NOTES ON WATERLINE DIAGRAM – OHA TANKS
The Front View in the diagram shows the plumbing for the outflow from the tanks. The Back View in the diagram shows the plumbing for the fill.
NORMAL OPERATION – OUTFLOW
During normal operation, both the 4” outflow valve at the base of the large black tank, and the small ball valve at the base of the smaller white tank should be open. The supply from both tanks operate as a joint system and are plumbed together down the line.
The entire system is fed by both tanks simultaneously. The outflow is located at the bottom of both tanks. The plumbing associated with the top of the tanks is related to the plumbing system joining the two tanks as a single source.
Valve B should be OFF during normal operation. It is listed as
an overflow/drain line on the diagram. It is in fact a drain line for the entire system. It appears to terminate in Baby Bottle Pond. Valve B in off position pictured:
Valves A, C, and D should all be ON during normal operation. This will allow the system to be fed from both tanks. (B, C, D pictured below.)
Valve C controls the hydrant. Valve D controls the horse troughs down the line. Valve C & D can be shut off individually to control supply or to allow for troubleshooting. (See instructions for shut off below – care must be taken!)
EMERGENCY CONDITIONS
The tank configuration allows us 3 reserves – 2 tanks plus the pond – and the potential to directly tap the flow from the spring downhill.
It is useful to remember that this entire system goes from our marvelous spring on the border of Plateau, Pond & Sullivan all the way down to the horse troughs below. This drop downhill allows good water pressure anywhere along the line, even in emergencies when we are using back-fill from the pond to the hydrant on El Toyonal. The valves at the tanks control the distribution of the flow, but the drop downhill from the tanks is what makes the system work – as long as we have no major leaks.
— EB (as explained by Alberto Mendo) 11/17/16
VALVE SHUT OFF/ON
The double tanks provide water at a very high pressure to downhill lines that are somewhat fragile. Therefore great care must be taken when turning water on or off in this line. Be gentle and don’t force things. Follow this procedure to avoid bursting the lines:
TURN OFF – close valves very slowly and incrementally. You should be able to count out at least fifteen seconds while closing.
TURN ON
– Open the wharf hydrant and all spigots fed by tanks (this will decrease the line pressure when you turn the water back on);
– Open tank valves extremely slowly and incrementally. Count out five seconds for each quarter turn;
– Slowly close the wharf hydrant, then close each spigot, one at a time.
— Kerry Blackwell 6/28/17
NOTES ON LOWER PASTURE WATERLINE
The Lower Pasture waterline originates from the springbox directly below the water storage tanks, in the fenced enclosure on the east (downhill) side of Baby Bottle fireroad. The pipe can be seen where it goes underground into the trench dug by John Fouhey on the downhill side of the springbox enclosure. Note the cleanout and cutoff. 
The LP line is next seen in a valve box just up from the Taj Manure beside Baby Bottle Road. From there it goes under El Toyonal to another valve box behind the Tuff Shed, as described in the original AGP project plan for the LP line: OHA LP waterline. This plan was later modified for pipe to run above ground, skirt the ravine side of the LP Corral, and join the existing underground pipe to the concrete Lower Pasture trough as shown.
There is also valve box next to the Pond Singletrack, just up from the Red Barn Enclosure singletrack gate, which is NOT part of the LP line; it holds the pipe which feeds the stalls & corrals in the Pavilion, Ring Pasture, and Red Barn Enclosure and appears to come directly downhill from Valve D in the Tank Diagram.
— Erica 3/2/20
