3.1 Source Water Quality & Watershed Management

Source Water Quality & Watershed Management

The Multi-Barrier Approach to Safe Drinking Water

In modern drinking water engineering and regulatory practice under the California State Water Resources Control Board (SWRCB) Division of Drinking Water (DDW), safeguarding public health relies on the multi-barrier approach. Rather than depending on a single treatment process to remove all hazards, the multi-barrier framework establishes consecutive, redundant layers of protection:

1. Source Water Protection & Watershed Management: Preventing contamination at the catchment basin, reservoir, or aquifer recharge zone.
2. Coagulation, Flocculation & Clarification: Destabilizing, aggregating, and settling colloidal particles, suspended matter, and microbial cysts.
3. Granular Media / Membrane Filtration: Physically removing remaining particulate matter, turbidity, and protozoan pathogens (Giardia lamblia and Cryptosporidium).
4. Primary & Secondary Disinfection: Inactivating surviving viruses, bacteria, and parasites using chemical oxidants or UV light, while maintaining a stable disinfectant residual.
5. Distribution System Integrity & Cross-Connection Control: Preventing post-treatment contamination in pipelines, storage reservoirs, and customer connections.

Source water protection represents the critical first barrier. High-quality raw water reduces chemical coagulant demand, minimizes the generation of regulated Disinfection Byproducts (DBPs), prevents membrane fouling, and lowers overall plant operating costs.

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Surface Water vs. Groundwater Quality Characteristics

Water utilities in California draw raw water from two primary hydrological sources: surface water (rivers, lakes, man-made reservoirs, the State Water Project, and the Colorado River Aqueduct) and groundwater (alluvial aquifers, confined artesian basins, and coastal groundwater basins). Each source exhibits distinct physical, chemical, and microbiological profiles.

                    [Surface Water Profile]
  Atmospheric Contact + Runoff ──► High Turbidity, NOM & Pathogens

                    [Groundwater Profile]
  Soil Percolation + Rock Contact ──► Low Turbidity, High Hardness & Fe/Mn

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Groundwater Under the Direct Influence of Surface Water (GWUDI)

Under both the federal Surface Water Treatment Rule (SWTR) and California Code of Regulations (CCR) Title 22, public water systems must distinguish between true groundwater and Groundwater Under the Direct Influence of Surface Water (GWUDI).

GWUDI Definition & Identification Criteria

GWUDI is defined as any water beneath the surface of the ground with:

1. Significant occurrence of insects or other macroorganisms, algae, or large-diameter pathogens such as Giardia lamblia or Cryptosporidium, or
2. Significant and relatively rapid shifts in water characteristics such as turbidity, temperature, conductivity, or pH that closely correlate with climatological or surface water conditions.

A well is evaluated for GWUDI status if it has shallow perforations (<50 feet), is located within 200 feet of a perennial surface water body, lacks a continuous sanitary surface seal, or exhibits coliform hits following rainstorms.

Microscopic Particulate Analysis (MPA)

When a well is suspected of being GWUDI, regulatory agencies mandate a Microscopic Particulate Analysis (MPA) using the EPA Consensus Method. Water is filtered through a 1-micron wound polypropylene cartridge filter over a 24-hour period (sampling at least 500 to 2,000 gallons). The trapped residue is centrifuged and examined under polarized light microscopy for surface water bio-indicators:

• Diatoms and Chlorophytes (Algae)
• Rotifers, Nematodes, and Crustaceans
• Plant debris, pollen, and vegetative matter
• Protozoan cysts (Giardia) and oocysts (Cryptosporidium)

Regulatory Consequence: A well classified as GWUDI loses its groundwater status and must meet all California Surface Water Treatment Rule requirements—mandating conventional, direct, or membrane filtration plus disinfection to achieve a minimum of 3-log (99.9%) Giardia removal/inactivation, 4-log (99.99%) virus removal/inactivation, and 2-log (99%) Cryptosporidium removal.

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Watershed Sanitary Surveys (California Title 22 Mandates)

Under California CCR Title 22, Section 64665, every public water system utilizing surface water or GWUDI must complete a comprehensive Watershed Sanitary Survey at least once every 5 years.

           ┌────────────────────────────────────────┐
           │ California Title 22 Sanitary Survey     │
           │       (Mandated Every 5 Years)         │
           └───────────────────┬────────────────────┘
                               │
     ┌─────────────────────────┼─────────────────────────┐
     ▼                         ▼                         ▼
[Point Sources]       [Non-Point Sources]       [Intake & Infrastructure]
- WWTP Discharges     - Agricultural Runoff     - Multi-level gates
- Industrial Outfalls - Urban Stormwater Flow   - Screen condition
- Septic Leach Fields - Wildfire Burn Scars     - Transmission conduits

Core Elements of a Title 22 Sanitary Survey

1. Watershed Delineation & Topography: Physical boundaries, geology, hydrology, and land ownership patterns.
2. Point Source Identification: Permitted NPDES discharges, wastewater treatment plants, industrial outfalls, and concentrated animal feeding operations (CAFOs).
3. Non-Point Source Pollution: Agricultural runoff (fertilizers, pesticides, manure), urban stormwater runoff (oils, heavy metals, road debris), timber harvesting, and recreational reservoir use (boating, swimming).
4. Wildfire & Post-Burn Impacts: Assessment of burn scars, ash deposition, and increased soil erosion yielding massive turbidity and TOC spikes during subsequent storms.
5. Raw Water Quality Trends: 5-year statistical analysis of microbial data (total coliform, E. coli), turbidity, nutrients (nitrate, phosphate), TOC/UV254, and bromide.
6. Intake Infrastructure & Watershed Controls: Physical integrity of intake towers, screen cleanliness, and local reservoir management policies.

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Eutrophication, Algae Blooms & Cyanotoxins

Eutrophication is the progressive nutrient enrichment of water bodies—primarily phosphorus ($P$) and nitrogen ($N$)—which fuels rapid proliferation of planktonic algae and cyanobacteria (commonly termed blue-green algae).

Taste and Odor Metabolites: MIB & Geosmin

When cyanobacteria (Anabaena/Dolichospermum, Microcystis, Oscillatoria, Planktothrix, Aphanizomenon) enter active growth or die, they release secondary cellular metabolites into the water column:

• 2-Methylisoborneol (MIB): Imparts a distinct musty, medicinal odor.
• Geosmin ($C_{12}H_{22}O$): Imparts an intense earthy, muddy odor.

The human olfactory system can detect MIB and Geosmin at extremely minute concentrations—threshold odor levels range from 5 to 10 nanograms per liter (ng/L or parts per trillion). Standard conventional coagulation, flocculation, and chlorination do not effectively remove MIB or Geosmin. Utilities must deploy Powdered Activated Carbon (PAC), Granular Activated Carbon (GAC), or Advanced Oxidation Processes (AOP: Ozone + Hydrogen Peroxide or UV + $H_2O_2$).

Cyanotoxins

Certain cyanobacteria strains produce potent cyanotoxins that pose severe health risks:

• Microcystins: Cyclic peptide hepatotoxins that cause acute liver damage (SWRCB Notification Level: $0.03,\mu\text{g/L}$; EPA 10-day health advisory: $0.3,\mu\text{g/L}$ for young children, $1.6,\mu\text{g/L}$ for adults).
• Cylindrospermopsin: Alkaloid cytotoxin affecting the liver and kidneys.
• Anatoxin-a: Potent neurotoxin causing neuromuscular blockage.

Algae Control with Copper Sulfate ($CuSO_4 \cdot 5H_2O$)

Reservoir algae blooms are often treated with copper sulfate pentahydrate. Dosing calculations are governed by volume and chemical constraints: $\text{Chemical Required (lbs)} = \text{Volume (MG)} \times \text{Dosage (mg/L)} \times 8.34\,\frac{\text{lbs}}{\text{gal}}$ $\text{If dosage is expressed as elemental } Cu: \quad \text{Copper Sulfate (lbs)} = \frac{\text{Copper Required (lbs)}}{0.254}$

Critical Water Chemistry Constraints:

• Alkalinity < 50 mg/L as $CaCO_3$: Uncomplexed cupric ions ($Cu^{2+}$) remain dissolved, creating severe toxicity to aquatic life and game fish (trout). Dosages must be drastically reduced.
• Alkalinity > 150 mg/L as $CaCO_3$: Free copper reacts rapidly with bicarbonate/carbonate ions, precipitating out as insoluble copper carbonate ($CuCO_3$). This inactivates the chemical, requiring chelated copper formulations.

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Reservoir Thermal Stratification & Seasonal Lake Turnover

During late spring and summer, solar radiation heats the surface of deep reservoirs, creating density gradients that separate the water column into three distinct thermal zones:

┌──────────────────────────────────────────────────────────┐
│ EPILIMNION (Top Layer)                                   │
│ • Warm (20–26°C), lower density, photic zone              │
│ • Oxygen-rich (DO 8–10 mg/L), active algae growth        │
├──────────────────────────────────────────────────────────┤
│ METALIMNION / THERMOCLINE (Transition Layer)              │
│ • Rapid temperature drop (>1°C per meter of depth)       │
│ • Sharp density barrier preventing vertical mixing       │
├──────────────────────────────────────────────────────────┤
│ HYPOLIMNION (Bottom Layer)                               │
│ • Cold (4–8°C), dense, dark                              │
│ • Anoxic / Anaerobic (DO 0 mg/L)                         │
│ • High dissolved Fe²⁺, Mn²⁺, H₂S, NH₃, and organics      │
└──────────────────────────────────────────────────────────┘

Hypolimnetic Chemical Reduction

In the hypolimnion, bacterial decay of settling dead algae and organic detritus completely exhausts dissolved oxygen. In this anaerobic, reducing environment:

• Insoluble Ferric Iron ($Fe^{3+}$) reduces to soluble Ferrous Iron ($Fe^{2+}$).
• Insoluble Manganese Dioxide ($MnO_2$ / $Mn^{4+}$) reduces to soluble Manganous Manganese ($Mn^{2+}$).
• Sulfate ($SO_4^{2-}$) reduces to Hydrogen Sulfide ($H_2S$), emitting rotten-egg odors.
• Organic nitrogen converts to ammonia ($NH_3$).

Seasonal Lake Turnover Mechanics

• Fall Turnover: In autumn, declining ambient temperatures cool the epilimnion. When surface water reaches 4°C (39.2°F), water reaches its maximum density. The heavy surface water sinks, forcing the lighter, anoxic, mineral-laden hypolimnetic water to the surface. Autumn winds drive complete vertical mixing across the entire water column.
• Spring Turnover: Occurs in cold climates when surface ice (0°C) melts, warms to 4°C, becomes dense, and sinks, mixing the water column prior to summer stratification.

Destratification Systems

To prevent hypolimnetic anoxia and turnover shocks, operators install:

• Diffused Compressed Air Aeration: Porous diffusers on the reservoir bottom release micro-bubbles, lifting cold bottom water to the surface to oxygenate the hypolimnion.
• Mechanical Solar-Powered Draft Mixers: Axial flow impellers continuously move surface water downward, breaking thermal density barriers.

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Operational Scenarios & Troubleshooting

Scenario 1: Managing Fall Turnover at the Treatment Plant

Situation: In late October, a treatment plant suddenly experiences severe raw water quality degradation: raw DO drops from 8.5 mg/L to 2.1 mg/L, raw water turns a murky brown-black color, chlorine demand surges by 3.5 mg/L, and consumers report swampy, metallic odors. Diagnostic: The reservoir has undergone seasonal fall turnover, mixing soluble $Fe^{2+}$, $Mn^{2+}$, and $H_2S$ throughout all intake depths. Operator Action:

1. Inspect intake tower multi-level gates; select the elevation with the highest dissolved oxygen and lowest dissolved metals.
2. Initiate pre-oxidation using Potassium Permanganate ($KMnO_4$) ahead of rapid mixing ($1.0,\text{mg/L } KMnO_4$ oxidizes $\approx 0.5,\text{mg/L } Mn^{2+}$ and $1.0,\text{mg/L } Fe^{2+}$) to precipitate the metals before sand filtration.
3. Increase pre-chlorine dosage to satisfy the elevated inorganic oxidant demand.

Scenario 2: High-Turbidity Runoff Following a Wildfire

Situation: Following a major wildfire in the watershed, the first winter storm washes ash and topsoil into the reservoir. Raw water turbidity spikes from 3 NTU to 180 NTU, and Total Organic Carbon (TOC) rises from 2.2 mg/L to 8.5 mg/L. Operator Action:

1. Switch from routine single-metal coagulant dosing to Enhanced Coagulation.
2. Adjust primary coagulant dose upward and feed caustic soda or lime to maintain coagulation pH in the optimal zone (5.8–6.5 for alum) to maximize TOC removal and prevent post-disinfection DBP violations.