2.6 Wells & Groundwater Systems: Construction, Pumps, Testing and Sanitary Protection (ADEM 335-7-5)

2.6 Wells & Groundwater Systems: Construction, Pumps, Testing and Sanitary Protection (ADEM 335-7-5)

The WPI Water Distribution Class I outline includes "maintain well and related equipment" and "maintain the sanitary condition of the well," and every WPI Water Treatment outline includes measuring static and pumping water levels and inspecting groundwater sources for contamination, flooding and wellhead protection. In Alabama these tasks sit under ADEM's groundwater rules, ADEM Admin. Code Chapter 335-7-5.

Well Components

Well Pumps

• Submersible pumps place the motor below the pump bowls in the well. The motor relies on water flowing past it for cooling, so a shroud is needed if the motor sits below the screen. Submersible motors are sensitive to frequent starts and voltage imbalance.
• Vertical turbine (lineshaft) pumps have the motor at the surface turning a long shaft. Lineshafts are water-lubricated or oil-lubricated; oil must be food-grade and leaks contaminate the well.
• The pump intake must stay submerged below the lowest expected pumping level, with margin for seasonal decline, to prevent air entrainment, cavitation and motor overheating.

ADEM Construction Rules (Rules 335-7-5-.03 to .05)

• Site. The top of the casing must be above the 100-year flood plain and not subject to contamination or sinkhole subsidence, a real concern in Alabama's karst limestone areas.
• Casing. Community and NTNC wells need unused steel casing meeting AWWA standards, with at least a 2-inch annular space around the casing. The casing's inside diameter should be at least 2 inches larger than the pump bowls, and the pump suction may not be placed in or below the screens.
• Above grade. The casing must be centered and project at least 12 inches above the finished concrete slab, and the slab must be at least 3 feet by 3 feet.
• Grouting. Community and NTNC well casings must be pressure cement grouted from the bottom up, continuously, until grout overflows at the surface, with at least 2 inches of grout around the casing. Non-community wells may use the tremie method with a 3-inch annular space, and wells deeper than 100 feet need at least 100 feet of grout seal.
• Non-community wells may use NSF-approved PVC well casing (ASTM F480).

Testing a New Well (Rules 335-7-5-.07 to .11 and .15)

• Aquifer test of a finished community production well determines storage coefficient and transmissivity, with drawdown readings every 2 minutes in the first hour and progressively less often afterward.
• Development removes sand, cuttings and drilling fluid; the permanent pump may not be used for development.
• Capacity test (community wells): pump at design capacity until the water level stabilizes within plus or minus 1.0 foot, continue for 24 hours, then pump at 150 percent of design capacity for 6 hours, then shut off and record recovery to the pre-test level. NTNC wells must hold a stable level at design capacity for at least 12 hours. The level may not be drawn down to the top of the uppermost water-bearing formation used.
• Water quality: at least three chlorine-free bacteriological samples during the capacity test and at least two more after the permanent pump is installed and disinfected, plus full primary and secondary chemical analyses before final inspection. Sand content after start-up may not exceed 1 part per million.
• Provisions must be made for periodic measurement of static and pumping water levels.

Measuring Water Level with an Air Line

An air line is a small tube of known length strapped to the drop pipe. Air is pumped in until the gauge reading stops rising; the gauge then reads the pressure of the water column above the bottom of the line.

$$\text{Depth to water (ft)} = \text{Air-line length (ft)} - (\text{Gauge psi} \times 2.31)$$

Example. A 120-foot air line reads 26 psi while the pump runs. The submerged length is $26 \times 2.31 = 60.1$ feet, so the pumping water level is $120 - 60.1 = 59.9$ feet below the reference point. If the static level was 41.0 feet, drawdown is 18.9 feet (Section 2.1 shows how to turn this into specific capacity).

Disinfection and the Ground Water Rule

• New, repaired or reconditioned wells and pumps are disinfected (AWWA C654 describes the procedures), pumped to waste and sampled before use.
• Rule 335-7-5-.17 requires a chlorine CT of at least 60 for groundwater sources with contamination risk when average turbidity is below 5 NTU, and a daily distribution residual of at least 0.2 mg/L free chlorine.
• Under the federal Ground Water Rule (adopted in Rule 335-7-5-.22), a total coliform-positive routine distribution sample triggers source sampling of each well in use within 24 hours for a fecal indicator such as E. coli. A positive source sample leads to additional sampling or corrective action, which can include fixing sanitary defects, eliminating the source of contamination, using another source, or providing 4-log treatment of viruses.

Protecting and Rehabilitating Wells

Inspect regularly for cracked slabs, missing caps, unscreened vents, standing water, flooding and nearby contamination sources inside the wellhead protection area. Watch these trends:

• Falling specific capacity or rising drawdown at the same pumping rate: screen encrustation, iron bacteria or sand plugging.
• Sand in the water: screen or gravel-pack failure, or pumping too hard.
• Rising motor amperage or vibration: pump wear or sand damage.

Rehabilitation may use acid, chlorine and surging. ADEM must be notified 14 days before reconditioning a well by blasting or chemical additives (Rule 335-7-5-.06), and water must be shown free of the additives before use. Abandoned wells must be filled and sealed, with neat cement in the top 20 feet (Rule 335-7-5-.14).