NOTES of DISCUSSION 1/5/04
There will be a meeting of the Cape Cod Watershed Management team on 2/4, 8:30-4:30, @ Cape and Islands Realtors Conference Center, 22 Mid Tech Drive, Yarmouth. There will be registration info available later; contact Karl if interested.
Ron Peterson of Atlantic Well Drilling gave considerable time educating the group about well drilling and drinking water on the Cape. Some highlights of his comments:
Hydrology:
The water table is at or about sea level, although a mounding effect of the surface of the water table occurs. This is higher where the Cape is wider, as in the upper Cape. The fresh water lens is quite thin at the water’s edge, and deepens in Eastham to at least 400 feet. The salt water/fresh water interface is not a sharp line, but is a gradual separation. The soil here ranges from clay, to silt, to fine sand, medium sand, coarse sand, and gravel (roughly in reverse order of desirability for wells); it is extremely diverse. While the bay side is rather predictably sandy, there is a good deal of clay in our soil, and its depth and spread is variable, although it seems to be more common in the southern and south eastern parts of town. It has a significant effect on water flow.
Wells:
Wells are sunk either into unconsolidated (loose, fragmented) soil or bedrock (solid, but fissured). The latter are also called artesian wells. On the Cape, unconsolidated soil is the norm. A high yield well produces a narrower and shallower cone of depression than a low yield well. Our soil gives high yields, more than is needed usually. A standard well produces c. 30-40 gpm; most residential users need 5-10 gpm. So, Peterson feels we are reasonably drought proof.
Off Cape, the typical residential well is composed of a 6” diam. steel case driven into the overburden (the soil above bedrock); if into bedrock, or at the point where bedrock is reached, the casing is unnecessary. In bedrock, water is derived from fissures or cracks in the rock, which may be at very deep levels and may be found only sporadically. Well yield is typically less than in our soils.
Eastham wells, sunk into unconsolidated soil, and often very sandy soil, are typically +/- 50 feet deep. Our wells must be cased to the bottom, where a screen is placed to filter out our small grained soil. Casing is usually 4” diameter PVC, which is inert and corrosion resistant. The screens, either PVC or stainless steel, are full of slots ranging from 7,000-20,000 ths inches, the most commonly used size being 12,000. The screen is typically 3 feet long.
The well driller’s goal is to find the coarsest sand, which stores the most water in its interstices, at the optimal level, that is, one which provides least sodium.
These new wells should last a very long time; on the Cape today, well drillers’ work is about 80% rehabbing existing wells. The old wells, installed 20 years or longer ago, are typically 2” steel pipe with inferior screens made of steel. The newer pumps, however, will still fail at some point.
The two basic factors in installing a well are
1. testing: a test hole is usually 6” diam, done with an auger. The driller tries for a 20’ long sample brought up on the auger. He/she observes the type of material, the color and smell; an experienced driller can determine porosity and rough iron level from this.
However, ph, nitrates, phosphorus, conductivity and other factors which must be tested for cannot be determined by the driller.
2. effective well development: using above described newer materials, the water where the well will be placed will be filtered to remove “fines”. The second drilling, for the finished well, is 12” diam. to prep for the 4’ diam. well.
Water Quality:
In general, deeper doesn’t improve quality; better quality water is found in shallower wells in Peterson’s experience. Lateral movement in well placement is often not possible because of set backs required for health, but if that movement can be achieved within the set backs, it is often adequate to produce clean water. Quality can only be determined by a sample sent to lab after well, including pump, is in place. 90 % of samples pass analysis. The following are some of the factors sampled.
PH: Cape soils naturally acid. Below neutral (6.8), acidity will corrode copper pipes inside house, causing staining. This is curable.
Iron: Over .03 ppm will cause staining, but not harmful to health. The deeper the well, the more likely high iron content. Iron bacteria are rare but do occur. Chlorination often will kill them, but not always. If not, a new well may be dug.
Nitrate: Very unpredictable as to location, but in his experience, higher in North Eastham. His guess is that this is caused by farming practices over 200 years. Long term residents tell him there were turnip farms in North Eastham, for example. He believes clay deposits are associated with higher concentrations of nitrate, found below them. Today nitrates rarely exceed the mandated limit of 10 ppm; however, he also believes the time will come when he can no longer overcome nitrate problems.
Conductance: This test measures suspended solids, which may in part be salt.
VOC’s: (volatile organic chemicals) these have been tested for since 1999.
Boelitz asked if there is anything Peterson feels the town could require of drillers which is not required now and which would make wells safer; he replied that for establishing wells there is not. However, he is concerned that there are no requirements for filling or plugging abandoned wells. Unfilled abandoned wells can be vehicles for seepage of surface pollutants into the water table.
Boelitz asked whether a seal, composed of rough concrete, placed vertically on the casing just above the screen would be helpful in reducing seepage of pollutants (this is done in some commercial/ large size wells.) Peterson replied in the negative.
The Cape Cod Commission will conduct a hearing on the Ocean Beach proposal on 2/11.
The meeting with the Orleans Board of Water Commissioners and George Meservey, Orleans Town Planner, will be held at Orleans Town Hall, room A, on 1/21, at 2:30. The Orleans participants are interested to hear what the Eastham WRAB and the WWMC are doing/have done, and to explore topics of mutual interest.
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