Ground water discharge to the Great Lakes around the Lower Peninsula of Michigan is primarily from recharge in riparian basins and proximal upland areas that are especially important to the northern half of the Lake Michigan shoreline. A steady-state finite-difference model was developed to simulate ground water flow in four regional aquifers in Michigan's Lower Peninsula: the Glaciofluvial, Saginaw, Parma-Bayport, and Marshall aquifers interlayered with the Till/"red beds," Saginaw, and Michigan confining units, respectively. The model domain was laterally bound by a continuous specified-head boundary, formed from lakes Michigan, Huron, St. Clair, and Erie, with the St. Clair and Detroit River connecting channels. The model was developed to quantify regional ground water flow in the aquifer systems using independently determined recharge estimates. According to the flow model, local stream stages and discharges account for 95% of the overall model water budget; only 50% enters the lakes directly from the ground water system. Direct ground water discharge to the Great Lakes' shorelines was calculated at 36 m3/sec, accounting for 5% of the overall model water budget. Lowland areas contribute far less ground water discharge to the Great Lakes than upland areas. The model indicates that Saginaw Bay receives only approximately 1.13 m3/sec ground water; the southern half of the Lake Michigan shoreline receives only approximately 2.83 m3/sec. In contrast, the northern half of the Lake Michigan shoreline receives more than 17 m3/sec from upland areas.

This report is written for municipalities, industries, institutions, con sultants, drillers, hydrologists, and other people interested in the ground water resources of the State. What this report contains Data on the yield of wells, pumpage, quality of water, and trends of ground water levels for the past 5 years are shown in the text. Many hydrographs are included to illustrate changes in water levels. Yield data are given as they were reported by water departments and consultants. Also included are data on municipal, public, and industrial water-supply facilities. Tables 1, 2, and 3 contain records of water levels in observation wells, well locations, depths, altitudes, aquifers tapped, water-level extremes, records of pumpage by most major groundwater users in the State, and water quality data from selected wells sampled during 1975-77. Figure 1 shows distribution of observation wells in the State. How records can be obtained Complete tabulations of water-level measurements, hydrographs for observa tion wells, records of chemical quality, water-temperature measurements, well records and logs, aquifer tests, records of pumping for public and industrial supplies, and water-resources reports are on file for public inspection. They may be examined at the Geological Survey Division,

A steady-state finite difference model was developed to simulate ground-water flow in four regional aquifers in Michigan's Lower Peninsula. The Glaciofluvial, Saginaw, Parma-Bayport, and Marshall aquifers were simulated as layers 1 through 4, respectively, in the model. Separately calculated vertical conductances input to the model were used to simulate the intervening Till/"Red Beds", Saginaw, and Michigan confining units, respectively. The model domain was laterally bound by a continuous specifiedhead boundary, formed from Lakes Michigan, Huron, St. Clair, and Erie, together with the St. Clair and Detroit River connecting channels.The model was developed to quantify regional ground-water flow in the aquifer systems using independently determined recharge estimates. The flow model showed that groundwater heads and flows in the Glaciofluvial aquifer are controlled by local stream stages and discharges, resulting in localized flow cells accounting for 95-percent of the overall model water budget. Simulation of recharge to an unspecified water table also enabled the estimation of ground-water discharge to three Great Lakes.A computer diskette contains all MODFLOW and MODFLOWP input files, as well as digital model surfaces and several Fortran processing routines used to construct the surfaces. The diskette also provides the data used for calibration and sensitivity analysis.

Water levels, locations, depths, and aquifers tapped are given for 117 observation wells. Tabulated data include extremes of water levels for 1982 and for the period of record, pumpage of most major groundwater users in the State, and quality data on selected wells. The largest reported user of groundwater , the city of Lansing, pumped 8.2 billion gallons from the Saginaw Formation and glacial deposits. INTRODUCTION Purpose This report makes available, through 1982, the records of water levels and related data for the principal aquifers of the State. It is written for municipalities, industries, institutions, consultants, drillers, hydrologists and other people interested in groundwater resources. Scope Data on yield of wells, pumpage, quality of water, and trends of groundwater levels for the past 5 years are shown in the text. Many hydrographs are included to illustrate changes in water levels. Records of water levels in observation wells, records of pumpage by most major groundwater users, and waterquality data from selected wells sampled during 1982 are given in tables 1, 2, and 3. Distribution of observation wells is shown in figure 1. Locations of wells selected for collection of water-quality samples and years sampled are shown in figure 2. EXPLANATION | | 0 observation wells [;! !;!;!] I to 4 observation wells 5 to ' 5 30 60 MILES 40 80 KILOMETERS Figure 1.-Distribution of observation wells. Water levels were monitored in 117 observation wells in 1982. 75 Water-quality collection site; number indicates last two digit of year collected Figure 2.-Water-quality collection sites and year sample collected (water-quality data are given in the annual groundwater report for year in which sample was collected except that data for the years 1975-76 are in the annual report for 1977). Groundwater records and reports Tabulations of water-level measurements, hydrographs for observation wells, records of chemical quality, water-temperature measurements, well records and logs, aquifer tests, records of pumping for public and industrial supplies, and water-resouurces reports are on file for public inspection. They may be examined at the Geological Survey Division,

Water levels, locations, depths, and aquifers tapped are given for 112 observation wells. Tabulated data include extremes of water levels for calendar year 1987 and for the period of record, pumpage of most major ground-water users in the State, and water-quality data from selected wells. The largest municipal user of ground water, the city of Lansing, pumped 7.8 billion gallons from the Saginaw Formation and glacial deposits in 1987. SUPERIOR 46 78 EXPLANATION WELL AT WHICH WATER-QUALITY DATA WAS COLLECTED-Number indicates last two digits of year data was collected 20 40 60 80 MILES 0 20 40 60 80 100 KILOMETERS Base from U.S. Geological Survey 1:500,000 map LAKE ERIE Figure 2. Water-quality sampling sites and year sample collected. (Water-quality data are given in the Michigan annual ground-water report for year in which sample was collected Data for the years 1975-76 are in the annual report for 1977.) Ground-Water Records and Reports Tabulations of water-level measurements, hydrographs of observation wells, chemical analyses, water-temperature measurements, well records and logs, aquifer tests, records of pumping for public and industrial supplies, and water resources reports are on file for public inspection.