CORRESPONDENCE_2007 (1/07 - 6/07)

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Corral Hollow Sanitary Landfo - 2 - 13 March 2007 an additional point placed southeast of HP-1 along a parallel line with the CHSL northeastern site boundary. 3. The delineation of the lateral and vertical extent of LFG in the vicinity of the southern boundary was not proposed. The Discharger must delineate the plume along this boundary. Staff recommends installing a minimum of three soil borings southeast of CHSL. These borings should be spaced a maximum of 300 feet apart with the focus around GW-6. This southerly line of borings should mirror the line of borings installed along the northern site boundary. 4. Shallow groundwater beneath the southern portion of the CHSL site is not adequately monitored to evaluate water quality changes due to the release from the unit. In accordance with Title 27, section 20415 [C], the Discharger is required to install at least one permanent groundwater monitoring well in the vicinity of GW-6. 5. The Discharger has proposed to install one groundwater monitoring well to an approximate depth of 85 feet bgs. The well construction detail indicates a well screen of 10 feet will be installed and according to the detail, the screen will be submerged. The work plan does not describe the rational of the well design. The well design proposed does not meet the standard specified in The Federal Code of Regulations Subtitle D Technical Manual for Groundwater Well Screen Interval Selection which states: "Proper selection-of the vertical sampling interval is necessary to ensure that the monitoring system is capable of detecting a release from the MSWLF unit. When monitoring an unconfined aquifer, the well screen typically should be positioned so that a portion of the well screen is in the saturated zone and a portion of the well is in the unsaturated zone (i.e., the well screen straddles the water table)." The well screen interval should be determined from historical shallow depth to groundwater data recorded from the onsite wells if available and field observations. If depth to groundwater information is not available, the Discharger shall conduct a search of domestic, agricultural, or industrial supply wells within a 1-mile radius of the site. 6. Staff recommends the wells be constructed with a minimum of 15 feet of well screen. The Discharger may consider a maximum of 20 feet of well screen depending on the seasonal fluctuation of the water table. Staff requests the Discharger to submit the amended work plan with the required information by 13 April 2007. Assessment delineation release report shall be completed by 6 June 2007. This report shall meet the objective described in Title 27, Section 20425(b). The Discharger shall update and submit to the RWQCB an Engineering Feasibility Study within 90 days (20 July 2007) of establishing an evaluation monitoring program per Title 27, Section 20425(c). The Discharger shall submit an amended report of waste discharge (ROWD) in accordance to Title 27, Section 20425(d) on 20 July 2007.