Mark Gross, Ph.D., P.E.
I have a friend who always told me “bad data is worse than no data at all.” That can certainly be true in the case of using analytical data to make a decision regarding the performance of a small wastewater treatment system.
In some cases, field performance verification is required for wastewater treatment systems. Also, nearly all National Pollutant Discharge Elimination System (NPDES) permitted wastewater treatment systems are required to be sampled and analyzed for compliance. When sampling and analyses are required to be reliable, believable, and most importantly, defensible, third party sampling and analysis is performed. Some states require field performance testing before a proprietary wastewater treatment system can be permitted in that particular state. Some may ask, “Why, if the treatment system has been tested and certified by NSF International, should it also be tested for field performance?” The answer is that test center data does not predict how a wastewater treatment system will perform under field conditions. In their report “Variability and Reliability of Test Center and Field Data: Definition of Proven Technology from a Regulatory Viewpoint,” Tom Groves and his co-authors make some strong statements regarding relying solely upon test center data for system approval. They say, “One data distribution set (such as test or field) cannot be used to accurately predict the other.” They go on to state, “An independent, trusted screening process (such as test center) is needed to make sure any technology has a reasonable chance of being successful. In addition, field testing is needed to help predict what the real-life performance of the system is going to be.” (Groves, et al, 2005)
Another way to look at this is that if a wastewater treatment system can’t pass the highly controlled test center challenge, it will be unlikely to perform at all in the field. Understanding the performance for passing the NSF International/ANSI standard for Class 1 systems may be helpful. It is commonly believed that a treatment system must meet CBOD5 and TSS levels of 25 mg/L and 30 mg/L respectively. But, those are the criteria for the 30-day average performance. The 7-day averages are allowed to be as high as 40 mg/L and 45 mg/L CBOD5 and TSS. In fact, a system can still pass the Class 1 criteria with excursions up to 56 mg/L and 63 mg/L for 7-day averages. (NSF International, 2010).
What do these analyses mean and what do they have to do with my septic system and drainfield?
BOD5 and CBOD5
BOD stands for Biochemical Oxygen Demand, and CBOD stands for Carbonaceous Biochemical Oxygen Demand. The subscript 5 means that these are measured over a 5-day period. The oxygen demand is an indirect measure of the amount of nutrients in the wastewater that can be degraded by the microbes in 5 days. The CBOD is only the part of the oxygen demand that is caused when the microbes degrade the organic carbon in the wastewater. In more familiar terms, the CBOD may be considered the carbohydrates in the wastewater. The remaining part of the oxygen demand (BOD) is caused by the proteins and nitrogen in the wastewater. The BOD and CBOD come from the things washed down the drain and flushed down the toilet in the building. The importance of lowering the BOD in the wastewater is that if the wastewater is discharged to a stream, the microbes will take the oxygen dissolved in the stream to metabolize the organic matter and nutrients in the wastewater. That can deplete the oxygen in the stream and stress the natural animals and plants in the water. If the oxygen level drops too low, it can cause a fish kill. High BOD applied to a drainfield can mean that the microbes don’t get enough oxygen and can operate in their anaerobic mode, resulting in thick slimes and clogging the soil in the drainfield. If adequate oxygen isn’t supplied to the microbes and wastewater, the treatment is incomplete. Most of us who work with small wastewater systems and drainfields have dug into failed drainfields to find black, gelatinous, slime covering the rock and filling the pores around the media in the trench. Putting a really high BOD into a drainfield can cause failure because the oxygen demand can’t be satisfied.
Total Suspended Solids
TSS stands for total suspended solids. TSS is measured by passing the wastewater sample through a filter and measuring the weight of solids contained in a particular amount (volume) of the wastewater. If the TSS is too high going into the drainfield, the soil pores can become clogged with solids and the wastewater will not move out of the trenches. The result is a mess of a malfunctioning system
Nitrogen
Nitrogen in sewage comes from urine and proteins that go down the drains. It may be ammonia or nitrate or organic nitrogen or maybe nitrite. Sometimes there is a limit placed on the amount of nitrogen that can go into the soil. If this is the case, additional treatment besides a septic tank and drainfield may be required.
Coliform
Coliform is a type of bacterium. Sometimes we talk about total coliform, and sometimes we talk about fecal coliform. Fecal coliform are bacteria that grow in the intestines of warm-blooded animals. When we find fecal coliform in a water sample, it means that somehow the contents of the intestines of a warm-blooded animal (that would be feces, right?) have gotten into the water where the sample was taken. Sometimes the soil is too coarse or the site may not effectively remove the fecal coliform before the water would get to the surface water or into drinking water, so treatment in addition to the septic tank and drainfield is needed.
So what does a Third-party sampling and analysis program look like?
One important factor in third-party sampling is that the samples are collected and analyzed by someone other than the manufacturer and certainly not by someone who has a financial interest in whether the treatment system performs to a particular standard. Independent sampling and testing is an absolute must. The sampler is typically a laboratory technician who is trained to sample wastewater systems. The technician should be trained to take the sample from the particular system so that any sample taken is representative of the effluent or influent sampled.
If the treatment system cycles, a cycle shouldn’t be forced just to make sampling more convenient. The system should be allowed to operate under its normal cycling frequency and the sample should be taken when it is available. The sample should be taken carefully so that no soil or particles are scraped from the walls. When analyses will be performed for constituents in the parts per million range, even a tiny particle of slime or soil can cause a huge change in the results. Some discussion has been seen regarding whether a grab sample or a composite sample should be used to determine a system’s performance. Although this is a consideration, that topic will not be included as part of this discussion.
The samples should be taken in the proper container, and the correct amount of sample should be taken. Standard Methods (APHA, 2005) specifies the type of container for the particular analysis. For example, samples for BOD are supposed to be taken in plastic or glass, and a minimum of 1 liter is required. Samples for Ammonia analyses should be taken in either plastic or glass and at least one-half liter of liquid is required. Samples for solids may be taken in plastic or glass. Samples to be analyzed for Fats, Oil and Grease (FOG) are supposed to be taken in wide-mouth calibrated glass containers.
Samples should be preserved and transported properly, observing the maximum holding times allowed for the particular analysis. Some samples such as those for BOD and Solids should be refrigerated. This is typically done by placing them in a cooler of ice. The samples must be in the laboratory and analyses begun within 48 hours (6 hours recommended). Samples for ammonia and nitrate plus nitrite should be acidified to a pH less than 2 with sulfuric acid and then refrigerated. The recommended holding time for ammonia is 7 days with a maximum of 28 days. The holding time for fecal coliform is 6 hours. Total coliform holding time is 24 hours. The holding times can affect how many systems can be sampled in a day and how far from the system the laboratory may be located.
Chain of custody forms must be completed and kept with the sample until the sample is finally analyzed and the results are recorded. Then the chain of custody form is kept in the permanent records for that sample. Without a chain of custody form, the sample documentation is incomplete, and it would be difficult to defend the validity of the sample. The chain of custody form includes information such as what the sample is, who took the sample, where and when the sample was taken, and when the sample was transferred to someone else (when and to whom custody was relinquished).
The laboratory analyzing the samples must be certified or accredited or approved, or whatever designation is used for laboratories in the state where the samples are collected and analyzed. In Oregon, wastewater laboratories are “accredited” by the Oregon Environmental Laboratory Accreditation Program through the Oregon Public Health Division. Gaining and maintaining accreditation is no simple matter. Nor is it inexpensive. Accredited laboratories must own and maintain high-quality expensive instrumentation. Accredited laboratories must maintain records of instrument calibration. Accredited laboratories must pass audits where the laboratory receives and must correctly analyze blind samples. Laboratory personnel are properly trained and have the proper credentials for their accreditation. Using an accredited laboratory is the only way to obtain defensible analytical results.
Analyzing the data
Once the laboratory analyses have been obtained, some method is used to determine its meaning. First, the data should be examined to see if it makes sense. If the results show that the BOD of a sample is extremely low, but the suspended solids are very high, there is a reason to question the laboratory analyses. If the effluent has been very clean for some period of time and a sample shows very high concentrations for analytical results, the sample should be questioned. Review the consistency of the results with each other for the same sample, and review the consistency with respect to trends for each system being sampled. Take a look at the influent and effluent to see if something has happened to cause the treatment system not to perform consistently. Check with the laboratory to determine that the results are correct. Sometimes samples get mixed up in the laboratory, and those mistakes can be found. Sometimes numbers get transposed or dilutions are written incorrectly, and those mistakes can be found.
The statistical analysis can be as simple or complex as desired, depending upon the available data. It is common to see the average (mean) concentrations reported. The mean may or may not be the best statistic to describe the performance of the system. The median value may better represent performance. The median is the value that is in the middle of all of the values when the values are arranged from smallest to largest. Sometimes it is helpful to report the highest value and the lowest value in the results. That provides an idea of the range of results. The standard deviation may also help to understand the performance results. The standard deviation gives some idea of the variability of the data. That is, whether or not most of the values are close to the mean or whether the values are widely scattered from high to low. The standard deviation can also be used to evaluate the results for outliers. An accepted method for eliminating outliers is to remove values that are greater than or equal to three times the standard deviation away from the mean.
Not all wastewater treatment systems are required to complete third party testing. It is not uncommon for operators or service providers for treatment systems having NPDES permits to collect the samples themselves. However, accredited laboratories analyze those samples. Accredited laboratories always analyze samples for compliance, and the appropriate chain of custody forms accompany those samples and they are taken in the correct sample containers with the proper preservation method. Few individual home wastewater systems are sampled and analyzed as a regular procedure or requirement for operation. Even though the systems have been permitted to meet a particular effluent quality, nominally based upon the site conditions, there is little if any evidence of whether those systems are in fact meeting that effluent quality.
Why isn’t third-party field performance testing a regular requirement?
For several reasons, states don’t require third-party field performance testing to determine whether or not a treatment system is eligible for sale. The testing program is expensive. If a manufacturer is required to prove that its system can perform consistently and reliably under field conditions, and is required to use third party testing and analysis to prove it, the cost is passed on as part of the product. In some states, the field performance was tested, but the manufacturer or the manufacturer’s dealer or distributor took the samples, and the least expensive laboratory or method of analysis was used. No laboratory accreditation, chain of custody, instrument calibration, or any other defensible documentation was provided, yet the state accepted the testing results. ”Bad data is worse than no data,” according to my friend. Also, products can be inexpensive if there are no costs for research and development and defensible third-party field testing. One way to produce a product inexpensively is to avoid incurring costs to get the product to market.
Defensible third-party field testing may result in some manufacturers’ products not passing. In some cases, manufacturers don’t have enough money for the field testing. Sometimes, rather than go through the field testing process, the manufacturer uses a political approach and brings pressure to bear through legislative or regulatory channels rather than proving the performance of the treatment system. In some cases, the regulatory community feels it’s their responsibility to prevent the market choices from being limited, so they approve products without proof that the system will perform in the field. In at least one case, the state regulatory agency lowered the passing standards when only one product successfully passed the stated standard. The reason given was that the market choices should not be limited.
Several states have required third party testing. NSF International has provided at least one contracted third-party field testing program in the eastern United States. A clear understanding of the third-party field-testing process may improve the likelihood that small wastewater treatment system products will perform reliably and sustainably and meet the effluent quality for which they have been permitted. It may also level the playing field for effective wastewater treatment systems in the market.
References
Groves, T. W., F. Bowers, E. Corriveau, J. Higgins, J. Heltshe, and M. Hoover. 2005. Variability and Reliability of Test Center and Field Data: Definition of Proven Technology From a Regulatory Viewpoint. Project No. WU-HT-03-35. Prepared for the National Decentralized Water Resources Capacity Development Project, Washington University, St. Louis, MO, by the New England Interstate Water Pollution Control Commission, Lowell, MA.
NSF International, 2011, NSF International Standard/American National Standard for Wastewater Technology – Residential Wastewater Treatment Systems, NSF International, PO Box 130140, Ann Arbor, Michigan 48113-0140, USA
American Public Health Association/Water Environment Federation/American Waterworks Association, Standard Methods for the Examination of Water and Wastewater, American Public Health Association, 2005, Ne