This week, TME Looks Back: Vietnam examines “Water for Vietnam” from the March-April 1967 issue of TME. Authored by two officers of the U.S. Navy Civil Engineer Corps, the article looks at the growing requirements for water by U.S. forces in Vietnam and how engineers were providing solutions throughout the area of operations.
The article appears below in mobile-friendly form.
In the summer of 2016, SAME will publish a special issue of The Military Engineer commemorating the service and contributions of military engineers in the Vietnam War. As part of the run-up to the publication, we will be featuring on Bricks & Clicks a special series entitled TME Looks Back: Vietnam featuring past articles, photos, advertisements, covers, and other material that first appeared in the magazine during the 1960s and early 1970s. [The TME editorial staff welcomes input as we develop the Vietnam Commemorative Issue. Contact Stephen Karl at firstname.lastname@example.org for more information or click here to contribute editorial content. Contact Stephanie Satterfield at email@example.com for sponsorship/advertising inquiries.]
Water for Vietnam
By Lt. Cdr. D.W. Harned, CEC, USN, and Lt. j.g. M.H. Ramaeker, CEC, USN
Concomitant with the build-up of American military forces in Vietnam, there has been a massive well-drilling program. Streams and shallow wells supplied the needs of the first troops to arrive, but as airfields, ports, and base camps were developed the requirement for more extensive and permanent sources necessitated the development of subterranean water supplies.
Criteria of the Military Assistance Command, Vietnam (MACV), authorize 50 gallons of water per capita per day (gped) in facilities without waterborne sewage, and 100 gped for cantonments which have conventional piped water and sewage systems. Since most of the installations do not have such systems, the aggregate ground-water demand in Vietnam is about 30,000,000 gallons a day (mgd), making due allowance for the substantial supplies from municipal systems, surface-water purification units, and Vietnamese wells. Well requirements at most sites were based on the 50-gped criteria and an estimated yield of 60 gallons per minute (gpm) per well throughout the country. In the light of experience as the drilling progressed and geological studies were made, the demand and the scope of the drilling were adjusted.
Military forces in Vietnam do not delay tactical operations because of water-supply problems. Under field conditions, units frequently operate on 5 gped or less. One small installation with piped water and sewage has operated on a 30-gped potable supply. Well production is sometimes limited by available pumping, storage, or trucking equipment, and, in rare cases by restricted treatment facilities, but all wells will be used to capacity when the necessary support is available.
The well drilling directed by the Officer in Charge of Construction (OICC) was divided into three elements: The major part was under contract to RMK-BRJ construction combine which provided complete wells; another contractor was engaged in exploratory drilling; and four rigs were operated seven months by the Seabees of MCB-4 and MCB-133.
South Vietnam has five major landforms that trol the rainfall runoff and ground-water storage. The lowest landform is the vast Mekong Delta, extending from a few meters above sea level to more than 1,500 feet below sea level. Underlying the recent deltaie sediments is an Old Alluvium which rises to the sun. at Saigon and forms a rolling terrace extend northward into Cambodia. The terrace is bordered by a plateau of black basalt and red soil, which also covers extensive parts of the Central Highlands. Towering above the plateau are the Annam Mountains, forming several ranges in the central and northern parts of Vietnam. Valleys in these mountains and the along the sea are filled with Recent Alluvium, underlain in places by Old Alluvium, following the coastal plain (Figure 1).
First observations of the region might indicate a plentiful water supply readily available for development. The mountain streams do flow abundantly during the rainy season but meagerly during the dry months. Base flow runoff is low. The streams are only sustained by ground-water storage. Most of the soils have a low infiltration rate because they are irony laterites and weathered rock that shed water easily. Transportation and evaporation consume 80 percent of the rainfall in some areas. The rice fields of the delta, supplied by the Mekong River system and tidal inflow from the sea permit salt-water intrusions over 100-km inland.
The tropical climate of Vietnam has a highly varied rainfall pattern. This produces a cover ranging from humid rain-forest jungle to semiarid desert of cacti and palms. The broad delta allows full sweep of the southwest monsoon, with moisture-laden winds blowing in from the warm Gulf of Thailand. This results in rain for six months in a summer thundershower manner, exemplified by the records for Bein Hoa in the delta and Pleiku in the highlands. The northeast monsoon blows from the Asian interior, Siberia, and Mongolia. The winds circulate east and south across the South China Sea to the Vietnam coast line. During January through April these winds are cool and dry, and there is little rain throughout the country in these months. The coastal areas, such as around Da Nang, Qui Nhon, and Cam Ranh, derive their principal rainfall during the transitions between monsoons.
VIETNAMESE WATER SUPPLIES
Most Vietnamese cities have relied on surface water supplies, with treatment plants in the more prosperous communities. River and canal water, often polluted by undesirable effluents and contaminated by salt water part of the year, provides an estimated 75 percent of the basic needs for a typical Vietnamese demand of about 10 gped. Many people in hamlets and small towns draw water from shallow dug wells. In some places during the dry season, these wells become brackish as intrusion occurs from nearby tidal streams. A few rudimentary sewage systems exist, but only in parts of a few major cities. Inadequate water supply of degraded quality has contributed to water-borne disease among the populace.
The Vietnamese are competent in constructing concrete-lined dug wells of about 1 meter in diameter. Such wells usually yield about 15 gpm. It is difficult to protect dug wells from pollution and from surface runoff. But they can be constructed at low cost with simple equipment, and the yield is sometimes adequate for the purposes intended, so they remain the dominant native small-demand sources in Vietnam.
Because major logistic efforts must rely on beachheads and port areas, special water-supply problems arose all along the coast of Vietnam, at such places as Da Nang, Qui Nhon, Tuy Hoa, Cam Ranh, and Vung Tau. The sand-bar deposits there are impressive in appearance but are very delicate water sources. Unlike the clay soil of the mainland of Vietnam, these areas are covered by sand with a very high infiltration capacity, accepting about 75 percent of the rainfall with little or no surface runoff, and losing only about 25 percent to evaporation and transpiration. Rainfall filters in to recharge a fresh water lens, which dynamically floats on salt water in deeper aquifers. When a well in the fresh water lens is pumped, it creates a drawdown in the water table around it which is reflected by a rapid rise in the salt-water level below: a rise which creates a danger of salting out the flow of the well. The subsurface geology must be thoroughly studied, the rates of permeability and storage of the sands calculated, and the spacing, depth, and yield of the wells controlled to afford the best production without damaging the system.
Ground-water quality varied widely, but many wells had water which was usable for most purposes. Ground-water in Vietnam is generally soft, of low alkalinity or acidity, and sometimes high in dissolved carbon dioxide (thus somewhat corrosive). There were occasional problems with hydrogen sulfide and iron. But most of the wells were usable with only chlorination treatment. Quality problems were generally less important than quantity, especially since even the non-potable wells were used for showers, vehicle washing, and other utility purposes. As would be expected in properly constructed wells averaging 170 feet in depth, there were no bacteriological quality problems. Well sites were selected with due attention to the existing or planned sewage systems.
Getting representative raw water samples and consistent laboratory analyses was a common difficulty. Most samples were examined by military public health units using field test kits. Reasonable evaluation of water quality was aided by military sanitary engineers throughout the country. In some places where several wells were connected to a central treatment and distribution system the quality in individual wells was not of significant concern in the blended water. In several cases, wells which were degraded with salt water up to 700 ppm chlorides were successfully used in potable systems by mixing their supply with water from other wells low in dissolved solids. At one site shallow large-diameter wells constructed on a sand bar adjacent to a typical turbid lowland river yielded water which was derived mainly from the river but required only a little treatment, as opposed to the rather extensive treatment required on most surface water sources in Vietnam.
The tidal salt-water intrusion into coastal streams is One of the most difficult water quality problems in Vietnam. The phenomenon is very complex, difficult to evaluate quantitatively in any short-range monitoring, and hazardous to predict from a few isolated water tests. Previous studies were analyzed to give an idea of the intrusion of salt water in river estuaries. Dual potable and nonpotable systems were constructed in some small cantonments where fresh-water sources would not sustain an adequate conventional system. Desalinization was used at one site.
THE DRILLING PROGRAM
The French introduced deep well drilling to Vietnam in the 1930’s, developing high-capacity wells for Saigon and some other cities. The United States Agency for International Development sponsored well drilling for the Vietnamese Directorate of Water Supply beginning in 1957. By 1966, a total of 1,830 wells had been drilled throughout the country, yielding 10 to 60 gpm, at an average depth of 100 feet.
Because major logistic efforts must rely on beachheads and port areas, special water-supply problems arose all along the coast of Vietnam, at such places as Da Nang, Qui Nhon, Tuy Hoa, Cam Ranh, and Vung Tau. The sand-bar deposits there are impressive in appearance but are very delicate water sources.
The American military forces had to develop their own water supply for the big construction build up because of the limited drilling resources available in Vietnam. The plans included extensive exploration but in view of the imperative need for water, exploration holes were developed into useful wells where. possible. In addition to the major work by contract, a small part of the well requirements were met by drilling detachments assigned to the military engineer construction units.
The program of drilling in the II, III, and IV Corps areas was directed by the OICC in Saigon; drilling in the I Corps was largely by Navy Seabee. units. Most of the contract drilling was in support of cantonments of the Army, a lesser part for Air Force facilities, and a few wells for other American activities. Specific sites for drilling were selected by reconnaissance parties consisting of an hydrologist or engineer, the respective sponsor’s water co-ordinator or local engineering staff, and often a representative of the drilling contractor. The sites were staked in the field at places dictated largely by troop needs, modi. fied by hydrologic considerations.
Wells were 8 inches in diameter, and were drilled with rotary rigs. Most of the exploratory holes were completed as wells, with 20 feet of wire-wound screen in a gravel-packed 15-inch hole. Pumps were installed by military engineer units. Wells drilled by the construction contractor were usually completed with 30 to 120 feet of shutter-type screen in a 17-inch gravel-packed hole. After development and testing, pumps sustained yield from a well, be tailored to the particular character the well and the distribution requirements.
To obtain maximum sustained yield from a well, the pump must be tailored to the particular characteristics of the well and the distribution requirements. While this was not entirely possible in Vietnam, stocks included pumps of several sizes from which the most suitable could be selected for each well. In most cases this system was satisfactory, especially since at the start of operation, potable water production was often limited by treatment or storage facilities Determining the proper pump size was sometimes difficult because of problems in accurately measuring yield.
The Army. Navy, and Air Force all have well-drilling sections in Vietnam. The Army engineer units are equipped with cable-tool percussion rigs which are more suited to rock drilling than work in the soft alluvial sediments in Vietnam. The Air Force Red Horse team drilling detachments use rotary rigs. The seabee units were equipped with combination rotary percussion rigs. The limited supplies, geological assistance, and equipment prevented military units from being able to meet the initial immediate requirement for some three hundred wells but, in spite of obstacles, the military drillers contributed appreciably to the program. With additional experience and the development of basic hydrological data, the military drilling teams’ performance will improve.
Engineering investigations were carried on concurrently with drilling to evaluate various related water resources. The possibility of using jet-driven wells in several areas was considered, a few large-diameter wells were studied, and hydrological reconnaissance was conducted to determine whether the drilled well program would be practical. Investigations into suitable desalinization systems were made for areas where the ground and surface waters are often brackish.
The supply of drilling mud was a particular problem. No bentonite was available in the country, and local kaolinite muds were inadequate. Until supplies of commercial muds were obtained, it was difficult to prevent the collapse of holes drilled in sedimentary materials. And in several places it was hard to maintain a supply of proper gravel for well-packing. Angular coarse sand and crushed rock sometimes had to be used as unsatisfactory expedients. The transportation of materials from the United States and inside Vietnam was hindered by priorities and shipping problems.
The Army. Navy, and Air Force all have well-drilling sections in Vietnam. The Army engineer units are equipped with cable-tool percussion rigs which are more suited to rock drilling than work in the soft alluvial sediments in Vietnam. The Air Force Red Horse team drilling detachments use rotary rigs. The seabee units were equipped with combination rotary percussion rigs.
For the most efficient operation, the rig superintendents were American drillers and the roustabouts ” local Vietnamese or nationals of other countries. Administrative control was hampered by uncertain communications and travel difficulties.
After the decision was made to provide major water supplies from drilled wells, the work was speeded to keep up with the military build-up. Twenty-one rigs were mobilized, starting in July 1966, and, in spite of many delays, by December 1966, all units were operating. Although there was little direct enemy activity, local base security sometimes permitted only twelve hours of operation. Critical requirements had been met by April, and the program was completed in September 1967.
The initially assumed yield of 60 gpm per well was modified as drilling progressed far enough to permit reassessment at each site. The overall anticipated yield was generally exceeded, as shown in Table 1, but large production wells are unusual in Southeast Asia. The average producing well yielded about 95 gpm; the highest reported test yield was 300 gpm. Wells exceeded 200 gpm only at a few sites. A primary aim was at least a modest yield from each attempted well. A success rate of 83 percent of the total holes drilled (Table 1) is noteworthy under the circumstances and in comparison with earlier drilling programs. As most wells are of moderate depth, their yield is increased during the rainy season, and all wells show significant seasonal recharge.
Deep drilling to more than 1,000 feet was limited to two wells in the delta. Most holes were near the average depth of 170 feet. Amounts of screen used varied considerably, depending upon the transmissibility of the aquifer. In exploration, the wire-wrapped screen permitted a greater circumferential intake area per unit length, while in construction the contractor and Seabees relied more on the shutter-type screen. There appears to be no difference in economics and yield between the two types, and the selection is a matter of preference between drillers and hydrologists.
Six months after the start of mobilization, peak production was reached, with wells being completed at a rate of nearly two a day. The yields increased faster than the number of producing wells, reflecting improvements in successive well design and development, resulting in an average of 10 percent more water from the later wells.
The exploration drilling contract was based on a cost-per-foot basis and the construction contract drilling was based on cost per rig per day.
This ground-water development program extended from July 1966 through September 1967, during which time 233 successful wells and 48 test holes were drilled at 25 sites. The scope of this work is reflected in the total depth drilled, 47,800 feet.
Most available data, specimen samples, and related water analyses records for the ground-water development for American forces in Vietnam are maintained at the Saigon office of the OICC. A library of some 7,500 drilling strata samples, 150 graphical sand logs, and 400 water test reports has been compiled. The inherent unknowns of any water-resources program in an underdeveloped country present significant obstacles, and a centralized collection of records is invaluable to geologists and engineers. Drilling samples and test pumping data may be studied and information extrapolated for unexplored areas. Basic hydrological data are being recorded on a special series of 1:25000-scale maps by the American Army Engineers in Vietnam. When in full operation, this system will be useful in furthering the success of well drilling in Vietnam.
[reprinted from TME / March-April 1967]