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Ryegrass Limited Purpose Landfill and Balefill Closed Landfill <br />Groundwater and Wachate Sampling and Analysis Plan <br />nititas County Solid WaVe <br />comparison can be conducted at each compliance well between existing intrawell background and <br />the potential set of newer background data. A non -significant result implies that the newer <br />compliance data can be re-classified as background measurements and added to the existing <br />intrawell background data set. On the other hand, a determination of significance suggests that the <br />compliance observations should be reviewed to determine whether a gradual trend or other change <br />has occurred that was missed by the intervening UPL or control chart tests. <br />The unified Guidance also recommends reviewing time series plots of concentrations to see if either <br />an overall trend in the combined data sets or distinct differences In the respective sets (background <br />and compliance) is suggested. In such cases Mann-Kendall/5en's Slope trend tests will be <br />conducted to compare short-term data (last eight samples) to long-term data (all data prior to the <br />last eight samples). A determination of a significant trend might occur even if the two -sample tests <br />are inconclusive. A trend in the newer data may reflect or depart from the historical data conditions. <br />The UPLs and control charts will initially be updated annually. This includes resetting the cumulative <br />sum [CUSUM] portions of control charts to zero after re -calculating the control limits and prior to <br />additional testing against those Ilmits. If no statistically significant increasing trends, statistical <br />exceedances of UPLs, or data outliers are observed, the past 2 years' data will be combined with the <br />background data sets and used to update the control charts and UPLs for the next 2 years (to <br />increase the sample size, and thus the power, of the background data sets). If an exceedance is not <br />explainable as an outlier or error, it may represent a portion of the background population that has <br />heretofore not been sampled. In that case, the data value could be included in the updated <br />background data set (along with the repeat sample) as evidence of the expanded but true range of <br />background variation. <br />3.2 Contingency Plan <br />If statistical analyses determine a significant increase over background, the Kittitas County will notify <br />Kittitas Health and Ecology within 30 days of the evaluation finding. If the increase is not <br />demonstrated to be attributable to a source other than the landfill, natural variation in groundwater <br />quality, or an error In sampling, analyses, or statistical evaluation, AND the concentrations of <br />constituents meet the groundwater quality criteria established by Chapter 173-200 WAC, Water <br />Quaflty Standards for Ground Waters of the State of Washington, Kittitas County in consultation with <br />KCHD and Ecology, will determine additional measures. Additional measures to be considered are to <br />characterize the chemical composition of the release and the contaminant fate and transport <br />characteristics by Installing additional monitoring wells; assess and, If necessary, implement <br />appropriate Intermediate measures to remedy the release; and evaluate, select, and implement <br />remedial measures as required by Chapter 173-340 WAC, the Model Toxics Control Act cleanup <br />regulation, where applicable. <br />3.3 Reporting <br />3.3.1 Quarterly Reports <br />Kittitas County will submit quarterly reports for the first, second, and third quarters of each year to <br />Kittitas Health and Ecology. The quarterly reports will summarize and interpret the following <br />information (for each quarter): <br />■ Groundwater monitoring laboratory and field data <br />■ Data validation Deport <br />April 2024 15511763•010 3-3 <br />Revised May 2024 <br />