Spring Water Gravel Pack Supplies
Introduction
An advanced method using gravel pack to improve spring water sources developed in Ecuador provides
high quality sustaining water supplies for rural communities. The design allows substantial adaptability
for the wide variety of spring water formations encountered throughout Ecuador and requires little if any
maintenance when well-constructed. Naturally filtered spring water precludes the entrance of most
pathogens into the water supply and most often avoids the need for water treatment which is not
practical for most rural communities in developing countries. Naturally filtered spring water contains
limited organic content minimizing the amount of chlorine required to disinfect the water and taste and
odor issues sometimes associated with chlorine disinfection. Hundreds of spring intake structures built
with pick and shovel by rural communities with technical supervision by experienced personnel provide
reliable clean water supplies.
This spring protection method bears similarity to a gravel pack well albeit constructed horizontally rather
than the vertical construction of a gravel pack well. This design approach includes:
●
●
●
collection of spring water subterranean using the aquifer and surrounding soil to filter the water
supply,
use of gravel pack to retain the surrounding aquifer materials and soil structure in place while
providing an easy flow path for water to enter a slotted collector pipe and flow to a receiving
tank without impounding spring water, and
protection of the collected spring water by covering the area with concrete to completely isolate
the water supply from surface water.
Studies by the Clean Water Institute of Calvin University (CWICU) indicates that this method provides
water deemed “No Risk” by the World Health Organization (WHO) in more than 50% of samples
collected. In comparison, no water samples collected from traditional spring capture methods achieved
this designation. This significant improvement provides motivation to disseminate information about this
method to promote wider use for rural water supplies. 1 2
Spring Protection Construction
Preparation
Evaluation of spring water sources includes measurement of the water quality and flow rate. The initial
results do not necessarily define the outcome, but rather only indicate of what can be expected.
Normally water quality improves after protecting the spring. The spring area can then be cleared of all
trees, stumps, and heavy vegetation.
To prepare for building the spring protection structure, a work force should be mobilized and all required
building materials conveniently available on site. Rural Ecuadorian communities customarily organize a
minga (work bee in English) in which all benefiting community members participate in the manual work.
Pea stone for the gravel pack should ideally be crushed stone 8 to 12 mm and free of fine particles and
sand to maximize voids so that water flows freely through the gravel pack. Gravel and concrete
1
2
World Health Organization
Ten Pas
aggregates should be stored on plastic sheeting to prevent them from mixing with topsoil or organic
materials. The necessary hand tools, construction buckets to place concrete and gravel, wheelbarrows,
and concrete mixer should be available. A flat area with a hard or impervious surface for hand mixing of
concrete should be prepared when it is impractical to use a concrete mixer.
Figure 1- Typical Spring Protection Structure
Basic Steps of Spring Protection Construction
The basic steps in building the spring protection structure are as follows.
1. Clear debris and vegetation from spring area.
2. Stockpile the estimated gravel and building materials required adjacent to spring.
3. Excavate spring area to expose water producing aquifer and the underlying less permeable
strata.
4. Place geotextile against the sides of the excavation to prevent soil sloughing into the excavation.
5. Place slotted collector pipe(s) appropriately to receive spring water.
6. Excavate for cutoff wall on the downstream side of spring.
7. Place washed gravel pack around and covering PVC collector pipe while also placing concrete for
cutoff wall.
8. Rinse gravel pack to remove fines and then disinfect gravel pack with high-strength chlorine
solution.
9. Place plastic sheeting over leveled gravel pack.
10. Place 8 cm of concrete on the plastic sheeting covering the gravel pack.
11. After the concrete cover cures, place excavated soil on concrete cover.
12. Build concrete/masonry collection tank to receive the protected spring water flow.
Excavation
The spring area should be adequately cleared of all debris and extraneous materials that could
contaminate or diminish the water quality. All loose stone, roots, soil, and organic matter should be
removed to expose the strata producing water. The water bearing strata should be excavated down to
the impermeable or less permeable underlying soil or rock layer.
Geotextile
After excavating the spring area, geotextile fabric can be used to line sides of the excavation to prevent
soil or loose material from sloughing into the excavation while the gravel pack and other materials are
placed. Large nails temporarily hold the geotextile fabric in place on the sides of the excavation. The
geotextile can be folded over the gravel pack after disinfecting the gravel pack. Openings in the
geotextile in areas of significant water flow allow those water streams to flow freely into the gravel pack
and collection pipe. Geotextile can be used on the floor of the excavation if necessary to stabilize the
underlying soil. Geotextile can be omitted in areas susceptible to root growth which can form a root mat
on the outside of the geotextile and impede water flow into the gravel pack.
Collector Pipe
The PVC collector pipe can be either a manufactured slotted pipe or be slotted in the field. Slots are
normally cut into the PVC pipe making 90 to 120-degree cuts at 1 to 2 cm spacing using a hacksaw. The
narrow width of the cuts or perforations allow water flow into the pipe while retaining the gravel pack.
The length and diameter of collector pipe should be sufficient to allow all spring water to freely enter the
pipe without ponding water higher than the center of pipe. If spring water ponds at an elevation higher
than its previous state, the risk exists that spring water may eventually find an alternate discharge route
reducing water flow or causing failure of the collection structure.
The collector pipe should be arranged with the necessary fittings and adequate branches to collect all
spring water produced. An open tee in the collector pipe is often placed immediately prior to the cutoff
wall to collect spring water behand the wall. Stones can be used to chock around open pipe ends to
prevent gravel from entering the collector pipe but allowing spring water to freely enter.
The unperforated pipe carrying spring water which extends downstream from the cutoff wall should be
sloped toward the collection tank. When the cutoff wall excavation is complete, plastic sheeting can be
cut for the upstream side of the cutoff wall with a hole for the collector pipe to pass through the plastic.
Gravel Pack
After installing the geotextile fabric, the slotted PVC collector pipe can be placed on gravel or granular
material, placement of the washed gravel pack around and over the pipe can begin. Gravel should be
washed adequately to flush out the fine particles before placement. The void spaces in the gravel pack
allow spring water to flow freely into the collector pipe. The extent of the gravel pack should be large
enough to minimize the velocity at the interface with the water bearing strata and prevent piping of fines
from the aquifer. Stones can supplement the volume of the gravel pack if necessary to reduce the
amount of gravel required to fill behind the cutoff wall. However, large stone should be separated from
the fragile collector pipe by a sufficient cushion of gravel pack to avoid damaging the pipe. Voids
between large stones should be filled with gravel to form an even top surface for the plastic sheeting to
be placed over the structure to form the concrete cover.
Cutoff Wall
Excavation for the cutoff wall should be done before placing the gravel pack. The 25 cm thick cutoff wall
should be keyed 30 cm into less permeable strata underlying the aquifer or to the depth practical to
prevent spring water flow from circumventing the collection structure. The cutoff wall should also be
keyed into abutments so that the water production area is completely enclosed, thus forcing the water
to enter the collection pipe. The concrete cutoff wall is constructed simultaneously during gravel pack
placement. The downstream side of the cutoff wall can be formed using conventional wood formwork
and plastic sheeting used on the upstream side, to separate the gravel pack and the concrete cutoff wall.
The weight of the gravel pack behind the cutoff wall provides essential pressure against the upstream
side of the plastic sheeting used to form the cutoff wall during placement of concrete. Figure X displays
this step being implemented in the field.
One of the construction challenges is that cutoff wall concrete must normally be placed in water. To
address this site, concrete should be placed as a stiff rich mix at one end of the trench excavated for the
cutoff wall to displace water out of the excavation while pouring the cutoff wall and minimizing
entraining water into the concrete. Dry concrete mix can be used as necessary.
Disinfection Rinse
When the cutoff wall is complete, the gravel pack should be rinsed with clean water and then disinfected
with a high-strength hypochlorite solution. Water discharged from the spring can be collected in buckets
and poured over the entire gravel pack surface multiple times until fines are removed and the water
discharged flows relatively clean. This reduces sediment and fine particles remaining in the gravel pack
after placement. Rinsing the gravel pack with hypochlorite solution reduces the presence of bacteria. A
hypochlorite solution of 300 ppm can be made using granular calcium hypochlorite or liquid bleach
(sodium hypochlorite). One tablespoon (5ml) of granular calcium hypochlorite mixed in 10 L of water
produces a 300-ppm solution. When preparing the disinfection solution, it is advisable to wear rubber
gloves and eye protection.
Spring Protection Cover
After disinfection of the gravel pack, plastic sheeting should be placed over the gravel pack and concrete
poured 8 cm thick to provide a protective concrete cover. The concrete cover should be keyed into the
surrounding soil structure so that neither rainwater nor surface water can penetrate the protection
structure without being filtered through the surrounding soil alluvium. Soil previously excavated from
the spring area should be placed over the concrete after it has adequately cured to further protect the
spring.
Trench Style Spring Protection
This spring protection method can be adapted to collect ground water produced over a larger area by
constructing a trench collector of the length necessary. Numerous spring protection structures of this
type can be used to collect spring water flowing to a single collector tank. Figure X shows a profile and
plan view of a spring protection structure used for localized springs.
The trench style spring protection structure can be built on an axis approximately perpendicular to
groundwater flow. On sloped spring areas, plastic sheeting placed on the downhill side of the trench
forces water to enter the collector pipe.
Figure 3- A Plan Schematic of a Trench Style