3.3 Harmful Algal Blooms (HABs) & Oregon Cyanotoxin Rules (OAR 333-061-0510)

Harmful Algal Blooms (HABs) & Oregon Cyanotoxin Rules (OAR 333-061-0510)

Harmful Algal Blooms (HABs) represent one of the most critical operational and public health challenges facing surface water treatment operators in Oregon. Although commonly referred to as "blue-green algae," the organisms responsible are actually cyanobacteria—ancient, single-celled, photosynthetic prokaryotes that share characteristics of both bacteria and true algae.

Cyanobacteria possess specialized intracellular gas vesicles that enable them to regulate their buoyancy, floating upward during daylight hours to capture solar irradiance for photosynthesis and sinking downward at night to absorb nutrients from deeper water layers. Under favorable environmental conditions—warm water temperatures ($>20^\circ\text{C}$), prolonged sunny days, extended hydraulic retention times in impounded reservoirs, and elevated nutrient concentrations (specifically bioavailable phosphorus and nitrogen)—cyanobacteria proliferate rapidly, forming dense surface scums and producing potent biological poisons known as cyanotoxins.

+-----------------------------------------------------------------------------------------+
|                         CYANOBACTERIA BLOOM DRIVERS IN OREGON                          |
|                                                                                         |
|  Elevated Water Temperatures (> 20°C)       +   High Solar Irradiance (Summer Photoperiod)
|  Prolonged Reservoir Retention Time         +   Excess Nutrients (Phosphorus & Nitrogen)|
|                                     |                                                   |
|                                     v                                                   |
|                   RAPID EXPONENTIAL CYANOBACTERIAL BLOOM                                |
|             (*Microcystis*, *Planktothrix*, *Dolichospermum*, *Aphanizomenon*)          |
|                                     |                                                   |
|                                     v                                                   |
|                             CYANOTOXIN RELEASE                                          |
|          Intracellular Toxins (Inside Cells) ===[ Lysis ]===> Extracellular Toxins       |
|          [Easily Removed by Coag/Sed/Filtration]             [Requires PAC/Ozone/BAC]   |
+-----------------------------------------------------------------------------------------+

---

Oregon Watersheds & The 2018 Salem Drinking Water Crisis

Western Oregon relies heavily on surface water impounded in multi-purpose flood control reservoirs constructed by the U.S. Army Corps of Engineers (USACE) along the western slopes of the Cascade Mountains. These reservoirs are highly susceptible to late-spring and summer cyanobacterial blooms:

• Detroit Reservoir: North Santiam River subbasin (primary drinking water source for the City of Salem and City of Stayton).
• Green Peter & Foster Reservoirs: South Santiam River subbasin (source for Lebanon and Albany).
• Cougar Reservoir: McKenzie River subbasin (upstream of Eugene Water & Electric Board's Hayden Bridge intake).
• Lookout Point, Dexter & Fall Creek Reservoirs: Middle Fork Willamette subbasin.
• Lost Creek Reservoir: Rogue River basin (source for the Medford Water Commission).
• Other bloom-prone waters: Upper Klamath Lake and Lake Billy Chinook east of the Cascades, and coastal lakes such as Tenmile Lakes.

The Salem Water Emergency of 2018

In late May 2018, a cyanobacterial bloom in Detroit Reservoir released toxins into the North Santiam River, Salem's source. The Geren Island slow sand filters removed cells well but could not remove dissolved toxins, and finished water tests found microcystins and cylindrospermopsin above the levels advised for vulnerable people. On May 29, 2018, Salem issued a do-not-drink advisory for vulnerable populations, including infants, young children, pregnant and nursing women, and people with liver conditions or on dialysis. Advisories recurred into early July, and the state helped distribute bottled water.

The event drove rulemaking. OHA adopted temporary cyanotoxin rules effective July 1, 2018 and permanent rules on December 21, 2018. Salem added treatment for dissolved toxins.

---

Cyanotoxin Classes, Health Effects & Toxicology

Cyanotoxins are divided into distinct chemical classes based on their molecular structures and primary physiological targets in the human body:

---

Oregon Cyanotoxin Rules (OAR 333-061-0510 through 0580)

Who is covered (OAR 333-061-0510)

The rules apply to water suppliers whose systems use a surface water source, or GWUDI, that OHA determines is susceptible to harmful algal blooms or cyanotoxins. They also apply to systems that purchase water from such a supplier. A source is susceptible if:

1. a harmful algal bloom has been documented, or a cyanotoxin detected, in the source or in a water system it supplies;
2. the source, or a waterbody upstream of it, is listed in DEQ's Integrated Report and 303(d) list for algae and aquatic weeds;
3. the intake is downstream of, or influenced by, another susceptible source; or
4. OHA finds it susceptible based on factors such as stagnant water, temperature, nutrients, water quality data, satellite imagery or toxin-producing genes.

OHA may exempt a source it finds unlikely to be susceptible. Under these rules, "cyanotoxins" means total microcystins and cylindrospermopsin.

Health advisory levels (OAR 333-061-0530)

"Vulnerable people" means infants, children under six, pregnant women, nursing mothers, people with pre-existing liver conditions, and people receiving dialysis. The levels come from EPA's 10-day health advisories.

Monitoring (OAR 333-061-0540)

RAW WATER, May 1 - Oct 31: sample at least every two weeks
   |
   |  microcystins >= 0.20 ug/L, cylindrospermopsin >= 0.30 ug/L,
   |  or a recreational use health advisory upstream
   v
RAW WATER weekly  +  ENTRY POINT weekly (start within 1 business day of the raw result)
   |
   |  any cyanotoxin detected at the entry point
   v
ENTRY POINT daily (start within 24 hours) + optimize treatment
   |
   |  entry-point result above a health advisory level
   v
CONFIRMATION sample at the entry point within 24 hours of the result
   |
   |  confirmation sample above a health advisory level
   v
HEALTH ADVISORY to customers within 24 hours + distribution sampling

• Raw monitoring returns to every two weeks after two consecutive weekly raw samples fall below 0.20 µg/L microcystins and 0.30 µg/L cylindrospermopsin, and no upstream recreational advisory is in place.
• Daily entry-point monitoring returns to weekly after two consecutive non-detects at the entry point.
• Methods (OAR 333-061-0550): EPA Method 546 (ELISA) for total microcystins. DEQ's ELISA method for cylindrospermopsin, with EPA Method 545 required for follow-up when cylindrospermopsin exceeds 0.7 µg/L at the entry point or in distribution. Labs must be ORELAP-accredited (or the DEQ lab) and start analysis within one business day.

Reporting and public notification (OAR 333-061-0560 and 0570)

• Report an initial entry-point or distribution result above a health advisory level to OHA and to all purchasing systems within 24 hours of receiving it. Report a confirmation result above a level within 8 hours.
• If the confirmation sample exceeds a level, the supplier and any purchasing systems must issue a health advisory that the water is not safe to drink for the affected population, no later than 24 hours after receiving the results. Delivery is by broadcast or social media, posting or hand delivery, as OHA approves.
• The advisory stays in effect until results are at or below the level in two consecutive samples at least 24 hours apart at the entry point and in two consecutive sets of distribution samples taken at least 24 hours apart.
• Detections go in the Consumer Confidence Report with the required health-effects language. Records are kept for 10 years.

---

Treatment Plant Optimization & Operational Interventions

Conventional drinking water treatment plants (coagulation, flocculation, sedimentation, and dual-media filtration) are designed to remove particulate turbidity, not dissolved chemical contaminants. Removing cyanotoxins requires specific operational strategies that distinguish between intracellular toxins (contained safely inside intact cyanobacterial cells) and extracellular toxins (dissolved in the water column):

+-----------------------------------------------------------------------------------------+
|                    CYANOTOXIN TREATMENT MECHANICS & PROCESS CONTROL                     |
|                                                                                         |
|  RAW WATER INTAKE: Adjust intake depth to avoid upper photic zone bloom layer            |
|                               |                                                         |
|                               v                                                         |
|  PRE-TREATMENT:   *** CRITICAL: SHUT OFF RAW WATER PRE-CHLORINATION ***                 |
|                   (Prevents cell lysis and release of dissolved intracellular toxins)   |
|                               |                                                         |
|                               v                                                         |
|  PHYSICAL REMOVAL: Optimize Coagulation / Flocculation / DAF / Sedimentation             |
|                    (Removes intact cyanobacteria cells intact without rupture)          |
|                               |                                                         |
|                               v                                                         |
|  DISSOLVED TOXIN  1. Powdered Activated Carbon (PAC): Dose 10-30 mg/L (Mesoporous wood) |
|  BARRIERS:        2. Ozone Oxidation (O3): Cleaves Adda functional group of microcystin |
|                   3. Biofiltration (BAC): Microbial biofilms enzymatically degrade toxin|
|                               |                                                         |
|                               v                                                         |
|  FINISHED WATER:  Post-chlorination with adequate CT for residual distribution protection|
+-----------------------------------------------------------------------------------------+

1. Source Intake Gate Management

Cyanobacteria concentrate heavily in the upper photic zone ($0-5 \text{ meters}$) of reservoirs to capture sunlight. If the intake structure features multiple intake elevations (selective withdrawal gates), operators should lower withdrawal gates to draw water from intermediate depths. However, operators must avoid withdrawing from the deepest, anoxic hypolimnion layers, which frequently contain elevated levels of dissolved iron, manganese, and hydrogen sulfide that interfere with subsequent treatment.

2. The Absolute Prohibition on Raw Water Pre-Chlorination

3. Physical Removal of Intact Cells

• Optimized Coagulation and Flocculation: Dosing metal salt coagulants (alum, ferric chloride, or polyaluminum chloride [PACl]) with coagulant aids (cationic or nonionic polymers) destabilizes negatively charged cyanobacterial cell walls, agglomerating intact cells into settleable flocs without shearing the cell membranes.
• Dissolved Air Flotation (DAF): Because cyanobacteria possess buoyant internal gas vesicles, they often settle poorly in conventional sedimentation basins. DAF systems introduce micro-fine air bubbles ($10-100 \ \mu\text{m}$) that attach to flocculated algal cells, floating them rapidly to the surface where they are scraped off as sludge without lysing the cells.

4. Adsorption via Activated Carbon

Dissolved extracellular cyanotoxins must be removed through adsorption or advanced oxidation:

• Powdered Activated Carbon (PAC): PAC can be fed into the raw water flash mix or dedicated slurry contact basins. The effectiveness of PAC depends heavily on carbon pore structure: wood-based mesoporous carbons (pore diameters $2-50 \text{ nm}$) exhibit vastly superior adsorption capacity for large microcystin molecules compared to microporous coal- or coconut-based carbons. Effective operational dosages typically range from $10 \text{ to } 30 \text{ mg/L}$, requiring a minimum contact time of 30 to 45 minutes before settling or filtration.
• Granular Activated Carbon (GAC): Post-filter GAC contactors provide deep-bed adsorption, though carbon beds must be regularly monitored for organic matter fouling and competitive adsorption.

5. Advanced Oxidation Processes

• Ozonation ($O_3$): Ozone is the most effective chemical oxidant for neutralizing microcystins and anatoxin-a. Ozone aggressively attacks and cleaves the conjugated diene double bond of the unique Adda amino acid functional group on the microcystin ring, permanently eliminating hepatotoxicity. An ozone residual of $0.3-0.5 \text{ mg/L}$ with a hydraulic contact time of $2-5 \text{ minutes}$ typically achieves $>99\%$ destruction of dissolved microcystin.
• Free Chlorine ($HOCl$): While pre-chlorination of raw water is prohibited, free chlorine can be applied to filtered water (after all intact cells have been removed). Chlorine can destroy dissolved microcystins, but its efficacy is strongly pH-dependent: hypochlorous acid ($HOCl$, dominant at $\text{pH} < 7.5$) oxidizes microcystin rapidly, whereas the hypochlorite ion ($OCl^-$, dominant at $\text{pH} > 7.5$) is far less reactive. Chlorine is virtually ineffective against anatoxin-a.

6. Biofiltration (Biological Activated Carbon [BAC])

When dual-media or GAC filters are operated in biological mode without maintaining an oxidant residual across the filter bed, naturally occurring biofilms develop on the media grains. Specialized bacteria—specifically strains of Sphingomonas, Pseudomonas, and Rhizobium—produce microcystinase enzymes (mlrA, mlrB, mlrC, mlrD) that sequentially cleave the cyclic microcystin molecule into linearized peptides and harmless amino acids, providing sustainable biological toxin destruction.