Water Leakage around Valve Component Container

My yard has two valve component containers, with three valves each, sunk into the ground with a removable lid. Since I started using the system in late spring, one component is always filled with water. The ground around it is muddy, suggesting that a continuous leak is ongoing. Or, maybe, one of the valves is not fully closed. Over the summer, the muddy area has been spreading below the container with the valves, as the yard is graded downwards towards the end of the property. A technician from Irrigation Professionals has come out several times but has not been able to diagnose the problem. Meanwhile my yard is getting muddier and muddier. If I turn off the water to the system, the water in the component container goes down after a week to below the valves and the mud in the yard dries up. If I just disable the closest zone, water remains in the container and the yard stays muddy. What are likely causes? Who can I call besides Irrigational Professionals? Thanks for any suggestions.

If you leave the system water on and all the valves off, does the water level go up? Can you hear water flowing from the valve box(es)?