2012-09-06_REVISION - M2008070 (25)

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Design and Operations Plan Westem Gravel E & P Waste Disposal Facility 3.4.5.1 LDS Construction October 24, 2011 Page 24 of 51 collection trenches located along the cell floor. The LDS shall collect and convey any potential leakage from the primary liner into a leak detection manhole that is located adjacent to each cell. An HDPE geonet will be placed across cell floors and sidewalls and between the secondary and primary HDPE liners and used as the primary LDS component. The geonet will be placed in the anchor trench similar to HDPE liner materials. Collection trenches will be constructed along the cell fl oor at the down - gradient edge and along the centerline trending perpendicular to the down - gradient edge. A plan showing the leak detection trench orientation and locations is provided on Figure 5, Detail 5A. Slotted, 4 -inch diameter, polyvinyl chloride (PVC) collection pipe (Schedule 40 well screen including max slot width = 0.04 -inch) shall be placed in the collection trench and bedded and surrounded with free draining sands exhibiting a permeability of 1 x 10 -2 cm/sec or greater. Leachate collection trench details are provided on Figure 5, Detail 5C. The slotted collection pipe will be connected to solid 4 -inch diameter, Schedule 40, PVC pipe at a point located a minimum of 5 feet from secondary liner penetration. The secondary liner must be proper ly booted to the solid pipe at liner penetrations. The solid pipe will extend from the down - gradient end of the perforated pipe, through the down - gradient cell berm, and discharge into a leak detectio n manhole (LDM). The section of trench where solid pipe is placed between secondary and primary liner materials will be backfilled with clays compacted to at least 95% of the maximum standard Proctor density per ASTM D698. The LDM will be constructed of a standard 48 -inch diameter concrete barrel manhole including water -tight sealants (e.g. gaskets, boots, and mastic) at all joints. The solid LDS pipe will enter the LDM at approximately two feet minimum from the LDM bottom. The LDM access will include a cast iron ring and cover. Materials used to construct the LDS shall meet properties listed in the CQA/QCP. Construction and testing procedures for these materials are provided in the CQA/QCP. LDM details are provided on Figure 5, Detail 5D. 3.4.5.2 LDS Operations The LDM constructed as a part of the LDS shall be inspected weekly for the presence of fluids. The presence of liquid could be the result of condensate, potential cell leakage, and/or anchor trench leakage. In the event that liquid is discovered in a LDM, CDPHE must be notified and analytical samples collected within 7 days of discovery. Analytical results must be reported to CDPHE within 7 days of sample analytical results receipt. At a minimum, collected samples will be analyzed for benzene, toluene, ethylbenzene, and xylene (BTEX), chloride, and sodium. Based upon analytical results, if cell leakage into the LDM is suspected, additional confirmation sampling may be conducted . In order to evaluate if observed liquid in the LDM is potentially liquid from the cell, BTEX, sodium, and chloride concentrations criteria will be used. A BTEX detection above the laboratory method detection limits (MDLs) will be considered potential leachate. However, potential laboratory and/or field cross contamination will be evaluated. A trip blank will be used in order to help evaluate potential sample cross contamination. In the event that analytical results suggest that sampled liquid could be cell leakage and similar to E &P waste and/or PCS, CDPHE shall be immediately notified in order to determine appropriate corrective action. Based upon analytical data evaluation, additional confirmation samples may be collected in order to help assess if the liquid source is potentially from the cell. LDS monitoring documentation shall be maintained in the Operating Record. NWCC, Inc.