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(1)Construction and installation of wells and piezometers must be appropriate to insure that ground water samples and head measurements characterize discrete hydrogeologic units; and to prevent leakage of ground water, surface water or contaminants along the well annulus. If leakage is detected it must be corrected or the well abandoned. Wells installed for the purpose of ground water sampling and analysis must be capable of producing samples low in turbidity.

(2)All ground water monitoring wells must be constructed of PVC well casing material. Monitoring well casing must have a minimum inside diameter of 2 inches. Wells constructed in unconsolidated material less than 100 feet in depth must be constructed using a minimum of schedule 40 PVC well casing.

(3)All casing must be constructed of flush threaded joints or threaded coupling joints. All joints must be fitted with an "O" ring or wrapped with Teflon tape. Solvent welded joints are not acceptable.

(4)Wells and piezometers may be placed individually or as clusters. Clusters consist of individual wells or piezometers at varying depths in close proximity, each installed in its own boring.

(5)Appropriate precautions must be taken during drilling and construction of wells and piezometers to avoid introducing contaminants into the borehole. Unless otherwise approved by the Department based on site-specific characteristics, only potable water may be used in drilling. In some cases, analysis of water used in drilling may be required.

(6)All equipment to be placed into the boring must be properly decontaminated before use at the site and between boreholes.

(7)Borings for wells and piezometers must not be placed through or into waste unless prior Department approval has been granted and sufficient safety precautions are employed.

(8)Well screens are required for all wells and for open standpipe piezometers. All screens must be factory slotted and sized to retain at least 90% of the grain size of the filter pack. Water table variations, site stratigraphy, expected contaminant behavior, and ground water flow must be considered in determining screen position and length. Unless otherwise approved by the Department based on site-specific characteristics, screens for water table observation wells and monitoring wells must not exceed 10 feet in length. Screens for piezometers must not exceed 2 feet in length. Technical justification for the screen length chosen must be provided.

(9)Well screens must be located to readily detect changes in ground water chemistry in each potentially affected hydrogeologic unit. Monitoring wells must not be screened across hydrogeologic unit boundaries. Where surficial hydrogeologic units exceed 20 feet in saturated thickness, a monitoring well cluster of two or more wells is required, the screens of which must each not exceed 10 feet in length.

(10) Proposals for alternate instrumentation for piezometric measurements in sediments with hydraulic conductivity of less than 10E-6 cm/sec may be submitted to the Department for review and approval.

(11) The sand pack surrounding the well screen must consist of clean, inert siliceous material. The sand pack must minimize the amount of fine material entering the well and must not inhibit the flow of water into the well. The sand pack must be placed in the annular space around the well screen and extend two feet or twenty percent of the screen length (whichever is greater) above the top, and six inches below the bottom, of the screen. The sand pack material must be placed using the tremie method and must avoid bridging. The sand pack must be checked for proper placement. A finer

Chapter 405: Water Quality Monitoring, Leachate Monitoring, and Waste Characterization

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