Septic Tanks Gravity treatment Separation Sludge sinks Scum floats Storage Septic Tanks, Holding Tanks & Pump Tanks Bacteria SCUM breakdown CLEAR ZONE Chemical SLUDGE WW Strength= Organic Load Effluent Screen Cleaning Effluent Screens Screen must be accessible Screen is washed off at the inlet end of the tank to protect against cleanings flowing directly out the outlet Some units have protection against outflow Surveying Abbreviations Installation Keys Level Bottom BM: Benchmark An established point with a permanent elevation [Set elevation] Elevation In & Out Dealing with material BS: Backsight (or TBM) Shifted bench mark (Temporary Benchmark) RR: Rod Reading Elevation reading [Today] HI: Height of Instrument The BM elevation + the Rod Reading on the BM *
The Math Elevations Grade rod 107.2 HI= 107.2 Height of Instrument {HI} = [BM elv] + RRBM 100 + 7.2 = 107.2 16.7 7.2 Bottom elevation = Plan Depth Bedding 100 = BM Existing Grade Tank 96 Outlet per Plan 96 5 0.5 = 90.5 Bottom Rod setting = HI Bottom elevation 60 107.2 90.5 = 16.7 Tank bottom Bedding = 6 (0.5 ) What s the rod reading for the bottom of the excavation? Being Safe is Important Accidents: Why do they happen? Rushing Eyes not on path Eyes not on Task Line of fire Cell Phone Site Safety Spoil Pile Vests Hard hats OSHA Competent Person At least 2 feet back from the edge of trench.
OSHA Soil Terms Cohesive Clay Sticks together Granular Sand Flows out of the bucket Soil Identification Solid Rock Type A (not Fill) Cohesive > 1.5 tsf Type B Not an A or C Type C Cohesive < 0.5 tsf Granular Water Visual Testing Manual Testing Soil Penetrometer Area Reading Locates Local One Call Soil sample Flat surface Size of a softball Excavation Soil Faces Safety Requirements Exits Within 25 Ladders [3 ] Protection Systems Shoring Trench boxes Sloping Push to red line Reading Tons per Foot2 [TSF] Sloping 7.5 Class A ¾:1 Class B 1:1 Class C 1.5:1 10 4 tank bottom
Calculating Tank Capacity Tank INSIDE dimensions Operating depth is measured to the INVERT of the OUTLET REMEMBER: 1 = 0.083 Ft, 1 cubic foot = 7.5 gallons Volume = Length X Width X Depth 4 x 7 x 60 /12 /ft = 140 cubic ft (ft3) 140 ft3 X 7.5 gallons/ft3 = 1050 gallons Materials Concrete Plastic Fiberglass Metal * Compartments Concrete Thoughts Single Small Dosing Tanks First tanks in series Weight Two Typical Septic tanks Watertightness Three For dosing from 3rd Comp Delivery of the Tank Delivery Placement Construction Poured in place Separation from saturated soil Concrete Tanks How? Additional work Can determine the tank material choice Top seam Mid-seam
Tank Seams Good Seams Integrated [Notched] Mastic material Mechanical connection Sealing Concrete Tank Seams Joint made at point of manufacture Butyl rubber band applied prior to installation Watertightness Testing Water balance Fill above the seams into the manhole Set for 24 hours Come back Refill 4 hour drop < 1 Hydrostatic test Standard C 1227, ASTM (1993) Vacuum Preparation Pass/fail criterion Seal tank, fill with water, and let stand for 24 hours. Refill tank. Approved if water level is held for 1 hour Seal tank, fill with water, and let stand for 8 to 10 hours. Refill tank and let stand for another 8 to 10 hours. Approved if no further measurable water level drop occurs Vacuum Test 4 hg for 5 minutes NPCA (1998) Preparation Pass/fail criterion Seal tank and apply a vacuum of 2 in. Hg. Approved if 90% of vacuum is held for 2 minutes. Seal tank and apply a vaccum of 4 in. Hg. Hold vacuum for 5 minutes. Bring vacuum back to 4 in. Hg. Approved if vacuum can be held for 5 minutes without a loss of vacuum. Vacuum Testing Vacuum pump Pipe seal Plate seal to top of riser or tank Gauge to measure vacuum
Risers & Other Penetrations Plastic Tank Thoughts Strength Backfilling & Bedding Material Water Watertightness Be careful of vacuum Compartment Walls Granular Backfill Lids with Screws How do I keep the screws from stripping?? 1. Start all screws thru lid into riser holes 2. Tighten all screws finger tight in star pattern 3. Finish tightening with hex wrench in star pattern Star Pattern 1 3 4 2
Burying Tanks Proper Backfill Backfilling Around Tanks Tied into Soil Fill with Water as Backfilling * Backfilling Around Tanks Backfilling Around Tanks 5th lift of backfill Setting tank on bedding 2nd lift of backfill 7th lift of backfill Pipe Bedding, Inlet & Outlet Pipe Installation Installing Risers 3rd lift of backfill First lift of backfill 4th lift of backfill Compaction Backfilling Around Tanks Final lift of backfill, Compaction & Grading 6th lift of backfill Backfilling Round Tanks Plastic or Fiberglass Tanks Properly backfilled tank excavation with compacted backfill & pipe bedding Compaction Force Bedding Movement Bellies in inlet & outlet pipes due to settling of supporting backfill Force Vector
Tanks w/ Granular Backfill ATU Basics Tank Air Source Distribution Return Access Floating Tanks Floating Tanks Properly Ballasted S T Buoyancy= B Vol. x 8.34 #/gal Times Safety factor [1.5] Restraining Force= Weight of soil [80 #/cuft]= S Weight of tank= T B Metal: Run & Hide! The Math Buoyancy from groundwater (B) = S 1,500 gal x 8.34 #/gal 12,510 # X 1.5 (safety factor) 18,765 # T B Force Down= Weight of Soil (S): 4 x 7 x 1.5 x 80 #/cuft = 3,360 # Total (S+T) = 3360# + 9200# =12,560# Plastic = 3360# + 500#= 3860#
Placing the Tank Access Requirements Proper elevation In Out 20 inch manhole Level bottom Within 6 of each edge Bedding Each compartment Tank Label Name, Model, Capacity Warning label Backfill Material Compaction Settling Keeping the Tank Safe Insulation [Cold Weather] 24 of Soil 1 of Insulation*= 12 of soil Always a plus Manholes *Closed cell, high density foam insulation At the surface for management Keeping the Tank Safe Tank & Riser Insulated Insulboard does not have to be tight against riser Fill space between riser and isulboard with soil
Holding Tanks Tank Materials Concrete Plastic Anchoring system Slide 44 Watertightness Access Requirements Critical 6 pump out stack Be EXTRA Protect from run off careful Sealing cement Siphon Discharge Siphon Discharge Required in some counties Alternate dosing device to pump Must have grade to use Alarm a Good Idea Usually installed by tank manufacturer Various sizes available Can be screened Must be primed before use Can be in 2nd or 3rd compartment
Siphon Discharge Demo Dual siphons in tank Note exit height 2 Discharge Pipe To 1.5 Laterals Siphon Discharge Demo 1.5 Sched 40 PVC Four 50 laterals 5/32 holes @ 24 OC Squirt Ht= 24-27 Pump Tanks Wiring Proper size Be careful of the power Watertight Combo Tanks Wall must be designed Hard conduit around the tank to handle the weight Sizing must be adequate Tank Abandonment Questions?