H2O - Healthy Hawaiian Oceans

“Malama o kekai, kekai o ke malama”

Take care of the sea, and the sea will take care of you

Post Office Box 895

Honaunau, Hawai`i 96726


Monday, April 30, 2018


Part II.  Alternatives to Conventional Septic Systems.  It’s the water!
R.H. Bennett Ph.D. Applied Life Sciences LLC
Healthy Hawaiian Oceans: H2O
It is the intention of this second part of the discussion about cesspools and septic systems is to look beyond what is the norm and endorsed by regulatory agencies. This conventionalism creates dichotomous choices in an attempt to meet the EPA mandate to phase out cesspools and cesspits in the state.
For the most part, civil engineers staff most state and federal agencies tasked with regulating private and public wastewater systems.  This expertise is about the mechanics of waste treatment based in part on antiquated and nonvalidated assumptions about the performance of a septic leach field.
Civil Engineers by their discipline and training are not scientists, but technicians.  Confounding this limitation to creativity skills is the onerous structure of the regulatory system for those employed there.  These government engineers operate within the constraints of administrative rules that implement the public law.  This reality overlays a dominant risk-averse conservatism.  It has been said by many agency engineers, I can only do what the rules allow, and budgets permit. With no significant constituency advocating a change in laws and regulations, we have a triumvirate of forces that virtually guarantee the future shall be defined in terms of the past.
Stepping out of the Box
So with the power of a few keystrokes, the triumvirate of anti-creativity is for the duration of this conversation, summarily set aside. The cesspool or septic system conundrum is a false dichotomy.  The public policy says cesspits are unacceptable under the law.  Administrative rules and the force of tradition says, in effect, the only option is a septic system.  This error of logic is compounded by mythological assumptions about mystical geophysical and geochemical processes that occur underground in the buried leach field.
Previous blogs document what science knows and what it does not know about this underground magical waste processing. Instead, the intent here is to examine age-old engineering assumptions and raise questions where it appears these assumptions are part of the problem.
It’s the Water
The first outside the box assumption is all about water.  Hundred of years ago the flush toilet was a huge convenience and improvement over the stinky privy. The first flush toilet arose as a gift for the Queen in 1592 (1).  The indoor “Water Closet” became a feature in the castles of royalty. Freshwater was used to flush a few ounces of human waste away.  Water very efficiently removed the unsightly, odiferous material. It was gone and no longer offended the senses of the elite.
 Poop was now out of sight and out of mind. That had to be about miraculous.  Those fortunate to have a real toilet were no doubt the envy of millions of folks that suffered the risk of frostbite of the most “sensitive’s” on subzero trips to the outhouse.  Indoor plumbing was the symbol of affluence and through this affluence human waste seemingly disappeared.
Waste without Water.
There was a family, Dad, Mom and three boys born in the age of the Boomers.  All newer homes in this southwestern region had flush toilets.  At least the kids knew no other.  Sure there was stories and tales of the harrowing trips to the kybo, grandma would tell, but least for the Boomer Boys all they knew was the whoosh of the flush. 
Father announced one day, we bought a cabin out in the desert wilderness.   The glee of excitement dampened upon the experience that weekends in the desert meant they all had to use the outhouse. It was a real Lua; a two holler, but no one wanted that kind of company.  After a day of use, the odor was gripping. Sometimes the more sensitive would merely refrain from enduring the olfactory terror until they got to the porcelain flush.  

This dessert outhouse was fundamentally waterless.  Dad and the Boomer Boys took “right of passage” fun in irrigating rocks and such rather than enter the “gas chamber."
 Let’s do a thought experiment. The outhouse, save the requisite additions of a few ounces of solid waste and urine is waterless.  Most months the daytime temperatures ranged from 80 to 110 digress F and relative humidity of less than 15%.  This is the meaning of dry.  Fecal waste is typically over 90% moisture. In this environment wastes dry out quickly, but too slow to abate the stink.   Ask then, what is the potential for the waste constituents to move downward in the porous sand and contaminate groundwater many hundreds of feet below?   Almost nil, correct?
Continuing the experiment, let’s install a 1960’s porcelain throne with a 3-gallon flush.  Water has become available.  A family now lives there full time and the cabin has a cesspit. The flush waster and wastewater from the house now about 280 gallons per day flows into the cesspit.  Will this water carry what it may deep into the underlying sand and rocks?  Absolutely.
The convenience of the flush creates and unseen and unrecognized liability.  The water has given the fecal solubles and microbes a river, albeit microscopic, and flow it does.  For the most part, this is the behavior of the modern cesspool and the septic leach field.
Composting Toilets Work and They Take Work.
Looking back to the outhouse days in rural America, some folks motivated by odor revulsion, tried all sorts of remedies from caustic chemicals to fodder.  Yes, old and moldy animal feed found its way into the latrine.  Something interesting happened.  The light, airy fibrous material provided a source of carbon and compost microbes while allowing air to penetrate the heap.  Walla, compost occurred.  The aerobic bacterial decomposition took over and out-competed the bacterial the don’t like air, and the odor producing anaerobes retreated.   This is the basis for the modern-day composting toilet.  With active management, they work well.   The problem is there a few of us willing to be active managers of compost toilets!  The compost has to be removed several times a year.  Any volunteers?  For more on Composting Toilets see (2).
Itʻs The Water
What is the point you may ask? The flush toilet is here to stay. Look at the table below.  This is how we use water.  Only about 20% is from the toilet.  It could be much lower.  The wastewater from all homes, not connected to sewers, finds its way to the cesspit or leach field and the water once again flows. It flows whatever it may, downward and outward. It will flow ultimately in search of its level, groundwater or the nearby shore.
What would happen if we used all that high-quality greywater and only put 1 gallon per toilet flush into our waste systems?   There would be less water, less force, and fewer microscopic streams.  Engineers and geologists call this force the hydraulic load.   The Hydraulic Loading Rate (HLR) has more to do with cesspit and leach field performance than the depth or nature of the soil at the site(3,4,5).  Reread the last sentence again.  The engineers extoll for virtues of soil and soil treatment as if that is the complete answer. Instead, the scientists say it the volume of water that is most important.

 “HLR is directly associated with the wastewater applied to the “soil," but it is also an indicator of contaminant mass flux. The high flux of contaminants in the soil reduces the efficiency of contaminant removal and increases the chance of the pollutants reaching groundwater.

For the most part, an engineer will design more surface area for infiltration, aka the leach field, only for soils with slow infiltration rates.  These soils tend to be higher in clay content.  For rocky lava “soils” with almost infinite water infiltration capacity, the infiltration area may be just a small sump or a leach field with two short drain pipes.  Controlling the HLR and the infiltration rates is not design consideration for today’s septic systems. In effect, fast drainage is desirable for the engineering and costs.  However rapid infiltration is a liability for the environment, especially in the coastal zone.

Getting the Water Out

One simple and convenient way to reduce the HLR is to divert the water from the laundry.  Laundry day for a family means many loads of wash.  Some washers use 35-50 gallons of water per load.   This considerable HLR and can overwhelm the system decreasing performance.  In poorly drained soils it means a wet spot in the lawn. On rocky and volcanic lands the water flows downward, and the depth is influenced by the HLR.  Eventually, all the wastewater in   "the coastal waters surrounding the islands will be the ultimate sink for wastewaters”(6).  This conclusion was first published in 1975.  Now some 43 years later, it took a citizens lawsuit provided for by the Clean Water Act to convince government they need to accept that water flows underground and downhill in Hawai‘i too (7).

Hawaii Guidelines Laundry Water Reuse   http://health.hawaii.gov/wastewater/files/2013/06/graywater_guidelines.pdf

The performance of any cesspit or leach field is improved by reducing the grey water loading.   This quick fix can buy us time to work on real solutions to the flush toilet problem.  For homes on post and pier foundations, this is a simple plumbing alteration will cost a mere fraction of a new waste system and it may perform better.
Greywater reuse is gaining popularity.  First and foremost it is water that has already been purchased and gets used again to irrigate the landscaping.  It is irrigation water that supplants new freshwater purchase and use. Graywater comes from the washer, the sinks, and the showers.  Kitchen sink water is loaded with organic material from the garbage disposer (another misnomer) and grease and therefore is not added to most greywater systems.  Composting all kitchen waste can render this water useable too.
Greywater reuse is practiced in many states and municipalities, and there is no scientific evidence to suggest that greywater reuse is a real risk to public health.  Recent studies document that greywater is not rife with disease agents (8) and greywater gets delivered to plants shrubs and trees and not likely to be ingested.
To put this issue into a practical perspective, our kitchens have more types and numbers of pathogens than greywater.  The juices from raw meats contain some nasty microbes. In a survey of metropolitan markets, 71% of raw chicken was contaminated with Campylobacter. When ingested it is a significant cause of GI disease(9).  Because we don't eat raw chicken or chew on the kitchen sponge, used to mop us the chicken meat juice, the risk is low. Since no one drinks the greywater; the phobia of a person wearing the engineer’s hat is entirely misplaced.
Where Does Home Wastewater Come From?
In the typical home without water conserving appliances and devices, the toilet generates 18.5 gallons of wastewater per person per day. All this water is used to flush a few ounces of human waste.  It is the single most significant contributor at 26.7%.   The modern low flow toilet generates only 8.2 gallons per person per day or 18% of the daily flow.   The water savings alone will pay for a new toilet.  Look for the WaterSense logo.
 According to a recent scientific review, the typical person produces 3.4 lbs of wet wastes or .2 lbs of dry matter waste per day (10). To manage that waste we use 18.5 gallons (154 lbs) of potable water each day.  As we move into drought and greater climate uncertainty and become critically aware how our reefs are impacted by human wastewaters, we need to ask, is the smart?
In WaterSense (11) efficient homes combined with laundry water reuse, we can cut wastewater flow to cesspits and septic systems by about 50%, and it is cost-effective.  Now that is more than smart; it is a wise first step.

Table 1. Per capita in-home water use: Traditional and Efficient Homes

 Table 2.   Reductions in wastewater with reuse


1.     https://en.wikipedia.org/wiki/History_of_water_supply_and_sanitation

2.     Del Porto, David, and Carol Steinfeld. composting toilet system book. Center for Ecological Pollution Prevention, 2000.

3.     McCray, John E., et al. "Model parameters for simulating fate and transport of onsite wastewater nutrients." Groundwater43.4 (2005): 628-639.

4.     McCray, J. E., et al. "Quantitative Tools to Determine the Expected Performance of Wastewater Soil Treatment Units." Water Environment Research Foundation, DEC1R06 (2010).
5.     Beal, C. D., et al. "Influence of hydraulic loading and effluent flux on surface surcharging in soil absorption systems." Journal of Hydrologic Engineering 13.8 (2008): 681-692.

6.     Lau, Leung-Ku Stephen, and John Francis Mink. Hydrology of the Hawaiian Islands. University of Hawaii Press, 2006.

7.     Hawai‘i Wildlife Fund et al. vs. Maui County  http://cdn.ca9.uscourts.gov/datastore/opinions/2018/03/30/15-17447.pdf.

8.     Keely, S. P., et al. "Characterization of the relative importance of humanand infrastructureassociated bacteria in grey water: a case study." Journal of applied microbiology 119.1 (2015): 289-301.

9.     Zhao, Cuiwei, et al. "Prevalence of Campylobacter spp., Escherichia coli, and Salmonella serovars in retail chicken, turkey, pork, and beef from the Greater Washington, DC, area." Applied and environmental microbiology 67.12 (2001): 5431-5436.

10.  Rose C, Parker A, Jefferson B, Cartmell E. The Characterization of Feces and Urine: A Review of the Literature to Inform Advanced Treatment Technology. Critical Reviews in Environmental Science and Technology. 2015;45(17):1827-1879.

11.  WaterSense Program.  https://www.epa.gov/watersense

Wednesday, April 4, 2018

Cesspool or Septic System, Neither are Appropriate

Cesspool or Septic System, Neither are Appropriate

Part One:  History, Nutrients, and Pathogens
Richard H. Bennett Ph.D
Applied Life Sciences LLC

Cesspools and septic systems are antiquated and inappropriate waste management technologies.  Both enjoyed the nod of the Department of Health since 1915!!  It is more than incredulous that the EPA (Environmental Protection Agency) and the Hawai‘i Department of Health consider these holes in the ground to be acceptable waste management in 2018.  Given the vast scientific literature and public information, one would expect that in 103 years, we would have made the initiative, akin to putting a man on the moon to clean up our, ah…wastes. Instead, we bury the tank or the pit placing the matter "out of sight and out of our political minds." 
The development of Hawai‘i since 1915 was “greased” by simple ignorance, that in effect said, "it's ok it's all underground."   This naive attitude ignored the wet stinky areas surfacing just over the buried tanks.  It was Irma Bombeck who famously titled her book “The grass is always greener over the septic tank” (1995).  Septic system failure was so common that it made its way into our urban folklore.
According to research by University of Hawai‘i Professor Roger Babcock, about one-third of the onsite waste systems on Oahu have failed (1).  Cities in Florida will spend millions of dollars to close septic systems because they contaminate ground waters and the ocean.  So why pray tell, is the State of Hawai‘i advocating a waste system the is hundreds of years out of date and known to pollute? 
Like ignoring the termites in the wood foundation, the State and the Federal Government allowed this happen.  The problem is not new by any means.  Ultimately State Policy is to blame, as are the people who administer it.   No wonder the homeowner is livid at the specter of the high cost of conversion to a septic system.  For many the state told them less than ten years ago it was perfectly ok to install a cesspit.  We watched an "approved” cesspit installation just a year ago and if they sell the home tomorrow, they may be forced to upgrade.

Old Technology

The Frenchman Mouras invented the first septic system in 1881.   The history timeline notes US septic systems became very popular and inexpensive in the post-WWII era.  Septic failures after a decade of use were common the 1960ʻs.  The 50ʻs and 60ʻs was a time of the enormous population growth in the West and septic systems were the cheapest option for developers.  It was then groundwater contamination tainted water all over the country and sewer systems advocated to protect water resources. 
In high-density urban areas, cities began building wastewater treatment plants.  The plants are expensive and without, the assistance of large grants and loans from the EPA, more homes might still be on septic systems.

Schematic cesspool (left), water, and constituents leach downward.  Septic leach field (below) works similarly depending on soil type and depth (3) (a).

Waste Treatment Plants
The modest size wastewater treatment plant Kealakehe in Kailua-Kona processes about two million gallons of sewage per day.  It was constructed with EPA funds to bring sewer service to the multitude of homes and businesses along the oceanfronts of Alii Drive.   After Los Angeles and San Francisco spent over four billion federal dollars for municipal waste treatment systems in the 1990ʻs, the attitude in Congress was “no more, let the states fend for themselves”.  That brings us full circle back to our conundrum.
In the ensuing years, the septic system became the only option for regions that did not have or afford centralized wastewater treatment plants.  Today approximate 25% of US homes use this 19th-century technology.

Indeed, the upfront cost was the primary concern, but the downstream costs of surface water and groundwater pollution require expensive mitigation to remain in compliance with the US Clean Water Act, were largely ignored.  Furthermore, the state failed to acknowledge the cost to the stateʻs economy as tourists encounter polluted beaches, microbial hazards, algal blooms and murky waters.
Under pressure from local activists and the EPA, the state has prioritized high-risk areas targeted for septic system installation.  Many of these regions are near the shore such as Puako, Hawai‘i or Hanalei Kauai and upslope from drinking water wells in Makawao, Maui.
We only need look back in time, to the shores of California and see that septic systems are not the solution.   Near Stinson Beach California, very high-value homes dot the hillsides.   Most of the locations have soils for the installation of a septic system and leach field. Standford University conducted near shore groundwater research at Stinson Beach and found nitrate and fecal indicator bacteria in the water contained in soils and sand (2).  Simply stated the septic systems removed some fecal indicator bacteria, but the nitrate was largely not mitigated.   This California problem is yet further documentation that this magical attribute some officials call "soil treatment” cannot be assured.

The graph shows as more water is added to the wastes the more constituents like virus move through toward groundwater. The effect is profound on well-drained ground.

In fact, the research community published a multimillion-dollar study that says, we cannot predict how soil treatment will work.   We cannot provide predictive evidence that any given system will remove or attenuate microbes and chemicals of concern. The variables are too complicated and site-specific to allow for accurate performance predictions. They state, “hydraulic loading rate appears to be more important than soil texture or soil depth within the first 30-60 cm (1-2 ft.), although both soil depth and texture remain important variables” (3,16).  In regions of the state where the soil is rare, and wastewater loading rates are reasonable to high, septic systems will fail to provide even modest treatment and allow rapid leaching to groundwater and the sea.
The Nitrate is Ours
Rest assured groundwater contamination with nitrate is a concern.  Drinking water with elevated nitrate is simply not good for public health, especially for infants.  Septic systems and cesspools add human waste nitrate to the ground and underlying ground waters.  Nationwide,  agricultural fertilization of irrigated farms is the primary source of nitrate.  In rural areas without irrigated agriculture or animal feedlots, the nitrate source in groundwater is home wastewater systems.

Until relatively recently we have not had to tool to look at groundwater nitrate with greater refinement.  The work of Dr. Meghan Dailer at UH Manoa is compelling. Dailer and coworkers collect nearshore limu or marine plants and measure the isoptic forms of nitrate to arrive at what is called the delta 15 N (δ 15N). The assay measures the stable isotopes of nitrogen. The expression is the ratio of the two isotopes.  Marine plants near the more urban shores on Maui and Hawai‘i Island have a higher value.  These signatures are indicative of human sourced nitrogen.  The most of the undeveloped beaches of N. Maui have a much lesser signal (4).

For a couple of decades, people have openly speculated about nitrogen in groundwater and nearshore oceans.  Since there was no apparent source like a feedlot or dairy, the conclusion erroneously drawn is the elevated nitrogen was the natural background state.  This assumption makes little sense in the light that nitrogen is a limiting nutrient in most ecosystems and highly conserved (5).  The nitrogen isotope studies confirm the nitrogen is not spilling from the ecosystem.

A Better Smoking Gun

For some time we have been looking for better tracers in human wastewater.  Researchers explored testing for caffeine, nicotine, and pharmaceutical drugs.  All have limitations, and many degrade too quickly in sewage and the environment and thus not reliable.  However recently a nearly ubiquitous household compound emerges as a valid chemical indicator of human wastewater pollution.  The nonnutritive sweetener Splenda or sucralose is a sucrose or table sugar reacted with chlorine.  It is very sweet but wholly indigestible and very stable throughout sewage treatment.  The Yale researchers declared it an ideal tracer and as we might expect it is an excellent marker for wastewater tracer in the environment (6).   Field research validates Sucralose as a tracer for groundwater contamination from septic systems (7). Analysis of sucralose in water is complicated, and few labs have the instrumentation.

What about the germs?
This next statement will come as complete heresy. Human fecal waste from healthy persons is not teaming with pathogens just lingering for an opportunity to start the next epidemic or for that matter put a household at risk.
The Human Microbiome Consortium (8) stated in 2014, “This overall absence of particularly detrimental [fecal] microbes supports the hypothesis that even given this cohort’s high diversity, the microbiota tends to occupy a range of configurations in health distinct from many of the disease perturbations studied to date.”  In simple terms, the feces of a large cohort of healthy persons is NOT populated with disease pathogens.
 Just because governments monitor something called Fecal Coliform and document its presence does not mean it indicates genuinely hazardous pathogens are present.  The fecal coliform is a 100 plus-year-old and arbitrary distinction that does not correlate with the presence of pathogens. Many agencies no longer use this test.  A more appropriate measure of microbial water quality is the typical bacteria E.coli.  Most E. coli are harmless, yet some strains like O157:H7, the infamous Jack in the Box undercooked hamburger strain is potentially lethal.   It is a typical resident in feedlot cattle feces and not humans.
 Science validates the monitoring of E. coli for drinking water safety assessment. Since we drink volumes of water, this allows the consumption of millions of bacteria at a time.  The “bad” E. coli have a minimum infective dose of about one million.  Consume less than that and disease is not likely.  
It is not the bacteria that is a concern; it is the virus. For example the infamous Cruiseship Virus, Norwalk has a minimum infective dose of less than 10.  Moreover, victims of this "24-hour stomach flu" will shed trillions of virus particles every day for a week or more.  It is the enteric virus that presents the real hazard in drinking and recreation waters. (9,10).

The graph to left depicts virus fecal shedding in a person infected with Norwalk virus. Maximum shedding about one trillion virus per day.

The question remains, how well do septic systems remove or otherwise attenuate virus? This question is exceptionally complicated .question.  It depends on the soil type, its pH, the ionic charge of the virus and the soil, the number of virus and the volume of water flushing through the system daily and significant pulses of water, as on laundry day.  The big picture answer is virus do breakthrough (11).  The risk to drinking water is more likely when the density of septic systems exceeds a few homes per acre of land in a square mile. (12). In West Hawai‘i, housing densities range from one to 5 home waste systems per acre and far away exceed the EPA recommended density.

 The graph to the right shows that significant virus survives in warm wastewater for over 140 days. Ample transit time to reach the shallow ground and nearshore waters (13).

The research suggests virus in the ground and water survive weeks to months depending on the conditions (13).  A key variable is the rate of movement. Fissures in rock and lava do allow for the very rapid flow of water and all suspended in it(14). However, all drinking water in municipal systems must disinfect to EPA standards. The process virtually eliminates the risk of infection.  Oceanwater, in contrast, appears to be a higher risk of exposure.  Fortunately, it is more hostile to the virus, and the combined influences of temperature, sunlight and predatory marine biota inactivate virus in a period of days to weeks again depending on site conditions.  However, the presence of this virus in urban recreation beaches is frequent (15).

Conclusion Part One.
The science is unequivocal; septic systems offer no substantial improvement of cesspools as both systems are antiquated and were never intended to isolate or attenuate wastewater nutrient or microbial constituents.  In very select sites with true and deep soils, some attenuation may occur but is incidental if not accidental.  In tropical environments with limited or no soils combined with high rainfall, septic leach field performance is a matter of speculation and not science.
 In the current time, it is more than unrealistic to promote expensive transitions to septic systems when the protection of groundwater and nearshore waters are negligible and the costs extreme.  It is most advisable to step back, set goals and apply the objectives of the of state and federal policies.  For the health of the people and their economy, we are compelled to implement human waste control strategies that meet and exceed those goals.  The lowest common denominator may be the least costly, then again we get what we pay for in the long run.

Coming soon Part Two,   Alternatives: Thinking Way Outside the Box


1.     Babcock, Roger W., et al. “Condition assessment survey of onsite sewage disposal systems (OSDSs) in Hawaii.” Water Science and Technology 70.6 (2014): 1083-1089.
2.     De Sieyes, Nicholas R., et al. “Submarine discharge of nutrientenriched fresh groundwater at Stinson Beach, California is enhanced during neap tides.” Limnology and Oceanography 53.4 (2008): 1434-1445.
3.     McCray, J. E., et al. “Quantitative Tools to Determine the Expected Performance of Wastewater Soil Treatment Units.” Water Environment Research Foundation, DEC1R06 (2010).
4.     Dailer, Meghan L., et al. “Using δ15N values in algal tissue to map locations and potential sources of anthropogenic nutrient inputs on the island of Maui, Hawai ‘i, USA.” Marine Pollution Bulletin 60.5 (2010): 655-671.
5.     Vitousek, Peter M., et al. “Nitrogen and nature.” AMBIO: A Journal of the Human Environment 31.2 (2002): 97-101.
6.     Soh, Lindsay, et al. “Fate of sucralose through environmental and water treatment processes and impact on plant indicator species.” Environmental Science & Technology 45.4 (2011): 1363-1369.
7.     Oppenheimer, Joan, et al. “Occurrence and suitability of sucralose as an indicator compound of wastewater loading to surface waters in urbanized regions.” Water Research 45.13 (2011): 4019-4027.
8.     Huttenhower, Curtis, et al. “Structure, function and diversity of the healthy human microbiome.” Nature 486.7402 (2012): 207.
9.     Yates, Marylynn Villinski, Charles P. Gerba, and Lee M. Kelley. “Virus persistence in groundwater.” Applied and Environmental Microbiology 49.4 (1985): 778-781.
10.  Gerba, Charles P., et al. “Failure of indicator bacteria to reflect the occurrence of enteroviruses in marine waters.” American journal of public health 69.11 (1979): 1116-1119.
11.  Scandura, J. E., and M. D. Sobsey. “Viral and bacterial contamination of groundwater from on-site sewage treatment systems.” Water Science and Technology 35.11-12 (1997): 141-146.
12.  Yates, Marylynn V. “Septic tank density and groundwater contamination.” Groundwater 23.5 (1985): 586-591.
13.  Kauppinen, Ari, and Ilkka T. Miettinen. “Persistence of Norovirus GII Genome in Drinking Water and Wastewater at Different Temperatures.” Pathogens 6.4 (2017): 48
14.  Allen, Martin J., and SMs Morrison. “Bacterial movement through fractured bedrock.” Groundwater 11.2 (1973): 6-10.
15.  Love, David C., et al. “Human viruses and viral indicators in marine water at two recreational beaches in Southern California, USA.” Journal of water and health 12.1 (2014): 136-150
16.  Yates, Marylynn V., Scott R. Yates, and Charles P. Gerba. "Modeling microbial fate in the subsurface environment." Critical Reviews in Environmental Science and Technology17.4 (1988): 307-344.

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