COMPLIANCE INFO_EW-5 INSTALL PERMIT PACKAGE 2/14/25

Home Browse Search

WELL INSTALLATION AND INTERIM REMEDIAL ACTION REPORT www.arcadis.com FINAL_Forward CHCF (CDCR) Well Installation Report_10182024 12 The step test data were also analyzed and included as part of the hydraulic parameter assessment for transmissivity and hydraulic conductivity using the Theis (1935) step test curve solution. Typically, all hydraulic parameters derived using the pumping well were approximately an order of magnitude lower than those derived from the observation wells. This indicated the influence of well losses on the pumping well dataset. The observation well hydraulic results were considered to be most representative of the aquifer parameters and, therefore, were preferentially used for aquifer parameter calculations. Using only the monitoring well data, the hydraulic conductivity was indicated to range between 199 and 247 feet per day (ft/day) (7.0 x 10-2 to 8.7 x 10-2 centimeters per second [cm/s]), with an average hydraulic conductivity of 228 ft/day (5.2 x 10-2 cm/s), which is indicative of medium to coarse sand, and/or sand and gravel mixes (Kruseman and de Ridder 2000). Storativity for the monitoring wells was between 7.0 x 10-3 and 2.6 x 10-1 cm/s, with an average of 7.5 x 10-2 cm/s, which is indicative of an unconfined or leaky aquifer system. Based on the monitoring well data, the aquifer transmissivity1 was indicated to range between 5,956 and 7,414 square feet per day (ft2/day), with an average transmissivity of 6,844 ft2/day. Hydraulic conductivity estimates were also calculated for gain size sample data (Appendix G-4) collected from depths adjacent to the screen zones of extraction well CDCR-EW-3. The grain size data were imported and assessed using HydrogeoSieve version 2.1 (Devlin 2015). The hydraulic assessment data are presented in Table 8, the output files from the analysis are presented in Appendix G-4, and the laboratory sieve data that were used are presented in Appendix C. Hydraulic conductivity calculated from the grain size data ranged between 5.0 and 60.1 ft/day (1.8 x 10-3 to 2.1 x 10-2 cm/s), with an average of 23.1 ft/day (8.2 x 10-3 cm/s), which is indicative of fine to medium sand and sand and gravel mixes. The hydraulic conductivity estimates calculated using the grain size data are lower than the aquifer testing estimates. The aquifer testing results are considered more accurate because the soil samples are locally derived from the borehole and the aquifer test indicates the entire response of the aquifer. 5.2.2 CDCR-EW-4 Hydraulic Testing Data Analysis Step and constant rate tests were conducted on extraction well CDCR-EW-4, which is screened across permeable sections of the shallow and intermediate WBZs on the CDCR property (Table 1, Figures 1 and 2). Step testing was performed by extracting groundwater from extraction well CDCR-EW-4 at incrementally increased flow rates while recording changes in water levels from CDCR-EW-4. The step testing results are presented in Table 3 and on Figure 4, and field data sheets are presented in Appendix D-2. Step testing was conducted at rates of 7.5, 13.0, 15.0, 17.0 and 23.0 gpm. The step test results indicated a specific capacity between 0.5 and 0.9 gallons per foot drawdown (Table 3). The specific capacity trend was consistent (Figure 4) for the first four steps, and the well reached drawdown stabilization. The fifth step, when pumping at a rate of 23.0 gpm, the well did not reach stabilization before the step test was concluded and was indicated to be dewatering the well. This indicates that a maximum well capacity and sustainable yield is between 17 and 23 gpm. A pumping rate of 20 gpm could theoretically be achievable but would expose the upper screen interval. Constant rate testing was then conducted with extraction well CDCR-EW-4 pumped at a rate of 16.5 gpm for approximately 8 hours and groundwater recovery monitored overnight. The hydraulic test design is presented in Table 5, and field data sheets are provided in Appendix D-3. A monitoring well network of six wells, located 1 Transmissivity equals hydraulic conductivity multiplied by saturated permeable thickness,