Additional WQARF Information
 

Preventing Vertical Cross Contamination

What is Vertical Cross Contamination?

Vertical cross-contamination between aquifers through conduit wells can be conceptualized by two modes of occurrence; well-casing flow and annular flow.

Well-casing flow can be illustrated by contaminated groundwater flowing into a well that is constructed with perforations in upper and lower hydrogeologic units (upper and lower aquifers).  If vertical movement exists within the well casing, contaminated groundwater can enter the well through inflow zones and exit through outflow zones (Example of Casing Flow).   Zones of inflow (groundwater enters the well through perforations or openings within the casings during non-pumping conditions) and outflow (groundwater exits the well during non-pumping conditions) can be determined by combinations of flow meter, tracer, and other geophysical tests during well inspections.

Annular flow can be illustrated b vertical movement of groundwater between the borehole and the well casing (Example of Annular Flow).    Modern wells are generally drilled and constructed properly, as they are sealed over appropriate depth intervals with a grout material that is inert with the contamination at the site.  Wells that have properly sealed annuli and have comparatively short-screened intervals do not provide a pathway for vertical cross-contamination.

Additionally, vertical cross-contamination may occur when contaminated water from a perched aquifer enters the well through openings within the casing and cascades through the well (Video of cascading 4.2 MB) or enters and descends through the annulus. (Example of Cascading Water  in aquifer).

Notice of Intent

A.R.S. § 45-605(E) requires that ADWR develop a review process of all “notices and applications regarding new or replacement wells to identify whether a well will be located where existing or anticipated groundwater contamination presents a risk of vertical cross-contamination by the well.”  The ADWR WQARF Support Unit currently reviews about 900 to 1,000 NOIs annually to drill, replace, or abandon wells within close proximity to existing or anticipated groundwater contamination.  The review requires the detailed analysis of available water quality and hydrogeologic data to ensure the wells are constructed in a manner to prevent vertical cross-contamination within an aquifer.  Modifications are often required that may involve changing or reducing well perforation intervals, or sealing annular spaces with impervious materials to prevent vertical migration of contaminated water.

ADWR rule A.A.C. R12-15-812(B) describes special aquifer conditions, specifically for mineralized or polluted water.  The rule states, “In all water-bearing geologic units containing mineralized or polluted water as indicated by available data, the borehole shall be cased and grouted so that contamination of the overlying or underlying groundwater zones will not occur.”  Although the rule states the objective, it does not specify the methods or materials for either the well drilling or abandonment.  ADWR issued a Substantive Policy Statement, Well Abandonment Handbook  (0.2 MB), dated September 20, 2001, which addresses a broad range of abandonment alternatives including options for areas of groundwater quality contamination.  The Handbook covers the design, procedures, and materials used to properly abandon a well to prevent vertical cross-contamination between an aquifer or aquifer layer and ensure the seal integrity.  However, site-specific guidance on aquifer boundaries and known areas of groundwater contamination is not given.  One of the main objectives of the ADWR WQARF Support Unit review process is to determine site-specific information in order to establish a proper well construction or abandonment design to prevent vertical cross-contamination within an aquifer.  Such site-specific information includes contaminants of concern, the hydrogeology, depth to water, hydraulic gradient, location of the well relative to the plume boundary, and proposed well construction/abandonment design.

Special Well Construction Requirements (see document)   (0.1 MB)

The ADWR has developed Special Well Drilling Requirements to provide general guidance to drillers and well owners in constructing wells to protect groundwater in areas of known or anticipated groundwater contamination that are located in, or within close proximity to state Water Quality Assurance Revolving Fund (WQARF), Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA), and Department of Defense (DOD) sites. Additionally, these general guidelines should be followed in any area of known groundwater contamination such as Resource Conservation and Recovery Act (RCRA) or Leaky Underground Storage Tank (LUST) sites.

Site-Specific Well Construction and Abandonment Procedures

The ADWR WQARF Support Unit reviews all applications to drill, deepen, modify, or abandon wells located in an area of known or anticipated groundwater contamination to insure the wells are designed or abandoned in a manner to prevent future vertical-cross contamination.  The ADWR WQARF Support Unit also provides guidance to well owners and drillers in constructing wells or performing abandonments by defining site specific well construction and abandonment procedures, which will assist with and expedite the NOI review process.

Eventually all areas with known or anticipated groundwater contamination will have procedures written that describe the local geology, hydrology, contaminants of concern, site-specific well design, construction, and abandonment methods, grout materials, and depth-specific seals.  Specific geographic areas will be defined for which special well-construction and abandonment procedures will apply.  The well design, drilling procedures, and construction materials used during the drilling or abandonment of a well must prevent vertical cross-contamination between an aquifer or aquifer layers.  These site-specific procedures apply to all well types within the defined WQARF area, in addition to the ADWR Statutes and Rules Governing Minimum Well Construction Standards (A.A.C. R12-15-80l through R12-l5-822).

Currently, site-specific well construction and abandonment procedures have been developed for the following WQARF sites:

• Pinal Creek WQARF site Special Well Construction Procedures
   
• <YMCAS Well Construction and Abandonment Procedures>  (0.7 MB)
   

Verifying and Improving Databases

Well Verification and Database Improvement Program

As recognized by the Ground Water Cleanup Task Force, a Well Verification and Database Improvement program is a necessary first step in the overall WQARF corrective action program, including the well inspection process.  The Well Verification and Database Improvement program requires comprehensive well inventories to be conducted for WQARF sites and other areas of water quality concern.

Well Inventories

Well inventories require extensive well information database searches, matching of duplicate database records, and field verification and GPS surveying of well locations.  Well inventories are also essential in providing accurate well identification, well location and well construction data to help facilitate ADEQ’s ongoing upload of water quality data into its Water Quality database.  At least five major databases exist in the state of Arizona that contain information on wells:

“Old” Arizona State Land Department Database (WELLS-35):
The first statewide registration of wells began in 1945, when all irrigation wells that pumped greater than 100 gallons per minute in Critical Groundwater Areas had to be registered with the Arizona State Land Department (ASLD).  This database is referred to as the WELLS-35 database because the ASLD began attaching 35-prefix numbers to wells sometime during the 1970’s and continued until the establishment of the Department of Water Resources in 1980.

ADWR Ground Water Site Inventory Database (GWSI):
This database was acquired from the United States Geological Survey (USGS) in 1983 to record groundwater levels and some groundwater quality data from designated “index” wells across the state.

 ADWR Well Registry Database (WELLS-55):
The Department’s database of registered wells in the state of Arizona.  All wells drilled before the Department's creation in 1980 are required to be registered in the WELLS-55 database and are assigned a number with a 55-prefix.

 Arizona Department of Environmental Quality Database:
This database contains water quality and water level information, and other related data collected by the various ADEQ programs.

University of Arizona (U of A) Collection of Well Records:
During the 1980’s, ADWR obtained a collection of approximately 3,700 paper copy well records from the U of A that included wells that were drilled prior to the 1950’s (mostly from 1908 through 1940).  Data contained within these records included not only general well construction data but also driller’s logs, water levels, and even some particle size logs and aquifer test logs.   The ADWR WQARF Support Unit has converted these paper records into a newly available electronic format.

To date, the ADWR WQARF Support Unit has completed the following well inventories.  The table includes the number of wells that were located, the fiscal years in which the inventory was conducted and the area (in square miles) that was covered for each project.

Phoenix Area

Tucson Area

Other Areas

Current Well Inventory:  West Van Buren in southwest Phoenix.

It is important to mention that the data developed from of the well inventories have already proven to be extremely useful in providing accurate well identification, well construction, and well location data to ADEQ and other Government entities.  For an example of the database discrepancies on well location data that were found in the Estes Landfill WQARF site well inventory, (see example).

Identify Current Cross Contamination

Well Inspections

The ADWR WQARF Support Unit has developed a multi-phase process to identify wells that may be acting as pathways for vertical cross-contamination of hazardous substances between aquifers or aquifer layers.  WQARF sites vary in areal extent, with sites ranging from less than 1 square mile to more than 23 square miles in size.  Since database searches generally indicate over 1,000 wells per site, it is essential to focus the investigations on those wells that pose the greatest risk and which should be inspected.

The ADWR well inspection program has been developed based upon the guidance of the recommendations of the Ground Water Cleanup Task Force and also upon the practical experience gained in actual field studies.  The well inspection program involves a phased process that is designed to identify and inspect wells that may potentially serve as significant conduits for vertical cross-contamination.  If a significant problem is found, remedial actions that may include well modification or well abandonment may be recommended.

Phase I - Identify Potential Conduit Wells – Conduit Well Analysis

• Identify wells that may be acting as potential conduits for vertical cross-contamination and provide recommendations for future work.  Wells are eliminated from further consideration by evaluating well construction details in relation to defined aquifer boundaries, extent of contamination, and horizontal and vertical groundwater flow.  The ADWR WQARF Support Unit has completed the first phase of a conduit well analysis  at the Miracle Mile and Silverbell Landfill WQARF sites in Tucson, Arizona, which resulted in the identification of several potential conduit wells in the project area.
   
  • Miracle Mile/Silverbell Landfill Conduit Well Analysis (available for purchase)

Phase II - Well Inspection

• Determine actual vertical groundwater flow and contaminant transport conditions in suspect wells through field inspections and recommend appropriate actions to eliminate the wells from acting as conduits.

Phase III - Remedial Action

• Wells that have been identified as significant conduits will undergo abandonment, modification or incorporation into an ADEQ remedial action.

The phased approach to identifying and inspecting potential conduit wells is necessary because of the high cost of conducting well inspections (estimates based on approved contractor costs range from $30K to $50K to inspect a typical well).  Based on the high inspection costs and limited funds available, it is very important to prioritize the well inspections based on a thorough analysis of all available data.

It is important to point out that the well inspection program is a voluntary program, and any inspections and/or remedial actions depend upon obtaining the consent of the well owner.  If owner consent for well inspection is not obtained, the well will remain identified as a potential conduit.  Those wells classified as potential conduits will be referred to ADEQ for ultimate disposition.  A well identified early in the process as a significant conduit will be recommended to ADEQ for interim action, which could result in an expedited inspection and possible remedial action.

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