Guidance Manua pdf
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- 7.3 CASE STUDY 2 - HIGH MIB "HOT SPOT" ALONG ARIZONA CANAL
- 7.3.2 Diagnosis
- 7.3.3 Treatment Selection
- Jul Aug Sep Oct Nov
- 7.3.4 Treatment Application
- 7.3.5 Follow-up Monitoring
56 0 20 40 60 80 100
120 A-99 N-99 F-00 M-00 A-00 N-00 F-01 M-01 A-01 N-01 J-02 M-02 MIB Concentration (ng/L) R8 R9A R9B R10
0 10 20 30 40 50 60 70 80 A-99 N-99
F-00 M-00
A-00 N-00
F-01 M-01
A-01 N-01
J-02 M-02
MIB Concentration (ng/L) R13
R14 R16
290 ng/L
that fall. MIB concentrations were somewhat higher in the CAP canal between September and November of 2001 due to MIB coming from the Colorado River (15 ng/L), but not from Lake Pleasant. MIB concentrations in the Arizona canal were maintained at < 30 ng/L at Squaw Peak WTP. Switching production from Deer Valley WTP to Union Hills WTP prevented any necessity to treat high MIB concentrations in water that would have otherwise reached Deer Valley WTP (Figure 7-2).
Figure 7-1. MIB in Salt River cluster (Saguaro Lake) from August 1999 through March 2002.
Figure 7-2. MIB in Arizona canal (SRP cluster) from August 1999 through March 2002. MIB in January 2002 (R16) was 290 ng/L.
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Throughout June and early July of 2001 significant production of MIB was observed in the Arizona Canal between Squaw Peak WTP and Deer Valley WTP, a distance of roughly 10 miles along the canal (Figure 7-3).
0
20 30 40 50 60 70 80 90 100 0 5 10 15 Distance (miles) MIB (ng/L) MIB-(6/26/01) MIB-(7/3/01) MIB-(7/8/01)
Figure 7-3. Increasing MIB along the Arizona Canal between Squaw Peak and Deer Valley WTPs
To determine the exact amount of MIB produced in the canal over time, Figure 7-4 was developed. It shows the MIB production between these two WTPs. Net MIB production was calculated as MIB concentration of raw water at Deer Valley WTP minus MIB concentration of raw water at Squaw Peak WTP.
58 -20 0 20 40 60 80 100 Net Change in MIB (ng/L)
Figure 7-4. Calculated net production of MIB in Arizona Canal between Squaw Peak and Deer Valley WTPs, by month, before, during and after canal brushing and copper application. 7.3.2 Diagnosis Based upon Figures 7-3 and 7-4 it was obvious that MIB was being produced in this section of the canal. SRP was contacted as to the pumping status of groundwater wells located around Central Avenue. We were informed that the wells which contained nitrate were in fact being operated (Well #12.5E13.1N has 12.6 mg NO 3 -N/L; Well #12E13.3N had 7.0 mg NO 3 -N/L). However the wells could not be turned off due to downstream water demands and lack of hydraulic capacity in the upper Arizona Canal to convey more surface water.
The canal management “toolbox” included several options, each of which are described for the above scenario:
1. Reduce nitrate input into canal from groundwater pumping. Based upon discussions with SRP this was not deemed feasible due to lack of surface water supplies (drought period) in conjunction with limited hydraulic capacity at the head of the Arizona canal for increased flow of surface waters. Nitrate-rich groundwater could not be diverted, and was probably a factor for the MIB production in this section of canal.
Cu
2+ on 7/9-10 at 7th street Canal
brushing
Cu 2+ on 8/24 at 56th street
Canal brushing: 8/1-2/01 (24th St - Central); 8/14-17/01 (24th St - 29th Ave) (Net change in MIB = MIB at 29th Ave - MIB at 24th St.)
59 2. Mechanically remove periphytic (attached) algae from canal walls. Mechanical brushing of canal walls was deemed feasible. Visual observations of the canal indicated a 3 to 6 cm thick mat of attached (periphytic) algae on the sides of the canal. SRP was contacted to schedule mechanical brushing. An approximately 2- week lead time was required.
3. Apply liquid biocides to canal water. Liquid copper addition was considered feasible for control of attached algae. It would be preferable to add copper after mechanical brushing removed dense algae from the canal walls. Copper would treat the walls and bottom of the canal.
4.
Apply fixed biocides to canal walls during canal dry-up. This option was only deemed feasible during canal dry-up (December to January), so this option was not implemented.
5. Shift finished water production to WTP with lower T&O levels. Deer Valley WTP was scheduled for a construction plant shut-down in September 2001, and had to be on-line during part of July 2001 for quarterly regulatory monitoring. After discussions with City of Phoenix water production staff it was decided that Union Hills WTP on the CAP Canal could increase production earlier and allow Deer Valley WTP to go off-line sooner. This would decrease the number of days Deer Valley WTP had to operate, and treat water with potentially high MIB levels. This option was implemented.
Several treatment options were implemented. Mechanical brushing was conducted on July 19-21, August 1-2 and again on August 14-17. Copper addition was applied between Squaw Peak and Deer Valley WTPs on July 10, 2000, at 7 th Street for 6 to 8 hours. Copper was also applied above Squaw Peak WTP throughout August and October (56 th Street and Beeline Highway) to address MIB “hot spots” further upstream. Copper residuals of 0.3 to 0.7 ppm were monitored for 5 to 7 miles downstream of the copper application point. Reductions in attached (periphytic) algae biomass indicated that both copper and brushing were effective for the duration of the application (2 to 3 weeks). Switching of water production to Union Hills WTP also proved very effective.
Figure 7-4 shows that after implementation of in-canal treatments the MIB production in the Arizona Canal between Squaw Peak and Deer Valley WTPs was maintained at < 5 ng/L. Later in the summer, as Deer Valley WTP production was shifted to other City of Phoenix WTPs, no further canal treatments along that section were implemented. MIB production in the canal increased again, but had no impact on the City of Phoenix’s water treatment plants. A combination of in-canal treatments and shifting production was effective at minimizing MIB levels entering the WTPs.
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