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C-PIT Hydrogeologic Investigations Technical Revision No. 8 2: Site Analysis and Field Activities Mining Permit M-1977-208 2.2.1.2 Swede Ditch Swede Ditch operations staff indicate that the ditch can carry up to 30 cfs, commencing in mid-April and continuing through mid-September to October 1. Field observations confirmed that the ditch was flowing full by mid-Apri12007, at a reported rate of approximately 25 cfs. This flow rate was maintained until mid- July, at which time flow essentially ceased due to lower St. Vrain Creek flows and water rights issues. Swede Ditch personnel report that ditch flows historically tend to ramp up to the 25-30 cfs level by mid-August. The Swede Ditch along the westem C-Pit highwall was placed in a corrugated metal pipe (CMP) by CEMEX in 1998 to eliminate seepage that had been observed along the highwall. Brown and Caldwell field inspections on May 3, 2007 and July 19, 2007 showed wet zones and seepage entering the pit through various locations in fractured zones on the westem highwall. Relatively mature vegetation in C-Pit along the toe of the highwall is another indication of likely seepage. The rate of inflow could not be quantified, but the source of the observed seepage can only be leakage from the CMP culvert containing the Swede Ditch flow, flow from saturated mining backfill west of the Swede Ditch that passes through the residual limestone and shale under the ditch, or some combination of the two. 2.2.1.3 Highland Ditch The Highland Ditch routes St. Vxain Creek water south along the CEMEX plant entrance road to the area northeast of the north end of C-Pit, and from there tutus southeast, and eventually discharges to the Foothills Reservoir south of A-Pit and Hygiene Road. See Figures 1 and 2. This ditch closely parallels that portion of the southern boundary of the St. Vxain alluvial valley that is adjacent to the C-Pit/A-Pit area. The ditch operator reports that the Highland Ditch suffers from limited access to water due to junior water rights, and in recent years has not carried significant flows. In good run-off years, flow may reach a maximum of 80 cfs, and typically ranges from 30 to 50 cfs. In late May of 2007, flows of 80 cfs were reportedly reached as the Foothills Reservoir was filled. Once river flows drop off the ditch tends to dry up, typically around late June ox early July. The ditch operator has indicated that no records or gauging data aze kept for Highland Ditch flows, as its only purpose is to Fill the reservoir when river flows axe adequate and when warranted by reservoir storage levels. Field inspection and topographic mapping confirm that the Highlands Ditch is sufficiently low in elevation relative to C-Pit that it is not a likely source of recharge to C-Pit. 2.2.2 Boulder Feeder Canal Gauging On July 19, 2007, Brown and Caldwell conducted two flow measurements at locations on the Boulder Feeder Canal west of the site to determine if canal losses due to seepage could be quantified. This portion of the Canal is cut into the shale bedrock. The upstream measurement was taken between 12:15 p.m. and 12:55 p.m., approximately 262 feet north of the CEMEX pumping station located on the reach of the Canal between piezometers P-002 and P-003. The downstream measurement was taken between 1:26 p.m. and 2:01 p.m., approximately 144-feet south of the B-Pit haul road access bridge across from the south end of C-Pit. The reach of canal bracketed by the gauging locations is approximately 1900-feet in length. Figure 2 shows the locations of the two gauging stations. Transects of approximately 24 feet in length were established perpendicular to the canal flow direction at both monitoring locations, and depths and velocities were measured at 1-foot intervals along the transects. A USGS-style Pygmy meter and top setting rod arrangement were used to obtain the required data. A 2-4 Use of contents on this sheet is suhlect ~o the Ilmttations specilietl al tha entl of this document. ~1BCDEN021pm)eclslDa~a1GEMCemex~TR~B\RepotlinglCEME%Repotl 0031-O7.doc