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• were in compliance with applicable water quality criteria and posed no toxicological effects. <br />Therefore, manganese was the only constituent requiring further consideration. <br />To evaluate potential risks of adverse human (health and nuisance effects) and ecological effects <br />associated with manganese in [he Rito Seco, potential human and ecological receptors and <br />exposure pathways were selected for evaluation. Human exposure scenarios included domestic <br />and recreational use of the Rito Seco water. Ecological receptors included free-range cattle and <br />terrestrial wildlife comprised of various species expected to use the Rito Seco as a drinking water <br />resource or habitat. These wildlife species likely include beaver, muskrat, raccoon, turtles, <br />reptiles, birds, deer, and elk. Representative receptors used to evaluate exposure and risk were <br />muskrat (aquatic mammal), white-tailed deer (terrestrial mammal), and free-range cattle. <br />Aquatic receptors on the Rito Seco likely include fish (e.g., sahnonids), benthic invertebrates, <br />amphibians, and aquatic plants. Aquatic organisms were evaluated as a group (i.e., <br />representative receptors aze not identified), because the chronic water quality criteria aze <br />designed to be protective of the majority of sensitive aquatic organisms. <br /> <br />The SLRA was conducted using a hazazd quotient (HQ) approach. The HQ equals the <br />representative manganese concentration (i.e., mean and maximum concentrations by location) <br />divided by [he applicable criterion. Hazazd quotients less than 1 indicate conditions that pose no <br />potential for adverse effects, whereas HQs greater than 1 are interpreted to indicate that some <br />potential risk may exist and that a more quantitative risk assessment may be appropriate. <br />Risk to human health and agricultural water use was evaluated by comparing representative <br />manganese concentrations in the Rito Seco to drinking water (maximum contaminant level <br />[MCL]) and agricultural water quality criteria. Risk to free-range cattle and wildlife was <br />evaluated by comparing a health-based exposure concentration (HBEC) to manganese <br />concentrations in the Rito Seco. The HBECs were developed from receptor-specific exposure <br />factors, and toxicity reference values (TRV) developed from no-observed-adverse-effect-level <br />data obtained from the scientific literature. Risk of adverse effects to aquatic organisms was <br />evaluated by comparing manganese concentrations in the Rito Seco to the chronic and acute <br />Balt(e Moumain Resources. Inc. <br />pa/001671reportslmarchrptltrl6wlrmngtmarch.doc 61 Marth 21, /999 <br /> <br />