State Clearinghouse No. 2010071036 Madera County, California
HYDROLOGY AND WATER QUALITY “GROUNDWATER IMPACTS” Assessment, Comments, Findings
PREPARED FOR: MADERA OVERSIGHT COALITION
PREPARED BY: TODD GROUNDWATER
2490 Mariner Square Loop Suite 215, Alameda, CA 94501
SUBMIT TO: MADERA COUNTY PLANNING DEPARTMENT
Attention: Mathew Treber 200 West 4th Street, Madera CA. 93636
1
EVALUATION OF POTENTIAL GROUNDWATER IMPACTS
AUSTIN QUARRY PROJECT MADERA COUNTY
November 3, 2014
2490 Mariner Square Loop, Suite 215
Alameda, CA 94501 510.747.6920
www.toddgroundwater.com
2490 Mariner Square Loop, Suite 215 | Alameda, CA 94501 |510 747 6920 | toddgroundwater.com
November 3, 2014
Mr. Bruce Gray Madera Oversight Coalition P.O. Box 1282 Coarsegold, CA 93614
Dear Mr. Gray:
Enclosed is the draft report entitled Evaluation of Potential Groundwater Impacts, Austin Quarry Project, Madera County. On behalf of Todd Groundwater, we appreciate the opportunity to work with you on this important topic.
Sincerely yours,
Iris Priestaf, PhD President
SIGNATURE PAGE
Iris Priestaf, PhD
President
Daniel J. Craig, PG, CHG
Senior Hydrogeologist
Eugene B. Yates, PG, CHG
Senior Hydrologist
Evaluation of Potential Groundwater Impacts Austin Quarry Madera Co. i TODD GROUNDWATER
Evaluation of Potential Groundwater Impacts Austin Quarry Madera Co. ii TODD GROUNDWATER
List of Figures
Figure 1. Site Location and Well Map Figure 2. Subsurface Geologic Cross-Section A-A’ Figure 3. Composite Groundwater Elevation Map, June 2009 Figure 4. Water Level Hydrographs for Shallow and Deep Wells Figure 5. Variations in Bedrock Permeability and Well Yields Figure 6. Rose Diagrams of Fractures in Boreholes 2008 B-1 and 2008 B-2 Figure 7. Water Quality in Shallow and Deep Wells Figure 8. Hypothetical Groundwater Drawdown during Full Quarry Dewatering
Todd Groundwater (Todd) has evaluated potential groundwater impacts of the proposed Austin Quarry Aggregate Mine Project, located in unincorporated Madera County twelve miles east of the City of Madera. For water supply, the Project proposes to pump groundwater from a bedrock well, and additional groundwater will be pumped from the quarry excavation as a part of dewatering operations. Concerns have been raised about the potential impacts on local and regional groundwater supply, groundwater elevations, and surface water features.
Our analysis draws on data presented in the Revised Draft Environmental Impact Report (RDEIR - Benchmark, 2014), but this report is not a point-by-point critique of the analysis and conclusions in the RDEIR. Additional information was obtained from readily available hydrologic and hydrogeologic studies, including the Kenneth Schmidt & Associates groundwater study (Schmidt, 2012), CDM geotechnical investigation (CDM, 2012), and initial studies completed for the original Draft Environmental Impact Report that was completed in August 2012.
Our evaluation of impacts is based on the project description, proposed reclamation, and information on topography, land use, geology, soil and rock characteristics, bedrock fractures and aquifer hydraulic properties, groundwater elevations, precipitation, evaporation rates, and water quality. This information provides the background for developing a conceptual hydrogeologic model of the local groundwater system. No new data were generated for this evaluation; rather existing hydrologic and hydrogeologic data were reviewed and interpreted independently.
In our opinion, based on our evaluation of the available information, there is the potential for major hydrologic impacts related to mining and quarry dewatering at the Austin Quarry:
• High rates of groundwater inflow to the quarry would be likely, and this groundwater would need to be pumped out of the excavation during operations. Potential impacts of a significant dewatering discharge on downstream channels, swales and vernal pools need to be considered.
• Water table drawdown would be large because of quarry dewatering. Drawdown could affect nearby wells, resulting in deteriorated water quality, reduced well yield or potentially drying up of shallow wells.
• If unmitigated, removal of groundwater from the connected sedimentary and fractured bedrock aquifer system would contribute to ongoing depletion of the overdrafted Madera Groundwater Basin.
• Groundwater inflow to the quarry after dewatering ceases would result in a deep lake. Potential impacts of a lake, such as evaporative losses, need to be assessed. Evaporative losses would further deplete the overdrafted groundwater basin.
The following sections briefly describe the Project, summarize our review of local groundwater and related surface water conditions, and provide our independent assessment of major potential impacts.
2. PROJECT DESCRIPTION
The proposed Austin Quarry Project is located southwest of the Highway 41/Road 145 intersection on three properties (Fenston, Urrutia, and Vulcan, termed Project property). The quarry site and related facilities are planned for the Vulcan parcel north of the Madera Canal. In brief, the Project would involve open-pit mining of hard rock plus production of asphalt, with planned reclamation of the site for dry land cattle grazing, open space and wildlife habitat.
The major feature of the Project will be a 258-acre quarry pit. A natural drainage channel on the property will be routed around the quarry pit site. Once soil and overburden are removed, the quarry will be excavated to depths as much as 400 feet below the ground surface. Figure 1 is a map showing the planned quarry site, Madera Canal, and locations of wells that provided data used in our analysis. For reference, nearby residential communities are located just east of Highway 41 and south of Avenue 15 (Bonadelle Ranchos) and also west of Road 38 (part of Madera Ranchos).
Figure 21 is a cross-section through the property (based on Schmidt, 2012) that illustrates geologic materials underlying the site and adjacent properties, local wells, the Madera Canal, groundwater levels and the superimposed location and depth of the proposed quarry pit. The location of the cross-section is shown on Figure 1. Note that the southern end (right margin) is about one mile northwest of Bonnadelle Ranchos. The Project water supply will be provided by a well in the northwest portion of the Vulcan property. Water demands of the Project are documented in a Water Supply Assessment (Tully & Young, 2012).
The pit will need to be dewatered during the mining phase because of inflow of groundwater, surface water, and rainfall. According to the Project description, some of this water will be used for dust control, process water, and landscape irrigation, and the remainder will be discharged to storage/percolation ponds and/or to drainages where water will be conveyed under the Madera Canal to unspecified downslope areas.
3. HYDROGEOLOGIC SETTING
3.1. MADERA GROUNDWATER BASIN
The Project site is located on the eastern edge of the Madera Groundwater Basin, which is characterized by alluvial and unconsolidated deposits that extend from the bedrock of the Sierra Nevada and thicken to the west. As defined and mapped by the Department of Water
1 Figure 2 is used here to illustrate the general geology and the quarry depth. This use does not imply acceptance of cross section details.
Resources in Bulletin 118, the edge of the groundwater basin is demarked by outcropping igneous bedrock near the base of the foothills. Most of the Quarry property (with the exception of the northeast corner) is within the basin; the water supply well for the Project is within the DWR-mapped basin area, as is much of the planned quarry pit.
The Water Supply Assessment asserts that the Project’s water supply well is constructed in bedrock and thus is not in the Madera Basin. However, the groundwater level contour maps and water level hydrographs shown in the RDEIR and Schmidt report document a continuity of groundwater levels and flow from bedrock north and east of the Project site, across the site, and into the alluvium. Analysis of information on bedrock fracture frequency and the results of groundwater pumping tests also indicate that groundwater readily flows between the fractured bedrock and sedimentary aquifers. Thus, although wells screened in bedrock may be asserted to be outside the alluvial basin, they extract immediately adjacent groundwater that is tributary to the basin and provides recharge to it. Loss of this pumped groundwater to evaporation and evapotranspiration (for example, through dust control and irrigation) represents diminished recharge to the overdrafted Madera Basin.
3.2. SITE GEOLOGY
Subsurface information for the site and nearby areas includes mapping of surface geology plus soil boring and well drilling investigations that involved logging of soil and rock types, documentation of characteristics of bedrock fractures, and conduct of aquifer (pumping) tests of wells that reveals the nature of the sedimentary and fractured bedrock aquifers. The southwestern portion of the Project property is underlain by thin alluvium and unconsolidated sediments of the Turlock Lake Formation that thicken to the southwest. The Turlock Lake Formation is composed of sandstone, siltstone, and claystone, and is an important water-bearing aquifer in the basin. The thickness of the alluvium and sediments ranges from zero to approximately 140 feet deep across the property, and the Turlock Lake Formation thickens to the southwest beneath the valley. Bedrock crops out in the northeastern corner of the property and along the northern boundary. The bedrock, which is the focus of the mining, includes a weathered zone overlying a deeper zone of harder bedrock. The weathered zone (as described in the RDEIR) is as much as 100 feet thick and may be more permeable than the underlying unweathered bedrock. However, the unweathered bedrock also is described as broken by closely spaced fractures on the order of a few feet or less. Groundwater occurs in and flows through the fractures.
Figure 2 illustrates the geology underlying a portion of the Project property and property to the south extending to Road 15. The cross section shows the thickening sequence of groundwater basin sediments to the south, where downgradient domestic and irrigation wells are located. It should be noted that this cross section, which is located on the eastern bedrock edge of the proposed quarry, does not show the full extent of the groundwater basin sediments across the quarry site. At other locations within the quarry area, alluvial materials are up to about 100 feet thick.
Groundwater occurs in the alluvium, weathered bedrock, and fractured bedrock. Available data indicate that groundwater in all three units is connected. Groundwater connection among the geologic units is consistent with a conceptual model that recognizes that the fractures in bedrock are sufficiently abundant and interconnected to convey regional groundwater flow even if localized bedrock areas have few fractures.
3.3.2. Groundwater Elevations and Flow
The 2012 Schmidt report provides groundwater level data from 15 wells on the property from as early as 2005 and extending into 2012. Recent groundwater level data are provided in a Schmidt 2013 letter (RDEIR Appendix H-7). The Schmidt report and RDEIR provide water elevation maps for September 2008 and June 2009. Groundwater elevations (relative to mean sea level, MSL) are highest in the northeast portion of the property and decrease to the southwest and south.
Depths to groundwater below the ground surface are generally 10 feet or more. Depths to groundwater are least (less than 10 feet) in monitoring well MW-5, located adjacent to the Madera Canal and the planned quarry. Depths to groundwater are greatest (over 120 feet) in wells near Avenue 15, about 2.5 miles southwest of the Project site.
In the Schmidt report and the RDEIR, groundwater elevation data for the alluvium and for bedrock are presented separately. However, the combined data provide a consistent pattern of groundwater contours. Figure 3 is a map of September 2009 groundwater elevations (from the Schmidt report) for both sedimentary and bedrock aquifer wells. This pattern indicates groundwater flow from northeast to southwest through the various geologic units. It is consistent with regional groundwater contour maps for the Madera Basin that show a large pumping depression southwest of the quarry (see Todd, 2002, Figure 2-6); this depression is associated with basin overdraft. The groundwater level data show that groundwater—originating on the property, from the Madera Canal, and from watersheds to the northeast—is flowing southwestward and providing recharge to downgradient wells and the overdrafted Madera Basin.
Water levels over time in the local sedimentary and bedrock aquifer wells parallel each other. Figure 4 is a hydrograph of measured groundwater elevations in both aquifers. Water levels in both aquifers have similar trends during wet and dry conditions. Examples include a declining trend during 2008, a rising trend during 2010 and a declining trend during 2012. These similarities indicate that the aquifers are inter-connected.
3.3.3. Pumping Tests and Aquifer Hydraulic Properties
The rate at which groundwater flows depends on the permeability of the sediments or rock (known as hydraulic conductivity) and the aquifer thickness. The product of the hydraulic conductivity and thickness is referred to as aquifer transmissivity.
In order to measure the transmissivity of the alluvial and bedrock at the quarry, pumping tests were conducted on wells completed in both aquifers. Pumping tests were performed in alluvial aquifer wells MW-1, MW-2, and MW-3 at rates of 60, 75, and 70 gallons per minute (gpm), respectively. Two bedrock wells (Northwest or NW Well, and 2008-A) were pumped at rates of 117 and 41 gpm, respectively. Estimated aquifer transmissivities ranged from 1,040 to 5,300 gallons per day per foot (gpd/ft) for the alluvial aquifer wells and 3,100 to 4,600 gpd/ft for the bedrock wells. Based on these well production rates and aquifer transmissivities, potentially significant amounts of groundwater would be expected to flow into the quarry excavation. It is recognized that additional bedrock borings were drilled and not tested because low yield and permeability were probable (e.g., lack of fractures). Accordingly, the presence of such borings, in addition to the tested wells, provides a range of likely transmissivities in bedrock from low values (untested and unknown) to known values of 3,100 to 4,600 gpd/ft.
Numerous fractures have been logged in bedrock boreholes across the quarry site, and several large fracture zones have been identified in bedrock wells NW and 2008-A at depths of 400 to over 500 feet below ground surface. The presence of fractures at various depths and the documented high groundwater production rates of wells constructed in these deeper zones indicate that large volumes of groundwater may need to be pumped to dewater the quarry excavation.
Because relatively few boreholes and wells have been drilled at the quarry, the three-dimensional distribution of permeability in the Project area remains unknown. There may be areas around and within the quarry where fracture density and the corresponding rate of groundwater flow are relatively low, and there may be areas of even higher fracture density than encountered in the existing boreholes. However, information collected during borehole drilling and video logging consistently shows significant fracturing; this indicates that relatively high bedrock aquifer permeability exists from the ground surface to depths of over 500 feet. Thus, available fracture data support a conclusion that bedrock has substantial overall capacity to transmit groundwater. Collection of additional data on fracture density, orientation, and water-bearing characteristics in areas around the full perimeter of the excavation might identify local areas of low fracture density, but due to its size, the quarry pit would undoubtedly intersect and drain groundwater from many fractures.
3.3.4. Bedrock Aquifer Fracture Characteristics
In the alluvial aquifer, groundwater flows though pore spaces between the sand grains in the unconsolidated sediments. In the bedrock, groundwater flow occurs through fractures. The rates and amounts of groundwater flow through the fractured rock are dependent in
part on the densities, widths, orientations, apertures (size), and inter-connectivity of the fractures. Figure 5 schematically illustrates the relationship between frequencies of fractures and corresponding well yields. In general, areas where more fractures occur are more permeable and yield higher rates of groundwater flow than areas of fewer fractures. Where fractures are predominantly oriented in a single direction, groundwater flow rates can be low or tend to follow the directions of the fractures. Conversely, where fractures are oriented in multiple directions, groundwater flow rates can be higher and groundwater can more easily flow laterally or vertically to different aquifer zones or adjacent areas of the groundwater basin.
Analysis of the fracture patterns at the site was conducted as a part of several site investigations. The presence and density of fractures were catalogued from core samples recovered from exploratory boreholes completed across the site. Fracture characteristics (including orientations) were measured in two of the core holes drilled in 2008 using an optical televiewer. Planar attitudes of the fracture features noted in the core samples and televiewer images were plotted on stereographic projections and rose diagrams to evaluate trends.
The 2008 borehole core samples from the weathered and unweathered bedrock showed relatively high-fracture density, with fracture spacing on the order of less than 1 foot. In addition, the fracture orientations and dip angles measured with the televiewer were almost randomly distributed. These diagrams show the direction (or azimuth) of the fracture surface and dip angle of the fracture from zero degrees (horizontal fracture) to 90 degrees (vertical fracture).
Figure 6 shows the fracture-orientation rose diagrams for two boreholes, as documented in the RDEIR. As illustrated, the boreholes encountered numerous fractures coming from different directions and angles. The high density and variable orientations of fractures at the site indicate the potential for significant groundwater flow through the weathered and unweathered bedrock. Pumping tests of onsite deep wells also confirm the relatively high bedrock aquifer permeability.
3.3.5. Inter-Connectivity of Sedimentary and Fractured Bedrock Aquifers
Numerous lines of evidence support a conclusion that groundwater in the bedrock and alluvium functions as a single, interconnected flow system, including vertical connection from shallow to deep fractures in the bedrock:
• Pumping tests in the bedrock wells resulted in drawdown in the alluvial wells. • Water levels in the bedrock and alluvium are very similar and can be mapped
together as a consistent water table. • The buried bedrock surface plunges steeply to the southwest beneath the alluvium.
There is no other physically plausible outlet for bedrock flow other than into the alluvium.
• The capacities of the Project supply well (Northwest or NW Well) and bedrock well 2008 are high and pumping can be sustained for long periods without apparent reduction in well production rates.
• The yield of the Project supply well is reported to be larger with the occurrence of seasonal rainfall (showing surface connection).
• The occurrence of elevated nitrate in sampled alluvial and bedrock wells indicates recharge from surface and near-surface sources (e.g., agriculture, livestock).
In brief, groundwater in the deep bedrock, shallow bedrock and alluvium occurs as a connected system. Any pumping, de-watering, or other removal of groundwater from the bedrock aquifer at the Project property will reduce the amount of groundwater flowing from the foothills and into the sedimentary aquifers of the Madera Basin.
3.3.6. Surface Water and Madera Canal Seepage
The Madera Canal is part of the Central Valley Project and conveys water from Millerton Lake to provide irrigation water to farmers in Madera County. Located on the southern boundary of the Vulcan property, the canal appears to seep water at a rate sufficient to create a small water-level rise in some nearby shallow wells, where the water table is typically only 10 to 15 feet below the ground surface. For example, water levels in Well MW-5 appear to rise by up to 1 foot and decline by a similar amount when flow in the canal starts and stops (see Figure 4). This water-table mounding is limited to the shallowest part of the aquifer system and is too small to affect the prevailing southwestward regional flow.
The shallow depth to the water table indicates that the canal and water table may be hydraulically connected. If so, then lowering of the water table will tend to increase canal seepage losses, and vice versa.
3.3.7. Groundwater Quality
Groundwater quality data are available for six alluvial and three bedrock wells sampled in October 2010 (Schmidt, 2010). The relative proportions of constituents in groundwater (e.g., cations and anions such as calcium and chloride) can be plotted to document the groundwater quality character. For example, the proportions of cations and anions for six of the nine wells are displayed in a Schoeller diagram in Figure 7. Data from wells MW-1 and MW-4 were omitted because the charge imbalance between cations and anions exceeded 5 percent, indicating inaccuracy, and well MW-7 was omitted because of very high TDS (2,340 mg/L) and other elevated constituents (including extremely high nitrate), suggesting local contamination.
The plot in Figure 7 shows that the relative proportions of cations and anions are generally similar among all wells and in any case do not exhibit patterns correlated to well depth. This suggests that shallow and deep fractures are connected as a single groundwater flow system.
It is more significant that nitrate concentrations in all of the wells range from 16.9 to 42.1 mg/L. While these concentrations remain within the drinking water standard of 45 mg/L (N as nitrate), they are elevated in both alluvial and bedrock wells. Given that nitrate in groundwater derives from surface or near-surface sources, this strongly indicates recharge from the ground surface to both alluvial and bedrock wells.
4. POTENTIAL IMPACTS OF GROUNDWATER PRODUCTION AND DEWATERING
4.1. ESTIMATED QUARRY DE-WATERING FLOW RATES
The quarry will be excavated from the ground surface to a maximum depth of about 400 feet. As described in the RDEIR, surface water and groundwater intercepted within the quarry excavation and plant site may be used as process water or discharged to percolation ponds or one of the natural drainage channels where water is conveyed under the Madera Canal. During the lifespan of the Project, the excavation will be deepened. The RDEIR (Section 2.4) provides a general phasing schedule for deepening the quarry over time. The quarry would be mined in six phases with Phase 6 beginning in 2080. As the quarry is deepened, groundwater would need to be pumped to successively greater depths in order to provide continuous dewatering of the excavation. The hydraulics of groundwater flow are such that higher pumping rates will be required to achieve greater drawdown and keep the pit dry as it is deepened.
In order to estimate the potential amount of groundwater inflow during quarry dewatering, we constructed a simple two-dimensional groundwater flow model that simulates natural regional groundwater flow in the bedrock aquifer, and the effects of pumping groundwater from the excavation. The model assumes homogeneous aquifer transmissivity and uniform natural recharge from precipitation. Using the bedrock aquifer transmissivity value of 4,600 gpd/ft (obtained from the NW Well pumping test), at full excavation to 400 feet (Project Phase 6), the amount of groundwater entering the excavation is estimated to be over 4,000 acre-feet per year (AFY).
This estimate does not account for possible additional inflow from the alluvial aquifer, leakage from the Madera Canal, or upward flow from deep aquifer zones below the bottom of the excavation. The area potentially contributing inflow to the quarry excavation has a radius of about 5 miles. Thus the quarry’s zone of influence on regional groundwater flow is significantly larger than the width of the quarry, just as the zone of influence of a pumping well is significantly larger that the width of a well itself.
The model provides a first-approximation estimate of the rate of dewatering that could occur at the maximum excavation depth. If overall aquifer transmissivities around the quarry are lower or higher than the transmissivity of the NW Well, the corresponding inflow rate would decrease or increase. For example, if the average bedrock aquifer transmissivity is 3,100 gpd/ft (the value estimated from the second bedrock well pumping test), then the amount of groundwater entering the excavation is estimated to be about 2,700 AFY.
It is recognized that the two dewatering estimates presented here are based on the pumping tests of the most promising test wells at the site; other test wells/borings were not successful and were not tested. Testing of these would have resulted in relatively low transmissivity values, but average transmissivity for the entire site would still be large enough to produce an estimate of dewatering flow on the order of thousands of acre-feet per year.
This large estimated flow of groundwater—for example, 4,000 AFY is equivalent to 5.5 cubic feet per second—would need to be discharged. Percolation ponds described in the RDEIR would be designed to handle stormwater only, not dewatering water. The dewatering discharge would be directed to surface drainages that flow under the Madera Canal. The capacity of these channels and the ultimate downslope fate of the discharged water should be evaluated. If the discharge water percolates back into the subsurface, it would reduce the potential impact of removing groundwater from the system, but this is not discussed in the RDEIR.
The amount of drawdown decreases with distance away from the pit but could be noticeable miles away.
4.2. DEWATERING INDUCED DRAWDOWN AND IMPACTS TO OTHER PUMPERS
As groundwater is pumped from the excavation, the water table in adjacent areas will begin to fall. This process is known as drawdown. The amount of drawdown in the quarry at full depth would be around 400 feet. Dewatering to a depth of 400 feet will cause drawdown not only in the quarry but in adjacent areas of the Madera Groundwater Basin.
The simplified groundwater flow model used to estimate the amount of excavation dewatering was also used to estimate drawdown in adjacent areas. Figure 8 illustrates the hypothetical amounts of drawdown (in feet) that could occur in areas surrounding the quarry at its full depth of 400 feet. In spite of its simplified representation of the flow system, the model indicates that the amount of drawdown could be significant at the Bonadelle Ranchos No. 9 subdivision, Madera Ranchos, and properties between Avenues 14 and 15, about 3 miles south of the quarry site.
Numerous domestic wells are known to exist at these nearby properties, and impacts to these wells could occur as a result of dewatering-induced drawdown. As illustrated on Figure 8, the model indicates potential drawdown as much as 50 to 100 feet. This drawdown would be additive to regional groundwater level declines. As documented in the RDEIR, water levels in the wells in the alluvial basin have decreased by 100 feet to 150 feet or more since the 1960s, with the depth to water ranging from approximately 100 feet to almost 300 feet bgs during that same period. By way of comparison, most of the wells in Bonadelle Ranchos range in depth from about 280 to 350 feet (Schmidt, 2012). This indicates that available saturated thickness for domestic wells is already decreasing at an alarming rate even without the Project. Potential impacts include reduced well yields, increased well power costs due to greater required lifts, corrosion and damage to the wells if the steel well
intake screens are exposed to air, and potentially drying up of wells, if the water table were to fall below the bottom of the well. Groundwater quality also may deteriorate as the affected wells draw in water from greater depths in the aquifer.
4.3. IMPACTS AFTER SITE RESTORATION
Following mining, the pit will be nearly 400 feet deep with a bottom area of 139 acres, a top area of 258 acres and rock sidewalls with a slope of 1:1 (RDEIR p. 2.0-43). The pit will have a draining effect on the surrounding groundwater system. When the dewatering wells are turned off after mining has been completed, groundwater will flow into the pit from all sides, raising the water level until a balance is established between water inflows and outflows. Currently, depths to groundwater are about 10-15 feet; the eventual water level in the pit will approximate that level, reflecting groundwater through-flow plus the lowering effect of lake evaporation. As a consequence, the pit will become a perennial, open body of water nearly 400 feet deep. It must be remembered that the pit functions like a large-diameter well. The pit will not remain dry when the pumps are turned off. Water levels will recover in the pit just as they do in normal wells after each pumping cycle.
The pit reclamation proposed in the RDEIR differs from the reclamation proposed in the DEIR. The RDEIR asserts that the bottom of the pit can be used for “passive groundwater recharge”. This is hydraulically impossible, because water does not flow uphill. The bottom of the pit will be nearly 400 feet below the surrounding regional water table. Water will flow from the bedrock aquifer into the pit, not vice versa.
4.4. OTHER IMPACTS
The Madera Basin is in overdraft. In 1980, DWR Bulletin 118-80 identified the Madera Basin as being in a critical condition of overdraft (wherein continuation would probably result in significant adverse impacts). The RDEIR and Schmidt groundwater report acknowledge that the basin is in overdraft, and report that average annual overdraft in southeast Madera County has been estimated at 22,000 AFY.
Any increase in consumptive use of groundwater by the Project is a significant contribution to overdraft in the downgradient portions of the basin. During the active mining phase of the project, this consumptive use will involve water demands as documented in the Water Supply Assessment. After mining is complete and dewatering is halted, consumptive use will be mostly lake evaporation, amounting to an estimated 1,000 AFY in perpetuity.2
2 Average annual pan evaporation at Friant Government Camp is 80 in/yr. Multiplying that rate by a pan-to-lake coefficient of 0.8 produces an estimate of 64 in/yr of lake evaporation. Subtracting average annual rainfall of 15 in/yr obtains a net evaporation rate of 49 in/yr. Multiplying that rate by the full-lake surface area of 258 acres yields an estimate of 1,050 AFY of net lake evaporation.
The preceding analysis indicates that the pumping rate required to dewater the quarry pit to a depth of 400 feet is probably very large, which would create challenges for disposal of water and would result in potentially large drawdown impacts at off-site wells. The required dewatering rate and its associated water-level impacts should be evaluated using a groundwater model that incorporates a more detailed representation of the groundwater system than the model constructed for this preliminary analysis. Future modeling would benefit from additional data regarding bedrock permeability, which can be quite spatially variable. Obtaining the data would require tests of existing bedrock wells on nearby parcels or drilling and testing of additional bedrock wells on the Project property.
The feasibility of disposing of up to 5 cubic feet per second of flow discharged from dewatering wells needs to be confirmed. In particular, the feasibility of percolating the water into the alluvial basin by means of percolation ponds or stream channel percolation should be studied.
The groundwater model developed for the above task should also be used to simulate post-reclamation conditions. Specifically, it could calculate the steady-state water level of the lake given rainfall, evaporation and groundwater inflows and outflows within the regional groundwater flow system.
Pumping tests, tracer tests and/or surface flow gaging should be used to confirm the degree of hydraulic coupling between Madera Canal and the water table. Alternatively, the Project description could be amended to include lining of the canal along the reach adjacent to the Project property.
CDM. 2007. Geotechnical Study, Austin Quarry, Madera County. August 7.
_____2010. Discussion of Surface Water Quality Data, Samples Collected June 2010, Austin Quarry. Letter to Cesar Aranda, Vulcan Materials. October 20.
EMKO. 2014. Stormwater Retention and Groundwater Recharge Concept for the Proposed Austin Quarry, Madera County, California. Memorandum from Andy Kopania to Bob Delp. EMKO Environmental, Inc. El Dorado Hills, CA. July 28, 2014.
HydroFocus, Inc. September 23, 2012. Comments on groundwater impact analysis in Austin Quarry Draft Environmental Impact Report. Prepared for Madera Oversight Committee. Submitted to Madera County Planning Department, Madera, CA.
Kenneth D. Schmidt and Associates. 2010. Austin Quarry. Letter to Cesar Aranda, Vulcan Materials. October 29.
_____________________________. 2012. Groundwater conditions in the vicinity of the proposed Vulcan Materials Austin Quarry, Madera County, California. Updated Report. Fresno, CA. Prepared for Vulcan Materials Company, Fresno, CA. May.
_____________________________. 2013. July 17, 2013 letter and attachments from Cheryl Lassotovitch (of Kenneth D. Schmidt and Associates) to Cesar Aranda regarding Vulcan Austin Quarry hardrock and alluvial monitor wells and offsite wells through June 2013.
Tully & Young, 2012. Water Supply Assessment. Sacramento, CA. Prepared for Vulcan Materials Company, Fresno, CA. Appendix H to the RDEIR. June 29.
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November 2014 Figure 1Site Locationand Well Map
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Cross Section A - A'Madera CanalProposed Quarry Pit
