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Presentation on theme: "LOADING RATES Sara Heger"— Presentation transcript:


2 LOADING RATES - THE THOUGHT PROCESS  The system should last a long time  The wastewater plugs the soil over the long term  Designing the system for plugging is CRITICAL

3 HOW DOES SOIL TREAT WASTEWATER? Groundwater Well Aerobic soil Aerobic soil is needed to treat – remove pathogens – and disperse the treated wastewater back into the environment Horizontal Setback

4 WHAT ARE AEROBIC SOIL CONDITIONS?  Pores filled primarily with air (oxygen)  Aerobic organisms present  Pores are open – not smeared  Air can move through pores – not compacted  Soil is NOT saturated or likely to become saturated

5 SOIL PROPERTIES THAT INFLUENCE WASTEWATER TREATMENT  Wetness conditions  Water movement  Texture  Structure  Restrictive zones or horizons  Landscape

6 TYPES OF FLOW UnsaturatedSaturated  Pores air-filled  Flow is adjacent to particles  Controlled by moisture content and pore diameter  Aerobic conditions  Slower than saturated flow  LTAR related to unsaturated flow  Pores water-filled  Flow is in large pores  Controlled by soils and site conditions  May result in anaerobic conditions  Faster than unsaturated flow

7 FLOW FROM THE TRENCH Zone of saturated or nearly saturated flow Zone of unsaturated flow, majority of flow is vertical Zone of saturation or a restrictive layer, flow will be down hill Sidewall infiltration is limited to depth of ponding in trench

8 Regulations vary: Vertical separation distance : The thickness of air filled soil required between the base of the drainfield and the water table. W WT wt

9 WASTEWATER TREATMENT AND RENOVATION IN SOILS WASTEWATER TREATMENT AND RENOVATION IN SOILS Controlling Factors : Environmental Temperature, moisture, and oxygen levels Wastewater characteristics Loading rates; wastewater strength Types of pollutants

10 WASTEWATER TREATMENT AND RENOVATION IN SOILS WASTEWATER TREATMENT AND RENOVATION IN SOILS Controlling Factors: Soil properties Physical - filtration and sedimentation Chemical - adsorption/precipitation (surface area) Biological - uptake, incorporation, predation, and transformations

11 TIME IS NEEDED FOR TREATMENT REACTIONS  Biochemical processes depend on detention time  Detention time is closely related to  hydraulic loading rates  rate of wastewater movement through soils  soil texture, structure, and density have a huge influence on detention and reaction times

12 SOIL PHYSICAL PROPERTIES - TEXTURE The relative proportion of soil separates (sand, silt & clay) in a soil. Texture influences: Soil permeability and moisture content Biomat formation Treatment of effluent System construction - Soil smearing and compaction

13 SOIL STRUCTURE & WATER MOVEMENT Void spaces between soil peds transmit air and water. Type of structure determines: Direction of voids (soil pores) Direction of water movement Relative rate of water movement Retention time for treatment processes

14 T 1 Biomat begins as incomplete layer at end of trench closest to D-Box where most of the loading is taking place.

15 Trench with a fully-developed biomat T m (mature) Even distribution of wastewater has occurred due to biomat acting as a membrane-type filter.

16 BIOMAT ACTING AS A MEMBRANE FILTER T s (steady state) Soil under biomat is aerobic and air filed. Amount of organic material removed from underside of biomat membrane by soil aerobic bacteria roughly equals amounts added from septic tank.

17 When organic inputs exceed removals and all soil pore spaces are clogged by organic material, then hydraulic failure occurs.

18 ALL SYSTEMS HAVE TWO VALUES  Hydraulic Flow  Organic Loading


20 WASTEWATER LOADING  Wastewater quantity  Hydraulic loading  Residential gallons per bedroom  Wastewater quality  Organic loading  Residential – 300 mg/l  Oxygen demand  Residential and commercial facilities

21 IMPORTANCE OF HYDRAULIC LOAD  The daily flow must not exceed the system’s hydraulic capability  Hydraulic detention time (HDT)  Example: solids are not able to settle in a septic tank if the water moves through too quickly.  Hydraulic overload of the soil  Effluent surfacing

22 TOO MUCH USE  Clean water  Groundwater drainage  Footing drain  Cooling water  Water treatment  Too much use  Over use  Wash day  Cleaning service  Change in use  Master bath  Added bedroom


24 MEASURED FLOWS? HOW OFTEN IS IT MEASURED?  Annually plus---  Average < 70%  Monthly  70-75%  Weekly  80%  Daily  Actual use  Surge flow is determined by measuring flow daily over an extended period of time

25 WHAT IS NEEDED TO CALCULATE HYDRAULIC LOADING  Cycle counter reading  Dose Volume  Time between readings (actual operation)  Elapsed time meter  Pump Rate  Change in value = Total number of units  Minutes  Hours  Time between readings (actual operation)  Water Meter  Present and last reading  Time between readings Pump delivery rate

26 WASTEWATER QUANTITY - SURGES  Surge flows  Daily  Weekly  Seasonal  Flow equalization?


28 COMMERCIAL WASTEWATER  Strength  Usually greater than residential  Operation based  Food preparation  Restrooms  Laundry

29 HIGH STRENGTH WASTEWATER  CIDWT glossary definition 1) Influent having  BOD 5 > 300 mg/L,  and/or TSS > 200 mg/L,  and/or fats, oils, and grease (FOG) > 50 mg/L entering a pretreatment component 2) Effluent from a septic tank or other pretreatment component that has:  BOD 5 > 170 mg/L,  and/or TSS > 60 mg/L,  and/or (FOG) > 25 mg/L and is applied to an infiltrative surface.  Local code definitions may vary

30 RESTAURANT RESULTS - MINNESOTAFOGmg/LTSSmg/L BOD 5 mg/L Restaurants Sampled, # Type of Restaurant Bar Golf Club Service Fast Food

31 RESTAURANT DATA - LESIKAR 2004 STUDY  28 restaurants located in Texas  Sampled during June, July, and August 2002  12 samples per restaurant and 336 total observations  Most conclusive study to date 31

32 PERCENT OF DATA CAPTURED (28 RESTAURANTS) (GEOMETRIC MEAN PLUS ONE STD. DEV.) Parameter Value (mg/L) % Data Covered BOD TSS66487 FOG19781 Lesikar et. al (2006)

33 SUMMARY STATISTICS Lesikar et. al (2006)

34 WASTEWATER ORGANIC RATES Type of Facility Flow(gal/cap/day) lbs. BOD 5 (cap/day) Apartments - multiple family Boarding houses Bowling alleys - per lane (no food) Campgrounds - per tent or travel trailer site - central bathhouse Churches – per seat Dwellings - single family Dwellings - small, and cottages, with seasonal occupancy Factories - gallons, per person, per shift (no showers) Add for showers Laundromats400Varies Office (no food) Schools – boarding Schools - day (without cafeterias, gyms, or showers) Schools - day (with cafeterias, but no gyms or showers) Schools - day (with cafeterias, gyms, and showers) Stores - per toilet room


36 WHAT'S NEXT? MASS LOADING Now that we know the hydraulic and organic values, we combine the two to determine the mass load

37 MASS LOADING  Calculate mass loading to a system  Concentration of constituent in the wastewater  Mass loading based on number of people  Mass (lb) = C (mg/l) x Q (gpd) x  Mass (lb) = P (# of people) x O L (lbs per capita- day)

38 MASS LOADING CALCULATION Residential strength  Calculate mass loading to a system  Concentration in wastewater  Volume of wastewater  Mass (lb) = 140(mg/l) x 200(gpd) x  Mass (lb) = 0.23 lbs per day Commercial strength  Mass (lb) = C (mg/l) x Q (gpd) x  Mass (lb) = 500(mg/l) x 600(gpd) x  Mass (lb) = 2.5 lbs per day

39 MASS LOADING  Calculate mass loading to a system  Number of people  Organic loading rate  Mass (lb) = P (# of people) x O L (lbs per capita- day)  Mass (lb) = 5 (# of people) x 0.17 (lbs per capita- day)  Mass (lb) = 0.85 lbs per day

40 WATER SAVING DEVICES  Decrease water quantity  Assuming no change in mass load  Wastewater strength increases

41 WATER SAVING DEVICE EXAMPLE  Example 4.2 Increasing concentration of TSS  A 4 person household produces 0.56 lbs/day TSS without water saving devices (75 gpd/person).  Then that family switches to water savings devices, and so they only use 60 gpd/person.  What is the change in TSS concentration after water saving devices are installed?

42 EXAMPLE CONT. TSS Concentration (before) = ____ 0.56 lbs/day___ = 224 mg ____ 0.56 lbs/day___ = 224 mg 300 gal x L 300 gal x L TSS Concentration (after) = ____ 0.56 lbs/day___ = 280 mg 240 gal x L 240 gal x L

43 WHAT'S NEXT? CONTOUR LOADING RATE Now that we know the flow and the biological values, we combine the two to determine the mass load

44 MUCH MORE WATER Soil Texture Approximate Natural Recharge to Groundwater (ft/year) Recharge to Groundwater from absorption area* of SSTS - based on ½ of design flow (ft/year) Sand1.030 Sandy Loam0.519 Loam0.415 Silt Loam0.312 Clay Loam0.2511

45 MUCH MORE WATER Soil Texture Typical Saturated Hydraulic Conductivity (in/day) Effluent Loading rate from SSTS - based on ½ of design flow (in/day) Sand9601 Sandy Loam300.6 Loam100.5 Silt Loam100.4 Clay Loam10.36

46 MUCH MORE WATER  It appears to be OK to use conventional soil loading rates for sizing the infiltration areas for both septic systems and MSTS (i.e. getting the effluent from the media into the soil)  The question is what does the effluent do once it gets into the soil?

47 STOP TO REVIEW  Actually 2 Loading Rates:  Infiltration/Absorption Loading  Amount of Effluent/Soil Texture  Organic Loading Rate  Contour/Mounding Loading Rate

48 TWO LOADING RATES Infiltration Capacity


50 WHAT IS GW MOUNDING? Simply, the rise in the groundwater when water is added by man.

51 SO WHAT IS THE PROBLEM?  Reduce the unsaturated zone for pathogen removal

52 SO WHAT IS THE PROBLEM?  Impede oxygen transfer needed to breakdown the biomat oxygen

53 SO WHAT IS THE PROBLEM?  Breakout in downslope areas

54 WHAT AFFECTS MOUNDING? Loading Rate Soil Texture (hydraulic conductivity) Restrictive Layers Depth to Periodically Saturated Soil Depth to Regional Watertable

55 WHAT AFFECTS MOUNDING? Distance to Surface Water Slope Landscape Position System Geometry

56 MOUNDING AND SEPTIC SYSTEMS Low surface area High surface area Sandy SoilHeavy Soil

57 CONTOUR LOADING RATE (OR LINEAR)  Amount of wastewater applied daily along the landscape contour.  It is expressed in gallons per day per linear foot along the contour (gpd/ft of contour)  Mounding is dealt with by limiting contour loading rates to 12 gal/linear foot


59 Contour lines Drainage Direction of groundwater flow CONTOUR LOADING Soil treatment area (Drainfield)

60 Drainage Direction of groundwater flow CONTOUR LOADING Soil treatment area (Drainfield)




64 SOIL TREATMENT SYSTEMS  Soil treatment  Biomat – restrictive layer at infiltrative surface  Biofilm – biological layer developing on soil particles  Biozone – active biological treatment volume in the soil

65 INFILTRATIVE SURFACE  Sized by the loading rate in gpd/ft 2  Loading rate determined by  Natural soil properties  Separation distance  Natural site conditions  Modified site conditions (drainage)

66 LONG TERM ACCEPTANCE RATE Design parameter expressing the rate that effluent enters the infiltrative surface of the soil treatment system Measured in volume per area per time, e.g. gallons per square foot per day (g/ft 2 /day) Determined by evaluating  Texture  Structure  Percolation rate  Effluent quality  Dosing method


68 WHAT CONTROLS LOADING RATE?  Infiltrative surface – biomat/soil interface  Least permeable layer in profile  Horizontal hydraulic conductivity above the least permeable layer

69 BIOMAT INFLUENCES  System: Food  Hydraulic loading  Organic loading  Site: Oxygen  Soil type  Texture  Structure  Separation  Depth  Resting  Pressurization  Geometry [Width]

70 HIGHER QUALITY EFFLUENT DISTRIBUTION  Distribution of higher quality effluent  Lower organic loading  No biomat formation  Greater soil acceptance rate

71 HIGHER QUALITY EFFLUENT DISTRIBUTION  Pressure distribution  Distributes effluent in space and time  Facilitates unsaturated zone below infiltrative surface  Biozone  Effluent treatment  Biofilm development on particles  Time for soil treatment

72 CALCULATING SOIL MASS LOADING RATE 200 (GPD) X 140 (BOD 5 ) X = 0.23 pounds/day For Soil Loading 0.23 / absorption area square feet = lb/day/square foot

73 ORGANIC LOADING TO SOIL (MN VALUES) Soil Texture Group Loading Rate gpd/ft 2 lbs of BOD 5 / ft 2 /day lbs of TSS/ ft 2 /day lbs of O&G/ ft 2 /day Sands Fine sands Sandy loam Loam Silt loam Clay loam, clay

74 RESIDENTIAL SOIL TREATMENT AREA  Soil absorption area based on hydraulic loading  A = Q / Loading Rate (soil hydraulic)  Soil absorption area based on organic loading  A= organic loading/loading rate (soil organic)

75 RESIDENTIAL DRAINFIELD AREA REQUIREMENTS Example: Size a soil trench system in silt loam soils for a system that is treating 400 gpd with BOD 5 effluent of 400 mg/L Based on hydraulic loading Ra = 0.50 gal / ft 2 -day Drainfield = 400 gal/day = 800 ft gal/ft 2 -day Based on organic loading R OL = lbs/ft 2 - day BOD 5 lbs/d = 400 mg/L x 400 gal/d x = 1.33 lbs/d Drainfield = 1.33 lbs/day = 2217 ft lbs/ft 2 -day


77 FLOW PATTERN IN A GRAVITY TRENCH  Biomat Growth (t = 0 = start )

78 FLOW PATTERN IN A GRAVITY TRENCH  Biomat Growth (t = growth)

79 FLOW PATTERN IN A GRAVITY TRENCH  Biomat Growth (t=mature)



82 SUMMARY  Aerobic soil conditions are necessary  All wastewater has two values  Hydraulic  Organic  Mass loading should be considered particular with HSW  CLR is an important variable to consider to minimize mounding


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