Reprinted with permission by its author, Thomas O. McGill this first appeared in Eye on Edgewood (8-5-2021). Mr. McGill has lived in Edgewood since 1978. As a concerned citizen with extensive experience in engineering, electronics, and high-level technology, Mr. McGill is uniquely qualified to analyze complex matters. He has worked at National laboratories, high-tech firms, and taught in academia.
Wastewater Plant Woes
Town Clerk Juan Torres says they cannot plan or budget for the wastewater plant because they are in survival mode. So, they budgeted $8000 for a necessary sensor and nothing else. I think this is less a survival mode than a pull-the-covers-over-your-head and hope it goes away mode.The following is a bad practice they could fix at no cost, if they would only pay attention. This is not Beer on the Bachelor, or landscaping for the town office. The waste plant is the biggest expense and the biggest liability you co-own as a taxpaying member of the town of Edgewood.
I understand if you don’t want to dive (sorry for the image) into the world of sewage treatment, so I will skip to the bottom line. Make sure you elect Commissioners who do care about this stuff and the welfare of their constituents this November.
I am posting my concerns because the Town administration is denying anything is wrong and even refusing to consider that there might be a problem. They are aggressively avoiding paying attention. Even after wastewater was lapping over the top of the pond edge, Operators were declaring to NMED they had 21 inches of freeboard, for example.
About the graph: What are these numbers?These are the reported amounts in gallons of waste water [Bar 1.] directed to the containment pond, and [Bar 2.] removed from the pond and sprayed on the ground east of the pond. The net volume is [Bar 3], the growing (in this case) quantity of waste water in the containment pond. It is measured from the volume reported in the month previous to this report. I reset the relative height of the wastewater from June 20 to zero for the purposes of determining actual NET increase. Again, these numbers do not represent the total quantity of water in the pond. The one-year increase in June 21, year over year, was 6,283,275 gallons, for example.
Where do these numbers come from?
These numbers are from a quarterly report required to be filed with the New Mexico Environmental Division for the second quarter 2021. These are the months of April, May and June. I acquired these documents through legal means. The Edgewood administration will not release this information.
How accurate are these numbers?
The numbers are accurate as reported. The volume in the pond is reduced by evaporation, but increased by rainfall. One inch of rain (or wastewater) will increase the volume by 60,000 gallons. The plant averages about 30,000 gallons of wastewater per day, seven days a week. For the purpose of calibration, I observed and recorded evidence of overtopping both in March and June.
For your own reference, compare the photo of February with the corresponding bar on the graph.
Overtopping was probably the result of wind forcing the high water over the edge of the pond liner, rather than water running out. I think it is likely that the freeboard line is consistently being violated. The pond wall profile starts changing from near vertical to more horizontal eight or ten inches below the measuring point for freeboard determination (see Photo). A strong wind can force water out of the pond even though the level is still several inches below the highest level of the liner.
What is the significance of the numbers?
The pond’s total capacity is 9.5 million gallons. It is not designed, however, to hold that much on a regular basis. The design limit is 7.5 million gallons. That quantity is reduced by sediment accumulation on the bottom of the pond and, significantly by subsidence. The North end of the pond was constructed by forming native soil into a berm. Over time the dirt has settled, lowering the height of that end of the pond by approximately 15 inches. That is the equivalent capacity of one million gallons of waste water. We can assume the legal capacity of the pond is less than 6.5 million gallons. In the real world, probably due to construction, the pond seems to be capable of holding a greater volume than required by design.
Why is this even important?
Good practice dictates that the pond level is reduced during dry summer months to create a reserve for the winter or emergencies. The level should be reduced to facilitate cleaning out the bottom sediment as ordered by NMED while the weather is good and the soil can absorb the displaced water. Some water level is desirable for evaporation and to protect the liner from Ultraviolet radiation.
I feel I should make you aware that draining the pond is simply turning on a pump during suitable weather conditions.
Any significant escape of wastewater can create cascade erosion that would very quickly empty the entire pond. Remember, each half inch of erosion will release an additional 30,000 gallons and further erosion.
Beyond the obvious, that is a Good Question! No one seems to care. However, it is important. Aside from the general bad practice of so casually violating ones permit, there are potential serious consequences of ignoring good management and the neglect this circumstance reveals.
One of the more significant concerns I have is that I have noticed an irregularity in the North West corner of the pond that makes me believe it is the precursor to total failure. What I would like to stress is that as catastrophic as the collapse of the dirt berm would be, the tearing (tensile failure) of the elastomer liner would be worse.
Below is an image I took in February as the water level was continuing to rise and some notes.
I am neither a professional engineer, nor hydrologist, nor do I have any expertise in any directly related discipline. I call on your common sense.
There is a deformation in the shape of the pond that MIGHT indicate an impending failure. Deformation of the berm indicates deformation of the elastomer liner which can only stretch a fraction of its thickness, even allowing for the loose fit of the installation. Failure of the liner would result in functional failure of the pond and almost certain total physical failure, as well. The deformation is exactly where it would be if there was a shear failure.
This is what an incipient failure would look like if initiated from high water forces. This type of failure is less likely to occur from a lower water level unless there is percolation; I see no evidence of percolation.
Intuitively, the berm looks substantial. However it appears to have been constructed of native material which appear to me to be prone to weakness and erosion when wet.
There is no way to know when the displacement occurred; it only becomes obvious at high water levels. This could be an unlikely artifact of manufacture.
My conclusion: I would avoid ever filling the pond beyond its design parameters in violation of the permit.
