Presentation on theme: "Selected Soil Related Topics"— Presentation transcript:
1 Selected Soil Related Topics WCCA 2005 Spring ConferencePresented By Matt JanzenWisconsin Department of Commerce
2 Discussion Agenda Minimum 6 Inch In Situ Soil Code Requirement Interpretative DeterminationsSiting Systems On A + 4 Soil Conditions
3 6 Inch Minimum Soil Requirement Comm 83.44 (3)(a) Wis. Adm. Code Comm 83.44(3)(a). The infiltrative surface of unsaturated soil to which influent is discharged shall be located at least 24 inches above the estimated highest groundwater elevation and bedrock.A 24 inch separation is adequate for final treatment of wastewater containing less than or equal to 10,000 cfu/100 mL fecal coliform .Greater separation (36-60 inches) is required for sandy soil with greater than 35 percent rock fragments.
4 6 Inch Minimum Soil Requirement Comm 83.44 (3)(b) Wis. Adm. Code Comm 83.44(3)(b)1. At least 6 inches of the soil separation required under par. (a) shall be an in situ soil type for which soil treatment capability has been credited under TableThe minimum soil depth (6”) must consist of naturally occurring (in situ) soil material, not fill.Possible Petition for Variance for sites with < 6”in situ soil.Except for material having more that 90 percent coarse fragments, all soil types are credited for treatment.Note that POWTS designs shall reflect restrictive soil horizons that adversely affect treatment or dispersal.
5 6 Inch Minimum Soil Requirement Comm 83.44 (3)(b) Wis. Adm. Code Comm 83.44(3)(b)2. The purpose of the 6 inches of in situ soil under subd 1. shall be to assure that the influent will be assimilated into the original subsurface soils without ponding on the ground surface.This requirement therefore addresses dispersal and not necessarily treatment.Note that surface discharge of domestic wastewater is not allowed as per Comm 83.32(1)(f) Wis. Adm. Code.Sewage is defined as having fecal coliform concentrations of > 200 cfu/100 mL.
6 6 Inch Minimum Soil Requirement Summary The 6-inch minimum in s. Comm 83.44(3)(b)1., applies to both limiting factors of soil saturation and bedrock and could be comprised of all A horizon material.Soil SaturationSites must have a minimum 6 inches of unsaturated soil to assimilate the influent wastewater without ponding on the ground surface.A + 4 conditions or better usually meet the 6 inch min. requirement.BedrockMust have a minimum 6 inches of non-bedrock material (i.e. soil material).Many bedrock controlled sites may not be affected by soil saturation, and simply need a soil cover of 6 inches to qualify as suitable.
8 Soil Saturation Determinations s. Comm 85.60(1)(a). Optional Documentation.A property owner, or their agent, may submitdocumentation to the Department to prove thatredoximorphic features, or other soil colorpatterns, at a particular site are not indicative ofperiodically saturated soil conditions or highgroundwater elevation.Expound using Freeze & Cherry’s statement of conditions for Saturated, Unsaturated, and Tension Saturated Zones. Note that the Code condition fits the Saturated Zone, but the tension saturated zone does not; yet the tension saturated zone promotes anaerobic conditions and forms mottles. (Exhibits: Comm 83.02(56) + Abbreviated list of conditions for the 3 zones).
9 A + 4 Soil Conditions“A + 4” is a Wisconsin POWTS trade term not found in any code or manual, but which generally refers to the soil interpretation limits of s. Comm 85.30(2)(b) which reads:
10 s. Comm 85.30(2)(b)Unless otherwise determined under s. Comm 85.60, the highest elevation of seasonal soil saturation shall be the ground surface where redoximorphic features are present within 4 inches of any of the following:An A-horizon that extends to the ground surfaceThe lower boundary of overlying fill where no buried A-horizon existsAn A-horizon buried by overlying fillFillAFillABThis section defines the conditions where the standard soil testing interpretation of “no mottles = not saturated” is no longer applicable due to the potential masking of redoximorphic features by the dark color of the A horizon, or by the presence of fill materials. The 4 inches is the safety zone that assures the establishment of a non-saturated soil condition below the A horizon or fill boundary in a standard soil test. It applies only to the limiting factor of the depth to soil saturation, not bedrock.C
11 Some Conditions Are Black And White A+ 4 or More OKWet to Surface4 in+Black Over Grey Walk Away
12 Others Conditions Require Additional Information to Make a Determination The statement “Unless otherwise determined under s. Comm ” found in Comm 85.30(2)(b) allows :The Interpretive DeterminationThe Soil Saturation DeterminationThe Hydrograph ProcedureThe Artificially Controlled Navigable Waters DeterminationThis presentation is limited to interpretative determinations under s. Comm 85.60(2) Wis. Adm. Code.
13 Alternative Determinations Results from any of the Comm 85.60 procedures can overturn the default interpretation of saturation to the ground surface required with < A + 4 conditions.The Interpretive Determination is often the preferred method for:Evaluating somewhat poorly drained natural (in situ) soil.Some fill sites where there is sufficient evidence available to establish a reliable depth of soil saturation.
14 Filled Sites Sites With Existing Fill Under the current code, there is no longer any prohibition placed on installation of any type of soil dispersal component in or on fill. However,The commonly used POWTS Component Manual designs are all limited to natural (in situ) soils so plans must be submitted as an Individual Site Design.In such cases, the Individual Site Design must show that the filled soil conditions will disperse and treat wastewater as well as natural soil.In addition, to place a dispersal cell in, or on, existing fill, a petition for variance to s. Comm 83.44(3)(b)1 would need to be approved if between the lower boundary of the fill and bedrock or saturated soil there is < 6 inches of natural soil.[Existing Fill ppt. Presenter’s Explanatory Note]The principle concern with installing soil dispersal components in existing fill is the potential for serious errors in estimating depth to soil saturation. The fundamental assumption that zones of soil saturation are indicated by redoximorphic features simply does not hold true for many manmade soils. The other limitations common to fill, such as lack of soil structure, variability in texture, and compaction, are usually revealed by the description of soil properties in the standard soil test.The ISD requirement would include mounds and at-grades placed on existing fill of any depth, and in-ground systems where the soil volume utilized for wastewater treatment includes existing fill materials. This would include soil material subject to side-wall infiltration as well as the depth below the infiltrative surface specified by Table
15 Putting An Interpretative Determination Together A more intensive soil study and report, under Comm 85.60(2), may be used to overturn the assumption of saturation to the ground surface where any of the conditions enumerated in s. Comm 85.30(2)(b) exist (i.e. < A + 4).Because of the 6 inch minimum limitation of s. Comm 83.44(3)(b)1, a Comm study becomes necessary to explore the potential for onsite wastewater dispersal where such conditions exist.
16 Details And Information Additional information is necessary such as:Morphology of the A or Ap horizon and immediately belowSubstratum morphologyType of saturation - episaturation or endosaturationMatrix colorReduced (low chroma or gley) colorsSoil organic matter contentRoot patternsRedox feature - type and occurrenceComparative landscape analysisUp slope/down slope and off lot soils & landscape reviewsSurface and subsurface hydrologySoil Survey informationTopographic mapsLiterature citations and supporting documentation
17 Comparative Landform Analysis And Site Clues Existing VegetationSlope PositionSlope ShapeSITE CLUES. Here is where you get your nose out of the dirt and look around to see what else may be affecting, or has been affected, by the soil drainage characteristic of the prospective site.TOPOGRAPHY - DRAINAGE - SUBSURFACE DRAINAGE. Use your X-ray eyes to look into the earth and see where is the water collecting, where does it go, and how fast. You do this by first examining the soils and then by applying the principles of hydrology to the landscape.EXISTING VEGETATION. Vegetation can be a very powerful tool in evaluating the long-term soil saturation of a given site. We cannot provide very much here except mention of some common indicators. A wetland delineation course would be very helpful in doing this type of work. Basically, suitability for pretreated effluent dispersal stops where a jurisdictional wetland begins.LAND USE HISTORY. Has the site been cropped? If so, with what? Are there indications that it has been too wet to plow in the spring?CAMPARATIVE LANDUSE ANALYSIS RELATING TO SOIL MORPHOLOGY AND SITE CLUES. The object here is to base your final determination on as much evidence as is available. Compare your prospective dispersal area with an adjacent wetter site wherever possible. The prospective site is a portion of a hydraulic system. Understand how it relates to the whole.INTERPRETATION AND PREDICTION. The objective of the evaluation is to establish that there is going to be enough unsaturated soil above the tension saturated zone throughout the year to accept system discharge and keep it below the surface of the ground.SEASONAL MINIMUM DEPTH TO SATURATION. The average thickness of an Ap horizon is about 9 inches. Nearly all of it must be unsaturated to accept system discharge.DURATION. Saturation close to the surface for periods greater than a few days will render a site unacceptable. This is particularly difficult to predict for the early spring.POTENTIAL SYSTEM IMPACTS. Site characteristics which effect the dimensions of the system will determine site suitability is some cases. Dispersion into theses soils require the availability of a long linear dimension.
18 Redoximorphic Features Redox ConcentrationsNodules and ConcretionsMasses (Fe)Pore LiningsRedox DepletionsIronReduced MatricesGley1. Redox ConcentrationsJust as the name implies, these features are accumulations of a product of oxidation-reduction reactions (redox) in the soil. The most familiar is the yellowish-red iron mottle (iron mass). There are others:a. Nodules and ConcretionsFirm to hard irregularly shaped bodies. Made of iron and/or manganese, they are usually dark red to black in color and can be individually picked out of the soil matrix.b. Masses (iron)This is the familiar high chroma mottle. These are color features that usually do not differ very much in physical character from the surrounding soil matrix.c. Pore LiningsAccumulations of redox products on the walls of larger pores and root channels. Made of iron and/or manganese, they may be yellowish red to dark red in color.2. Redox DepletionsThese are zones were a substance has been removed from a zone by the action of past redox reactions. The most familiar is the gray mottle (iron depletion).a. Iron DepletionsThese are the low chroma mottles and are zones where iron has been removed leaving a gray, colorless, mineral matrix. Soil scientists are evenly divided as to whether seasonal soil saturation is best indicated by chroma of 2 or less, or by a chroma of 3 or less. Some research suggests it is a matter of duration. Iron depletions are commonly found in close association with iron concentrations. This is because when iron is chemically reduced, it is relatively soluble, and moves with the soil water from one point to another. When the soil dries out, the reduced iron (ferrous) re-oxidizes back to ferric iron compounds that are insoluble. The result, after many years, is separate areas of iron depletion and areas of iron concentration. This is the fundamental way that high and low chroma mottles are formed. An iron depleted matrix is where an entire soil horizons that have been stripped of iron leaving a gray to white, colorless soil material. This removal of iron is not always the result of redox reactions. Some E horizons become striped of iron by a different process that does not necessarily involve soil saturation (pseudogley and gley).b. Clay Depletions*3. Reduced MatricesThese are soil horizons that have a low chroma because the iron has been reduced from reddish ferric iron to greenish ferrous iron. Unlike the iron depleted matrix, the iron has not been removed and may be re-oxidized (quite rapidly) upon exposure to air.Reduced matrices are usually found in soil zones that have prolonged periods of saturation.
19 Low Chroma Colors Value of 4 or more and a chroma of 2 or less. Redox depletionsReducing conditionsSuspicious conditions with chromas of 3 or less.
27 Relationships Between Saturation and Oxidation and Reduction Redox feature formation requires:Anaerobic conditionsSaturationNear SaturationOrganic matterTemperaturepHIron (Fe) and Manganese (Mn)Biogeochemical ProcessIron Depletion and Concentration
28 Chemical Oxidation-Reduction Oxidation e- lossReduction e-gainOxidation is the loss of electrons.Reduction is the gain of electrons.Fe+3 <----> Fe+2O2 <----> H2OMn+3 <----> Mn+2One half of the reaction where there is a transfer of electron(s) from one molecule to another. Examples are paper burning and cars rusting. Oxygen is reduced by taking electrons from the carbon and iron, which are oxidized.
29 Microbial Redox Sequence OxygenNitrateManganeseIronSulfurInvisibleVisibleOdorGreater Reducing ConditionsIn water-logged soil, dissolved oxygen is quickly used up, and cannot be readily replenished from the atmosphere. Other substances, such as Red (ferric) iron, is used instead by the microbes to oxidize organic compounds.Oxidation and reduction of some substances in soil leave behind visible evidence of their past occurrence. This is particularly true of iron, but there are others as well. There are two general categories of redoximorphic features based on the past movement (translocation) of substances.
30 Interpretative Determination Objective You are basically trying to prove that a pipe-in-the-ground soil saturation determination does not need to be performed because you can show the Department where the zone of soil saturation is, and where it is not.“Conclusively Demonstrate” means that the interpretive determination can be made with a high level of confidence.This usually means it is supported by information from more than one source
31 Required Information Local Hydrology Such as: Type of water table (perched or basal) and gradientElevations and location of streams, ponds, lakes or ditches.Substratum Characteristics - Need one deep soil boring.
32 Required Information Local Geomorphology Such as: Describe the landform (summit, backslope, outwash plain, etc.)Glacial deposit or bedrock as appropriate to the site.This also could include natural changes in the water table in the distant past due to changes in lake or stream levels.
33 Required InformationSoil disturbance and hydraulic modification. Such as:Include agricultural tillage along with any cut and fill as soil disturbance.Hydraulic modifications would include drainage ditches, tile drain piping, as well as surface drainage from parking lots, roads, and roof tops.REPORT CONTENTS: There may be some overlap with other information topics. Information reported under one topic does not need to be repeated in another.
34 Required Information Landscape position and local topography Such as: Relative position on the landform.Local topography would include slope morphology both parallel and perpendicular (convex, concave, or smooth).Other local land surface features as applicable.
35 Required InformationSoil Survey map unit for the tested area and adjacent units on the landscape.If you are aware of a soil saturation determination previously performed for the same mapping unit, or on a nearby parcel, include the data.If Department or County staff have been on the site, mention it in your report and include any written letters or reports.
36 The Report: Conclusion The conclusion is a statement of results addressing the specific objective.Identifying depth and/or elevation of seasonal soil saturation.State why you believe your interpretation of conditions is conclusive enough to predict the depth to saturation.Recommend other soil-related design parameters such as maximum linear loading rate and hydrologic modifications.APPROVEDSITE CLUES. Here is where you get your nose out of the dirt and look around to see what else may be affecting, or has been affected, by the soil drainage characteristic of the prospective site.TOPOGRAPHY - DRAINAGE - SUBSURFACE DRAINAGE. Use your X-ray eyes to look into the earth and see where is the water collecting, where does it go, and how fast. You do this by first examining the soils and then by applying the principles of hydrology to the landscape.EXISTING VEGETATION. Vegetation can be a very powerful tool in evaluating the long-term soil saturation of a given site. We cannot provide very much here except mention of some common indicators. A wetland delineation course would be very helpful in doing this type of work. Basically, suitability for pretreated effluent dispersal stops where a jurisdictional wetland begins.LAND USE HISTORY. Has the site been cropped? If so, with what? Are there indications that it has been too wet to plow in the spring?CAMPARATIVE LANDUSE ANALYSIS RELATING TO SOIL MORPHOLOGY AND SITE CLUES. The object here is to base your final determination on as much evidence as is available. Compare your prospective dispersal area with an adjacent wetter site wherever possible. The prospective site is a portion of a hydraulic system. Understand how it relates to the whole.INTERPRETATION AND PREDICTION. The objective of the evaluation is to establish that there is going to be enough unsaturated soil above the tension saturated zone throughout the year to accept system discharge and keep it below the surface of the ground.SEASONAL MINIMUM DEPTH TO SATURATION. The average thickness of an Ap horizon is about 9 inches. Nearly all of it must be unsaturated to accept system discharge.DURATION. Saturation close to the surface for periods greater than a few days will render a site unacceptable. This is particularly difficult to predict for the early spring.POTENTIAL SYSTEM IMPACTS. Site characteristics which effect the dimensions of the system will determine site suitability is some cases. Dispersion into theses soils require the availability of a long linear dimension.
37 Basic Design Parameters For Sites With Shallow Depth To Limitations
39 Hydraulics and System Design Three ParametersHydraulic Conductivity (Ksat)Hydraulic Gradient2-Dimensional flux area perpendicular to hydraulic gradientDesign VariablesDispersion perpendicular to the hydraulic gradient (linear loading)Advection parallel to the hydraulic gradient (toe extension)We shall examine these using Darcy’s Law which describes saturated flow through a porous medium:Darcy’s Law: Q=K(dh/dl)A Where: Q is the discharge as volume per unit timeK is the Saturated Hydraulic Conductivity of the soilDh/dl is the hydraulic gradient as change in head per change in length of flow pathA is the 2-dimensional area perpendicular to the flow path that is available.THE HYDRAULIC CONDUCTIVITY. The intrinsic ability of a porous media to transmit a given liquid. It is a constant of proportionality and is in the dimensions of velocity (length per unit time) It is among the most widely varying properties in nature, ranging from 1.0 m/s for coarse gravel to m/s for compacted clay.THE HYDRAULIC GRADIENT. This is the sum of pressure head plus elevation head. When working with the surface of a water table or groundwater mounding. We can confine our attention to elevation head. This is basically the pitch of the flow path.THE 2-DIMENSIONAL FLUX AREA PERPENDICULAR TO THE HYDRAULIC GRADIENT. The discharge (Q) will also depend upon the area through which the flow can take place. This is somewhat analogous to the effect of diameter on flow though a pipe.THE DESIGN VARIABLES. A mound system dispersing pretreated effluent into a shallow unsaturated soil zone can be expected to create a groundwater mounding effect (GWME) beneath the dispersion cell. Permeable soils with a high Ksat will develop a low GWME with steep side slopes (high hydraulic gradient) whereas GWMEs in lower Ksat soils will be comparatively higher and wider with a lower hydraulic gradient. Therefore, it is the sites with slower permeability in the upper horizons that will be at greatest risk for a wet toe. Protection from compaction during construction is critical.DISPERSION PERPENDICULAR TO THE HYDRAULIC GRADIENT (LINEAR LOADING). The actual dimensions of this groundwater mound for a given set of site, soil, and wetness conditions will depend predominantly of the length of the dispersion cell (linear loading rate). A longer cell provides more area (A) for subsurface flow as well as a narrower groundwater mound. A long cell mound system can disperse at a higher discharge rate (Q) and is at less risk of developing a wet toe than a wider one.ADVECTION PARALLEL TO THE HYDRAULIC GRADIENT (TOE EXTENSION). The groundwater mounding effect diminishes with increasing distance from the source. By making the side slope fill flatter than the hydraulic gradient of the GWME, the saturated zone can be maintained below the surface.