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The Harney Lane Sanitary Landfill is located to the north of ephemeral South Paddy Creek. Article 5 requires background surface water monitoring points which represent surface water quality that has not been affected by landfill activities. Background monitoring point S-1 is sampled in South Paddy Creek above the detention basin inlet, and downstream monitoring point S-2 is sampled at the point of discharge into South Paddy Creek from the stormwater detention basin. There are no unsaturated zone monitoring facilities at the Harney Lane Sanitary Landfill. Although Article 5 requires monitoring of the unsaturated zone at waste management units, the lack of information regarding the landfill base configuration makes unsaturated zone monitoring unfeasible. 3.1.2 Revisions to the Monitoring ram The first phase of the evaluation program will be to continue with the current monitoring program sampling frequency and conduct statistical analysis for MW-2 data. As required by WDR Order No. 93-093, quarterly monitoring of all the monitoring wells for VOCs will be continued. The WQPS report specifies that the tolerance interval method be used where statistical comparison is applicable. Because VOCs are not naturally occurring, the concentration limit for most VOCs is its detection limit. Therefore, once VOCs are detected, the trend analysis method is more appropriate. The Kendall-tau test for trend is proposed for the site monitoring program to evaluate the correlations between time and monitoring parameter concentrations.A detailed description of the trend analysis method is contained in Appendix C. Consistent with the use of trend analysis, the concentration limits for the organic monitoring parameters in well MW-2 be "no statistically significant upward trend." 3.2 Assessment of Nature and Extent of Release Section 2550.9(x) of Article 5 requires the County to assess the nature and extent of the release from the waste management unit. Section 2550.9(b) requires that the discharger collect and analyze all data necessary to assess the nature and extent of the release to determine the spacial distribution and concentration of the constituents of concern throughout the zone affected by the release. This section also requires that the discharger complete this assessment within 90 days of establishing an evaluation monitoring program. An assessment of the nature and extent of the observed release will be conducted in a phased approach. The first phase will entail a review of the historical groundwater data for the site and from other sites in the Central Valley that have VOC releases. Since the RWQCB has already indicated a concern that MW-4 might be impacted from off-site sources, EMCON proposes that a review of analytical results from the adjacent waste SAC/pj0 093M390011.8a1-94/lfc:9 Rev.0. 10/17/94 0939-001.18 6