Thursday, December 23, 2010

Groundwater for Irrigation


If you (or someone you love) are considering drilling a well for irrigation, please save yourself some money and collect some empirical information about your water supply. The only way to understand it, is to conduct some kind of "stress", "aquifer", or "pump" test on the water supply. There are number of sound reasons to conduct some kind of test on the well. But the number one reason I tell my clients is that it protects their investment.

As an example, look at the photo above. It was proclaimed that the well yielded "100 gallons per minute (gpm)". Really? For how long? "...well, for the 10 minutes we "blew" it out of the hole". Hmmm, ok.

Why spend $10K to $20K on a well, pump, piping and irrigation system to find out later that your 100 gpm well is really a 10 gpm well. The water is "the dog that wags the tail" for the entire enterprise; yet, I am amazed at the number of intelligent people who ignore the need to collect at least some minimum data regarding the capabilities of the aquifer beneath their feet.

I had a client who required 7500 gallons of water twice a week for his irrigation needs. He decided that before he invested an enormous amount of money for his irrigation system that he would have me conduct a limited pump test.

We first conducted a "STEP" test on the well. A STEP test is a "pre-test" for the main pumping event and is conducted to determine a pumping value for a longer period pump test. You start pumping the well at low rate- measure the drawdown and "STEP" it up after it appears it will hold. Here on the right is the graph of time vs drawdown for STEP test on this well. In this case we started at 5 gpm. This is a semi-log plot and it is clear that the well could handle 5 gpm (at least for awhile). So, we "stepped" up to 10 gpm. And the curve began to adopt an asymptotic shape. All good. Then we jumped it to 17 gpm. And lookie there!! It held steady at around 50 feet then the "angle" got a "little" steep. So steep that we needed to slow down!!! WHoaaaa Nelly!! So, we stepped back to 11 gpm and called it good for the day.

So, we allowed the well to rest from this activity and went back to work on the Alberene Soapstone patio in my yard (here on the right). This soapstone is a Proterozoic-age ultra mafic rock that was recrystallized by metamorphic processes. These emplacement "pods" make up a portion of the Lynchburg Group of rocks in central Virginia. Anyway, we went to quarry and bought several truckloads of scrap ($75/load)-hauled them back home and cut them with a wet saw that belongs to Terry Waggener (seen in previous post). He is a lengendary stone mason who knows more about geology than most graduate students (certainly more than me). The retaining wall in the background was made from precambrian-age granite gneisses, cambrian-age catoctin greenstones and the base layer were rocks from the arkosic sandstone/quartzites of the Lynchburg group (similar age as the soapstone).

Back to the test: we
returned to the property to conduct a limited withdrawal of the well only to find everything frozen up and had to spend several hours unthawing the pipes.

Sunday, December 12, 2010

Petroleum Storage Tanks and The Virginia Reimbursement Program

The state of Virginia operates a program that reimburses homeowners and businesses for expenses of cleaning up legitimate tank leaks that are considered a threat to the environment or human health. Please follow the link on my website to learn more about the program (VPSTF). Most of us (tank owners) will have no reason to suspect that our tanks are leaking unless our fuel bills increase unexpectedly or if they come to the attention of professionals hired to screen environmental threats. In the picture to the right is my pal, Terry, posing next to an underground storage tank with an auger in his hand. The fill pipe is sticking up out the ground to the right. True North was hired to determine if there was any evidence to suggest that the tank had leaked. The Tank Fund is there because it is expensive to clean up spills from these leaking tanks. Anyone buying gasoline in the state of Virginia contributes (unwittingly) to this fund. It has made it possible for homewoners to rectify environmental hazards on their property and in so doing protecting their real estate investment. And the homeowner is only
out $500 - and sometimes less-. The reason for this is that environmental consultants are eager to perform this work and will usually waive the $500 fee just to have the work (yes, including us!!). A whole industry has sprung up that represents the interests of the homeowner (one hopes) and conducting the cleanups and working with DEQ to make sure the job gets done.


We recently were hired to conduct an environmental screening of the property above. A part of this work included soil around a buried gasoline tank. Field observations and laboratory analysis indicated that the soil was clean. After the property was purchased the owners hired True North to supervise and document the removal of the gasoline tank. Everything looked good and the tank removals proceeded swimmingly. For those interested heres a video of a portion of the tank removal. PLease forgive the language- we're just a bunch of unrefined good 'ol boys- so please excuse the profanity.....
video