Graduation date: 1997

The contamination of ground water resources represents a serious problem and a prominent threat to the health of our society. This study focuses on the leaching of inorganic anions as a function of agricultural practices under natural field conditions. In order to enhance the understanding of such leaching processes, this thesis evaluates the spatial variability of the leaching characteristics of a site, the factors controlling percolation, and the use of a cereal rye cover crop to reduce nitrate leaching. Thirty-two Passive Capillary Wick Samplers (PCAPS) and 32 suction cups were installed at a depth of 120 cm under row crop produced in a Woodburn Variant loam (fine-loamy mixed mesic Aquultic Argixeroll). Significant correlation for the water flux was seen at the 2.0 m distance, beyond which values were uncorrelated. No spatial correlation was seen in hydrodynamic dispersion coefficients. Percolation was independent of field saturated hydraulic conductivity, while the quantity of incident water was strongly correlated with percolation. The occurrence of preferential flow affected the leaching process as documented by solute breakthrough ahead of the main solute peak. Rates of nitrogen fertilizer application were proportional to observed nitrate leaching losses. The cover crop significantly reduced the amount of nitrate leaching at all N fertilizer application rates. At the recommended rate, nitrate-N concentrations were lowered on average from 22.2 to 9.9 mg/l; cumulative N mass losses were cut by 62% due to plant uptake by the cover crop. The study demonstrated the importance of conducting long-term field experiments under natural conditions to accurately assess leaching processes. / Graduation date: 1996

Assessment of the environmental impacts of an agricultural production system requires information on both soil water quality and solute flux. Passive Capillary Samplers (PCAPS), which sample water from the vadose zone using fiber glass wicks, have shown potential to provide both flux and solute concentration in unsaturated zone sampling but have not been tested under long-term, natural, rainfall conditions. The objectives of this study are to (1) evaluate PCAPS operation under non-steady, natural rain and irrigation fed conditions, (2) determine the samplers ability to estimate recharge, and (3) estimate the loss of nutrients resulting from agricultural production. 32 PCAPS and 78 suction cup samplers were installed below the root zone at 16 commercial fields in Lane County, Oregon. PCAPS' were installed in positions using ground penetrating radar such that PCAPS' were placed in homogeneous or concave profile locations. Two PCAPS and six suction cups were installed at each site. Rain gages and TDR probes were installed at eight of the 16 sites. These data were used to develop a mass balance for each of the eight special study sites. Comparison to mass balance data indicates that the PCAPS flux measurements were within 10% of the mass balance estimated recharge. Surface runoff of potential drainage water during periods of high rainfall was a point of concern for estimated recharge discrepancies because runoff was not measured. The saturated hydraulic conductivity was shown to be the most influential design parameter for matching wick and soil types. On the other hand, the incident flux, rather than conductivity, determined the ultimate ground water recharge. PCAPS collection was found to be significantly correlated (average R��=0.75) to the mass balance monthly estimated recharge. To estimate the mean monthly recharge at each site with a 30% bound on the mean and 95% confidence level, 20 PCAPS would be required at each site. PCAPS were found to be superior to suction cup samplers for estimating ground water recharge concentrations because PCAPS were able to sample both flux and resident concentrations. Mint and row crop, organic and inorganic, production systems contributed to the largest adverse environmental impacts with average recharge concentrations for mint and row crop of 24 mg L����� and 28 mg L�����, respectively. Orchard and blueberry production systems had little impact with their seasonal concentrations averaging below the EPA water quality standard. Amounts of percolation were key in determining which management systems were inefficiently operated. Over-irrigation during the summer lead to increased losses of nitrogen for the mint production systems in the summer as well as the winter. Over-fertilization was important for creating significant differences in seasonal mass losses of nitrogen from row crop production systems. Overall, the PCAPS estimated nitrogen loss was 12% lower than that calculated using a simplified nitrogen mass balance approach. Best management practice suggestions concerning irrigation, fertilization and cover cropping were provided as a direct result of the findings of the project. With technical support and increase in concern over nitrate contamination, farmers should be able to control leaching losses without the use of quotas or allotments. / Graduation date: 1995

Volcanic tuffs and tuffaceous sediments are frequently associated with elevated As groundwater concentrations even though their bulk As contents (~ 5 mg kg-1; Savoie, 2013) are only marginally greater than the average crustal abundance of 4.8 mg g-1 (Rudnick & Gao, 2003). Thus, As mobilization must be facilitated by conditions particular to these rocks. Alkaline desorption, anionic competition, reactive glass dissolution, and reductive dissolution of iron oxides are proposed processes of As release from volcanic rocks. Geogenic As contamination of groundwater in the southern Willamette Valley in western Oregon has been well-documented since the early 1960s, and previous studies have identified the Little Butte Volcanics Series and Fisher and Eugene Formations as the source of As contamination. This study examines 19 samples from 10 units of ash flow tuffs and tuffaceous sediments within the Fisher Formation and Little Butte Volcanics Series, representing a range of weathering and devitrification, to determine conditions of mobilization and mineralogical constraints that control As release into solution. Leachate studies were conducted over a range of pH from 7 to 11, phosphate concentrations from 10 μM to 100 mM, and in time series from 4 to 196 hours. Results demonstrate that silicic volcanic tuffs are capable of mobilizing As in concentrations above regulatory limits at pH conditions produced naturally by the tuffs (pH 8-9) or with moderate concentrations of P (10-100 μM). Alteration products, e.g. zeolites and clays, appear to be the primary host phases for mobile As. Samples that do not contain these alteration products tend to produce concentrations of As well below regulatory limits and often below the instrument detection limits of this study. The type of alteration may influence As mobilization: tuffs containing more clays tend to mobilize As through surficial desorption, and tuffs containing more zeolites tend to mobilize As by dissolution or formation of colloids. Additionally, one volcaniclastic sample demonstrates that extremely elevated concentrations of As, up to 1000 μg/L are possible as a result of oxidative dissolution of As-bearing sulfide phases.

Soils of 49 agricultural and 2 "native condition" sites in the Lower Umatilla Basin, Oregon were sampled for nitrate-nitrogen, ammonium-nitrogen, chloride, and pH beginning in Fall of 1992. Several sites were sampled in Spring and Fall 1993 in order to indicate movement or loss of residual soil nitrogen over time. This study was prompted by current concern over contamination of public drinking water supplies by nitrate and the designation of over 550 square miles of this region as a Ground Water Management Area. This study sought to identify links between agricultural management practices-primarily irrigation, fertilization, and crop rotation systems, and deep soil nitrate levels. Soil profiles were divided into 3 "management zones:" 0-3', 3-6', and beyond 6' in depth. These depths represent average rooting depths for the major agricultural crops of the study area. In general, the effective rooting depth of most area-crops does not extend beyond 6', therefore, it was determined that residual soil-nitrate found at this depth or beyond may be a potential source of ground water contamination if not managed correctly. Results of the study indicate that proper management of irrigation, fertilization, and cropping rotation can significantly reduce the potential for contaminating ground water. Deep soil nitrate levels under most agricultural fields were consistent with the concept that some loss of nitrate below the root zone is inevitable, however, this condition can be minimized through intensive crop management. This study concludes that responsible management of agriculture can minimize impacts on ground water, while providing quality food and fiber products to an ever-growing population. In addition, more research is needed in the area of crop physiology and response to intensively managed systems. Such research may provide insight into more efficient methods of crop production and environmental protection. / Graduation date: 1995

Excessive nitrates in drinking water pose a human health threat, especially to infants. Methemoglobinemia, or blue-baby syndrome, is a potentially fatal condition that inhibits the ability of red blood cells to bind and transport oxygen. Nitrates/nitrites have also been linked to such conditions as cancer, birth defects, and behavioral and developmental abnormalities. Nitrates are frequently found in wells in rural farming areas because synthetic fertilizers (containing nitrates) leach from the soil into the groundwater. The Lower Umatilla Basin (LUB) in Morrow and Umatilla counties of Oregon represents an intensively farmed and irrigated area in which relatively high amounts of nitrates are present in the groundwater and domestic well water. This study investigated population demographics for the rural Lower Umatilla Basin, comparing these data to identified well-water nitrate levels for the purpose of estimating nitrate exposures and potential risk of adverse health effects in the survey area. Results of the investigation revealed that 25 percent of the domestic-use wells in the survey area had nitrate levels that were in excess of the 10 ppm nN MCL for drinking water, as established by the U.S. Environmental Protection Agency. From access to these wells, 23 percent of the surveyed population was exposed to nitrate concentrations in excess of the MCL standard. However, resident infants were neither exposed to well-water nitrates in excess of the standard, nor were they exposed to illness that could have increased the risk of methemoglobinemia. The LUB survey population was generally older than the populations from cities in the LUB or the combined populations of rural areas of Morrow and Umatilla counties. The population included few women of childbearing age, and it was not subject to an appreciable increase in the proportion of younger to older families. These factors reduced the likelihood of a significant increase in the infant population, which also minimized the risk of methemoglobinemia to this population. Even though the risk of methemoglobinemia to infants was low in the LUB area, it is recommended that exposures to well-water nitrates be prevented, if possible even for adults, to reduce the potential for chronic, adverse health effects from excess nitrate ingestion. Continued monitoring of private wells by state agencies is recommended, with attention directed at domesticuse wells with nitrate levels in excess of 10 ppm nN. This information should be shared with local health departments for follow-up, investigation, and educational efforts as needed. Future studies by the Oregon DEQ, or other agencies which seek to document the sources of well-water nitrate contamination in the LUB, should include an investigation of the influence of local sources of nitrate contamination. / Graduation date: 1993

The Safe Drinking Water Act ensures that public systems provide water that meets health standards. However, no such protection exists for millions of Americans who obtain water from private wells. Concern for safety is warranted as most wells draw from underground aquifers, and studies demonstrate that groundwater is affected by a range of contaminants, most often nitrate. Oregon's Domestic Well Testing Act (DWTA) links well testing to property sales, enabling continuous data collection by the State. This research addresses a need for identifying datasets for characterizing exposure to private well contaminants by evaluating DWTA data for use in a sentinel surveillance system. Validation of DWTA data was accomplished by developing a land use regression (LUR) model based on agricultural nitrogen inputs and soil leachability to predict nitrate concentrations in well water. Geographic information systems (GIS) were used to advance methods for high resolution spatial modeling of fertilizer and manure nitrogen with statewide coverage. Hazard mapping with these datasets suggests that nearly half of recently drilled wells are susceptible to nitrate contamination. Spearman's rank correlation demonstrated a significant correlation between LUR-predicted nitrate levels and levels reported in the DWTA dataset. These results suggest that DWTA data is valid for use in a sentinel surveillance system, such that evidence of nitrate contamination in a single well may indicate an area-wide health hazard. However, a low fraction of variance explained by the LUR model highlighted the need for specific improvements to datasets crucial for understanding nitrate contamination in well water, including the DWTA. / Graduation date: 2012