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HEALTH CONSULTATION

Perchlorate Contamination in the Mather Air Force Base Water Service Area

AEROJET-GENERAL CORPORATION
RANCHO CORDOVA, SACRAMENTO COUNTY, CALIFORNIA


Table 1:

Mathers Air Force Base Drinking Water Well Descriptions and Perchlorate Sampling Results
Well Drawing Depth
(ft bgs)
Status of Well Capacity
(gpm)
Perchlorate Analysis (ppb)
2/97 3/25/97 4/10/97 5/13/97 6/19/97 7/9/97 8/14/97
Main Base - Well 1 262-531 Off-line on 3/21/97 1,130 ns 67 72 ns ns ns ns
Main Base -Well 2 186-494 Off-line on 3/14/97 900 ns 120 130 ns ns ns ns
Main Base -Well 3 249-501 Back up status on 4/1/97 900 ns 14 16 ns 17 19 18
Main Base -Well 4 246-500   670 ns <4.0 <4.0 <4.0 <4.0 <4.0 <4.0
Family Housing -Well 1 280-500   1,350 ns <4.0 ns <4.0 <4.0 <4.0 <4.0
Family Housing -Well 2 205-500 Destroyed
Family Housing -Well 3 348-400 Temporarily off-line 1,350 ns ns ns ns ns ns ns
Family Housing -Well 4 360-570   2,200 ns <4.0 ns <4.0 <4.0 <4.0 <4.0
Family Housing -Well 5 450-544   1,500 ns <4.0 ns <4.0 ns <4.0 <4.0
Family Housing -Well 6 246-409 Temporarily off-line 1,900 ns ns ns ns ns ns ns
ns= not sampled ft bgs= feet below ground surface gpm= gallons per minute
Data from references (8, 13, 15, 16).  




Table 2.

Perchlorate Contamination in the Main Base Area-Completed Exposure Pathway for Different Receptor Populations
Receptor Group
Pathway Name
Source Environmental medium Point of Exposure Route of Exposure Exposed Population Time
Worker exposure at Mather Main Base Area businesses Aerojet, McDonnell Douglas (?) Groundwater wells in the Main Base Water System Business Tap Ingestion Workers Past
Frequent customer or visitor at Mather Main Base Area businesses Aerojet, McDonnell Douglas (?) Groundwater wells in the Main Base Water System Business Tap Ingestion Frequent customer; Frequent visitor Past
Temporary resident at transitional housing in Main Base Area Aerojet, McDonnell Douglas (?) Groundwater wells in the Main Base Water System Transistional Housing Tap Ingestion Temporary resident Past





Table 3.

Exposure Factors for Each Receptor Population of the Completed Exposure Pathway at the Main Base Area
Pathway Name Exposure Parameter Value
Worker exposure at a Mather Main Base Area business
Ingestion Rate 3.7 liters (15.6cups)/day
Body Weight 70 kilograms (154 pounds)
Exposure Frequency 8 hours/day
5 days/week
50 weeks/year
Averaging Factor 365 days/year
Frequent customer or visitor at a Mather Main Base Area business
Ingestion Rate 0.24 liter (1 cup)/visit
Body Weight 70 kilograms (154 pounds)
Exposure Frequency 5 days/week
50 weeks/year
Averaging Factor 365 days/year
Temporary resident at the transitional housing in the Main Base Area
Ingestion Rate 2 liters (8.4 cups)/day
Body Weight 70 kilograms (154 pounds)
Exposure Frequency 15 hours/day
7 days/week
14 weeks/year
Averaging Factor 24 hours/day
98 days/year
Patient at the McClellan Hospital in the Main Base Area
Ingestion Rate 2 liters (8.4 cups)/day
Body Weight 70 kilograms (154 pounds)
Exposure Frequency 7 days/week
14 weeks/year
Averaging Factor 14 days/year




Figure 1. Perchlorate Groundwater Plume in Relation to Aerojet and Mather Air Force Base

Figure 2. Water Distribution System of Mather Air Force Base



APPENDIX A. RESPONSE TO COMMENTS FROM SITE TEAM REVIEW

In 1995, EHIB formed a site team to assist us in identifying public health concerns and to oversee what we do during the health assessment process for the Aerojet General site. The site team is composed of community residents, state and federal environmental and health agency staff, Aerojet staff, as well as EHIB staff. Health consultations that are produced as apart of the health assessment process are released for comment to site team prior to them becoming final. We received comments on this health consultation from the Drinking Water Branch of CDHS, U.S. EPA, DTSC, Aerojet, and RWQCB. In this appendix, we will respond to the submitted comments. (Some of the commenters used the Cordova Water System Health Consult as the basis for their comments and asked them to be applied to other health consultations when applicable. Thus, some of the comments make reference to the Cordova Water System and not the Sacramento County Sunrise District, but we included the comment in this health consultation if it seemed applicable.)

COMMENTS RECEIVED FROM THE DRINKING WATER BRANCH OF CDHS

The Drinking Water Branch of CDHS regulates water purveyors in the state, and their comments were minor technical corrections to the numbers we cited in the text. These corrections were made to the original document.

COMMENTS RECEIVED FROM THE U.S ENVIRONMENTAL PROTECTION AGENCY

The EPA offers the following comments for your consideration:

USEPA comment: Page 7 - fourth sentence - the statement that "ammonium perchlorate has relevant physical and chemical characteristics similar to cadmium chloride does not appear to be justified. Although both of these compounds are salts, on dissolution (a necessary step in absorption) perchlorate would become an anion (negative charge) and cadmium would become a cation (positive charge). Therefore, one could conclude on this basis alone that cadmium would not be an appropriate surrogate for perchlorate. Comment applies to all reports but Fair Oaks Water District Report.

CDHS response: According to a highly regarded dermal absorption reference source, the permeability of charged ions is extremely low and membranes appear to be more permeable to cations than anions (46). Thus, the comparison of perchlorate should not be made between the cation, cadmium, but the anion, chloride, that is found when cadmium chloride is in solution.

USEPA comment: Page 8 - third paragraph - NOAEL term use - The NOAEL is an experimentally derived value that is often used as a basis for the RfD, however, the NOAEL is not regarded by EPA as a value that "would not be expected to be associated with any adverse effect". Rather, this definition better fits the RfD that is derived from a NOAEL after considering uncertainties in the database. Comment applies to all reports but Fair Oaks Water District Report.

CDHS response: We have corrected the use of NOAEL and RfD in the text.

USEPA comment: Page 23 -Table 3 - Worker exposure - The tap water ingestion rate for workers is listed as (3.7 liters/day) which is almost twice the assumption that is used for a residential scenario. Should this be 0.37? This applies to Mather Air Force Base Water Service Area Report Table 3 - page 21 and the Sunrise District of the Sacramento County Water Service Report Table 2 - page 18. Also, the Citizens Utilities' Suburban & Security Park Water Service Areas Report Table 3 - page 19 lists worker exposure at 2.0 liters/day should this be 0.37?

CDHS response: We are using a reference from USEPA document entitled "Exposure Factors Handbook", published in 1989. In this document, the total fluid intake for a moderately active man is cited as being 3.7 liters/day. This document cites the Report of the Task Group on Reference Man from the International Commission on Radiological Protection, published in 1981 for this number. This higher intake of water does seem appropriate given the labor-intensive commercial businesses that are located near the perchlorate-contaminated wells.

USEPA comment: Figure 1 - Is it possible to make the Cordova System standout? Found figure hard to use.

CDHS response: Unfortunately, this figure is copied from a hard copy and is not electronically produced, so it is probably not possible to improve upon the quality.

USEPA comment: In discussions with the USEPA RPM for Mathers, she indicated exposure had ended at Mathers.

CDHS response: The description of the Mather Base system is based on conversations we have had with Mather Base Conversion Agency staff, and according to them, as of the time when well #3 was put in the backup mode to well#4, April 1997, no perchlorate-contaminated water has been added to the Main Base System. This is stated on page 6 of the health consultation.


COMMENTS RECEIVED FROM THE CALIFORNIA DEPARTMENT OF TOXIC SUBSTANCES CONTROL

Below are DTSC's comments which may be considered as the documents are finalized.

DTSC comment: In the "Exposure Pathways" sections of the Arden Cordova, Mather Air Force Base and the Sacramento County water district consultations, it is stated that Aerojet began reinjecting water from their treatment plants on the west boundary of the site in 1984 and 1985. The assumption is then made that it took "a couple of years for the perchlorate to move from the reinjection wells" to the water district's wells. An accurate assessment of when the perchlorate contamination occurred and the location of the source of the perchlorate cannot be made without further information and analysis. The reinjection field nay not be the source of the perchlorate contamination in many of the affected wells. Aerojet is currently investigating the extent of the perchlorate contamination to the west of its facility pursuant to an order from the Regional Water Quality Control Board. A technical memorandum documenting the results of that investigation is currently scheduled to be submitted in May of 1998, with an Engineering Evaluation/Cost Analysis of remedial alternatives to be submitted in October of 1999. Additional investigations of groundwater to the west of the Inactive Rancho Cordova Test Site (IRCTS), the likely source of perchlorate in several of the affected wells, are also proceeding. DTSC's Project Manager for the IRCTS is Mr. Marvin Woods who can be reached at (916) 255-3666.

CDHS response: EHIB recognizes that a good analysis of the perchlorate migration which would allow us to know when the perchlorate reached the public drinking water supply well, has not yet been done. In fact, we start off the first paragraph in the "Exposure Pathways" section by saying, "It is not clear when the perchlorate contamination reached the Mather wells, ...". However, since the reinjection of treated water is at least one source of the perchlorate found in some of the drinking water supply wells, we found it was important to share information about this source with the reader. We look forward to reviewing the reports that DTSC is referring to, and hope that they will give a more accurate picture of past well contamination levels.

DTSC comment: In the third paragraph of the consultations, it is stated that the Regional Water Quality Control Board is the lead regulatory agency. While this is correct for some aspects of the project, the lead regulatory agency controlling water district activities is the Department of Health Services, Office of Drinking Water. For matters concerning the Aerojet Superfund Site, the United States Environmental Protection Agency is the lead federal regulatory agency. A co-lead situation exists for certain matters covered under the Aerojet Superfund Site Partial consent Decree (United States District Court, Eastern District of California, Civil Action Nos. CIVS-86-0063-EJG and CIVS-86-0064-EJG).

CDHS response: Being a part of the complex government oversight at this site, we appreciate the clarification to the agency responsibilities. We have tried to rectify this in the text.

COMMENTS RECEIVED FROM AEROJET GENERAL CORPORATION:

Aerojet comment about the attribution of source of the perchlorate in public water supply wells: Each draft Health Consultation assumes that perchlorate being found in public water supply wells came from the Aerojet Operating Plant, specifically from the reinjection wells associated with the GET facilities. There are numerous locations where such references appear. (See, for example, Arden Cordova Health Consultation at:

Page 6, paragraph 2 and page 22, Table 2.) This assumption is used to project length of exposure and concentrations in the wells over time. The conclusion is made for each well, for every water purveyor, regardless of the well's location, chemical concentrations or differing hydrogeological conditions.

We are aware of no detailed evaluation of sources, groundwater conditions and groundwater and contaminant movement undertaken by DHS or any other agency that would support statements in the DHS Consultations that attempt to link perchlorate in a well to an upgradient source, and it does not appear necessary for DHS to ascribe a source to reach its conclusions. The Health Consultations should identify that potential sources of perchlorate include the Aerojet Operating Plant, Purity Oil site, and the McDonnell Douglas (MDC) Site. DHS should not assert that the only source of the perchlorate is the GET facility recharge wells on the Aerojet Operating Plant. Neither should the period of operation of the GET wells form the basis for assumptions of exposure of potential receptors. As the Health Consultations discuss potential sources, it should discuss the various uses of perchlorate, other than in rocket motor manufacturing, such as the use of perchlorate in pyrotechnics (fireworks), explosives and other industrial activities. It should also note that perchloric acid, which is used in various industrial activities, including metal-plating, in laboratories, and in other operations, when released can result in the formation of perchlorate and its movement into soils and groundwater.

Aerojet believes that there have been no health impacts associated with any exposure to perchlorate in the water supply. If the Health Consultations seek to discuss long term impact by assuming exposure for some period (e.g., 10 years), they can do so without assigning a source, but simply by positing the potential for such exposure (without reference to a source) and developing an exposure assessment.

CDHS response: These health consultations are written as a part of CDHS's public health review of the impact of the Aerojet General site. Thus, the documents are written in respect to Aerojet General and not to other sites or facilities. We do recognize that perchlorate may have also gotten into the groundwater from sources other than Aerojet and that is why in last sentence of the third paragraph on page 1, we refer to the RWQCB's investigation of "other sources of the perchlorate such as the McDonnell Douglas (now Boeing) and Purity Oil Sales sites."

Aerojet comment about the toxicology: Aerojet recommends modifications to the discussion on toxicology. We are concerned that the draft consultations do not provide sufficient information about what is known about perchlorate toxicity (thyroid function) and end up, unintentionally, providing a less balanced presentation of the potential for impact and risk. For example, we believe there should be more discussion related to the past use of perchlorate in the treatment of Graves patients and its current use in Europe at very high doses without ill effects. Similarly, we recommend the inclusion of a statement that the mechanism of perchlorate on the thyroid as well as basic thyroid functions are well understood and we believe that the discussion as to exposure associated with children may lead to unnecessary concern and should be changed. Finally, we believe that there ought to be mention of the ongoing studies being conducted at the direction of the Air Force.

CDHS response: We did provide more information in the toxicology section. For instance, we have added more information about past and current uses of perchlorate and what is known and not known about toxicity to the developing fetus and young child. We did have a reference in the recommendations section about the on-going studies by the Air Force and the Perchlorate Study Group and we have added a sentence in the toxicology section referring the reader to the recommendations section for more information about these studies.

Aerojet comment about the water system operations: The draft Health Consultations, especially in the background sections, contain statements of fact as to the manner of well and system operation of each water entity over time, including detail on well construction and operation in tables. Aerojet has not had an opportunity to complete an evaluation of the accuracy of such statements. We further note that the factual statements generally do not seem to impact the exposure assessment, as the exposure assessment is based upon an assumed concentration that is not generally associated with the specifics of well interties or well operation. We would recommend the Health Consultations state that the water system information is based on current understanding unless DHS has had the opportunity to perform a detailed evaluation of the information.

CDHS response: In each health consultation, we cite the CDHS reports or other reports from which we gained this information. We refer Aerojet to those documents if Aerojet would like to evaluate the accuracy of such statements. We do think it is important to describe for the reader the basic structure of a particular water system; on the other hand, we don't want to add more information then is necessary. We hope that the amount of information we have provided will allow a Mather Main Base System customer to more easily understand that only some of the water wells in the system have been contaminated with perchlorate. By describing the water system information in this document, it also helps us to decide where we might consider follow-up activities, like an exposure dose reconstruction.

Aerojet comment about the Exposure Conclusions: The draft Health Consultations are based upon a set of assumptions, including assumed receptors, exposure rates, and concentrations. From these assumptions, an assumed dose is calculated and then compared to the provisional RfD. We believe that the Health Consultations should carefully describe each assumption upon which the Health Consultations were based, and clarify that these assumptions have not been fully evaluated. For example, a preliminary assessment of proximity to a well is used to determine the type of "receptor" (e.g., resident, worker), but the exposure does not assume any dilution of water from that well with water from any other well.

CDHS response: All of the exposure parameters are listed in the table and a Mather Main Base Water System user can look at these exposure parameters and apply them to their own situation. Thus it does not seem necessary to explain distributions of exposure parameters or in any other way describe each assumption.

With these general comments identified, we now progress to the specifics. We use the Arden Cordova Health Consultation as the template for our comments, and emphasize that typically the same issue exists in the other draft Health Consultations.

Aerojet comment: Page 1, Paragraph 2 and Throughout: The term "perchlorate contamination" is subject to misinterpretation and references should be to "water containing perchlorate" or like phrase.

CDHS's response: In Webster's New Collegiate Dictionary, it says "contaminate" means "to make impure or unclean". Perchlorate is not typically found in groundwater, as would be the case with certain chemicals like arsenic or sulfates which are naturally occurring in groundwater. Thus it does seem appropriate to describe the "contamination" of groundwater by a chemical such as perchlorate. Likewise, it may be appropriate to describe "water containing arsenic" if you are describing water which contains unusually high levels of arsenic due to natural reasons and arsenic-contaminated water if higher levels than normal may be due to non-natural reasons.

Aerojet comment: Page 1, Paragraph 3: The description of Aerojet operations and Cordova operations has been taken from earlier documents. Aerojet has historically pointed out the inaccuracies in the statements and rather than do so again we recommend, at a minimum, elimination of a reference to Cordova Chemical Company, because we do not believe it used perchlorate. We also recommend an elimination of the reference to the deep injection wells, because they are not relevant to the issue and can result in confusion when there is later discussion about recharge or reinjection wells associated with the GET facilities, which are different wells.

CDHS response: In the background paragraph, we are describing the lay of the land regarding the general site issues and thus we did not directly suggest that Cordova Chemical did use perchlorate, but rather this company was a part of the history of the site. Since perchlorate is reinjected at the site boundary as a part of the GET operations, we do not agree that reference to these should be eliminated.

Aerojet comment: Page 1, Paragraph 3: Delete "property" after "Aerojet's."

CDHS response: This incorrect grammar has been corrected in the text.

Aerojet comment: Page 1, Paragraph 3: Aerojet is not reinjecting treated water at the site's northern boundary.

CDHS response: This has been changed in the text.

Aerojet comment: Page 1, Paragraph 3: The Regional Water Quality Control Board (RB) is not the lead Agency; DTSC, USEPA and RB together provide oversight pursuant to the Partial Consent Decree.

CDHS response: The description of the lead agency/agencies was changed in the text.

Aerojet comment: Page 3, Paragraph 1: The discussion as to detection of perchlorate ought to be rewritten. Prior to the summer of 1996, Aerojet's laboratory used an ion specific electrode method. In 1997 Aerojet's laboratory did not use a different analytical method for perchlorate analysis to obtain the detection limit of 35 ppb but rather refined or improved the sensitivity of the existing ion chromatography method. In addition, it is accurate to say the "method" detection limit.

CDHS response: Based on this comment and a similar comment by other reviewers, the description of the analytical method was revised in the text.

Aerojet comment: Page 3, Third Full Paragraph: The drinking water standard for nitrate as N03 is 45 ppm.

CDHS response: This was corrected in the text.

Aerojet comment: Page 6, Paragraph 1: See the discussion above regarding the history of perchlorate sampling. It is not accurate to say that the analytical method Aerojet had been using was not sensitive to adequately assess the migration of perchlorate. It would be more accurate to state that Aerojet's historical analytical method's practical quantitation limit (PQL) for perchlorate was 400 ppb. As stated previously, there was no "alternative analytical method" used but the existing method was refined or improved and the PQL lowered.

CDHS response: According to the third sentence of the comment, the older method was indeed not sensitive enough to detect the perchlorate contamination. We did, however, revise the text to reflect the last two sentences of the comment.

Aerojet comment: Page 6, Paragraph 2 and following: This paragraph, as well as others below which need not be separately itemized, make an assumption about source and length of exposure which is not presently supportable. See discussion in general comments.

CDHS response: We realize that historical monitoring of the drinking water wells at low enough detection limits and thus we do not have a good understanding of the migration of perchlorate and past exposures to the Mather Main Base System customers. We also realize that we have not yet seen any attempts to model the movement of perchlorate based on groundwater flow patterns and perchlorate levels in monitoring wells. Thus in trying to review the past exposures, we are left to make the best assumptions possible.

Aerojet comment: Page 8, Continuing Paragraph and following: We refer you to the general comments on toxicology above. The draft Health Consultations would be better balanced if there was more discussion related to the use of perchlorate in the treatment of Graves patients and its current use in Europe at very high doses without ill effects. A strong statement that stresses how unlikely it would be to suffer any of these side effects at the levels addressed in the health consultation would be appropriate. In particular, the draft Health Consultations ought to point out that perchlorate has been used successfully and without incident in a fairly large patient population and with a very small number of reports of aplastic anemia even at the very high therapeutic concentrations A statement that the mechanism of perchlorate on the thyroid as well as basic thyroid functions are well understood would help to clarify the presentation. While the provisional RfD is stated as a level in drinking water at 18 ppb, the remaining levels discussed in the document are stated in terms of mg/kg/day. A direct comparison of those doses with the LOAEL/NOAEL and the provisional RfD in the same unit of PPB's would be very useful to give perspective to the dose issue.

CDHS response: As noted on the response to a General Comment from Aerojet, we did provide more information in the toxicology section. For instance, we have added more information about past and current pharmacological uses of perchlorate and what is known and not known about toxicity to the developing fetus and child. We also added a statement in the toxicological section that equates the dose to the drinking water concentrations.

Aerojet comment: Page 8, Continuing and Paragraph 1: The discussion of animal studies should be modified. There are animal studies where toxicologists have interpreted a NOAEL [(e.g. Mannisto (1970) and Caldwell (1996)]. As to the reference to children, in two places there is a discussion that suggests that nothing can be said about children. Aerojet is concerned that the reference might leave the reader with the impression that toxicologists do not consider impact to the thyroid as the focus of the evaluation or it might cause the reader to think that toxicologists view the child's thyroid as not understood. It would be more accurate to state that the mechanism of perchlorate intake on the thyroid is understood and that in evaluating the dose, one must evaluate the possibility that the child may have less iodine reserve which must be considered in evaluating how the child's thyroid compensates in comparison to an adult thyroid. However, any reference should also include the fact that all new-borns are routinely tested for thyroid hormone levels. Aerojet believes that it would be inappropriate for the Health Consultations to be construed as indicating that children are at risk at the provisional RFD or that exposure to the higher concentrations before well shut down would be associated with any health impact.

While it appears in the text, we believe there should be a clear reference both in the toxicology discussion and in the exposure section, that perchlorate is discharged from the body very quickly and that one would not expect to see any continuing impact on the thyroid once the exposure ends.

CDHS response: See response to previous comment.

Aerojet comment: Page 8, Paragraph 3: Regarding the discussion of safety factors, various toxicologists believe that the hypothyroid individual would not be a sensitive subpopulation. Also, the Health Consultations should recognize that the sensitive subpopulation factor is already being accounted for with respect to DHS comments on exposure of children.

CDHS response: Comment noted.

Aerojet comment: Page 9, Paragraph 3: See discussion above on children. We believe that the two locations of discussion on children should be combined in one location.

CDHS response: See previous responses.

Aerojet comment: Page 9, Third Full Paragraph: The statement that perchlorate levels in Mather wells as well as other water supply wells have remained fairly constant is generally true for the brief period of data collection cited by this consultation but extrapolation back in time is suspect based on the information available.

CDHS response: Comment noted.

Aerojet comment: Page 9, Paragraph 4: Exposure discussion includes the volume of tap water consumed per day in liters and perhaps the inclusion of a unit like the number of 8 oz. glasses per day would benefit the average reader, or public citizen. This could be included in the text and in the Table.

CDHS response: We have added this information to the text and table.

Aerojet comment: Page 9, Paragraph 4 and following: While the Health Consultations do note the potential for mixing of water from various sources within the water distribution system, they assume that the person exposed was exposed at the level reported for the well on the date closest to well closure. The Health Consultations should explain that the evaluation uses the assumed concentration at a well to assess impact of a receptor using the well, even though further evaluation may show that mixing and blending of water during water distribution potentially could occur and reduce the estimated level of exposure. CDHS response: See previous responses to similar comments. Aerojet comment: Page 9, Paragraph 4 and Following: There is the repeated statement that the estimated doses for [identified type of exposure] from well # [identified well number] exceeded the provisional RfD range and a conclusion stating "health effects may have occurred." The phrase "may have occurred" could be misinterpreted as it may suggest a higher level of risk than existed, given the low levels of perchlorate found in relation to the provisional NOAEL described. Given the uncertainty factors associated with the provisional RfD, Aerojet believes that it would be more appropriate for the Consultations simply to conclude that the level was over the RFD and then follow with a conclusion as to the unlikely nature of any health impact. If DHS does continue to want to use "may have occurred" language, then the "may have occurred" language should be clarified when presented by referring to the key assumptions, the exposure assessment, etc., (e.g., the number of 8 ounce glasses of tap water needed to be consumed). The health consultations should also stress that there is a significant range between the provisional RfD of 18 ppb and the NOAEL level translated to 4900 ppb (assuming a NOAEL of .1 4 mg/kg/day and a 70 kilogram male drinking 2 liters per day). It would also be useful either to change the reference of "uncertainty" factors to "safety" factors or use the term uncertainty (safety) factors" for the benefit of the reader.

CDHS response: Comment noted.

Aerojet comment: Page 12, Paragraph 2: See the above comments regarding speculation as to source.

CDHS response: See previous response to similar comments.

Aerojet comment: Page 12, Paragraph 4: There are a number of paragraphs that repeat statements made in the exposure section. See discussion above (page 9) relative to language about dose above the RfD. Aerojet does not believe that it is appropriate to conclude that there "may" have been a "health hazard." If language as to hazard is described, it should not be separated from the DHS assumptions about exposure nor should it be stated without the conclusion as to the unlikeliness of any impact. Aerojet further notes that the various Consultations do not always use the same language on "health hazard," and the differences in language do not appear justified (e.g., see Mather page 12 paragraph 3).

CDHS response: Comment noted.

Aerojet comment: Page 13, Bullet #3 and Page 14, Bullet #4: The reference should be to the Perchlorate Study Group, not Perchlorate Work Group.

CDHS response: This has been corrected in the text.

Aerojet comment: Page 14, Bullet #2: The use of the word "safe" is inappropriate, Reference should be to the provisional RfD.

CDHS response: We have modified the text so as to remove the word "safe".

Aerojet comment: References, No. 17. The citation to the authors should be corrected.

CDHS response: This citation has been corrected.

Aerojet comment on Table 1: We have not had adequate opportunity to evaluate the descriptions of all of the wells and the well system. We note that the comments in the Table are based upon assumptions made as discussed in the text and our comments apply.

CDHS response: Comment noted.

Aerojet comment on Table 2: We believe a "source" category for this Table is inappropriate. Please see general comment above on sources.

CDHS response: Comment noted.

Aerojet comment on Figures 1 and 2: The figures are illegible at this size and difficult for the reader to understand. The figures that present chemical distributions were draft figures and were not prepared for the purpose being used and are not reflective of present understanding of groundwater conditions.

CDHS response: We apologize for the quality of the figures. They are only meant to give the reader a basic layout of the perchlorate flow and the well locations and hopefully, this information is still conveyed with these poor quality figures.


COMMENTS FROM THE CENTRAL VALLEY REGIONAL WATER QUALITY CONTROL BOARD

Regional Board staffs comments on the documents are supplied below.

RWQCB General Comment: We recommend that the use of the term "contaminated" be selectively used. Contaminated should be used when the water represents a hazard to the public health. In the case of perchlorate, "contaminated" should not be used when discussing concentrations less than 18 ppb. It is even unclear whether the term should be applied to those concentrations that are currently found in some of the groundwater supply wells (up to 300 ppb). Instead of saying "perchlorate-contaminated water", we would recommend saying "water containing perchlorate".

CDHS response: As was stated under a similar comment raised by Aerojet, in Webster's New Collegiate Dictionary, it says "contaminate" means "to make impure or unclean". Perchlorate is not typically found in groundwater, as would be the case with certain chemicals like arsenic or sulfates which are naturally occurring in groundwater. Thus it does seem appropriate to describe the "contamination" of groundwater by a chemical such as perchlorate. Likewise, it may be appropriate to describe "water containing arsenic" if you are describing water which contains unusually high levels of arsenic due to natural reasons and arsenic-contaminated water if higher levels than normal may be due to non-natural reasons.

RWQCB General Comment: There is a paragraph in each of the health consultations which discusses the "reporting level to the RWQCB" of 400 ppb and a change in method which allowed for a detection level of 35 ppb. In the early 1990's, up until around 1995/96, Aerojet was using a ionspecific electrode to measure perchlorate concentrations in water with a detection level of 400-500 ppb. Aerojet then developed an alternate method using a GC which provided a detection level of 35 ppb and a reporting level of 400 ppb. This method was then used by Aerojet in all work required under the Partial-Consent Decree. In early 1996 RWQCB staff requested Aerojet to report all concentrations between the detection level (35 ppb) and reporting level (400 ppb) as trace. Aerojet was then able to lower their PQL to 100 ppb, while maintaining their detection level at 35 ppb. No method changes were made to get to the lower reporting level. It was in February 1996 that the concentrations in the off-site water supply wells were first reported.

CDHS response: Based on this comment and comments by others, the text was revised.

RWQCB General Comment: When discussing the nitrate levels, make sure that the values reported are designated as milligrams per liter as nitrate, or milligrams per liter as nitrogen. The MCL for nitrate should be expressed in the same units. There are two values for the MCL used in the five health consultations, 20 and 45 mg/l. A single value for the MCL should be used.

CDHS response: We have corrected this in the text.

RWQCB General Comment: We will not supply comments on the toxicological issues presented in the documents. We will rely on the experts at the Department of Health Services to make those evaluations.

CDHS response: Comment noted.

RWQCB comment: Page 2, paragraph 5. The value for the MCL for nitrate should be supplied to allow the reader to determine the significance of the values presented.

CDHS response: We have added the MCL as a reference in the text.

RWQCB comment: Page 5, paragraph 2. Comment B.4. also applies here. This is even a greater stretch given the distance from Aerojet and the IRCTS.

CDHS response: We look forward to the RWQCB or other agencies supplying us with better historical information about the historical movement of perchlorate; in the absence of this, we have clearly stated our assumptions as to when perchlorate contamination may have affected drinking water wells.

RWQCB comment: Page 5, paragraph 5, and page 6, paragraph 3. The page paragraph refers to Main Base well No. 3 , which contains perchlorate, being used periodically as the backup well to Main Base Well No. 4. The page 6 paragraph says that once Main Base Well No. 4 became the permanent lead well, no water containing perchlorate was being added to the water system. The period of time that Main Base Well No. 3 actually pumped as a backup well to No. 4 should be presented to avoid the apparent discrepancy.

CDHS response: We have corrected the confusion over the use of well #3 after it was placed in the backup mode in April 1997.

RWQCB comment: Page 6, paragraph 2. There is quite a bit of supposition in the statement that "perchlorate was probably a contaminant in the Cordova System wells since 1987". GET E started injecting in 1985 and GET F did not start injecting until late 1988. Without historical data, it is a stretch to provide a specific date. If the 1987 date remains the uncertainties and assumptions used in deriving that date should be supplied. This comment also applies to the second paragraph of page 12.

CDHS response: We look forward to the RWQCB or other agencies supplying us with better historical information about the historical movement of perchlorate; in the absence of this, we have clearly stated our guesses as to when perchlorate contamination may have affected drinking water wells.

RWQCB comment: Page 13, second paragraph. Insert a "the" after "actions" in the second line.

CDHS response: There was a grammatical problem in the sentence, which we have corrected.

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