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Kent Becher

Publications and source records attributed to Kent Becher.

16 recordsLinked to original sources
USGS2021

Evaluation and application of the Purge Analyzer Tool (PAT) to determine in-well flow and purge criteria for sampling monitoring wells at the Stringfellow Superfund site in Jurupa Valley, California, in 2017

The U.S. Geological Survey and U.S. Environmental Protection Agency are developing analytical tools to assess the representativeness of groundwater samples from fractured-rock aquifers. As part of this effort, monitoring wells from the Stringfellow Superfund site in Jurupa Valley in Riverside County, California, approximately 50 miles east of Los Angeles, were field tested to collect information to assist in the evaluation and application of in-well flow as computed by the analytical model called the Purge Analyzer Tool, which computes in-well groundwater travel times for simple piston transport of inflowing groundwater from open intervals of a monitoring well to the pump intake and can provide insight into optimal purging parameters (duration, rate, and pump position) needed for the collection of representative groundwater samples. Field testing of wells included hydraulic, chemistry, and dye tracer analysis to investigate travel times in wells under pumping conditions. The Purge Analyzer Tool was able to replicate dye velocities (travel times) for one of three wells that had appreciable inflow from the aquifer but not the other two wells, which are screened in low-permeability sediments and rock, where flow was dominated by borehole storage. A set of criteria was established to help assess the ability to collect representative groundwater chemistry from monitoring wells; criteria included understanding the height of the static well water column and relative exchange rate between the aquifer and the well.

California↗
USGS2019

Differentiating anthropogenic and natural sources of uranium by geochemical fingerprinting of groundwater at the Homestake Uranium Mill, Milan, New Mexico, USA

A multiparameter geochemical-isotopic fingerprinting approach was used to differentiate natural and anthropogenic signatures of uranium contamination near the Homestake uranium mill site (Site), near Milan, New Mexico, USA. The Site consists of two tailings piles from milling operations and groundwater contamination from these tailings have been noted. The Site lies within the lower San Mateo Creek Basin with multiple regional sources of U contamination from mining and mill operations and is underlain by a heterogeneous alluvial aquifer, which is underlain by basement rock of the Chinle Group and the lowermost San Andres-Glorieta aquifer. To help decipher signatures, several statistical approaches were used including PCA, NMDS, and cluster analysis. Trilinear piper diagrams indicate two end member water types at the Site, sulfate-Na-K and sulfate-Ca. Natural alluvial aquifer groundwater in this area, relatively unaffected by mining or milling, appears to be more dominated by bicarbonate than sulfate and the deeper San Andres-Glorieta aquifer that has a mixture of sulfate and bicarbonate. Uranium concentrations from the Site fall into three broad categories, less than the drinking water standard of 30 µg/L (n=3), from 30 to 100 µg/L (n=9) and greater than 100 µg/L (n=8). Component loadings in a principal component analysis are highest for uranium isotopes, 228Ra, gross alpha-beta, molybdenum, chloride, uranium, and sodium, which affect the similarities or differences among wells sampled. Results suggest that several alluvial wells upgradient from the Site have anthropogenic fingerprints from regional sources related to upgradient mining. Wells with higher uranium concentrations have uranium activity ratios close to 1, which is indicative of mining or milling signatures. These same wells have elevated radon activities. This information can be used to inform Site managers on the source of water related to uranium at the Site and provide an approach for geochemical fingerprinting.

New Mexico↗
USGS2019

Identifying natural and anthropogenic variability of uranium at the well scale, Homestake Superfund site, near Milan, New Mexico, USA

The San Mateo Creek Basin in New Mexico, USA is located within the Grants Mineral Belt-an area with numerous uranium (U) ore deposits, mines, and milling operations. Six monitoring wells set in an alluvial aquifer near the Homestake Mining Co. Superfund site in the lower San Mateo Creek Basin were logged with a suite of borehole geophysical tools including spectral gamma-ray (SGR), vertically profiled with passive samplers for U and selenium (Se) concentrations, and purged sampled for same constituents. The integrated approach allowed for an assessment on the role of heterogeneity (both physical and chemical) in determining U concentrations in groundwater. Uranium, as measured with SGR logging, is ubiquitous in the alluvial aquifer and the underlying Chinle Group. Aqueous U concentrations appear to be inversely related to thorium (Th) concentrations, as measured by the SGR log, indicating the possibility that U is bound in or adsorbed to clays in the aquifer. The stratigraphy of the alluvium likely plays a role in elevated concentrations of aqueous U. Interbedded clay and sand layers allow for the mobilization of U in oxic sandy layers from U adsorbed in sediments in reduced clay layers. The stratigraphy also plays a role in the degree of mixing of groundwater in the formation and well. Mixing can obscure the ability to identify U sources. Mixing is exacerbated by the relatively long screens (> 20 ft long or > 6.1 m) of the monitoring wells.

New Mexico↗
USGS2018

Determination of representative uranium and selenium concentrations from groundwater, 2016, Homestake Mining Company Superfund site, Milan, New Mexico

In 2016, the U.S. Geological Survey, in cooperation with the U.S. Environmental Protection Agency, collected data on isotopes, age dating, and geochemistry including aqueous uranium concentrations of samples from 20 locations in the vicinity of the Homestake Mining Company Superfund site near Milan, New Mexico. The 20 sampled locations include 19 groundwater wells and 1 treatment plant for water used for injection into aquifers. At 6 of the 19 wells, multiple samples were collected by several different sampling methods, including passive, micropurge, and volumetric methods. Aqueous uranium concentrations were adjusted on the basis of comparisons between three sampling methods (called sample adjustments). These adjustments were specific to passive sample results because they underestimated uranium concentrations compared with results from purge samples (micropurge and volumetric). Sample adjustments were also made on aqueous selenium concentrations from previously published data for passive sampler results following a similar procedure. Aqueous uranium concentrations in dissolved and total form were adjusted from the original analytical values (called laboratory analytical adjustments) on the basis of a rigorous comparison to several external tests, including reruns and analysis by a different laboratory after accuracy issues were identified in data from the original laboratory. The original laboratory analytical results were found to be two to five times greater than historical concentrations at the same locations, which prompted further evaluation, as described in this report.

New Mexico↗
USGS2007

Nutrients discharged to the Mississippi River from eastern Iowa watersheds, 1996-1997

The introduction of nutrients from chemical fertilizer, animal manure, wastewater, and atmospheric deposition to the eastern Iowa environment creates a large potential for nutrient transport in watersheds. Agriculture constitutes 93 percent of all land use in eastern Iowa. As part of the U.S. Geological Survey National Water Quality Assessment Program, water samples were collected (typically monthly) from six small and six large watersheds in eastern Iowa between March 1996 and September 1997. A Geographic Information System (GIS) was used to determine land use and quantify inputs of nitrogen and phosphorus within the study area. Streamliow from the watersheds is to the Mississippi River. Chemical fertilizer and animal manure account for 92 percent of the estimated total nitrogen and 99.9 percent of the estimated total phosphorus input in the study area. Total nitrogen and total phosphorus loads for 1996 were estimated for nine of the 12 rivers and creeks using a minimum variance unbiased estimator model. A seasonal pattern of concentrations and loads was observed. The greatest concentrations and loads occur in the late spring to early summer in conjunction with row-crop fertilizer applications and spring nmoff and again in the late fall to early winter as vegetation goes into dormancy and additional fertilizer is applied to row-crop fields. The three largest rivers in eastern Iowa transported an estimated total of 79,000 metric tons of total nitrogen and 6,800 metric tons of total phosphorus to the Mississippi River in 1996. The estimated mass of total nitrogen and total phosphorus transported to the Mississippi River represents about 19 percent of all estimated nitrogen and 9 percent of all estimated phosphorus input to the study area.

Iowa↗
USGS2003

Water-quality assessment of the eastern Iowa Basins: Selected pesticides and pesticide degradates in streams, 1996-98

Water samples were collected in streams of the Eastern Iowa Basins study unit from 1996 to 1998 as part of the U.S. Geological Survey’s National Water-Quality Assessment (NAWQA) Program. More than 350 samples were collected to document the occurrence, distribution, and transport of pesticides and pesticide degradates. The Eastern Iowa Basins study unit encompasses about 50,500 square kilometers (19,500 square miles) in eastern Iowa and southern Minnesota and is drained by four major rivers—the Wapsipinicon, Cedar, Iowa, and Skunk—which flow into the Mississippi River at the eastern border of Iowa. The most commonly detected pesticides— acetochlor, alachlor, atrazine, cyanazine, and metolachlor—were those most heavily used on crops during the study. Atrazine and metolachlor were detected in 100 percent, and acetochlor, alachlor and cyanazine were detected in more than 70 percent of all surface-water samples. Four pesticide degradates—metolachlor ethane sulfonic acid, alachlor ethane sulfonic acid, metolachlor oxanilic acid, and acetochlor ethane sulfonic acid were detected in more than 75 percent of the samples. Only one nonagricultural herbicide, prometon, was detected in more than 80 percent of the samples. Carbofuran, the most commonly detected insecticide, was found in 16 percent of all samples. Mixtures of pesticide compounds commonly occurred in the samples. Five or more parent pesticide compounds were detected in 50 percent of the samples. Four or more pesticide degradates were detected in 68 percent and seven or more pesticide degradates were detected in 17 percent of the samples. Acetochlor, alachlor, atrazine, cyanazine, and metolachlor were generally present at low concentrations; median concentrations ranged from 0.01 to 0.22 microgram per liter. However, median concentrations for the pesticide degra-dates, 0.07 to 3.7 micrograms per liter, were larger than their parent compounds. Acetochlor, alachlor, atrazine, cyanazine, and metolachlor pesticide compounds were detected at an order of magnitude or higher in the late spring and summer than at other times of the year. Pesticide concentrations generally peak following application in May and June and decrease during the growing season. A small secondary peak of atrazine, acetochlor, alachlor, cyanazine, and metolachlor concentrations occurred in late winter at all sites. The seasonal patterns for the triazine (atrazine and cyanazine) degradates were similar to the parent compounds (increasing in the spring), but the triazine degra-dates often had higher median concentrations than their parent compounds in the fall and winter. The chloroacetanilide (acetochlor, alachlor, and metolachlor) degradates did not follow a strong seasonal pattern like their parent compounds. In general, the chloroacetanilide degradates had constant and higher median concentrations when compared to their parent compounds throughout the year. The median concentrations for the chloroacetanilide pesticide degradates were often an order of magnitude higher than their parent compounds. Concentrations of pesticides varied by land-form region. Atrazine and cyanazine and their degradates were present in significantly greater concentrations in streams of the Southern Iowa Drift Plain than streams of either the Des Moines Lobe or the Iowan Surface.

Iowa, Minnesota↗
USGS2003

Bathymetric mapping, sediment quality, and water quality of Lake Delhi, Iowa, 2001-02

Lake Delhi was formed in 1929 when the Interstate Power Company dammed the Maquoketa River near Delhi, Iowa, for generation of hydroelectric power. The resulting 450-acre lake became a popular area in eastern Iowa for boating, swimming, and fishing. Hydroelectric power generation ended in 1973, and lakeside residents purchased the dam to maintain the recreational opportunities of the lake. Increasing concerns about sediment deposition and water quality by lakeside residents led to a 2-year study that included a bathymetric survey, an assessment of sediment quality, and an assessment of water quality of Lake Delhi. A bathymetric map of Lake Delhi was constructed using more than 300,000 data points from echo sounding results and GIS (geographic information system) software. Results of bathymetric mapping showed that the upstream reach through most of the upstream-middle reach of Lake Delhi (approximately 3 miles) from about 0.25 mile upstream from the Greenslades coring site through Clair View Acres were particularly affected by sedimentation, with water depths ranging from less than 1 foot to a few areas that were as much as 10 feet deep. Numerous areas in the upstream-most 1-mile of the lake (about 0.25 mile upstream from the Greenslades coring site to just downstream from The Cedars coring site) had depths of only 1 to 2 feet and were nearly impassable by boats. The middle reach of Lake Delhi (an approximately 2.5-mile segment) from about one-half mile upstream from the Linden Acres coring site to just downstream from the Hartwick Dredge coring site was less affected by sedimentation with water depths from less than 1 to 16 feet. The deepest section (26 feet) of the lake was near the dam. Eleven trace metals and phosphorus were analyzed in 20 samples from seven lake-bottom sediment cores. The median and average traceelement concentrations from the sediment cores were less than the U.S. Environmental Protection Agency threshold-effects-level and probableeffects-level guidelines for toxic biological effects. Water-quality samples from eight sites (Maquoketa River, three lake sites, and four tributaries) were collected for five sampling periods (June 2001–July 2002). Water-quality samples were analyzed for physical properties (specific conductance, pH, temperature, turbidity, dissolved oxygen, and alkalinity), nutrients (nitrate, ammonia, and phosphorus), bacteria (total coliform and E. coli ), and suspended sediment. Selected water samples were analyzed for major ions, trace elements, and pesticides. Water-quality sampling results indicate areas affected by elevated nutrient and bacteria concentrations in the lake and tributary streams. The tributary streams had the highest median nitrate concentrations (12.1 milligrams per liter) when compared to median nitrate concentrations in the lake (8.7 milligrams per liter) or the Maquoketa River (10.5 milligrams per liter). The maximum nitrate concentrations detected for Maquoketa River, lake, and tributary sites were 13.5, 13.5, and 18.6 milligrams per liter, respectively. Nitrate concentrations in the late summer decreased from 2 Bathymetric Mapping, Sediment Quality, and Water Quality of Lake Delhi, Iowa, 2001–02 the upstream (7.8 milligrams per liter) to the downstream (5.0 milligrams per liter) one-third of Lake Delhi and most likely were the result of uptake of nitrate by algae and aquatic biota in the lake. Median concentrations of total coliform and E. coli bacteria for the lake sites were 450 and 17 colonies per 100 milliliters of sample, respectively. The U.S. Environmental Protection Agency criteria for full body contact (swimming or bathing) are 200 colonies per 100 milliliters for fecal bacteria and 126 colonies per 100 milliliters for E. coli bacteria. The highest bacteria concentrations in the lake occurred after a rain and were 25,000 colonies per 100 milliliters total coliform and 1,900 colonies per 100 milliliters E. coli .

Iowa↗
USGS2001

Water-quality assessment of the eastern Iowa basins– Nitrogen, phosphorus, suspended sediment, and organic carbon in surface water, 1996–98

Twelve sites on streams and rivers in the Eastern Iowa Basins study unit were sampled monthly and during selected storm events from March 1996 through September 1998 to assess the occurrence, distribution, and transport of nitrogen, phosphorus, suspended sediment, and organic carbon as part of the U.S. Geological Survey’s National Water-Quality Assessment Program. One site was dropped from monthly sampling after 1996. Dissolved nitrogen and phosphorus were detected in every water sample collected. Nitrate accounted for 92 percent of the total dissolved nitrogen. About 22 percent of the samples had nitrate concentrations that exceeded the U.S. Environmental Protection Agency’s maximum contaminant level of 10 milligrams per liter as nitrogen for drinking-water regulations. The median concentration of total dissolved nitrogen for surface water in the study unit was 7.2 milligrams per liter. The median total phosphorus concentration for the study unit was 0.22 milligram per liter. About 75 percent of the total phosphorus concentrations exceeded the U.S. Environmental Protection Agency recommended total phosphorus concentration of 0.10 milligram per liter or less to minimize algal growth. Median suspended sediment and dissolved organic-carbon concentrations for the study unit were 82 and 3.5 milligrams per liter, respectively. Median concentrations of nitrogen, phosphorus, and suspended sediment varied annually and seasonally. Nitrogen, phosphorus, and suspended-sediment concentrations increased each year of the study due to increased precipitation and runoff. Median concentrations of dissolved organic carbon were constant from 1996 to 1998. Nitrogen concentrations were typically higher in the spring after fertilizer application and runoff. During winter, nitrogen concentrations typically increased when there was little in-stream processing by biota. Nitrogen and phosphorus concentrations decreased in late summer when there was less runoff and in-stream processing of nitrogen and phosphorus was high. Dissolved organic carbon was highest in February and March when decaying vegetation and manure were transported during snowmelt. Suspendedsediment concentrations were highest in early summer (May–June) during runoff and lowest in January when there was ice cover with very little overland flow contributing to rivers and streams. Based on historical and study-unit data, eastern Iowa streams and rivers are impacted by both nonpoint and point-source pollution. Indicator sites that have homogeneous land use, and geology had samples with significantly higher concentrations of total dissolved nitrogen (median, 8.2 milligrams per liter) than did samples from integrator sites (median, 6.2 milligrams per liter) that were more heterogeneous in land use and geology. Samples from integrator sites typically had significantly higher total phosphorus and suspended-sediment concentrations than did samples from indicator sites. Typically, there was very little difference in median dissolved organic-carbon concentrations in samples from indicator and integrator sites. Concentrations of nitrogen and phosphorus varied across the study unit due to land use and physiography. Basins that are located in areas with a higher percentage of row-crop agriculture typically had samples with higher nitrogen concentrations. Basins that drain the Southern Iowa Drift Plain and the Des Moines Lobe typically had samples with higher total phosphorus and suspended-sediment concentrations. Total nitrogen loads increased each year from 1996 through 1998 in conjunction with increased concentrations and runoff. Total phosphorus loads in the Skunk River Basin decreased in 1997 due to less runoff and decreased sediment transport, but increased in 1998 due to higher runoff and increased sediment transport. Total nitrogen and total phosphorus loads varied seasonally. The highest loads typically occurred in early spring and summer after fertilizer application and runoff. Loads were lowest in January and September when there was typically very little runoff to transport nitrogen and phosphorus in the soil to the rivers and streams. Total nitrogen loads contributed to the Mississippi River from the Eastern Iowa Basins during 1996, 1997, and 1998 were 97,600, 120,000, and 234,000 metric tons, respectively. Total phosphorus loads contributed to the Mississippi River from the Eastern Iowa Basins during 1996, 1997, and 1998 were 6,860, 4,550, and 8,830 metric tons, respectively. Suspendedsediment loads contributed to the Mississippi River from the Eastern Iowa Basins during 1996, 1997, and 1998 were 7,480,000, 4,450,000, and 8,690,000 metric tons, respectively. The highest total nitrogen and total phosphorus yields typically occurred in samples from indicator sites. Sampling sites located in drainage basins with higher row-crop percentage typically had higher nitrogen and phosphorus yields. Sites that were located in the Des Moines Lobe and the Southern Iowa Drift Plain typically had higher phosphorus yields, probably due to physiographic features (for example, erodible soils, steeper slopes). Synoptic samples collected during low and high base flow had nitrogen, phosphorus, and organic-carbon concentrations that varied spatially and seasonally. Comparisons of water-quality data from six basic-fixed sampling sites and 19 other synoptic sites suggest that the water-quality data from basic-fixed sampling sites were representative of the entire study unit during periods of low and high base flow when most streamflow originates from ground water.

Iowa, Minnesota↗
USGS2001

Occurrence, distribution, and transport of nutrients in Eastern Iowa Rivers

Eleven streams in the Wapsipinicon, Cedar, Iowa, and Skunk River basins in eastern Iowa were sampled monthly from March 1996 through September 1998 to assess the occurrence, distribution, and transport of nitrogen, phosphorus, and suspended sediment as part of the U.S. Geological Survey's National Water-Quality Assessment Program. At least one form of dissolved nitrogen and phosphorus was detected in every sample collected. Nitrate accounted for 92 percent of the dissolved nitrogen. About 22 percent of the samples contained nitrate that exceeded the U.S. Environmental Protection Agency's Maximum Contaminant Level of 10 milligrams per liter (mg/L) as nitrogen in drinking water. The median concentration of total nitrogen for surface water in the study area was 7.2 mg/L. Dissolved phosphorus was predominately in the form of orthophosphate. The median total phosphorus concentration for the study area was 0.22 mg/L. About 75 percent of the total phosphorus concentrations exceeded the U.S. Environmental Protection Agency recommended total phosphorus concentration of 0.10 mg/L or less to minimize algal growth in streams not discharging directly into lakes or impoundments. Median suspended-sediment concentration for the study area was 82 mg/L. Nitrogen, phosphorus, and suspended-sediment concentrations varied annually and seasonally. Nitrogen, phosphorus, and suspended-sediment concentrations increased each year of the study due to increased precipitation and runoff. Concentrations were typically higher in the spring after fertilizer application and runoff. In winter, nitrogen concentrations typically increased when there was little instream assimilation by aquatic plants and algae. Nitrogen and phosphorus concentrations decreased in late summer when there was less runoff and instream assimilation of nitrogen and phosphorus by aquatic plants and algae was high. Suspended-sediment concentrations were highest in early summer during runoff and lowest in January when there was ice cover with very little overland flow contributing to rivers and streams. Streams draining small- to medium-sized watersheds that have uniform land use and geology had significantly (p < 0.05) higher total dissolved-nitrogen concentrations (median, 8.2 mg/L) than did samples from large rivers (median, 6.2 mg/L) that drain basins with mixed land use and geology. Samples from large rivers typically had significantly (p< 0.05) higher total phosphorus and suspended-sediment concentrations than did samples from small rivers and streams. Concentrations varied between drainage basins due to land use and physiography. Basins that are located in areas with a higher percentage of row-crop agriculture typically had samples with higher nitrogen concentrations than did basins with less row-crop agriculture. In addition, basins that drain the Southern Iowa Drift Plain and the Des Moines Lobe typically had samples with higher total phosphorus and suspended-sediment concentrations than did basins that drain other landform regions. Total nitrogen and total phosphorus loads were typically proportional to the size of the drainage basin. Total nitrogen loads increased each year from 1996 through 1998 in conjunction with increased concentrations and runoff. However, total phosphorus loads in the Skunk River Basin decreased in 1997 due to less runoff. Total phosphorus loads followed the same pattern as total nitrogen loads with increases in 1998. Total nitrogen and total phosphorus loads varied seasonally and the highest loads typically occurred in early spring and summer after fertilizer application and runoff. Loads were lowest in January and September when there was little runoff to transport nitrogen and phosphorus to the rivers and streams. Total nitrogen loads contributed to the Mississippi River from the Eastern Iowa Basins during 1996, 1997, and 1998 were 97,000, 120,000, and 230,000 metric tons respectively. Total phosphorus loads contributed to the Mississippi River from the Eastern Iowa Basins during 1996, 1997, and 1998 were 6,900, 4,600, and 8,800 metric tons, respectively. The highest nitrogen and phosphorus yields typically occurred in streams draining small watersheds that were dominated by a single land use and geology. Sampling sites located in drainage basins with higher row-crop percentage typically had higher nitrogen and phosphorus yields. Sites that were located in the Des Moines Lobe and the Southern Iowa Drift Plain typically had higher phosphorus yields probably due to more erodible soils and steeper slopes.

Iowa↗
USGS2001

Water quality in the eastern Iowa basins

This article summarizes major findings about nutrients in surface and groundwater in the eastern Iowa basins (see map) between 1996 and 1998. The data were collected as part of the U.S. Geological Survey (USGS) National Water-Quality Assessment Program (NAWQA). Water quality is discussed in terms of local and regional issues and compared with conditions found in all 36 National NAWQA study areas assessed to date. Findings are explained in the context of selected national U.S. Environmental Protection Agency (EPA) benchmarks, such as those for drinking water quality and the protection of aquatic organisms. The Eastern Iowa Basins Study Unit includes the Wapsipinicon, Cedar, Iowa, and Skunk River basins and covers approximately 19,500 square miles in eastern Iowa and southern Minnesota. More than 90 percent of the land in the study unit is used for agricultural purposes. Forested areas account for only 4 percent of the land area.

Iowa, Minnesota↗
USGS2001

Occurrence and distribution of pesticides in streams of the Eastern Iowa Basins, 1996-98

The U.S. Geological Survey began collection of water samples in streams of the Eastern Iowa Basins in 1996 for the analysis of pesticides and pesticide degradates as part of the National Water Quality Assessment Program (NAWQA). This study provides some of the first large scale monitoring data on pesticides and pesticide degradates in Eastern Iowa. Three hundred and forty-four samples were collected from 1996-98 to document the occurrence, distribution, and transport of pesticide compounds. Pesticide analysis included 80 pesticide compounds and 10 pesticide degradates. The Eastern Iowa Basins study encompasses about 50,500 square kilometers (19,500 square miles) and is drained by four major rivers--the Wapsipinicon, Cedar, Iowa, and Skunk. Agriculture accounts for approximately 93 percent of the land use in the study area. The most commonly detected pesticides were those most heavily used on crops. The triazine (atrazine and cyanazine) and chloroacetanilide (alachlor, acetochlor, and metolachlor) pesticides are some of the most heavily used (by weight) historically and during the period of data collection 1996-98. Atrazine and metolachlor were detected in all samples. Acetochlor, alachlor, and cyanazine were detected in more than 70 percent of all surface-water samples. Few non-agricultural herbicides were detected. One exception, prometon was detected in more than 80 percent of the samples at very low concentrations (less than 0.1 micrograms per liter). Pesticide degradates were some of the most frequently detected pesticide compounds in the study. Four pesticide degradates--metolachlor ethane sulfonic acid (metolachlor ESA), alachlor ethane sulfonic acid (alachlor ESA), metolachlor oxanilic acid (metolachlor OA), and acetochlor ethane sulfonic acid (acetochlor ESA) were detected in more than 75 percent of the samples. A few insecticides that may pose potential risk to aquatic invertebrates were detected in streams from May through September, the months when most application normally occurs. Carbofuran was the most commonly detected insecticide (16 percent of all samples). Although detected in less than 20 percent of all samples, carbofuran was detected in 68 percent of the samples in June. When present, carbofuran concentrations were generally less than 0.80 micrograms per liter. Chloropyrifos was detected in about seven percent of the samples. As with other insecticides, chlorpyrifos was detected most frequently in June (30 percent). The highest concentration was 0.06 micrograms per liter. Diazinon, a common urban insecticide found in other NAWQA studies throughout the Nation, was detected in only 2 percent of the samples in the Eastern Iowa Basins study. Pesticides were found to occur in mixtures with several compounds rather than individually. Four or more parent pesticide compounds were detected in 91 percent of the water samples and seven or more parent compounds were detected in 46 percent of the water samples. Four or more pesticide degradates were detected in 93 percent of the water samples and seven or more pesticide degradates were detected in 46 percent of the water samples. Commonly applied parent pesticide compounds (acetochlor, alachlor, atrazine, cyanazine, and metolachlor) were generally detected at low concentrations with median concentrations ranging from 0.01 to 0.22 micrograms per liter. The median concentrations for the pesticide degradates were larger than their parent compounds. Median concentrations for the pesticide degradates ranged from 0.07 to 3.7 micrograms per liter. Acetochlor, alachlor, atrazine, cyanazine and metolachlor pesticides compounds were present at least an order of magnitude or higher in the late spring and summer than at other times of the year. The maximum measured concentrations for acetochlor, atrazine, cyanazine and metolachor were approximately 11 to 48 micrograms per liter (the maximum for alachlor was 0.56 micrograms per liter). In contrast, maximum measured concentrations for the total pesticide degradates were lower than their parent compounds and ranged from approximately 0.7 to 12 micrograms per liter. The maximum measured concentration of a single pesticide compound was for atrazine at 48 micrograms per liter. Seasonal patterns of atrazine, acetochlor, alachlor, cyanazine, and metolachlor generally show peak concentrations following application in May and June and decreasing during remainder of the growing season. In addition, a small secondary peak in atrazine, acetochlor, alachlor, cyanazine, and metolachlor concentrations occurred at all sites in late winter. This secondary peak may be attributed to early "winter thaw" that can release pesticide residue from soil, making pesticides available to be transported to surface water by snowmelt and early spring rains. Pesticide degradates account for a significant portion of the total pesticide load at all sites. Eighty-one percent of the total pesticide load in samples from Iowa River near Rowan, Wolf Creek near Dysart, and the Iowa River at Wapello were as pesticide degradates. The pesticide degradates for the triazine compounds tended to follow the load pattern of the parent pesticide compounds closely throughout the year. In general, the degradate loads calculated for the triazine compounds were smaller than loads calculated for their parent pesticides. The loads for the chloroacetanilide degradate compounds were larger than those for the parent pesticides. The loads for alachlor were found to be small or nonexistent. Alachlor has been heavily used in the past, but since 1995 has been largely replaced by acetochlor or other herbicides. The loads for all degradates were higher than the parent compounds during the winter months. Overland flow may be diminished during the winter months, but shallow sub-soil drainage and ground-water flow may be a source of many pesticide degradates during the late fall and winter. Occurrence of pesticide compounds varied by landform region. The triazine herbicides, atrazine and cyanazine and their degradates were present in significantly greater concentrations in the Southern Iowa Drift Plain (predominantly loess soils) than either the Des Moines Lobe or the Iowan Surface (predominantly till soils). Less atrazine and cyanazine are applied to till soils because of pH and organic carbon content. Alachlor, metolachlor, and acetochlor have often been used to offset triazine pesticide reductions in area with till soils.

Iowa↗
USGS2000

Water quality in the eastern Iowa basins, Iowa and Minnesota, 1996-98

The water quality in rivers and streams and in selected aquifers in eastern Iowa and part of southern Minnesota is described and illustrated. Major ions, nitrogen and other nutrients, and pesticides and some of their breakdown compounds were analyzed in both surface and ground water. Biological communities that included fish, invertebrates, and algae, were described in relation to stream water quality. Volatile organic compounds that originate from fuels, solvent, and industry were analyzed from ground-water samples. Agricultural and urban land-use effects on shallow ground-water compared and contrasted.

Iowa, Minnesota↗
USGS1999

Water-quality assessment of the eastern Iowa basins: Data, September 1995 through September 1996

The U.S. Geological Survey began data-collection activities in the Eastern Iowa Basins study unit of the National Water-Quality Assessment Program in September 1995 with the purpose of determining the status and trends in water quality. Surface-water data were collected, beginning in March 1996, on a monthly basis with occasional extra high- and low-flow samples. Data collected from 12 sites on rivers and streams in the study unit included determinations of the physical properties and concentrations of nutrients, major ions, organic carbon, trace elements, suspended sediment, and dissolved pesticides. Data collected at four additional sites included physical parameters and determination of the concentration of dissolved pesticides. In addition, bed-sediment and fish-tissue samples were collected at 16 sites and analyzed for trace elements and hydrophobic pesticides. There were two ground-water studies conducted in June and July 1996. The first looked at the quality of ground water in the Silurian-Devonian and Upper Carbonate aquifers and sampled 33 wells once, and the second examined the effects of agriculture on shallow ground water of the Iowa River alluvial aquifer and sampled 23 wells once. Ground-water samples were analyzed for physical properties, nutrients, major ions, organic carbon, trace elements, dissolved pesticides, and volatile organic compounds.

Iowa, Minnesota↗
USGS1999

Selected nutrients and pesticides in streams of the eastern Iowa basins, 1970-95

Water-quality data from 17 surface-water monitoring sites were compiled for 1970 through 1995 and analyzed to determine historical waterquality conditions and possible trends in the Eastern Iowa Basins study unit as part of the U.S. Geological Survey's National Water-Quality Assessment Program. The Eastern Iowa Basins encompasses the Wapsipinicon, Cedar, Iowa, and Skunk River Basins and covers about 19,500 square miles. Seven of the monitoring sites were sampled by the Iowa Department of Natural Resources, three sites by the Minnesota Pollution Control Agency, three sites by the University of Iowa Institute for Hydraulic Research, and four sites by the U.S. Geological Survey. Water-quality analyses typically consisted of nitrate, ammonia, total nitrogen, and total phosphorus, with limited analyses available for organic nitrogen, dissolved phosphorus, dissolved orthophosphate, and water-soluble pesticides. Long-term historical nutrient and pesticide data were not available for the Wapsipinicon River Basin. Median concentrations for total nitrogen ranged from 4.6 to 9.4 milligrams per liter, and maximum concentrations of total nitrogen ranged from 4.6 to 31 milligrams per liter. The majority of nitrogen transported in surface waters of the Eastern Iowa Basins study unit is in the form of nitrate (nitrogen). Median concentrations of total phosphorus ranged from less than 0.10 to 0.66 milligram per liter, and maximum concentrations of total phosphorus ranged from less than 0.10 to 5.4 milligrams per liter. Nitrate varied seasonally. Median concentrations of nitrate were largest during the spring and the winter (6.0 to 7.0 milligrams per liter) compared to the summer and fall (2.0 to 4.0 milligrams per liter). Concentrations of nitrate greater than 10 milligrams per liter typically occurred during spring runoff. Median ammonia concentrations generally were highest during the winter (approximately 0.3-0.5 milligram per liter) compared to the spring and summer when ammonia concentrations were often close to the detection limit (0.01 milligram per liter). In general, the median concentrations of total phosphorus varied less than 0.1 milligram per liter between seasons. The statistical analysis of the nutrient data typically indicated a strong positive correlation of nitrate with streamflow. Total phosphorus concentrations with streamflow showed greater variability than nitrate, perhaps reflecting the greater potential of transport of phosphorus on sediment rather than in the dissolved phase as with nitrate. Ammonia and ammonia plus organic nitrogen showed no correlation with streamflow or a weak positive correlation. Seasonal variations and the relations of nutrients and pesticides to streamflow generally corresponded with nonpoint‑source loadings, although possible point sources for nutrients were indicated by the data at selected monitoring sites. Statistical trend tests for concentrations and loads were computed for nitrate, ammonia, and total phosphorus. Trend analysis indicated decreases for ammonia and total phosphorus concentrations at several sites and increases for nitrate concentrations at other sites in the study unit.

Iowa, Minnesota↗