1998 305(b) PART IV:
GROUND WATER ASSESSMENT

Table 4.1 is designed to provide an indication of the most critical contaminant sources and contaminants impacting ground water resources in Louisiana. Table 4.2 provides a summary of Louisiana ground water protection programs. It provides an overview of legislation, statutes, rules, and/or regulations that are in place. It also provides an indication of how comprehensive ground water protection activities are in Louisiana.

The Ground Water Protection Division’s Baseline Monitoring Project provides water quality data from fresh water aquifers around the State. Wells producing from a common aquifer are sampled in a narrow time frame. The smaller aquifers can be sampled in one or two days, whereas, the larger aquifers may take several months to complete. At such time when all project wells of a particular aquifer have been sampled, a summary report is written.

For this report, EPA has encouraged States to select an aquifer or hydrogeologic setting and discuss available data that best reflects the quality of the resource. For 1998, the baseline monitoring network for the Chicot Aquifer is discussed.

Index to Table 4.1

Factors in selecting a contaminant source

1. Human health and/or environmental risk (toxicity)
2. Size of the population at risk
3. Location of the sources relative to drinking water sources
4. Number and/or size of contaminant sources
5. Hydrogeologic sensitivity
6. State findings, other findings
7. Documented from mandatory reporting
8. Geographic distribution/occurrence
9. Other criteria - high to very high priority in localized areas of the state

Contaminants

1. Inorganic pesticides
2. Organic pesticides
3. Halogenated solvents
4. Petroleum compounds
5. Nitrate
6. Fluoride
7. Salinity/brine
8. Metals
9. Radionuclides
10. Bacteria
11. Protozoa
12. Viruses
13. Other - sulfates from gypsum stacks

Table 4.1. Major Sources of Ground Water Contamination

Table 4.2. Summary of State Ground Water Protection Programs

Ambient Monitoring Network For The Chicot Aquifer

The data that follows were derived from the Baseline Monitoring Project of the Water Quality Management Division (WQMD) of the Louisiana Department of Environmental Quality. The project is conducted as a Clean Water Act, Section 106 activity and the objective of the project is to provide water quality data from freshwater aquifers across Louisiana which will be used to aid the WQMD in formulating and implementing Ground Water Protection Strategy for the State.

Figure 4.1 shows the geographic locations of the Chicot Aquifer and the associated project wells, whereas Table 4.4 lists the wells in the aquifer along with their total depths and the use made of produced waters.

These data show that from July, 1996, through October, 1996, a total of 26 wells were sampled which produce freshwater from the Chicot Aquifer. Eleven of the 26 wells are classified as public supply, five are industrial wells, five are observation wells, four are domestic wells, and one is classified as an irrigation well. The wells are located in 13 separate parishes extending from Rapides Parish in the central, to St. Martin Parish in the south central, and to Cameron Parish in the southwest parts of the state.

Project Field and Analytical Parameters

The field parameters checked at each sampling site and the list of water quality analytical parameters are shown in Table 4.5. Those project inorganic (total metals) parameters analyzed in the laboratory are listed in Table 4.6. These tables also show the field and analytical results determined for each analyte.

In addition to the above mentioned water quality analytical parameters, a list of project analytical parameters includes three other categories of compounds: volatiles, semi-volatiles, and pesticides/PCBs. As only one semi-volatile compound of these three categories of compounds was reported in three of the 26 Chicot water wells sampled, tables were not prepared. However, in order for the reader to be aware of the total list of analytes, Tables 4.7, 4.8, and 4.9 were included in this report. The tables list the project analytes along with their Practical Quantitation Limits (PQLs) used during processing.

Discussion of Water Quality Data

Federal Primary Drinking Water Standard: Laboratory data show that one Vermilion Parish observation well exceeded the 15 ppb action level for lead. This well, VE-650, reported 29.3 ppb of lead. Twenty-one of the 26 Chicot Aquifer wells sampled exceeded the Maximum Contaminant Level (MCL) for turbidity. Of these, eight are public supply, four each are industrial and observation and one is classified as an irrigation well. (See Table 4.5 for turbidity levels).

The MCL for turbidity is set at 5 TU for a two-day average, or 1 TU when tested and averaged over a period of one month. As all Chicot wells were sampled on a one-day grab sample basis, a definitive level of this parameter was not obtained.

As mentioned earlier, one semi-volatile compound was reported in three of the 26 Chicot wells sampled. This compound, bis(2-ethylhexyl)phthalate (BEHP), was reported as exceeding the BEHP MCL of 6 ppb in wells AC-539, BE-488, and VE-862 with values at 11 ppb, 29 ppb, and 28 ppb, respectively. Duplicate samples were taken immediately following the originals for wells BE-488 and VE-862. The original sample of BE-488 and the duplicate sample of VE-862 reported measurable concentrations of BEHP, whereas the duplicate sample of BE-488 and the original sample of VE-862 were reported to be below the Practical Quantitation Limit by the laboratory for this compound. Taking this into consideration and information contained in the Guidance for Data Usability in Risk Assessment EPA 1992 document, it is felt that the BEHP reported in these wells are due to field/laboratory contamination and are to be considered false positives.

Federal Secondary Drinking Water Standards: Secondary standards are defined as non-enforceable taste, odor, or appearance guidelines. Field and laboratory data contained in Tables 4.5 and 4.6 show that from one to 22 wells sampled in the Chicot Aquifer exceeded the Secondary Maximum Contaminant Levels (SMCL) for six analytes in this category.

pH (SMCL= 6.5 SU to 8.5 SU) The following six wells fell below the lower limit of 6.5 SU: BE-412, BE-486, Be-488, CU-869, R-5428Z, and V-535.

TDS (SMCL=500 ppm) Four wells, CN-92, CU-1023, SMN-109, and VE-862, exceeded the secondary limit for TDS. Their values ranged from 587 ppm to 846 ppm.

Color (SMCL = 15 PCU) Only four of the 26 Chicot wells sampled were within the secondary standard for color. The values of the 22 wells exceeding the 15 PCU limit ranged from 20 PCU to 60 PCU.

Chloride (SMCL = 250 ppm) One well, CN-92, exceeded the chloride limit, reporting a value of 328 ppm.

Iron (SMCL = 300 ppb) Nineteen of the 26 Chicot wells sampled exceeded the secondary standard for iron. Their values ranged from 438 ppb to 16,097 ppb.

Zinc (SCML = 5,000 ppb) St. Martin Parish well SMN-109 exceeded this standard with a value of 5,031 ppb, while a duplicate sample of this same well was just below the 5,000 ppb limit at 4,930 ppb. No other well sampled in the Chicot Aquifer exceeded the SMCL for zinc.

SELECTED WATER QUALITY MAPS: For the readers convenience, maps showing the contoured values for pH, TDS, chloride, and iron are included in this summary report in Figures 4.2 through 4.5.

Summary and Recommendations

In summary, the included data show the water produced from the Chicot Aquifer project wells to be safe and potable with the exception of the one Vermilion Parish observation¹ well which exceeded the Action Level for lead.

The elevated turbidity levels and exceedences of Secondary Drinking Water Standards are characteristic of the waters produced from the Chicot Aquifer and are consistent with historical sample analyses from this aquifer.

It is recommended that the project wells assigned to the Chicot Aquifer be re-sampled as planned, in approximately three years. In addition, several wells should be added to the 26 currently in place to increase the well density for this aquifer.