Why is coolant leaking on passenger side and vibration in main pulley. Is it the water pump?

I'd have to see it in person to comment. The water pump is on the passenger side of the van.
A mechanic would fill the cooling system then pressure test it for leaks.

Drain all the coolant.Jack up the car on the front passenger side.Remove the passenger side wheel.Put a jack under the oil pan.Detach the engine mounts on the passenger side of the car.Remove all external belts.Remove the upper timing belt cover boltsLower the engine using the jack.Remove the water pump pulley. (3 bolts)Remove the upper timing belt cover.Disconnect the coolant line running across the front of the engine from the water pump. (2 bolts on a flange)Pull the timing belt.Pull the water pump.Installation is just reversed.

This leaking on the passenger side sounds like possibly the water pump. I THINK that this is a cross-mounted engine, with the drive belt on the passenger side. If so, it is almost certainly the water pump leaking. Get a flashlight and a small inspection mirror and search around under the water pump drive pulley for signs of water dripping. If no water is found there, it probably is not the pump. Have you checked the cooling fans for proper operation? Tested the temperature sender that controls the cooling fan?

The pulley that releases tension is on the passenger side and has a 1/2" square breaker bar hole to put a 1/2" breaker bar (2 feet long) into that you can get from Sears or an auto parts store that sells tools.

I would check the fluid level in the overflow tank to make sure there is enough coolant in the system.

Then, I would consider having it flushed and filled with new coolant.

I would check for slow leaks out of the water pump area on the passenger's side. There is an oil and coolant cover gasket on the side of the engine that sometimes leaks in the vicinity of the water pump.

We have a 1998 Ford Taurus that had this problem, and it took a few hundred dollars to fix the leak.

Yes,it can,if the bearings in the water pump are shot.

Water Pump REMOVAL & INSTALLATION VG30E Engine The water pump is located in the front center of the engine. Fig. 1: The timing belt cover must be removed to fully access the water pump
NOTE: Be careful not to spill coolant on the timing belt when performing this procedure.

1. Drain the cooling system through the drain plug at the bottom of the radiator, and the drain plugs on both sides of the block. CAUTION
   Never open, service or drain the radiator or cooling system when hot; serious burns can occur from the steam and hot coolant. Also, when draining engine coolant, keep in mind that cats and dogs are attracted to ethylene glycol antifreeze and could drink any that is left in an uncovered container or in puddles on the ground. This will prove fatal in sufficient quantities. Always drain coolant into a sealable container. Coolant should be reused unless it is contaminated or is several years old.
   
2. Remove the upper radiator hose.
3. Loosen and remove the drive belt(s) from the water pump pulley.
4. To make the operation easier, remove the timing belt cover. If necessary, remove the thermostat housing and gasket for access.
5. Remove the water pump-to-engine bolts (noting different lengths) and remove the pump. If the water pump has excessive end play or rough operation, replace it. To install:
   
6. Clean the gasket mounting surfaces.
7. Use a new gasket and coat the gasket with sealant. Reinstall the pump and torque the water pump-to-engine bolts evenly to 12–15 ft. lbs. (16–21 Nm).
8. If the thermostat housing was removed, install it with a new gasket. Install the cruise control unit if removed.
9. Install the tensioner, tensioner bracket, air conditioning belt and adjust the belt correctly.
10. Install the upper radiator hose.
11. Refill the cooling system. Connect the negative battery cable.
12. Start the engine, run to normal operating temperature and check for the correct coolant level and for leaks.

VE30DE Engine The water pump is located in the front center of the engine. Fig. 2: Water pump location and torque specifications — VE30DE engine

1. Remove the splash shield on the passenger side of the vehicle.
2. Drain the cooling system. CAUTION
   Never open, service or drain the radiator or cooling system when hot; serious burns can occur from the steam and hot coolant. Also, when draining engine coolant, keep in mind that cats and dogs are attracted to ethylene glycol antifreeze and could drink any that is left in an uncovered container or in puddles on the ground. This will prove fatal in sufficient quantities. Always drain coolant into a sealable container. Coolant should be reused unless it is contaminated or is several years old.
   
3. Remove the upper radiator hose to access the upper water pump bolts.
4. Remove the small hose attached the upper part of the water pump. Fig. 3: Removing the upper radiator hose will allow better access to the upper bolts and the small hose attached to the pump
   
   
5. Remove the drive belts from the front of the engine.
6. Remove the tensioner pulley for the air conditioning compressor belt. Fig. 4: Removing the A/C belt tensioner will allow more room to remove the pump once it's unbolted from the engine
   NOTE: It is recommended that the crankshaft damper be removed to make water pump removal and installation easier.
   
7. Remove the water pump pulley-to-water pump bolts, followed by the pulley. Fig. 5: Use a prybar with a square edge to hold the pulley in place while loosening the bolts; then unscrew them by hand
   
   
8. Remove the water pump-to-engine bolts. Label each bolt, noting location, and bolt length. WARNING
   Failure to install the bolts of different lengths in their proper locations could result in a cracked timing chain cover, requiring time consuming and costly repair. Be sure to label each bolt and its location.
   
9. Remove the water pump from the engine. If the water pump has excessive end play or rough operation, replace it. Fig. 6: The water pump has to be carefully positioned for removal
   Fig. 7: Use locking pliers and carefully twist out the timing pointer if pump removal is difficult
   To install:
   
10. Clean the gasket mounting surfaces and grooves.
11. Using liquid sealant, apply a continuous bead to the gasket mounting surfaces of the water pump.
12. Install the water pump and torque water pump-to-engine bolts to 12–15 ft. lbs. (16–21 Nm).
13. Install the water pump pulley and torque the water pump pulley-to-water pump bolts to 4.6–6.1 ft. lbs. (6.3–8.3 Nm).
14. Install the tensioner pulley for the air conditioning compressor belt.
15. Install the crankshaft damper, if removed.
16. Install the timing pointer, if removed.
17. Install the drive belts from the engine and set the proper tension.
18. Install the splash shield on the passenger side of the vehicle.
19. Attach the hoses to the upper water pump and the main inlet pipe.
20. Refill the cooling system to the appropriate capacity.
21. Start the engine, run to normal operating temperature and check for the correct coolant level and for leaks.

Make sure it's cool, pop the radiator cap, Remove the shield on the passenger side between the tire and front of engine. Relieve the tension on the serp belt,draw yourself a diagram of the pulleys and belt routing in case the sticker is gone on the strut tower, remove the serp belt. Take the bolts out of the pulley on the front of the water pump (3). Remove the lower radiator hose at the front cover to drain the coolant. Remove the 6 mm bolts holding the water pump to the front cover housing. tap on the pump with a rubber hammer. Install a new gasket on the new pump, and a weap hole diverter in the pump (round black about hte size of a quarter), use old one if there's no new one. Install pupm and tighten bolts snug with a 1/4" ratchet. Install pulley and 3 bolts. Install belt, top off radiator with 50/50 mix green coolant. start engine and run to operating temperature,make sure the belt is seated in all of the pulleys and is running true, radiator fans should come on. Shut engine down and let cool overnight. Check level in radiator and overflow bottle, top off as necessary.

Probably a water pump seal unfortunately. Pressurize the system, with the engine off, use a mirror to look under the water pump pulley to see if any fluid is dripping from the water pump seal weep hole.
If it is, change the water pump.
Good luck, let me know.
Regards,