Geology topics

Research about Michigan

Source-linked reports with geographic coverage including Michigan.

At least 289 records · Page 16Linked to original sources

USGS2005

Mortality of Rocky Mountain elk in Michigan due to meningeal worm

Mortality from cerebrospinal parelaphostrongylosis caused by the meningeal worm ( Parelaphostrongylus tenuis ) has been hypothesized to limit elk ( Cervus elaphus nelsoni ) populations in areas where elk are conspecific with white-tailed deer ( Odocoileus virginianus ). Elk were reintroduced into Michigan (USA) in the early 1900s and subsequently greatly increased population size and distribution despite sympatric high-density (≥12/km 2 ) white-tailed deer populations. We monitored 100 radio-collared elk of all age and sex classes from 1981–94, during which time we documented 76 mortalities. Meningeal worm was a minor mortality factor for elk in Michigan and accounted for only 3% of mortalities, fewer than legal harvest (58%), illegal kills (22%), other diseases (7%), and malnutrition (4%). Across years, annual cause-specific mortality rates due to cerebrospinal parelaphostrongylosis were 0.033 (SE=0.006), 0.029 (SE=0.005), 0.000 (SE=0.000), and 0.000 (SE=0.000) for calves, 1-yr-old, 2-yr-old, and ≥3-yr-old, respectively. The overall population-level mortality rate due to cerebrospinal parelaphostrongylosis was 0.009 (SE=0.001). Thus, meningeal worm had little impact on elk in Michigan during our study despite greater than normal precipitation (favoring gastropods) and record (≥14 km 2 ) deer densities. Further, elk in Michigan have shown sustained population rates-of-increase of ≥18%/yr and among the highest levels of juvenile production and survival recorded for elk in North America, indicating that elk can persist in areas with meningeal worm at high levels of population productivity. It is likely that local ecologic characteristics among elk, white-tailed deer, and gastropods, and degree of exposure, age of elk, individual and population experience with meningeal worm, overall population vigor, and moisture determine the effects of meningeal worm on elk populations.

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USGS2004

A hydrogeologic model of stratiform copper mineralization in the Midcontinent Rift System, Northern Michigan, USA

This paper presents a suite of two-dimensional mathematical models of basin-scale groundwater flow and heat transfer for the middle Proterozoic Midcontinent Rift System. The models were used to assess the hydrodynamic driving mechanisms responsible for main-stage stratiform copper mineralization of the basal Nonesuch Formation during the post-volcanic/pre-compressional phase of basin evolution. Results suggest that compaction of the basal aquifer (Copper Harbor Formation), in response to mechanical loading during deposition of the overlying Freda Sandstone, generated a pulse of marginward-directed, compaction-driven discharge of cupriferous brines from within the basal aquifer. The timing of this pulse is consistent with the radiometric dates for the timing of mineralization. Thinning of the basal aquifer near White Pine, Michigan, enhanced stratiform copper mineralization. Focused upward leakage of copper-laden brines into the lowermost facies of the pyrite-rich Nonesuch Formation resulted in copper sulfide mineralization in response to a change in oxidation state. Economic-grade mineralization within the White Pine ore district is a consequence of intense focusing of compaction-driven discharge, and corresponding amplification of leakage into the basal Nonesuch Formation, where the basal aquifer thins dramatically atop the Porcupine Mountains volcanic structure. Equilibrium geochemical modeling and mass-balance calculations support this conclusion. We also assessed whether topography and density-driven flow systems could have caused ore genesis at White Pine. Topography-driven flow associated with the Ottawan orogeny was discounted because it post-dates main-stage ore genesis and because recent seismic interpretations of basin inversion indicates that basin geometry would not be conductive to ore genesis. Density-driven flow systems did not produce focused discharge in the vicinity of the White Pine ore district.

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USGS2004

Fleet dynamics of the commercial lake trout fishery in Michigan waters of Lake Superior during 1929-1961

Understanding fishing fleet dynamics is important when using fishery dependent data to infer the status of fish stocks. We analyzed data from mandatory catch reports from the commercial lake trout ( Salvelinus namaycush ) fishery in Michigan waters of Lake Superior during 1929–1961, a period when lake trout populations collapsed through the combined effects of overfishing and sea lamprey ( Petromyzon marinus ) predation. The number of full-time fishermen increased during 1933–1943 and then decreased during 1943–1957. Addition of new fishermen was related to past yield, market prices, World War II draft exemptions, and lost fishing opportunities in Lake Huron and Lake Michigan. Loss of existing fishermen was related to declining lake trout density. Large mesh (≥ 114-mm stretch-measure) gill net effort increased during 1929–1951 because fishermen fished more net inshore as lake trout density declined, even though catch per effort (CPE) was often higher in deeper waters. The most common gill net mesh size increased from 114-mm to 120-mm stretch-measure during 1929–1957, as lake trout growth increased. More effort was fished inshore than offshore and the amount of inshore effort was less variable over time than offshore effort. Relatively stable yield was maintained by increasing gill net effort and by moving some effort to better grounds. Because fishing-up caused yield and CPE to remain high despite declining lake trout abundance, caution must be used when basing goals for lake trout restoration on historical fishery indices.

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USGS2004

Late Holocene lake-level variation in southeastern Lake Superior: Tahquamenon Bay, Michigan

Internal architecture and ages of 71 beach ridges in the Tahquamenon Bay embayment along the southeastern shore of Lake Superior on the Upper Peninsula of Michigan were studied to generate a late Holocene relative lake-level curve. Establishing a long-term framework is important to examine the context of historic events and help predict potential future changes critical for effective water resource management. Ridges in the embayment formed between about 4,200 and 2,100 calendar years before 1950 (cal. yrs. B.P.) and were created and preserved every 28 ± 4.8 years on average. Groups of three to six beach ridges coupled with inflections in the lake-level curve indicate a history of lake levels fluctuations and outlet changes. A rapid lake-level drop (approximately 4 m) from about 4,100 to 3,800 cal. yrs. B.P. was associated with a fall from the Nipissing II high-water-level phase. A change from a gradual fall to a slight rise was associated with an outlet change from Port Huron, Michigan/Sarnia, Ontario to Sault Ste. Marie, Michigan/Ontario. A complete outlet change occurred after the Algoma high-water-level phase (ca. 2,400 cal. yrs. B.P.). Preliminary rates of vertical ground movement calculated from the strandplain are much greater than rates calculated from historical and geologic data. High rates of vertical ground movement could have caused tectonism in the Whitefish Bay area, modifying the strandplain during the past 2,400 years. A tectonic event at or near the Sault outlet also may have been a factor in the outlet change from Port Huron/Sarnia to Sault Ste. Marie.

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USGS2004

The importance of hyporheic sediment respiration in several mid-order Michigan rivers: Comparison between methods in estimates of lotic metabolism

Metabolism was measured in four Michigan streams, comparing estimates made using a flow-through chamber designed to include the hyporheic zone to a 20 cm depth and a traditional closed chamber that enclosed to a 5 cm depth. Mean levels of gross primary productivity and community respiration were consistently greater in the flow-through chamber than the closed chamber in all streams. Ratios of productivity to respiration (P/R) were consistently greater in the closed chambers than the flow-through chambers. P/R ratios were consistently <1 in all streams when estimated with flow-through chambers, suggesting heterotrophic conditions. Maintenance of stream ecosystem structure and function therefore is dependent on subsidies either from the adjacent terrestrial system or upstream sources. Our results suggest that stream metabolism studies that rely on extrapolation of closed chambers to the whole reach will most likely underestimate gross primary productivity and community respiration.

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USGS2004

Analysis of modern and Pleistocene hydrologic exchange between Saginaw Bay (Lake Huron) and the Saginaw Lowlands area

Two numerical models, one simulating present groundwater flow conditions and one simulating ice-induced hydraulic loading from the Port Huron ice advance, were used to characterize both modern and Pleistocene groundwater exchange between the Michigan Basin and near-surface water systems of Saginaw Bay (Lake Huron) and the surrounding Saginaw Lowlands area. These models were further used to constrain the origin of saline, isotopically light groundwater, and porewater from the study area. Output from the groundwater-flow model indicates that, at present conditions, head in the Marshall aquifer beneath Saginaw Bay exceeds the modern lake elevation by as much as 21 m. Despite this potential for flow, simulated ground-water discharge through the Saginaw Bay floor constitutes only 0.028 m 3 s −1 (∼1 cfs). Bedrock lithology appears to regulate the rate of groundwater discharge, as the portion of the Saginaw Bay floor underlain by the Michigan confining unit exhibits an order of magnitude lower flux than the portion underlain by the Saginaw aquifer. The calculated shoreline discharge of groundwater to Saginaw Bay is also relatively small (1.13 m 3 s −1 or ∼40 cfs) because of low gradients across the Saginaw Lowlands area and the low hydraulic conductivities of lodgement tills and glacial-lake clays surrounding the bay. In contrast to the present groundwater flow conditions, the Port Huron ice-induced hydraulic-loading model generates a groundwater-flow reversal that is localized to the region of a Pleistocene ice sheet and proglacial lake. This area of reversed vertical gradient is largely commensurate with the distribution of isotopically light groundwater presently found in the study area. Mixing scenarios, constrained by chloride concentrations and δ 18 O values in porewater samples, demonstrate that a mixing event involving subglacial recharge could have produced the groundwater chemistry currently observed in the Saginaw Lowlands area. The combination of models and mixing scenarios indicates that structural control is a major influence on both the present and Pleistocene flow systems.

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USGS2004

Influence of near-surface stratigraphy on coastal landslides at Sleeping Bear Dunes National Lakeshore, Lake Michigan, USA

Lake-level change and landslides are primary controls on the development of coastal environments along the coast of northeastern Lake Michigan. The late Quaternary geology of Sleeping Bear Dunes National Lakeshore was examined with high-resolution seismic reflection profiles, ground-penetrating radar (GPR), and boreholes. Based on sequence-stratigraphic principles, this study recognizes ten stratigraphic units and three major unconformities that were formed by late Pleistocene glaciation and postglacial lake-level changes. Locally high sediment supply, and reworking by two regressions and a transgression have produced a complex stratigraphy that is prone to episodic failure. In 1995, a large landslide deposited approximately 1 million m3 of sediment on the lake floor. The highly deformed landslide deposits, up to 18 m thick, extend 3-4 km offshore and unconformably overlie well-stratified glacial and lacustrine sediment. The landslide-prone bluff is underlain by channel-fill deposits that are oriented nearly perpendicular to the shoreline. The paleochannels are at least 10 m deep and 400 m wide and probably represent stream incision during a lake-level lowstand about 10.3 ka B.P. The channels filled with sediment during the subsequent transgression and lake-level highstand, which climaxed about 4.5 ka B.P. As lake level fell from the highstand, the formation of beach ridges and sand dunes sealed off the channel and isolated a small inland lake (Glen Lake), which lies 5 m above the level of Lake Michigan and may be a source of piped groundwater. Our hypothesis is that the paleochannels act as conduits for pore water flow, and thereby locally reduce soil strength and promote slope failure.

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USGS2004

Michigan lakes: An assessment of water quality

Michigan has more than 11,000 inland lakes, that provide countless recreational opportunities and are an important resource that makes tourism and recreation a $15-billion-dollar per-year industry in the State (Stynes, 2002). Knowledge of the water-quality characteristics of inland lakes is essential for the current and future management of these resources. Historically the U. S. Geological Survey (USGS) and the Michigan Department of Environmental Quality (MDEQ) jointly have monitored water quality in Michigan's lakes and rivers. During the 1990's, however, funding for surface-water-quality monitoring was reduced greatly. In 1998, the citizens of Michigan passed the Clean Michigan Initiative to clean up, protect, and enhance Michigan's environmental infrastructure. Because of expanding water-quality-data needs, the MDEQ and the USGS jointly redesigned and implemented the Lake Water-Quality Assessment (LWQA) Monitoring Program (Michigan Department of Environmental Quality, 1997).

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USGS2004

Factors affecting ground-water quality in Oakland County, Michigan

Ground water is water stored in pores within soil and rock beneath the land surface. When these pores are connected so that water can be transmitted to wells or springs, these bodies of soil and rock are termed aquifers, from two Greek words meaning “water” and “to bear.”

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USGS2004

Arsenic, nitrate, and chloride in groundwater, Oakland County, Michigan

In 1996, the U.S. Geological Survey (USGS), in cooperation with the Michigan Department of Environmental Quality (MDEQ) and nine southeast Michigan counties, began a study of the factors controlling arsenic concentrations in drinking water. The early results of this study raised broader concerns in Oakland County about the quality of groundwater in general and drinking water in particular. In response to these concerns, Oakland County worked with the USGS and the Center for Applied Environmental Research at the University of Michigan – Flint (CAER) to study distributions of arsenic, nitrate, and chloride in groundwater, with emphasis on sites where concentrations of these constituents exceeded the Maximum Contaminant Levels (MCL’s) and Secondary Maximum Contaminant Levels (SMCL’s) set by the U.S. Environmental Protection Agency (USEPA). The maps produced for this report are based on historical data compiled from MDEQ records. This fact sheet is a revision of USGS Fact Sheet 135-98, “Arsenic, nitrate, and chloride in groundwater in Oakland County in Oakland County, Michigan” (Aichele and others, 1998) to incorporate revisions to the USEPA MCL for arsenic.

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USGS2004

Simulation of ground-water flow in the Vevay Township area, Ingham County, Michigan

Ground water is the primary source of water for domestic, public-supply, and industrial use within the Tri-County region that includes Clinton, Eaton, and Ingham Counties in Michigan. Because of the importance of this ground-water resource, numerous communities, including the city of Mason in Ingham County, have begun local Wellhead Protection Programs. In these programs, communities protect their groundwater resource by identifying the areas that contribute water to production wells and potential sources of contamination, and by developing methods to manage and minimize threats to the water supply. In addition, some communities in Michigan are concerned about water availability, particularly in areas experiencing water-level declines in the vicinity of quarry dewatering operations. In areas where Wellhead Protection Programs are implemented and there are potential threats to the water supply, residents and communities need adequate information to protect the water supply. In 1996, a regional ground-water-flow model was developed by the U.S. Geological Survey to simulate ground-water flow in Clinton, Eaton, and Ingham Counties. This model was developed primarily to simulate the bedrock ground-waterflow system; ground-water flow in the unconsolidated glacial sediments was simulated to support analysis of flow in the underlying bedrock Saginaw aquifer. Since its development in 1996, regional model simulations have been conducted to address protection concerns and water availability questions of local water-resources managers. As a result of these continuing model simulations, additional hydrogeologic data have been acquired in the Tri-County region that has improved the characterization of the simulated ground-water-flow system and improved the model calibration. A major benefit of these updates and refinements is that the regional Tri-County model continues to be a useful tool that improves the understanding of the ground-water-flow system in the Tri-County region, provides local water-resources managers with a means to answer ground-water protection and availability questions, and serves as an example that can be applied in other areas of the state. A refined version of the 1996 Tri-County regional ground-water-flow model, developed in 1997, was modified with local hydrogeologic information in the Vevay Township area in Michigan. This model, updated in 2003 for this study, was used to simulate ground-water flow to address groundwater protection and availability questions in Vevay Township. The 2003 model included refinement of glacial and bedrock hydraulic characteristics, better representation of the degree of connection between the glacial deposits and the underlying Saginaw aquifer, and refinement of the model cell size. The 2003 model was used to simulate regional groundwater flow, to delineate areas contributing recharge and zones of contribution to production wells in the city of Mason, and to simulate the effects of present and possible future withdrawals. The areal extent of the 10- and 40-year areas contributing recharge and the zones of contribution for the city of Mason's production wells encompass about 2.3 and 6.2 square miles, respectively. Simulation results, where withdrawals for quarry operations were represented by one well pumping at 1.6 million gallons per day, indicate that water levels would decline slightly over 1 foot approximately 2 miles from the quarry in the glacial deposits and in the Saginaw aquifer. With a reduction of the local riverbed conductance or removal of local river model cells representing Mud Creek, water-level declines would extend further west of Mud Creek and further to the north, east, and south of the simulated quarry. Simulation results indicate that water withdrawn for quarry dewatering operations would decrease ground-water recharge to nearby Mud Creek, would increase ground-water discharge from Mud Creek, and that local water levels would be lowered as a result.

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USGS2004

Simulation of the ground-water-flow system in the Kalamazoo County area, Michigan

A ground-water-flow model was developed to investigate the ground-water resources of Kalamazoo County. Ground water is widely used as a source of water for drinking and industry in Kalamazoo County and the surrounding area. Additionally, lakes and streams are valued for their recreational and aesthetic uses. Stresses on the ground-water system, both natural and human-induced, have raised concerns about the long-term availability of ground water for people to use and for replenishment of lakes and streams. Potential changes in these stresses, including withdrawals and recharge, were simulated using a ground-water-flow model. Simulations included steady-state conditions (in which stresses remained constant and changes in storage were not included) and transient conditions (in which stresses changed in seasonal and monthly time scales and storage within the system was included). Steady-state simulations were used to investigate the long-term effects on water levels and streamflow of a reduction in recharge or an increase in pumping to projected 2010 withdrawal rates, withdrawal and application of water for irrigation, and a reduction in recharge in urban areas caused by impervious surfaces. Transient simulations were used to investigate changes in withdrawals to match seasonal and monthly patterns under various recharge conditions, and the potential effects of the use of water for irrigation over the summer months. With a reduction in recharge, simulated water levels declined over most of the model area in Kalamazoo County; with an increase in pumping, water levels declined primarily near pumping centers. Because withdrawals by wells intercept water that would have discharged possibly to a stream or lake, model simulations indicated that streamflow was reduced with increased withdrawals. With withdrawal and consumption of water for irrigation, simulated water levels declined. Assuming a reduction in recharge due to urbanization, water levels declined and flow to streams was reduced based on steady-state simulation results. Transient results indicated a reduction of water levels with the simulated use of water for irrigation over the summer months. Generally the transient simulation with recharge only in the winter provided the best fit to observed water levels collected during synoptic water-level measurements in some wells and to the trends observed in water levels for other wells. Analysis of the regional hydrologic budgets provides an increased understanding of water movement within the ground-water-flow system in Kalamazoo County. Budgets for the steady-state simulations indicated that with reduced recharge, less water was available for streamflow and less water left the model area through the model boundaries. Similarly, with an increase in pumping rates, less water was available to enter streams and become streamflow. When recharge was assumed to remain constant and when it was allowed to vary throughout the year, the amount of water that entered storage was greater than that which left storage. However, when recharge was distributed through October?May only or when recharge rates were reduced from October to May, the amount of water that entered storage was less than that which left storage. Thus, on the basis of model simulations, with reduced recharge or increased withdrawals, water must come from storage, rivers, or from ground-flow-system boundaries to meet withdrawal demands.

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USGS2004

Predicting water quality by relating secchi-disk transparency and chlorophyll a measurements to satellite imagery for Michigan inland lakes, August 2002

Inland lakes are an important economic and environmental resource for Michigan. The U.S. Geological Survey and the Michigan Department of Environmental Quality have been cooperatively monitoring the quality of selected lakes in Michigan through the Lake Water Quality Assessment program. Through this program, approximately 730 of Michigan's 11,000 inland lakes will be monitored once during this 15-year study. Targeted lakes will be sampled during spring turnover and again in late summer to characterize water quality. Because more extensive and more frequent sampling is not economically feasible in the Lake Water Quality Assessment program, the U.S. Geological Survey and Michigan Department of Environmental Quality investigate the use of satellite imagery as a means of estimating water quality in unsampled lakes. Satellite imagery has been successfully used in Minnesota, Wisconsin, and elsewhere to compute the trophic state of inland lakes from predicted secchi-disk measurements. Previous attempts of this kind in Michigan resulted in a poorer fit between observed and predicted data than was found for Minnesota or Wisconsin. This study tested whether estimates could be improved by using atmospherically corrected satellite imagery, whether a more appropriate regression model could be obtained for Michigan, and whether chlorophyll a concentrations could be reliably predicted from satellite imagery in order to compute trophic state of inland lakes. Although the atmospheric-correction did not significantly improve estimates of lake-water quality, a new regression equation was identified that consistently yielded better results than an equation obtained from the literature. A stepwise regression was used to determine an equation that accurately predicts chlorophyll a concentrations in northern Lower Michigan.

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USGS2004

Geostatistical analysis of effective vertical hydraulic conductivity and presence of confining layers in the Shallow Glacial Drift Aquifer, Oakland County, Michigan

About 400,000 residents of Oakland County, Mich., rely on ground water for their primary drinking-water supply. More than 90 percent of these residents draw ground water from the shallow glacial drift aquifer. Understanding the vertical hydraulic conductivity of the shallow glacial drift aquifer is important both in identifying areas of ground-water recharge and in evaluating susceptibility to contamination. The geologic environment throughout much of the county, however, is poorly understood and heterogeneous, making conventional aquifer mapping techniques difficult. Geostatistical procedures are therefore used to describe the effective vertical hydraulic conductivity of the top 50 ft of the glacial deposits and to predict the probability of finding a potentially protective confining layer at a given location. The results presented synthesize the available well-log data; however, only about 40 percent of the explainable variation in the dataset is accounted for, making the results more qualitative than quantitative. Most of the variation in the effective vertical hydraulic conductivity cannot be explained with the well-log data currently available (as of 2004). Although the geologic environment is heterogeneous, the quality-assurance process indicated that more than half of the wells in the county’s Wellkey database (statewide database for monitoring drinking-water wells) had inconsistent identifications of lithology.

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USGS2004

Environmental factors and chemical and microbiological water-quality constituents related to the presence of enteric viruses in ground water from small public water supplies in southeastern Michigan

A study of small public ground-water-supply wells that produce water from discontinuous sand and gravel aquifers was done from July 1999 through July 2001 in southeastern Michigan. Samples were collected to determine the occurrence of viral pathogens and microbiological indicators of fecal contamination (“indicators”), determine whether indicators are adequate predictors of the presence of enteric viruses, and determine the factors that affect the presence of enteric viruses. Small systems are those that serve less than 3,300 people. Samples were analyzed for specific enteric viruses by reverse transcriptase-polymerase chain reaction (RT-PCR), for culturable viruses by cell culture, and for the indicators total coliforms, Escherichia coli (E. coli) , enterococci, and F-specific and somatic coliphage. Ancillary environmental and water-quality data were collected or compiled. A total of 169 regular samples and 32 replicate pairs were collected from 38 wells. Replicate pairs were samples collected at the same well on the same date. One well was sampled 6 times, 30 wells were sampled five times, 6 wells were sampled twice, and 1 well was sampled once. By use of RT-PCR, enterovirus was found in four wells (10.5 percent) and hepatitis A virus (HAV) in five wells (13.2 percent). In two of these wells, investigators found both enterovirus and HAV, but on different sampling dates. Culturable viruses were found one time in two wells (5.9 percent), and neither of these wells was positive for viruses by use of RT-PCR on any sampling date. If results for all viruses are combined, 9 of the 38 small public-supply wells were positive for enteric viruses (23.7 percent) by either cell culture or RT-PCR. One or more indicators were found in 18 of 38 wells. Total coliforms, E. coli , enterococci, and F-specific and somatic coliphage were found in 34.2, 10.5, 15.8, 5.9, and 5.9 percent, respectively, of the wells tested. In only 3 out of 18 wells were samples positive for an indicator on more than one date at the same well. The co-occurrence of enteric viruses and any indicator was 55.6 percent; five out of the nine virus-positive wells were also found to be positive for an indicator. Two wells with detections of viruses had a detection of total coliforms, one well had a detection of E. coli , one of enterococci, and one of F-specific coliphage. On a per sample basis, of 11 samples that were positive for enteric viruses, indicator bacteria co-occurred in only 2 samples, and coliphage were not present in any. More virus-positive samples were found at sites served by septic systems than those served by sewerlines. Sampling condition (ground water or a mixture of tank and ground water), distance to septic system, type of and distance to nearest surface-water body, well characteristics, or land use were not related to the presence of viruses or indicators. Among continuous water-quality variables, statistically significant relations were found between total coliforms and dissolved organic carbon and between total coliforms and iron. There was a statistically significant relation between chloride concentrations >20 mg/L and detections of total coliforms. Presence of nitrate and nitrite was related to the presence of other indicators ( E. coli , enterococci, and F-specific and somatic coliphage) or enteric viruses, but not to total coliforms. The data indicated that chloride-to-bromide (C1:Br) ratios may be useful as a screening tool for total coliforms and enteric viruses but not for E. coli , enterococci, and F-specific and somatic coliphage. This study provides evidence for fecal contamination of ground water from small public-supply wells, at least on an intermittent basis. Collecting data on multiple lines of evidence would be needed to reliably predict the presence of enteric viruses and protect public health. Future data collection toward this end could include repeat sampling several times a year for different indicators, measuring dissolved-organic carbon, nitrate plus nitrite, and (or) chloride concentrations, or determining C1:Br ratios. The presence of a site served by a septic system is an indication that the well may be more vulnerable to contamination than a site served by a sewerline.

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USGS2004

Sediment characteristics and configuration within the Otsego City Dam impoundment on the Kalamazoo River, Michigan, 2001-02

The removal of the Otsego City Dam on the Kalamazoo River at Otsego, Mich., is under consideration by the Michigan Department of Environmental Quality and the city of Otsego. The historical discharge of papermill waste containing polychlorinated biphenyls from sources upstream from the dam has led the U.S. Environmental Protection Agency to designate the Kalamazoo River from Morrow Dam near Comstock to its mouth near Saugatuck as a Federal Superfund site. The papermill waste is concentrated in organic sediment and kaolinite clay, with the sediment containing as much as 94 milligrams per kilogram polychlorinated biphenyls. This contaminated sediment could move if the dam is removed; therefore, it is necessary to estimate the characteristics and configuration of the sediment before removal plans begin. Data from augered sections and sediment cores show that the current Otsego City impoundment sediments were deposited in two distinctly different sedimentary environments: (1) lacustrine sediments consisting of organic-rich silt and clay, fine to medium sand, and some gravel deposited in a repetitive, cyclic fashion related to former stream velocities when the Otsego City impoundment water levels were 2-4 feet higher (1880s-1960s), and from downstream movement of lacustrine sediments during the removal of the upstream Plainwell Dam superstructure in the 1980s; and (2) more recent (1980s-2002) coarse-grained alluvium deposited on top of the lacustrine sediments. The volume of instream sediment contained within the Otsego City impoundment is estimated to be about 457,270 cubic yards. This estimate is based on the composite thicknesses of the lacustrine deposits and overlying alluvium, which were determined to contain PCBs, and does not include bank or flood-plain deposits.

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USGS2004

Hydrogeology and simulation of regional ground-water-level declines in Monroe County, Michigan

Observed ground-water-level declines from 1991 to 2003 in northern Monroe County, Michigan, are consistent with increased ground-water demands in the region. In 1991, the estimated ground-water use in the county was 20 million gallons per day, and 80 percent of this total was from quarry dewatering. In 2001, the estimated ground-water use in the county was 30 million gallons per day, and 75 percent of this total was from quarry dewatering. Prior to approximately 1990, the ground-water demands were met by capturing natural discharge from the area and by inducing leakage through glacial deposits that cover the bedrock aquifer. Increased ground-water demand after 1990 led to declines in ground-water level as the system moves toward a new steady-state. Much of the available natural discharge from the bedrock aquifer had been captured by the 1991 conditions, and the response to additional withdrawals resulted in the observed widespread decline in water levels. The causes of the observed declines were explored through the use of a regional ground-water-flow model. The model area includes portions of Lenawee, Monroe, Washtenaw, and Wayne Counties in Michigan, and portions of Fulton, Henry, and Lucas Counties in Ohio. Factors, including lowered water-table elevations because of below average precipitation during the time period (1991 - 2001) and reduction in water supply to the bedrock aquifer because of land-use changes, were found to affect the regional system, but these factors did not explain the regional decline. Potential ground-water capture for the bedrock aquifer in Monroe County is limited by the low hydraulic conductivity of the overlying glacial deposits and shales and the presence of dense saline water within the bedrock as it dips into the Michigan Basin to the west and north of the county. Hydrogeologic features of the bedrock and the overlying glacial deposits were included in the model design. An important step of characterizing the bedrock aquifer was the determination of inputs and outputs of water—leakage from glacial deposits and flows across model boundaries. The imposed demands on the groundwater system create additional discharge from the bedrock aquifer, and this discharge is documented by records and estimates of water use including: residential and industrial use, irrigation, and quarry dewatering. Hydrologic characterization of Monroe County and surrounding areas was used to determine the model boundaries and inputs within the ground-water model. MODFLOW-2000 was the computer model used to simulate ground-water flow. Predevelopment, 1991, and 2001 conditions were simulated with the model. The predevelopment model did not include modern water use and was compared to information from early settlement of the county. The 1991 steady-state model included modern demands on the ground-water system and was based on a significant amount of data collected for this and previous studies. The predevelopment and 1991 simulations were used to calibrate the numerical model. The simulation of 2001 conditions was based on recent data and explored the potential ground-water levels if the current conditions persist. Model results indicate that the ground-water level will stabilize in the county near current levels if the demands imposed during 2001 are held constant.

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USGS2004

Lake level variability in Silver Lake, Michigan: a response to fluctuations in lake levels of Lake Michigan

Sediment from Silver Lake, Michigan, can be used to constrain the timing and elevation of Lake Michigan during the Nipissing transgression. Silver Lake is separated from Lake Michigan by a barrier/dune complex and the Nipissing, Calumet, and Glenwood shorelines of Lake Michigan are expressed landward of this barrier. Two Vibracores were taken from the lake in February 2000 and contain pebbly sand, sand, buried soils, marl, peat, and sandy muck. It is suggested here that fluctuations in the level of Lake Michigan are reflected in Silver Lake since the Chippewa low phase, and possibly at the end of the Algonquin phase. An age of 12,490 B.P. (10,460±50 14 C yrs B.P.) on wood from a buried Entisol may record the falling Algonquin phase as the North Bay outlet opened. A local perched water table is indicated by marl deposited before 7,800 B.P. and peat between 7,760-7,000 B.P. when Lake Michigan was at the low elevation Chippewa phase. Continued deepening of the lake is recorded by the transition from peat to sandy muck at 7,000 B.P. in the deeper core, and with the drowning of an Inceptisol nearly 3 m higher at 6,410 B.P. in the shallower core. A rising groundwater table responding to a rising Lake Michigan base level during the Nipissing transgression, rather than a response to mid-Holocene climate change, explains deepening of Silver Lake. Sandy muck was deposited continually in Silver Lake between Nipissing and modern time. Sand lenses within the muck are presumed to be eolian in origin, derived from sand dunes advancing into the lake on the western side of the basin.

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