any ideas about how to improve the performance of the existing AccuWeb system. 

Mr. Hauser did admit that the current plant's operation could be adjusted to meet the new limits for most of the year. The plant would just have trouble for the two or three ski season months. As the current plant was able to meet both the old 5 mg/L ammonia limit and the 10 mg/L nitrate limit during the ski season, perhaps minor improvements will allow the plant to meet the new 2.1 mg/L ammonia and the relaxed 18 mg/L nitrate limits. Such lower cost ski-season only solutions have not been investigated.

Summary

The draft permit reduces the amount of ammonia that DSPUD can discharge into the South Yuba, and slightly increases the amount of nitrates. The nitrate limit, however, may end up staying at the current 10 mg/L limit if the flow in the river does drop to zero during some months. DSPUD had hoped to receive, but was denied, a much higher nitrate limit of 245 mg/L based upon the average yearly flow in the South Yuba, not a monthly flow.

Items not in the current tentative permit, but which the State indicated may be added are a flow gage at DSPUD and monitoring and limits placed on the river flow 500 feet below the DSPUD discharge point.

Plant upgrades to meet the new ammonia limit may be as high as $10M to $20M, but there are indications that the plant may be able to meet the new limits with smaller and much cheaper changes. In a private conversation, Tom Skjelstad, DSPUD general manager, made assurances that all lower cost options will be examined before expensive upgrades are made.

In addition, any upgrades will be scrutinized by Sierra Lakes Water District (SLCWD) which would have to pay 44% of any upgrade cost. In their board meeting a few days later, the board hired Waterworks Engineers to review any planned upgrades.