6.2 TOTAL EXISTING AND FUTURE STORAGE REQUIREMENTS

Table 6-1 shows a summary of the City's existing storage by zone.

Table 6-1
Existing Storage Capacity by Zone

Pressure Zone	Tank Name	Volume (MG)
Zone 1	Airport 1	4
	Airport 2 1	4
	Cemetery 1	2.5
	Sub-total	10.5
Zone 2	Grizzly 1	4
	Grizzly 2	4
	Old Bingham	2
	Sub-total	10
Zone 3	Barney's Wash 1	3
	Barney's Wash 2	3
	Zone 3 North 1	3
	Sub-total	9
Zone 4	Terminal 1	3
	Terminal 2	4
	U-111	4
	Sub-total	11
Zone 6	Bench	3
	Bingham Jct 1	3
	Sub-total	6
Total		46.5
1 Tank is not active, but is in construction and nearing completion at the time of this report

 

The evaluation of equalization, fire and emergency storage for existing conditions is shown in Table 6-2. The storage evaluation for existing and previously approved development is shown in Table 6-3 and for buildout conditions in Table 6-4 for the buildout planning scenario.

Table 6-2
Existing Storage Evaluation

Pressure Zone	Existing ERCs 1	Current Storage (MG)	Equalization Storage (MG)	Fire Storage (MG)	Emergency Storage (MG)	Total Storage (MG)	Surplus / (Deficit)
1	11,807	10.5	7.7	1.2	4.7	13.6	(3.1)
2	5,878	10	3.8	1.2	4.8	9.8	0.2
3	8,111	9	5.3	1.0	0.0	6.3	2.7
3A	410	0	0.3	0.0	0.0	0.3	(0.3)
3B	1,316	0	0.9	0.0	0.0	0.9	(0.9)
4	6,311	11	4.1	1.2	1.6	6.9	4.1
5	6,288	0	4.1	1.2	0.0	5.3	(5.3)
6	1,858	6	1.2	1.2	1.0	3.4	2.6
Total	41,979	46.5	27.3	7.0	12.1	46.4	0.1

 

Table 6-3
Existing & Previously Approved Storage Evaluation

Pressure Zone	Existing & Approved, Not Constructed ERCs	Current Storage (MG)	Equalization Storage (MG)	Fire Storage (MG)	Emergency Storage (MG)	Total Storage (MG)	Surplus / (Deficit)
1	12,329	10.5	8.0	1.2	4.7	13.9	(3.4)
2	5,950	10	3.9	1.2	4.8	9.9	0.1
3	8,609	9	5.6	1.0	0.0	6.6	2.4
3A	435	0	0.3	0.0	0.0	0.3	(0.3)
3B	1,396	0	0.9	0.0	0.0	0.9	(0.9)
4	7,618	11	5.0	1.2	4.8	11.0	0.0
5	8,463	0	5.5	1.2	0.0	6.7	(6.7)
6	3,815	6	2.5	1.2	1.0	4.7	1.3
7	0	0	0.0	0.8	0.0	0.8	(0.8)
Total	48,615	46.5	31.6	7.8	15.3	54.7	(8.2)

 

Table 6-4
Buildout Storage Evaluation

Pressure Zone	Buildout ERCs	Current Storage (MG)	Equalization Storage (MG)	Fire Storage (MG)	Emergency Storage (MG)	Total Storage (MG)	Surplus / (Deficit)
1	12,800	10.5	8.3	1.2	4.7	14.2	(3.7)
2	6,106	10	4.0	1.2	4.8	10.0	0.0
3	8,631	9	5.6	1.0	0.0	6.6	2.4
3A	414	0	0.3	0.0	0.0	0.3	(0.3)
3B	2,102	0	1.4	0.0	0.0	1.4	(1.4)
4	15,178	11	9.9	1.2	4.8	15.9	(4.9)
5	11,621	0	7.6	1.2	0.0	8.8	(8.8)
6	6,869	6	4.5	1.2	1.0	6.7	(0.7)
7	2,532	0	1.6	0.8	0.0	2.4	(2.4)
Total	66,253	46.5	43.1	7.8	15.3	66.2	(19.7)

 

The tables show a storage evaluation by zone, as well as for the system as a whole. As mentioned previously, it is not required that all storage be in the exact zone that it is needed, as long as the water can be transferred to the zone. The City's pressure zones are all connected by PRVs, such that any higher zone (Zone 7 being the highest and Zone 1 being the lowest), could pass water to the zone below it.

In the City's existing system, the analysis shows a slight overall surplus of 0.1 million gallons. At an individual zone level, Zones 1 and 5 show specific deficiencies. Zones 3A and 3B also show deficiencies, but are sub-zones of Zone 3, which has adequate storage to accommodate these sub- zones.

Zone 1 shows a current deficit of 3.1 MG. The City is in the process of adding second storage tank at the Cemetery site, which will add 3.0 MG of storage to the zone and reduce the current deficit. Zone 5 does not currently have a storage tank, but a 4.0 million gallon tank is in the process of design and construction and will reduce the 5.3 MG shortage. Once this storage is complete, there will still be a small storage deficiency in the zone. However, Zone 6 has enough surplus that it will be able to provide the storage currently needed by Zone 5, which is how the system is currently operated.

When approved development is added to the existing storage analysis, the slight surplus changes to a 8.2 MG deficit. Specifically the deficits in Zones 1 & 5 increase and there is no longer enough surplus in Zone 6 to provide for Zone 5. It is necessary to construct currently planned additional storage to provide this development that has already been approved.

In the buildout scenarios, the analysis shows a total system deficit of 19.7 million gallons. When each zone is analyzed separately, potential deficits are identified in Zones 1, 4, 5, 6, and 7. A zone specific analysis for these zones shows whether or not additional storage is needed:

   •   Zone 1 is the City's largest existing zone and will have total storage volume of 13.5 million gallons when the second Cemetery tank is completed. Despite the large volume of storage, the analysis indicates the zone will be about 0.7 million gallons short of projected needs at buildout. However, there are two reasons that constructing additional storage in this zone is likely not needed. First, the fire storage for this zone (1.2 MG) is greater than the calculated short fall and is the same as the fire storage requirement for Zone 2. The fire storage in Zone 2 could be made available to Zone 1 and the deficiency eliminated. Second, Zone 1 includes 4.7 million gallons of pump station operational storage. While this storage is desirable, it is not a strict requirement and could be trimmed slightly to eliminate the apparent deficiency. Given these considerations and the relatively small volume of the shortfall, no additional storage is recommended in Zone 1 at buildout.

   •   Zone 4 is expected to see significant growth as the City approaches buildout. While the zone currently has a 4.1 MG surplus, that is expected to become a 4.9 MG deficit by buildout. To accommodate the future growth in this zone, an additional 4 MG of storage be constructed in this zone. Similar to the discussion in Zone 1, the remaining deficit can be considered as a part of overall needs in higher zones.

   •   Zone 5 shows a deficit of 8.8 MG at buildout. The City does not currently have any storage in this zone and storage is handled by the Zone 6 tanks. To reduce the reliance on the Zone 6 storage, the City is in the process of constructing a 4 MG tank to serve Zone 5. However, this leaves a 4.8 MG deficit at buildout, even after the tank for the zone is completed. The City is also planning an additional 3.0 MG storage tank in Zone 6, which will then have surplus storage that can be used to satisfy at least a portion of this deficiency. If excess Zone 6 storage is applied to Zone 5, the deficiency is reduced to about 2.5 million gallons. Based on this conclusion, it is recommended that the needs of both Zone 4 and Zone 5 be addressed through the construction of up to 4 million gallons of additional storage in Zone 5.

It should be noted that it is not always prudent to rely on storage from an upper zone to satisfy deficiencies in a lower zone. Specifically, when a zone does not have enough storage to satisfy its own equalization storage, this practice can result in having to deliver water from a higher zone on a daily basis, which wastes energy and pumping capacity. However, as long as the carry down storage is associated with rarely used emergency or fire flow storage, accounting for this storage in an upper zone is a reasonable approach. With the recommended construction of storage in Zone 5, it will have adequate storage to satisfy its own equalization storage and use of excess storage in Zone 6 is reasonable.

   •   Zone 7 does not currently have any storage or demand. Prior to connecting any services in this zone, a storage tank will need to be constructed. Based on the projections of this report, that needed storage will be two approximately 2 MG tanks.

Based on the conclusions above, a summary of the buildout storage requirements for the City's projected growth are shown in 6-5.

Table 6-5
Additional Storage Needed at Buildout

Pressure Zone	Tank Site	Additional Storage at Buildout (MG)
Zone 1		3
	Cemetery 2	3
Zone 3		3
	Zone 3 North	3
Zone 4		4
	U-111 2	4
Zone 5		8
	Zone 5 North	4
	Zone 5 South	4
Zone 6		3
	Bingham Junction 2	3
Zone 7		4
	Zone 7 North	2
	Zone 7 South	2
Total		25