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Expanding the Applications of Micro-Irrigation “Drip” Treatment and Disposal Systems in Delaware

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan

Citation:  Pp. 601-605 in On-Site Wastewater Treatment, Proc. Ninth Natl. Symp. on Individual and Small Community Sewage Systems (11-14 March 2001, Fort Worth, Texas, USA), ed. K. Mancl., St. Joseph, Mich. ASAE  701P0009.(doi:10.13031/2013.6067)
Authors:   J. G. Hayes Jr.
Keywords:   On-site wastewater treatment, Advanced treatment, Seasonal high water table

An 18-month field evaluation of four micro-irrigation "drip" treatment and disposal systems was conducted to determine if reducing the separation distance between the bottom of the drip-line and the seasonal high water table (limiting condition) could be reduced from 45 cm to 30 cm. In this study three systems did not have advanced treatment while the remaining system was used in conjunction with an aerobic advanced treatment unit (ATU). The seasonal high water table (SHWT) was estimated during the site evaluation and monitor wells were installed to collect grab samples quarterly. The monitor wells were placed up-gradient of the system, inside the drainfield and down-gradient of the system. The grab samples were analyzed for Nitrate/Nitrite-N, Ammonia-N, Kjeldahl-N, Total N, pH, specific conductivity and fecal coliform bacteria. Two of the three systems, without the ATU, had SHWTs at 50 cm while the third was estimated at 27 cm. The system with the ATU had a SHWT at or near the soil surface. All of the systems appear to be functioning properly with no adverse environmental impacts. Nitrate/Nitrite-N did not increase significantly from the background samples taken before system operation. The ATU system had a significant increase in the Nitrate/Nitrite-N levels within the wells that were located within the drainfield. This is expected due to the aerobic properties of the ATU which nitrifies the wastewater creating Nitrate/Nitrite-N. This form of nitrogen is readily absorbed by plant roots. Fecal coliform bacteria levels were all generally less than 20/100mL with 79% of the total being less than 10/100mL. The reduction of the isolation distance from 45 cm to 30 cm appears to have no adverse impact on the ground water quality within the soils of Delaware. Further water sampling, plus soil sampling at four inch intervals, during the next year will provide more complete results and allow to see longer term exposure of the sites to wastewater treatment and disposal.

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