06-096 C.M.R. ch. 405, § 5 - Standards for the Installation, Construction and Maintenance of Wells and Piezometers, and for the Advancement of Borings

This section describes requirements for wells, piezometers and borings for all types of monitoringand investigations at all types of facilities.

A. Construction of wells and piezometers. Monitoring wells and piezometers must be installed in a manner that maintains the integrity of the bore hole. The design and construction of the well or piezometer directly affects the quality and representativeness of the samples collected. The following criteria must be followed during the construction of wells, piezometers and borings:

(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 grained sand pack material (100% passing the No. 30 sieve and less than 2% passing the No. 200 sieve) six inches thick must be placed above the sand pack and below the bentonite seal;

(12) Bentonite must be placed above the sand pack using the tremie or other approved method to form a seal at least three feet thick. If pellets or chips are used, sufficient time (usually 4 to 24 hours) must be allotted to allow for sufficient hydration of the bentonite prior to placement of overlying materials;

(13) Grout of cement and bentonite, bentonite alone, or other suitable, low permeability material, if approved by the Department, must completely fill the remaining annular space to the base of the surface seal. The sealing material must set up without being diluted by formation water, and must displace water in the annular space to insure a continuous seal. The sealant must be placed under pressure using a tremie or other method approved by the Department. Backfill of native material to construct the annular seal is prohibited; and

(14) A bentonite or concrete surface seal and protective, lockable steel casing must be installed around all monitoring wells and long-term observation wells and piezometers. If a concrete surface seal is constructed, it must extend from below the level of frost action at least to the ground surface. The surface seal must prevent surface water or runoff from ponding around the well casing. The protective steel casing must be set at least six inches lower than the base of the surface seal and extend approximately two inches above the top of the PVC riser. The surface seal must be designed to minimize or eliminate heaving due to frost action. Both the surface seal and the protective steel casing must be designed and constructed so that neither is mechanically coupled to the PVC riser. The diameter of the protective casing must be at least two inches larger than the PVC riser. The protective casing, as well as the PVC riser, must be vented near the top to allow the escape of gasses and the equilibration of water level with atmospheric pressure changes. The protective casing must also have a drain hole at the base. A permanent, distinctive and readily visible marker identifying the well's designation must be affixed to the protective casing or near the well; and a means to locate the well during periods of high snow cover must also be provided. In areas of traffic, bumper guards or other suitable protection for the well are required.

B. Geologic sampling. A boring program is necessary to define site hydrogeology. Borings must be carefully sampled to provide surficial and lithological information.

(1) Borings must be continuously sampled throughout the length of the hole at all locations where surficial stratigraphy and bedrock characteristics have not previously been determined.

(2) In any additional borings not continuously sampled, samples must be taken at five foot intervals, at each stratigraphic change, and at the screened interval in surficial deposits and, in rock, as required by the Department.

(3) At a minimum, the screened interval of each surficial installation must be analyzed.

(4) At well or piezometer clusters, continuous samples must be taken from the surface to the base of the deepest boring. Other wells or piezometer borings in the cluster must be sampled at the screened interval.

(5) Bedrock must be sampled with a standard size NX or larger diameter core barrel. All other materials must be sampled using the split spoon or equivalent method.

(6) Bedrock refusal must be distinguished from boulder refusal by a minimum of ten feet of continuous rock core. Where core lithology does not conform to known bedrock characteristics, a longer core may be required to confirm bedrock refusal.

(7) Core samples must be securely stored and accessible throughout the life of the facility.

(8) Unconsolidated samples must be retained for five years after the original permit is issued. The location of the storage area must be designated in the operating record for the solid waste facility.

C. Well and piezometer development. Monitoring wells and piezometers must be constructed, installed and developed in a manner which assures that the well or piezometer is in good hydraulic contact with the hydrogeologic unit and that samples obtained will be representative of formation water. Wells installed for the purpose of ground water sampling and analysis must be capable of producing samples low in turbidity.

(1) All wells and piezometers must be developed as soon as possible after installation but not before the well seal and grout have set.

(2) Water must not be introduced into the well except with approval from the Department.

(3) Any contaminated water withdrawn during development must be properly managed.

(4) The entire saturated screened interval must be developed.

(5) Well development methods selected must insure that sediment-free water can be obtained. The Department may require multiple attempts at well development to ensure that sediment-free water can be obtained.

(6) Acceptable well development methods are specified in US EPA (1992A) "RCRA Ground-Water Monitoring: Draft Technical Guidance", and references listed therein. The development method selected must be appropriate for the stratigraphy/conditions encountered. Placement of screens in fine grained strata may require gentle development techniques to avoid pulling sediments into the well. The selected method must minimize to the greatest extent possible the amount of turbidity in the well.

D. In-situ hydraulic conductivity testing and well performance evaluation. In-situ hydraulic conductivity testing of each monitoring well must be performed to provide information on the hydraulic conductivity in the immediate vicinity of the monitoring well. A well performance evaluation must be performed on each monitoring well to determine the rate at which each well can be pumped without significant continued drawdown. In-situ hydraulic conductivity testing must be done in all monitoring wells and piezometers. The testing methods must not introduce contaminants into the well. Any contaminated water removed from the well must be properly managed.

E. Report on the Design, Construction and Development of Monitoring Wells and Piezometers. The following information on the design, construction and development of monitoring wells and piezometers must be submitted to the Department after development of monitoring wells is completed.

(1) Standard drillers logs showing driller's name, start and finish data, boring designation, casing, sampler, core barrel and hammer specifications, sample blow counts, vane readings, moisture content, location of the water table during drilling, water lost during drilling, degree of sample recovery and other appropriate information must be submitted for each boring.

(2) A well installation detail diagram with a minimum vertical scale of 1 inch equals 5 feet showing the complete borehole and the complete well or piezometer installation in cross section, including well or piezometer designation; the elevations of riser and screen and of all annular materials; the surface elevation and the of top of riser and top of protective casing. Sampling intervals, sample designations, and if practical, analytical results must also be included. Borehole stratigraphy, as interpreted by the geologist in charge of the installation is also required as part of the installation diagram. Logs of surficial deposits should include a description of matrix and clasts, mineralogy, roundness, color, odor, appearance, and behavior of materials. Rock core logs must describe the lithology, mineralogy, degree of cementation, color, grain size, and any other physical characteristics of the rock noted, percent recovery and the rock quality designation (RQD). The logging system used to provide the information must be a geological logging system. Engineering logging systems are not acceptable.

(3) Information on the method of well development used for each monitoring well and the results of the development.

F. Routine Inspection, Maintenance and Testing of Monitoring Wells. All monitoring wells must be maintained in a manner that ensures their continued performance according to design specifications over the life of the monitoring program. All results, as well as a description of any maintenance conducted, must be included in the reports submitted to the Department.

(1) Inspections of surface seals for heaving, settling and cracks must occur each time sampling and/or water elevation measurements are carried out, and the results recorded on the field sheets.

(2) At least annually, the depth of each well must be determined, and the results reported in the annual report.

(3) At each monitoring well where low-flow sampling is not used, a performance evaluation of the monitoring well must be conducted at least annually, to determine the pumping rate at which the well will be purged and sampled. This data must be included in the annual report for the facility.

G. Replacement of wells and piezometers. All wells and piezometers must be properly protected and maintained to insure their integrity. If water quality or any other data show that the integrity of a monitoring well is lost, the well must be replaced and sampled within a time period not exceeding 120 days after written notification by the Department. When a well is damaged or for any other reason cannot be sampled, the Department must be notified in writing no later than fifteen days from the discovery of the damage.

(1) A location for the replacement well or piezometer must be approved by the Department prior to its installation.

(2) The initial sample for a replacement well at MSW landfills must consist of the Appendix A of this chapter,Column 3 parameters.

H. Abandonment of wells, piezometers and borings. Wells, piezometers and borings abandoned for any reason must be fully and completely sealed in a manner appropriate to the geologic conditions to prevent migration of water or contaminants along the borehole. Generally such sealing must include:

(1) Removal of all material installed in the original borehole including casing, screen and annular materials to the greatest extent possible. Any casing which cannot be withdrawn intact must be ripped and perforated and then augered or washed from the hole.

(2) Sealing by pressure injection from bottom to top with cement bentonite or other appropriate material to within five feet of the ground surface. The upper five feet may be backfilled with native material, and the entire site must be restored to a safe condition. Where the surrounding geologic deposits are highly permeable, alternative methods of sealing may be required by the Department to prevent migration of grout into the surrounding formation.

(3) Documentation of the abandonment through a written description of the procedures employed, drilling methods and depths, borehole depth and volume and type of sealant employed is required.

Notes

06-096 C.M.R. ch. 405, § 5