Irrigation with Reclaimed Water: Implications for Subsurface Recharge
Singer, Rebecca E.
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To determine the suitability of using reclaimed water for subsurface recharge, a soil column greenhouse study was performed to examine the leaching characteristics of two soil types irrigated with two types of class A reclaimed water: 1) membrane bioreactor (MBR) and 2) sand filter (SF) tertiary filtered wastewater, with tap water for a control. The two soils used in this study were Alderwood sandy loam and Earlmont-Snohomish silt loam. Each soil column was irrigated with one water type at one of three rates for 4 months. Irrigation rates were the standard agronomic rate of 250m3ha-1, twice the agronomic rate (2X), and four times the agronomic rate (4X). At 2 months, grass was planted in each column to determine productivity under the varying irrigation rates and water types. Water characteristics examined before and after irrigation were pH, conductivity, total metals, ammonia, phosphate, nitrate and total EDC potency. Soil characteristics examined were pH, conductivity, total metals and total carbon and nitrogen. The pH was influenced by the source water but remained within the recommended EPA and WA State standards. Conductivity decreased with increased irrigation rate and soils remained non-saline throughout the study. EDC potency of MBR reclaimed source water and leachate did not differ from the control source water or leachate from either soil types. SF source water had high estrogenic potency that was significantly reduced via soil filtration. Overall metal leachate concentrations were below standards for EPA drinking water and WA State Groundwater Quality (GWQ) with the exception of arsenic. All source waters including the tap water were above WA State GWQ standards as were the leachates, however, all metal concentrations met EPA recommended constituent limit for irrigation with reclaimed water. Orthophosphate and ammonia concentrations were low in both the source waters and leachates. Arsenic and nitrate leachate concentrations appear to be influenced by soil. Productivity was highest under the 4X irrigation rate for the control and SF water. The MBR 2X rate was only slightly higher than the 4X rate. This suggests that irrigation above the agronomic rate will not reduce productivity and has potential for recharge of groundwater based on the parameters measured in this study.
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