SDI Environmental Services, Inc. 13911 N. Dale Mabry Hwy. Suite 201, Tampa, FL 33618; (813) 961-1935 MEMORANDUM TO: FROM: SUBJECT: Dave Slonena, P.G., Pinellas County Cathleen Beaudoin Jonas RAI Responses Related to East Lake Road Wellfield Drawdown Analysis, WUP No. 20012943. SDI Project No. PCF-180. DATE: The following are the requested responses to the Request for Additional Information for the above-referenced WUP. Question 9: Response: Please provide spatial representations of the transmissivity, leakance, storativity, and recharge values on maps of the local area. Each map shall display a single type of parameter values. Explain how the transmissivity leakance, storativity and recharge values used in the withdrawal impact simulations were derived. Spatial representations of model UFAS transmissivity, leakance between the SAS and UFAS, and storativity values are provided in Figures 9.1 through 9.3. The recharge package is transient and varies on a weekly time step over the annual simulation. Recharge represents 1990 conditions and was calculated from an integrated model. Figure 9.4 represents the average annual net recharge. Negative values typically occur in discharge areas along streams and the coast. The simulated drawdown is not affected by the recharge distribution because the same recharge rates are used in both the base and scenario simulations. Aquifer parameters were derived from published values and model calibration. The modeled UFAS transmissivity value in the East Lake Wellfield area is within the range of measured values from aquifer performance testing at production well EL-18. Question 10: If the aquifer parameter values were derived through model calibration, please provide an explanation of the method and procedure used. Response: This model has been used and submitted in support of numerous WUP applications and modifications approved by the District. Documentation of the model development and calibration can be found in SDI Environmental Services, Inc., 1997. Water Resources Evaluation and Integrated Hydrologic Model of the Central Northern Tampa Bay Region. Prepared for the West Coast Regional Water Supply Authority and SDI Environmental Services, Inc., 1998. Water Resources Evaluation and Integrated Hydrologic Model for Brandon Urban Dispersed Wells Project, prepared for
Page 2 West Coast Regional Water Supply Authority. The use of the decoupled MODFLOW groundwater portion of the above integrated model used for this analysis and generation of the transient weekly recharge package is described in SDI Environmental Services, Inc., 1998. Part VI Hydrogeology Refinement and Application of a Groundwater Flow Model for Assessing Brandon Urban Dispersed Wells Project: Response to Clarification Letter WUP Application No. 2011732.01, Prepared for Tampa Bay Water. Question 11: Please provide simulated drawdown impacts in the surficial aquifer and Floridan aquifer that show the 0.0-feet drawdown contour line, when the simulated results of the model are rounded to the nearest tenth of a foot. Response: The model has been re-run at an average annual rate of 294,000 gallons per day (gpd). A CD Rom containing the model input and output is attached. The simulated drawdown impacts in the surficial aquifer and Floridan aquifer due to 290,000 gpd average annual pumpage are attached as Figures 11.1 and 11.2, respectively. The location of the 0.0 ft drawdown contour should only be used as guidance. The groundwater model is conservative, in that it over estimates drawdown because the groundwater model does not account for increased recharge in the pumping scenario due to ET capture. As part of MFL rules, the District has set Salt Water Intrusion Minimum Aquifer Levels (SWIMAL) at designated monitor wells. The predicted UFAS drawdown at all of the MFL saltwater intrusion wells near the EL is less than 0.1 foot (Figure 11.2). Table 1 lists the simulated UFAS drawdown at each of the seven monitor wells near the EL. The predicted UFAS drawdown of 0.06 foot at the closest monitor well, 2s, would be an undetectable change. Table 2 shows that the observed long-term and recent water levels at the four wells north of the East Lake Wells are above the SWIMAL levels. As seen in Table 2, the resulting change in the long-term average hydraulic gradient toward the coast is 0.000, therefore, the proposed pumpage would have no impact on saltwater intrusion. Question 13: Pursuant to Florida law, please note that all geologic analyses, including lithologic logs, boring logs, geologic cross-sections, aquifer performance tests, groundwater flow models, and analyses of impacts to rivers and springs must be signed and sealed by the responsible Professional Geologist or other qualified professional. Alternatively, a cover letter, which references the analyses and has been signed and sealed by the responsible Professional Geologist or other qualified professional may be submitted. Response: A submittal cover letter signed by a Professional Geologist is attached. Attachments
Page 3 Figure 9.1 Modeled Spatial Distribution of UFAS Transmissivity in the East Lake Wellfield Area.
Page 4 Figure 9.2 Modeled Spatial Distribution of Leakance in the East Lake Wellfield Area.
Page 5 Figure 9.3 Modeled Spatial Distribution of Storativity in the East Lake Wellfield Area.
Page 6 Figure 9.4 Modeled Average Annual Recharge Distribution in East Lake Wellfield Area.
Page 7 Figure 11.1 Simulated SAS Drawdown after One Year Due to 0.294 mgd Average Annual Pumpage.
Page 8 Figure 11.2 Simulated UFAS Drawdown After One Year Due to 0.294 mgd Average Annual Pumpage.
Page 9 Table 1. Simulated Average Annual Drawdown at Saltwater Intrusion Monitor Wells. Average Annual Drawdown Monitor Well (ft) Tarpon Rd Deep 0.01 SWI-18s 0.03 201-M 0.04 2s 0.06 RMP-8d 0.01 RMP-13d 0.01 RMP-16d 0.01 Table 2. Change in Aquifer Levels and Gradients in Saltwater Intrusion Wells due to Proposed Average Annual Pumping. Average Water Level (ft) Well SWIMAL Long Term Long Term minus EL Recent (WY03- Recent minus EL Drawdowns (WY00-WY05) Drawdown WY05) Tarpon Rd 9.9 9.97 9.96 10.45 10.44 SWI-18s 14.8 15.53 15.50 16.91 16.88 201-M 13.7 15.69 15.65 18.52 18.48 EW-2s deep 10.3 15.13 15.07 19.92 19.86 SWI-18s to Tarpon Rd Gradient 0.001 0.001 0.001 0.001 Change in Gradient with Drawdown 0.000 0.000