SALTFRONT MONITORING WELLS INSTALLATION

1/15/2025 10:00:00 AM

Scope of Work: (Contractor must obtain and submit all permits prior to performing any work). The purpose of this project is the Installation (drilling) of fourteen (14) Salt-Front Monitoring Wells (MWs) at different proposed locations along the east portion of Miami Dade County. Seawater encroachment continues to represent a major threat to the freshwater resources of coastal Miami-Dade County. The installation of these 14 wells will help to further delineate the extent of saltwater intrusion in areas where the saltwater front is currently estimated, to better define the saltwater front in areas where existing monitoring wells are already on the saltwater side of the front, and to better understand the hydrology of the Biscayne aquifer along the salt front. The objective of this project is to drill 14 salt front monitoring wells (SF 22-1 through SF 22-14), that can be drilled with a conventional drill bit but they must fully penetrate the Biscayne aquifer and have a stable and clean borehole for geophysical data collection. Sonic drilling will not be allowed in this project. Each well will be screened at the bottom of the deepest transmissive layer within the Biscayne aquifer, and additional sample tubes and filter packs may need to be installed in shallower flow zones, depending on the results of the geophysical logs. Due to unforeseen permitting time delays, the installation of the 14 wells may be delayed accordingly. The installation of the 14 saltfront monitoring wells will be as follows: 1. Drilling a 6-inch borehole to a depth of 95 feet (ft) below land surface (bls) for logging and to construct the well with a 2-inch polyvinyl chloride casing (PVC) casing. This well identification (ID) is shown as SF22-1 in Figure 1. 2. Drilling a 6-inch borehole to a depth of 121 ft bls for logging and to construct the well with a 2-inch PVC casing. This well ID is shown as SF22-2 in Figure 1. 3. Drilling a 6-inch borehole to a depth of 150 ft bls for logging and to construct the well with a 2-inch PVC casing. This well ID is shown as SF22-3 in Figure 1. 4. Drilling a 6-inch borehole to a depth of 150 ft bls for logging and to construct the well with a 2-inch PVC casing. This well ID is shown as SF22- 4 (and alternate location for SF22-4) in Figure 1. 5. Drilling a 6-inch borehole to a depth of 161 ft bls for logging and to construct the well with a 2-inch PVC casing. This well ID is shown as SF22-5 (and alternate location for SF22-5) in Figure 1. 6. Drilling a 6-inch borehole to a depth of 260 ft bls for logging and to construct the well with a 2-inch PVC casing. This well ID is shown as SF22-6 in Figure 1. 7. Drilling a 6-inch borehole to a depth of 270 ft bls for logging and to construct the well with a 2-inch PVC casing. This well ID is shown as SF22-7 (and alternate location for SF22-7) in Figure 1. 8. Drilling a 6-inch borehole to a depth of 200 ft bls for logging and to construct the well with a 2-inch PVC casing. This well ID is shown as SF22-8 in Figure 1. 9. Drilling a 6-inch borehole to a depth of 280 ft bls for logging and to construct the well with a 2-inch PVC casing. This well ID is shown as SF22- 9 (and alternate location for SF22-9) in Figure 1. 10. Drilling a 6-inch borehole to a depth of 135 ft bls for logging and to construct the well with a 2-inch PVC casing. This well ID is shown as SF22-10 in Figure 1. 11. Drilling a 6-inch borehole to a depth of 203 ft bls for logging and to construct the well with a 2-inch PVC casing. This well ID is shown as SF22-11 in Figure 1. 12. Drilling a 6-inch borehole to a depth of 105 ft bls for logging and to construct the well with a 2-inch PVC casing. This well ID is shown as SF22-12 in Figure 1. 13. Drilling a 6-inch borehole to a depth of 175 ft bls for logging and to construct the well with a 2-inch PVC casing. This well ID is shown as SF22-13 in Figure 1. 14. Drilling a 6-inch borehole to a depth of 172 ft bls for logging and to construct the well with a 2-inch PVC casing. This well ID is shown as SF22-14 in Figure 1. It is the intent of this project to drill into at least 20 feet of the uppermost part of the semiconfining unit beneath the Biscayne aquifer as determined by the site geologist for each deep test borehole. Therefore, the actual depth of the test borehole will vary, based on site aquifer properties. It is assumed that total depths of boreholes will vary from 95 feet to 280 feet BLS. The Miami-Dade Water and Sewer Department (WASD) and the United States Geological Survey (USGS) will oversee the completion of the drilling contract. Actual geologic conditions may require changes to the drilling process described here. WASD and or the USGS Site geologists will determine any changes to the planned work in consultation with the driller. Each test borehole will be completed as a 2-inch monitoring well and prior to drilling will have a temporary 8 or 10-inch diameter (as determined by the site geologist) schedule 40 PVC surface casing within a 12 or 14-inch diameter borehole, installed from the land surface to the depth where it is necessary to begin drilling the 6-inch borehole, (about 5- to 10-feet below land surface, but could be deeper). If temporary casing cannot be removed it may be grouted as needed, trimmed below grade, and left in place. Upon completion of drilling each test borehole, because the Optical Borehole Imaging (OBI) logging will be conducted, the CONTRACTOR will airlift the borehole with compressed air to remove excess sand and cuttings, so as (1) to prevent the borehole from filling in, (2) to clear the water filling the borehole of particulate, and (3) to develop flow within the well. USGS staff will log each borehole with geophysical tools, collect digital image logs of the borehole wall, and measure hydraulic properties of the borehole with flow meter logs. The CONTRACTOR will clear the borehole at their expense if bridging or sand infilling occurs. If a sand layer is discovered within the limestone bedrock an attempt will first be made to clear the hole using the airlift. If that fails, the CONTRACTOR in consultation with the USGS and WASD geologists will do the following: If the sand is in the lower part of the aquifer, the CONTRACTOR will raise the drill casing to a point just below the deepest sand bed of the Biscayne aquifer and air lift the open hole, so that geophysical and optical logging can be conducted over that part of the borehole where competent rock was drilled and the borehole remains open. After logging, the CONTRACTOR will raise the drill casing and airlift the remaining open hole of the borehole for preparation of geophysical and optical logging. The staged airlift may be done up to three times for the borehole in order to airlift and collect geophysical and optical logs over the competent parts of the borehole. If the sand is in the upper part of the aquifer near the surface, temporary slotted PVC casing may be installed down to competent rock below the sand. The borehole will then be airlifted and logged. The temporary casing will be removed during construction of the monitoring well. If significant sand as determined by the site geologist exists, then logging will be done in the completed well. The CONTRACTOR will be responsible for producing a straight and stable hole filled with clear ground water to be used for geophysical logging and construction of the fourteen monitoring wells. Drilling of each borehole should be done with the same drilling casing and a casing advancer. Use of a roller bit to drill the wells is not recommended, and if used, the driller must ensure the borehole is straight, roller bit does not “walk” in cavities creating a crooked borehole and does not impede borehole geophysical logging. If the borehole drilled with a roller bit is not straight, the contractor will run 6-inch casing to TD at their own expense to straighten the borehole for logging. If the borehole collapses prior to or during borehole geophysical logging, the CONTRACTOR will be responsible for adequately clearing out the borehole for successful logging operations (meaning that all specified tools reach the total depth in a continuous manner, record the appropriate data, and are successfully retrieved). Any downtime related to geophysical logging problems (e.g., probe stuck down-hole, or bridging) is the responsibility of the CONTRACTOR. The expected time required for the USGS to complete the logging is 2 days. Logging should be finished by noon the second day and based on the logs, the USGS will design the well construction plan, therefore, it is estimated that well construction will begin the next working day. No drill crew support will be needed during logging; therefore, no standby time will be available for the drill crew during the logging activities. Upon successful completion of geophysical logging, the monitoring well will then be constructed per section 3.5 and figures 2 and 3 (again, additional smaller diameter wells in the same bore hole may be added at additional cost). All monitoring wells will be protected by flush mount 15-inch diameter ‘meter’ type protective boxes (or other size as approved by the site geologist) and concrete pad. Each completed monitoring well opening will be protected inside the wellhead protector with a 2-inch locking cap. The CONTRACTOR will be responsible for installing straight, stable, unbent, unbroken, properly sealed, monitoring wells. The main 2-inch diameter deep monitoring well at each salt front site, must allow a 62.2-inch-long by 1.5-inch diameter induction probe to be lowered smoothly down the well. The CONTRACTOR will be responsible for properly developing the monitoring wells per EPA guidelines (Handbook of Suggested Practices for the Design and Installation of Ground-Water Monitoring wells, EPA/600/4-89/034). If the monitoring wells fail to provide proper communication with the aquifer materials, or if the installed casings and screens are damaged, obstructed, separated, or bent during installation to the extent that they do not meet these specifications, the CONTRACTOR will be responsible for correcting the installations at their expense. Teams Meeting Link: Microsoft Teams Need help? Join the meeting now Meeting ID: 260 311 462 109 Passcode: eR3su7qv ________________________________________ Dial in by phone +1 786-628-2782,,523951581# United States, Miami Find a local number Phone conference ID: 523 951 581#

Water well contractor; General building Contractor;