25E - AGMT - ON-CALL ENGINEERING SRVS

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ON-CALL ENGINEERING SERVICES M WuICr peGaurces � Op,bn A hollowing the initial steps In the rehabilitation of the well, then there are additional preliminary well rehabilitation operations that could be performed in the well. Howevet,'fibal Well rehabilitation operatioris need to ba determined following a more complete review of the newly - generated date and Information from the above listed Initial approach tasks. hallowing this, a set of Tochnioal Specifications can be developer) to provide the final wall rehabilitation operations. These operations may and.will likely include the following rehabilitation options:. 1. installation of a full, stainless-steolw1re•wrapped well screen easing liner and a new gravel' pack, 2. Mechanical cleaning, including wire brushing and using the A1rBur6ting9, .Blare Slastinge, or Sonawet6 methods. I Pool swab alrHiting and swabbing (Let, mechonioai development), Including chemical treatment, using appropriate :available solutions or aclds determined necessary by :earlier findings (i.e., performing a video survey). 4. Fie»developing and to-testinU the wail with a temporary test primp to dstsrmine the new past•rohabilitation specific Capacity of the well (Le., to check for possible improvements In specific !capacity). Based on theresults of new testing of the well. following liner installation, it may be necessary for the City to install a new pump and motor. A memorandum will be prepared discussing the findings and oonclut ions regarding the new pumping rates and specific capacities in the well. Important to the preparation of the Technical SpoolficationA is to evaluate options for the: discharge of fluids generated from the wall, via the National Pollutant Discharge Elimination System (NPDES) permit, and to provide p program for having the Contractor treat the discharge so that Contractor-oompliance with the City's NPDES permit is achieved at the well site. It will also be possible to have the Contractor obtain a discharge permit for the site. In this way,, the burden of the permitting, sampling, and reporting is shifted from the City to the Contractor. Well Modifications The sample project has a well approximately 30 years old that humps to an existing onsite reservoir, and has a maximum yield of 2,000 gpm and a 250 hp motor, Based on the summary of the City's :existing wells, none of the existing wells match these conditions. The only wells that have a design capacity of 2,000 gpm that pump to a reservoir are Well No. 16 (pumps to Walnut) and Wall No. 18 (pumps to John Oarthe). However., both of these wells have 150 hp motors. As noted above, the installation of a stainless steel liner casing will Impact the well flow capacity as well as the well's specific capacity. in addition, pumping directly into the distribution system instead of adjaoent reservoir will .greatly impact the pump capacity as it will increase the design head required by additional 180 to 200 feet. If assume a reduced well production by the liner of 60%, the.pump will need to meet the following conditions; 1,600 gpm at 420 feet lift which would require a 250 hp motor. For the sample project, the City has stated the well hat a 250 hp motor so the motor will not be required to be upsized. However, the pump will need to be changed due to the liner as well as the new well design conditions. The sample project did not mention where the existing sodium hypochlorite generation facilities are located (at'the well or at the reservoir). if the existing chlorination facilities treat the water at the reservoirs and not at the well, a new chlorination facility will be required If the well pumps directly Into the distribution system, in addition, changing the well operation to pump directly to Crfy or$ante Ann .10- TETRA TECH 25E-175