Noah Kugler H20Geosolutions on Hydrogeology impacts of CEMEX application

December 10, 2014

Noah Kugler comments to planning

 

 December 1, 2014
Hernando County Planning Department
20 North Main Street
Brooksville, FL 34601
Re: CEMEX CPAM 1102
Dear Planning Department Member:
H2O GeoSolutions LLC (H2O) has reviewed documentation in support of and against the above
referenced proposed mine expansion as well as local geology and hydrogeology and has found
reasonable cause to perform further impact assessment(s). This assessment is limited by the
known details of the proposed mining such as depth of excavation and need for dewatering, and
local and site-specific and geology and water level information. The primary factors contributing
to this conclusion are:
1) The proposed mine lies directly down-gradient from the local topographic high which occurs
within hundreds of feet of the northern boundary. The irregular topography that occurs at the
proposed mine site changes by up to 100 feet from the northwestern extent (up-gradient
direction at approximately 210 feet NGVD) to the southeastern extent (down-gradient
direction at approximately 110 feet NGVD or less). Excavation of surficial sediments and
mining of rock strata that is proposed covers more than one (1) mile in the east-west
direction. Due to removal of material across the mine area, a decline of groundwater levels
within the mine that is equivalent to the land surface elevation at the southern extent of
the mine excavation may occur. This could significantly affect local flow and drainage
patterns outside the mine area.
Diagrams showing interpreted surface and shallow groundwater flow directions under
current conditions with annotated areas that may be impacted by mining operations (Figure
1) and a generalized diagram showing pre and potential worst case post-mine hydrogeologic
conditions (Figure 2) are included.
2) Surface drainage via karst should be further evaluated. Although the applicants report that
exploratory site borings did not find large cavities in karst, it is difficult to identify karst
and flow conduits by this method. The proposed mine area is likely underlain by limestone to
various degrees of dissolution which is covered by varying thickness and compositions of
sand, silt, clay and shell. The limestone typically moves large volumes of water quickly
underground, even in the absence of large karst features.
3) A decline in water levels within the mine area could lead to significant reduction in
moisture at plant root zones and altered hydroperiods, particularly north and west of the mine
area. This could lead to enhanced erosion of upland areas which could deposit large
amounts of sediment into the mine area.

4) A decline in water levels within the mine area could lower water levels in wells particularly
north and west of the mine area.
5) Once the surficial sand, silt, clay and shell are removed to access target rock, there is a
direct hydraulic connection for sediment and pollutants to enter the aquifer.
6) Extensive shallow permeable limestone in the area would allow for potentially long travel
distance of sediment and pollutants potentially impacting groundwater and wells at distance
from the mine. Water quality south of mine is likely to be impacted.
7) The topographic high north of the proposed mine site and the proximity to Peck Sink, which
lies south east of the mine site at approximately 140 feet in elevation below the topographic
high, create high flow gradients between areas within the proposed mine and the sink.
This provides a potential for rapid movement of groundwater across the area of the proposed
mine to the sink. The topographic high and relatively steep elevation drop also create
conditions for artesian and spring flow in the area.
The potential for impacts to the hydrology, hydrogeology and water quality of the area further
warrants cumulative impact assessment from neutral parties. The following are
recommendations for consideration under further related impact assessment efforts:
• Perform a review of wells and geology in the area of the proposed mine with a focus on
seasonal water levels and karst/sinkhole occurrence;
• Perform a site area inspection of surface water features: lakes, streams, springs, seeps, sinks,
etc. in the area of the proposed mine;
• Perform Pollution source investigation;
• Perform Pre and post-condition mining surface and shallow groundwater flow path
assessment;
• Research Special Protection Area (SPA), Groundwater Protection Ordinances (GPO), and
Wellhead Protection Areas (WHPA) related to the proposed mining activities;
• Perform tracer dye survey(s) to assess groundwater flow path and velocity between the
proposed mine area and Peck Sink.
• Perform surface and/or groundwater modeling.
Should you have any question regarding this preliminary assessment please do no hesitate to
contact me.
Respectfully,
Noah B. Kugler, P.G.
Principal

 

Map H20Hydrogeology001Map H20Hydrogeology002

 

 

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