Septic System: Hillside Installation (1976)

the manual of septic-tank practice is still the best publication ever provided for the septic contractor or environmentalist one of the most important items covered in the new manual is the use of drop boxes drop boxes should be used where the fall of the ground exceeds approximately six inches in any direction an improperly installed system on a hill leads to many such failures a failing septic system may contain many soil is a natural resource do not destroy it protection of the natural absorption properties of the soil is important working soils when they are wet is probably the most harmful thing a contractor could do underground utilities can short-circuit a drop box system stripping a lot destroys the texture and porosity of the soil as well as compacting the subsoil before the contractor starts on the field he must inspect the site to be sure that the system can be installed in compliance with local ordinances in most cases a contractor is provided with a plot plan on how the septic system should be installed these plot plans are prepared by the homeowner septic contractor or engineer contour lines are shown on the plot plan but it is important that the absorption trenches follow the ground surface contours so there are no variations in trench depth check the soil to see that the moisture content is not too high a handful should not mould when squeezed together in the hand locate the required distance from all lot lines 10 feet is quite common staking out the field before construction begins will save time and eliminate problems the required distance from the lake is measured and marked 50 feet is quite common neighbors Wells must be located and the distance to the proposed field measured also mark the location of the new well the instrument is set up and leveled the distance from the foundation to the proposed tank is measured and marked room is left for the patio the soil pipe must be located and the flowline elevation recorded an elevation of the tank location will determine the depth of the tank hole and if a riser will be needed the length of the tank is measured and marked then the distance to the first drop box is measured a rule of thumb to follow is that the elevation of the first seepage line be the same or lower than the elevation of the flow line of the cast-iron at the house five foot six is lower 30 feet is measured off we will find the same elevation of five foot six and mark the spot the lines must follow the ground surface contours and do not have to be straight flags or grade stakes are used to mark the contours the distance to within 10 feet of the lot line is measured the five foot six elevation will be found and marked each line will be laid out in a similar manner following the exact contour the distance between lines is measured and marked three times the width of the trench is common the elevation of the second line is shot seven foot two is read and recorded each line is laid out and measured a new plot plan is prepared showing all elevations and lengths of lines a copy of this plot plan is used for the permanent record after the system is laid out the supplies and gravel can be ordered place the gravel where it will be handy it is important that the tank hole is not dug too large or deeper than needed a sight rod can be used to measure down to determine the proper depth after the tank hole is dug it is leveled off by hand if dug too deep sand should be used for fill the tank can be measured if necessary normally the supplier will provide you with this information after the hole is dug if at all possible try to route the tank truck around the seepage filled area the tank outlet is normally three inches lower than the inlet make sure the tank Inlet is toward the house this one compartment tank is normally used but available research indicates that a two compartment tank with the first compartment equal to 1/2 to 2/3 of the total volume provides better suspended solids removal which may be especially valuable for protection of the soil absorption system before the tank is disconnected check the elevations to determine if the tank is level the trench between the house and the tank is done very carefully so it will not get too deep the finished grade for all sewer lines should be dug by hand so that they are on a firm base and will maintain a proper pitch a pitch of 1/8 to 1/4 inch per foot is recommended all joints in the sewer line must be watertight and route proof the cast iron must not be pushed too far into the tank the trench for the line between the tank and the first drop box is dug carefully a four inch pitch is recommended the first drop box is set and all joints are cemented the soil between each drop box cannot be any deeper than the top of the gravel in the proceeding line this undisturbed soil acts as a dam to prevent the sewage from running down the slope this is probably the most important point in installing a septic system on a hill the operator can follow the flags and maintain a uniform depth while digging the seepage lines the elevations of the bottom of the trench are shot constantly to ensure that they are leveled a shallow trench such as this has many distinct advantages normally the porousness of the soil is much greater near the surface than it is at a deeper depth and the grass roots will pick up some nitrogen from the sewage the required gravel is then placed on the bottom of the trench and is leveled to the required depth the tile is placed in the drop box the tile must be held in place by rods before the gravel is placed on top to prevent sliding of the tile the gravel is then leveled again making sure that none of the gravel is higher than the flowline out of the drop box untreated building paper is placed over the gravel remember work the soil only when dry lay out the entire field before construction starts dig the line between the drop boxes very carefully the undisturbed soil acts as a dam check the elevation of all lines during construction make sure the top of the gravel is level place untreated building paper straw or newspaper over the gravel to ensure no silt or clay is washed into the trench to plug the pores of the soil after the system is installed and inspected backfilling can begin back filling should be done the same day a rainstorm could completely ruin the system the Health Department should make every effort to inspect a system as soon as completed although it is recommended that the trenches be backfilled by hand it is doubtful that anyone will undertake this operation care should be taken when backfilling around the drop boxes instead of pushing the dirt over the drop boxes carefully drop the dirt on top of them the drop boxes must be marked to warn other contractors that a septic system has been installed for this new home