Suitability assessment of Ohio's soils for soil-based wastewater treatment. (1).

Mancl, Karen ; Slater, Brian

ABSTRACT. Each of Ohio's 467 soil series was assessed to determine the depth of the soil to bedrock, the depth to a limiting soil condition, the depth to seasonal saturation, and the soil permeability. Each soil series was placed into one of three categories; suited for traditional leach fields or mound systems, suited for mound systems only, or not suited for soil-based treatment. In a mound system, a layer of sand is placed on top of the natural soil to augment its treatment capacity. Statewide only 6.4% of the land area is suited for soil absorption systems using traditional leach lines. This amounts to 1,680,020 acres of land. Soil series suited for mound systems are present in 25.4% of Ohio's land area accounting for 6,667,579 acres of land.

OHIO J SCI 101 (3/4):48-46, 2001

INTRODUCTION

In Ohio, almost one million homes are beyond the reach of community sewage systems (Bureau of Census 1990). Each year many more homes are built in rural Ohio and all must consider treating and disposing of wastewater on the lot.

The ability of the soil to purify wastewater has been recognized for decades. The goal in any sewage treatment system is to remove pollutants such as disease-causing organisms, ammonia, organic matter, and solids, before the wastewater reaches ground or surface water. Some naturally occurring soils have the capacity to accomplish pollutant removal to protect the water resource. While many soil processes assist in wastewater treatment, researchers recognize three properties as the most important; the depth of the soil column, its permeability, and aerobic (or unsaturated) conditions.

To renovate sewage effluents, soil must have several physical characteristics. Pores in the soil must be fine enough to trap suspended solids and disease-causing organisms. These same soils, however, must still have sufficient permeability to allow for the movement of air and water to accommodate the biological degradation of organic matter and ammonia by aerobic bacteria that colonize the soil matrix. Finally, the soil must have the capability to adsorb viruses and other water pollutants, like phosphorus.

Duncan and others (1994) found that fecal coliform bacteria were removed through a 45 cm column of unsaturated fine loamy soil. BO[D.sub.5] levels of septic tank effluent were reduced to less than 4.0 mg/l in the same columns. Phosphorus was undetectable after 15 cm. Widrig and others (1996) looked at BO[D.sub.5], total suspended solids, and ammonia removal from septic tank effluent through columns of sand. After moving through 45 cm of unsaturated sand, BO[D.sub.5], total suspended solids and ammonia-N were reduced to 31 mg/l, 25 mg/l and 0.89 mg/l, respectively. After 60 cm of unsaturated sand the BO[D.sub.5], total suspended solids and ammonia-N was further reduced to 20 mg/l, 16 mg/l and 0.39 mg/l, respectively.

In an extensive survey of the published literature, Gerba and others (1975) considered the removal of bacteria and viruses by soil. They found that the movement of bacteria through soil was related to its permeability. Bacteria moved as little as 60 cm downward through fine sandy loam but 180 cm downward through fine-grained sand. Bacteria were primarily removed by mechanical straining through mats of suspended solids and biological growth that occurs at the wastewater infiltration surface. Bacteria that move through this mat were then adsorbed onto clay minerals in the soil matrix.

Virus removal was found by Gerba and others (1975) to be more limited. Virus particles are very small and are difficult to filter. The primary mechanism of virus removal is adsorption onto clay minerals in the soil matrix. Viruses from sewage effluents were removed in soil columns ranging from 19 to 46 cm. Adsorption of viruses by soil is complicated, however, by the presence of organic matter in wastewater. Organic matter was found to interfere with virus adsorption. Soluble organic matter was found to compete for adsorption sites, decreasing virus removal and even causing the release of sorbed virus particles. To effectively remove viruses from sewage effluents, it is important to first remove and decompose the dissolved organic matter.

Gerba and other (1975) also reported on the movement of viruses through saturated soil. Viruses were found in wells 60 to 120 meters from the point where the viruses were introduced into saturated soils.

Figure 1 summarizes the findings of the various investigators. The figure shows the ranges of depths for soil types ranging from sands to loams.

[FIGURE 1 OMITTED]

Regulatory agencies often require unsaturated soil depths from 60 to 120 cm beneath the level of application to remove solids, BO[D.sub.5], ammonia and bacteria from sewage effluents. Depths of 120 cm or greater in sandy soils appear necessary to remove viruses. The Ohio Administrative Code (1977) requires a 120 cm deep soil layer between the bottom of a sewage leaching trench and a limiting soil condition.

Limiting conditions are considered to be soil or geologic layers that are either insufficiently or excessively permeable. In Ohio, limiting conditions include ground or perched water tables, hard, unfractured bedrock, dense glacial till, compacted zones, dense clays, pans such a fragipans, sand, gravel and fractured rock.

Converse (1978) presented an onsite wastewater treatment system design that could be used in areas with shallow soil depths to a limiting condition. Known as a mound system, a layer of sand is placed on top of the natural soil to augment its treatment capacity. The sand layer of up to 60 cm acts to reduce suspended solids, BO[D.sub.5], and ammonia with continued removal, along with bacteria and virus removal in the underlying soil. Converse found that with sand augmentation, onsite wastewater treatment systems could be used in areas with more slowly permeable soils, with permeabilities as low as 0.5 inches per hour. Widrig and Mancl (1990) adapted the concept of a mound presented by Converse to apply to Ohio's soil conditions and regulatory requirements.

A comprehensive program to describe, classify, map and interpret Ohio's soils began in 1899. The program has involved cooperation between the United States Department of Agriculture -- Soil Conservation Service (now the Natural Resources Conservation Service), together with state agencies and The Ohio State University. Soil survey information is available for all 88 Ohio counties, each with a range of characteristics. Each soil is described in terms of sequences of layers, called horizons, that have developed through time from a variety of parent materials, under the influence of climate, living organisms and the position of the soil on the landscape. Each soil horizon and each integrated soil profile presents a unique set of conditions for effluent treatment.

Of course, as pointed out by Miller and Wolf (1975), soil is not present in the landscape in discrete units, but rather as a continuous spectrum of soil associations and geologic conditions with varying capabilities to renovate sewage effluents. The soil maps, therefore, serve as a guide to help assess the extent and diversity of the soil resource.

The objective of this study was to estimate the extent of Ohio's land area that is suited to soil-based wastewater treatment. Both soils with the capability to treat wastewater through traditional leach lines as soil absorption systems and soils which can be augmented with a layer of sand, to utilize mound systems, were considered in this assessment.

METHODS

Each of Ohio's 467 soil series characterized by National Cooperative Soil Survey (1960-2000) were tabulated and assessed to determine the depth of the soil to bedrock, the depth to a limiting soil condition, the depth to seasonal saturation, and the soil permeability. Each soil series was placed into one of three categories; suited for traditional leach fields or mound systems, suited for mound systems only, or not suited for soil-based treatment. The criteria used to distinguish soil series is listed in Table 1.

Each county soil survey contains a table listing the acreage and proportionate extent of the soils in that county. All 88 tables were reviewed to determine the extent of each soil category by county.

RESULTS

Eighty-four soil series were considered suited for traditional leach lines or mound systems in Ohio. These soils are deep, well drained and are listed in Table 2. Figure 2 presents a cross-section of one of these soil series. Figure 3 shows where these 84 soil series occur in Ohio. Most are present along a band from northeastern to southwestern Ohio. Only small areas of these soils occur in northwest Ohio.

[FIGURES 3 OMITTED]

One hundred and sixty-eight soil series were considered suited for mound systems only in Ohio. These soils are shallower and less permeable than those suited for soil absorption systems and are listed in Table 3. Figure 4 presents a cross-section of one of these soil series indicating the presence of the limiting condition. Figure 5 shows where these 168 soil series occur in Ohio. Their occurrence mirrors the soils suited for traditional leach lines, with only small areas of these soils occurring in northwest Ohio.

[FIGURE 5 OMITTED]

The remaining 215 soil series are not suited for soil-based sewage treatment. These soils are identified in Table 4 along with a major reason they were considered unsuited. Soils may not be appropriate for soil-based wastewater treatment systems because they are hydric, are shallow to water table or a restrictive layer, are subject to frequent flooding or are very slowly permeable. It is important to note that some of these soils may be unsuited for more than one reason. Figure 6 presents a cross-section of one of these soil series indicating the depth of the limiting condition.

Statewide only 6.4% of the land area is suited for soil absorption systems using traditional leach lines. This amounts to 1,680,020 acres of land. Soil series suited for mound systems are present in 25.4% of Ohio's land area accounting for 6,667,579 acres of land. The overall occurrence of soils suited to soil-based treatment through traditional leach lines and mound systems is presented in Figure 7.

[FIGURE 7 OMITTED]

CONCLUSIONS AND RECOMMENDATIONS

Soil absorption systems and mound systems are important tools in enabling homes to be built beyond the reach of sewer systems while still protecting the public health and the environment. Care in evaluating sites must be practiced to ensure that ground and surface waters are not contaminated and that untreated sewage does not surface in yards or seep into ditches.

Soil maps, while important useful tools, do not guarantee the presence of the soil series mapped at every spot identified. Soil maps indicate the predominant soil type in an area. Small inclusions of contrasting soils are often present within mapping units. Also many soils throughout Ohio have been disturbed and eroded. Individual site assessment to determine suitability is always necessary before designing and constructing a soil absorption system or mound.

Soils in Ohio suited for traditional leach lines are rare and valuable, because of the soil's ability to easily and inexpensively renovate sewage to protect ground and surface water. These deep, well-drained soils are also valuable agricultural soils and are well suited for construction projects. The most highly settled areas of Ohio also have the largest acreages of deep, well-drained soils. Much of this soil has already been disturbed. The remaining areas should be identified and protected from damage caused by construction, excavation or filling. It has taken natural processes thousands of years to create these soils. They can be quickly destroyed if not recognized and guarded.

Larger land areas in Ohio are suited to mound systems only. A survey conducted by Mancl (1999) revealed little use of mound systems throughout Ohio. The findings of this study indicate that mounds should receive greater consideration with Ohio's large areas of shallow soils to seasonal water tables and restrictive layers. The use of mound systems can greatly impact rural development and environmental and public health protection in counties. For example, in Clermont County less than 10% of the land area is suited for soil absorption systems but over 40% of the land area is suited for mound systems.

Most of Ohio's land area is not suited to soil-based treatment. Construction of homes without sewer service in these areas must proceed cautiously. While technologies exist to treat and dispose of wastewater onsite, such as sand bioreactors (Mancl and Rector 1999) and reuse of treated wastewater through irrigation (Mancl and Rector 1997), these approaches have limitations. They are more expensive than soil-based treatment and require more maintenance. Also at least a 30 cm depth of unsaturated soil is needed to accommodate onsite irrigation of treated wastewater. Many soils, including Ohio's 92 hydric soil series, would require subsurface drainage to lower a seasonal high water table to below 30 cm before treated wastewater could be irrigated.

As Ohio communities begin to plan for the future, they need to consider how best to provide sewage treatment services. Through careful use of soil-based sewage treatment and disposal systems, homes can be constructed in rural Ohio while still protecting the public health and Ohio's valuable water resources. TABLE 1 Soil characteristic to determine suitability for soil-based wastewater treatment. Traditional leach Mound soil absorption lines soil system augmented with Characteristic absorption system suitable sand Depth to bedrock at least 4 feet at least 2 feet Depth to restrictive at least 4 feet at least 2 feet layer Depth to seasonal at least 4 feet at least 2 feet high water table Soil permeability between 1 in/hr -- at 18 inch depth and 20 in/hr Soil permeability -- between 0.5 in/hr at soil surface and 20 in/hr TABLE 2 Soil series suited for traditional leach line systems or mound systems. Alford Hazelton Shelocta Allegheny Hennepin Sisson Ashton Hickory Spargus Beasley Kanawha Sparta Belmore Leoni Spinks Birkbeck Lumberton Tyner Bionnell Lybrand Uniontown Boyer Martinsville Watertown Brownsville Mechanicsburg Waupecan Cedarfalls Mentor Wea Chavies Mertz Wellston Chenango Negley Westmore Chili Nineveh Westmoreland Cidermill Oakville Wheeling Clymer Ockley Williamburg Colonie Oshtemo Zurich Conotton Otisville Crider Parke Donnelsville Pike May be subject Duncannon Platville to flooding Elkinsville Princeton Chagrin Frankstown Riddles Cuba Fredricktown Rigley Genesee Gallia Rossburg Gessie Gallman Rush Haymond Grayford Russell Jules Hackers Saylesville Landes Hartshorn Scioto Pope Hayter Sewell Ross TABLE 3 Soil series suited for mound systems only. Aaron Crane Jeneva Pacer Tiro Alexandria Cruze Jessup Parr Trappist Amanda Culleoka Jimtown Perrin Tremont Ava Cygnet Johnsburg Pierpont Tuscola Bepre Dana Kane Pinegrove Upshur Berks Darroch Keene Plainfield Vandalia Bixler Dekalb Kelloggs Plumbbrook Vandergrift Blairton DelRay Kendallville Prout Vaughnsville Bogart Digby Kensington Rainsboro Wakeman Boston Dunbridge Ladig Raub Warsaw Braceville Edenton Lakin Rawson Waynetown Brady Elba Libre Reesville Weinbach Bratton Eldean Licking Richland Wernock Brecksville Elliott Lily Rittman Westgate Brenton Ellsworth Lordstown Rodman Wharton Bronson Ernest Loudon Rossmoyne Whitaker Brooke Faywood Loudonville Sardinia Woods field Brookside Fincastle Lowell Savona Woolper Broughton Fitchville Lykens Schaffenaker Wooster Brushcreek Fox Markland Sciotoville Wyatt Cambridge Gallipolis Miami Sees Wynn Cana Geeburg Miamian Seward Xenia Caneadea Germano Milton Shawtown Zanesville Canfield Gilpin Mitiwanga Shinrock Captina Glenford Monongahelia Sleeth Cardinal Gosport Morley St. Clair Casco Guernsey Morrisville Steinsburg May be subject Castalia Haney Muse Stringley to flooding Celina Hanover Muskingum Summitville Lobdell Centerburg Harbor Nicholson Switzerland Medway Cincinnati Heverlo Odell Tarhollow Nolin Clarksburg Homer Ogontz Tarlton Sligo Coblen Homewood Omulga Teegarden Tioga Corwin Ionia Ottokee Tilsit Coshocton Iva Otwell Tippecanoe TABLE 4 Soil series not suited for soil-based wastewater treatment. Depth to Restrictive Layer Depth to Water Table Bethesda Aetna Mahoning Biglick Algansee McGary Channahon Algiers Mespo Colyer Atlas Metamora Enoch Aurand Minoa Fairmount Avonburg Mortimer Fairpoint Bennington Nappanee Farmerstown Blount Newark Gasconade Canal Painesville Lewisburg Cardington Pekin Lorenzo Cavode Platea Marblehead Ceresco Pyront Morristown Claverack Randolph Opequon Claysville Rarden Richey Coolville Ravenna Strawn Crosby Red Hook Titusville Crosier Remsen Tuscarawas Darien Rimer Weikert Defiance Schaffer Dixboro Shoals Doles Smothers Very slowly Dubois Stafford permeable Eel Stanhope Eden Etnora Stendal Lawshe Fulton Stone Lucas Galen Taggart Pate Gavers Tedrow Roselms Glynwood Thackery Gresham Thrifton Haskins Tiderishi Haubstadt Tygart Henshaw Tyler Holton Vanlue Hornell Venango Houcktown Wadsworth Hyatts Wakeland Jenera Wallington Jonesboro Waphani Kibbie Westboro Lamberjack Wilbur Latham Williamson Lockport Flooding Hydric Soils Clifty Adrian Mermill Flatrock Allis Milford Harrod Alvada Millgrove Hartshorn Atherton Milldale Huntington Beaucoup Miner Kinn Blanchester Montgomery Knoxdale Bonnie Muskego Lanier Bono Olentangy Lindside Brookston Olmsted Moshannon Canadice Pandora Orrville Carlisle Patton Philo Clermont Paulding Sarahsville Cohoctah Peoga Senecaville Colowood Pewamo Skidmore Condit Pinnebog Stonelick Conneaut Piopolis Damascus Purdy Drummer Ragsdale Edwards Rensselaer Frenchtown Risingsun Fries Rockmill Gilford Rollersville Ginat Romeo Glendora Roundhead Granby Sandusky Holly Saranac Hoytville Sebring Ilion Secondcreek Joliet Sheffield Kerston Sloan Killbuck Swanton Kingville Tawas Kokomo Toledo Kyger Treaty Lamson Trumbull Latty Wabasha Lenawee Wallkill Linwood Warners Lippincott Washtenaw Lorain Wauseon Luray Wayland Mahalasville Westland Marengo Wetzel Martinisco Weyers McGuffey Willette Melvin Zipp FIGURE 2. Soil suitbale for traditional leach line system -- Wheeling Series. a) Description of a single example profile: Ho- Depth ri- In- Struc- Consis- Re- Perm. zon ches Color Texture ture tence dox In/hr Ap 0-10 brown silt weak friable 0.6-6 (10YR4/ loam fine 3) granular E 10-14 yello- silt weak friable 0.6-6 wish loam medium brown and fine (10YR5/ sub- 4) angular blocky Bt 14-34 dark silty moderate firm 0.6-2 yello- clay medium wish loam sub- brown angular (10YR4/ or 4) angular blocky BC 34-58 light very weak firm 0.6-2 yello- fine coarse wish sandy sub- brown loam angular (10YR6/ blocky 4) 2BC2 58-60 dark very very friable 0.6-2 brown gravelly weak (7.5YR4/ sandy coarse 2) loam sub- angular blocky 3C 60-72 dark stra- 6-20 grayish tified brown very (10YR4/ gravelly 2) sand [ILLUSTRATION OMITTED] FIGURE 4. Soil suitable for mound system -- Miamian Series. a) Description of a single example profile: Ho- Depth ri- In- Tex- Struc- Consis- Perm. zon ches Color ture ture tence Redox In/hr Ap 0-9 brown silt moderate friable 0.2-0.6 (10YR4/ loam medium 3) sub- angular blocky parting to weak fine granular Bt1 9-12 dark clay moderate friable 0.2-0.6 yello- loam medium wish sub- brown angular (10YR4/ blocky 4) Bt2 12-18 dark clay moderate firm 0.2-0.6 yello- loam medium wish sub- brown angular (10YR4/ or 4) angular blocky Bt3 18-26 yello- clay weak firm 0.2-0.6 wish medium brown pris- (10YR5/ matic 4) parting to strong medium sub- angular and angular blocky BCt 26-33 yello- loam weak firm few 0.2-0.6 wish coarse fine brown sub- promi- (7.5YR4/ angular nent 2) blocky strong brown (7.5YR5/ 8) iron accumu- lations Cd 33-80 yello- loam massive very few 0.2-0.6 wish firm promi- brown nent (10YR5/ strong 4) brown accumu- lations [ILLUSTRATION OMITTED] FIGURE 6. Soil unsuitable for waste application -- Kokomo Series. a) Description of a single example profile: Ho- Depth ri- In- Tex- Struc- Consis- Perm. zon ches Color ture ture tence Redox In/hr Ap 0-9 very silty weak friable 0.6-2 dark clay fine and gray loam medium (10YR3/ granular 1) A 9-16 black silty moderate firm 0.6-2 (10YR2/ clay fine and 1) loam medium angular blocky Btg1 16-31 dark silty moderate firm common 0.2-0.6 gray clay medium medium (5YR4/ loam and fine dis- 1) sub- tinct angular dark and yello- angular wish blocky brown (10YR4/ 4) and few medium promi- nent yello- wish brown (10YR5/ 6) iron oxide masses Btg2 31-50 olive silty moderate firm common 0.2-0.6 gray clay coarse coarse (5YR5/ loam sub- promi- 2) angular nent blocky strong brown (7.5YR 5/6) and yello- wish brown (10YR5/ 8) iron oxide masses 2C 50-64 brown loam massive friable 0.2-0.6 (10YR5/ 3) [ILLUSTRATION OMITTED]

ACKNOWLEDGMENTS. Salaries and research support provided by State and Federal funds appropriated to the Ohio Agricultural Research and Development Center of The Ohio State University.

LITERATURE CITED

Bureau of Census. 1990. Detailed housing characteristics, Ohio. Structural characteristics. US Dept of Commerce. p 81.

Converse JC. 1978. Design and construction manual for Wisconsin mounds. Small Scale Waste Management Project 15.5. Univ of Wisconsin, Madison, WI. 80 p.

Duncan CS, Reneau RB, Hagedorn C. 1994. Impact of effluent quality and soil depth on renovation of domestic wastewater. Proceedings of the 7th International Symposium on Individual and Small Community Sewage Systems. ASAE, St. Joseph, MI. p 219-28.

Gerba CP, Wallis C, Melnick JL. 1975. Fate of wastewater bacteria and viruses in soil. J Irrigation and Drainage Division ASCE 101(IR3):157-73.

Mancl K. 1999. Survey of approved practices for onsite sewage treatment systems in Ohio. Ohio J Sci 99(3):38-43.

Mancl K, Rector D. 1997. Reuse of reclaimed wastewater through irrigation for Ohio communities. Ohio State Univ Extension Bull 860. Columbus, OH. 33 p.

Mancl K, Rector D. 1999. Sand bioreactors for wastewater treatment in Ohio communities. Ohio State Univ Extension Bull 876. Columbus, OH. 20 p.

Miller FP, Wolf DC. 1975. Renovation of sewage effluents by the soil. Second National Conference on Individual Onsite Wastewater Systems. NSF, Ann Arbor, MI. p 87-101.

Ohio Administrative Code. 1977. Chapter 3701-29.

National Cooperative Soil Survey. 1960 - 2000. Soil surveys for counties in Ohio. 88 different volumes with one for each Ohio county. Can be obtained through the Soil and Water Conservation District office in each county.

Widrig D, Mancl K. 1990. Mound systems for on-site wastewater treatment ... siting, design and construction in Ohio. Ohio State Univ Extension Bull 813. Columbus, OH. 20 p.

Widrig D, Peeples J, Mancl K. 1996. Intermittent sand filtration for domestic wastewater treatment: Effects of filter depth and hydraulic parameters. Applied Engineering in Agriculture 12(4):451-9.

KAREN MANCL AND BRIAN SLATER, Food, Agricultural, and Biological Engineering and Natural Resources, The Ohio State University, Columbus, OH 43210

(1) Manuscript received 30 May 2000 and in revised form 3 November 2000 (#00-09).