25E - AGMT - ON-CALL ENGINEERING SRVS

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ON-CALL ENGINEERINQ SERVICES WwwrW owm-OMbnA static water level have remained consistent; and/or the well begins to pump send and/or gravel pack, or even. displays large amounts of entrained air in the pumped dlscharge. The causes for these observed conditions can. be due to many reasons; incI40Ing: "pump, motor, and/or electrical prcblitins, resulting In decreased production rates; biological foullino of the perforations and.grovel pack, resulting in plugged conditions, thereby decreasing the production rate and spedific capacity and deepening of the pumping levels, and even loss of pump efficiency; and/or development of holes in the well casing and/or enlargement of the perforations, resulting in the production:of sand. When conslderlog wail rehabilitation; site.-speolfladata from the well in question needs to be evaluated to determine what could be causing the observed conditions. Therefore, it is Imperative to Obtain and review available data on both historic and current values for: statfo,and pumping water levels; water quality; specific capacity; well construction records; previous wall rehabilitation work, production rates; and video logs, etc. Only through"revlew of such data"by qualifier. hydrogeoiogists Can the potential reason(s) for the decreases in well Iperformanoe and the Idehtiffoatlon of rehabilitation steps be defined, It is understood That the subject of the Santa Ana Water Project Is reported as "being 34 years old and Is currently producing sand. Because it is constructed of low carbon steel the: casing may be reaching near the end of Its useful Ilfe. and further operations may lead to complete failure, e.g., by a potential casing collapse, However,. the life of the existing well could be extond6d eornewhat longer by the installation of full, stainless-steel' liner casing In the well and this is.the prime recommended course of action that can.now be undertaken on the well, The proj%t can be approached iii One of two ways by the:Clty. An initial approach, and one that Is less efficient, is to conduct this Initial work as part of a prepared set of Technical Specifications where all rehabilitation options are included. However, a second, and more efficient approach, would be for the City to contract with a well rahabilfjaflon Company to conduct Initial Investigatory operations on the well to determine the eurrent downhole conditions In the well. This would Include conducting an Initial short-term pumping test to obtain the current, pro-rehabliltation specific capacity of the well. This would be Immediately followed by removing the pump and running a down -wolf video survey to determine the observable condition of the casing and the perforations, and depth of the sand In the well. This would be a preferred approach, because by determining the current Condition of the well, a set of Technical Specifications can be prepared with the necessary rehabilitation operations already provided. This is the approach that Tetra Tech is using on the Well No. 32 Rehabilitation Project for the laity. The tasks for this preferred initial approach would be as follows: I . Following removal of the pump motor, column and bowls from the well, Inspect and measure all apparatus (conducted by the contractor In the field and at the pumping contraotor's shop). 2. Sound the bottom of the casing to determine the current amount (and type) of sediment fill and then ball that sediment from the bottom of the casing; examine the collected sediments and possibly conduct laboratory analysis. Check carefully for the possible presence of gravel pack and/or formation sand in the bailed material. 3, Perform a current video survey of the well to determine the depth to which sand has filled the well; check for possible holes in the casing, and the possible extent of plugging of the perforations. City of Santa Ana .9_ T97"RA TEEM 25E-174