§ 98-56. Monitoring well standards.

(a)

General requirements. General requirements for monitoring wells are as follows:

(1)

Application to well type. The standards in this section apply to all types of monitoring wells, as well as to vapor extraction wells, where applicable, and any other well installed in an area where special precautions are necessary to protect groundwater quality, except as prescribed in subsection (a)(2) of this section, which pertains to exemptions for unusual conditions, and subsection (a)(3) of this section, which pertains to exclusions. Before a change in use of a well is made, any standards for the new use must be complied with.

(2)

Exemptions for unusual conditions. Under certain circumstances, the enforcement agency may waive compliance with these standards and prescribe alternate requirements. These standards may be waived where they are impractical or ineffective because of unusual conditions or would result in an unsatisfactory condition or well function. In waiving any of these standards, the enforcement agency shall, if at all possible, require measures be implemented to provide the same or greater level of water quality protection that would otherwise be provided by these standards.

(3)

Exclusions. Most standards in subsection (b) of this section, which pertains to monitoring well construction, do not apply to exploration holes. However, subsection (c) of this section, which pertains to destruction of monitoring wells, and section 98-62, which pertains to well completion reports, do apply directly to exploration holes.

(4)

Special standards. The enforcement agency may prescribe measures more stringent than standards presented in this section, where needed to protect public safety or protect water quality.

(b)

Monitoring well construction. Construction standards for monitoring wells are as follows:

(1)

Well location with respect to pollutants and contaminants, and structures. Standards for well location, with respect to pollutants and contaminants, and structures are as follows:

a.

Separation. Monitoring wells shall be located an adequate distance from known or potential sources of pollution and contamination, including those listed in section 98-55(b)(1)a, which pertains to separation, of the water well standards, unless regulatory or legitimate data requirements necessitate they be located closer.

b.

Flooding and drainage. Monitoring wells should be located in areas protected from flooding, if possible. Provisions for locating monitoring wells in areas of flooding and drainage are contained in section 98-55(b)(1), which pertains to flooding and drainage, of the water well standards.

c.

Accessibility. All monitoring wells shall be located an adequate distance from buildings and other structures to allow access for well maintenance, modification, repair, and destruction, unless otherwise approved by the enforcement agency.

d.

Disposal of wastes when drilling in contaminated or polluted areas. Drill cuttings and wastewater from monitoring wells or exploration holes in areas of known or suspected contamination or pollution shall be disposed of in accordance with all applicable federal, state, and local requirements. The enforcement agency should be contacted to determine requirements for the proper disposal of cuttings and wastewater.

(2)

Sealing the upper annular space. General discussion of sealing methods and requirements for monitoring wells is contained in section 98-55(b)(2), which pertains to sealing the upper annular space, of the water well standards. Special requirements for monitoring wells include the following:

a.

Minimum depth of annular seal. The minimum depth of annular seal shall be in accordance with the following:

1.

Water quality monitoring wells and monitoring wells constructed in areas of known or suspected pollution or contamination. The annular space shall be sealed from the top of the filter pack or monitoring zone to ground surface, unless otherwise approved by the enforcement agency. The top of the filter pack or monitoring zone shall not extend into another water-bearing unit above the single water-bearing unit being monitored unless otherwise approved by the enforcement agency. The filter pack or monitoring zone shall not extend into any confining layers that overlie or underlie the unit to be monitored, unless otherwise approved by the enforcement agency. The annular surface seal shall be no less than 50 feet in length.

Seal lengths less than 50 feet are permissible only if shallow zones will be monitored and approval has been obtained from the enforcement agency.

2.

Other monitoring wells. The upper annular seal shall extend from the ground surface to a minimum depth of 50 feet. An annular seal less than 50 feet in length is permissible if provisions in subsection (b)(2)a.1 of this section, which pertains to water quality monitoring wells and monitoring wells constructed in areas of known or suspected pollution or contamination, are followed.

3.

Sealing-off strata. Additional annular sealing material shall be placed below the minimum depth of the upper annular seal, as is needed, to prevent the movement of poor-quality water, pollutants, and contaminants through the well to zones of good quality water. Requirements for sealing off zones are in section 98-55(b)(6), which pertains to sealing-off strata, of the water well standards.

4.

Vaults. At the approval of the enforcement agency, the top of the annular seal and well casing can be below ground surface where traffic or other conditions require. In no case shall the top of the annular seal be more than four feet below ground surface.

The top of the annular seal shall contact a suitable, watertight, structurally sound subsurface vault, or equivalent feature, that encloses the top of the well casing in accordance with subsection (b)(3)e of this section, which pertains to vaults. The vault shall extend from the top of the annular seal to at least ground surface.

b.

Sealing conditions. Sealing conditions are as follows:

1.

Temporary conductor casing. If temporary conductor casing is used during drilling, it shall be removed during the placement of the casing and annular seal materials, as described in section 98-55(b)(2), which pertains to sealing the upper annular space, of the water well standards. If the temporary conductor casing cannot be removed, as defined in section 98-55(b)(2), sealing material shall be placed between the conductor casing and borehole wall and between the well casing and conductor casing, in accordance with methods described in section 98-55(b)(2). Sealing material shall extend to at least the depths specified in subsection (b)(2)a of this section, which pertains to minimum depth of annular seal.

2.

Permanent conductor casing. If a permanent conductor casing is to be installed, the monitoring well borehole diameter shall be at least four inches greater than the outside diameter of the conductor casing. The inner diameter of the permanent conductor casing shall in turn be at least four inches greater than the outside diameter of the well casing.

Sealing material shall be placed between the permanent conductor casing and the borehole wall and the conductor casing and the well casing. The sealing material shall extend to at least the depths specified in subsection (b)(2)a of this section, which pertains to minimum depth of annular seal.

c.

Radial thickness of seal. A minimum of two inches of sealing material shall be maintained between all casings and the borehole wall, within the interval to be sealed, except as noted in section 98-55(b)(2), which pertains to sealing the upper annular space, of the water well standards. At least two inches of sealing material shall also be maintained between all casings in a borehole, within the interval to be sealed, unless otherwise approved by the enforcement agency. Additional space shall be provided, where needed, to allow casings to be properly centralized and spaced and allow the use of a tremie pipe during well construction, if required, especially for deeper wells.

d.

Sealing material. Sealing material shall consist of neat cement or sand cement. Concrete shall be used only with the approval of the enforcement agency.

Sealing material shall be selected based on required structural, handling, and sealing properties, and the chemical environment into which it is placed. Used drilling mud or cuttings from drilling shall not be used for any part of the sealing material.

1.

Water. Water used for sealing mixtures should generally be of drinking water quality, shall be compatible with the type of sealing material used, shall be free of petroleum and petroleum products, and shall be free of suspended matter. Only drinking-quality water of known composition should be used for preparing sealing mixtures for monitoring wells to be used for sensitive water-quality determinations.

2.

Cement-based sealing materials. Standards for cement-based sealing materials are contained in section 98-55(b)(2), which pertains to sealing the upper annular space, of the water well standards. Special considerations that apply to monitoring wells are as follows:

i.

Additives. Care should be exercised in the use of special additives for cement-based sealing materials, such as those used for modifying cement setting times. Some additives could interfere with sensitive water quality determinations.

ii.

Cooling water. For water quality monitoring wells, care should be exercised in the use of circulating cooling water to protect plastic casing from heat buildup during setting of cement-based sealing materials. Water introduced and/or circulated in a well for cooling could interfere with water quality determinations.

e.

Transition seal. A bentonite-based or fine sand transition seal, up to five feet in length, must be placed in the annular space to separate filter pack and cement-based sealing materials, as described in section 98-55(b)(2)f.3, which pertains to foundation and transition seals, of the water well standards.

f.

Placement of annular seal material. All loose cuttings and other obstructions shall be removed from the annular space before sealing materials are placed. Sealing may be accomplished by using pressure grouting techniques, a tremie pipe, or equivalent. Sealing materials shall be installed as soon as possible during well construction operations. Sealing materials shall not be installed by freefall from the surface unless the interval to be sealed is dry and less than 30 feet deep.

Casing spacers shall be used within the interval to be sealed to separate individual well casing strings from one another in a borehole of a nested monitoring well. The spacers shall be placed at intervals along the casing to ensure a minimum separation of two inches between individual casing strings. Spacers shall be constructed of corrosion-resistant metal, plastic, or other nondegradable material. Wood shall not be used as spacer material.

Any metallic component of a spacer used with metallic casing shall consist of the same material as the casing. Metallic spacer components shall meet the same metallurgical specifications and standards as the casing to reduce the potential for galvanic corrosion of the casing.

The spacing of casing spacers is normally dictated by casing materials used, the orientation and straightness of the borehole, and the method used to install the casing. Spacers shall not be more than 12 inches in length and shall not be placed closer than ten feet apart along a casing string within the interval to be sealed, unless otherwise approved by the enforcement agency.

Casing spacers shall be designed to allow the proper passage of a tremie and distribution of sealing material around casing within the interval to be sealed.

Additional discussion and standards for placement of the annular seal are contained in section 98-55(b)(2), which pertains to sealing the upper annular space, and section 98-55(b)(6), which pertains to sealing-off strata, of the water well standards, and appendix B of bulletin 74-81.

(3)

Surface construction features. Additional requirements for surface construction features are in section 98-55(b)(3), which pertains to surface construction features, of the water well standards.

a.

Locking cover. The top of a monitoring well shall be protected by a locking cover or equivalent level of protection to prevent unauthorized access.

b.

Casing cap. The top of a monitoring well casing shall be fitted with a cap or sanitary seal to prevent surface water, pollutants, or contaminants from entering the well bore. Openings or passages for water level measurement, venting, pump power cables, discharge tubing, and other access shall be protected against entry of surface water, pollutants, and contaminants.

c.

Flooding. The top of the well casing shall terminate above ground surface and above the regulatory flood datum (RFD), except where site conditions, such as vehicular traffic, will not allow.

d.

Bases. Unless otherwise approved by the enforcement agency, a concrete base or pad shall be constructed around the top of a monitoring well casing at ground surface and contact the annular seal, unless the top of the casing is below ground surface as provided by subsection (b)(3)e of this section, which pertains to vaults. The base shall be at least four inches thick and shall slope to drain away from the well casing. The base shall extend at least two feet laterally in all directions from the outside of the well boring, unless otherwise approved by the enforcement agency.

The base shall be free of cracks, voids, and other significant defects likely to prevent water tightness. Contacts between the base and the annular seal and the base and the well casing must be watertight and must not cause the failure of the well casing or annular seal.

Where cement-based annular sealing material is used, the concrete base shall be poured before the annular seal has set, unless otherwise approved by the enforcement agency.

e.

Vaults. At the approval of the enforcement agency, the top of the well casing may be below ground surface because of traffic or other critical considerations. A structurally sound watertight vault, or equivalent feature, shall be installed to house the top of a monitoring well that is below ground surface. The vault shall extend from the top of the annular seal to at least ground surface. In no case shall the top of the annular seal be more than four feet below ground surface.

The casing shall extend at least six inches above the top of the annular seal.

The vault shall contact the annular seal in a manner to form a watertight and structurally sound connection. Contacts between the vault and the annular seal and the vault and the well casing, if any, shall not fail or cause the failure of the well casing or annular seal.

The vault shall be set into or contact the annular seal material before it sets, unless otherwise approved by the enforcement agency.

Cement-based sealing material shall be placed between the outer walls of the vault and the excavation into which it is placed to form a proper, structurally sound foundation for the vault and to seal the space between the vault and excavation.

Sealing material surrounding a vault shall extend from the top of the annular seal to the ground surface. If cement-based sealing material is used for both the annular seal and the space between the excavation and vault, the sealing material shall be placed between the vault and excavation and contact the cement-based annular seal before the annular seal has set.

The vault cover or lid shall be watertight. Any vents shall meet the specifications contained in section 98-55(b)(3)a, which pertains to openings, of the water well standards. The lid shall be fitted with a security device to prevent unauthorized access. The lid shall be clearly and permanently marked "monitoring well." The vault and its lid shall be strong enough to support vehicular traffic where such traffic might occur.

The top of the vault shall be set at or above grade so drainage is away from the vault. The top of the well casing contained within the vault shall be covered in accordance with requirements under subsection (b)(3)a of this section, which pertains to locking cover, and subsection (b)(3)b of this section, which pertains to casing cap, so that water, contaminants, or pollutants that may enter the vault will not enter the well casing.

f.

Protection from vehicles. Protective steel posts, or the equivalent, shall be installed around a monitoring well casing where it is terminated above ground surface in areas of vehicular traffic. The posts shall be easily seen and shall protect the well from vehicular impact.

(4)

Filter pack. Monitoring well filter pack material shall consist of nonreactive, smooth, rounded, spherical, granular material of highly uniform size and known composition. Filter pack material shall not degrade or consolidate after placement. The grain size of the filter pack shall be matched to the grain size of the aquifer, so that aquifer materials do not enter the filter pack, and the slot size of the screen shall then be matched to the grain size of the filter pack so the filter pack materials do not enter the well.

Filter pack material shall be obtained from clean sources. Filter pack material should be washed and properly packaged for handling, delivery, and storage, if used in monitoring wells constructed for sensitive water quality determinations.

Care should be exercised in the storage of filter pack materials at a drilling site to ensure the material does not come into contact with pollutants or contaminants. Care should also be exercised to prevent the introduction of foreign substances, such as clay or vegetative matter, that might interfere with the placement and function of the filter pack.

Filter pack material shall be placed in the well boring by use of a tremie pipe or equivalent. The depth of the top of the filter pack shall be carefully checked and the volume of emplaced filter pack material verified to determine that filter pack materials have not bridged during installation.

(5)

Casing. For the purpose of these standards, the term "casing" applies to screens, collars, risers, and blank casing, and other specialized products used to maintain the well bore. Additional standards for casing materials are contained in section 98-55(b)(5), which pertains to casing, of the water well standards. Special considerations that apply to monitoring well casing are described as follows:

a.

Casing material. Casing material shall be in accordance with the following:

1.

Chemical compatibility. Special consideration shall be given to the selection of casing materials for monitoring wells installed in environments that are chemically hostile. The selected casing shall resist chemical attack and corrosion.

Special consideration should be given to the selection of casing materials for wells to be used for sensitive water-quality determinations.

2.

Plastic and steel casing. Standards for thermoplastic well casing are in section 98-55(b)(5), which pertains to casing, of the water well standards. Fluorocarbon casing materials include fluorinated ethylene propylene (FEP) and polytetra- fluoroethylene (PTFE). Fluorocarbon casing materials shall meet the following specifications, including the latest revisions thereof:

i.

ASTM D3296, Standard Specification for FEP-Fluorocarbon Tube.

ii.

ASTM D3295, Standard Specifications for PTFE Tubing.

Stainless steel casing shall meet the provisions of ASTM A312, Standard Specification for Seamless and Welded Austenitic Stainless Pipe, and shall meet general requirements for tubular steel products in section 98-55(b)(5), which pertains to casing, of the water well standards.

b.

Multiple screens. Monitoring well casing strings shall not have openings in multiple water-bearing units (multilevel monitoring wells), if poor-quality water, pollutants, or contaminants in units penetrated by the well could pass through the openings and move to other units penetrated by the well and degrade groundwater quality, unless otherwise approved by the enforcement agency.

c.

Bottom plugs. The bottom of a monitoring well casing shall be plugged or capped to prevent sediment or rock from entering the well.

d.

Casing installation. Discussion and standards for the installation of casing materials are in section 98-55(b)(5), which pertains to casing, of the water well standards. Special considerations for monitoring wells are:

1.

Cleanliness. Casing, couplings, centralizers, and other components of well casing shall be clean and free of pollutants and contaminants at the time of installation.

2.

Joining plastic casing. Plastic casing shall be joined (threaded or otherwise coupled) in a manner that ensures its water tightness. Organic solvent welding cements or glues should not be used for joining plastic casing if glues or cement compounds could interfere with water-quality determinations.

3.

Impact. Casing shall not be subjected to significant impact during installation that may damage or weaken the casing.

(6)

Well development. Monitoring well development, redevelopment, and reconditioning shall be performed with care so as to prevent damage to the well and any strata surrounding the well that serve to restrict the movement of poor-quality water, pollutants, and contaminants. Development, redevelopment, and reconditioning operations shall be performed with special care where a well has been constructed in an area of known or suspected pollution or contamination.

Water, sediment, and other waste removed from a monitoring well for development operations shall be disposed of in accordance with applicable federal, state, and local requirements. The enforcement agency should be contacted concerning the proper disposal of waste from development operations.

Development methods that may be acceptable under certain circumstances include mechanical surging, overpumping and pump surging, air development, water jetting, and chemical development. The following standards shall be followed where applicable:

a.

Mechanical surging. Plungers, bailers, surge blocks, and other surging devices shall incorporate safety valves or vents to prevent excessive pressure differentials that could damage casing or screen.

b.

Water jetting. Water used in jetting operations shall be free of pollutants and contaminants.

c.

Chemical development. Extreme care shall be exercised in the use of chemicals for monitoring well development. It is often unacceptable to use chemicals for developing monitoring wells to be used for water-quality determinations. Chemicals introduced for development shall be completely removed from the well, filter pack, and water-bearing strata accessed by the well immediately after development operations are completed.

The various methods described in this subsection are sometimes used in combination.

(7)

Rehabilitation and repair of monitoring wells. For the purpose of these standards, the term "well rehabilitation" includes the treatment of a well to recover loss in yield caused by incrustation or clogging of the screen, filter pack, and/or water-bearing strata adjoining the well. Well rehabilitation methods that may, in certain cases, be acceptable for monitoring wells include mechanical surging, backwashing or surging by alternately starting or stopping a pump, surging with air, water jetting, sonic cleaning, chemical treatment, or combinations of these.

Rehabilitation methods shall be performed with care to prevent damage to the well and any barriers that serve to restrict the movement of poor-quality water, pollutants, or contaminants. Chemicals used for rehabilitation shall be completely removed from the well, filter pack, and water-bearing strata accessed by the well immediately after rehabilitation operations are completed. Chemicals, water, and other waste shall be disposed of in accordance with applicable federal, state, and local requirements. The enforcement agency should be contacted regarding the proper disposal of waste from rehabilitation operations.

Rehabilitation methods should be compatible with the use of the monitoring well. Special care should be given to the selection of rehabilitation methods for water-quality monitoring wells.

Materials used for repairing well casing shall meet the requirements of section 98-55(b)(5), which pertains to casing, of the water well standards.

(8)

Temporary cover. The well or borehole opening and any associated excavations shall be covered at the surface to ensure public safety and to prevent the entry of foreign material, water, contaminants, and pollutants whenever work is interrupted by such events as overnight shutdown, poor weather, and required waiting periods to allow setting of sealing materials and the performance of tests. The cover shall be held in place or weighted down in such a manner that it cannot be removed except by equipment or tools.

During prolonged interruptions (i.e., one week or more), a semipermanent cover shall be installed. For wells cased with steel, a steel cover, tack-welded to the top of the casing, is adequate.

(c)

Destruction of monitoring wells. Procedures for the destruction of monitoring wells are as follows:

(1)

General requirements. All permanently inactive or abandoned monitoring wells and exploration holes subject to these requirements shall be properly destroyed.

(2)

Requirements for destroying monitoring wells and exploration holes. General requirements for destroying monitoring wells and exploration holes are contained in section 98-55(c), which pertains to destruction of wells, of the water well standards. Special considerations for monitoring wells and exploration holes are as follows.

a.

Monitoring wells. Monitoring wells shall be destroyed in accordance with the following requirements and section 98-55(c), which pertains to destruction of wells, of the water well standards, irrespective of their original date of construction:

1.

The monitoring well casing, and any other significant voids within the well, shall, at a minimum, be completely filled, under pressure, with sealing material, if the following conditions exist:

i.

The monitoring well is located in an area of known or potential pollution or contamination; and

ii.

The well was constructed and maintained in accordance with these standards.

Casing left in place may require perforation or puncturing to allow proper placement of sealing materials.

2.

A monitoring well shall be destroyed by removing all material within the original borehole, including the well casing, filter pack, and annular seal, and the created hole completely filled with appropriate sealing material, if the following conditions exist:

i.

The well is located in an area of known or potential pollution or contamination; and

ii.

The well's annular seal, casing, screen, filter pack, or other components were not constructed or maintained according to these standards.

3.

Monitoring wells shall, at a minimum, be destroyed in accordance with the requirements of section 98-55(c), which pertains to destruction of wells, of the water well standards, if located in an area free of any known or potential contamination or pollution.

b.

Exploratory borings. Exploratory borings shall be completely filled with appropriate sealing material from bottom to top.

The boring shall be inspected immediately prior to filling and sealing operations. All obstructions and pollutants and contaminants that could interfere with filling and sealing operations shall be removed prior to filling and sealing. The enforcement agency shall be notified as soon as possible if pollutants or contaminants are known or suspected to be in a boring to be destroyed. Well destruction operations may then proceed only at the approval of the enforcement agency. The enforcement agency should be contacted to determine requirements for proper disposal of removed materials.

c.

Placement of material. The placement of sealing material for monitoring wells and exploratory borings is generally described in section 98-55(c), which pertains to destruction of wells, of the water well standards. The following additional requirements shall be observed when placing sealing material for monitoring well or exploratory boring destruction:

1.

Placement method. The well or exploratory boring shall be filled with appropriate sealing material using a tremie pipe or equivalent, proceeding upward from the bottom of the well or boring.

Sealing material shall be placed by methods, such as the use of a tremie pipe or equivalent, that prevent freefall, bridging, and dilution of sealing materials, and/or prevent separation of aggregate from sealants. Sealing material may be placed by freefall only where the interval to be sealed is dry and no more than 30 feet in depth.

2.

Timing of placement. Sealing material shall be placed in one continuous operation, or "pour," from the bottom to the top of the well or boring, unless conditions in the well or boring dictate that sealing operations be conducted in a staged manner, and prior approval is obtained from the enforcement agency.

3.

Groundwater flow. Special care shall be used to restrict the flow of groundwater into a well or boring while placing sealing material, if subsurface pressure producing the flow is significant.

4.

Sealing pressure. Pressure required for the placement of cement-based sealing materials shall be maintained long enough for cement-based sealing materials to properly set.

5.

Verification. It shall be verified that the volume of sealing material placed during destruction operations equals or exceeds the volume to be sealed.

d.

Sealing materials. Materials used for sealing exploratory borings and monitoring wells shall have low permeabilities so that the volume of water and possible pollutants and contaminants passing through them will be of minimal consequence. Sealing material shall be compatible with the chemical environment into which it is placed and shall have mechanical properties consistent with present and future site uses.

Suitable sealing materials include neat cement and sand cement, as described in section 98-55(b)(2), which pertains to sealing the upper annular space, of the water well standards. Drilling mud or drill cuttings are not acceptable as any part of sealing material for well destruction. Concrete may be used as a sealing material at the approval of the enforcement agency.

e.

Additional requirements for monitoring wells and exploratory borings in urban areas. The following additional requirements shall be met for destroying monitoring wells and exploratory borings in urban areas, unless otherwise approved by the enforcement agency:

1.

The upper surface of the sealing material shall end at a depth of five feet below ground surface; and

2.

If the well casing was not extracted during destruction and sealing operations, a hole shall be excavated around the well casing to a depth of five feet below ground surface after sealing operations have been completed and the sealing material has adequately set and cured. The exposed well casing shall then be removed by cutting the casing at the bottom of the excavation. The excavation shall be backfilled with clean, native soil or other suitable material.

f.

Temporary cover. The well or borehole opening and any associated excavations shall be covered at the surface to ensure public safety and to prevent the entry of foreign material, water, pollutants, and contaminants whenever work is interrupted by such events as overnight shutdown, poor weather, and required waiting periods to allow setting of sealing materials and the performance of tests. The cover shall be held in place or weighted down in such a manner that it cannot be removed, except by equipment or tools.

During prolonged interruptions (i.e., one week or more), a semipermanent cover shall be installed. For wells cased with steel, a steel cover, tack-welded to the top of the casing, is adequate.

(d)

Recovery well pumps. All permanent recovery well pumps shall be constructed and installed so as to provide protection against contamination and pollution of the aquifers. Applicable provisions of section 98-55(d), which pertains to pump standards, of the water well standards, shall be followed.

(Ord. No. 97-01, § 2(6.28.050), 1-2-1997; Ord. No. 97-13, § 2, 3-26-1997; Ord. No. 97-17, § 2, 9-24-1997)