Village of Lake Isabella

Transcription

1 Village of Lake Isabella Suitability of On-Site Water Supply For The Plats of: Lake Isabella Airpark and Canterbury Estates Drafted by: Rowe Professional Services Company May 2009 Project# 08M0063

2 Table of Contents I. Background..1 II. III. IV. Water Sampling Well Log Analysis....2 Discussion/Recommendations V. Conclusion 3 Appendices: Appendix A Brighton Analytical Laboratory Water Testing Results Appendix B Well Log Information MDEQ Water Well Viewer Website Appendix C Department of Transportation, Consumer and Industry Services, and Environmental Quality, Subdivisions of Land rules filed with the Secretary of State on January 23, 2001

3 I. Background In December 2008, the Village of Lake Isabella requested their engineering consultant ROWE Professional Services Company (ROWE) to review all available well log information, obtain a representative number of potable water samples, coordinate the analytical testing of the samples, and provide recommendations regarding the installation of future residential wells in the plats of Canterbury Estates and Lake Isabella Airpark. The above work was determined to be the next step, as agreed upon with the Michigan Department of Environmental Quality (MDEQ) and the Central Michigan District Health Department (CMDHD), to proceed with the determination of septic field suitability in both plats. It was determined that the water sampling and analysis was required to fulfill the requirements of R Approval for Suitability of on-site water supply as set forth in the Department of Transportation, Consumer and Industry Services, and Environmental Quality, Subdivisions of Land rules filed with the Secretary of State on January 23, It was agreed between all parties that the water needed to be tested at a state-certified laboratory for the presence of Arsenic, Coliform Bacteria, and Nitrate. II. Water Sampling All of the home/airplane hangar owners who had potable wells in the two plats were contacted by the Village Manager in order to obtain permission to perform the sampling. Nine property owners who had wells granted written permission. ROWE contacted Brighton Analytical L.L.C. and had sterile, sealed sample bottles delivered to their office during the morning of April 27, After the bottles were received, a representative from ROWE obtained eight water samples, seven of which were from potable water wells within the two plats. One of the permitted sites was an airplane hangar which was locked, and the representative was unable to access the water spigot. The representative turned on the external water spigot at the sites, ran the water for approximately five minutes, and then put on latex gloves prior to opening the bottles and obtaining the samples. Three samples were obtained at each location; one to be tested for each of three agreed upon elements. Once the samples were obtained, the samples were sealed and placed in a secured cooler. In all but one location, the representative was able to sample the water directly from an external spigot. Sample E was provided to the representative by the homeowner from an un-sealed, one-gallon water jug. Once all of the samples were obtained, the representative delivered the samples to their office in Mt. Pleasant, where a representative from the testing laboratory met them and took custody of the samples, and delivered them to their laboratory in Brighton, MI for analysis. Once the analysis was completed, the results were sent to ROWE s office for review

4 Upon review, only one of the samples (sample B ) contained a detectable amount of arsenic. The analysis revealed a level of 2 ug/l which is below the maximum allowable concentration of 10 ug/l for an acceptable potable water supply. Three of the samples contained nitrate (samples E, H, and I ) with levels ranging from 60 ug/l to 1100 ug/l, but again, the levels were far below the maximum allowable concentration of 10,000 ug/l. The final test which was completed was for the detection of Coliform Bacteria, and one of the samples had a positive result. This was sample E which was not obtained directly from the water spigot by the ROWE representative, but furnished by the homeowner in an un-sterilized, un-sealed water container. Because of this, it is ROWE s opinion the positive reading was likely caused by contamination within the water container, not by the presence of bacteria directly from the well s aquifer. The sampling locations are displayed on the exhibit contained within this report. III. Well Log Analysis The next task to be completed in order to determine the suitability for additional septic fields to be constructed within the two plats was to analyze the available well logs. This analysis was necessary to determine whether a minimum depth for new residential wells needed to be established to ensure the quality of the onsite water supply. As shown on the exhibit contained within this report, fourteen well logs were obtained. In general, the soil stratification consists of sand, over clay, over sand. The clay layer varies in thickness and depth, as does the sand layers. From the well logs, the wells in the two plats vary in depth from 29 to 100. The bottom of the clay layer varies from 22 to 70 respectively. The thickness of the clay varies from 2 to 48. The static water level for the area appears to vary from a depth of 16 to 46. According to R Well Protection from the Department of Transportation, Consumer and Industry Services, and Environmental Quality, Subdivisions of Land rules filed with the Secretary of State on January 23, 2001, subrules (a) Penetration of an impervious layer which is of sufficient areal extent, but which is not less than 10 feet thick, (b) Maintaining a minimum of 50 feet from the static water level to the bottom of the casing or top of the screen in an unconfined aquifer, and (c) An increase in the minimum horizontal isolation distance between the well and a source from which groundwater contamination may occur, should be given consideration. But, as stated in subsection (d), a combination of methods (a-c) could determine adequate protection for the on-site water supply. IV. Discussion/Recommendations This section of the report contains discussion regarding the potable water sampling, water sample analysis, review of the well logs, and ROWE s recommendations. Overall, the sampling locations should provide a general representation of the potable water available in the two plats. The sampling - 2 -

5 locations are spread out over the entire geographical area. Except for the presence of bacteria in one of the samples (which in ROWE s opinion should be disregarded since the test for bacteria is very sensitive, and it is likely the container which provided the potable water sample was contaminated since it was not sterilized, nor sealed), all of the other samples reveal that the aquifer within the plats is capable of producing a suitable on-site water supply. The detection levels of both arsenic and nitrate in the samples were also below the maximum allowable limits for drinking water, so those results also provide support that the aquifer should be viewed as an acceptable potable water source. The well log analysis identified the presence of a generally, geographically consistent clay layer, separating the upper sandy strata, from the deeper, sandy sub-strata where most of the existing well screens were installed. The static water level for the area varied, but where it was deeper, it was protected by a preceding clay layer exceeding 15 in thickness. As summarized in Part III of this report, it is acceptable to have a combination of the three subrules when determining adequate protection of the on-site water supply. It is our opinion, adequate protection could be accomplished in this way. Since the maximum, known depth of the bottom of the confining clay layer is approximately 70, and the static water table averages approximately 31 in depth, it is ROWE s recommendation that all future wells have a minimum screen depth of 80. Wells installed at this minimum depth should provide adequate protection from all of the existing and future on-site septic systems in the two plats. V. Conclusion In summary, the Village of Lake Isabella, in conjunction with the MDEQ, CMDHD, and Rowe Professional Services Company, have all agreed that the next step in determining septic field suitability in the plats of Canterbury Estates, and Lake Isabella Airpark was to provide support that the area has a suitable on-site water supply. It was determined that a representative number of water samples were to be obtained, and sent to a state-certified laboratory in order to test the samples for the presence of Arsenic, Coliform Bacteria, and Nitrate. Also, as part of the analysis it was decided to review the well logs to see if a minimum well depth would be necessary to ensure a suitable on-site water supply. From ROWE s analysis of the water samples and well logs, it appears if a minimum depth of 80 was mandated as a requirement for the construction of all new water wells, adequate protection should be provided for all new on-site water supplies

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