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When the Philadelphia Water Department needed an innovative biosolids management alternative that would utilize biosolids during winter months, the idea of growing hybrid poplars to reclaim mine lands presented many benefits. A similar operation in Maryland has been recognized as a successful approach to biosolids recycling and reclamation. The project places biosolids in deep row troughs that can be installed during winter seasons. This application technique supplies nitrogen for the establishment and maintenance of a hybrid poplar tree plantation over an eight year growing cycle. After two growing season at the mine site, this approach to reclamation has stabilized the disturbed site, has supported strong sapling growth, and resulted in no apparent adverse environmental impacts.The deep row placement of biosolids is a concept developed by ERCO, Inc. (ERCO), for supplying nutrients at degraded sites over time for deep-rooted tree clones. In this approach, the deep rows are dug to a depth of approximately 30 inches (76 cm) and a width of approximately 42 inches (107 cm). Biosolids are placed into these rows at a depth of approximately 18 inches (45 cm) and the row is then filled with the excavated material. After biosolids application, stecklings from hybrid poplar, Populus spp., are planted on ten-foot centers.The preliminary findings show that the hybrid poplar trees fertilized with biosolids grow faster during the first two years after planting than un-fertilized poplars. The deep row method can reduce or eliminate the occurrence of off site odors. When incorporating biosolids into a tree plantation using deep rows, the usual assumptions about mineralization rates used when biosolids are surface applied and incorporated are not usually applicable, and loss of nitrogen is minimal. During the first 2 years of growth, no significant difference in performance of the two clones of trees used in the demonstration was observed. Planting location (between the rows or directly above the deep rows) did not result in significant growth rate differences.

Using deep row biosolids application to grow hybrid poplar trees (Populus spp.) on sand and gravel mine spoils is a unique and innovative beneficial-use technique that solves many of the conventional problems. The technique was developed on 50 ha (125 ac) site in the Washington, D.C. metro area by a private company (ERCO, Inc.). Research has been carried out since 2001 to develop a better understanding of water quality impacts, operational methods, clonal selection, hybrid poplar growth and nutrition, and the factors affecting economics and profitability. There are no indications of nitrate leaching and the tree plantation systems are performing well. Given the large acreage of mine spoils in the metro area, deep row application has the potential to utilize significant amounts of biosolids produced in the region.

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