ORDER NO. 17980 APPROVAL OF TEMPORARY ADOPTION OF GUIDE TO SOIL SUITABILITY FOR ON-SITE WASTEWATER SYSTEM, SOIL RESOURCE GROUP A THROUGH E, INCLUSIVE, AS RECOMMENDED BY DR. B. L. CARLILE, P. E., CPSS On this the 28th day of June 1988, upon motion made by Commis- sioner Holland, seconded by Commissioner Ray, the Court unanimously approved temporary Adoption of GUIDE TO SOIL SUITABILITY FOR ON-SITE WASTEWATER SYSTEMS, SOIL RESOURCE GROUP A through E, inclusive, as recommended by Dr. B. L. Carlile, P. E., CPSS, in his May 1988 Report. (Copy of Report on file, but not recorded.) Rave been satisfied. r. GUIDE TO SOIL SUITABILITY FOR ON-SITE WASTEWATER SYSTEMS For Kerr County, Texas _3 Prepared for Kerr County Government by Dr. B. L. Carlile, P.E., CPSS May 1988 r "te _.. t a ~ _.. Y,. ~.. _._.,.. TABLE OF CONTENTS I. INTRODUCTION. II. TREATMENT OF WASTEWATER IN SOILS. , III. SOIL RESOURCES OF KERR COUNTY . IV, SOIL RESOURCE GROUPINGS . 1. Soil Resource Group A , 2, Soil Resource Group B . '~` 3. Soil Resource Group C . ~~ 4. Soil Resource Group D . t ~I~ 5. Soil Resource Group E , f V. SUMMARY OF SOIL GROUPINGS .. VI. SOIL EVALUATION PROCEDURES. . 1. Soil Loading Rates. 2. Soil Factor's and Evaluation . 3. Site Factors and Evaluation 4. Determination of Overall Site Suitability , VII. MINIMUM LOT SIZE REQUIREMENTS , VIII. DEVELOPING A DATA BASE. 1. Soil Data Base. 2. System Design Options 3. MoniCOring Program. ~ IX. REFERENCES. Page 1 1 4 7 7 9 12 15 17 18 20 21 22 29 31 32 37 37 39 39 40 I I2+'TRODUCTION The conventional septic tank system or normal system, as described in House Bill 1875 and the "Rules" of the Texas Department of Health, is not particularly effective in treatment of wastewater contaminants in fragile settings such as is found in much of Kerr County. A program of implementa- tion and management of appropriate on-site wastewater systems is needed as described in the companion report on "Proposed Strategies for On-Site Wastewater Management in Kerr County". These strategies are primarily concerned with protecting the high quality as well as the aesthetic and economic value of surface and ground waters presently found in Kerr Coun- ty. Since soil treatment of wastewater plays an important part in these strategies, the following sections describes some of the important concepts in soil treatment systems. II TREATMENT OF WASTEWATER IN SOILS ,t _. As outlined in the companion report on "Strategies for On-Site Waste- water Management in Kerr County", the basis of design of on-site systems in Kerr County is to require system performance similar to that required for discharging systems. Therefore, the quality of wastewater leaving a prop- erty boundary from an on-site system, either by surface or subsurface flow, should meet the following parameters: Biochemical Oxygen Demand (BOD) - 20 mg/1 Total Suspended Solids (TSS) - Ammonium Nitrogen - Total Phosphorus - F_cal Coliform Eacteria - 15 mg/I 2 mg/1 1 mg/1 200 FC/100 mI z Since on-site systems are routinely installed as close as 10 feet to property boundaries, all system installations should insure that the waste- water is treated to the above limits after treatment through no more than 10 feet of subsurface soil material. Properly functioning septic tank/soil absorption systems can treaC wastewater to the above levels. A review of literature on the treatment capabilities of many functioning septic tank systems by Hansel and N,achmeier (1980) indicated little or no problem with water quality of sur- face or subsurface water. The study found values of BOD were reduced from 270-400 mg/1 in septic tank effluent to less than 1 mg/1 at a point 1 foot below the drainfield trench. Values of TSS were reduced from 300-400 mg/1 in septic tank effluent to zero one foot~beldt~ the trench bottom. Fecal coliform bacteria were reduced from Levels of 1-4 million/100 ml in septic tank effluent to less than 1/100 ml at depths of 3 feet below the drainfield. Ammonium ' nitrogen and phosphorus were all reduced to background levels within the same distance. Studies in high water table areas of North Carolina (Cogger, et al, 1984} and in Virginia (Stewart and Reneau, 1981) show the separation dis- tance between trench bottom and restrictive zone (water table, rock, etc.) to be the most significant factor affecting system performance. In conven- tioaal septic tank/soil absorption systems using gravity distribution, maintenance of a 2 foot separation from the trench bottom to the restric- tive zone was adequate to provide needed treatment of all waste compo- nents. These separations were only adequate where hydraulic loading to the soil trench was controlled at a proper rate. 3 It should be apparent that excellent treatment of human wastes can be obtained with a properly functioning septic tank/soil absorption system. However, numerous factors can diminish the efficiency of treatment in these systems. The conventional design criteria that a system "works" if efflu- ent does not come to the surface of the ground is not necessarily true. .Treatment of wastes may be seriously impaired if the following conditions are not met :^" a)~ Maintenance of the trench bottom at least two foot distance above a restrictive horizon such as a water table, rock layer or other non-soil material. _b) ~ Hydraulic loadings matched to soil conditions. r c)'~ Unsaturated and aerobic conditions ~mair'r[ained around the drain- field. d) Soil absorption trenches no deeper than 18 to 24 inches below the surface. From the above discussion, it becomes obvious that a key to design of conventional systems to meet water quality standards is the treatment of the wastewater through at least 2 feet of aerobic, unsaturated soil materi- al .' Other materials, such as caliche, limestone, marl, etc., are not likely to offer the degree of treatment required for design standards for on-site systems in Kerr County. Based on this criteria, only sites with 3 foot depth of soil material are suitable, assuming a trench depth of 1 foot. Since only a limited number of sites in Kerr County have soil depths of 3 feet, there is the apparent requirement for alternative type systems i€ water quality standards are to be met with on-site systems. _ i 4 Modified and alternative systems are all designed to serve one or two functions: a) reduce the clogging affects in the soil trench and thus maintain near natural permeability of the soil b) enhance the treatment capabilities of the soil system around the absorption area. Systems to accomplish one or both of the above functions have been in use in many areas of the country for the past 10 years. These systems provide one or more of the following: 1) improved distribution of wastewater in the soil to prevent over- loading u 2) dosing and resting of wastewater within-or'between drainfields to enhance the aerobic status of the soil 3) optimized placement of the wastewater in the soil zone to main- tain maximum separation distances 4) pretreatment of the wastewater prior to application in the natural soil. A brief review of various modified and alternative type systems will be presented in the section on system design. These systems will be presented as the means of addressing particular soil and site problems in each soil resource group of Kerr County. III SOIL RESOURCES OF KERR COUNTY The Soil Survey Report of Kerr County, developed and published by the U. S. Soil Conservation Service, provides a general inventory of the soil resources of Kerr County. The soil map and accompanying interpretations of those maps show the distribution of soils on the landscape and their characteristics. Like any map, it has a limit of scale and generally the smallest mapping delineation shown will be 6 to 8 acres. Therefore, land management decision on parcels smaller than this must be made with care when using the Soil Survey Report. A soil map is most appropriately utilized as an initial planning guide. It provides a preliminary assessment of expected soil conditions. It is not intended to provide site-specific information on individual lots. For soil evaluations for on-site waste systems, each site should be evaluated through soil borings taken in the area to be used for the soil absorption system. Several such borings (3`~or'''more) with a hand auger, power auger or backhoe pit should be made to a depth of 48 to 60 inches or until hard rock is encountered. Ftom these borings and observations of core samples, the significant soil characteristics can be evaluated and a determination made as to the suitability of the soil to absorb and treat wastewater. The soils of Kerr County can be categorized into soil resource groups. These groupings can be readily used in the field by the site evaluator to determine within which so31 group a site would be classified and a determination of appropriate technology and system design suitable for that soil group and specific site. Additional classification of the site into appropriate soil textural class then allows the determination of an appropriate hydraulic application rate and system size for the various systems proposed in this report. c The soil resource groupings are identified as a group of individual soils, as identified in the soil survey report, which reflect the follow- ing: 1) Soils with similar physical and hydraulic properties 2} Soils with similar site restrictions 3) Soils with similar system design requirements. The waste systems to be recommended for each soil resource group will be those of least expense and simplest in design and operation but which can be reasonably expected to pro[ect public health and meet the defined water quality limitation. The soil textural classes are simplified into five categories which should be readily determined by the site eyalua'tor. The soil classifica-4 F •• tion for a site is determined by the most restrictive horizon within 3 feet of the surface or 2 feet below the expected trench bottom or zone of sewage application for the system selected. In summary, the approach presented here for the soil evaluation and w site classification takes a systematic approach to the problem of ~ite° approval, system selection. and system sizing. This approach, while seeming- ly arbitrary by those not familiar with soil evaluations, is inherently more precise than decisions based on unreliable data such as percolation tests. This approach also allows the basis for developing a data base from which to gain confidence in the system instead of re-inventing the wheel on every site. A program for developing this data base is detailed in section VIII of this report. ~~ IV SOIL RESOURCE GROUPINGS The following information provides a summary of the major features of ,~ each soil resource group in Kerr County relative to their use for on-site wastewater disposal. This summary is meant to highlight important features of the soil group, discuss the potential of each group for sewage treatment and disposal, and list the type of system design expected to function on this site to meet water quality standards. For each soil group an abbreviated description of a typical profile is given and the depth at which a given problem becomes limiting is graphi- cally illustrated. The illustration represents an average condition and various horizons may be thicker or thinner at specific sites. The narra- tive gives the ratings of each soil group forfvarious systems and the limiting site factors where applicable. Table 1 summarizes the ratings for each soil resource group for the various types of system designs recom- mended for use in Kerr County. Soil Resource Group A This soil resource group includes the following soil mapping unit: Soil Name Mapping Unit Percent of County Boerne Be, OB 0.7 Nuvalde NuB, NwA, UdB 1.6 Oakalla Oa, Uk 1.9 Sunev SuA 0.2 4.4 t Detailed soil data of each of the above named soils can be found in [he Kerr County Soil Survey Report and is not included here. This soil resource group, which makes up about 4.4 percent of Kerr County have only slight to moderate limitations for on-site waste disposal .w ~ 8 and are generally suitable for conventional septic tank systems. The major variation within this group is the textural classification of the control section. The Boerne soil will fall within textural class II while the other soils will fall within textural class IZI and some Nuvalde soils may even fall into IVa classification (see pages 24-26). The major design criteria for soil of this group will be in sizing the system properly for the soil texture found on the site. The report on design criteria for conventional systems shows typical loading rates to be used with specific soil classes. Ranges for this group may be from 2.0 ft2/gal to as high as 3.2 ft2/gal. Some areas of lower slope positions of Sunev and Nuvalde soils may receive excess water from upslope sites during 4wet"weather'and develop temporary perched water table conditions. Such condition can usually be detected by soil color and mottling in the lower soil profile. Such condi- ~ tions should be countered by very shallow placement of the field absorption trenches or by installation of a curtain drain (French drain) immediately upslope of the drainfield. Typical Properties of Soil Resource Group A There are well-drained soils on nearly level to gently sloping topog- raphy that formed in alluvial sediments along stream terraces. Most of the soils were formed in acient alluvium although some sites are subject to occasional flooding. The seasonal water table is generally greater than 3 feet and bedrock is usually 40 inches deep or greater. f y Depth 0 Tvoe of Svstems to be Used: Surface Soil. Sandy loam to silty clay loam, brown to dark grayish brown to very dark gray. 12 Subsoil: Sandy loam to silty clay loam or silty 24 clay, light brown to dark brown,to dark grayish brown. 36 Substratum: 36-60 inches, hard, massive silty clay or silty clay loam, as much as 48 50 percent limestone pebbles and calcium carbonate concre- tions. 60 Suitable Substratum Recommended -Conventional gravel system or gravel-less pipe system Alternatives - LPP, - •. a Loading Rate to be Used: Conventional System - 2.0 ft2/gal to 3.2 ft2/gal for class IZ and III soils respectively. LPP System - Use loading rates for Class ZI and III soils as appropriate. " Soil Resource Group B This soil resource group includes [he following soil mapping units: Soil Name Mapping Unit Percent of County Barbarosa Ba A 0.2 Denton DnB, DrB 1.0 Depalt DpB 0.4 Krum KrC,KrB,KuB 4.8 6.4Y. ' Detailed soil data of each of the above named soils can be found in the Kerr County Soil Survey Repor*_ and is not included here. This sail resource group, which makes up 6.4 percent of Kerr County, has greater limitations .`cr cn-s'_te •es^_= ?:=_^csal tt.a^, t`.=_ _r_~:ious ~rouo lu and is only provisionally suitable for conventional septic tank systems. This means some provisions must be made to overcome the limitations of the soil conditions. The major limitation of these soils is the slow permeability, high shrink-swell potential, and susceptibility of clogging of the soil-trench interface when used for conventional systems. To overcome this problem, some means of dosing should be employed to minimize the clogging problem.! If conventional systems are used, dual, alternating fields with a switching value should be installed as described under system description and criteria. This will allow one field to rest and rejuvenate while the second field is functioning. When such systems are moderately loaded (2.5 - 3 ft2fgal) in each field, the system should function adequately for many 4 years. As long as the valve is switched out effluent is not allowed to surface, water quality standards should be easily met. The conventional system utilized on these sites can be the standard gravel type system or the gravel-less type systems as described in the system description report. If the gravel-less type system is used, a sandy loam backfill should be used around the large diameter pipe. The other alternative type system that would function well on these b soils is the Low Pressure Pipe (LPP) system. This system does require a',' pump and better system design and operation. The LPP System is recommended where the field lines are best installed up-slope from [he house or where field lines are to be installed in a wooded area. The design report gives recommended loading rates of the LPP system. Class IV textured soils as found in Kerr County will require loading rates of 12 to 20 ft2/gal. _..,~ .... i 1 As noted in the previous section, some soils of this group, particu- larly the Krum clay, is subject to excess water flowing downslope from areas above, creating perched water table conditions during wet periods. These conditions must be countered by very shallow placement of the system or installation of curtain drains above the field area. A minimum of 1' foot separation between the trench bottom and the seasonal high water table is necessary. Typical Properties of Soil Resource Group B Well drained soils found on nearly level to gently sloping topography along valley bottoms and toe slopes. These soils were formed in clayey and limestone sediments and have appreciable levels Hof shriek-swell clays a throughout the profile. Depth to rock or seasonal water table is generally greater than 36 inches although the Rrum soil may have perched water tables at depths of 18 inches or even less when located on a concave topographic position. These conditions may last for several weeks during extended wet `° periods. Depth Surface Soil: Silty clay ~~ to silty clay loam, dark brown to dark gray. 12 ---------------- Subsoil: Clay to silty Provisionally clay, dark reddish brown Suitable to dark grayish brown. 24 Substratum: 43-60 inches, subsoil weakly consolidated to 36 cemented limestone to marly or gravelly silty clay loam. 48 ---------------- Substratum xxxxxxxxxxxxxxxx XX?: XY X:CX XX l"XXX XX 1° Type of System to be Used: Recommended - Dual alternating field of conventional gravel system, V-trench system or gravel-less pipe system. Alternatives - LPP, Pretreatment and Surface application. Loading Rates to be Used: Alternating field system - two separate fields of equal size with a total area of 5 to 6 ft /gal/day. Krum soils to have largest fields, Denton soils smaller fields, others intermediate. Other Systems - Use appropriate loadings for Class IVa or IVb soils as appropriate. Soil Resource Group C This soil resource group includes the following soil mapping units: Soil Name Mapping Unit Percent of County a; i Doss Ds C, DTD, DsD 2.8 Kerrville Ku G, KeD, KfF 9.8 Spires STC 2.9 15.5X?' Detailed soil data of each of the above named soils can be found in the ~ Kerr County Soil Survey Report and is not included here. This soil resource group, which makes up 15.5 percent of Kerr County has greater limitations for on-site waste disposal than the previous group. This soil resource group is general unsuitable for conventional septic tank systems. If sites on this soil resource group are to be used for on-site wastewater treatment and disposal, an alternative system should be used. The major limitation with this soil group in the shallow depth of soil over marl and cemented limestone. An additional problem occurs with soils of this group when found on the mid to lower slope positions in the .. :~ landscape. During wet periods, water accumulates on top of the cemented limestone and flows downslope to create temporary perched water tables in the soil profile and may even create springs and seeps at various locations on downslope sites. The soils of this resource group have soil depths of over 18 inches but generally less than 36 inches, thus making the sites unsuitable for conven- tional systems. However, there is suitable soil depth for adequate treat- ment and disposal if the wastewater is applied at proper depth, under uniform distribution and dosed at a conservative loading rate. The system of choice for this resource group will be the Low Pressure Pipe system,'• with distribution lines placed 8 to 12 inches below the ground surface. With uniform distribution and low loading rates, these soils should provide f adequate treatment of the wastewater. The exception to this would be areas where the perched water table may rise within 12 to 18 inches of the soil surface. These areas should be avoided for field line placement or a curtain drain must be installed immediately upslope of the field area to intercept this water and divert it off the field area. Loading rates for the LPP systems on test sites should be conservative, ranging from 5 to 6 ft2/gal for the Kerrville soil and 6 to 7 ft2/gal for the Doss and Spires soils. The pretreatment system for the LPP system, should consist of a two compartment septic tank and a pump tank of suitable size to afford at least 1 day of storage above the pumping capacity,. On some sites of this resource group, soil depths may not achieve the minimum 18 inch requirement. On these sites, some fill material may be brought in to cover [he field [o a depth of 3 to 4 inches to achieve the i :~ minimum depth requirement. This fill should be topsoil quality and suit- able for lawn establishment. Typical Properties of Soil Resource Group C Well drained soils on sloping, undulating and hilly terrain that formed in interbedded limestone and calcerous marl or indurated limestone. These soils are moderately deep with soils depths generally ranging from 18 inches to 40 inches. The soils have no seasonal high water table but may have a temporary perched water table during wet periods. This results from water perching on the cemented limestone ledges underneath the soil and flowing laterally on these ledges to the point of coming to or near [he surface at points downslope. This results in the ty~"ical springs and seeps 4 common on these hillside soils. Surface Soil: Clay loam to silty clay, dark gray- ish brown to reddish brown. Subsoil: Clay to silty clay loam, dark red to reddish brown to yellow- ish brown. Substratum: Indurated fractured limestone to interbedded marl and weakly cemented limestone. Depth 12 24 x, 36 xxxxxxxxxxxxxxxx, xxxxxxxxxxxxxxxx~, xxxxxxxxxxxxxxxx Provisionally Suitable Unsuitable Substratum 48 60 ~~ i Type of System to be Used: Recommended - Low pressure Pipe System Alternatives - Pretreatment and surface application. Loading Rates to be Used: LPP - 5.0 to 7 ft2/gal/day with higher loadings on Kerrville soils and lower loadings on Doss and Spires soils. Alternatives - Use appropriate loadings for Class IVa soils. Soil Resource Group D ? This soil resource group includes the following soil mapping units: Soil Name Napping Unit Percent of County Comfort ECC 5.1 Eckrant ERG, ECC, TTC 24.3 Purees PTD 7.6 Real KnG ,:3.5 , Roughcreek TRC f 1.6 Tarpley TRC, TpB, STC 5.7 Tarrant TTC, PTD 20.4 68.29. Detailed soil data of each of the above named soils can be found in the Kerr County Soil Survey Report and is not included here. This soil resource group constitutes the major soil group of the county, occupying approximately 68% of the land area. This soil group has severe limitations with regard to on-site waste treatment. These soils are characterized by conditions of steep slopes with less than 18 inches of soil present over cemented but fractured lime- stone. These soils offer the highest potential for contamination of sub- surface and surface waters of Kerr County. Due to the limited amount of soil present on sites of this resource group, adequate treatment of wastewater cannot be accomplished by the ..-, 16 natural soil. Therefore, pretreatment of the wastewater beyond that offered by a septic tank will be necessary before final soil application and disposal.Y This pretreatment should consist of aerobic degradation of the wastewater organics and disinfection of the treated effluent prior to soil application. The aerobic treatment alternatives are described in the system design report and should be sufficient to produce secondary quality effluent, namely 20 mg/1 BOD, 20 mg/1 TSS, and nitrify the ammonium to less than 4 mg/1. Disinfection should be sufficient to meet recreational water quality standards. The treated effluent can then be applied to the soil, on or near the surface for final polishing and phosphorus removal. Surface ror subsurface.,, irrigation as described in the system design..-report would be the desired- v method of soil application. The other alternatives on sites of this soil resource group would be elevated fill systems or evapotranspiration beds. Both of 'these alterna- tives are very expensive to install due to the need to import large amounts of fill material and gravel. The concern with leaking liners is ET systems: are great enough that, on these soils, such systems should be installed with double liners and leak detection or with aerobic pretreatment systems to meet the above listed limits of treatment and disinfection. Many sites in this soil resource group will have areas of rock out- crop and slopes exceeding 15 percent. These areas should be avoided when installing the final disposal field. It is necessary that final treatment in the soil be done on a vegetated site to offer final polishing of the effluent. '~' i ; Typical Properties of Soil Resource Group D Well drained soils found on undulating, steep and hilly terrain that formed in weathered limestone or interbedded limestone and marls. These soils are shallow with typical soil depths of 8 to 16 inches. Depth Surface Soil: Clay to clay loam, dark reddish brown to dark grayish brown to dark grey. 12 Subsoil: Clay, dark reddish brown to dark greyish brown. 24 Substratum: Fractured indurated limestone to weakly cemented limestone 36 and marl. '~ 48 60 Unsui[able Substratum xxxxxxxxxxxxxxxx, xxxxxxxxxxxxxxxx', xxxxxxxxxxxxxxxxl xxxxxxxxkxxxxxxx; xxxxxxxxxxxxxxxxl xxxxxxxxxxxxxxxxl Type of System to be Used: Recommended - Pretreatment and irrigation. Alternatives - ET and elevated fill system. Loading Rates to be Used: I~ ~ Pretreatment and irrigation - Use the recommended rate as given in the system design manual. ,~ Other - Recommended design rate for ET and fill system. Soil Resource Group E' This soil resource group includes the following soil mapping unit: Soil Name Mapping Unit Percent of County Rock Outcrop ERG 5.1 Orif OE 0_4 ,. is Detailed soil data of each of the above named soils can be found in the Kerr County Soil Survey Report and is not included here. This soil resource group, while officially makes up 5.5 percent of Kerr County, is actually somewhat more prevalent than this number indi- Cates. Many areas within soil resource group D, having rock outcrop and slopes exceeding 15 percent, should be included in soil resource Group E. Soils of this group have such severe limitations with regard to on-site wastewater treatment, that they are generally unsuitable for any type of on-site system as these soils are characterized by conditions of steep slopes with little or no soil present or sites along creeks and streams subject to frequent flooding. Since there are usually soils of the other resource groups immediately adjacent to soils>:of this .group, usually 4 a sufficient area of usable soils can be found on most sites. Typical Properties of Soil Resource Group E Since the soils of this group are basically non-soils or unusable soils such as rock outcrop or gravelly or stony soils immediately adjacent to creek banks, Lypicai descriptions or system data is not appropriate for this group. This group is not usable for on-site waste disposal.. V SUMMARY OF SOIL GROUPINGS The following table summarizes the ratings for on-site waste disposal systems for the soil resource groups of Kerr County. Through the selection of appropriate modified and alternative systems, on-site waste disposal systems can be successfully operated on 95 percent of the land area in Kerr County. This compares to only 4.4 percent of the land area deemed suitable 19 for conventional septic tank/soil absorption systems as classified by the "Construction Standards of the Texas Department of Health." The systems proposed in this report are systems that have been researched, demon- strated, ad evaluated under actual field operating conditions for several years in numerous locations in Texas and other states across the U. S. As more experience is gained and data generated as to the operation and success of alternative systems under Kerr County conditions, other modifications or alternative type systems may be recommended to reflect system success under the variable soil and site conditions found in the county. System design and recommendations in this early stage of the program is, by necessity, conservative in nature to ensure adequate F protection of the water of the region. '= ' e Table 1. Summary of Ratings Soil Conventional Modified LPP Pretreatment ET or Resource or Conventional Systems and Soil off-site Group Gravel-less Systems Surface Disposal Systems Application A S S S S -- B US S S S -- C US US S S -- D US US US S S E US US US US S S - Suitable for Use US - Unsuitable for Use ~~. VI SOIL EVALUATION PROCEDURES Since on-site soil absorption systems are dependent on the soil for final absorption and treatment of the wastewater prior to such entering the water cycle, a thorough and complete soil evaluation is needed for any site prior to permitting and construction of an on-site waste system. 1. Soil borings with a hand or power auger or backhoe pits should be taken in the area to be used for soil absorption systems. Several such borings on a 50 grid should be taken to depths of at least 48 inches unless hard rock is encountered at a lesser depth. 2. Evaluation of these borings by experienced field soil scientists or soil evaluators should determine such chara„cteristics as soil texture, ,~. soil structure, soil drainage, shrink-swell potential, soil depth, and soil permeability. The soils on a site will then be placed in one of five soil classes as follows: Class I - Sandy Class II - Coarse Loamy Class III - Fine Loamy Class IVa - Clayey, low to moderate shrink-swell potential Class IVb - Clayey, high shrink swell potential Each soil factor listed above will be evaluated under criteria listed in Table II of this report. 3. Overall site suitability will then be determined by the total site and soil evaluation procedures as detailed in Table II. This procedure indicates the site to be suitable, provisionally suitable, or unsuit- able for the conventional, septic tank, soil trench absorption system. ^^<1 4. Soil loading rate determination shall then be made only after a soil site evaluation had indicated the soil to be suitable or provisionally suitable for an on-site waste system including alternative systems. A permeability or percolation test or other approved methods of deter- mining soil permeability shall be estimated to determine the rate at which sewage effluent can be expected to be absorbed by [he soil. This rate shall be determined by using a value of 4 to 10 percent of the soil permeability to calculate the trench bottom required to prop- erly dispose of the projected daily sewage flow. 5. The depth of the permeability test holes shall not be determined until a soil evaluation is completed and the limiting zone, if any, is iden- tified. The depth of the test holes shall beFas follows: ' (a) If the limiting zone is located 48 inches or more from the min- eral soil surface, the zone of the permeability holes shall be 6 inches below the depth of the proposed infiltration surface bottom. (b) If the limiting zone occurs at least 20 inches, but less than 48 inches from the soil surface, the permeability holes shall be excavated to a depth of 20 inches. 6. The soil permeability can be estimated from soil evaluation procedures and experience of the evaluator. Until a data base of background information is generated, soil permeability can be run by the double- time method at appropriate depths. 7. If the percolation test is to be run to provide the estimated soil permeability, the procedures to be followed are detailed in the Construction Standards Y.andbook .002 (g). M~ LL SOIL LOADING RATES Once the soil and site evaluation is completed, the suitability of the site determined and the estimated soil permeability or percolation rate measured, the soil absorption rates and corresponding absorption area requirements can then be determined. These rates for various systems are found in the system design manual. SOIL FACTORS AND EVALUATION Unless soil characteristics have been previously established, soil !~ borings should be taken in the area to be used for soil absorption systems. Several such borings should be taken to depth of at least 48 inches or until hard rock is encountered. From these soil. borings ad observation of rs core samples, most of the significant soil characteristics can be evaluated and a determination can be made as to the suitability of the soil to absorb septic tank effluent. The important soil characteristics which should be determined by the inspector or local health department are as follows: (1) Texture - The relative amounts of the different sizes of mineral particles in a soil ate referred to as soil texture. All soils are composed of sand, (2.0-0.05 mm in size); silt, which includes inter- mediate-sized particles that cannot be seen with the naked eye, but feels like flour when pressed between the fingers (0.05-0.002 mm in size); and clay, which is extremely small in size and is the mineral particle that gives cohesion to a soil (less than 0.002 mm in size). The texture of the different horizons of soils may be classified into four general groups and shall be used for determining the application rates shown in the system design manual. '~~ 23 TABLE II Su-..;.pry of criteria for gzou^.d absorptio^ of seczge effluent developzd for site spacif is evaluatio r.s. FACTORS - ~ CLASSIFICATIOS PROBISI05:+LLY SLIIA3LE (S) StiIL'.~LE (PS) 1/ CSSCI T.45LE (C) 1. Topography Slopes 0-li£ Slopes 15-30: Slopzs greater than 307,. Conplex slopzs. 2. Subsoil Soil Class I L II Soil Class III b ri'a Soil Class ICb Texture Sandy Soils Clayey soils Clayey soils cith high Loary Soils cith loo shrink- high shrink-sve11 svall potential petzr.tizl 3. Subsoil Sandy Soils Angular or Sub- P_zty Structure Structure Lowy Soils zr.gular blocky leathered reek D;assicz clayey soils. 4. Soil Depth lezthered rock leztF.ei ed bedrock , Faat herad rock or ten- or consolidzted or cotta olio_ted selidated bedrock le>s bedrock greater chin rock fron 35 to 48 tF.=_a 35 ire hzs bzloc ES ir.c hes below ground ir.c hes bete: ground ground surface. surfzce su:fzce. 5. Rzstrictice Sonz w-i thin 35 i^.c hzs Res :ricace ho: izon of th=_ ground surface. cithin 35 in ch=_s of tha gr oua'_ surface er be loo the tranch bo ttor. 6. Soil Draicage a. Ir,te rn_1 No 2taira ge Drainage nottles nottles cichir. (ch:on_ 2 er less) 36 i.-.c hes of the cichin % inches of ground surf zee. thz ground surface. b. External Arzas subject to a 10 gear flood. Depressioral zrzzs cithout zdeyuate drzir,z gz. 7. Soil Pzrnezbility >0.6 ir./hr 0.2-0.6 in/h: <0.2 ir./hr (30 ein pert) (30-9D r.ir. part) (>90 ci r. part) b. O:he: :ill ra:zria 1. ?o czr,t ial hez lch hazards or ground- vater contaaina[ion. 1/ Site cay be recl assified iron tinsuitable co Procis Tonally Suitable under certain conditions using acceptable site or syster. nodif icacions. (a) SOIL CLASS I - Sandy texture soils contain more than 70 percent sand-sized particles in the soil mass. These soils do not have enough clay to be cohesive. Sandy soils have favorable sewage application rates, but may have a low filtering capacity leading to malfunction due to contamination of ground water. The sandy group includes the sand and loamy sand soil textural classes and are generally considered SUITABLE with respect to texture. (i) Sand: Sand has a gritty feel,, does not stain the fingers, and does not form a ribbon or ball when wet or moist. (ii) Loamy Sand: Loamy sand has a gritty feel, stains the fingers (silt and clay), forms~a,weak ball, and cannot q.. ,: be handled without breaking. (b) SOIL CLASS II - Coarse loamy texture soils contain more than 30 percent sand-sized particles and less than 20 percent clay-sized particles in the soil mass. They exhibit slight or no sticki- ness. The coarse loamy group includes sand loam and loam soil textural classes and are also generally considered SUITABLE with respect to texture. (i) Sandy loam: Sandy loam has a gritty feel and forms a ball that can be picked up with the fingers and handled with care without breaking. (ii) Loam: Loam may have a slightly gritty feel but does not show a finger print and forms only short ribbons of from 0.25 inch to 0.50 inch in length. Loam will form a ball that can be handled without breaking. 25 (c) SOIL CLASS III - Fine loamy texture soils contain less than 35 percent clay-sized particles and not more than 30 percent sand- sized particles in a soil mass. They exhibit slight to moderate stickiness. The fine loamy group includes sandy clay loam, silt loam, clay loam, and silty clay loam textural classes and are generally considered PROVISIONALLY SUITABLE with respect to tex- Lure. (i) Silt Loam: Silt loam has a floury feel when moist and will show a fingerprint but will not ribbon and forms only a weak ball. (ii) Silt: Silt has a floury feel when moist and sticky when wet but will not ribbon and forms a ball that will , tolerate some handling. (iii) Sandy Clay Loam: Sandy clay loam has a gritty feel but contains enough clay to form a firm ball and may ribbon to form 0.75-inch to 1.00-inch long pieces. i (iv) Silty Clay Loam: Silty clay loam is sticky when moist and will ribbon from one to two inches. Rubbing silty '~ clay loam with the thumbnail produces a moderate sheen. Silty clay loam produces a distinct fingerprint. (v) Clay Loam: Clay loam is sticky when moist. Clay loam forms a thin ribbon of one of two inches in length and produces a slight sheen when rubbed with the thumb- nail. Clay loam produces a nondistinct fingerprint. .~ ~~ (d) SOIL CLASS IV - Clayey texture, soils contain 35 percent or more clay-sized particles and sandy clay, silty clay, and clay. These soils are further divided into two subclasses according to type of mineralogy. Subclass IVa -These soils have more than 40 percent calcium car- bonate. When wet they are slightly sticky to sticky; when moist, are friable to firm and when dry, are slightly hard to hard. They do not shrink or swell extensively when dried or wetted. Subclass IVa should be considered provisionally SUITABLE as to '~ texture. Subclass IVb - These soils have Montmorrilonite clay mineralogy or a mixture of Montmorrilonite and other clay minerals. They f have less than 40 percent calcium carbonate. Montmorilonite is a 2:1 clay which has a very high shrink-swell potential. The 2:1 and mixed mineralogy clays, when wet, are very sticky and very ,~ plastic; when moist they are very hard to extremely hard. Sub- 41~~ class IVb should be considered UNSUITABLE as to texture. ~~ (2) Soil Structure - Zn many soils, the sand, silt, and clay particles tend to cling to stick to one another to form a ped or a clump of soil. This is known as soil structure. Soil structure may have a significant effect on the movement of effluent through a soil. The structure may determine the rate of movement of liquids through clayey soils. Structure is not important in sandy-textured soils or in loamy-textured soils, and these types of soils are generally considered SUITABLE as to structure. The three kinds of soil ~ structure that are most significant in movement of sewage effluent ~' z ~ through clayey soils ate blocky platy, and the absence of soil structure or massive conditions, are described as follows: (a) Blocky Soil Structure - In clayey soils, if the soil exhibits many peds of angular and subrounded peds, then the soils have blocky structure. The sewage effluent may move between the cracks of these blocky types of peds. Blocky soil structure in clayey soils is frequently destroyed by mechanical equipment manipulating the soil when it is too wet. Trenches for nitrification lines being placed in clayey soils with blocky structure should be considered PROVISIONALLY SUITABLE as to structure. (b) Platy Soil Structure - If clayey sods fall out into plate- like sheets, then the soil would have platy structure. Water or effluent movement through these horizons would be extremely slow and the structure should 'be considered I' UNSUITABLE. k4~~ (c) Absence of Soil Structure - Some clayey soils exhibit no structure aggregates. In these kinds of soils, percolation would be zero or extremely slow. Such structure should be considered UNSUITABLE. (3) Soil Depth - The depth of soils classified as SUITABLE OR PROVI- SIONALLY SUITABLE as to texture and structure should be at least 36 inches when conventional ground absorption systems are to be u*_ilized. Shallower depths may be used provided the bottom of the nitrification trench is constructed at least two feet above bedrock. -~ _