Dealing With

Holding Tank

Wastes at BLM Sites

by Pat Fleming

Lead Civil Engineer

National Science and

Technology Center

Background

As recreational use of the lands managed

by BLM increases and as regulatory

agencies give increased scrutiny to

smaller domestic water and wastewater systems, more attention must be

given to this infrastructure at our sites.

Minor aspects of this infrastructure that

can have significant adverse impacts on

the resources BLM is charged with

managing are the facilities that receive,

treat, and dispose of holding tank

wastes from recreational vehicles and

boats. While these facilities are typically

valued by the public that uses them, they

are often expensive to properly construct,

operate, and maintain. Improper operation, however, can lead to pollution of

ground and/or surface waters.

Moreover, pollution can occur unnoticed for extended periods when waste

facilities fail.

BLM administers two very unique

recreation sites near Yuma, Arizona,

designated as Long-Term Visitor Areas

(LTVA) by Congress. Essentially, the

sites are large tracts of land near the

Colorado River where a recreation

vehicle (RV) can remain as long as 7

months continuously for a modest

monthly fee (approximately $100). No

utility services are available, but BLM

provides potable water available from

storage tanks and waste holding tanks.

One of the “dump stations” serving the

South Mesa LTVA, on the California

side of the Colorado River, was cited by

the California Regional Water Quality

Control Board for noncompliance due

to high levels of nitrogen and total dissolved solids being discharged into the

underground disposal drainfield. BLM

personnel subsequently performed

laboratory analyses on the waste received

at the dump station and conducted some

research on the chemicals used in these

holding tanks.

The Nature of the Problem

Most wastewater treatment facilities,

including septic tanks and lagoon systems for small developments, employ

biological processes to stabilize and

remove pollutants from wastewater

streams. These biological processes

perform best when they approach

steady-state conditions which include

constant waste stream temperature,

flow rate, and composition. In reality,

each of these variables tend to fluctuate

seasonally and weekly as a result of typical recreation use patterns.

Holding tanks on boats and RVs are

used to keep all sanitary wastes onboard

when a sewer system is unavailable.

Since little or no carriage water is used,

as is in typical domestic sanitary waste

streams, holding tank wastewater is far

more concentrated than typical domestic wastewater. Compounding the

problem at South Mesa, additives are

introduced into these tanks, primarily to

control odors. There are a wide variety of

such additives used, the most common of which are formaldehyde-based

compounds (including the popular

Aqua-Kem®). Other types include

those based on quaternary ammonium

compounds (“quats,” which often impart

a pine scent) and enzyme formulations.

In general, while these additives work

well to control odors aboard the boat

or RV, they complicate the treatment

and disposal of the resulting mixture.

Generally, treatment facilities are

designed on the basis of two primary

parameters: hydraulic capacity (gallons

per day) and organic strength (biochemical oxygen demand, or BOD) of

the waste stream. Usually it is much

easier to predict the hydraulic capacity

needed for a treatment facility than the

organic strength of the wastewater that

it will receive. Highly concentrated

holding tank wastes, containing variable amounts and types of chemical

additives, make proper design of treatment facilities difficult. Further, the

typical mode of introducing wastes into

the receiving station - dumping - is not

conducive to the steady-state flow needed for optimal biological treatment.

Chemical Variables 

Formaldehyde is a relatively simple

organic compound, and is biodegradable, breaking down into water and

carbon dioxide in one step. It does

not control odors by killing the

microorganisms that generate them,

as is popularly believed. Instead, it

reacts chemically with odor-causing

compounds to render them less odorous. However, the organic strength of

most formaldehyde-based deodorizers

is so high that the resulting mixture in

a holding tank is fifteen to twenty

times stronger than typical domestic

wastewater, even after several days residence in the tank. Chemical toilet

wastes, which use higher concentrations of chemical deodorizers, can be

over one hundred times as strong.

Biodegradability is desirable but is

not necessarily an indication of ease

of or acceptability for treatment.

Formaldehyde is likely to be more closely

regulated in the future, particularly when

part of a wastewater disposal system.

Quats are not biodegradable and

deodorize by killing the microorganisms in the holding tank. Studies have

shown that even in very low concentrations, quats can adversely affect wastewater treatment processes. Fortunately,

these compounds are far less popular

than formaldehyde-based chemicals

due to their higher cost and reduced

effectiveness.

Enzyme-based products employ natural

organic chemicals. They are far less popular for use in holding tanks due to less

reliability, effectiveness for odor control,

and higher cost. However, these compounds are biodegradable and somewhat

lower in organic strength than formaldehyde compounds.

Failure of 

Traditional Solutions

The problem at South Mesa is not

unique. Additional RV dump stations

at BLM recreation sites have been

closed due to failure, while other closures

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NO. 38 DATE 08/15/00

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HazardousMaterials
are being considered. In addition, the

expense of keeping up with “haul

away” dump station systems is prohibitive. The bottom line is that waste

discharged from holding tanks requires

even more treatment than the equivalent waste stream from a permanent

home, due to the chemicals added.

The treatment facility needed to serve

1,000+ RVs is even more elaborate

than one needed to serve 1,000 houses. 

Technical literature1 in wastewater

treatment usually recommends that

concentrated wastes such as septage

pumped from vault or chemical toilets,

or holding tank wastes, be slowly

metered into the treatment facility so as

not to upset the biological processes

used. The dearth of practical recommendations for on-site treatment and

disposal of such wastes (as opposed to

hauling to a municipal treatment

facility) may be due to a lack of truly

successful installations. Some literature

indicates the practical limitations of

treatment facilities in terms of the maximum concentrations of formaldehyde

or BOD that can be withstood by the

specific treatment processes, but these

values vary.

The recorded system failures are most

often due to the shock imparted on the

biological processes by intermittent,

rapid introduction of these high

strength wastes. Treatment facility

designs often have not recognized the

magnitude of organic strength and are

undersized as a result. Undersized septic

tank failures are generally manifested as

solids carryover into the underground

disposal systems which, in turn, fail by

clogging and sending effluent to the

ground surface or “backing up.” Lagoon

system failures are characterized by poor

effluent quality, noxious odors, and

excessive sludge. Accumulations of

sludge can be toxic.

Preventing Failures

The key to preventing failures of waste

treatment and disposal facilities that

receive holding tank wastes is recognition of the characteristics of these

wastes by the designer of the facilities.

The controlling design criteria will nearly always be those related to organic

loading as opposed to hydraulics.

General practical rules of thumb for

receiving, treating, and disposing of

wastes from holding tanks, chemical

toilets, and vault toilets are:

• Employ whatever means are available to blend holding tank contents with other waste streams to

reduce the organic strength of

these concentrated wastes prior to

treatment. In small developments,

this often means providing a mixing or dilution tank upstream from

a septic tank in which domestic

wastewater from plumbed restrooms

or other facilities is mixed with holding tank wastes.

• Size treatment facilities adequately.

Generally, required septic tank volumes are significantly more than

indicated by the typical hydraulic

capacity designs used for treating

domestic wastewater. Requirements

can be 2 to 15 times the volume

resulting from traditional methods. Underground disposal fields

also need to be roughly twice as big

as those sized for an equivalent

flow of domestic wastewater, due

to the higher strength of the

resulting effluent.

• Monitor septic tank scum and

sludge accumulations frequently and

pump the tank out whenever the

“clear zone” diminishes to roughly

30 percent of the total liquid depth.

• Size lagoons such that surface loading rates do not exceed values that

are recommended (by regulators or

sanitary engineers) in the specific

locale of the facility. Try to maintain

liquid depth between 3 and 5 feet.

• Take advantage of opportunities to

educate RV and boat users about

the chemicals that they use in their

holding tanks, including how to

avoid using excessive amounts (and

unnecessary expense), and how they

affect things downstream.

Design, construction, operation, and

maintenance costs for wastewater

treatment are quite significant.

Recognizing the impact of recreational

holding tank wastes on the facilities

needed for this function is very important in making the appropriate related

decisions. Scott DeBock and I have

designed new non-discharging treatment

facilities for the South Mesa site. A construction contract is imminent.

For Further Reading

Formaldehyde and Other Aldehydes,

National Academy Press, Washington,

DC, 1981.

Treatability of Recreational Vehicle

Wastewater at Highway Rest Areas,

Charles A. Brown, Thesis for the

University of Washington, 1982

The Effect of Boat Holding Tank

Chemicals on Treatment Plant

Performance, John T. Novak, C. Russel

McDaniel, and Samuel C. Howard,

Journal of the Water Pollution Control

Federation,Volume 62, Number 3,

May/June 1990, pp. 288-295.

Toxicity of Additives Used to Control

Odors in Recreational Vehicle

Wastewater, Ervin Hindlin,

Washington State Transportation

Center, March 1994.

Contact

Pat Fleming

National Science and Technology

Center, Denver Federal Center

Building 50

P.O. Box 25047

Denver Colorado, 80225-0047

phone (303) 987-6856

fax (303) 987-6873

email Pat_Fleming@blm.gov.

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Resource Notes are intended to be early

announcements of technical and informational topics for

Bureau of Land Management personnel and some of their customers.

Information in this Resource Note is based on the opinion and

experience of the author and has not been peer-reviewed. Conclusions

and opinions expressed herein do not

necessarily represent those of BLM. Use of trade names does not

imply U.S. Government endorsement of commercial products.

If you have received a copy of or found out about Resource

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NAME, TITLE, MAILING ADDRESS and a list of the two or three

subject areas that you are most interested in or that most directly

relate to your job. Send this information to Phil Dittberner, BLM,

RS-140, P.O. Box 25047, Denver, CO. 80225-0047 or

phil_dittberner@blm.gov or FAX 303-236-3508.

If you would like to prepare a Resource Note for

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Thank you for your interest in Resource NoteS.

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1

The most thorough discussion of all aspects of holding tank and chemical toilet wastes is a 1984 manual published by EPA entitled

Septage Treatment and Disposal.