Research: beachhead for an underground revolution 



There are over two million septic 

 tanks in North Carolina, with some 

 50,000 new ones each year. Nowhere 

 do they fail with more consequence 

 than along the coast, where half a 

 million residents use them, and where 

 an estimated 70 to 90 percent of the 

 soils are now thought to be unsuitable 

 for conventional, on-site sewage 

 disposal. 



Because the stakes were so high, and 

 the alternatives to septic tanks so 

 limited and expensive, Sea Grant 

 began funding research into coastal 

 septic systems in 1977. The research, 

 led by Bobby Carlile of North 

 Carolina State University (NCSU), in- 

 spired an underground revolution in 

 on-site sewage disposal. What Carlile 

 discovered was that many of the septic 

 tank's limitations could be overcome if 

 the flow of effluent from the tanks into 

 distribution lines was controlled in 

 even "doses." This he managed with 

 low-pressure pumps, which 

 periodically filled each distribution 

 line, along its entire length, and used 

 the greatest possible area of soil for 

 treatment. For marginal soils, es- 

 pecially dense clays with moderately 

 high water tables, the distribution 

 lines could be laid 12 inches deep. The 

 cost remained low, about $800 for 

 gravel, pipes and pumps (labor was ad- 

 ditional). 



For very severe cases, on sites with 

 impermeable clays or very high water 

 tables, Carlile built his low-pressure 

 systems into mounds of soils layered to 

 percolate the wastewater safely. Since 



the mound was essentially a distribu- 

 tion field construction above ground, 

 soils had to be moved to the site, and 

 costs ran into several thousands of 

 dollars. 



On test sites along the coast and in- 

 land, Carlile built these systems and 

 tested them. Around them he dug sam- 

 pling wells, where he measured water 

 quality in the surrounding soils. The 

 systems worked; wastewater was con- 

 tained and treated. On test sites near 

 estuaries, sampling showed that the 

 new systems could operate without 

 raising the level of contaminants in the 

 water. 



With the designs thoroughly tested, 

 Carlile and his research associate, 

 Dennis Osborne, took them directly to 

 county health departments, 

 workshops, conferences and training 

 sessions, where the team schooled 

 sanitarians and contractors on how the 

 system worked. Half of the state's 

 coastal counties wrote the new "alter- 

 natives" into their sewage-disposal 

 guidelines. New construction valued 

 well into the millions of dollars began 

 on sites once classified as unsuitable 

 for development. But just as impor- 

 tantly, dozens of failing septic systems 

 were replaced with the new designs. 



It was something of a renaissance for 

 the lowly septic tank, and demand for 

 Carlile's help began to reach him from 

 the Piedmont, the mountains, and 

 from other states. But the real frontier 

 turned out to be back home, along the 

 state's barrier islands. 



There, the antagonists were named 



Corolla, Leon or Duckston, the wet 

 sandy soils so vastly different from the 

 clays just a short drive inland. On the 

 islands, growth was explosive, and 

 most of it still depended upon septic 

 tanks. 



Bob Rubin, an NCSU extension 

 specialist who has often worked with 

 Carlile applying the new designs, says 

 that "about fifteen percent of the land 

 on our barrier islands is suitable for 

 conventional on-site sewage disposal, 

 and much of that is in maritime 

 forest." 



Of course, much more than that 

 amount of property is being developed, 

 often with septic tanks. Are they all 

 failing? 



"Until relatively recently, most peo- 

 ple on the barrier islands did not know 

 they had septic-tank problems," 

 Rubin says. "Those sandy soils are so 

 porous that the effluent doesn't rise to 

 the surface. But it's usually not being 

 treated either. Very often, you can't 

 tell a system's failing, and most people 

 don't try to find out. You know, 'out 

 of sight, out of mind.' " 



But many acres of valuable shellfish 

 waters were closing along such places 

 as Atlantic Beach and Surf City, and 

 the blame was laid on septic tanks. 

 Carlile sampled dredge-and-fill sites 

 along finger canals at Atlantic Beach 

 and found coliform bacteria counts 10 

 times higher on some sections 

 developed with conventional septic 

 tanks than he found on undeveloped 



Continued on next page 



Drawing by Daphne Webster 



ill , SURFACE 



SEPTIC TANK | | PUMPING CHAMBER | MOUND DRAINAGE 



FOB DOSING DIVERSION 



A mound system, designed for high water tables and poor soils 



