Pergamon Chemosphere, Vol. 39, No. 11, pp.1781-1794, 1999 © 1999 Elsevier Science Ltd. All rights reserved 0045-6535/99/$ - see front matter PII: S0045-6535(99)00072-7 OCCURRENCE AND BEHAVIOR OF WASTEWATER INDICATORS IN THE SANTA ANA RIVER AND THE UNDERLYING AQUIFERS Wang-Hsien Ding" ~' z, Jennifer Wu 1, Marco Semadeni 1, Martin Reinhard t ~Department of Civil and Environmental Engineering, Stanford University, Stanford, CA 94305, USA 2Department of Chemistry, National Central University, Chung-Li, Taiwan, 32054 (Received in Germany 17 September 1998; accepted 24 February 1999) ABSTRACT The occurrence and behavior of wastewater indicator compounds in the Santa Arm River (SAR) water and the underlying aquifer recharged by the SAR has been studied. The SAR contains a high proportion of tertiary treated wastewater effluents, up to 100% during summer and fall. The following water quality parameters were quantified: four specific wastewater indicator compounds, ethylene diaminetetraacetic acid (EDTA), nitrilotriacetic acid (NTA), a naphthalene dicarboxylate (NDC) isomer, alkylphenol polyethoxy carboxylates (APECs), and selected haloacetic acids (HAAs), nitrate, dissolved oxygen (DO), DOC, total carbohydrate, and phenolic substances. Statistical analysis indicated that normal distribution was adequate to describe the probability distribution of the constituents in most cases. In the river, the concentrations of wastewater indicator compounds decreased as the fraction of storm runoff increased. EDTA and NDC were detected in a monitoring well near the river and in two production wells 1.8 and 2.7 km down gradient with little apparent attenuation. By contrast, NTA, APECs, bromochioro- and dibromoacetic acids appeared to be attenuated significantly during infiltration of river water and groundwater transport. © 1999 Elsevier Science Ltd. All fights reserved 1. INTRODUCTION Replenishing depleted potable aquifers by groundwater recharge with river water or reclaimed wastewater is an increasingly important practice to replenish aquifers, especially in the water-short areas of the Southwestern States in the USA. The benefits of percolating surface water into an aquifer have long been recognized (1-6). The process of percolating treated effluents through soil is referred to as "soil- aquifer-treatment" (SAT). While most SAT studies have focused on the processes that occur during percolation, very little is known of organic carbon transformations that occur during groundwater transport on a regional scale and whether specific organic contaminants originating from effluents can reach distant production wells. Processes in the percolation zone are relatively fast and occur on a time-scale of days to ' To whom correspondence should be addressed. Central University, Chung-Li, 32054, Talwan. The current address: Department of Chemistry, National 17811782 months to years. Hydrophobic trace organics (1,2) and metals (3,4) removal in the percolation zone has been documented. Some contaminants such as EDTA, NTA, nonylphenol ethoxylates and their metabolites were shown to percolate with limited attenuation (5,6). The organic carbon fraction which originates from wastewater is of particular interest because of potential health concerns, its composition is poorly characterized, and its behavior during SAT is unknown. The study site is located in northeastern Orange County, California, in the cities of Yorba Linda and Anaheim, adjacent to the Santa Ana River (SAR). The river is one of the most important water sources for potable water in Orange County, California (Figure 1). ~sio,at ~r Xx~C~x w, a=~ ~'~" "~" ~ Olttld~Cater Prado SW-2 X X SAR PW-2 PW-1 MW-1 SAR , I---- 0.9 km I 1.8 kaf X = effluent discharge • = sampling location Figure 1. Schematic cross section of sampling sites and groundwater sampling depths at Santa Ana River study area. Vertical arrows indicate the hypothesized surface recharge of storm runoff. The SAR flow consists of major two components: (i) a relatively constant flow of highly treated wastewater effluents discharged by upstream municipalities, and (ii) a variable flow of storm runoff. The effluents make nearly 100% of its flow during base-flow conditions usually lasting from summer through late fall. During the rainy season a significant portion of the flow consists of surface runoff collected by Prado Dam. The blend of surface runoff and tertiary effluents is then slowly released until base-flow conditions are reached, which is typically in late spring. Down stream of Prado Dam, a significant fraction of the river's flow is used to recharge the groundwater basin, which is the water supply for 2 million people. The water1783 pumped from the aquifer is from four principal sources: SAR, water imported from Northern Califomia or the Colorado River, and surface recharge. The latter is difficult to quantify. The proportions of these sources vary depending on location and time, but are difficult to predict locally due to the complex hydrogeology of the underlying aquifer. Knowing the origin of the water - especially the water from wastewater origin - at the various production wells is important for managing the groundwater basin. The purpose of this study was to evaluate the occurrence and fate of wastewater indicator compounds in the SAR and the underlying aquifers in order to assess the impact of water from wastewater origin on the basin. As wastewater indicator compounds, we have used ethylene diamintetraacetic acid (EDTA), nitrilotriacetic acid (NTA), a napthalene dicarboxylic acid isomer (NDC), alkylphenolethoxy carboxylates (APECs) and haloacetic acids (HAAs). These compounds were selected because they are commonly found in reclaimed wastewater (7,8). EDTA is found in many water systems because of its widespread domestic and industrial use and its poor biodegradability. NTA, a widely used complexing agent, is biodegradable during sewage treatment (9,10) and surface water (11). NDC is of unknown origin although it is suspected to be a biological metabolite of diaikyl naphthalenes, anthracene or phenanthrene, commonly found contaminants in sewage effluents, rivers and sediments. APECs are biological metabolites of alkylphenol polyethoxylates (APEOs), a common class ofnonionic surfactants. APECs are typically present as a complex mixture in the river and were quantified as the total APECs (12,13). HAAs are found as chlorination