1115515 LIBRARY I , Michigan State it 9 University This is to certify that the thesis entitled BIOMAT FORMATION IN EXISTING ON-SITE WASTEWATER TREATMENT SYSTEMS AS FOUND IN THE INGHAM COUNTY POINT-OF-SALE PROGRAM, INGHAM COUNTY. MICHIGAN presented by Lisa M. McGiveron has been accepted towards fulfillment of the requirements for the Master of degree in Crop and Soil Science Science (MW/mt Major Professor’s Signature D€¢ 7 , 2. (0‘7 Date MSU is an Affirmative Action/Equal Opportunity Employer -.-—.--.—.- PLACE IN RETURN BOX to remove this checkout from your record. To AVOID FINES return on or before date due. MAY BE RECALLED with earlier due date if requested. DATE DUE DATE DUE DATE DUE 5/08 K:IProj/Acc&Pres/ClRC/DateDue.indd BIOMAT FORMATION IN EXISTING ON-SITE WASTEWATER TREATMENT SYSTEMS AS FOUND IN THE INGHAM COUNTY POINT-OF-SALE PROGRAM, INGHAM COUNTY, MICHIGAN By Lisa M. McGiveron A THESIS Submitted to Michigan State University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Crop and Soil Science 2009 ABSTRACT BIOMAT FORMATION 1N EXISTING ON—SITE WASTEWATER TREATMENT SYSTEMS AS FOUND IN THE INGHAM COUNTY POINT-OF-SALE PROGRAM, INGHAM COUNTY, MICHIGAN By Lisa M. McGiveron It has long been thought that formation of a soil-clogging layer of a black tar-like substance, or biomat, at the soil-gravel interface in sub-surface on-site wastewater treatment systems is inevitable, although the process by which it develops is not fully understood. A study was conducted to evaluate the occurrence and severity of biomat in Ingham County, Michigan. The Ingham County Point-of—Sale program, which is a program designed to identify failing or non-conforming septic systems, was used to gather information about existing on—site wastewater treatment systems. Ingham County inspectors evaluated on—site wastewater treatment systems and rated the biomat levels in these systems. The objectives of this study were to (1) evaluate biomat levels in existing wastewater treatment systems, evaluate the age of systems, and evaluate the soil texture of the systems inspected for the Ingham County Point of Sale program and (2) inspect, in situ, fifty existing drainfields fi'om the Point of Sale program, each being more than thirty years old. It was surprising to find that 83% of trench and bed type systems Showed no evidence of biomat and upon re-inspection, 70% of systems that were 30 years old or older, showed no Sign of biomat which is contrary to current thinking within the on-site industry. ACKNOWLEDGEMENTS The author wished to express deepest gratitude to Dr. Delbert L. Mokma, the author’s major professor, for his constant and greatly appreciated guidance, assistance, direction, academic and moral, and his support for this project as well as throughout the duration of the author’s academic career. He inspired me, mentored me, and gave me both direction and opportunities for my career. I want to also thank Dr. Mokma for all of the treasured resource materials as well as numerous on-site stories shared in the laboratory that I will never forget. The author also wishes to express her appreciation to her guidance committee: Dr. Brian Teppen, with whom I have enjoyed numerous classes and Dr. Steven Safi'erman for his inspiration and valuable on-site information. I wish to also thank them for their direction and guidance. I would also especially like to thank Garry Rowe, Demand Area Supervisor for Ingham County Environmental Health. I wish to thank him for believing in me and giving me the opportunity to use the Point-of-Sale information for my research. I also want to thank him for teaching me my “life lessons” and what it truly means to be a sanitarian. I also would like to thank Garry, Jim Wilson, Mark Piavis, and Diane Gorch of Ingham County for allowing me to continue working even afier my probation was finished. Special thanks go to Mark Banghart, Bill Haun, Randy Fedewa, and Pat Marrison, of the Ingham County Health Department, for all of their technical assistance, and for iii allowing me to accompany them on their field evaluations. The author also wishes to i thank them for their valuable advice and support, but most of all, for putting up with my constant questions. Last, but not least, I wish to thank my family, without whom none of this would have been possible. iv TABLE OF CONTENTS Page LIST OF TABLES ........................................................................................................... vii LIST OF FIGURES ......................................................................................................... viii Chapter I. INTRODUCTION ....................................................................................... 1 II. LITERATURE REVIEW ............................................................................ 4 On-site Wastewater Treatment Characteristics ............................................ 4 Function of Biomat in On-site Wastewater Treatment Systems .................. 8 Biomat Formation in Onsite Wastewater Treatment Systems .................. 11 Microorganisms Found in Biomat in On-site Wastewater Treatment Systems .......................................................................................... 19 Appearance of a Biomat in On-site Wastewater Treatment Systems ........ 20 Time for Biomat Development in On-site Wastewater Treatment Systems .......................................................................................... 21 Process of Biomat formation in On-site Wastewater Treatment Systems.21 Benefits of a Biomat in On-site Wastewater Treatment Systems .............. 23 Recovery of Drainfields in On-site Wastewater Treatment Systems after Biomat Development ..................................................................... 24 Limits Of Biomat Development in On-site Wastewater Treatment Systems .......................................................................................... 25 Conclusion ................................................................................................. 26 III. BIOMAT FORMATION IN EXISTING ON-SITE WASTEWATER TREATMENT SYSTEMS AS FOUND IN THE INGHAM COUNTY POINT-OF-SALE PROGRAM, INGHAM COUNTY, MICHIGAN ....... 27 Introduction .................................................................................... 27 Methods and Materials ................................................................... 29 Study Area ......................................................................... 29 P08 and Re-Inspection Methods ....................................... 29 Results and Discussion .................................................................. 34 P08 Overall Data ............................................................... 34 Re-Inspection Data ............................................................ 39 Page Soils ................................................................................... 45 Beds vs. Trenches .............................................................. 46 IV. SUMMARY AND CONCLUSIONS ........................................................ 48 V. FURTHER STUDY ................................................................................... 50 REFERENCES .................................................................................................................. 52 vi Table 10. LIST OF TABLES Page Raw Sewage Characteristics ........................................................................ 5 Septic Tank Effluent Characteristics ........................................................... 6 Biomat Evaluation Criteria ........................................................................ 29 Total Point-of-Sale Evaluations ................................................................. 35 Biomat Data ............................................................................................... 35 Re-Inspection Biomat Data ........................................................................ 41 Biomat Level Comparison ............. _ ............................................................ 43 Comparison of the POS Biomat Levels with Re-Inspection Levels for Beds ................................................................................................... 44 Comparison of the POS Biomat Levels with Re-Inspection Levels for Trenches ................................................................................................ 45 Re—Inspection Soil Data ............................................................................. 47 vii Figure LIST OF FIGURES Page Seepage of Effluent ...................................................................................... 9 Biomat Development ................................................................................. 10 Drainfield Inspection Process for Trenches ............................................... 33 Drainfield Inspection Process for Beds ..................................................... 33 Number of Systems According to Age and Biomat Level for Trench Style ' Systems ................................................................................................. 38 Number of Systems According 'to Age and Biomat Level for Bed Style Systems ................................................................................................. 39 viii CHAPTER 1 INTRODUCTION It has long been thought that formation of a soil-clogging layer of a black tar-like substance, or biomat, at the soil-gravel interface in sub-surface on-site wastewater treatment systems is inevitable, although the process by which it develops is not fully understood. Most researchers agree that biomat formation is a combination of physical, chemical, and biological factors such as an accumulation of organic matter, soil aggregation, and microbial processes (Jones and Taylor, 1965; Thomas et al., 1966; Bouma, 1975; Siegrist and Boyle, 1987; Finch etal., 2007; McKinley and Siegrist, 2007) and that biomat formation helps in the even distribution and treatment of septic tank effluent. Researchers agree that if it is not managed, biomat formation can lead to reduced hydraulic conductivity of septic tank effluent in the drainfield‘to the point that on-site systems fail (Allison, 1947; Avnimelech and Nevo, 1963; Jones and Taylor, 1965; Thomas etal., 1966, Bouma, 1971; Daniel and Bouma, 1974; Frankenberger et al., 1979; Tyler, 2001; McKinley and Siegrist, 2007). When failure occurs, effluent can begin to pond on the surface, creating an imminent health hazard. On-site wastewater treatment systems collect, treat, and release about 4 billion gallons of treated effluent per day. There are approximately 23 percent of the estimated 115 million occupied homes in the United States being served by on-site systems (U .8. Census Bureau, 1997). In the past, most on—site wastewater treatment systems were installed as a temporary solution to rapidly expanding populations in rural areas until municipal sewer and treatment systems could be expanded to capture this growth (U .8. EPA, 2002). However, the United States Environmental Protection Agency (U .8. EPA, 2002) and most public health officials now recognize that on-site wastewater treatment systems are a viable method of treating wastewater. In the best of conditions, on-site wastewater systems are expected to fail after twenty to thirty years in use (Noah, 2006). Most homeowners take an “out of sight, out Of mind” mentality regarding their septic systems resulting in little to no maintenance or management of their systems. This reason led some health departments, like the Ingham County Health Department, to enact a Point of Sale program that allows them to inspect,- or have inspected by county certified inspectors, the on-site wastewater treatment systems of all homes being sold in the county. Prior to the point of sale program, health departments only inspected systems after a complaint was received. Now, however, the Point of Sale program allows them to evaluate a more complete cross-section of on-Site wastewater treatment systems. During the teaching of existing systems evaluator courses a number of onsite systems were inspected. Many borings were made through the trenches in each system. It was surprising to find that biomat was not observed in most of the systems (Mokma, 2006). As a result, the long held belief that biomat’s formed over time was questioned and forms the basis of this research. The objectives of this research were to (1) evaluate biomat levels, age of systems, and soil texture of the systems inspected for the Ingham County Point of Sale program and (2) inspect in more detail fifty existing drainfields from the Point of Sale program, each being more than thirty years old. CHAPTER II LITERATURE REVIEW On-site Wastewater Treatment Characteristics Wastewater consists of discharge from the toilet, shower, Sink, laundry, and kitchen. This wastewater, or sewage, leaves the home and enters the septic tank, whose primary purpose is to separate out any solids and provide preliminary treatment of components before the sewage leaves the tank as effluent to be treated by the soil in an onsite drainfield. A summary of typical raw sewage characteristics is given in Table 1. Wastewater flow and the type of waste generated affect wastewater quality. For typical residential sources, the peak flow and peak loading rate does not occur at the same time (Tchobanoglous and Burton, 1991; US. EPA, 2002). F low and component concentrations vary hourly and daily. Table 1: Raw Sewage Characteristics Component Concentration Range Typical Concentration Total Suspended Solids, TSS 155 — 330 mg/L 250 mg/L 5-Day Biochemical Oxygen 155 — 286 mg/L 250 mg/L Demand, BOD5 pH 6 -9 s.u. 6.5 s.u. Total Coliform Bacteria CFU/ 100 s 10 109 10 — 10 mL Fecal Coliform Bacteria CPU/100 6 s 107 mL 10 — 10 Ammonium—Nitrogen, 4 - 13 mg/L N 10 mg/L N NH4-N Nitrate-Nitrogen, NO3—N Less than 1 mg/L N Less than 1 mg/L N Total Nitrogen 26 — 75 mg/L N 60 mg/L N Total Phosphorus 6 - 12 mg/L P 10 mg/L P Source: US. EPA Onsite Wastewater Treatment Design Manual, 2002 mg/L = milligrams per liter s.u. = standard units CPU/100 mL = Colony-Forming Units per 100 milliliters After leaving the source where it is produced, the sewage enters the septic tank. Heavy solids settle to the bottom of the tank and become the sludge layer, lighter organics float to the top to become a scum layer, and component removal or inactivation occurs. Anaerobic bacteria in the tank begin to decompose the solids by hydrolyzin g the proteins and converting them to volatile fatty acids, most of which are dissolved in the water phase. The volatile fatty acids still exert much of the biochemical oxygen demand (BOD) that was originally in the organic suspended solids (EPA, 2002). BOD is the measure of the amount of oxygen needed by microorganisms to oxidize, or break down, the organic compounds in wastewater. Nitrogen enters the septic tank primarily in the form of organic matter and ammonia. Upon leaving the tank, nitrogen is primarily in the form of ammonia (Crites and Tchobanoglous 1998). Phosphorous removal mainly occurs in the soil. Phosphorous is controlled by sorption and precipitation reactions with iron and aluminum minerals in strongly acid to neutral systems and on calcium minerals in neutral to alkaline systems (US EPA, 2002). Sorption of phosphorous to the soil is limited, and phosphorous sorption will continue to move downward in the soil profile. Table 2 shows the levels of BOD, nitrogen, and phosphorous in septic tank effluent before it enters the soil where final treatment occurs. Table 2: Septic Tank Effluent Characteristics Component Concentration Typical Range Concentration Total Suspended Solids, TSS 36 - 85 mg/L 60 mg/L 5-Day Biochemical Oxygen Demand, 118 - 189 mg/L 120 mg/L BOD 5 pH 6.4 —— 7.8 s.u. 6.5 s.u. Fecal Coliform Bacteria CFU/ 100mL 10"— 107 1()6 Ammonium-Nitrogen, 30 — 50 mg/L 40 mg/L NH 4-N Nitrate-Nitrogen, NO3-N 0 — 10 mg/L 0 mg/L Total Nitrogen 29.5 — 63.4 mg/L 60 mgL Total Phosphorus 8.1 — 8.2 mg/L 8.1 mg/L Sources: EPA Onsite Wastewater Treatment System Manual, 2002, EPA/625/R-00/08 and Small and Decentralized Wastewater Management Systems, McGraw-Hill, 1998 When hydraulic conductivity or permeability decrease in the on-site wastewater treatment system, sewage may back up into the home or surface on the ground above or adjacent to the drainfield. Despite a lack of investigation of the soil of failing septic systems, biomat is Often thought to be the cause. Anaerobic microbial activity, clogging of soil pores, a decrease of the amount of oxygen present, and an accumulation of organic material at the gravel-soil interface are thought to foster biomat formation and thus decrease permeability and hydraulic conductivity (Bouma et al., 1972). In a well drained soil, aerobic organisms will generally break down compounds that produce BOD and suspended solids, preventing a biomat formation. Saturated conditions, however, inhibit oxygen diffusion in the soil so that any incoming oxygen is insufficient to sustain the decomposition of organic matter. It is these anaerobic conditions that favor biomat formation in existing on-site wastewater treatment systems (Bouma et al., 1972). Conventional on-site wastewater treatment systems fail for several reasons. The National Small Flows Clearinghouse (N SFC) has identified five common causes of system failure. The first cause of failure is hydraulic overloading. This occurs when the amount of water that flows into an on-site wastewater treatment system is greater than the amount that can permeate the soil. This can be a result of improper design, leaking plumbing, hydraulic stress on the system, clogged soils, biomat formation, or use of fine textures soils. When overloading occurs, sewage can back-up into the home or surface on the ground. The second cause is the development of a biomat. Excess BOD and suspended solids can clog soil pores creating an anaerobic environment in the trench. Biomat can reduce hydraulic conductivity and reduce treatment of septic tank effluent, eventually causing sewage to surface. Poor design or installation is the third reason that on-site wastewater treatment systems fail. Systems that are too small or are placed in soils that are not suited for on- site systems can fail. Smearing or destruction of soil structure, at the soils’ surface during installation, or installation during inclement weather can also lead to failure. The fourth reason for failure is compaction of the soil during installation. Compaction is when the pores in the soil are damaged or compressed. This prevents water from infiltrating downward causing effluent to rise and eventually surface. Compaction occurs when heavy equipment is allowed to drive over the area where the drainfield will be installed. Soil-mineral bonding is the fifth cause of failure in on-site wastewater treatment systems. This occurs when native soil cations are replaced with other cations, causing causes chemical changes in the soil. The result can cause the formation of impermeable layers on the trench walls and bottom, again causing reduced hydraulic conductivity resulting in effluent ponding on the surface or backing up into homes or buildings. Function of Biomat in On-site Wastewater Treatment Systems Biomat function and formation in on-Site wastewater treatment systems has been thought of as natural and inevitable. Bouma et al., (1972) stated that all studied conventional systems in continuous use and over six months in age, appeared to have a crust (biomat) at the bottom and part of the sidewall of the seepage bed, as indicted by ponded effluent in the trench and unsaturated soil around it (Figure 1). Yet despite its potential for creating anaerobic conditions, biomat is also thought to be a very important feature in a properly functioning on-site system. Siegrist and Van Cuyk (2001) stated that biomat formation is an important, if not critical, process that contributes to the advanced treatment potential of on-site wastewater treatment systems. Biomat houses the bacteria that break down components in wastewater, it de-activates or sorbs pathogens, and it helps filter wastewater before it reaches the groundwater. Biomat is also helpfirl in that it leads to a more even distribution of wastewater over the infiltrative surface by allowing the water to flow over the clogged area to an area of unclogged soil, allowing for unsaturated flow. As more and more of the unclogged soil receives wastewater, that soil itself eventually will become clogged with a biomat (Figure 2). This has been termed a progressive maturation, progressive clogging, progressive biological biomat formation, and finally, progressive failure (Bamstable County Department of Health). Figure 1. Seepage of Effluent : _' « “33848 “34°C 3 £30343 “3% 3 Unsaturatedl £ 3 Saturated Flow Flow —‘5 an: "a: -4: ’13-‘05 0‘3 (IQ/14300.nh «alt: 09v v w 1 Saturated Flow Unsaturated I l Flow .‘u . W .‘.__. “ “—- *.. . \‘ivxi : “SESSIIIIIIIHIII Figure 2 source: Bouma et al., Soil Absorption of Septic Tank Effluent, University of Wisconsin Extension. 1972., pg 160 Figure 2 demonstrates how biomat develops over time. Saturated flow and hydraulic conductivity are both reduced as biomat levels increase. Effluent passes over soils, creating clogged area. Over time, these clogged areas lead to unsaturated flow at the gravel-soil interface. Biomat Formation in Onsite Wastewater Treatment Systems Biomat formation and its effect on the hydraulic conductivity of on—site wastewater drainfields has been the subject of many studies. Allison (1947) added nutrient-rich water to sterile and non-sterile sandy loam and loam soil columns to study permeability rates under prolonged submergence. Sterile soil reached its maximum permeability and remained highly permeable throughout the experiment but the non- sterile soil columns clogged rapidly. Microbial activity appeared to be the cause of the low permeability. Reductions in permeability appeared to occur in a three step-process: l) structural changes occurred as the soil aggregates swelled and dispersed; 2) a small increase in permeability then occurred as trapped air was removed by solution; and 3) a large reduction occurred as the soil pores further clogged with biomass (Otis 1984). Allison concluded that biomat formation was entirely a microbial phenomenon and that the observed changes in soil aggregates and dispersion were a result of microbial actions. In order to quantify the microbial processes leading to biomat formation Mitchell and Nevo (1964) and Avnimelech and Nevo (1963) conducted studies on polysaccharides, which are the components of cell capsules of bacteria. These studies found polysaccharide-producing microorganisms predominantly in biomat layers, demonstrating that microbial polysaccharide production positively correlated with the formation ofbiomats in sands. Loss in hydraulic conductivity thus could be attributed to the accumulation of dead cells that clog pore spaces in soils. This is a result of polysaccharides being sticky and attracting cells that die. It was also noted that anaerobic bacteria were less efficient at utilizing waste material than were aerobic bacteria, 11 resulting in a greater accumulation of waste products that can clog soil pores (Wood and Bassett 1975). Jones and Taylor (1965) found that biomat formation occurred at the gravel- sand interface. The rate at which the biomat formed was directly proportional to the volume of effluent added and to the amount of organics in the effluent. Septic tank effluent was also added to columns of coarse, medium, and fine sand that were overlain with gravel to simulate the gravel-sand interface in drainfields. The gravel-sand interface had the highest amount of organic deposits and the most rapid amount of biomat formation than others areas in the columns. This was attributed to the presence of an anaerobic environment. Areas with an anaerobic environment clog faster than those with an aerobic environment. Thomas et a1. (1966) showed that biomat formation was influenced by organic matter present at the soil-gravel interface, a decrease in oxygen levels, or both. When effluent was added to soil columns, not only did organic matter stimulate biomat formation, but the recovery of infiltration rates was accompanied by a decrease in the concentration of total organic matter from effluent in the soil. The decrease in hydraulic conductivity and the increase of organic matter at the soil-gravel interface led to a reduction in the amount of oxygen in the soil atmosphere. This reduction caused the BOD to fall below the biological requirement in the soil, making the environment anaerobic, and anaerobic microbial activity then led to the formation of biomat (Allison, 1947; Thomas et al., 1966). The level of oxygen in the soil environment determined the equilibrium between the amount of biomat formed and the decomposition of organic materials (Mitchell and Nevo, 1964). 12 To simulate turbidity, Behnke (1969), studied soil columns dosed with water mixed with sieved sands or un-sieved sands. Soil clogging was less severe for un-sieved sands than for the sieved sands. Behnke attributed this to the fact that if turbid suspensions have a range of grain sizes (un-sieved), then gravitational grading initiates soil clogging and only a slight decrease in hydraulic conductivity occurs. As the deposited layers became more graded, the uppermost pores became small enough to strain out the remaining particles. He concluded that clogging is a sealing process that occurs at the surface. Daniel and Bouma (1974) also studied turbidity by performing field and column studies with simulated septic tank effluent and simulated aerated effluent. Daniel and Bouma found that hydraulic conductivity was a function of effluent quality. The columns with aerated effluent had more biomat than those that were ponded with septic tank effluent. Research concluded that the size and‘shape of the suspended solids may be the reason that the simulated aerated effluent columns developed a more pronounced biomat. The finely divided particles in the simulated aerated effluent could easily penetrate the finer pores, creating a “bottleneck” effect in the pores that reduced the overall hydraulic conductivity. Daniel and Bouma concluded that the nature of the suspended solids in effluent plays an important role in biomat formation With the large amounts of BOD that Daniel and Bouma (1974) were loading their columns with, it was expected to see large amounts of trapped gas from microbial fimctions (Allison 1947) contributing to biomat formation. Instead, it was discovered that the columns with the most BOD applied actually had the least amount of gas production. The field studies also found that poor construction practices during 13 drainfield installation can cause compaction and smearing of soil surfaces, leading to ponding of water at the infiltration surface and a reduced level of hydraulic conductivity, independent of biomat formation. Bacteria counts, nutrient levels, and bacteria byproducts also play an important role in biomat formation. Frankenberger et a1. (1979) applied distilled water and glucose water to sterile soil columns, some being continuously submerged and some subject to wetting and drying cycles. The columns both submerged and cyclical, receiving glucose water had the lowest hydraulic conductivities. This was attributed to the presence of bacteria and their metabolic products. Since the soil columns were sterile at the beginning of the experiment, the columns that had only distilled water added to them continued to show no bacterial growth. The glucose columns that were submerged or under water and hence were anaerobic, yielded extremely low bacterial numbers. Frankenberger et a1. (1979) speculated that submergence promoted early bacterial activity and that this bacterial activity led to early biomat formation and decrease in hydraulic conductivity, whereas constant submergence eventually reduced bacterial numbers. The glucose columns subjected to wetting and drying cycles, and which hence were aerobic, showed the largest bacterial numbers and the largest amount of phosphatase activity. Frankenberger et al. (1979) found that aeration was responsible for the increase in bacterial numbers and therefore led to the lowest hydraulic conductivity. They concluded that bacterial counts were significantly and positively correlated with phosphatase activity and that hydraulic conductivity decreased as the bacterial population and phosphatase activity increased. 14 Simons and Magdoff (1979) studied the effects of loading rates and temperature on mound systems. Mounds systems are on-site wastewater treatment systems that are constructed above ground so that required distances between the infiltrative surface and a soil limiting layer are met. Lowering and raising temperatures between 20 °C to 1 °C, found that systems receiving high loading rates, or high amounts of organic substances, developed a biomat layer faster than those receiving low loading rates and that this biomat progressed as the temperature was lowered. Simons and Magdoff also studied biomat formation under simulated anaerobic conditions, finding that columns maintained under continuous N2 clogged at about the same rate as those with high loading rates. They concluded that biomat formation occurred when soil was dosed with high loading rates or an increase in organic substances, was exposed to low temperatures, or was maintained under low oxygen conditions. Kristiansen (1981a, 1981b) studied the effect of septic tank effluent on sand filter trenches using different temperatures and at different loading rates. Trenches A and C were lightly loaded and trench B was heavily loaded. Trench A was held at a minimal 12°C and trenches B and C were held at a minimal 4°C. Contrary to Simons and Magdoff (1979), Kristiansen found that the biomat layer in the warmest sand filter (A) was localized to the gravel/ sand interface and that trench A had a more pronounced biomat formation than the other two columns. Since trenches A and C had different temperatures but the same loading rates, and B was more heavily loaded, Kristiansen concluded that temperature seemed to be the only reason for a more pronounced biomat formation in A (Kristiansen 1981a). 15 Kristiansen (1981b) also looked at the concentration of fecal coliforms in the biomat and the leachate from the sand filters (Kristiansen 1981b). Trench A had the most coliforrns in the biomat and the greatest reduction in bacteria counts with depth. Trenches B and C had little to no reduction in counts with depth. Concentrations of fecal colifonns were highest in the leachate from the trenches that were least clogged and that operated at the lowest temperatures. The amount of coliforrns in the heavily loaded and warmest trench remained consistently low. His studies concluded that temperature affected biomat formation and that the fate of bacteria in the soil was dependent on biomat formation. Siegrist (1987) performed studies on in-situ soil cells to determine if a biomat would develop under increasing amounts of hydraulic loading rates. Biomats formed in the cells that had domestic septic tank effluent and graywater septic tank effluent added to them as opposed to cells that had only tapwater added to them. The cells with graywater septic tank effluent exhibited biomat formation only at the highest loading rates, whereas the cells with septic tank effluent exhibited biomat formation at all loading rates. Siegrist found that biomat formation was characterized by a three-phase soil clogging process that was consistent with previous studies by Jones and Taylor (1965) and Thomas et al., (1966). Siegrist found that biomat formation may have been caused by processes similar to humus development in natural soils from readily degradable organic compounds (suspended solids) in cool temperatures, high humidity, and a restricted aeration, with an influx of organic materials and nutrients, BOD, fi'om septic tank effluent. Conditions at the soil-gravel interface can create conditions that mimic conditions for humus development. Clogging pores can lead to a high moisture content, 16 reducing conditions, and an anaerobic environment at the infiltrative surface and stimulate humus development. Siegrist (1987) concluded that BOD and suspended solids are a major factor in biomat formation and that highly treated effluent, with reduced levels of BOD and suspended solids, can reduce the biomat formation phenomenon in drainfields. Vandevivere and Baveye (1992b) also found that micrObial byproducts, specifically slime-producing bacteria, can affect biomat formation. They added nutrients to sand columns that were inoculated with four different types of bacteria. One type of bacterium formed a capsule, one produced slime layers, and two did not produce any detectable exopolymers, the last two being nonmucoid variants of the first two strains. Of the four bacterial strains tested; only the slime-producing had a substantial effect on hydraulic conductivity. The variation in strains did not appear related to population densities in the columns Since the glucose consumption rate was similar in all of the columns. It was also found that severe biomat formation was a result of slime production and not the accumulation of cells, because the cell densities inside of the columns did not differ. The slime produced affected the porosity of the soil, reducing hydraulic conductivity and forming a biomat. The cell-bound capsular exopolymers had no significant effect on hydraulic conductivity, nor did they produce a biomat. Contrary to prior research, Ronner and Wong (1998) measured the amount of extracellular polysaccharides (EPS) that were produced from bacteria in soil columns at various temperatures. Both clogging and non-clogging bacteria were able to adhere to sand grains and produce visible amounts of EPS, and therefore, gross EPS production was not an indicator of clogging ability in soils. It was also found that EPS was 17 apparently water soluble because much greater amounts of EPS were found in column leachate than was attached to the sand grains. However, it was noted that more EPS adhered to the sand grains at lower temperatures. One reason for this may have been that EPS is more viscous at lower temperatures, causing more plugging of pores that leads to more biomat formation at lower temperatures (Ronner and Wong, 1998; Simons and Magdoff, 1979). Biomat formation in soils was observed to be related to the concentration of poorly biodegradable humic substances and polysaccharides at the soil-gravel infiltrative surface (McKinley and Siegrist 2007). After applying septic tank effluent to in-sz'tu soil treatment units over a 3.2 year study, the authors concluded that biomat formation was found to occur in a three step process. The first step was the filtration and accumulation of suspended solids at the infiltrative surface. This accumulation acted as a food source for the microorganisms present at the infiltrative surface, resulting in the formation of a layer of low hydraulic conductivity, an increase in the amount of polysaccharides present and the development of a biomat. The second step was that dissolved organic materials and nutrients in the septic tank effluent also provided a food source for microorganisms. These microorganisms then produced byproducts that were composed of negatively charged polysaccharides and humic substances that adhere to soil grains. The final step was that the negatively charged substances were able to capture cations in the septic tank effluent. This resulted in a more compact biomat of even lower hydraulic conductivity (McKinley and Siegrist 2007). 18 Microorganisms Found in Biomat in On-site Wastewater Treatment Systems Kristiansen (1981b) preformed studies on the amounts and sizes of microorganisms that were found at different depths and in different clogging intensities of sand filters. With the addition of septic tank effluent, Kristiansen found that rods of about 0.3 um3 and coccoid organisms of about 0.06 and 0.5 pm3 were prevalent. Smaller coccoid bacteria, 0.06 pm3, were found with increasing depth suggesting that smaller bacteria types had the ability to travel deeper into the profile. Aerobic bacteria, facultative anaerobic bacteria and sulfate-reducing bacteria are some of the microorganisms that were found in samples taken from clogged soils in studies by Baveye et al. 1998. Clogging layers are usually associated with an anaerobic environment and reduced hydraulic conductivity. The black, slimy biomat that is present in these environments has been associated with FeS deposits from anaerobic metabolism and the slow decomposition of organic matter and the thickest layers of biomat have been associated with increased amounts of FeS from soil submerged with wastewater (Thomas et al., 1966; Wood and Bassett, 1975; Kristiansen, 1981a; Siegrist, 1987). Ferric oxihydroxides deposition can also clog soils and cause biomat formation (Baveye et a1. 1998). Soils contain iron and if anaerobic conditions prevail, bacteria will reduce Fe3+ and F e2+ to obtain oxygen. Iron reducing bacteria, such as Gallionella, Leptothrix, and T hiothrix have been found repeatedly and abundantly in clogged drainage systems (Kuntze, 1982). Ronner and Wong (1998) preformed studies to determine what organisms were found in the clogging zone of onsite-wastewater treatment systems by obtaining samples 19 of active, in-site, biomat from ponded mound systems. About 160 different kinds of microorganisms were isolated. Of the 160, about 63% were Gram negative. Eighty—one were screened for clogging ability and 30% were found to cause clogging in sand columns. The organisms found, such as Pseudomonas, Aeromonas, Bacillus, Xanthomonas, Agrobacter, and Acinetobacter are typical of soil environments. Those that are found in septic systems and soil are Enterobacter, Klebsiella, Staphylococcus, and Serratz'a. Of those found, microorganisms such as Pseudomonas, Bacillus, Klebsiella, Staphylococcus, and Serratz'a are known clogging organisms and induced clogging within 2 weeks of inoculation of soil columns (Ronner and Wong 1998). Appearance of a Biomat in On-site Wastewater Treatment Systems Biomat can be described as a black, slimy substance that appears on the surfaces of the walls and on the bottom of trenches and seepage beds (Bouma et al., 1972; Washington Health Department, 2006). Wood and Bassett (1975) state that biomat is found in the black, jellylike zones of soil cores exhibiting a gelatinous-like consistency. Siegrist (1987) observed biomat to be in the form of a black matter occurring at the soil infiltrative surface and that the black matter could easily be scraped away. Ronner and Wong (1998) identified biomat as zones in soil columns that had a black, slimy appearance and occurred at the gravel and sand interface. Owens et a1 (2004) identified biomat as the black gelatinous masses that occluded the trenches in their studies. 20 Time for Biomat Development in On-site Wastewater Treatment Systems The length of time for a biomat to develop in the soil is relatively unknown. Otis (1984) stated that studies under a variety of conditions showed that biomat develops immediately with wastewater application and proceeds slowly with time. Check et al. (1994) stated that biomats reach mattuity in 4 to 6 weeks. Kristiansen (1981a) found that biomats usually occur within the first few months 'of full operation of a soil absorption system. Postrna et al. (1992) concluded that after eight to fifteen months of continuous wastewater input, a conventional soil absorption system develops a biological clogging mat of reduced permeability at the interface between the native soil and the constructed absorption system. According to the Bamstable County Department of Health, it may take from six months up to one year for a mature biomat to develop. Christopherson et al. (2007) assumed that 75% of trenches had biomat after five years or more of operation. Process of biomat formation in On-site Wastewater Treatment Systems Biomat development over any length of time is essentially a combination of physical, biological, and chemical factors in the soil (Jones and Taylor, 1965; Thomas et al., 1966; Daniel and Bouma, 1974; Bouma, 1975; Frankenberger et al., 1979; Siegrist and Boyle, 1987; Baveye et at., 1998: Beal et al., 2005; Finch et al., 2007; McKinley and Siegrist, 2007). Poor construction practices, such as smearing and compacting of the soils, are physical processes that can lead to biomat formation (Daniel and Bouma 1974). If 21 construction traffic is allowed to continually drive across the area designated for drainfield construction, the soil becomes compacted, soil aggregates and soil structure are compromised, soil surfaces become smeared, and soil pore spaces are destroyed. These factors lead to excessive ponding of water at the infiltrative surface, causing anaerobic conditions and increased biomat formation (Beal et al., 2005). Silt and clay particles washed from gravel in drainfields can also lead to clogging of pores. Septic tank effluent that contains excessive amounts of suspended solids can produce a biomat faster than effluent without excessive suspended solids (Beal et al., 2005). Suspended solids that are larger than the pores in the soil can physically clog pore Spaces, resulting in reduced hydraulic conductivity. This reduction can lead to a saturated (anaerobic) environment in the soil. Prolonged saturation can lead to the breakdown of soil aggregates and a dispersion of their constituents into the surrounding pore space (Baveye etal., 1998). The excessively clogged and saturated pores result in physical biomat formation. An anaerobic environment can also leads to biological biomat formation. Organic compounds in septic tank effluent become food for anaerobic microorganisms at the soil absorption site. As these microorganisms break down the compounds, byproducts are released into the environment. These byproducts clog soil pores, reducing hydraulic conductivity and resulting in biomat formation (Jones and Taylor, 1965; Thomas et al., 1966; Daniel and Bouma, 1974; Bouma, 1975; Frankenberger et al., 1979; Siegrist and Boyle, 1987; Baveye et at., 1998: Beal et al., 2005; Finch et al., 2007; McKinley and Siegrist, 2007). 22 Chemical biomat formation can also result fiom the breakdown of soil aggregates, from increased biological oxygen demands on the soil environment, from an increase in suspended solids, fiom diffusion of oxygen at the gravel—soil interface, and fi'om the breakdown of organic compounds and suspended solids from microbial activity. Benefits of a Biomat in On-site Wastewater Treatment Systems Biomat, with its highly organic nature, can be beneficial in the treatment of septic tank effluent. Postrna et al. (1992) stated that biomat formation promotes even distribution of effluent throughout the trenches of the drainfield, allowing the effluent to come into contact with more of the reactive surfaces in the drainfield. Biomat can also create a more unsaturated, aerobic environment by slowing the rate of infiltration into the soil. The organic nature of biomat also allows for more sorption and deactivation of pathogens in septic tank effluent before these bacteria, viruses, and protozoa can reach the groundwater (Postrna et al. 1992). Van Cuyk and Siegrist (2001) also stated that biomat is very important for purifying BOD and suspended solids from septic tank effluent before the effluent reaches the groundwater. Biomats also slow the movement of effluent and thus keeps the ground fi'om becoming saturated. This also allows the effluent a longer retention time in the biogeochemically reactive biomat zone. McKinley and Siegrist (2007) stated that the production of polysaccharides in the soil may actually be beneficial in that they build structure and 23 stability in the soil. Structure and stability, in the form of soil aggregates, help maintain soil pores and aerobic condition. Recovery of Drainfields in On-site Wastewater Treatment Systems after Biomat Development Bouma et al. (1974) found that the mechanisms within the biomat which are responsible for recovery, or a increase in hydraulic conductivity, are thought to be associated with decomposition of accumulated organic compounds by oxidative respiration and the drying and contracting of microbial by-products (Beal, Gardner, Vieritz, and Menzies, 2004). These processes allow for larger macropores to be developed in the soil allowing for greater or increased hydraulic conductivity within the soil. Simons and Magdoff (1979) did experiments on various columns heights of sand that had reduced hydraulic conductivity because of biomat formation. These columns were drained and rested before being returned to a daily dosing regimen. Simons and Magdoff found that columns with a low dosing rate were able to operate satisfactorily again until the end of the experiment (210 days). Columns with a high dosing rate were not able to recover during the duration of the experiment. The 10 cm columns of sand did not recover, but columns of 30, 60, and 90 cm length did recover after the resting period but failed again within 24 days of renewed daily dosing. Finally, columns that rested under low oxygen environments also did not recover. Simons and Magdoff 24 concluded that infiltrative capacities can be rejuvenated after a resting period only if loading is kept minimal. Limits of Biomat Development in On-site Wastewater Treatment Systems Previous research has shown that the development and extent of biomat in an on- site system determine the life of that system. Some researchers, however, have Shown that biomat development does not mean that a septic system will fail. When Frankenberger et al. (1979) conducted experiments to determine the relationship between biomat development and hydraulic conductivity, for example, they found that hydraulic conductivity decreased and eventually stabilized at a constant rate, suggesting that biomat did the same. Owens et al. (2004) studied septic systems that were allowed to rest for periods of time. Effluent rates significantly improved after these resting times, assuming that any biomat that had developed would deteriorate from oxidation during the resting time. Simons and Magdoff (1979) also found that when failed soil columns were drained and the clogged surfaces were well aerated naturally or by artificial means, infiltrative capacities were rejuvenated, but when dosing was resumed before full recovery, infiltrative surfaces reclogged rapidly. Wood and Bassett (1975) found that the black biomat zones in their soil columns that were opened lengthwise, oxidized to a normal light brown color after being exposed to the atmosphere for two hours. Suggesting that oxidation helps in the breakdown of organic biomats. 25 Conclusion Most researchers would agree that biomat is an inevitable soil phenomenon that occurs in all on-site wastewater treatment systems. Biomat development occurs quickly and continues to develop until on-site wastewater treatment systems eventually fail. Failure in systems occurs from reduced hydraulic conductivity that is directly related to the amount of biomat present. Biomat development is a microbial process and consists of bacteria, bacterial by- products, cell mass and suspended solids, and is directly related to the amount of nutrients present in septic effluent and the rate at which it is applied. Anaerobic conditions in the soil promote biomat development at the gravel-soil interface. Biomats control the dispersion of effluent through the on—site wastewater treatment systems and assist in pathogen and nutrient removal. It is these reason that the on-site wastewater treatment industry believes that biomat development. can not and should not be stopped. 26 CHAPTER III BIOMAT FORMATION IN EXISTING ON-SITE WASTEWATER TREATMENT SYSTEMS AS FOUND IN THE INGHAM COUNTY POINT-OF-SALE PROGRAM, INGHAM COUNTY, MICHIGAN lntrodution It has long been thought that the formation of a soil clogging layer, or biomat, at the soil-gravel interface in sub-surface on-site wastewater treatment systems is inevitable, although not fully understood. Chaffee (2000) stated that biomat formation cannot be prevented in conventional systems, but proper and regular maintenance may slow the rate of formation. Machmeier (2002) stated that biomats form in all gravity distribution soil treatment systems but do not form in pressure distribution systems. Most researchers agree that biomat formation is a combination of physical, chemical, and biological factors such as an accumulation of organic matter, soil aggregation, and microbial processes (Jones and Taylor, 1965; Thomas et al., 1966; Bouma, 1975; Siegrist and Boyle, 1987; Finch et al., 2007; McKinley and Siegrist, 2007) and that biomat formation helps in the even distribution and treatment of septic tank effluent. If not managed, soil clogging can lead to reduced hydraulic conductivity of 27 septic tank effluent in the drainfield to the point that the on-site system fails (Allison, 1947; Avnimelech and Nevo, 1963; Jones and Taylor, 1964; Thomas et al., 1966, Bouma, 1971; Daniel and Bouma, 1974; Frankenberger et al., 1979; Tyler, 2001; McKinley and Siegrist, 2007). When this occurs, effluent will pond at the surface resulting in an imminent health hazard. Most homeowners take an “out of sight, out of mind” mentality regarding their septic systems resulting in little to no maintenance of their systems. It is this reason that has led health departments, like the Ingham County Health Department, to enact a Point of Sale (POS) program that allows them to inspect, or have inspected by county certified inspectors, the on-site wastewater treatment systems of all homes being sold in the county. This also allows them to evaluate the state of on-site wastewater treatment systems in the area, as well as giving them the authority to facilitate the corrections of or replacement of failing systems. Since hydraulic overloading and biomat formation (N SFC) are the leading causes of on-site wastewater treatment system failure and biomat development has been thought to be inevitable, it would seem likely that biomat formation would be seen in most existing drainfields, especially older systems. The objectives of this study were to (l) evaluate biomat levels, age of systems, and soil texture of the systems inspected for the Ingham County Point of Sale program and (2) inspect, in situ, fifty existing drainfields from the Point of Sale program, each being more than thirty years old. 28 METHODS AND MATERLALS Study Area This research was preformed exclusively in Ingham County, Michigan. lngharn County is in the south-central part of the lower peninsula of Michigan. The total area is about 357,000 acres, or about 558 square miles (Ingham County Soil Survey, 1979). This research was conducted with the help of the Ingham County Health Department, specifically the Point-of—Sale program. Inspectors in the program are required to identify, on their report to Ingham County, the level of biomat that they observed in a drainfield. The criteria for evaluating the amount of biomat are based on the condition of the stone in the existing drainfield (Table 3). Table 3 Biomat Evaluation Criteria Level 0 biomt . No biomat observed Level 1 biomat % of stone has biomat Level 2 biomat 1/2 of stone has biomat Level 3 biomat 3%: or more of stone has biomat POS and Re-Inspection Methods To compare the biomat level, age of systems, and soil texture of the Ingham County POS inspections, an Excel spreadsheet was maintained starting in June 2006 and running through December 2008. A total of 859 evaluations were presented to the Ingham County Health Department during that time. These evaluations included trench, 29 bed, pressure dosed mound, gravity mound and other type systems. All were logged and recorded for the above mentioned items as well as POS number and location. One . hundred and sixty six evaluations were dismissed from the study because of missing or incomplete data leaving a total of 693 inspections. Inspectors make 2 or 3 borings in a drainfield during an inspection. To determine if this is a sufficient number of observations and if evaluations were correct, fifty, of the 693, inspections were randomly chosen to be re-evaluated based on drainfield type and age of system only. Thirty nine were trench type systems and eleven were bed type systems. Pressure dosed mounds, gravity mounds, and other type systems, i.e. dry wells, alternative media systems etc., were not looked at because of pumps, aerobic treatment units, and even distribution systems that would affect natural biomat formation. All fifty systems were verified to be functioning drainfields that have been in operation for at least thirty years. A cross check was done through the Ingham County Health Department permitting process to verify that no repair permits had been issued between the time of installation and the evaluation. The permits were used to verify that the inspector’s site plan and the Ingham County site plan matched. Once this was established, a copy of the inspectors report and the original permit was made to assist in locating the drainfield and septic tank as well as to compare the evaluator’s biomat observations with the re-inspection findings. After the fifty systems were chosen, each was evaluated to verify the results of the POS inspectors. Biomat levels and soil types were determined by doing a site visit. At the Site, the septic tank and drainfield were located with a Mighty Probe soil probe and flags were placed on the tank as well as the four comers of the drainfield. At this point, if 30 the system was a trench style system, the trench lines were located and marked-with flags as well. From the permit and inspectors report, the header of the system was established and verified with the probe. All soil auger borings that were preformed, were done completely through gravel and no less than 3 inches into the native soils below the gravel-soil interface. The determination of the amount of biomat present, or lack of biomat, was done according to Table 3 but the conditions of each individual drainfield were also taken into consideration. Some drainfields had 12 inches or more of stone and some had less than 6 inches of total stone. The amount of biomat present was then determined based on the amount of total stone present. The amount of biomat was also determined by averaging the amount throughout the observed areas throughout the drainfield. Discontinuous areas of heavy biomat or lack of biomat in an otherwise biomat consistent trench were averaged according to the total area of the discontinuity. A drainfield that had 3 trench lines of level 1 biomat but that had '/4 of the last trench with level 2 biomat or level 0 biomat, the total system was averaged as a level 1 biomat. If a drainfield was found with level 3 biomat in 2 lines and 2 lines that were dry and clean. If was assumed that the last 2 lines were not receiving effluent for some reason and only the first 2 lines were used in determining the biomat level. For trench type drainfields, soil auger borings were done on either Side of the header to determine if any biomat had developed in the header. If a biomat was present, soil auger borings were done approximately every five feet from the original boring to determine the extent ofbiomat development. Borings were then done at the start of each 31 trench line to determine, as well, the extent of biomat development. Borings were done every ten feet if no biomat was present. If any, or all, of the trench line exhibited a biomat, then borings were done every five feet to determine the extent of development (Figure 3). At this point, the drainfield was given a rating according to the biomat evaluation criteria (Table 3). If the drainfield was a bed type system, the same procedure applied except that there were no trench lines to follow. Auger borings were made in the header and proceded throughout the bed at ten foot intervals until biomat, if present, was observed. If biomat was observed then borings were made every five feet to determine the extent of the biomat (Figure 4). At this point, the drainfield was given a rating according to the biomat evaluation criteria (Table 3). 32 Figure 3: Drainfield Inspection Process for Trenches Trench Systems Inspected Septic ___________________________ Tank X -------*--------X ---------- Inspection Procedures: Locate drainfield and evaluate biomat Figure 4. Drainfield Inspection Process for Beds Bed System Inspected Septic k Tank Inspection Procedures: Locate drainfield and evaluate biomat A soil auger boring was also done adjacent to the field to determine the native soils. Soils were textured, recorded, and verified by the Ingham County Soil 33 Survey and depth to redoximorphic features (mottles) was determined by Si ght and was also recorded. Number of bedrooms, design flow, number of occupants, garbage disposals, laundry and dishwashing equipment and practices were not recorded because the homes that were evaluated were recently sold, as per the Point-of-Sale program, and historic information such as previous number of occupants and loading information was not available from new owners. All data were mapped and recorded in an Excel spreadsheet as well as site evaluation drawings, original permits, inspector’s evaluations, and soil information. RESULTS AND DISCUSSION Point-Of-Sale Overall Data A total of 859 evaluations were presented to the lngharn County Health Department. One hundred and sixty six evaluations were dismissed from the study because of missing or incomplete data leaving a total of 693 inspections. These systems ranged from one year to over 50 years in age. Out of the 693 inspections, 15% were beds, 73% were trenches, 6% were pressure mounds, 3% were gravity mounds, and 3% were other type systems (Table 4). Out of the 693 inspections, 83% of all drainfields had a level 0 biomat, 14% had a level 1 biomat, 2% had a level 2 biomat, and 1% had a level 3 biomat (Table 3 and 5). This was surprising because as research suggested, drainfields should begin to exhibit signs of biomat development from immediately upon use to within 2‘ years of use (Waller, 2000; Kristiansen, 1981a: Postrna, 1992) and that biomat development will lead to certain hydraulic failure of on-site wastewater treatment 34 systems (Allison, 1947; Avnimelech and Nevo, 1963; Jones and Taylor, 1964; Thomas et al., 1966, Bouma, 1971; Daniel and Bouma, 1974; Frankenberger et al., 1979; Tyler, 2001; McKinley and Siegrist, 2007). Table 4. Total POS Evaluations. Total in Study 693 Percent Total Beds 106 15% Total Trenches 502 73% Total Pressure Mounds 43 6% Total Gravity Mounds 24 3% Total Other 1 8 3% Table 5. POS Biomat Development Level 0 Biomat Pressure Gravity Percent __Age of System Bed Trench Mound Mound Other by Year 0-8 Years 1 52 25 6 2 15% 9-13 Years 7 55 1 1 1 2 13% 14-18 Years 12 32 2 1 2 9% 19-23 Years 14 26 1 3 1 8% 24-28 Years 6 12 1 2 1 4% 29-33 Years 6 34 0 2 1 8% 34-38 Years 4 44 1 3 0 9% 39-43 Years 5 31 0 1 0 6% 44-48 Years 5 19 0 1 1 5% 49-53 Years 5 13 0 2 0 3% 54-58 Years 4 13 0 O 0 3% 59 Years or More 18 71 2 1 8 17% TOTAL 87 402 43 23 18 100% Percent 82% 80% 100% 96% 100% Total level 0 Percent Biomat 573 83% 35 Table 5. POS Biomat Development, cont. Level 1 Biomat ‘ Age of System a: 3. Trench Pressure Mound Gravity Mound Other Percent by Year 0-8 Years 2 0 0 O 2% 9-13 Years 1 % 14-18 Years 7% 19-23 Years 4% 24-28 Years Alum—s 1% 29—33 Years 1 9% 34-38 Years 1 7% 39-43 Years 11% 44-48 Years 9% 49-53 Years 3% 54-58 Years 4% 59 Years or More k-‘A-‘OO—‘O-h-hoo OOOOOOOOOOO OOOOOOOO-‘OO OOOOOOOOOOO 22% TOTAL a w A O 100% Percent 12% 17% 0% 4% 0% Total level 1 Biomat 100 Percent 14% Level 2 Biomat ‘ Age of System tn 8. Trench Pressure Mound Gravity Mound Other Percent by Year 0-8 Years 0 0 O 0% 9-13 Years 0% 14—1 8 Years 7% 19-23 Years 0% 24-28 Years 0% 29-33 Years 21 % 34-38 Years 14% 39-43 Years 0% 44-48 Years 7% 49-53 Years 1 4% 54-58 Years 0% 59 Years or More NOO-‘OOOOOOOO OOOOOOOOOOO OOCCOOOOOOO OOOOOOOOOOO 36% Total 00 :womoomwoo-xoo O O O 100% Percent 3% 2% 0% 0% 0% Total level 2 mafl 14 Percent 2% 36 Table 5. POS Biomat Development, cont. Level 3 Biomat Pressure Gravity Percent fie of System Bed Trench Mound ' Mound Other byYear 0-8 Years 0 0 0 0 0 0% 9—1 3 Years 0 0 0 0 0 0% 14-18 Years 0 1 O 0 0 17% 19-23 Years 0 0 O 0 0 0% 24-28 Years 0 1 0 0 0 17% 29-33 Years 0 1 0 0 0 17% 34-38 Years 0 O 0 0 O 0% 39-43 Years 0 0 O 0 0 0% 44-48 Years 2 0 0 0 0 33% 49-53 Years 0 0 0 0 O 0% 54-58 Years 0 0 0 0 0 0% 59 Years or More 1 0 0 0 0 1 7% Total 3 3 0 0 0 100% Percent 3% 1% 0% 0% 0% Total level 3 Percent Biomat 6 1% Figures 5 and 6 show that biomat did not develop in drainfields as previous thought. Only 17% of the 693 POS inspections showed any evidence of biomat development. 37 m_w>w._ I ~_w>w.. l :23 ... o _m>m._ l Eou>m we uu< 2.39m 23m 5:2... .8 _m>m._ amEoE ucm mm< 3 mEE8u< mESm>m *o 33:52 swazsAs waaqwnN .mEBmxm cram cocoa... .8.“ 354 3:55 Ea ow< 2 mEEooo< mEBmmm mo 53.52 .m Sam:— 38 883m co mu< 223 I 233 u H_m>mn., o as: I i ii iii. ms _ ON 2533 23m tom .0». _m>m._ meoE new mm< 3 95882 mEBm>m *o .3832 swarsAs piaqwnN .mEonxm Bbm com 5c .33 SE05 new um< 9 wEEooo< mEBmxm mo 53:52 .0 2sz 39 Re-Inspection Data When evaluating on-site wastewater treatment system drainfields, several observations were made. It became clear that only a percentage of most drainfields are utilized, no matter what the age of the system. Since all of the systems that were inspected had been in use for 30 years or more, it was thought that 100 percent of the system would show evidence of use, including the presence of a biomat. Whether the system was a bed or a trench, it became clear that even after 30 years of use, effluent was not reaching 100 percent of the drainfield. This could be a result of poor installation practices, settling of pipes, stone, or fill, compaction, or uneven landscape. It is not likely that all 693 systems had these problems. Therefore, biomat formation is not as has been thought Since effluent was not reaching 100 percent of a system, biomat levels were based on the portion of the system that was receiving effluent. Several of the systems that were evaluated had one or two trench lines that were not being used or were found to be dry. The first two lines may have had evidence of biomat but the last two lines were clearly not being used; therefore, only the first two lines, the only lines receiving effluent, were used in evaluating biomat levels. Some systems had biomat evidence only in part of the trench lines. The first half of the lines had biomat while the last half had no evidence of effluent and therefore no biomat. Again, only the area of the lines that had effluent evidence was used to determine biomat levels. 40 Two of the systems evaluated had man-made intrusions that may have impacted biomat formation. One system had very large landscaping boulders placed on the trench lines. Only the areas around the boulders showed biomat because of compaction of the soil and trench line. Another system had lawn sprinklers installed over one trench line. This resulted in increased hydraulic activity and an increased anaerobic environment over the line, resulting in biomat development in that area. These two incidences were discarded and not used in determining biomat development and levels. Of the 50 systems that were re-inspected, 39 were trenches and 11 were bed type systems. Of these systems, 70% had a level 0 biomat, 18% had a level 1 biomat, 6% had a level 2 biomat, and 6% had a level 3 biomat (Table 6) Table 6. Re-Inspection Biomat Data Level 0 Biomat Age of System Bed I Trench 1 Percent by Year 0-8 Years 9-13 Years 14-18 Years Not Inspected 19—23 Years 24-28 Years 29-33 Years 3 4 20% 34-38 Years 2 6 23% 39-43 Years 0 3 9% 44-48 Years 1 3 1 1% 49-53 Years 0 3 9% 54-58 Years 1 1 6% 59 Years or More 2 6 23% TOTAL 9 26 100% Percent 82% 67% Total level 0 Biomat 35 70% 41 Table 6. Re-Inspection Biomat Data, cont. Level 1 Biomat ‘ Age of System Bed I Trench I Percent by Year 0-8 Years 9—1 3 Years 14—1 8 Years 19—23 Years 24-28 Years Not Inspected 29-33 Years 33% 34-38 Years 22% 39-43 Years 0% 44-48 Years 11% 49-53 Years 11% 54-58 Years 11% 59 Years or More OO—‘OOO—h AAOAONN 11% TOTAL 2 100% Percent 18% 18% Total level 1 Biomat 18% Level 2 Biomat ‘ Age of System Bed 1 Trench I Percent bLYear 0-8 Years 9-13 Years 14-18 Years 19-23 Years 24-28 Years Not Inspected 29-33 Years 0% 34-38 Years 0% 39-43 Years 0% 44-48 Years 0% 49-53 Years 67% 54-58 Years 0% 59 Years or More OOOOOOO AONOOOO 33% TOTAL 0 1 00% Percent 0% 8% Total level 2 Biomat 6% 42 Table 6. Re-Inspection Biomat Data, cont. Level 3 Biomat ‘ Age of System Bed [Trench1 Percent by Year 0-8 Years 9-13 Years 14-18 Years Not Inspected 19-23 Years 24-28 Years 29-33 Years 0 0 0% 34-38 Years 0 1 33% 39-43 Years 0 1 33% 44-48 Years 0 1 33% 49-53 Years 0 ‘ 0 0% 54-58 Years 0 0 0% 59 Years or More 0 ' 0 0% TOTAL 0 3 100% Percent 0% 8% Total level 3 Biomat 3 6% When comparing the biomat level of the 50 systems that were re-inspected with the original inspectors data, the biomat levels differed 24% of the time. The inspectors’ level of biomat was less than that of the re—inspection 20% of the time and greater 4% of the time (Table 7, 8, and 9). This is not surprising because the Ingham County certified inspectors are only required to make two auger borings into drainfields whereas during re-inspection, no less than six auger borings were preformed on each system. Table 7. Biomat Level Comparison Over Under Estimated by Estimated by Inspector Inspector Bed 1 0 Trench 9 2 Percentage 20% 4% 43 Table 8. Sysuun of the POS Biomat levels with Levels for Beds Year Installed Level Biomat Level Bed 1900 Bed 1900 Bed 1950 Bed 1957 Bed 1964 Bed 1972 Bed 1973 Bed 1975 Bed 1976 Bed 1976 Bed 1979 0 0 0 0 0 0 0 0 0 1 0 O-AOOOOO-‘OOO 44 Table 9. Comparison of the POS Biomat levels with Re-inspection Levels for Trenches System Year Installed Level Biomat Level Trench 1 900 Trench 1 905 Trench 1 925 Trench 1 940 Trench 1942 Trench 1 947 Trench 1 948 Trench 1 948 Trench 1950 Trench 1952 Trench 1955 Trench 1 955 Trench 1955 Trench 1 956 Trench 1 959 Trench 1 960 Trench 1 960 Trench 1 960 Trench 1 960 Trench 1 962 Trench 1967 Trench 1967 Trench 1967 Trench 1969 Trench 1970 Trench 1970 Trench 1971 Trench 1 972 Trench 1 972 Trench 1 972 Trench 1973 Trench 1 974 Trench 1 974 Trench 1 975 Trench 1 977 Trench 1 977 Trench 1977 Trench 1977 Trench 1978 COCOA—IODOAOWO—‘OOOOOO-IOOJOOOONON—‘ONAOOOOOO 0 1 0 0 0 0 0 2 0 0 2 0 1 0 1 0 0 2 0 1 0 0 1 0 0 1 0 2 0 0 0 0 0 0 0 0 0 0 0 45 Because effluent does not reach all areas of drainfields inspectors may have augered into areas receiving less effluent, therefore, the lower biomat level ratings. To obtain a more accurate evaluation of biomat level, more than two or three observations must be made. Soils It was the intent of this study to compare the soil textures recorded by the Ingham County inspectors with the soil texture found upon re-inspection. None of the inspectors for Ingham County are soil scientists nor do they have backgrounds in soil texturing. It became clear as the Point-of-Sale data were analyzed, that soil data were often listed as “unknown,” “clay,” “clay with sand,” or “sand with clay,” depending on the individual inspector. “Clay with sand” and “sand with clay” do not exist as soil textures as per the Natural Recourses Conservation Service. “Sandy clay”idoes exist on the textural triangle but upon speaking with the inspector, it was clear that the individual was not referring to sandy clay as per the NRCS. “Clay,” as a texture by itself, does not exist in Ingham County. Also, the inspectors were not required by the county to do a separate soil boring to determine native soils. Therefore, for the purpose of this study, the soil data listed by inspectors cannot be used to compare soil texture data. 46 Table 10. Re-Inspection Soil Data** Re-lnspection Soil Data Biomat Level Biomat Biomat Biomat Soils Level 1 Level 2 Level 3 Total Colwood-Brookston Ioams 1 1 Marlette fine sandy loam 2 2 1 5 Capac loam 2 1 3 Oshtemo-Spinks loamy sands 1 1 Owosso-Marlette sandy Ioams 2 2 Urban Land—Marlette Complex 1 1 Spinks loamy sand 1 1 Cohoctah silt loam 1 1 ** The remaining 35 systems had a 0 level biomat This is quite surprising because when soil evaluations are done to determine soil and site suitability for on-site wastewater treatment systems; loam, sandy loam, and loamy sands are preferred over finer textured, heavier soils. Yet, biomat appears to occur most often in finer-textured soils. Beds vs. Trenches When comparing the performance of beds verses trenches, bed systems appear to last as long as trench systems and have the same amount of biomat development. It is commonly thought throughout the on-site industry that bed systems fail faster than trench systems because of a lack of oxygen, or anaerobic environment, at the gravel-soil interface. The Ingham County Health Department has even begun to limit the amount of bed systems that can be installed on the belief that they fail faster than trench systems do. The POS data shows that out of 502 total trench systems, only 100 systems, or 20%, showed any sign of biomat. Out of the 106 bed systems, only 19, or 18%, showed any sign of biomat. The re-inspection data of systems at least 30 years old, shows that out of 39 trench systems, 13 systems, or 34%, showed signs of biomat and out of 11 bed 47 type systems, only 2, or 18%, showed any sign of biomat. These data show that bed systems must be receiving an adequate amount of oxygen to maintain aerobic conditions so that biomat development is controlled and that bed systems appear to last as long as trench style systems. 48 CHAPTER IV. Summary and Conclusions A study was conducted to evaluate the occurrence and severity of biomat in Ingham County, Michigan. The Ingham County Point-of-Sale program was used to gather information about existing on-site wastewater treatment systems. Ingham County inspectors evaluated on-site wastewater treatment systems and rated the biomat levels in these systems. The objectives of this study were to (1) evaluate biomat levels, age of systems, and soil texture of the systems inspected for the Ingham County Point of Sale program and (2) inspect, in (situ, fifty existing drainfields from the Point of Sale program, each being more than thirty years old. On the basis of field data, the following ' conclusions were reached: 1. Biomat was only found in 17% of the Ingham County Point-of-Sale inspections on existing systems and only 3% of the 693 systems had biomat evident in ‘/2 or more of the stone. 2. Of the 50 existing systems that were re—inspected, biomat was evident in only 30% of the systems. Only 12% of the systems had biomat evident in 1/2 or more of the stone. 3. These data suggest that biomat does not develop in all systems and is not inevitable as per prior research. 49 4. On-site wastewater treatment systems are lasting longer than the industry suggests. Each system that was re-evaluated was 30 years old or older and still functioning as intended. 5. Bed style on-site wastewater systems appear to function as well and last as long as trench style on-site wastewater systems. 50 CHAPTER V. Further Study Further study and research should be conducted in these areas to fully understand biomat development; 1. Research needs to be conducted as to exactly how biomat develops and its affect on on-site wastewater systems. It has long been thought in the on-site industry that biomat is inevitable. Per this research, biomat is not developing as previously thought and more research needs to be conducted regarding the lack of biomat development in on-site wastewater treatment systems. Research is needed to determine if laboratory studies are adequately designed to reflect actual onsite systems. Systems in laboratory studies may be oxygen limited because oxygen does not enter those systems from the sides. More in-situ studies should be done on existing systems. The addition of observation ports on systems could'be beneficial in observing soil/ gravel interfaces and biomat development. Most of the systems in this study were in use for 30 years or more. The on- site industry needs to do further research regarding the expected life span of on-site wastewater treatment systems. More research needs to be conducted on oxygen levels in bed and trench style on-site wastewater treatment systems. Per this research, beds seem to 51 perform as well as trench systems and last just as long which is contrary to industry belief. Loading rates of drainfields placed in sandy soils are greater than the loading rates for finer-textured soils. As biomats develop, the pore difference between sandy soils and the biomat area is greater than the pore difference between finer-textured soils and the biomat pores. More research needs to be conducted to see if it is this pore difference that causes more sandy soil drainfields to fail, as found in this study, than drainfields that are placed in finer-textured soils. 52 References Allison, L. E. 1947. Effect of microorganisms on permeability of soil under prolonged submergence. Soil Sci. 63:439-450. Avnimelech, Y., and Z. Nevo. 1963. Biological clogging of sands. Soil Sci. 98:222-226. Bamstable County Health Department. 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