According to Soils Extension 

 Specialist Bobby Carlile of North 

 Carolina State University these poor 

 soil conditions are not restricted to a 

 single geographic area. They can be 

 found just about anywhere. Along the 

 coast these conditions are confounded 

 by the presence of high water tables. 

 And from Carlile's perspective, that's 

 where the real headaches begin for 

 waste disposal. 



Confounding the issue 



"When you try to put sewage in 

 ground with a high water table, it's 

 just like trying to put water into a jug 

 that's already full," he explains. "You 

 don't get the degree of treatment that 

 you have in aerated soils." 



Carlile estimates that in many areas 

 of coastal North Carolina nearly 90 

 percent of the soils are unsuitable for 

 conventional septic systems. 

 Nationally, the United States Environ- 

 mental Protection Agency estimates 

 that as much as one-half of the soils are 

 unsuitable. Faced with those grim 

 statistics, property owners in the past 

 have had little choice but to invest in 

 expensive chemical treatment units or 

 drainage systems or simply sell their 

 land. But Carlile believes that this isn't 

 always necessary. In many instances 

 the homeowner or developer can install 

 a modified septic system that will work 

 where a conventional one won't, and at 

 only a slightly higher cost. The key he 

 says, "is to make the system fit the 

 site." 



And that's exactly what Carlile has 



been doing over the past three years 

 with UNC Sea Grant. To date his two 

 most successful designs involve a low 

 pressure distribution system and a 

 mound system. 



The low pressure system 



The low pressure distribution system 

 utilizes the natural soils at the site. In 

 theory it is nearly identical to the con- 

 ventional septic system except that a 

 low pressure pump enables the effluent 

 to be distributed more efficiently and 

 uniformly over the entire soil absorp- 

 tion area. Distribution is accomplished 

 by pumping the effluent under low 

 pressure through a network of small 

 diameter, perforated PVC (plastic) 

 pipe. In addition, the pumping station 

 doses or limits the amount of effluent 

 entering the field at a given time. The 

 combined effects of better distribution 

 and dosing help prevent the soil in the 

 absorption field from becoming clogged 

 and saturated. Because the soil is then 

 able to "dry out" and re-aerate be- 

 tween doses, the level of effluent treat- 

 ment is improved. 



In the conventional system, the 

 force of gravity moves the effluent 

 through the system and the overall 

 orientation of the system must be 

 downhill. Unfortunately, in low-lying 

 areas typical of the coastal plain, such 

 sites are rare or often located 

 dangerously near sources of ground 

 and surface water. With the low 

 pressure distribution method a pump 

 rather than gravity is used to move 

 wastewater through the system. Dis- 



tribution lines do not have to be placed 

 as deeply in the ground, and, if 

 necessary, the effluent can be pumped 

 upward, away from water tables and 

 into better soils. 



Carlile estimates the cost of the 

 typical low pressure system at be- 

 tween $1,200 and $1,500, about 25 per- 

 cent more than a conventional septic 

 system. But it requires virtually the 

 same amount of land as a conventional 

 absorption field. 



The mound system 



The mound system is another 

 modified system that Carlile has 

 worked with. Because an essentially 

 "artificial" system must be built, he 

 considers the mound technique "a last 

 resort" for areas where natural site and 

 soil conditions are extremely poor. 



In this system the absorption field is 

 constructed above ground in a soil 

 mound. The mound itself is a layered 

 hill of loamy fill, gravel and sand which 

 effectively treats the wastewater 

 before it reaches the natural soil sur- 

 face. A low pressure system is placed 

 inside the mound to ensure that the ef- 

 fluent is evenly distributed. 



The one drawback to the mound 

 system is its cost — nearly double that 

 of the low-pressure system, depending 

 on how far the fill material must be 

 transported. Despite the high price 

 tag, Carlile believes it is one of the least 

 costly alternatives for property own- 

 ers faced with particularly troublesome 

 sites. 



While the alternative systems are 



