WORK PLANS - Laserfiche WebLink

Home Browse Search

Geosyntec consultants 4. COC CONCENTRATION TREND EVALUATION GSI Environmental, Inc. (GSI)'s Monitoring Remediation Optimization System (MAROS) software Version 2.2 prepared for the Air Force Center for Engineering and the Environment(AFCEE)as a public-domain data management and evaluation tool was used to provide a statistical review of long-term groundwater monitoring data at RRI. COCs at RRI selected for analysis were benzene, PCE, TCE, cis-1,2-DCE, and VC. The water quality monitoring data, statistical analyses, and results are discussed in the following sections. 4.1 Methodology Island-wide groundwater monitoring data collected between 1990 and 2016 and included in the project database for benzene, PCE, TCE, cis-1,2-DCE, and VC was used in the analysis. Over this period, 345 wells were sampled for benzene and 340 wells were sampled for PCE, TCE, cis-1,2-DCE, and VC. There were 10 historic wells at RRI that did not have any historical VOC data reported in the project database. Non-detect flags are used as input for the statistical interpretations at locations where groundwater samples were collected but chemical concentrations were below the RL. Non-detect flags were replaced by the RL values during the interpolation, a conservative assumption because non-detect samples may, in fact, contain no contaminants whatsoever. Prior to 2008, only the total 1,2-DCE concentration was included in the database. Therefore,total 1,2-DCE data was pulled for pre-2008 sampling dates and cis-and trans- 1,2-dichloroethene (trans-1,2-13CE) data were summed for post-2008 sampling dates. Based on a comparison of the post-2008 data, the cis-1,2-DCE detections are generally several orders of magnitude higher than the trans-1,2-DCE detections. MAROS does not include total-1,2-DCE as a COC option; therefore, the total and summed total 1,2-DCE data was input into MAROS as cis-1,2-DCE. Concentration trends for each well and parameter were determined using the non- parametric Mann-Kendall method and linear regression method. The null hypothesis for the Mann-Kendall tests is that there is no trend in the series. The three alternative hypotheses are that there is a negative, non-null, or positive trend. RRI Groundwater Monitoring Work Plan 20 1 June 2018