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Home My WebLink AboutWHPA Executive Summary t". ';i .,. WHPA Executive Summary Assessment of the Effects of Proposed Mine Expansion at the South Mueller Property on Public Water Supply Wells near Carmel, Indiana 10th August 2004 Introduction Carmel's municipal drinking water is currently supplied by approximately 20 production wells, most of which are located within a mile of the White River in south-central Hamilton County, Indiana. Some of the wells have been in operation since before 1960 but most of the production comes from the most recent additions to the system at Plants 4 and 5. Most of the wells are screened in sand and gravel along the edge of a thick outwash aquifer that roughly coincides with the flood plain of the White River. The wells vary in both depth and yield. In order to satisfy the pace of residential growth in the area the annual production of the four water plants nearly doubled between 1997 and 2002. Carmel's average annual production in 2000-2003 was approximately 8 mil- lion gallons per day (MGD) with Plant 4 pumping and average of 0.7 MGD. It is expected that water use will continue to increase rapidly in the future; 1 '". ~ " for example, the proposed annexation of land outside the current corporate boundary would greatly expand the demand for drinking water. Martin Marietta Minerals, Inc. has operated gravel pits and aggregate mines along the southern border of Hamilton County for decades. In the area South of l06th street there are several abandoned pits and ponds as well as a large open pit limestone mine. As growth in the area continues there is increasing demand for gravel and aggregate for roads, bridges, and buildings. So far, these operations have coexisted with the water wells with- out negative effects. However, Martin Marietta has proposed an expansion of its current facilities. Martin Marietta proposes to expand the current op- erations in the vicinity of the Plant 4 wellfield. In addition, they are plan- ning to open sand and gravel pits at new locations over a period of years to satisfy the growing demand for aggregate. There are separate applications for expansion at two properties: the North Mueller property, which includes the area north of l06th street be- tween Hazel Dell Parkway and Gray Road, and the South Mueller property which is located just south of l06th Street between Hazel Dell Parkway and Gray Road. The proposed mining at North Mueller would include some additional removal of sand and gravel as well as new underground lime- stone aggregate mining. Mining at the South Mueller property would be done in stages. The first stage would be the removal of the sand and gravel while water removal occurs along the edges. The next phase is to expand the boundaries of the existing open pit to the North to serve the North In- dianapolis Plant. As Carmel's role as a regional drinking-water supplier grows, it is crit- ical that the city protects the aquifers from any deterioration in yield. Our report was written to answer an important question raised by the recent growth in the area: Will the proposed new mining activity affect Carmel's drinking-water supply? How much do these two activities conflict with one another and how compatible are they? We have used groundwater models to investigate these issues. The mod- els include regional boundary conditions and flow in the unconsolidated aquifers, with local refinement in the vicinity of the proposed mining works. Our analysis provides information about changes in the hydrology of Plant 4 that would result from the expanded Martin Marietta operations. This analysis was done with data provided by the City about the configuration 2 '. -.I.' , of the gravel deposits in the subsurface, information provided by the Indi- ana Department of Natural Resources from domestic well logs, and stan- dard groundwater modeling tools. The effects of mining operations and reduced recharge were considered together to better understand unknown future conditions. This study is part of a larger ongoing water-supply planning effort be- ing conducted by the Utility that includes subsurface data collection and organization, wellhead protection planning, and water-supply expansion planning. Summary of findings There is no single index of the "effects of mining" that captures all of the changes that could take place once the proposed excavations are underway. Instead, we considered two types of impacts: changes in water levels in the aquifer near the Plant 4 well field, and changes in the source water pumped by the well field. The first of these is an indicator of the reduc- tion in yield that results from the competition between the drinking-water wells and around the mine pits. We examined impacts both during and after mining. . Additional mining could reduce groundwater levels at the Plant 4 well field by about 2-3 ft while the mines are active (Figure). The amount of water pumped by a well is roughly proportional to the drawdown in the well. Since the original pumping tests showed about 16 ft of drawdown when the wells were pumped at capacity and the model- ing predicts an additional 2 - 3 ft of decline, this translates to roughly 15% reduction in total wellfield capacity during mining. . Previous groundwater modeling suggested that the water pumped from the Plant 4 wells comes from the aquifer northwest of the well field. Our analysis shows that this was not the case (Figure 2) ; under current operating conditions about half of the water in the wells comes from the gravel pits south of the Plant 4 wells. This result is supported by water chemistry information collected at the well field. This implies that the well field and the gravel pits are in close hydraulic communi- cation and water quality in the ponds affects the raw water pumped 3 ", " 4 + 0.2 , o 0.2 Miles LEGEND l't;7f.". Wittman Hydro Planning As5o<iot'es :fiii\\\ \'~19-Rl;w.....~I'l.o_.."~C,"".u-" ."..... ........ . Carmel wells N Linesinks N Roads a .. Range of water level change from current conditions (ft) Hydrology Figure 1: Modeled changes in water levels (in jt) resulting from the South Mueller expansion project. At each of the marked locations, a range of pre- dicted water-level changes is reported; this results from analysis of sensitiv- ity due to model parameter uncertainty. The green lines are the locations of elements that represent hydrologic features in the model. . . 5 " " ( + WiHman Hydro Planning Associotes \',......t'k~P!;nl..C;<.....t.a-J\, . Carmel wells N Linesinks N Hydrology N Roads ,--, Composite L-....J captu re zone LEGEND Pathlines N Calibration N Low conductivity N Low transmissivity N High transmissivity 0.1 o 0.1 Miles Figure 2: Delineation of a composite capture zone for the Plant 4 wells. "Pathlines" represent hypothetical particles of water, traced backwards from the well screens for up to 5 years, and were computed based on sev- eral sets of model assumptions for sensitivity analysis. Note that about half of the pathlines originate in the gravel pit ponds. .. by the city. A water quality and water level monitoring system is needed to protect the supply. . In the 20 years that the proposed mines are active there would be an increase in the amount of drinking water that comes from abandoned gravel pits and ponds. Currently we estimate that approximately one- half of the water pumped at the Plant 4 well field had been in a pit or pond within the last five years. While the mines are active this will increase to more than 70% of all the water in the well field. . With conditions of reduced recharge, the effects of the proposed min- ing will be to decrease water levels by 3 It compared to reduced recharge under current conditions. With reduced recharge there are changes in water use and stage along the river that may alter the actual condi- tions at the well field. This is a result of reductions in regional flow from the till aquifers west of Plant 4 and the increasing importance of the White River. 6