22-WTP_PipeExam.pdf

T E C H N I C A L M E M O R A N D U M

Fort Irwin - Bicycle Basin Pipe Spool Examination PREPARED FOR: USACE WTP Project

PREPARED BY: CH2M HILL

COPIES:

DATE: 19 March 2012

The following summarizes Pipe Coupon analysis and investigation performed by CH2M HILL in 2007.

Background A 5-foot section of 16-inch water pipeline from the Bicycle Basin wells was removed for inspection. Two small pieces of detached mortar lining were sent to Seattle for visual examination. The spool piece was removed approximately 2 to 3 weeks prior to delivery of the lining specimens to the Seattle office on July 18, 2007.

The pipeline was approximately 30 to 35 years old, and was mortar-lined inside and out (thin-wall, spiral wound reinforced, concrete cylinder pipe). The water is not chlorinated at this point in the Domestic Water distribution system, so this spool piece is not necessarily representative of the overall Domestic Water distribution system.

The two small pieces of interior lining were examined, and the observations are described below.

Visual Examination Both specimens were layered (stratified) and were similar in appearance, so the observations apply to both pieces of the interior mortar lining.

Four stratified zones are evident and each is described below.

a. Layer closest to the pipe wall – The mortar lining was comprised of a portland cement-sand aggregate mixture approximately 5/8-inch thick.

b. Dark grey layer above the mortar lining – A 1/16-inch layer looked like it had been applied intentionally as a coating over the coarser mortar substrate. It did not contain sand or other aggregate material, but bound to some of the sand grains from the interface with the underlying mortar layer. An elongated void, apparently a trapped air bubble, suggests this layer was applied, and was not a water-formed deposit.

c. “Ivory-white” deposit above the dark grey layer – An ivory-white deposit approximately 1/32-inch thick appeared to be a water-borne deposit because it had a faintly layered texture. An area of cross-plane spallation showed that there was a very thin transitional zone between the ivory-white layer and a more recently deposited rust-colored layer in contact with the flowing water. This transitional zone

FORT IRWIN - BICYCLE BASIN PIPE SPOOL EXAMINATION

contained at least two thin dark bands, similar to the rust layer at the water-pipe interface.

d. The inner-most layer (liquid-solid interface) – This layer had a reddish-brown caste and was too thin to be measured with the available tools. If this layer could be separated from the underlying layer, a micrometer would be needed to measure its thickness. What is puzzling is that only this outer layer is distinctly discolored and not the underlying layers. This indicated that the appearance of the iron and/or manganese is a relatively infrequent event, having occurred only one or two times relatively recently.

A senior CH2M HILL engineer was consulted about mortar-lined pipes and they indicated single mortar layer is the norm, but sometimes a second coating is applied.

This further indicated that the ivory-white and reddish-brown layers were depositional, but that the dark grey layer could have been applied as a coating over the main mortar lining.

Reaction of Layers to Acidification Dilute Acetic Acid One of the mortar-lined specimens was exposed to white rice vinegar at each of the 4 layers.

No effervescence characteristic of calcium carbonate occurred; instead the liquid was absorbed into each of the layers.

Concentrated Hydrochloric Acid The four individual layers of same specimen were exposed to concentrated (approximately 30 percent) hydrochloric acid, and this time, each layer effervesced.

Effervescence is an indication that calcium carbonate is probably present, and that the two inner-most layers (the ivory-white and the reddish brown layers) were deposited from soluble, water-borne constituents. This is a little surprising because recent Bicycle Basin samples were low in calcium, and the water was apparently not supersaturated with calcium carbonate. (LSI was negative in some samples, indicating that calcium carbonate should not be deposited in the line.)

The original mortar lining effervesced, which is typical of concrete that has been in place for a length of time. The dark grey layer also effervesced, which indicated it, is also concrete-based material, and for reasons previously noted, was probably a protective layer over the coarse mortar lining in contact with the pipe wall.

The thin, surficial, reddish brown layer also effervesced, indicating it, too contained calcium carbonate. This inner-most layer (in contact with flowing water) appeared to be depositional, as noted above.

Conclusions

1. The two layers closest to the pipe wall were probably applied during manufacture of the mortar-lined pipe.

2. The third, “ivory-white” layer is probably depositional and contains little, if any iron or manganese, based on color.

FORT IRWIN - BICYCLE BASIN PIPE SPOOL EXAMINATION

3. The inner-most, reddish-brown layer is probably depositional, but the origins of the iron and/or manganese it contains cannot be explained with certainty. There are two likely explanations:

i. There has been a change in groundwater chemistry, leading to more iron and/or manganese, and/or a lower percentage of calcium carbonate than occurred in earlier deposits. (This seems unlikely because the aquifers are believed to be oxidized, which would not be conducive of dissolution of iron and/or manganese.)

ii. Pipes, well pumps or well casings have begun to corrode, leading to discoloration or the inner-most layer of deposited solids.

4. This spool piece may not be representative of lined sections in the Domestic Water distribution system because the water has not been chlorinated.

5. The (presumed) iron oxide-rich surface layer is likely to have absorbed some arsenic from the groundwater. However, the iron-arsenic minerals that form are insoluble and would typically be unaffected by the altered water produced by the new water treatment facility.