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2008-01-23_REVISION - M2003016
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2008-01-23_REVISION - M2003016
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Last modified
6/16/2021 5:36:20 PM
Creation date
3/28/2008 9:40:07 AM
Metadata
Fields
Template:
DRMS Permit Index
Permit No
M2003016
IBM Index Class Name
REVISION
Doc Date
1/23/2008
Doc Name
Surety reduction request
From
SW Chambers LLC
To
DRMS
Type & Sequence
SR1
Email Name
ACS
Media Type
D
Archive
No
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Page 2 <br />Mr. Carl Mount <br />March 9, 2007 <br />~~ <br />CIVIL RES's~URCES,LLC <br />calculated aquifer flow currently being conveyed through the Heit Pit above and below each run of <br />underdrain pipe. <br />Due to the pit configuration and existing topographic features, the West and South underdrain systems are <br />designed to gravity drain to Little Dry Creek. Both underdrains daylight at the same point, roughly 120 feet <br />west of the southwest corner of the slurry wall, onto a riprap pad and surface flow though an existing <br />drainage swale to Dry Creek. <br />South Side Underdrain <br />The south side of the proposed slurry wall is within the modeled ground water "shadow" of the Koenig Pit <br />immediately south. Based on WWE's groundwater model Figure 2 (see Attachments) this shadow <br />decreases the average groundwater gradient to a localized gradient of 0.0022 feeUfoot paralleling WCR 20. <br />The shadow has also caused. the phreatic surface elevation drop on the upslope side of the Heit Pit by <br />roughly 1.3 feet. The shadow impacted groundwater surface elevations are considered the historic, pre-Heft <br />slurry wall, elevations, as modeled by WWE. <br />The South Side Underdrain collects water in a 6 inch diameter perforated ADS pipe covered with a filter <br />sleeve. The pipe run is 800 feet in length at a flat grade day lighting at elevation 4849.0 feet into an existing <br />drainage swale. Refer to construction drawings Sheet 2. <br />This pipe is sized to capture potential groundwater flows above the pipe invert and thereby limit groundwater <br />mounding. Groundwater flows to this pipe were calculated based on Darcy's Equation using the phreatic <br />surface gradient of 0.0022 feet/foot and a hydraulic conductivity (K) of 450 feet/day, from WWE. The total <br />bedrock to phreatic surface potential groundwater flow is 159 gallons per minute (gpm) (0.35 cubic feet per <br />second (cfs)). At the maximum allowable mounding elevation, the average head above the underdrain pipe <br />is 1.5 feet which matches the head necessary for the pipe to carry the'0.35 cfs of water using the Hazen- <br />Williams friction coefficient. The perforated pipe will accept all the groundwater inflow as the pipe will inflow <br />a calculated 100 gpm per linear foot of pipe with 1.5 feet of head, per ADS Technical Note 2.105. This flow <br />will exit the pipe at 1.8 ft/s onto riprap and surface flow to Little Dry Creek. <br />Total bedrock to phreatic surface groundwater flow 159 gpm <br />Inflow rate of pipe ea r foot of pipe ai 1.5 feet of head 100 gpm <br />Pipe flow capacity at 1.5 feet of head 159 gpm <br />West Side Underdrain <br />The west side of the proposed slurry wall is impacted slightly by the modeled groundwater °shadow" of the <br />Koenig Pit and more importantly by the water surface elevation defined by the proximity of Little Dry Creek <br />to the west. The groundwater flows that could mound on the west side of the constructed Heit slurry wall <br />are controlled by Little Dry Creek, the South Side Underdrain, and the proposed west side underdrain pipe. <br />Little Dry Creek is a natural drainage control feature with a flowline elevation five to seven feet below the <br />ground surface elevation at the proposed slurry wall. Normal groundwater levels are likely at or near the <br />invert of Little Dry Creek as evidenced by the established wetlands in the channel bottom. Therefore, <br />groundwater that begins to mound will naturally release to Little Dry Creek. Groundwater flowing north <br />along the west side of the Koenig Pit will be intercepted by the proposed south side underdrain pipe and <br />Little Dry Creek, however, a short length of underdrain pipe has been designed for the west side of the pit to <br />further reduce the mounding potential. <br />
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