3.2 Groundwater, Wells & Source Water Protection

3.2 Groundwater, Wells & Source Water Protection

Groundwater Hydrology and Well Hydraulics

Groundwater is water stored in subsurface pore spaces and rock fractures beneath the water table. To operate a well station correctly, operators must master hydraulic terminology and well diagnostics.

Pumping Well Hydraulic Profile

           Measuring Point (Top of Casing)
                  │
──────────────────┼───────────────────────── Ground Surface
                  ▼
            ═════════════  ◄─── Static Water Level (SWL) (Well idle)
           │             │
           │  Drawdown   │   Cone of Depression
           │  (PWL - SWL)│ ╲                      ╱
           │             │  ╲                    ╱
            ═════════════    ◄── Pumping Water Level (PWL) (Pumping at Q gpm)
           │             │    ╲                ╱
           │             │     ╲              ╱   Radius of Influence (R)
           │             │      ╲            ╱  ◄─────────────────────────►
           │    Well     │       ╲          ╱
           │   Casing    │        ╲        ╱
           │             │         ╲      ╱
           ├─────────────┤          ▼    ▼
           │ Well Screen │ ░░░░░░ Gravel Pack ░░░░░░
           └─────────────┘

Aquifer Types: Unconfined vs Confined

• Unconfined (Water Table) Aquifer: The upper boundary of saturation is the water table, which rises and falls at atmospheric pressure. Recharged directly by overhead rainfall. Specific yield ($S_y$) ranges from 0.05 to 0.30, meaning significant water drains by gravity from pore spaces as the water level drops.
• Confined (Artesian) Aquifer: Sandwiched between upper and lower impermeable confining aquitards (such as dense clay layers). Water is confined under hydrostatic pressure. The level to which water rises in a tightly cased well defines the potentiometric (piezometric) surface. If the potentiometric surface lies above the ground surface, water flows freely without a pump (flowing artesian well). The storage coefficient ($S$) of a confined aquifer is very small ($10^{-5}$ to $10^{-3}$), meaning pressure drops propagate rapidly over great distances when pumping begins.

Essential Well Hydraulics Terminology & Formulas

1. Static Water Level (SWL): The vertical distance (in feet) from a standardized measuring point (usually top of well casing) down to the water surface when the well is shut down and fully recovered.
2. Pumping Water Level (PWL): The vertical distance (in feet) from the measuring point down to the water surface while the well is actively pumping at a stabilized, constant discharge rate ($Q$).
3. Drawdown ($DD$): The net distance the water level drops during pumping: $\text{Drawdown (ft)} = \text{Pumping Water Level (ft)} - \text{Static Water Level (ft)}$
4. Cone of Depression: The three-dimensional inverted conical depression formed in the water table or potentiometric surface centered around an active pumping well.
5. Radius of Influence ($R$): The horizontal radial distance from the well casing outward to the boundary where drawdown becomes zero.
6. Well Yield ($Q$): The stabilized discharge flow rate sustained by the well pump, expressed in gallons per minute (gpm) or million gallons per day (MGD).
7. Specific Capacity ($SC$): The single most vital metric of operational well performance, defined as the well yield per unit of drawdown: $\text{Specific Capacity (gpm/ft)} = \frac{\text{Well Yield (gpm)}}{\text{Drawdown (ft)}}$
8. Well Interference: When the cones of depression of two or more adjacent pumping wells overlap, additive drawdown occurs. Both wells experience deeper pumping levels, diminished specific capacity, and increased energy consumption.

Diagnostic Application of Specific Capacity

Specific capacity normalizes well yield against hydraulic stress. Operators track specific capacity monthly at identical pumping rates:

$\text{Baseline: } Q = 600\text{ gpm}, \text{ SWL} = 30\text{ ft}, \text{ PWL} = 60\text{ ft} \implies DD = 30\text{ ft} \implies SC = \frac{600}{30} = 20.0\text{ gpm/ft}$

If testing one year later reveals that at 600 gpm the PWL has dropped to 75 ft with the same SWL of 30 ft ($DD = 45\text{ ft}$), specific capacity has plummeted:

$SC_{\text{current}} = \frac{600}{45} = 13.3\text{ gpm/ft} \quad \left(\frac{20.0 - 13.3}{20.0} \times 100\% = 33.5\% \text{ decline}\right)$

A decline in specific capacity exceeding 10% to 15% is an urgent call for well rehabilitation. Common causes include:

• Screen Encrustation: Precipitation of calcium carbonate ($\text{CaCO}_3$) scale or iron/manganese oxides across screen openings.
• Biofouling: Proliferation of iron-oxidizing bacteria (Gallionella ferruginea, Leptothrix, Sphaerotilus) that produce thick, gelatinous ferric hydroxide slime sheaths clogging the screen and gravel pack.
• Fine Sand Packing: Migration of formation fines and silt into the artificial gravel pack due to over-pumping.

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Sanitary Well Construction Standards (N.J.A.C. 7:9D)

Under New Jersey Administrative Code N.J.A.C. 7:9D (Well Construction and Maintenance; Sealing of Abandoned Wells) and the Recommended Standards for Water Works (10-States Standards), public community water supply wells must incorporate strict sanitary construction safeguards to protect deep aquifers from surface pollution:

Sanitary Wellhead & Casing Assembly
┌────────────────────────────────────────────────────────┐
│ [Downward Casing Vent] ── Fitted with 24-mesh screen   │
│ [Sanitary Well Seal]   ── Gasketed compression flange  │
│ [Casing Extension]    ── ≥12–18 in above grade/flood   │
│ [Raw Water Tap]       ── Smooth-nosed, unthreaded      │
│ [Check Valve]         ── Upstream of all treatment     │
├────────────────────────────────────────────────────────┤
│ [Annular Grout Seal]  ── Pressure-pumped tremie pipe   │
│                          Neat cement or bentonite      │
│                          Min depth: 20 to 50+ feet     │
│ [Well Casing]         ── Watertight steel or PVC       │
├────────────────────────────────────────────────────────┤
│ [Artificial Gravel Pack] Graded clean silica sand      │
│ [Well Screen]         ── Continuous-slot stainless wire│
└────────────────────────────────────────────────────────┘

1. Well Casing: Watertight steel pipe (or heavy-duty thermoplastic) extending from the intake screen up to at least 12 to 18 inches above finished floor/grade and at least 1 to 2 feet above the 100-year flood plain elevation.
2. Annular Grout Seal: The annular void between the drilled borehole and the outer well casing must be filled with impermeable neat cement grout (Class A cement mixed with 5 to 6 gallons of water per 94-lb sack) or high-solids bentonite slurry. Grout must be pumped under positive pressure from the bottom upward using a tremie pipe to ensure no voids or bridging occur. N.J.A.C. 7:9D mandates a minimum continuous grouting depth of 20 to 50+ feet (or fully seated into the first competent confining aquitard/bedrock) to prevent surface stormwater runoff, agricultural chemicals, and septic plumes from channeling down the outside of the casing into the aquifer.
3. Well Screen: Precision continuous-slot, wire-wrapped stainless steel screen (e.g., Johnson screen) sized based on sieve analysis of aquifer formation samples. Screen slot openings must retain 90% of the artificial gravel pack, maintaining entrance velocities below 0.1 ft/s (0.03 m/s) to prevent turbulent headloss and sand migration.
4. Artificial Gravel Pack: Graded, clean, rounded silica gravel placed in the annular space between the screen and borehole wall to stabilize the formation, prevent sand pumping, and maximize radial flow entry.
5. Sanitary Well Seal: A vermin-proof, elastomeric-gasketed compression seal or welded steel flange sealing the top of the casing around the pump discharge column pipe, power cables, and airline.
6. Sanitary Casing Vent: An inverted "U" or gooseneck pipe terminating downward at least 18 inches above finished floor or grade. The vent must be equipped with a non-corrodible, fine-mesh 24-mesh stainless steel, brass, or copper screen. This allows air to enter during drawdown and escape during recovery while preventing insects, spiders, rodents, and windblown contaminants from falling down the well.
7. Raw Water Sample Tap: A dedicated, smooth-nosed, unthreaded sample tap pointed downward, located on the pump discharge piping upstream of any chemical injection points, filters, or check valves.
8. Discharge Piping Hardware: Must include a check valve (preventing water hammer and backspin of pump impellers), an air/vacuum relief valve, a calibrated water flow meter, and a totalizing recorder.

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Practical Operational Scenarios & Exam Traps

[!WARNING] Exam Trap: Confusing Pumping Water Level with Drawdown A common exam question gives: Static Water Level = 45 ft; Pumping Water Level = 105 ft; Discharge Flow = 900 gpm. It asks for specific capacity. A trap answer divides $900 \div 105 = 8.57\text{ gpm/ft}$. The operator must first calculate drawdown: $\text{Drawdown} = 105 - 45 = 60\text{ ft}$. The correct specific capacity is $900 \div 60 = 15.0\text{ gpm/ft}$.

[!CAUTION] Exam Trap: Sanitary Well Vent Screen Size Questions frequently ask for the required mesh size of a sanitary well vent screen. Options often list 10-mesh, 16-mesh (standard residential window screen), 24-mesh, and 100-mesh. The regulatory standard under N.J.A.C. 7:9D and 10-States Standards is strictly 24-mesh non-corrodible screen.

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Wellhead Protection & Source Water Protection Programs

Treatment is the last line of defense; source protection is the first. WPI's Source Water Characteristics content area (14 of 100 questions on the Water Treatment Class IV exam) is built almost entirely around inspecting sources and following protection plans, and New Jersey has one of the most developed programs in the country.

New Jersey Well Head Protection Areas (WHPAs)

NJDEP delineates a Well Head Protection Area around every public community and public nontransient noncommunity well. The WHPA is the land surface area that contributes ground water to the well, delineated by time of travel in three tiers:

Operators use WHPA maps to inventory potential contaminant sources inside the capture zone: underground storage tanks, dry cleaners, septic systems, agricultural chemical storage, road salt piles, junkyards, and known contaminated sites. A new potential source appearing inside Tier 1 is a source-protection event, not merely a land use event.

Physical Wellhead Inspection

Every routine well visit should verify the physical barriers that keep surface contamination out of the aquifer:

• Casing extension: at least 12 inches above finished grade and above the 100-year flood elevation, with the surrounding grade sloped away from the casing.
• Sanitary well seal: a watertight, vermin-proof cap or pitless adapter. A cracked or loose seal is the single most common route for surface bacteria into a well.
• Annular grout seal: continuous cement grout in the annular space to prevent short-circuiting of surface water down the outside of the casing.
• Vent: screened, downturned, and above flood elevation.
• Sample tap: a smooth-nosed, non-threaded raw-water tap ahead of any treatment, for source sampling.
• Site condition: no ponding, no fuel or chemical storage within the immediate zone, secure fencing or a locked wellhouse, and no cross connections.

Surface Water Source Inspection

For reservoirs and intakes, the corresponding routine inspection looks for conditions that change raw water quality: algal blooms and cyanobacteria mats, invasive species such as zebra and quagga mussels colonizing intake screens, non-native aquatic plants, shoreline erosion and sedimentation, waterfowl concentrations, and unauthorized recreational access. Reservoir inspection, cleaning, and maintenance are explicit WPI job tasks, as is managing stored water release based on forecasted demand.

Source Water Protection Plans and Public Education

• A Source Water Assessment identifies the sources, inventories potential contaminants, and rates susceptibility. New Jersey completed assessments for every public water system and makes them available to purveyors.
• A Source Water Protection Plan or watershed management plan converts that assessment into action: land acquisition, conservation easements, ordinance support, best management practices for agriculture and stormwater, spill response coordination with local emergency services, and monitoring.
• Operators are expected to educate the community on source water protection and conservation — household hazardous waste days, proper pharmaceutical disposal, septic maintenance, fertilizer and de-icing practices, and reporting of illicit discharges.

Exam Trap Alert: WHPA tiers are defined by time of travel, not by fixed radius. A high-yield well in a transmissive aquifer can have a Tier 1 area extending thousands of feet, while a low-yield well in tight material may have a small one. Any answer that gives a WHPA as a fixed number of feet is wrong.